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Environmental Conditions Promoting Non-native Phragmites australis Expansion in Great Lakes Coastal Wetlands

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The invasion and expansion of the non-native Phragmites australis in Great Lakes coastal wetlands is of increasing concern, but quantitative studies of the extent, rate, and causes of invasion have been lacking. Here we revisited 307 plots in 14 wetlands along the Great Lakes coast in 2005 that had previously been sampled for vegetation in 2001–2003. During the 2–4years between sample events, Phragmites occurred in 101 plots. Genetic analysis revealed that none of the Phragmites samples collected at the 14 wetlands belonged to the native genotype. Decreases in water depth and bare soil area were associated with the greatest increases in Phragmites cover. Phragmites invasion was greater on Lakes Michigan, Huron, and Erie than it was on Lake Ontario, and occurred predominantly on sandy substrates. Soil water concentrations of NO3-N, NH3-N, and soluble reactive P did not differ significantly between plots with and without Phragmites. Monitoring coastal wetlands where water level has dropped and controlling Phragmites at early stages of invasion are essential for maintaining healthy Great Lakes coastal wetlands of high species diversity and wildlife habitat. This becomes important as water levels in the Great Lakes have reached extreme lows and are expected to decline with future climate change. KeywordsExotic species-Invasion-Invasive species-Nutrients-Soil-Water level
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ORIGINAL PAPER
Environmental Conditions Promoting Non-native
Phragmites australis Expansion in Great Lakes
Coastal Wetlands
Mirela G. Tulbure & Carol A. Johnston
Received: 24 August 2009 / Accepted: 15 February 2010 / Published online: 18 May 2010
#
Society of Wetland Scientists 2010
Abstract The invasion and expansion of the non-native
Phragmites australis in Gre at Lakes coastal wetlands is of
increasing concern, but quantitative studies of the extent,
rate, and causes of invasion have been lacking. Here we
revisited 307 plots in 14 wetlands along the Great Lakes
coast in 2005 that had previously been sampled for
vegetation in 20012003. During the 24 years between
sample events, Phragmites occurred in 101 plots. Genetic
analysis revealed that none of the Phragmites samples
collected at the 14 wetlands belonged to the native
genotype. Decreases in water depth and bare soil area were
associated with the greatest increases in Phragmites cover.
Phragmites invasion was greater on Lakes Michigan,
Huron, and Erie than it was on Lake Ontario, and occurred
predominantly on sandy substrates. Soil water concentra-
tions of NO
3
-N, NH
3
-N, and solub le reactive P did not
differ significantly between plot s with and without Phrag-
mites. Monitoring coastal wetlands where water level has
dropped and controlling Phragmites at early stages of
invasion are essential for maintaining healthy Gre at Lakes
coastal wetlands of high species diversity and wildlife
habitat. This becomes important as water levels in the Great
Lakes have reached extreme lows and are expected to
decline with future climate change.
Keywords Exotic species
.
Invasion
.
Invasive species
.
Nutrients
.
Soil
.
Water level
Introduction
Phragmites australis (Cav.) Trin. ex Steud. (hereafter
Phragmites) has expanded tremendously in North America
with the introduction of the M Eurasian genotype, and has
become one of the most invasive plants in wetlands along
the Atlantic coast (Ailstock et al. 2001; Minchinton 2002;
Bart et al. 2006). The species has become a problem more
recently along the Great Lakes coast, where rapid Phrag-
mites expansion has been noted on Lake Erie (Wilcox et al.
2003; Ghioca-Robrecht et al. 2008) and Green Bay (Pengra
et al. 2007; Tulbure et al. 2007). Lacking the salinity
gradients that limit the seaward expansion of Phragmites on
ocean coasts (Meyerson et al. 2000; Bart and Hartman
2003), wetlands of the Great Lakes coast may b e
particularly susceptible to future invasion by Phragmites.
Research is needed to understand the mechanisms and
factors that make coastal wetlands in this region susceptible
to Phragmites invasion.
