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Determining the influence of soil salinity and tidal inundation on the growth, distribution, and diversity of salt marsh vegetation: implications for the restoration of the Nisqually Delta, Washington
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Date
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2012
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Creator
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Belleveau, Lisa
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Subject
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Environmental Studies
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extracted text
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Determining the influence of soil salinity and tidal
inundation on the growth, distribution, and diversity
of salt marsh vegetation: implications for the
restoration of the Nisqually Delta, Washington
By
Lisa Belleveau
A Thesis
Submitted in partial fulfillment
of the requirements for the degree
Master of Environmental Study
The Evergreen State College
2012
© 2012 by Lisa J. Belleveau. All rights reserved.
i
This Thesis for the Master of Environmental Study Degree by Lisa J. Belleveau has been
approved for The Evergreen State College by:
________________________
Gerardo Chin-Leo, Ph.D.
Member of the Faculty
________________________
Kelley Turner, M.S.
Restoration Biologist
USGS Western Ecological Research Center
________________________
Jean E. Takekawa
Refuge Manager
Nisqually National Wildlife Refuge Complex
________________________
Date
ii
ABSTRACT
Estuaries are biologically productive and diverse ecosystems that protect inland areas
from flooding, filter fresh water entering marine waters, and provide economic,
recreational, and aesthetic value. The Nisqually Delta in Washington State is an estuary
that has been modified by restricting tidal flow to reclaim tidal lands for agriculture.
Recently, the Nisqually National Wildlife Refuge, working in collaboration with the
Nisqually Indian Tribe and Ducks Unlimited, restored a large amount of the tidal flows as
part of the largest estuary tidal marsh restoration project in the Pacific Northwest. This
thesis contributes to understanding vegetation response to estuary restoration by
determining the elevation and pore-water salinity field conditions for nine common salt
marsh species in the Nisqually Delta: Carex lyngbyei, Distichlis spicata, Grindelia
integrifolia, Jaumea carnosa, Juncus balticus, Potentilla anserina, Salicornia virginica,
Spergularia sp., and Triglochin maritimum. Vegetation surveys were conducted from
March to September of 2010 at 21 plots to measure growth over time. In August of 2010
an additional 30 plots were surveyed to estimate peak growth. At each of the plots, porewater salinity, substrate elevation (as an indicator of submergence time), as well as
percent cover, stem density, and maximum height was measured for each species. Using
these data, the elevation and salinity range of each species was determined. Correlation
analysis was conducted to explore the relationships among biological (percent cover,
height, and density) and physical parameters (salinity and elevation). The seasonal plots
were analyzed by establishing salinity and elevation zones and investigating the growth
patterns within these zones over time. Overall, pore-water salinity and elevation had a
positive influence on the salt marsh vegetation species studied. These species can tolerate
high salinities, but submergence time (i.e. elevation) may be the dominant factor
explaining differences in their growth and distribution. This research provides knowledge
that can be used to identify suitable locations for salt marsh habitat restoration, and to
ensure successful colonization of native species. Future research suggestions include
continued monitoring of the Nisqually Delta vegetation along with the sedimentation and
subsidence processes that affect their distribution and colonization success.
TABLE OF CONTENTS
List of Figures…………………………………………………………………………….vi
List of Tables……………………………………………………………………….……..x
Acknowledgements………………………………………………….……………………xi
INTRODUCTION………………………………………………………..……………….1
1.1 Research Significance and Project Summary…………………………………………1
1.2 Nisqually River History……………………………………………..……………….. 4
1.3 Recent Nisqually Delta History…………………………………………………….....5
1.4 Management of the Nisqually Delta…………………………………………..………9
1.5 Salinity and its effects on vegetation growth……………………...............................11
1.6 Elevation and its effects on vegetation distribution……………………….…………12
1.7 Vegetation Studies of the Nisqually Delta…………………………………...………13
1.8 Vegetation Descriptions……………………………………………………...………16
1.9 Research Question and Hypotheses……………………………………………….…20
2. METHODS……………………………………………………………………..……..22
iii
2.1 Study site………………………………………………………………..……………22
2.2 Survey methods…………………………………………………………..…………..23
2.2.1 Vegetation…………………………………………………………..……………. 23
2.2.2 Soil Pore-Water Salinity……………………………………………….…………..25
2.2.3 Elevation……………………………………………………………………...……26
2.3 Statistical analysis……………………………………………………………………26
3. RESULTS and DISCUSSION……………………………………………….………..28
3.1 Soil pore-water salinity and elevation at the study sites……………………………..28
3.2 Salinity Ranges of Nisqually salt marsh vegetation…………………………..……..32
3.3 Elevation Ranges of Nisqually salt marsh vegetation……………………..…...…….35
3.4 Analysis of Vegetation Growth across Salinity and Elevation Gradients………...…38
3.4.1 Carex lyngbyei………………………………………………………………..……41
3.4.2 Distichlis spicata………………………………………………………………..… 45
3.4.3 Grindelia integrifolia………………………………………...…………………….49
3.4.4 Jaumea carnosa…………………………………...……………………………….53
3.4.5 Juncus balticus……………………………………………………..………………57
iv
3.4.6 Potentilla anserina…………………………………...……………….……………61
3.4.7 Salicornia virginica……………………………...….………………….………….65
3.4.8 Spergularia sp………………………………………...………………………...….69
3.4.9 Triglochin maritimum………………………………………………………..…….72
3.5 Comparison of expected tolerance levels and Nisqually results………………….... 75
3.6 Species Richness……………………………………………………………………..77
3.7 Site Conditions of the Restoration Area on the Nisqually National Wildlife Refuge.79
4. CONCLUSION and RECOMMENDATIONS…………………………………...…..85
Literature Cited…………………………………………………………………………..88
v
List of Figures:
Figure 1: Location of the Nisqually estuary in Washington State………………………...3
Figure 2: The four study locations within the Nisqually Delta……………………………8
Figure 3: Monitoring locations within the Nisqually Delta……………………………...29
Figure 4: Salinity and elevation gradients of all four study sites (REF, P1, P2, and AS).30
Figure 5 (a & b): Soil pore-water salinity and elevation of the plots located within the
marine marshes…………………………………………………………………………..31
Figure 6 (a & b): Soil pore-water salinity and elevation of the plots located within the
brackish marshes…………………………………………………………………………32
Figure 7: Soil pore-water salinity of all species observed on the Nisqually Delta in the
vegetation surveys of 2010………………………………………………………………34
Figure 8: Elevation of all species observed on the Nisqually Delta in the vegetation
surveys of 2010…………………………………………………………………………..37
Figure 9: Kendall’s correlation analysis of Carex lyngbeyi percent cover, height, and
density across salinity and elevation gradients within the Nisqually Delta……………...43
Figure 10: Seasonal growth patterns of Carex lyngbyei across salinity and elevation
gradients within the Nisqually Delta……………………………………………………..44
vi
Figure 11: Soil pore-water salinity and elevation of the plots where Carex lyngbyei was
present……………………………………………………………………………………45
Figure 12: Kendall’s correlation analysis of Distichlis spicata percent cover, height, and
density across salinity and elevation gradients within the Nisqually Delta……………...47
Figure 13: Seasonal growth patterns of Distichlis spicata across salinity and elevation
gradients within the Nisqually Delta……………………………………………………..48
Figure 14: Soil pore-water salinity and elevation of the plots where Distichlis spicata was
present……………………………………………………………………………………49
Figure 15: Kendall’s correlation analysis of Grindelia integrifolia percent cover, height,
and density across salinity and elevation gradients within the Nisqually Delta…………51
Figure 16: Seasonal growth patterns of Grindelia integrefolia across salinity and
elevation gradients within the Nisqually Delta………………………………………….52
Figure 17: Soil pore-water salinity and elevation of the plots where Grindelia integrefolia
was present……………………………………………………………………………….53
Figure 18: Kendall’s correlation analysis of Jaumea carnosa percent cover, height, and
density across salinity and elevation gradients within the Nisqually Delta……………...55
Figure 19: Seasonal growth patterns of Jaumea carnosa across salinity and elevation
gradients within the Nisqually Delta……………………………………………………..56
vii
Figure 20: Soil pore-water salinity and elevation of the plots where Jaumea carnosa was
present……………………………………………………………………………………57
Figure 21: Kendall’s correlation analysis of Juncus balticus percent cover, height, and
density across salinity and elevation gradients within the Nisqually Delta……………...59
Figure 22: Seasonal growth patterns of Juncus balticus across salinity and elevation
gradients within the Nisqually Delta.…………………………………………………….60
Figure 23: Soil pore-water salinity and elevation of the plots where Juncus balticus was
present……………………………………………………………………………………61
Figure 24: Kendall’s correlation analysis of Potentilla anserina percent cover, height, and
density across salinity and elevation gradients within the Nisqually Delta……………...63
Figure 25: Seasonal growth patterns of Potentila anserina across salinity and elevation
gradients within the Nisqually Delta……………………………………………………..64
Figure 26: Soil pore-water salinity and elevation of the plots where Potentila anserina
was present……………………………………………………………………………….65
Figure 27: Kendall’s correlation analysis of Salicornia virginica percent cover, height,
and density across salinity and elevation gradients within the Nisqually Delta…………67
Figure 28: Seasonal growth patterns of Salicornia virginica across salinity and elevation
gradients within the Nisqually Delta……………………………………………………..68
viii
Figure 29: Soil pore-water salinity and elevation of the plots where Salicornia virginica
was present……………………………………………………………………………….69
Figure 30: Kendall’s correlation analysis of Spergularia sp. percent cover, height, and
density across salinity and elevation gradients within the Nisqually Delta……………...70
Figure 31: Seasonal growth patterns of Spergularia sp. across salinity and elevation
gradients within the Nisqually Delta……………………………………………………..71
Figure 32: Soil pore-water salinity and elevation of the plots where Spergularia sp. was
present……………………………………………………………………………………72
Figure 33: Kendall’s correlation analysis of Triglochin maritimum percent cover, height,
and density across salinity and elevation gradients within the Nisqually Delta…………73
Figure 34: Seasonal growth patterns of Triglochin maritimum across salinity and
elevation gradients within the Nisqually Delta…………………………………………..74
Figure 35: Soil pore-water salinity and elevation of the plots where Triglochin maritimum
was present……………………………………………………………………………….75
Figure 36: Species richness versus soil pore-water salinity……………………………...78
Figure 37: Species richness versus elevation…………………………………………….79
Figure 38: Pore-water salinity and elevation ranges of the study sites on the Nisqually
National Wildlife Refuge in 2010………………………………………………………..81
ix
Figure 39: Elevation of the Nisqually Delta based on a 2011 LIDAR flown by Watershed
Sciences…………………………………………………………………………………..84
List of Tables:
Table 1: List of all species encountered on the 2010 surveys……………………………35
Table 2: Salinity and elevation values for the nine species correlation analysis………...39
Table 3: Salinity and elevation tolerance ranges according to a literature review by
Hutchison (1988), and the result of this research in the Nisqually estuary……………...76
x
Acknowledgments:
I would like to thank all the people who made this research possible: Kelley Turner for
her knowledge, support, and guidance through this entire thesis project as well as her
persistent yet gentle reminders of my deadlines, the field crew and volunteers for their
help and dedication, Gerardo Chin-Leo for his thoughtful and timely edits of my drafts,
his excellent ideas and encouragement, and his patience with my delayed drafts, Isa woo,
Jean Takekawa, and Jesse Barham for their multiple reviews and thoughtful feedback, my
family and friends for listening to my long discussions about my studies, and especially
my children for all your love, interest, and support. I could not have done this without
you.
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1. INTRODUCTION
1.1 Research Significance and Project Summary
Estuaries are semi-enclosed coastal bodies of water where seawater is measurably
diluted by freshwater drainage (Cameron and Pritchard 1963). These areas are some of
the most productive and sensitive landscapes on Earth (USFWS 2004; Adam 1990). They
support many species of plants and animals, protect inland areas from flooding, filter
sediments, nutrients and pollution, as well as provide economic, recreational, and
aesthetic value (Kruckeberg 1991; Scavia et al. 2002; USFWS 2004). Estuaries provide
abundant food resources and sanctuary for resident and migratory birds; many
commercially valuable fish species rely on estuaries as nursery grounds while they build
biomass and acclimate to the salty water of the sea (Smith et al. 2000).
Many of these important habitats have been degraded or destroyed over the last 150
years. Currently, eighty percent of historic estuarine habitats in the Puget Sound region
have been destroyed or severely degraded (USFWS 2004; Dean et al. 2001). Human
influences such as damming of rivers, pollution, and development continue to degrade the
physical condition and resilience of estuaries; leaving them vulnerable to additional
impacts (Apostel and Sinclair 2006; Adam 1990). To reverse this trend, it is essential to
conserve, restore, and protect these valuable habitats.
Even though many estuaries in the Pacific Northwest have been impacted by human
activities since the 1800’s, some are still rather unaltered and are ideal study sites for
understanding how these ecosystems function (Thom et al. 2003). The Nisqually River,
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though degraded, is one of Washington’s least developed major river systems; making it
a prime candidate for restoration. According to Apostol and Sinclair (2006), “an
important first step in developing a restoration plan is linking valued resources (i.e.,
important plants and animals or wetland functions) with the factors hypothesized to
control these factors.”
Estuaries are tidally influenced landscapes affected by changing salt concentrations and
varying periods of inundation as the tides ebb and flow. Understanding how salinity and
inundation influence salt marsh vegetation is important for developing restoration and
adaptive management goals. Depth and duration of inundation has direct influence on salt
marsh vegetation composition and density (Adam 1990). Several studies (Bertness et al.
1992; Boumans et al. 2002; and Hinkle and Mitsch 2005) have shown that vegetation
communities can change dramatically along elevation and salinity gradients.
The Nisqually Delta can be categorized into four major habitat types; estuarine (including
mudflat and salt marsh), freshwater wetland, riparian, and forested upland. This thesis
will focus on the estuarine habitat of the Nisqually Delta and in particular, the vegetated
intertidal areas which are known as salt marsh habitats. It will contribute to estuarine
restoration science by examining the conditions that can result in successful
establishment of salt marsh vegetation. Specifically, the role of pore-water salinity and
inundation in determining the vegetation growth patterns of nine dominant species found
throughout the Nisqually estuary, including the Nisqually National Wildlife Refuge,
located in Washington State (Figure 1). By studying salinity and inundation in relation to
2
salt marsh vegetation growth, land managers will have a fuller understanding of the
requirements necessary to restore or establish salt marsh habitat. This research can be
used to estimate the type and locations at which salt marsh vegetation may colonize the
recently restored estuarine environment on the Nisqually National Wildlife Refuge.
Figure 1: Location of the Nisqually estuary in Washington State.
3
1.2 Nisqually River History
The Nisqually Delta was formed about 13,000-18,000 years ago from the retreat of the
glaciers in the last ice age (Kruckeberg 1991). As the Puget Lobe glaciers receded they
carved some of the waterways we know today as Puget Sound, Nisqually River, and
McAllister Creek. In addition to the glacier retreat, the subduction of the Pacific Plate, as
it collided with North America, helped shape the landscape of Puget Sound by forming
mountains and valleys (Kruckeberg 1991). The rapid fill of sediment and the isostatic
rebound as the last glacier retreated has kept the Puget Sound trough at about sea-level
for the last several thousand years (Kruckeberg 1991).
The Nisqually River flows 78 miles from the Nisqually Glacier at Mount Rainier to the
southern edge of Puget Sound to form the Nisqually Delta (Pierce County Public Works
& Utilities; Kruckeberg 1991). The Nisqually River Basin is approximately 760 square
miles (Pierce County Public Works & Utilities; Kruckeberg 1991). The Nisqually River
passes through lands that are used in different ways, and has varied ownership including
Mt. Rainier National Park, state parks, timberlands, hydropower projects, farmland, the
Nisqually Indian Reservation, Fort Lewis, and the Nisqually National Wildlife Refuge
(USFWS 2004). It also encompasses a multitude of habitats from old growth forests in
Mt. Rainier National Park to glacial outwash lowland prairies, and finally to the tidal
mudflats and estuarine habitat of the delta (Pierce County Public Works & Utilities).
The Nisqually Basin receives an average annual rainfall of 33-50 inches (83-127 cm) in
the lowlands while the higher elevations receive more than 70 inches (177 cm) (Pierce
4
County Public Works & Utilities). The mouth of the Nisqually River mixes with the
waters of Puget Sound thus creating the estuarine environment of the Nisqually Delta.
The tidal regime in the Puget Sound is very distinct and dramatic; it has two high and two
low tides, differing in size every day (semi-diurnal mixed tide regime) and the difference
between the maximum yearly high and the minimum yearly low is approximately 20 feet
or ~6 m (http://tidesandcurrents.noaa.gov/).
The people of Nisqually came from the Great Basin to settle in the Nisqually watershed
thousands of years ago and were known as the Squalli-absch, which translates to, “people
of the river and the grass” (http://www.nisqually-nsn.gov/). Once the Nisqually people
had crossed the Cascade Mountain range one of their first major settlements was
constructed on the Mashel River, which is a tributary of the Nisqually River. The
Nisqually people lived off the Nisqually River, Puget Sound, and the local grasslands
(prairies). They harvested fish, shellfish, crabs, oysters, and other seafood from the river
and Puget Sound, and harvested berries and tubers (mainly camas) from the surrounding
grasslands (Kruckeberg 1991, http://www.nisqually-nsn.gov/).
1.3 Recent Nisqually Delta History
Over the last century, tidal restriction, agriculture, and cattle grazing have degraded the
historic estuarine condition of the Nisqually Delta. The first settlers to file a claim to the
land west of the Nisqually River arrived in 1854, and in 1873 a Northern Pacific Railroad
executive purchased the claim. The land was later sold to Alson Lennon Brown in 1904
(Nielsen 1980). Even though he only owned the land for 15 years, Brown is the most well
5
known previous owner of the Delta because he purchased so much land, constructed a
five mile dike to keep out the tides of Puget Sound, and created one of the area’s biggest
agricultural farms (Nielsen 1980). After Brown lost the land in 1919 it was leased to
various agricultural enterprises over the next 55 years (Nielsen 1980). One of the primary
uses of the land was a dairy farm.
The continuous grazing of cattle can have many detrimental affects to a landscape. The
removal of vegetation alone causes degradation of the soils by limiting organic matter.
The vegetation and soil is further damaged by trampling, and the animal waste disturbs
the nutrient cycles as well as decreasing water quality (Goble and Hirt 1999). However,
the farming practices in the Nisqually Delta were relatively low impact, leaving many of
the historic tidal channel beds still intact within the diked areas.
In the 1960’s the Delta was threatened with further development because of the proximity
to urban centers (USFWS 2004). Local citizens initiated a grass roots movement to
protect the Delta from development into a port through organized meetings and letters to
the city, county, and state politicians (USFWS 2004). Development was stopped mostly
due to a land purchase of the northern portion of the Nisqually Delta by the WDFW in
1966-67 (USFWS 2004). The Nisqually Delta was designated a National Natural
Landmark by the Department of Interior in 1971 (USFWS 2004). In 1972, the Nisqually
River Task Force, initiated by dedicated citizens, recommended that the delta be set aside
as wildlife habitat, and in 1974 the United States government purchased the land and
established it as a National Wildlife Refuge (USFWS 2004).
6
In the mid 1800’s Joel Meyers purchased a large amount of property in the Nisqually
Delta east of the Nisqually River. This property was sold to Olie O. Braget who, in 1905,
built a dike to create farming and grazing land for his cattle (Clemmens 2002). This land
was used for grazing habitat for almost 100 years with continued alterations (levees and
drainage ditches) through the mid 1900’s.
The Nisqually Tribe purchased the land in 2000, and in 2002 began a phased estuarine
restoration program which has restored approximately 140 acres of salt marsh by
reconnecting the hay fields to tidal flow (USFWS 2004; Ellings 2008; Wiltermood 2008).
In 2005, the Nisqually Indian Tribe and Nisqually NWR signed a Cooperative
Agreement, which authorized the Refuge to manage the tribal lowlands as part of the
Refuge with provisions which enabled the Tribe to proceed with habitat restoration.
In the year 2000 a three phase restoration project was planned for portions of the diked
lowlands within the 310 acre Braget farm (Wiltermood 2008). In 2002 the first phase
began with the removal of dikes along the east and south portions of a 39 acre parcel
(Phase 1; Figure 2) on the north end of the Braget Marsh (Wiltermood 2008). In 2006 the
second phase (Phase 2) began with the return of tidal influence to the largest portion of
the Braget Marsh restoration project; approximately 150 acres, 100 acres of salt marsh
and 50 acres of riparian habitat (Wiltermood 2008). The third phase took place in August
of 2011.
7
Figure 2: Outline of the four study locations within the Nisqually Delta used in this research, as well
as the Nisqually National Wildlife Refuge restoration area.
8
1.4 Management of the Nisqually Delta
On Refuges, the land is managed for wildlife and habitat needs first and foremost. The
goals of the Nisqually National Wildlife Refuge are given in detail in the Comprehensive
Conservation Plan (USFWS 2004) and are to; “1) Conserve, manage, restore, and
enhance native habitats and associated plant and wildlife species representative of the
Puget Sound lowlands, with a special emphasis on migratory birds and salmonids, 2)
Support recovery and protection efforts for Federal and State threatened and endangered
species, species of concern, and their habitats, 3) Provide quality environmental
education opportunities focusing on the fish, wildlife, and habitats of the Nisqually River
delta and watershed, 4) Provide quality wildlife-dependent recreation, interpretation, and
outreach opportunities to enhance public appreciation, understanding, and enjoyment of
fish, wildlife, habitats, and cultural resources of the Nisqually River delta and
watershed.”
Since the establishment of the Nisqually NWR in 1974, the land inside the five mile dike
had been managed as freshwater wetland habitat. It took several years of planning and
comments from public agencies, businesses, local governments, and private citizens
before a preferred alternative was selected and funding secured to restore the Refuge
lands to historical estuarine habitat. Many different restoration scenarios were examined
for their effectiveness in fully restoring natural processes to the delta (USFWS 2004).
The restoration alternative selected restores the most estuarine habitat (75% of historic),
9
reconnects many of the historic slough channels creating a more functional estuarine
system; while maintaining freshwater wetland and riparian habitats within the Refuge
(USFWS 2004). This restoration will provide diverse habitats for many wildlife species,
including migratory birds and threatened fish, as well as opportunities for the public to
view active restoration and adaptive management, increasing their understanding of the
restoring estuary and overall enjoyment of the Nisqually Delta (USFWS 2004).
Having a diversity of stakeholders can create challenges for managing the watershed.
Scientific, technical, and policy experts must work together in a multidisciplinary manner
in order to balance the desires and interests of all the stakeholders with the knowledge
and needs of the ecosystem (Capobianco et al. 1998). Scientific research and monitoring
is essential for supporting adaptive management. The Nisqually National Wildlife Refuge
partnered with the Nisqually Indian Tribe and Ducks Unlimited to make restoration of the
Nisqually Estuary possible. The monitoring of this restoration effort is an important
contribution to our understanding of these complex ecosystems. The US Geological
Survey in partnership with the Refuge and Nisqually Tribe is implementing the
monitoring plan and evaluating habitat development and changes within this large scale
restoration project (Ellings 2008, http://nisquallydeltarestoration.org/).
The Brown Farm dike was removed in 2009 allowing the historic tidal system to return to
the landscape. The Nisqually National Wildlife Refuge restored 762 acres of estuarine
habitat and enhanced 263 acres of freshwater wetland and riparian habitats within the
Delta (USFWS 2004). In combination with the Nisqually Tribe’s restoration projects on
10
the east side of the river, over 900 acres of the Nisqually Delta are currently being
restored making it the location of the largest estuary restoration project in the Pacific
Northwest at this time (Ellings 2008). Restoration of the Nisqually Delta has the potential
to expand critical habitat for threatened salmon species, migratory birds, as well as assist
in the recovery of Puget Sound as a whole.
The research conducted for this thesis will add to our understanding of estuary restoration
by examining the pore-water salinity, elevation, and vegetation present on both reference
sites and recently restored sites. This information can be used to make predictions about
the restoration site on the Nisqually National Wildlife Refuge, by comparing site
conditions of the Refuge with the vegetation present at similar site conditions on the
restoring sites.
1.5 Salinity and its effects on vegetation growth
Seawater is a mixture of salts comprised primarily of six ions: chloride (Cl-), sodium
(Na+), sulfate (SO4-2), magnesium (Mg+2), calcium (Ca+2), and potassium (K+)
(Wildberger, 1993). Salinity is the amount (grams) of solid material dissolved in a
kilogram of seawater and is expressed as parts per thousand (ppt) or practical salinity
units (psu). For this research I used a refractometer to measure pore-water salinity in ppt.
Salinity has been shown to influence plant growth patterns, including salt marsh
vegetation. High salinity concentrations within the soil can prevent germination and
establishment of plants (Zedler 2001). Bertness et al. (1992) studied eight typical New
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England high marsh species and in a controlled setting watered them with water of
different salinities likely to be encountered in the marsh plain. They found that many of
the species were significantly stunted in photosynthetic rate by higher salinities, with the
exception of a few species (Distichlis, Atriplex, and Aster) that showed photosynthetic
rates independent of the variations in salinity.
According to Adam (1990), salinity has adverse effects on plants because the levels of
sodium and chloride can become toxic, thus interfering with nutrient uptake and lowering
the external water potential. Interference with nutrient uptake can inhibit the plant’s
ability to create biomass thus limiting growth. A lowered external water potential is when
the water outside of the plant cannot enter the plant during seawater inundation. This
happens because of the differing ion concentrations between the external and internal
water. In a tidally influenced landscape the salts of the water inundating the plant are
much more concentrated than the internal water. Due to osmosis, the water inside of a
plant submerged in salt water will flow out of the plant potentially leading to
dehydration. Salt marsh plants surviving in this harsh environment must either exclude
the salts at the roots or develop methods of excretion in order to maintain lower salinity
within their cells (Hutchinson 1988, Adam 1990, Zedler 2001).