Great Lakes coastal wetlands are dynamic, with average
annual water levels changing by a meter or more over
decadal time scale s (Wilcox et al. 2007). These water level
fluctuations are a major factor controlling the composition
of native vegetation in Great Lakes coastal wetlands,
producing and maintaining plant species diversity by cycles
of drawdown and flooding (Keddy and Reznicek 1986;
Hudon 1997; Keddy 2000; Gathman et al. 2005). When
non-native aggressive taxa such as Phragmites germinate,
proliferate and form monotypic stands, the germination of
native species dependent on fluctuating water levels is
obstructed (Haslam 1972; Thiet 2002; Herrick and Wolf
M. G. Tulbure (*)
:
C. A. Johnston
Department of Biology and Microbiology,
South Dakota State University,
Brookings, SD 57007, USA
e-mail: Mirela.Tulbure@sdstate.edu
Present Address:
M. G. Tulbure
Geographic Information Science Center of Excellence,
South Dakota State University,
Brookings, SD 57007, USA
Wetlands (2010) 30:577587
DOI 10.1007/s13157-010-0054-6
2005). This reduces plant species diversity and wetland
functionality (Chambers et al. 1999; Galatowitsch et al.
1999).
Average annual lake levels on Lakes Michigan and
Huron were >0.5 m below the long-term average between
2000 and 2008 (http://www.glerl.noaa.gov/data/now/wlevels/
levels.html), which may have contributed to the recent
expansion of Phragmites on their coasts. Prolonged low
Great Lakes levels exposed unvegetated lake bottom sedi-
ments, providing a substrate for colonization by new plants,
such as invasive Phragmites (Pengra et al. 2007; Tulbure et
al. 2007). Repeat visits to a Green Bay coastal wetland in
2001 and 2004 showed a 100-fold increase in Phragmites
cover (Tulbure et al. 2007).UnlikethelakelevelofLake
Ontario, which has been partially regulated since 1958,
lakes Erie, Michigan, and Huron are not regulated and
their lake levels therefore respond more to climatic and
other large scale changes (Sellinger et al. 2008). Wetland
values such as diversity, primary productivity, and habitat
for wildlife and waterfowl will be affected if an increase in
frequency and duration of low w at e r levels res u lt s from
future climate change (Mortsch 1998).
A numbe r of factors have been shown to facilitate
Phragmites invasion, including land use changes in a
wetlands watershed (King et al. 2007), increases in nitrate
and the concentration of other nutrients (Marks et al. 1994 ;
Bertness et al. 2002; Minchinton and Bertness 2003), the
presence of exposed mineral soil (Tulbure et al. 2007), and
alterations of the hydrologic regime by roads, dikes, and
ditches ( McNabb and Batterson 1991; Bart and Hartman
2000, 2003;Herrick and Wolf 2005; Maheu-Giroux and de
Blois 2007; Johnston et al. 2008). The use of dikes is a
prevalent feature in coastal wetlands on the southwestern
shore of Lake Erie (Kroll and Gottgens 1997; Gottgens et
al. 1998 ).
Once it invades, Phragmites expands rapidly via
rhizomes and seeds (Haslam 1973; Bart and Hartman
2003) and becomes monodominant in a wetland, displacing
the native flora (Marks et al. 1994; Chambers et al. 1999;
Meyerson et al. 2000). Phragmites expands vegetatively by
horizontal rhizome growth at a rate of 12 m/yr (Haslam
1972), grows taller and has higher biomass than other
marsh species (Meyerson et al. 2000), outcompeting co-
occurring plant species by shading and litter mat formation
(Haslam 1973). The native subspecies Phragmites australis
subsp. americanus Saltonstall, P.M. Peterson & Soreng,
which is endem ic to the Great Lakes, is considered to be
less aggressive than the non-native M Eurasian genotype
(Saltonstall et al. 2004).