1.6 Elevation and its effects on vegetation distribution
In this research I have used measures of elevation as a proxy for inundation, with lower
elevations having longer submergence time. Elevation has been established as a relative
measurement of inundation, one of the driving factors of a tidally influenced landscape.
12
Roman, James-Pirri, and Heltshe (2001) noticed vegetation patterns on the New England
marshes and attributed tidal inundation frequency and duration as the delineation between
the high and low marsh. The low marsh being inundated twice daily and less frequent
inundation as elevation increased. Boumans et al. (2002) defined low elevation marshes
as being frequently flooded and high elevation marshes as occasionally flooded. Though
this definition is rather vague, they were still able to identify that salt marsh vegetation
species are distributed along a tidal gradient.
In the field guide “Wetland Plants of the Pacific Northwest” Weinmannn et al. (1984)
describes marsh zonation patterns along a tidal gradient with eelgrass beds occurring
below mean high water (MHW), low marsh occurring above MHW and high marsh
occurring above mean higher high water (MHHW). In order to examine how marsh
elevation influences the soil salinity of bare patches, Bertness et al. (1992) used days per
month flooded to define 4 elevation ranges of (1) daily flooded, (2) 15 days per month,
(3) 10 days per month, and (4) 5 days per month. Hinkle and Mitsch (2005) stated that
elevations below mean high tide would support low marsh species, and in order to
support high marsh species one should aim for elevations above MHW. For the purposes
of this study the elevation of the MHW level was used to delineate between high and low
marsh.
1.7 Vegetation Studies of the Nisqually Delta
Multiple studies have been conducted to characterize the vegetation at the Nisqually
Delta. Mason et al. (1974) mapped the Refuge vegetation within the diked area and a
13
narrow portion outside on the delta flats to the north. No elevation or salinity
measurements were taken with this vegetation survey. On the delta flats they found an
even distribution of Distichlis spicata, Triglochin maritimum, Salicornia virginica,
Jaumea carnosa and Carex spp. The outermost reaches of the delta flats contained
monoculture stands of Distichlis spicata as well as some pure stands of Salicornia
virginica. They also found Juncus spp. species growing in circular patches as well as
scattered throughout, Grindelia integrifolia along the slough edges and Triglochin
maritimum as a constant member of the salt marsh community. The areas influenced by
the Nisqually River, and thus influenced by freshwater, were dominated by Carex spp. in
the lower areas and in higher areas the community was comprised of Deschampsia
cespitosa, Potentilla anserina spp. pacifica, and Triglochin maritimum.
In 1975 Burg et al. conducted a study analyzing the above ground biomass at 138
quadrats within the undiked portions of the Delta in order to define the plant associations
within the salt marsh (Burg et al. 1980). They identified a total of twelve plant
associations on the Nisqually salt marsh. In the lower salt marsh areas they observed a
dominance of Spergularia marina, Salicornia virginica, and Distichlis spicata, however,
low areas closer to the Nisqually River were dominated by Carex lyngbyei. As they
surveyed further up into the marsh plain they found communities with up to 15-16
different species with Jaumea carnosa, D. spicata, Plantago maritimum, Triglochin
maritimum, Grindelia integrifolia, Cuscuta salina, and Glaux maritimum being the most
dominant. In the higher marsh areas, Deschamsia cespitosa, Juncus balticus and Festuca
rubra were observed. Burg et al. (1980) stated that on the Nisqually salt marsh salinity
14
and elevation appear to be the two main environmental gradients influencing vegetation
zonation patterns. They were able to state this because they identified that proximity to
freshwater might be the determining factor for species presence or absence, while
elevation determines the vertical distribution of species within these salinity boundaries.
In preparation for the Nisqually National Wildlife Refuge Comprehensive Conservation
Plan Tanner et al. (2000) conducted a partial survey of elevations outside the diked area
in order to determine more precise elevation distributions of certain plant communities.
The rough estimations made by this limited study concluded that low marsh areas near
the Nisqually River were dominated by Carex lyngbei and that areas away from
freshwater influence were dramatically different with low marsh dominated by Salicornia
virginica, and Distichlis spicata while the high marsh was dominated by Deschampsia
cespitosa.
Clemmens (2002) conducted a vegetation study located on the Tribal property east of the
Nisqually River. He found that Carex lyngbei dominated the lower portions of the
channels and as the top of the channel banks were reached the community changed into a
combination of Distichlis spicata, Potentilla anserina spp. pacifica, and Atriplex patula.
The higher marsh contained Scirpus and Juncus dominated areas along with Potentilla
anserina spp. pacifica, Distichlis spicata and Jaumea carnosa.
The Wiltermood (2008) reports based on the Nisqually Tribe’s restoration projects
concluded that Phase 1 (six years restored) was dominated by sand-spurry (Spergularia)
15
and spikerush (Eleocharis) in the lower areas, while Distichlis spicata and Jaumea
carnosa dominated the higher areas. The Phase 2 (two years restored) report findings
concluded that some areas remained upland pasture, Salicornia virginica and Spergularia
were the dominant species in the lower areas, while Distichlis spicata was dominant in
both the high and low marsh areas.
1.8 Vegetation Descriptions
Based on the previous studies of the Nisqually Delta, I selected nine dominant species for
an in-depth review. The nine species selected also cover a gradient of salinity tolerance
levels ensuring that the effects of salinity and elevation were studied across a full range
of plant salinity tolerance levels. The nine vegetation species nomenclature follows
Hitchcock and Cronquist (1973) and are listed in alphabetical order: Carex lyngbyei
(Lyngby’s sedge), Distichlis spicata (seashore saltgrass), Grindelia integrifolia (entireleaved gumweed), Jaumea carnosa (salt marsh daisy), Juncus balticus (Baltic rush),
Potentilla anserina (silverweed), Salicornia virginica (pickleweed), Spergularia sp.
(sand-spurry), and Triglochin maritimum (sea arrow-grass).
Below is a summary of the major characteristics of the dominant plant species considered
in this study. Much of the current literature focused on only one species and those were
mostly from East coast marshes which could be quite different from the species in the
Pacific Northwest. For this reason an older paper was used to base salinity hypotheses on,
(Hutchinson 1988), which reviewed several different publications covering salinity
tolerance levels for many species from Pacific Northwest marshes. Elevation hypotheses
16
for the species considered in this study were derived from Pacific Northwest specific
plant identification books, (Weinmann et. al. 1984) & (Pojar and Mackinnon 1994), and a
Nisqually specific study (Mason et al. 1974).
Carex lyngbyei (Lyngby’s sedge) is a native, perennial found in areas of greater
freshwater influence (Mason et al. 1974). It is commonly dominant along the inner delta
sloughs in dense, often pure stands. This species is a true hydrophyte (loves water), and
can be found in low and high marshes (Weinmann et. al. 1984). Hutchison (1988) reports
that this species is not present when salinities reach above 20 ppt. Sedges are adapted to
withstand inundation for long periods of time which allows it to survive at lower
elevations, but it is found along the rivers edge because it is not able to withstand
concentrated saline environments. Carex lyngbyei is an important brackish mudflat
colonizer because the young plant provides a good source of protein for wildlife as well
as promoting sedimentation as it grows (Pojar and Mackinnon 1994).
Distichlis spicata (seashore saltgrass) is a native, perennial grass of tidal marshes and
seashores (Pojar and Mackinnon 1994). This grass can tolerate extremely high salinity by
excreting excess salt through the pores in its leaves and can grow on the mudflats as well
as in the high marsh (Mason et al. 1974). Hutchison (1988) reports that this species can
withstand salinities greater than 50 ppt.
Grindelia integrifolia (entire-leaved gumweed) is a native, perennial aster that grows
along beaches, rocky shores, and salt marshes (Pojar and Mackinnon 1994). It is most
17
common in the high marsh and sometimes even in non-wetland locations (Weinmann et.
al. 1984). Along with arrow grass (Triglochin maritimum), it is the tallest species in the
salt marsh plain, and is found most often along slough edges (Mason et al. 1974).
Hutchison (1988) reports that this species is found within salinities of less than 15 ppt.
Jaumea carnosa (salt marsh daisy) is a succulent, native, perennial aster, which is
common on beaches, tidal mudflats, and marshes (Pojar and Mackinnon 1994). It is
found in both high and low salt marsh (Weinmann et. al. 1984). Hutchison (1988) reports
that has optimal growth at 9 ppt but is able to survive in salinities as high as 39 ppt.
Juncus balticus (baltic rush) is a perennial rush found in both brackish and saline marshes
in the lower to mid elevations (Pojar and Mackinnon 1994). Juncus species have been
reported to have 52% reductions in growth at salinities as low as 9 ppt, and 87%
reduction at 17-29 ppt (Hutchison, 1988) However, Juncus balticus is one of the more
salt tolerant of the rushes and may thrive at slightly higher salinities (Pojar and
Mackinnon 1994, Weinmann et. al. 1984).
Potentilla anserina spp. pacifica (silverweed) is a native, perennial herb that is found
most often in the high marsh meadows, at or above MHHW (Weinmann et. al. 1984,
Hutchison 1988). Hutchison (1988) reports that this species is often found in salinity
ranges of 0-12 ppt. This species is not restricted to estuarine habitats and can be found
along stream edges as well as in the high salt marsh meadows (Pojar and Mackinnon
1994).
18
Salicornia virginica (pickleweed) is a native, fleshy perennial that is often found in the
lower marsh where it gets inundated twice daily (Weinmann et. al. 1984). Mason et al.
(1974) found this species in the higher marsh but in the areas where evaporation had
concentrated the salinity. Hutchison (1988) states that this species has a salinity range of
20-80 ppt, which shows that it is a true halophyte and can handle, in fact flourish at high
salinities.
Spergularia sp. (sand-spurry) is an annual species of the pink family, and is common on
beaches, mudflats and marshes in either saline or brackish environments (Pojar and
Mackinnon 1994). Spergularia is a pioneer species most often found in the low marsh and
is adapted to withstand both high salinities and regular inundation (Weinmann et. al.
1984). Hutchison (1988) reports that this species is found within the salinity range of 620 ppt, and that it shows an increase of growth in brackish water versus fresh water;
suggesting that it is a true halophyte and flourishes in moderate salinities.
Triglochin maritimum (sea arrow-grass) is a native, fleshy perennial herb and is often
found in tidal marshes, mudflats, brackish meadows and sloughs (Pojar and Mackinnon
1994). This species is most commonly found in the low marsh where it is inundated twice
daily, but occasionally found in the high marsh where it is inundated only once per day
(Weinmann et. al. 1984). Mason et al. 1974 found this species to be a constant member of
the salt marsh but never in high densities. Hutchison (1988) reports that Triglochin has
variable growth in response to salinity and is found at salinities of 0-21 ppt.
19
1.9 Research Question and Hypotheses
My research question was, “How do salinity and inundation affect the growth,
distribution and diversity of salt marsh vegetation?”
My hypotheses were:
•
Salinity will be negatively correlated to species richness because high salinity
environments are stressful areas for plant survival, thus fewer species will be
present in the higher salinity environments.
•
Elevation will be positively correlated to species richness because most species
cannot handle long term inundation and so they seek refuge in the higher
elevations, thus increasing the number of species present in the higher elevations.
•
Salt marsh vegetation growth (cover, height and density) will differ along salinity
and elevation gradients because salt marshes are tidally influenced landscapes
where the stresses of high salinity and inundation are a daily occurrence, which
will affect each species differently depending on their adaptations to these
stresses.
Specifically, I expect Distichlis spicata, Jaumea carnosa, and Salicornia virginica to
show a positive relationship with pore-water salinity, because they are adapted to tolerate
20
the stress of higher salinity environments; and without the competition from other species
they will be able to reach maximum growth. Since these species are found throughout the
low and high marsh plain, I expect no significant relationship between these species and
elevation. I expect that pore-water salinity will be the determining factor of their
distribution because of their ability to withstand such high salinities.
I expect Spergularia and Triglochin maritimum to show a weak relationship with porewater salinity, if any at all, because they are both adapted to medium salinity (15-25 ppt).
I expect that these two species will show more of a salinity tolerance threshold; meaning
that there will not be a clear linear relationship with growth and salinity, but rather an
absence of these species from the plots with high (>25 ppt) pore-water salinities. These
two species are both common to lower elevation areas; therefore, I expect that elevation
will have a negative relationship on their distribution, because as elevation increases
more species less tolerant of inundation may crowd them out and cause them to seek
refuge in the lower elevations.
I expect Carex lyngbyei, Grindelia integrifolia, Juncus balticus, and Potentilla anserina
spp. pacifica to show a negative relationship with pore-water salinity, because they are
not adapted to tolerate the stress of saline environments, and as salinity increases it will
have detrimental effects on their ability to grow. I expect elevation to have different
relationships with these four species: G. integrifolia and P. anserina I expect to have a
positive relationship with elevation, because neither species is common in the lower
marsh where inundation is a regular occurrence. Both G. integrifolia and P. anserina are
21
unable to withstand either high salinity or inundation; therefore I expect both pore-water
salinity and elevation to be the determining factors of their distribution. C. lyngbyei is
common in the lower marsh, and has adapted to withstand daily inundation; therefore, I
expect that elevation will have a negative relationship with this species. J. balticus is
common in the lower and mid elevations, so I expect no significant relationship between
this species and elevation. However, both C. lyngbyei and J. balticus are not able to
withstand high salinity, thus I expect salinity will be the determining factor in their
distribution.
2. METHODS
2.1 Study site
This study was conducted on four different marshes throughout the Nisqually Delta,
Washington, USA, 47.08°N 122.70°W (Figure 2). Two of the marshes, Phase 2 and
Animal Slough, have significant freshwater inputs and thus represent brackish habitats.
The other two marshes, Phase 1 and Reference, are primarily influenced by seawater and
represent marine habitats. Pore-water salinity in the brackish sites varied from 2 to 26 ppt
throughout the growing season (June-September 2010), and in the marine sites porewater salinity varied from 15 to 45 ppt. The sampled substrate elevation within all four
study sites varied from 2.08 to 3.08 m (NAVD88) for a total range of 1 m. One of each of
the brackish (Phase 2) and marine (Phase 1) marshes were isolated from tidal influence
and converted to agricultural lands in the early 1900’s. They have recently been
reintroduced to tidal influence; Phase 1 in 2002 and Phase 2 in 2006. The other brackish
(Animal Slough) and marine (Reference Marsh) marshes serve as control sites because
22
they have never been tidally restricted. The brackish sites contained a combination of
vegetation typical of both fresh (Typha sp., Carex sp., and Juncus sp.) and salt marshes
(Triglochin maratimum, Potentilla anserina ssp. pacifica, and Distichlis spicata) of the
Pacific Northwest. The restored brackish marsh, Phase 2, still contains several pasture
grass species. The marine sites contained vegetation typical of both high (Deschampsia
cespitosa, Hordeum sp., and Potentilla anserina ssp. pacifica) and low (Salicornia
virginica, Jaumea carnosa, and Distichilis spicata) salt marshes of the Pacific Northwest.
The restored marine marsh, Phase 1, has much more bare ground in comparison to the
control site.
2.2 Survey methods
2.2.1 Vegetation
A combination of seasonal and annual vegetation survey plots were used to inform this
study. Both vegetation surveys were led by the U.S. Geological Society and the seasonal
plots were part of a larger study looking at fish prey resources led by the Nisqually Indian
Tribe. Field work was conducted by USGS biological technicians and volunteers. I was
employed as one of the USGS technicians and assisted in the collection of all the data
used in this thesis.
The goal of this research is to determine the possible relationship between vegetation
parameters (percent cover, height, density, and species richness) and physical parameters
(pore-water salinity and elevation). Measurements of salinity, elevation, and salt marsh
vegetation characteristics were taken at 51 plots within brackish and marine marsh
23
wetlands throughout the Nisqually Delta. Approximately thirty marsh species were
observed and nine were selected for further analysis. The nine selected species were
common in Pacific Northwest salt marshes and cover a range of salinity and inundation
tolerances. Those nine species were: Carex lyngbyei (Lyngby’s sedge), Distichlis spicata
(seashore saltgrass), Grindelia integrifolia (entire-leaved gumweed), Jaumea carnosa
(salt marsh daisy), Juncus balticus (Baltic rush), Potentilla anserina (silverweed),
Salicornia virginica (pickleweed), Spergularia sp. (sand-spurry), and Triglochin
maritimum (sea arrow-grass).
To quantify vegetation growth patterns over time, seasonal vegetation surveys were
conducted at all sites from March to September of 2010. A total of 21 quarter meter
quadrat plots were surveyed monthly over the growing season; 9 plots were established in
the marine marsh sites (Reference n = 6, Phase 1 n = 3) and 12 plots were established in
the brackish marsh sites (Animal Slough n = 6, Phase 2 n = 6). Roman, James-Pirri and
Heltshe (2001) have shown that there is no significant difference in defining vegetation
communities using 0.25, 0.5, 0.75 and 1 m2 quadrats. Zedler (2001) states that a quarter
meter quadrat proved suitable for salt marsh vegetation surveys. For the purposes of this
study and time efficiency the smaller quadrat was used. Within each quadrat, percent
cover, stem density, and maximum height were recorded monthly for each species
present. Percent cover was determined using ocular estimation, where the observer stands
over the quadrat and visually estimates the cover of each species present within the
quadrat, stem density was determined by counting each individual plant rooted in the
quadrat, and maximum height was measured using a measuring tape.
24
In August 2010, at the peak of the growing season, additional vegetation surveys were
conducted. To capture environmental gradients, transects were placed perpendicular to
channels within the study sites extending 50 meters into the marsh plain. Along each
transect, using the point intercept method, the tallest species and height was recorded at 1
m intervals and 0.25 m2 quadrat plots were placed and surveyed at 0, 20, and 40 m.
According to Elzinga et al. (1998) point intercept combined with quadrat sampling is a
good method for increasing the likelihood of capturing even the rare species. With the 21
seasonal plots surveyed monthly and the additional 30 plots along the transects surveyed
in August, there was a total of 51 vegetation plots surveyed throughout the Nisqually
Delta in the month of August 2010.
2.2.2 Soil Pore-Water Salinity
In estuaries, the input of freshwater as well as fine sediment and organic particles from
rivers can complicate salinity measurements. To determine the exact composition of salts
in water, complex methods such as titration are needed. For the purposes of this study,
where the changes in concentration of total salts were more important, we chose to use a
handheld NaCl refractometer (SPER SCIENTIFIC). This instrument is relatively
inexpensive, requires no batteries and is easily transported into the field.
Pore-water salinity was measured by squeezing the pore-water from the substrate,
through a coffee filter, onto the refractometer. In order to document species growth
patterns over time in differing salinity ranges, pore-water salinity was measured monthly
25
from June thru September 2010 in the 21 seasonal plots. Pore-water salinity was recorded
in all 30 annual plots in August 2010 to document peak growth conditions in relation to
salinity.
2.2.3 Elevation
Elevation at each quadrat and at every meter along each transect was determined using a
Leica Viva CS-15 real time kinematic global positioning system (RTK-GPS). This
instrument uses satellite and cellular communications with a reference station to receive
real time elevation corrections at centimeter-level accuracy.
2.3 Statistical analysis
Descriptive statistics (mean and range values) were used to describe the pore-water
salinity and elevation ranges for the species encountered in the surveys. For the elevation
ranges, both quadrat and transect data were used. For the salinity ranges, only the quadrat
data were used because salinity was not measured at every meter along transects.
For correlation analysis the August 2010 quadrat survey data were used for a total of 51
observations. Correlation analysis was conducted to explore the strength of linear
dependence among the peak vegetation growth parameters (percent cover, height, and
density) and the physical parameters (salinity and elevation). The data from these 51
plots did not meet the assumptions for parametric analysis, so Kendall’s non-parametric
correlation analysis was used (Kendall 1938).
26
The 21 plots measured monthly throughout the growing season of 2010 were analyzed by
establishing salinity and elevation zones and investigating the growth patterns within
these zones. The three salinity zones (low, medium and high) were chosen based on the
greenhouse study conducted by Bertness et al. (1992) and the field studies of Crain et al.
(2004). Bertness et al. (1992) used three salinity treatments in the greenhouse study; fresh
(0 g/kg), brackish (15 g/kg), and saline (30 g/kg). Crain et al. (2004) found ranges within
different marshes to be: fresh (0-10 ppt), brackish (15-25 ppt), and marshes exposed to
seawater (27-33ppt). Using these two studies the salinity ranges were established as: low
(<15 ppt), medium (15-25 ppt) and high (>25 ppt). For the 21 plots measured over the
growing season of 2010 there were 5 low, 11 medium, and 5 high salinity plots.
The two elevation zones (high and low marsh) were established using the tidal datum
from closest gauge station to the Nisqually Delta, the Dupont Wharf tide gauge station
(http://tidesandcurrents.noaa.gov/). The data from this gauge station is based on an older
tidal epoch; from observations collected in 1978. This tidal datum includes the relation
between datum planes (tidal and land) and has been used by others (Tanner et al. 2000)
on the Nisqually Delta to establish elevations in both a land datum (NAVD88) and a tidal
datum format. Using this tidal datum, local water levels were identified in the land datum
(NAVD88) as: mean lower low water (MLLW, -3.7 ft.), mean high water (MHW, 8.9 ft)
and mean higher high water (MHHW, 9.8 ft). Then a simple conversion from feet to
meters was done for comparison to the species elevation ranges identified in this study.
The MLLW (-1.1 m) levels are inundated by even the lowest tides, MHW (2.7 m) is
inundated twice daily by the average high tide and the MHHW (3 m) is inundated by only
27
the high tides. In this study, elevation is used synonymously with inundation therefore the
MHW was used for the level at which the low and high marshes were separated.
Anything below MHW (2.7 m) is considered low marsh and anything above is high
marsh.
A 2011 LIDAR raster (Watershed Sciences) was used in GIS to make an elevation map
of the newly restored marsh at the Nisqually National Wildlife Refuge. In order to
capture bare earth elevations, the LIDAR was flown at low tide in the winter of 2011 so
that interference of water and vegetation would be minimized. Using the RTK-GPS
elevation measurements collected at each sampling location, a local scale elevation range
for each species encountered was created. Using the LIDAR data of the newly restored
marsh plain along with the local scale species elevation ranges, elevations necessary for
establishment of salt marsh plant communities can be identified; and estimations of likely
plant type and cover can be made about the recently restored area.
3. RESULTS and DISCUSSION
3.1 Soil pore-water salinity and elevation at the study sites
This study was conducted on four marshes throughout the Nisqually Delta (Figure 3):
Reference Marsh (REF), Phase 1 (P1), Phase 2 (P2), and Animal Slough (AS). The
monitoring stations within the restoration area on the Nisqually National Wildlife Refuge
(NNWR) were not used for the vegetation analysis because the recent tidal restoration
activities will be the dominant factor determining vegetation presence on this landscape
at this time. The four sites used in this study (REF, P1, P2, and AS) cover both the
28
salinity and elevation gradients likely to be encountered on the newly restoring estuary
within the Nisqually National Wildlife Refuge (Figure 4).
Figure 3: Monitoring locations within the Nisqually Delta. The white circles represent the annual
vegetation transects, and the red dots represent the seasonal vegetation plots.
29
Figure 4: Salinity and elevation gradients of all four study sites (REF, P1, P2, and AS). Salinity
values are taken from the 51 annual plots of August 2010; 8 plots were too dry to obtain a salinity
value and are not plotted here. Outlined in grey horizontally are the salinity ranges of high (>25 ppt),
medium (15-25 ppt), and low (<15 ppt). Outlined in grey vertically are the elevation zones of high
(>2.7 m) and low (<2.7 m).
Based on the data collected in this research each of the four study sites had a different
salinity and elevation range. These classifications are based on data gathered from the
plots and may not be characteristic of the entire site. The marine sites, Reference and
Phase 1, both were within the mid to high salinity ranges; with Reference in the higher
elevations while Phase 1 is much lower (Figure 5). The brackish sites, Phase 2 and
Animal Slough, were within the mid to lower salinity ranges; with Phase 2 in the higher
elevations while Animal slough has both high and low elevations (Figure 6). This
illustrates that the plot locations at each of the four study sites has differing
characteristics that cover wide salinity and elevation gradients (Figure 4).
30
Marine Marshes
Salinity and Elevation of Reference Marsh
Salinity (ppt)
a.
50
45
40
35
30
25
20
15
10
5
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
2.9
3
3.1
3.2
Elevation (m)
Salinity and Elevation of Phase 1
Salinity (ppt)
b.
50
45
40
35
30
25
20
15
10
5
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
Elevation (m)
Figure 5 (a & b): August 2010 soil pore-water salinity and elevation of the plots located
within the marine marshes. Both of these sites have salinity values in the mid to high ranges,
with the exception of one plot with a value of 12 ppt. Reference Marsh (a) is the higher
marine marsh with only 3 plots below 2.7 m elevation; while Phase 1 is the lower marine
marsh with only 3 plots above 2.7 m elevation.
31
Brackish Marshes
a.
Salinity (ppt)
Salinity and Elevation of Phase 2
50
45
40
35
30
25
20
15
10
5
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
2.9
3
3.1
3.2
Elevation (m)
Salinity and Elevation of Animal Slough
Salinity (ppt)
b.
50
45
40
35
30
25
20
15
10
5
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
Elevation (m)
Figure 6 (a & b): August 2010 soil pore-water salinity and elevation of the plots located
within the brackish marshes. Both of these sites have many salinity values in the mid to low
ranges. Phase 2 (a) is the higher marine marsh with only 1 plot below 2.7 m elevation; while
Animal Slough is the lower brackish marsh with 3 plots above 2.7 m elevation.