Despite anecdotal accounts of recent Phragmites expan-
sion on the Great Lakes, quantitative studies of the rate and
extent of Phragmites invasion are lacking. The EPA-funded
Great Lakes Environmental Indicators (GLEI) project
collected data on plant species of Great Lakes coastal
wetlands during 20012003 (Johnston et al. 2007a). This
provided baseline vegetation data and a unique opportunity
to assess Phragmites shifts in time. In the present study, we
returned in 2005 to 14 Great Lakes coastal wetlands in the
Eastern Broadleaf Forest ecoprovince (Keys et al. 1995)
that had some Phragmites present when first sampled, and
quantified short-term changes in the extent of Phragmites
cover.
The overarching aim of this study was to determine what
characteristics caused coas tal wetlands in the southern
Great Lakes region to be susceptible to Phragmites
invasion. Specific objectives were to: (1) determine the
nativity of Phragmites, (2) determine whether Phragmites
expanded since first sampled at the 14 revisited wetlands;
(3) identify natural and anthropogeni c factors that influ-
enced invasive Phragmites success at these wetlands; (4)
assess whether short-term change in Phragmites cover
differed on different soil types, and whether nutrient
concentrations were different in Phragmites versus non-
Phragmites stands, and (5) examine whether the increase in
Phragmites cover was greater on Great Lakes wetlands in
which there was a drop in water levels between 1999 and
2001 (i.e., Lakes Michigan, Huron, Erie) than on the lake
where there was an increase in water levels between 1999
and 2001 (i.e., Lake Ontario).
Methods
Site Selection and Vegetation Sampling
The GLEI project sampled 35 Great Lakes coastal wetlands
within the Eastern Broadleaf Forest (EBF) ecoprovince,
which encompasses Lake Ontario, Lake Erie, and southern
Lakes Huron and Michigan (GLEI sites listed in Johnston
et al. 2007a). Of these wetlands, we revisited 14 of the 16
that contained Phragmites in 20012003 when they were
first sampled as part of the GLEI project; time constraints
prevented us from revisiting the other two (Fig. 1, Tables 1
and 2). We focused on the EBF region because the invasive
genotype was documented to occur in numerous coastal
wetlands of the southern Great Lakes but not the no rthern
Great Lakes (Saltonstall 2002). A total of 307 1-m×1-m
plots were sampled at the 14 wetland sites and the number
of plots sampled per wetland ranged from 8 to 96
proportional to wetland size (Table 1).
Geographic coordinates of each 1-m×1-m plot within
the wetland study sites had been recorded using a hand held
Garmin GPSMAP 76 unit (Garmin International Inc.,
Olathe, KS) during initial sampling in 20012003, and
were used to return to the same locat ions during the
summer of 2005. Plot loc ations were the average of
578 Wetlands (2010) 30:577587
hundreds of readings recorded by a tripod-mounted GPS set
to continuously record as field researchers were collecting
vegetation data at each plot (Johnston et al. 2009a). All the
sites were herbaceous wetlands in level terrain, therefore
errors introduced by blocked or multipath signals due to
topography or canopy cover were minimal.
Plots were distributed along randomly placed transects
within areas mapped as emergent vegetation (Cowardin et
al. 1979) by national and state wetland inventories along
the Great Lakes. Transects were established with a
geographic information system (GIS) prior to field
campaigns, using a program called Sample (http://www.
quantdec.com/sample ) to randomize transect placement.
Each transect intersected a randomly selected point
generated by the Sample program, and was oriented
along the perceived water depth gradient, extending from
open water to the upland boundary. Transect length and
target number of plots were determined in proportion to
the size of the wetland to be sampled (20 plots/60 ha,
minimum transect length=40 m, minimum plots/site=8).
Plot locations were established in the field by dividing
each transect into 20 m segments and randomly locating
a plot in each segment using a random number table
(Bourdaghs et al. 2006). Within each plot percent cover of
Phragmites was estimated visually according to modified
Braun-Blanquet cover class ranges (ASTM 1997): < 1%, 1
to<5%, 5 to < 25%, 25 to<50%, 50 to<75%, 75 to 100%.
Prior to data analyses, cover classes were converted to the
midpoint percent cover of each class using the algebraic
mid-points of the six cover class ranges (0.5, 3.0, 37.5,
62.5, 87.5).
Leaf samples were collected from Phragmites stands at
each wetland revisited and identified as native or non-native
genotype using the genetic analysis described in (Tulbure
et al. 2007) and based on Saltonstalls(2002)protocol.
Table 1 Comparison of Phragmites cover at 14 Great Lakes wetland study sites between first and second sampling. Invaded = plots where
Phragmites was not present in 2001, but expanded in 2005; Increased/decreased = plots where Phragmites was present in 2001 but increased/
decreased in cover by 2005; Remained unchanged = plots where Phragmites cover did not change from 2001 to 2005
Site name Lake Mean Phragmites
cover per plot (%)
at each site
Number of
samples (plots), n
Number of plots
with Phragmites
Number of plots where Phragmites
200103 2005 200103 2005 Invaded Increased Decreased Remained
unchanged
Kalamazoo River Michigan 0.03 0.65 96 1 1 1
White Feather Creek Huron 0.09 7.63 27 5 8 3 4 1
Neuman Road Huron 0.04 0.08 13 1 2 1 1
Blind Pass Huron 4.34 24.48 22 10 12 5 5 3 2
Wildfowl Bay Huron 8.07 24.00 22 10 12 5 4 3 3
Caseville Huron 35.63 78.44 8 8 8 6 2
Otter Creek Erie 12.73 21.88 24 7 6 1 3 2 2
Toledo Beach Erie 26.25 26.25 10 3 3 3
Bay Creek Erie 17.50 32.15 13 4 8 5 1 2 1
Little Lake Creek Erie 64.05 73.80 10 10 10 3 7
Kelly Doty Drain Erie 52.50 39.14 11 10 7 2 4 4
Presque Isle Erie 2.70 19.30 15 2 10 8 2
Braddock Bay Ontario 0.60 2.50 25 1 1 1
Fox Creek Ontario 0.27 0.05 11 1 1 1
Total number of plots (n) 307 73 89 28 32 15 26
Table 1 Comparison of Phragmites cover at 14 Great Lakes wetland
study sites between first and second sampling. Invaded = plots where
Phragmites was not present in 2001, but expanded in 2005; Increased/
decreased = plots where Phragmites was present in 2001 but
increased/ decreased in cover by 2005; Remained unchanged = plots
where Phragmites cover did not change from 2001 to 2005
Fig. 1 Location of the 14 wetland sites (black triangles) re-sampled in
2005
Wetlands (2010) 30:577587 579
Abiotic Factors
Thirteen abiotic environmental factors were measured in
the field or derived from mapped data for each of the 14
study sites (Table 3). At each plot, vegetation data were
collected, water depth was measured, and bare soil area was
estimated using the same six cover class ranges used for
plants. Water depth was measured using a meter stick,
which was inserted until we felt resistance from bottom
sediments without applying pressure. The values obtained
in 2005 were subtracted from comparable values for water
depth and bare soil area measured initially by t he GLEI
project t o compute change in water depth (WaterDepth-
Diff) and bare soil (BareSoilDiff). The substrate at each
plot was examined to a depth of 30 cm below the litter
layer using a soil probe, and assigned to one of the
following broad categories: organic, sand, silt, clay.
Organic soils were those composed of organic soil
material (peat or muck) in a histic epipedon (Soil Survey
Staff 199 9 ); undecomposed plant litter overlying the soil
surface was excluded when m aking this determination.
The texture of mineral soils (i.e., sand, silt, clay) was
determined by feel using standard field methods (Soil
Survey Staff 1951).
In 2005 we measured nitrate (NO
3
-N), ammonia (NH
3
-
N), and soluble reactive phosphorus (SRP) in soil water in
Phragmites versus non-Phragmites stands at each wetland
site. Phragmites stands were chosen that were 100%
covered with Phragmites and along or close to the initial
GLEI sample transect, but not necessarily coinciding with
it. Non-Phragmites stands were chosen that had no
Phragmites present and were at the same elevation and as
close as possible to the Phragmites stands so as to minimize
confounding differences due to edaphic conditions. We dug
holes using an auger in the plant rooting zone, and water
that accumulated in the holes was used for nutrient analysis.