3.2 Salinity Ranges of Nisqually salt marsh vegetation
Salinity ranges were determined for every species encountered by using the salinity and
vegetation data from all the quadrats, both seasonal and annual (Figure 7). The plot
shows the ranges of salinity associated with the presence of a given species. Using the
average salinity values for each of the species observed; six species (Carex lyngbyei,
Cotula coronopifolia, Hordeum brachyantherum, Juncus balticus, Lilaeopsis
32
occidentalis, and Scirpus maritimus) were found to occur in soils with low pore-water
salinity (< 15 ppt), sixteen species (Brown algae, Agrostis alba, Green algae, Atriplex
patula, Distichlis spicata, Deschampsia cespitosa, Eleocharis acicularis, Elymus repens,
Glaux maritimum, Hordeum jubatum, Jaumea carnosa, Potentilla anserina, Puccinellia
nutkaensis, Salicornia virginica, Spergularia sp., and Triglochin maritimum) were found
to occur in soils with medium pore-water salinity (15-25 ppt), and five species (Cuscuta
salina, Grindelia integrifolia, Plantago maritimum, Spergularia canadensis, and Stellaria
humifusa) were found to occur in soils with high pore-water salinity (> 25 ppt). Most of
the species observed in the Nisqually Delta occurred in the brackish salinity range (15-25
ppt), and were observed in a large range of pore-water salinity values, indicating a
tolerance of mid to high salinity for most Nisqually salt marsh species.
33
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Pore Water Salinity Ranges of Nisqually Delta Salt Marsh Vegetation
34
Figure 7: Soil pore-water salinity of all species observed on the Nisqually Delta in the vegetation surveys of 2010. This includes data from both the
seasonal and annual surveys. The points represent mean values and the error bars represent the maximum and minimum salinity values which that
species was encountered. Parentheses denote the number of observations; and the four letter species codes are listed in Table 1.
Salinity (ppt)
Table 1: List of all species encountered on the 2010 surveys.
Spp. Code
AGAL
ALGB
ALGG
ASSU
ATPA
CALY
COCO
CUSA
DECE
DISP
ELAC
ELRE
GLMA
GRIN
HOBR
HOJU
JACA
JUBA
LACA
LIOC
PLMA
POAN
PUNU
SAVI
SCMA
SPCA
SPSP
STHU
TRMA
Common Name
Redtop
Brown algae
Green algae
Douglas' aster
Patent saltbush
Lyngby's sedge
Brass buttons
Salt-marsh dodder
Tufted hairgrass
Seashore saltgrass
Needle spikerush
Ryegrass
Sea milkwart
Entire-leaved gumweed
Meadow barley
Foxtail barley
Salt marsh daisy
Baltic rush
Canadian lettuce
Western lilaeopsis
Sea plantain
Silverweed
Pacific alkali grass
Pickleweed
Seacoast bullrush
Canadian sand-spurry
Sand-spurry
Salt-marsh chickweed
Sea arrow-grass
Scientific Name
Agrostis alba
N/A
N/A
Aster subspicatus
Atriplex patula
Carex lyngbyei
Cotula coronopifolia
Cuscuta salina
Deschampsia cespitosa
Distichlis spicata
Eleocharis acicularis
Elymus repens
Glaux maritimum
Grindelia integrifolia
Hordeum brachyantherum
Hordeum jubatum
Jaumea carnosa
Juncus balticus
Lactuca canadensis
Lilaeopsis occidentalis
Plantago maritimum
Potentilla anserina
Puccinellia nutkaensis
Salicornia virginica
Scirpus maritimus
Spergularia canadensis
Spergularia sp.
Stellaria humifusa
Triglochin maritimum
3.3 Elevation Ranges of Nisqually salt marsh vegetation
Elevation ranges were determined for every species encountered by using the elevation
and vegetation data from both quadrat and point intercept surveys along each transect
(Figure 8). Using the average elevation values for each of the species observed, only four
species’ (Brown algae, Green algae, Eleocharis acicularis, and Spergularia sp.) average
35
elevation occurred in low marsh (<2.71 m), while twenty four species’ (Agrostis alba,
Aster subspicatus, Atriplex patula, Carex lyngbyei, Cotula coronopifolia, Cuscuta salina,
Deschampsia cespitosa, Distichlis spicata, Elymus repens, Glaux maritimum, Grindelia
integrifolia, Hordeum brachyantherum, Hordeum jubatum, Jaumea carnosa, Juncus
balticus, Lactuca canadensis, Plantago maritimum, Potentilla anserina, Puccinellia
nutkaensis, Salicornia virginica, Scirpus maritimus, Spergularia canadensis, Stellaria
humifusa, and Triglochin maritimum) average elevation occurred in high marsh (>2.71
m). Almost all of the species observed in the Nisqually estuary are distributed within the
high marsh elevation. However, fifteen species (Brown algae, Green algae, Atriplex
patens, Carex lyngbyei, Cotula coronopifolia, Distichlis spicata, Eleocharis acicularis,
Glaux maritimum, Hordeum brachyantherum, Jaumea carnosa, Salicornia virginica,
Spergularia canadensis, Spergularia sp., and Triglochin maritimum) had elevation ranges
that span both the high and low marsh, while the remaining thirteen species’ (Agrostis
alba, Aster subspicatus, Cuscuta salina, Deschampsia cespitosa, Elymus repens,
Grindelia integrifolia, Hordeum jubatum, Juncus balticus, Lactuca canadensis, Plantago
maritimum, Potentilla anserina, Puccinellia nutkaensis, Scirpus maritimus, and Stellaria
humifusa) entire elevation range was confined to the high marsh (>2.71 m).
36
)
4) 16) (8) ( 5) 31) 7 0) 32) 26) ( 2) 15) 18) 65) 11) 36) (9 ) (5) (6) 21) 2 6) 11) 37) (2) (9) 14) ( 28 28) ( 2) 10)
1
(
(
( (
(
(
( (
( (
(
( (
(
(
(
(
B P GG LAC LY V I A P (2 C O B R P A A A CA C A OJU S A A L A E BA TH U N U A N IN RE CA U
G
S
S
U
M
C
M
L
A
P
U
A
M
R
M
O
A
S
T
L L S
A L S P A E C S S C D I C H O A T R GL J A S H C A G P L D E J U S P P O G E
A
2
2.25
2.5
2.75
3
3.25
3.5
Elevation Ranges of Nisqually Delta Salt Marsh Vegetation
37
Figure 8: Elevation of all species observed on the Nisqually Delta in the vegetation surveys of 2010. This includes data from both the seasonal and
annual surveys; including point intercept data. The points represent mean values and the error bars represent the maximum and minimum elevation
values which that species was encountered. Parentheses denote the number of observations; and the four letter species codes are listed in Table 1.
Elevation (m, N A VD 88)
3.4 Analysis of Vegetation Growth across Salinity and Elevation Gradients
Pore-water salinity and elevation ranges were plotted for all species observed on the 2010
surveys, but only nine were selected for an in-depth analysis. These nine species were
chosen based on their dominance in previous studies of the Nisqually Delta and their
documented salinity tolerances. Species with tolerances from each zone (high, medium,
and low salinity) were selected to ensure the affects of salinity and elevation were studied
across a full range of plant salinity tolerance levels. The nine species chosen were: Carex
lyngbyei (Lyngby’s sedge), Distichlis spicata (seashore saltgrass), Grindelia integrifolia
(entire-leaved gumweed), Jaumea carnosa (salt marsh daisy), Juncus balticus (Baltic
rush), Potentilla anserina (silverweed), Salicornia virginica (pickleweed), Spergularia
sp. (sand-spurry), and Triglochin maritimum (sea arrow-grass).
In order to examine the species-environment relationships correlation analysis was
conducted using the 51 annual vegetation plots surveyed during the peak of the growing
season in late July to early August of 2010. The data from the 51 plots did not meet the
assumptions for parametric analysis, so Kendall’s non-parametric correlation analysis
was used (Kendall 1938). All possible combinations were tested which yielded 54
correlation scatter plots. For clarity, the results are summarized in Table 2. The scatter
plots are included in the analysis and discussion of each species. Brief descriptions of the
overall results are presented below.
38
Table 2: Salinity and elevation significance values for the nine species correlation
analysis. The * indicates a statistically significant relationship (* p<0.1, ** p< 0.01,
and *** p< 0.001). The +/- indicates a positive or negative relationship.
species
salinity
elevation
Carex lyngbyei % cover
Carex lyngbyei height
Carex lyngbyei density
Distichlis spicata % cover
Distichlis spicata height
Distichlis spicata density
*** -
-
*** -
-
*** -
-
** +
+
-
+
** +
+
Grindelia integrifolia % cover
Grindelia integrifolia height
Grindelia integrifolia density
Jaumea carnosa % cover
Jaumea carnosa height
Jaumea carnosa density
Juncus balticus % cover
Juncus balticus height
Juncus balticus density
Potentilla anserine % cover
Potentilla anserine height
Potentilla anserine density
Salicornia virginica % cover
Salicornia virginica height
Salicornia virginica density
Spergularia sp. % cover
Spergularia sp. height
Spergularia sp. density
Triglochin maritimum % cover
Triglochin maritimum height
Triglochin maritimum density
*+
** +
*+
** +
*+
*** +
** +
** +
+
*+
** +
** +
*-
*+
*-
** +
*-
*+
-
** +
-
** +
-
** +
** +
+
*+
+
** +
+
*+
+
*+
+
*+
+
+
*+
-
*+
+
*+
Of the 51 plots, 8 occurred in the low salinity range (<15 ppt), 15 in the medium (15-25
ppt), 20 in the high (>25 ppt), and 8 plots were too dry in August to get a salinity reading.
The low elevation range (< MHW; 2.71 m) contained 16 of the 51 plots while the high
marsh (>MHW; 2.71 m) contained the remaining 35 plots.
39
Increased pore-water salinity showed a negative relationship with three of the nine
species (Carex lyngbyei, Juncus balticus, and Potentilla anserina) indicating that most
species studied for this thesis are adapted to tolerate higher salinities (Table 2). Increased
elevation showed a negative relationship with only one of the nine species (Carex
lyngbyei) indicating that most species studied for this thesis are not adapted to tolerate
long term inundation, and will most often be found in the higher marsh where they are
inundated only once per day (Table 2).
Carex lyngbyei was negatively influenced by both pore-water salinity and elevation, with
a highly significant influence by pore-water salinity indicating that salinity is the
determining factor for this species’ growth and distribution (Table 2). Grindelia
integrifolia and Potentilla anserina were the two species most influenced (positive
relationship) by elevation, indicating that submergence time is the determining factor for
these species’ growth and distribution (Table 2).
Overall, pore-water salinity and elevation both have a positive influence on the salt marsh
vegetation species studied. These species can tolerate high salinities, but submergence
time (i.e. elevation) may be the dominant factor explaining differences in growth and
distribution. According to the results of this research many species have both salinity and
elevation thresholds at which growth is stunted or the species become absent altogether.
This threshold appears to be at 30 ppt for salinity and below 2 m for elevation.
40
When comparing the seasonal plots to the annual plots used in the correlation analysis,
the salinity and elevation of the seasonal plots were also well distributed throughout both
the salinity and elevation gradients. The seasonal analysis was done using the 21 plots
that were surveyed monthly throughout the growing season (March – September) of
2010. Of the 21 plots, 5 occurred in the low salinity range (<15 ppt), 11 in the medium
salinity range (15-25 ppt) and 5 in the high salinity range (>25 ppt); 8 of the 21 plots
occurred in the low marsh (<MHW; 2.71 m) and 13 in the high marsh (>MHW).
Below are more detailed results for each of the nine species, including both the seasonal
and annual survey analysis. Each point in the correlation scatter plot represents the
presence of that species in a given plot and the points with a value of zero represents
absence of that species for those plots.
3.4.1 Carex lyngbyei
For Carex lyngbyei pore-water salinity had significant negative relationships with percent
cover, height, and density (p-values < 0.001; Table 2; Figure 9). The seasonal analysis of
Carex lyngbyei reveals similar relationships; with an absence from every plot with high
pore-water salinity and maximum growth reached in the plots with lowest pore-water
salinity values suggesting that pore-water salinity is the limiting factor in the growth and
distribution of this species (Figure 10). Density did not show a clear difference between
the high and low elevations in the seasonal analysis, while percent cover and height
reached maximum values in plots with lower elevations, suggesting the ability to
withstand inundation (Figure 10). Although Carex lyngbyei was present in only 13 of the
41
51 annual plots and 9 of the 21 seasonal plots the results still indicate that it is not capable
of withstanding high salinity environments, but may be capable of withstanding
inundation or grow taller in lower elevations in order to reduce the inundation time
(Figure 11). These data suggest that the presence of a tall, dense stands of Carex lyngbyei
in the Nisqually estuary are likely to occur in a lower elevation area near a significant
freshwater influence.
42
CALYpercent cover
2.2
10
30
40
Elevation (m)
2.6
3.0
Kendall's r = -0.14
p = 0.205
Salinity (ppt)
20
Kendall's r = -0.439
p = 0.00034
30
Salinity (ppt)
20
40
2.2
Elevation (m)
2.6
3.0
Kendall's r = -0.137
p = 0.213
10
Kendall's r = -0.455
p = 2e-04
30
Salinity (ppt)
20
40
2.2
Elevation (m)
2.6
3.0
Kendall's r = -0.136
p = 0.217
10
Kendall's r = -0.449
p = 0.000235
43
Figure 9: Kendall’s correlation analysis of Carex lyngbeyi percent cover, height, and density across salinity and elevation gradients within the Nisqually
Delta.
CALYpercent cover
60
0 20
60
0 20
CALYheight
CALYheight
150
0 50
150
0 50
CALYdensity
CALYdensity
150
0 50
150
0 50
% Cover
March
March
Marc h
April
April
April
May
May
May
June
CALY Density
June
CALY Height
June
July
July
July
August
September
September
September
August
August
high
med
low
high
med
low
high
med
low
CALY
June
CALY Height
June
July
July
Augus t
August
September
September
200
180
160
140
120
100
80
60
40
20
0
0
20
40
March
April
May
June
CALY Density
July
Augus t
September
44
high
low
high
May
May
low
April
April
60
March
March
high
low
80
100
120
140
0
20
40
60
80
100
CALY % Cover
Elevation
Figure 10: Seasonal growth patterns of Carex lyngbyei across salinity and elevation gradients within the Nisqually Delta. The salinity gradients are
defined as low (<15ppt), med (15-25ppt) and high (>25ppt); and elevation gradients as low (< MHW) and high (>MHW).
0
50
100
150
200
250
80
60
40
20
0
180
160
140
120
100
100
90
80
70
60
50
40
30
20
10
0
CALY %Cover
Salinity
-2
Height (cm)
Stems 0.25m -2
% Cover
Height (cm)
Stems 0.25m
Salinity (ppt)
Plots with CALY present
50
45
40
35
30
25
20
15
10
5
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
Elevation (m)
Figure 11: Soil pore-water salinity and elevation of the plots where Carex lyngbyei was present.
3.4.2 Distichlis spicata
For Distichlis spicata pore-water salinity had significant positive relationships with
percent cover and density (p values < 0.01; Table 2; Figure 12). The seasonal analysis of
Distichlis spicata reveals similar relationships; with maximum percent cover and density
reached in the plots with highest pore-water salinity values (Figure 13). Distichlis
spicata, however, grew 35 cm taller on average in low salinity areas (Figure 13). This
height difference could be due to less energy expenditure on salt excretion and thus more
energy available for height growth (Hutchinson, 1988). Elevation did not show a strong
relationship with any of the growth metrics (percent cover, height and density) in either
the correlation or seasonal analysis. Distichlis spicata was the most widespread species in
the Nisqually Delta, with a presence in 38 of the 51 annual plots and 18 of the 21
seasonal plots; indicating that it is capable of withstanding the high salinity and
45
inundation of salt marsh environments. These data suggest that Distichlis spicata is likely
to be present at elevations above 2m throughout the Nisqually Estuary marsh plain, with
increased presence in the higher salinity environments (Figure 14).
46
DISPpercent cover
2.2
10
30
40
Elevation (m)
2.6
3.0
Kendall's r = 0.06
p = 0.549
Salinity (ppt)
20
Kendall's r = 0.338
p = 0.00226
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.035
p = 0.724
2.2
10
Kendall's r = -0.123
p = 0.259
30
Salinity (ppt)
20
40
2.2
Elevation (m)
2.6
3.0
Kendall's r = 0.0746
p = 0.451
10
Kendall's r = 0.283
p = 0.00951
47
Figure 12: Kendall’s correlation analysis of Distichlis spicata percent cover, height, and density across salinity and elevation gradients within the
Nisqually Delta.
DISPpercent cover
80
40
0
80
40
0
DISPheight
DISPheight
80
40
0
80
40
0
DISPdensity
DISPdensity
800
400
0
800
400
0
% Cover
April
May
June
July
August
September
April
May
June
July
August
September
March
April
May
June
July
August
September
high
med
low
DISP
June
DISP Height
June
July
July
Augus t
Augus t
Septem ber
Septem ber
0
50
100
150
200
250
300
350
400
0
10
20
March
April
May
June
DISP Density
July
August
September
high
low
high
May
May
low
April
April
30
March
March
high
low
40
50
60
70
0
10
20
30
40
50
60
DISP % Cover
Elevation
48
Figure 13: Seasonal growth patterns of Distichlis spicata across salinity and elevation gradients within the Nisqually Delta. The salinity gradients are
defined as low (<15ppt), med (15-25ppt) and high (>25ppt); and elevation gradients as low (< MHW) and high (>MHW).
0
100
200
300
400
500
600
0
10
DISP Density
high
30
March
med
40
20
low
50
60
70
80
0
10
DISP Height
high
30
March
med
40
20
low
50
60
70
80
DISP % Cover
Salinity
-2
Height (cm)
Stems 0.25m-2
% Cover
Height (cm)
Stems 0.25m
Salinity (ppt)
Plots with DISP present
50
45
40
35
30
25
20
15
10
5
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
Elevation (m)
Figure 14: Soil pore-water salinity and elevation of the plots where Distichlis spicata was present.
3.4.3 Grindelia integrifolia
For Grindelia integrifolia both pore-water salinity and elevation showed significant
positive relationships with percent cover, height, and density (p-values < 0.05; Table 2;
Figure 15). However, elevation shows a much stronger relationship (p-values < 0.001;
Table 2; Figure 15). The seasonal analysis of Grindelia integrifolia reveals similar
relationships; with presence only detected in the mid to high salinity and high elevation
areas (Figure 16). Although Grindelia integrifolia was present in only 8 of the 51 annual
plots and 4 of the 21 seasonal plots the results still indicate that this species is capable of
withstanding high salinity environments, but may not be adapted to withstand long term
inundation (Figure 17). The results of this research show that Grindelia integrifolia was
present only in salinities above 20 ppt, which is not consistent with the literature review
by Hutchinson (1988) stating that Grindelia integrifolia is found at salinities below
15ppt. These data suggest that Grindelia integrifolia is likely to be present at higher
49
elevation locations within the Nisqually estuary, with an increased presence in areas with
brackish to high pore-water salinity. However, Grindelia integrifolia appeared in so few
plots that the trends detected may not be representative of the entire population. More
data on this species is needed to confirm these trends.
50
30
Salinity (ppt)
20
40
3.0
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.358
p = 0.00153
2.2
10
Kendall's r = 0.296
p = 0.0183
GRINdensity
GRINdensity
0 20 40 60
0 20 40 60
GRINpercent cover
GRINpercent cover
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.373
p = 0.000974
2.2
10
Kendall's r = 0.288
p = 0.0218
51
Figure 15: Kendall’s correlation analysis of Grindelia integrifolia percent cover, height, and density across salinity and elevation gradients within the
Nisqually Delta.
Elevation (m)
2.6
Kendall's r = 0.365
p = 0.00138
2.2
10
GRINheight
GRINheight
60
0 20
60
0 20
Kendall's r = 0.29
p = 0.00226
0 10 20 30
0 10 20 30
% Cover
Height (cm)
0
1
2
3
4
0
5
10
15
20
25
30
35
0
1
2
3
4
March
March
March
April
April
April
May
May
May
June
July
GRIN Density
June
July
July
GRIN Height
June
GRIN % Cover
Salinity
August
August
August
September
September
September
high
med
low
high
med
low
high
med
low
GRIN
March
April
May
June
July
August
September
June
GRIN Density
June
July
July
August
August
September
September
0
1
high
May
May
low
April
April
1
March
March
high
low
2
2
3
0
5
10
15
20
25
30
0
GRIN Height
high
1
1
low
2
2
3
GRIN % Cover
Elevation
52
Figure 16: Seasonal growth patterns of Grindelia integrefolia across salinity and elevation gradients within the Nisqually Delta. The salinity gradients
are defined as low (<15ppt), med (15-25ppt) and high (>25ppt); and elevation gradients as low (< MHW) and high (>MHW).
Stems 0.25m-2
% Cover
Height (cm )
Ste m s 0 .2 5 m -2
Plots with GRIN present
50
45
Salinity (ppt)
40
35
30
25
20
15
10
5
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
Elevation (m )
Figure 17: Soil pore-water salinity and elevation of the plots where Grindelia integrefolia was present.
3.4.4 Jaumea carnosa
For Jaumea carnosa both pore-water salinity and elevation showed significant positive
relationships with percent cover and density (p-values < 0.05; Table 2; Figure 18). Height
of Jaumea carnosa showed a significant relationship with elevation (p-value < 0.05), but
not pore-water salinity (Table 2; Figure 18). The seasonal analysis of Jaumea carnosa
reveals similar relationships; with maximum percent cover and density in the higher
salinity and higher elevation areas; and height showing no discernable pattern among the
soil pore-water salinity and elevation ranges (Figure 19). These results show that Jaumea
carnosa has a wide pore-water salinity tolerance range, but not for elevation (Figure 20).
This is not consistent with the literature review of Hutchinson (1988) stating that Jaumea
carnosa has a wide range of salinity tolerance. Jaumea carnosa is, however, one of the
most widespread species in the Nisqually Delta with presence in 27 of the 51 annual plots
and 11 of the 21 seasonal plots. These data suggest that Jaumea carnosa is likely to be
53
present at the higher elevation locations within the Nisqually estuary, with an increased
presence in high elevation areas that have higher pore-water salinity.
54
30
Salinity (ppt)
20
40
0 20 40 60
0 20 40 60
JAC
Apercent cover
JACApercent cover
3.0
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.225
p = 0.0296
2.2
10
Kendall's r = 0.0191
p = 0.868
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.316
p = 0.00221
2.2
10
Kendall's r = 0.333
p = 0.00358
55
Figure 18: Kendall’s correlation analysis of Jaumea carnosa percent cover, height, and density across salinity and elevation gradients within the
Nisqually Delta.
Elevation (m)
2.6
Kendall's r = 0.318
p = 0.00225
2.2
10
Kendall's r = 0.304
p = 0.00834
JAC
Aheight
JAC
Aheight
20 40 60
0
20 40 60
0
JACAdensity
JAC
Adensity
400
200
0
400
200
0
% Cover
20
15
10
5
0
45
40
35
30
25
0
10
20
30
40
50
60
March
March
March
April
April
April
May
May
May
June
JACA Density
June
JACA Height
June
July
July
July
JACA % Cover
Salinity
August
August
August
September
September
September
high
med
low
high
med
low
high
med
low
JACA
180
160
140
120
100
80
60
40
20
0
0
10
20
30
40
50
60
0
10
5
15
20
30
25
35
40
March
March
March
April
April
April
May
May
May
June
JACA Density
June
JACA Height
June
July
July
July
JACA % Cover
Elevation
August
August
August
September
September
September
high
low
high
low
high
low
56
Figure 19: Seasonal growth patterns of Jaumea carnosa across salinity and elevation gradients within the Nisqually Delta. The salinity gradients are
defined as low (<15ppt), med (15-25ppt) and high (>25ppt); and elevation gradients as low (< MHW) and high (>MHW).
0
50
100
150
200
250
300
Height (cm)
Stem 0.25m -2
% Cover
Height (cm)
S te m s 0 .2 5 m -2
Salinity (ppt)
Plots with JACA present
50
45
40
35
30
25
20
15
10
5
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
Elevation (m)
Figure 20: Soil pore-water salinity and elevation of the plots where Jaumea carnosa was present.
3.4.5 Juncus balticus
For Juncus balticus pore-water salinity showed a significant negative relationship with
height (p-value < 0.05; Table 2; Figure 21). Pore-water salinity showed negative
relationships with percent cover and density also, but not quite as strong a relationship (pvalue < 0.1; Table 2; Figure 21). Elevation showed significant positive relationships with
percent cover, height, and density of Juncus balticus (p-value < 0.05; Table 2; Figure 21).
The seasonal analysis of Juncus balticus reveals similar relationships; with maximum
percent cover and density in the low salinity and high elevation areas; presence was only
detected in the mid to low salinity plots, and height showed no discernable pattern among
the pore-water salinity and elevation ranges (Figure 22). Although Juncus balticus was
present in only 10 of the 51 annual plots and 5 of the 21 seasonal plots the results still
indicate a low tolerance of high salinity environments, and may not be adapted to
withstand long term inundation either (Figure 23). These data suggest that Juncus
57
balticus is likely to be present only at the locations within the Nisqually estuary that are
at higher elevations with a significant freshwater influence.
58
JUBApercent cover
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.271
p = 0.0159
2.2
10
Kendall's r = -0.234
p = 0.0638
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.292
p = 0.00903
2.2
10
Kendall's r = -0.249
p = 0.0483
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.271
p = 0.0154
2.2
10
Kendall's r = -0.231
p = 0.0665
59
Figure 21: Kendall’s correlation analysis of Juncus balticus percent cover, height, and density across salinity and elevation gradients within the
Nisqually Delta.