All nutrients were measured in the field using a Digital
Hach PortableDR/890 Colorimeter (Hach Company, Love-
land, CO). Nutrient measurements were taken at three
locations in each stand type (Phragmites vs. non-Phrag-
mites). Nitrate was measured using the Chromotropic Acid
Method (estimated detection limit, EDL, of 0.3 mg/L NO
3
-
N); ammonia was measured using the Salicylate Method
(EDL of 1 mg/L NH
3
-N), and SRP using the Ascorbic Acid
Method (EDL of 0.05 mg/L PO
4
; Hach Company 2005).
We examined digital orthophotos taken 18 years prior
to the initial field work (USGS 2007) to determine if sites
were previ ously diked. The agriculture and urban indices
were developed by the GLEI project using methods
described by Danz et al. (2007), but were calculated for
watersheds draining to the specific wetland s studied
(Hollenhorst et al. 200 7). The agricultural index was
derived from 21 variables characteristic of the major types
of stresses in a wetlands watershed associated with
agricultural activities (e.g., nutrient runoff, fertilizers,
pesticide application, and erosion), and the urban index
was derived from 14 variables associated with human
population, r oad density, and developed land in the
Table 2 Description of water level at 14 wetland sites. Lake level changes based on July average monthly levels (see Table 4) except where
indicated. Negative numbers indicate declines in water levels
Site Lake Initial sample
year
Lake level
change, m
Diked? Number of plots where water level
increased decreased same
Kalamazoo River Michigan 2002 0.14 N 4 18 74
White Feather Cr. Huron 2003 0.15 N 21 1 5
Neuman Road Huron 2003 0.15 N 9 0 4
Blind Pass Huron 2003 0.15 N 8 6 8
Wildfowl Bay Huron 2003 0.15 N 7 0 15
Caseville Huron 2003 0.15 N 1 2 5
Otter Creek Erie 2002 0.02 N 4 9 11
Toledo Beach Erie 2002 0.02 Y 7 1 2
Bay Creek Erie 2002 0.02 N 0 4 9
Little Lake Creek Erie 2003 0.04 Y 0 3 7
Kelly Doty Drain Erie 2003 0.04 Y 3 2 6
Presque Isle
a
Erie 2003 0.04 N 0 8 7
Braddock Bay
ab
Ontario 2002 0.53 N 0 18 7
Fox Creek
a
Ontario 2001 0.17 N 0 5 6
a
2005 lake level from August used to correspond with final sampling date
b
lake level from June used to correspond with initial sampling date
580 Wetlands (2010) 30:577587
watershed (Danz et al. 2007). Principal component analysis
was carried out for each category of variables, and the
resulting principal components were standardized so that
the mean equaled 0 and the standard deviation equaled 1.
Index values for all GLEI EBF wetland study sites ranged
from 0.11 (least stress) to 1.14 (most stress) for the
agricultural index and from 2.09 to 1.82 for the urban
index. The values of the agricultural index at our revisit
sites ranged from 0.25 to 1.14, while the urban index
ranged from 1.11 to 1.82. Areal proportions of row crop
and development within wat ersheds around the National
Wetlands Inventory boundary were computed to account
for anthropogenic disturbance at different spatial scales
(Brazner et al. 2007).
Data Analysis
To gain insight into the drivers of change in Phragmites
cover between the two sampling events, we used mixed
models incorporating both fixed and random effect varia-
bles with PROC MIXED, SAS Version 9.1 (SAS Institute
Inc. 2001), with plots nested within wetland sites. We used
13 explanatory variables as fixed effects, which were
hypothesized to influence Phragmites change (Table 3).
We assessed the degree of multicollinarity among the
continuous explanatory variables by co mputing variance
inflation factors (VIF, Neter et al. 1990). Five variables
(agriculture PC, watershed to wetland area, watershed area,
row crops, and development in the watershed) with the
highest VIFs were eliminated from the model to reduce
collinearity, which resulted in VIFs <= 10 in the new mixed
model.
A one-way ANOVA followed by Tukeys HSD compar-
ison test was used to analyze: a) initial Phragmites cover on
four different soil types (i.e., sand, silt, clay, and organic); b)
change in Phragmites cover at wetland sites located on
Great Lakes in which there was a drop in water levels
between 1999 and 2001 (i.e., Lakes Michigan/Huron, and
Erie) versus lakes where there was an increase in water
levels between 1999 and 2001 (i.e., Lake Ontario). The
Table 3 Coefficients and p-values from the mixed model of difference in Phragmites cover as a function of explanatory variables
Variables Description Unit of
measure
Type
a
Scale Reference Mixed model
with 13 variables
Mixed model
with 8 variables
Estimate p-value VIF Estimate p-value VIF
Intercept 55.92 30.54
Lake Great Lakes (Michigan-
Huron or Erie-Ontario)
unitless C see text 0.98 0.02
Substrate clay,organic, sand, silt unitless C plot see text 0.67 0.57
WaterDepthDiff difference in water depth
between first and second
sampling
cm N plot see text 0.96 0.19 1.33 1.31 0.05 1.07
BareSoilDiff difference in bare soil area
between second and first
sampling
% N plot see text 0.26 0.12 1.26 0.3 0.05 1.04
UrbanIndex urban PC unitless N watershed Danz et al.
2007
82.58 0.12 7.69 4.65 0.36 1.46
AgIndex agriculture PC unitless N watershed Danz et al.
2007
11.04 0.53 10.25
Nitrogen field-measured average
inorganic nitrogen
mg/L N wetland see text 33.96 0.18 9.34 12.06 0.13 1.76
Phosphorus field-measured soluble
reactive phosphorus
mg/L N wetland see text 3.67 0.87 2.61 1.39 0.89 1.27
Ratio watershed to wetland
area ratio
unitless N wetland Brazner et al.
2007
0.21 0.13 13.34
watershed area ha N watershed Brazner et al.
2007
0.01 0.15 13.78
WetlandArea wetland area ha N wetland Brazner et al.
2007
0.01 0.53 1.62 0.01 0.19 1.26
RowWatershed row crops areal
fraction
N watershed Brazner et al.
2007
76.45 0.56 38.29
UrbanWatershed development areal
fraction
N watershed Brazner et al.
2007
82.93 0.37 28.61
Variables with bolded VIF values were eliminated from the initial mixed model to reduce multicollinearity
a
The type of variable is denoted by N = numerical, C = categorical
Wetlands (2010) 30:577587 581
years 19992001 were chosen as a surrogate for exposure
of bare soil during the first year of sampling. We used
Wilcoxon non-parametric two-sample tests to examine
differences in nutrients between Phragmites versus non-
Phragmites stands. All tests were conducted in SAS ® 9.1
(SAS Institute Inc. 2001). All data were arcsine transformed
prior to data analysis (none of the data sets was normally
distributed).
Results
Phragmites Nativity and Expansion
Phragmites occurred in about one-third of the 307 plots
sampled at the 14 wetland sites. PCR/RFLP genetic
analysis of leaf samples revealed that none of the
Phragmites sampled at the 14 wetland sites belonged
to the native genotype. Out of the 307 plots revisited at
14 wetlands along the Great Lakes, Phragmites occurred
in 101 plots. At the other 206 plots, Phragmites was
absent during the first and second sampling events. Out of
the 101 plots that had Phragmites, Phragmites invaded 28
plots, increased cover in 32 plots, disappeared or
decreased cover in 15 plots, and remained unchanged in
26 plots (Table 1).