JUBApercent cover
20
0 5 10
20
0 5 10
JUBAheight
JUBAheight
80
40
0
80
40
0
JUBAdensity
JUBAdensity
80
40
0
80
40
0
% cover
Height (cm)
August
August
September
September
May
June
July
August
September
0
April
20
30
40
50
10
high
med
low
60
90
80
70
60
50
40
30
20
10
0
0
2
4
6
8
10
0
March
JUBA Density
JUBA
10
20
30
40
50
60
70
0
10
20
high
July
July
med
June
JUBA Height
June
30
May
May
low
April
April
40
March
March
high
med
low
50
60
70
80
0
2
4
6
8
10
12
14
JUBA % cover
Salinity
March
March
March
April
April
April
May
May
May
June
JUBA Density
June
JUBA Height
June
July
July
July
JUBA % Cover
Elevation
August
August
August
September
September
September
high
low
high
low
high
low
60
Figure 22: Seasonal growth patterns of Juncus balticus across salinity and elevation gradients within the Nisqually Delta. The salinity gradients are
defined as low (<15ppt), med (15-25ppt) and high (>25ppt); and elevation gradients as low (< MHW) and high (>MHW).
Stem s 0.25m -2
% Cover
Height (cm)
Stem s 0.25m -2
Salinity (ppt)
Plots with JUBA present
50
45
40
35
30
25
20
15
10
5
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
Elevation (m)
Figure 23: Soil pore-water salinity and elevation of the plots where Juncus balticus was present.
3.4.6 Potentilla anserina
For Potentilla anserina pore-water salinity showed very weak negative relationships with
percent cover, height, and density (p-value > 0.1); while elevation showed significant
positive relationships with percent cover, height, and density (p-value < 0.01; Table 2;
Figure 24). The seasonal analysis of Potentilla anserina reveals similar relationships;
with presence only detected in the mid salinity and high elevation areas (Figure 25).
Although Potentilla anserina was present in only 9 of the 51 annual plots and 3 of the 21
seasonal plots the results still indicate that it may not be adapted to withstand high
salinity environments, and is not capable of withstanding long term inundation either
(Figure 26). These data suggest that Potentilla anserina is likely to be present only at
locations within the Nisqually estuary that are at higher elevation with a significant
61
freshwater influence. However, Potentilla anserina appeared in so few plots that the
trends I detected may not be representative of the entire population. More data on this
species is needed to confirm the observed trends.
62
P
O
A
Npercent cover
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.343
p = 0.00225
2.2
10
Kendall's r = -0.175
p = 0.167
0 20 40 60
0 20 40 60
P
O
A
Nheight
P
O
A
Nheight
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.317
p = 0.00478
2.2
10
Kendall's r = -0.198
p = 0.116
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.338
p = 0.00265
2.2
10
Kendall's r = -0.179
p = 0.156
63
Figure 24: Kendall’s correlation analysis of Potentilla anserina percent cover, height, and density across salinity and elevation gradients within the
Nisqually Delta.
P
O
A
Npercent cover
10 20 30
0
0 10 20 30
P
O
A
Ndensity
P
O
A
Ndensity
40 80
0
40 80
0
% Cover
Height (cm)
June
POAN Density
June
July
July
July
POAN Height
June
August
August
August
September
September
September
high
med
low
high
med
low
July
June
POAN Density
June
July
July
POAN Height
June
August
August
August
September
September
September
high
low
10
high
May
May
May
low
April
April
April
high
low
15
March
March
March
POAN % Cover
Elevation
20
25
30
35
10
5
0
30
25
20
15
45
40
35
0
May
May
May
1
0
3
2
5
4
5
April
April
April
high
med
low
7
6
0
March
March
March
POAN % Cover
POAN
5
10
15
20
25
30
35
10
5
0
30
25
20
15
45
40
35
0
1
2
3
4
5
6
7
Salinity
64
Figure 25: Seasonal growth patterns of Potentila anserina across salinity and elevation gradients within the Nisqually Delta. The salinity gradients are
defined as low (<15ppt), med (15-25ppt) and high (>25ppt); and elevation gradients as low (< MHW) and high (>MHW).
Stems 0.25m-2
% Cover
Height (cm)
Stems 0.25m -2
Salinity (ppt)
Plots with POAN present
50
45
40
35
30
25
20
15
10
5
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
Elevation (m)
Figure 26: Soil pore-water salinity and elevation of the plots where Potentila anserina was present.
3.4.7 Salicornia virginica
For Salicornia virginica pore-water salinity showed significant positive relationships with
percent cover, height, and density (p-value < 0.01; Table 2; Figure 27). Elevation did not
show significant relationships with percent cover, height, or density (p-value > 0.1). The
seasonal analysis of Salicornia virginica reveals different relationships; with maximum
percent cover and height observed in the low salinity areas, maximum density observed
in the medium salinity areas, and low elevations reaching maximum percent cover and
density (Figure 28). Salicornia virginica was one of the most dominant species observed
in the Nisqually Delta, with a presence in 24 of the 51 annual plots and 10 of the 21
seasonal plots (Figure 29). Salicornia virginica has rather large salinity and elevation
tolerance ranges (Figures 7 & 8). These data suggest that Salicornia virginica is likely to
be present throughout the entire Nisqually estuary, with an increased presence in the
lower elevations with high pore-water salinity. However, these data are somewhat
conflicting; the correlation analysis showed a positive relationship with pore-water
65
salinity, while the seasonal analysis showed increased growth in areas with lower porewater salinity. Also, the seasonal analysis showed increased growth in the lower
elevations while the presence graph showed most occurrences to be in the higher
elevations. This conflicting data indicates that another physical or biological parameter
(such as; nutrient availability, soil type, pH, competition, herbivory, ect.) may be the
determining factor in the distribution and growth of this species. More research on
Salicornia virginica is needed to identify trends in growth and distribution.
66
SAVI percent cover
2.2
10
30
40
Elevation (m)
2.6
3.0
Kendall's r = 0.12
p = 0.252
Salinity (ppt)
20
Kendall's r = 0.337
p = 0.00381
0 20 40 60
0 20 40 60
SAVI height
SAVI height
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.128
p = 0.221
2.2
10
Kendall's r = 0.277
p = 0.0171
30
Salinity (ppt)
20
40
2.2
Elevation (m)
2.6
3.0
Kendall's r = 0.0909
p = 0.382
10
Kendall's r = 0.376
p = 0.00115
67
Figure 27: Kendall’s correlation analysis of Salicornia virginica percent cover, height, and density across salinity and elevation gradients within the
Nisqually Delta.
SAVI percent cover
80
40
0
80
40
0
SAVI density
SAVI density
400
200
0
400
200
0
%Cover
Height (cm)
0
100
200
300
400
500
600
0
10
20
30
40
50
60
0
10
20
30
40
50
60
70
March
March
March
April
April
April
May
May
May
June
SAVI Density
June
SAVI Height
June
July
July
July
SAVI % Cover
Salinity
August
August
August
September
September
September
high
med
low
high
med
low
high
med
low
SAVI
0
200
400
600
800
1000
1200
45
40
35
30
25
20
15
10
5
0
0
20
10
30
40
60
50
70
80
March
March
March
April
April
April
May
May
May
June
SAVI Density
June
SAVI Height
June
July
July
July
SAVI % Cover
Elevation
August
August
August
September
September
September
high
low
high
low
high
low
68
Figure 28: Seasonal growth patterns of Salicornia virginica across salinity and elevation gradients within the Nisqually Delta. The salinity gradients are
defined as low (<15ppt), med (15-25ppt) and high (>25ppt); and elevation gradients as low (< MHW) and high (>MHW).
Stems 0.25m-2
% Cover
Height (cm)
Stems 0.25m-2
Salinity (ppt)
Plots with SAVI present
50
45
40
35
30
25
20
15
10
5
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
Elevation (m)
Figure 29: Soil pore-water salinity and elevation of the plots where Salicornia virginica was present.
3.4.8 Spergularia sp.
For Spergularia sp. pore-water salinity showed positive relationships with percent cover,
height, and density (p-value < 0.1; p-value < 0.05; p-value < 0.1 respectively); while
elevation showed no significant relationships with percent cover, height, or density of (pvalue > 0.1; Table 2; Figure 30). The seasonal analysis of Spergularia sp. reveals slightly
different relationships; with the maximum percent cover and density reached in the
medium salinity and low elevation areas (Figure 31). Spergularia sp. was present in 13 of
the 51 annual plots and 9 of the 21 seasonal plots, and the results of the presence graph
indicate that Spergularia sp. may be adapted to withstand both high salinity and long
term inundation environments (Figure 32). These data suggest that Spergularia sp. is
likely to be present throughout the entire Nisqually estuary, with an increased presence in
the lower elevations with high pore-water salinity.
69
SPSPpercent cover
60
30
Salinity (ppt)
20
40
2.2
Elevation (m)
2.6
3.0
Kendall's r = 0.0274
p = 0.806
10
Kendall's r = 0.238
p = 0.0529
2.2
10
30
40
Elevation (m)
2.6
3.0
Kendall's r = 0.11
p = 0.317
Salinity (ppt)
20
Kendall's r = 0.275
p = 0.0235
30
Salinity (ppt)
20
40
2.2
Elevation (m)
2.6
3.0
Kendall's r = 0.0082
p = 0.941
10
Kendall's r = 0.235
p = 0.0522
70
Figure 30: Kendall’s correlation analysis of Spergularia percent cover, height, and density across salinity and elevation gradients within the Nisqually
Delta.
SPSPpercent cover
SPSPheight
SPSPheight
0 20
60
0 20
SPSPdensity
SPSPdensity
10 20 30
0
10 20 30
0
0 100 250
0 100 250
%Cover
Height (cm)
June
SPsp Density
June
SPsp Height
June
July
July
July
August
August
August
September
September
September
high
med
low
high
med
low
June
SPsp Density
June
Spsp Height
June
July
July
July
August
August
August
September
September
September
high
low
40
high
May
May
May
low
April
April
April
high
low
60
March
March
March
SPsp % Cover
Elevation
80
100
120
140
0
5
10
15
20
25
30
0
10
0
May
May
May
20
April
April
April
20
30
40
50
60
0
March
March
March
high
med
low
SPsp
20
40
60
80
100
120
140
0
5
10
15
20
25
40
35
30
25
20
15
10
5
0
SPsp % Cover
Salinity
71
Figure 31: Seasonal growth patterns of Spergularia sp. across salinity and elevation gradients within the Nisqually Delta. The salinity gradients are
defined as low (<15ppt), med (15-25ppt) and high (>25ppt); and elevation gradients as low (< MHW) and high (>MHW).
Stems 0.25m-2
% Cover
Height (cm)
Stems 0.25m-2
Salinity (ppt)
Plots with SPsp present
50
45
40
35
30
25
20
15
10
5
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
Elevation (m)
Figure 32: Soil pore-water salinity and elevation of the plots where Spergularia sp. was present.
3.4.9 Triglochin maritimum
For Triglochin maritimum pore-water salinity showed no significant relationship with
percent cover, height, or density (p-value > 0.1); while elevation showed significant
positive relationships with percent cover, height, and density of (p-value < 0.05, p-value
< 0.05, p-value < 0.1, respectively; Table 2; Figure 33). The seasonal analysis of
Triglochin maritimum reveals slightly different relationships, with maximum percent
cover, height, and density reached in the medium soil pore-water salinity areas, while
maximum percent cover and density occurred in the high elevation areas (Figure 34).
Triglochin maritimum was present in 20 of the 51 annual plots and 11 of the 21 seasonal
plots, and the results of the presence graph indicate that Triglochin maritimum may be
adapted to withstand high salinity environments, but is not capable of withstanding long
term inundation (Figure 35). These data suggest that Triglochin maritimum is likely to be
present only at the locations within the Nisqually estuary that are at higher elevation,
regardless of soil pore-water salinity.
72
TRMApercent cover
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.227
p = 0.0348
2.2
10
Kendall's r = 0.0265
p = 0.823
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.235
p = 0.0299
2.2
10
Kendall's r = -0.0249
p = 0.835
30
Salinity (ppt)
20
40
Elevation (m)
2.6
3.0
Kendall's r = 0.201
p = 0.0623
2.2
10
Kendall's r = 0.0249
p = 0.835
73
Figure 33: Kendall’s correlation analysis of Triglochin maritimum percent cover, height, and density across salinity and elevation gradients within the
Nisqually Delta.
TRMApercent cover
40
20
0
40
20
0
TRMAheight
TRMAheight
140
0 40 80
140
0 40 80
TRMAdensity
TRMAdensity
40 80 120
0
40 80 120
0
% Cover
Height (cm)
0
10
20
30
40
50
60
70
0
10
20
30
40
50
60
70
0
5
10
15
20
25
30
March
March
March
April
April
April
May
May
May
June
TRMA Density
June
TRMA Height
June
July
July
July
TRMA % Cover
Salinity
August
August
August
September
September
September
high
med
low
high
med
low
high
med
low
TRMA
June
TRMA Height
June
July
July
August
August
September
September
0
10
20
30
40
50
60
0
10
20
March
April
May
June
TRMA Density
July
August
September
high
low
high
May
May
low
April
April
30
March
March
high
low
40
50
60
70
0
5
10
15
20
25
30
TRMA % Cover
Elevation
74
Figure 34: Seasonal growth patterns of Triglochin maritimum across salinity and elevation gradients within the Nisqually Delta. The salinity gradients
are defined as low (<15ppt), med (15-25ppt) and high (>25ppt); and elevation gradients as low (< MHW) and high (>MHW).