Eight sites exhibited increases in Phragmites cover of
7.5 percenta ge points or more. This ranged from 7.54
percentage points at White Feather Creek wetland, which
had 0.09% mean Phragmites cover (as mean plot value per
site) in 2003 and increased to 7.63% by 2005. A high
increase of 42.8 percentage points occurred at Caseville
wetland, which started with a mean Phragmites cover of
35.63% in 2003 and reached 78.44% by 2005. The change
is even more dramatic given that it took place only 2 or
3 years after the initial sample date (Table 1 ). One site
(Kelly Doty Drain) first sampled in 2003 exhibited a 13.4%
decrease in Phragmites cover. The remaining five sites
(Kalamazoo River, Neuman Road, Toledo Beach, Braddock
Bay, and Fox Creek) remained essentially unchanged
between first and second sampling times (Table 1). Four
out of the five Lake Huron sites experienced large increases
in Phragmites, as did four sites on Lake Er ie, but the Lake
Michigan and Lake Ontario sites did not change substan-
tially. The increase in Phragmites was due either to
invasion of new plots or increase in cover at plots where
it already occurred (Table 1). At two sites, Bay Creek and
Presque Isle, the n um ber of pl ot s newly inv ade d by
Phragmites was greater than the number of plots where it
merely increased in cover (Table 1 ). Phragmites disap-
peared completel y from most of the plots that exhibited a
decrease in Phragmites cover between the initial and 2005
sampling (12 out of 15 plots).
Water depth changes in the plots sampled were generally
consistent with the overall lake level trends from initial to
2005 sampling: increases occurred primarily at sites where
the lake level was at least 10 cm higher in 2005 than during
the initial sampling (e.g., Lake Huron), and decreases
occurred primarily at sites where the lake level was at least
10 cm lower in 2005 (e.g., Lake Ontario, Table 2; USCOE,
http://www. lre.usace.army.mi l/grea tlakes/). All plo ts that
lacked water standing above the soil surface were assigned
a water depth of 0, regardless of depth to the water table
beneath the soil surface, which explains the predominance
of
same values recorded. Plot-scale water level decreases
in Little Lake Creek despite lake level increases are
probably due to artificial water level control by dikes. The
relatively few undiked plots in which the plot-scale change
in water depth is inconsistent with the lake level change
may be due to changes in bottom configuration (e.g.,
dredging, siltation).
Natural and Anthropogenic Factors that Influenced
Phragmites Success
The VIF-adjusted, 8-variable mixed model related change
in Phragmites cover with difference in water depth,
difference in bare soil area, urban PC, nitrogen, phospho-
rus, wetland area, lake, and substrate (Table 3). Three of
these variables were individually statistically significant:
difference in water depth, difference in bare soil area, and
lake. An increase in Phragmites cover was associated with
decreasing water depth and less bare soil, and Phragmites
cover increased more on Lake Michigan-Huron than on
Lake Erie-Ontario (t-value=2.35, df=74, p=0.02). Of these
variables, the lake and decrease in water d epth are
environmental factors promoting Phragmites invasion,
whereas the decrease in bare soil area is a consequence of
that invas ion. The greatest decrease in bare soil occurred at
plots where Phragmites increased in cover (Fig. 2a),
suggesting that the newly exposed substrate was colonized
by Phragmites. Plots invaded by Phragmites experienced a
decrease in measured water depth from first to second
sampling, plots where Phragmites increased in cover had
relatively stable water levels, plots exhibiting a decrease in
Phragmites cover had water depth increases averaging
7 cm, whereas other plot s experienced little change in water
depth over the same time period (Fig. 2b). Even though
Urban Index was not a significant predi ctor of change in
Phragmites cover, Phragmites first appeared where the
Urban Index was low, but it increased where it was
dramatically higher (Fig. 2d). This might suggest that
Phragmites expansion is facilitated by disturbance and
urban land uses along wetland-terrestrial b orders, as
previous studies have found (Bertness et al. 2002;Minchinton
and Bertness 2003;Kingetal.2007).
582 Wetlands (2010) 30:577587
Substrate and Nutrients
Phragmites cover was significantly greater on sand than on
clay and organic soils (F=5.19, df=4, p<0.01), with the
highest average cover of 13.5% on sand, 6.2% on sil t, 2.2%
on clay, and 1.7% on organic soil. Although initial substrate
type was not a significant predictor of Phragmites cover
change, 59% of the plots where Phragmites occurred had
sandy substrate, whereas 52% of the plots where Phrag-
mites did not occur had organic soils (Fig. 3).