Stems 0.25m -2
% Cover
Height (cm)
Stems 0.25m -2
Salinity (ppt)
Plots with TRMA present
50
45
40
35
30
25
20
15
10
5
0
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
Elevation (m)
Figure 35: Soil pore-water salinity and elevation of the plots where Triglochin maritimum was
present.
3.5 Comparison of expected and observed tolerance levels
When the results of this study are compared to what was hypothesized (Table 3) only two
(Carex lyngbyei and Distichlis spicata) of the nine species analyzed responded as
expected. Both Grindelia integrifolia and Potentilla anserina were present at higher
salinities; Jaumea carnosa, Juncus balticus, and Salicornia virginica all showed presence
in the high marsh elevations rather than keeping to the low marsh; and both Spergularia
sp. and Triglochin maritimum showed results that diverge from the hypotheses for both
salinity and elevation. Spergularia sp. (SPsp) was found throughout salinity and elevation
gradients and is not limited to low marsh areas with medium to low salinity; and
Triglochin maritimum was found in a range of salinities, most often present in the high
marsh, not the low marsh.
75
Table 3: Salinity and elevation tolerance ranges expected versus results.
Expected
Nisqually (2010)
Spp.
Code
Scientific Name
Salinity
(ppt)
CALY
Carex lyngbyei
< 20
DISP
GRIN
Distichlis spicata
Grindelia integrifolia
50+
< 15
JACA
Jaumea carnosa
10-40
Elevation
low and
high
low and
high
high
low and
high
Salinity
(ppt)
JUBA
POAN
Juncus balticus
Potentilla anserina
10-30
0-12
low to mid
high
5-28
10-30
SAVI
Salicornia virginica
20-80
low
5-45
SPSP
Spergularia sp.
6-20
low
11-45
TRMA
Triglochin maritimum
0-21
low
10-45
< 30
40+
> 20
4-45
Elevation
low and
high
low and
high
high
low and
high
low and
high
high
low and
high
low and
high
low and
high
The papers that Hutchinson (1988) reviewed were all studies based in the Pacific
Northwest, however many of even these studies gathered salinity data from the closest
water bodies rather using in situ data like this study did. Also Hutchinson (1988)
converted all parameters and units described in the literature review into salinity in parts
per thousand (ppt) in order to standardize the results. The resulting salinity values include
information derived from soil, inundating water, and growing medium salinities. There
can be significant differences in soil salinity versus the salinity of inundating waters.
These factors could explain some of the differences between the results and hypothesized
relationships.
Other factors that may explain the differences between the hypotheses and results are the
many environmental factors influencing plant establishment, growth, and distribution,
such as: soil chemistry (including organic matter, pollutants, and nutrients), type, and
76
moisture; distance from channels, drainage/tidal retention time, water quality, and
competition (Bornman et al. 2008, Gutrich et al. 2009, Howard 2010, Wolanski and
Richmond 2008).
3.6 Species Richness
Species richness was expected to decrease as pore-water salinity increased because high
salinity environments are stressful areas for plant survival. It was also expected that
species richness would increase as elevation increased because many species seek refuge
from inundation in the higher marsh. The results of this research showed no strong
relationship between salinity and species richness (Figure 36); while the relationship
between elevation and species richness was quite clear (Figure 37). The greatest number
of species observed in the low marsh plots was six, and more often only two species are
present in the low marsh plots. However, in the high marsh there were often six or more
species present in one plot.
The number of species present varies throughout all salinity values, most likely due to the
fact that many salt marsh species have adapted to the higher salinities and have large
tolerance ranges. More species are present at higher marsh plain elevations, most likely
due to the fact that many species are not adapted to inundation (i.e. lower elevations);
therefore occur at higher elevations to avoid the long inundation times.
77
12
8
6
2
4
Species Richness
10
Kendall's r = 0.0767
p = 0.499
10
20
30
40
Salinity (ppt)
Figure 36: Species richness versus soil pore-water salinity. For this research salinity ranges were
established as low (<15ppt), medium (15-25ppt), and high (>25ppt).
78
12
8
6
2
4
Species Richness
10
Kendall's r = 0.526
p = 2.48e-07
2.2
2.4
2.6
2.8
3.0
Elevation (m)
Figure 37: Species richness versus elevation. For this research the separation between high and low
marsh was established at 2.7m.
3.7 Site Conditions of the Restoration Area on the Nisqually National Wildlife Refuge
Within the Nisqually National Wildlife Refuge (NNWR) estuary restoration area there
are five tidal slough channels which are the location of fifteen survey locations (Unit 1, 2,
79
3, 4, and Madrone; Figure 2). Survey locations along each slough were established at the
north (mouth), middle, and the southern (most inland) portion of the channel (Figure 3).
The pore-water salinity of the survey locations within the restored area of the NNWR
varied from as low as 3 ppt to 32 ppt over the 2010 survey season (Figure 38). Most
salinity values of these sites fell within the brackish (15-25 ppt) to marine (>25 ppt)
salinity range. Two sites (Unit 3 middle and south) averaged a salinity value of <15 ppt
(fresh); five sites (Unit 3 north, Unit 2 north and mid, Unit 4 mid, and Madrone mid)
averaged 15-25 ppt (brackish); and eight sites (all of Unit 1, Madrone north and south,
Unit 4 north and south, and Unit 2 south) averaged >25 ppt (marine). Unit 3 averaged the
three lowest pore-water salinity values; most likely due to the proximity of Unit 3 to the
Nisqually River, whereas the rest of sites within the restored area on the NNWR are more
influenced by the waters of Puget Sound resulting in higher salinity values (Figure 2).
The elevations of the fifteen survey sites along the five main slough channels in the
NNWR restoration area range from 1.12-2.97 m, with the maximum elevation at Unit 2
south and the minimum at Unit 2 north (Figure 38). None of the sites averaged an
elevation above the MHW (2.71 m) level, and only three transects (Unit 2 mid and south,
and Madrone north) had a maximum elevation at some point that occurred within the
high elevation range (>2.71 m). The low elevations on the Refuge are likely due to the
lack of sediment influx and subsidence over the last century in response to the land
alterations for farming.
80
Salinity of Nisqually NWR
a.
35
Salinity (ppt)
30
25
20
15
10
5
MS
MN
MN
MM
4S
4S
4M
4N
3S
3M
3N
2S
2M
2N
1S
1M
1N
0
Channel Transect Location
Elevation of Nisqually NWR
b.
3.5
Elevation (m)
3
2.5
2
1.5
1
0.5
MS
MM
4M
4N
3S
3M
3N
2S
2M
2N
1S
1M
1N
0
Channel Transect Location
Figure 38: Pore-water salinity and elevation ranges of the study sites on the Nisqually National
Wildlife Refuge in 2010. The dot represents the mean and the error bars represent the maximum and
minimum elevation values. The number indicates the study unit and the letter indicates the station
(North, Middle or South). Both the salinity (30 ppt) and elevation (2 m) thresholds established by this
research are highlighted here.
Vegetation data from the NNWR survey locations were not used in this research because
the recent restoration activities would be the dominant factor affecting vegetation growth
and distribution. However, the salinity and elevation data can be used along with the
vegetative results of this research to predict habitat types likely to colonize the recently
restored site. The results of this research indicate a salinity threshold of 30 ppt for some
salt marsh species (Figure 7). Most of the survey locations on the NNWR are at or below
this threshold, which means that salinity will most likely not be the limiting factor for salt
81
marsh vegetation establishment in the newly restored estuary. The results above also
indicate an elevation threshold of 2 m below which no vegetation was observed. Most of
the survey locations on the NNWR are below this elevation threshold indicating a need
for sediment influx. However, according to the 2011 LIDAR data (Figure 39) over half of
the NNWR estuary restoration area is currently at elevations that are capable of
supporting salt marsh vegetation (>2 m), and since the dike removal in 2009 sediment
accretion has been measured across the restoration site (Turner et al. 2011).
Since submergence time (i.e. elevation) appears to be the dominant factor for estuarine
vegetation growth estimations are not based solely on the fifteen survey location’s
elevation data but are combined with LIDAR data to capture more elevation coverage of
the restored estuary. The habitats likely to be found within the restored estuary on the
NNWR are mudflat (<2 m), low marsh (2 - 2.7 m (MHW)) and high marsh (>2.7 m
(MHW); Figure 39). According to the LIDAR over half of the NNWR estuary restoration
area is currently at elevations that are capable of supporting salt marsh vegetation (>2 m).
Most salt marsh species in this study were detected at a minimum elevation of 2.5 m
(NAVD88) which represents approximately 16% of the NNWR restoration site. Of that,
approximately 9% is considered high marsh (>2.7); which is where, according to this
research, the greatest diversity of species is present. However, Carex lyngbyei was found
to be negatively influenced by both pore-water salinity and elevation (Table 2) suggesting
that areas within the restored estuary that have lower elevations with a significant
freshwater influence may not become unvegetated mudflat, but rather dominated by
Carex lyngbyei. Both Distichlis spicata and Spergularia sp. are able to withstand low
82
elevations and high pore-water salinity suggesting that a large portion of the NNWR will
be dominated by these two species. The higher elevations within the restored estuary are
likely to contain a diversity of salt marsh species, and the higher areas with a freshwater
influence is where it will be likely to find Juncus balticus and Potentilla anserina.
83
Figure 39: Elevation of the Nisqually Delta based on a 2011 LIDAR flown by Watershed Sciences.
84
4. CONCLUSION and RECOMMENDATIONS
The Nisqually River Delta is an estuary that has been modified by restricting tidal flow to
reclaim lands for agriculture. Recently, the Nisqually National Wildlife Refuge, working
in collaboration with the Nisqually Indian Tribe and Ducks Unlimited, restored a large
amount of the tidal flows as part of the largest estuary tidal marsh restoration project in
the Pacific Northwest.
Over time, salt marsh vegetation has adapted to withstand the high salinity and periodic
inundation associated with intertidal landscapes. This thesis explored this relationship in
the salt marshes of the Nisqually Delta in order to quantify the tolerance ranges as well as
the optimal growing conditions for several common salt marsh species. This research
provides knowledge that can be used to identify suitable locations for salt marsh habitat
restoration, and to ensure successful colonization of native species.
Vegetation survey results above indicate an upper salinity threshold of 30 ppt for some
salt marsh species. Most of the survey locations on the NNWR are at or below this
threshold, which means that salinity will most likely not be the limiting factor for salt
marsh vegetation establishment in this newly restored estuary. The results above also
indicate an elevation threshold of 2 m below which no vegetation was observed. Over
half of the NNWR estuary restoration area is currently at elevations that are capable of
supporting salt marsh vegetation (>2 m). This research shows that both pore-water
salinity and elevation have a positive influence on the salt marsh vegetation species
studied. Indicating that these species can tolerate high salinities, but submergence time
85
(i.e. elevation) may be the dominant factor explaining differences in their growth and
distribution.
This thesis examined salinity and elevation influences on vegetation, however, there are
several environmental factors influencing plant establishment, growth, and distribution,
such as: soil chemistry (including organic matter, pollutants, and nutrients), type, and
moisture; distance from channels, drainage/tidal retention time, water quality, and
competition. Bornman et al. (2008) found that soil moisture was most influential on
species with large salinity tolerance ranges, while species with narrow salinity ranges
were limited by salinity and thus forced into drier habitats or areas with freshwater
influence. Howard et al. showed that soil type and salinity were significantly related, and
that soil type was a determining factor in plant growth in Louisiana marshes. Future
research suggestions include continued monitoring of the Nisqually Delta vegetation
along with the sedimentation and subsidence processes that affect their distribution and
colonization success, as well as studying more environmental factors that may be
contributing to salt marsh vegetation growth and distribution.
Currently, there is concern in the Pacific Northwest about the condition of Puget Sound
and the many estuarine habitats along the shoreline. Most of these estuaries have been
degraded due to anthropogenic activities and are in need of restoration. Restoration of
any landscape takes many years, but since the dike removal in 2009, sediment accretion
has already been measured on the NNWR restoration site. In estuaries, salt marsh
vegetation helps trap and stabilize sediment leading to additional sediment accretion and
thus increased elevations over time (Adam 1990). Restoration of the Nisqually Delta has
86
the potential to expand critical habitat for threatened salmon species, migratory birds, as
well as contribute to the recovery of the Puget Sound ecosystem. The full removal of the
dike at NNWR, as opposed to breaches, allows for more connectivity and sediment
deposition avenues throughout the landscape; thus increasing the ability of the restoration
site to build elevation levels, a key factor in salt marsh vegetation growth and
distribution.
87
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