Average NO
3
-N concentration was 0.28 mg/L in
Phragmites stands compared to 0.32 mg/L in non-Phrag-
mites stands; both values were clos e to the detection
limit, and their difference was not stat istically si gnificant
(χ
2
=0.65, df=1, p=0.42). Average NH
3
-N concentrations
were also close to the detection limit, and no statistically
significant difference was noted be tween the two groups
(χ
2
=0.22, df=1, p=0.64) in Phragmites (1.05 m g/L)
versus no n-Phragmites (1.02 mg /L) sta nds. Average
concentrations of SRP were well above detection limits,
but no statistically signi ficant difference was observed in
SRP concentrations (χ
2
=0.33, df=1, p=0.56) between
Phragmites (0.3 mg/L) versus non-Phragmites stands
(0.43 mg/L) when data were analyzed togethe r for all
fourteen sites.
Antecedent Lake Levels
Between 1999 and 2001, prior to the initial sampling event,
average July lake levels in Lakes Erie an d Michigan/Huron
dropped 19 and 35 cm, respectively, to levels that were 28
to 55 cm below average (Table 4). The rapid water level
decline exposed large areas of lake bottom along their
shorelines. Lake Ontario experienced no such decrease; its
lake level increased slightly between 1999 and 2001 and
was close to the long-term average in 2001 . Phragmites
cover increased an average of only 1.25% in the Lake
Ontario sites, as opposed to 7.4% in the sites on Lakes
Michigan, Huron, and Erie (F=2.74, df=1, p=0.09).
Fig. 3 Substrate type of Phragmites plots on the first sampling event
Fig. 2 Plot environmental
conditions in relation to Phrag-
mites cover change categories
(A = invaded, B = increased,
C = decreased, D = same, and
E = was zero). Mean values and
standard errors for (a) Change in
bare soil area (%). Negative
values indicate a decrease in
bare soil area between first
sampling date and 2005, (b)
Agricultural index, (c) Change
in water depth (cm). Negative
values indicate a decrease in
water levels between the first
sampling date and 2005. (d)
Urban index
Wetlands (2010) 30:577587 583
Discussion
Our research demonstrated that Phragmites invasion can
occur very rapidly: Phragmites cover greatly expanded at
four of our five Lake Huron sites in only 2 years (all first
sampled in 2003). All of the Lake Huron sites are in
Saginaw Bay, which is characterized by lakebed wetlands
with gently sloping bathymetry (Burton et al. 2 002; Mink
and Albert 2002). All of our Lake Huron sites were open-
coast wetlands, with emergent vegetation relatively
exposed to wave action (Johnston et al. 2007a). Wetlands
with direct exposure to wave action usually have sandy
soils, which is conducive to Phragmites expansion. The
gentle slope of Saginaw Bay plus the presence of mineral
substrates creates very fertile sand flats when lake levels
drop. In healthy coastal wetlands these newly exposed flats
would be colonized by native, early successional species that
are adapted to these cycles, such as Bidens cernua L. (Wilcox
et al. 2007). However, the newly exposed flats created by
rapidly receding water levels, as occurred in Lakes Michigan
and Huron, provided excellent substrate for introduced
Phragmites colonization. In other regions, Phragmites seed-
lings can germinate on exposed bottoms without standing
water, but cannot colonize submerged or densely vegetated
substrates (Weisner and Ekstam 1993).
Neuman Road is the only Lake Huron site we revisited
that did not experience increase in Phragmites cover. In
contrast, the nearby White Feather Creek site had increases
in Phragmites cover despite comparable agricultural index
in the watershed, water level change, and amount of
change in bare soil. One of the major differences between
the two sites is the small watershed area of Neuman Road,
which might result in lower total nutrient inputs from the
watershed.
Previous studies have suggested that once it has
invaded, Phragmites alters soil properties and nutrient
pools (Windham and Lathrop 1999;Ehrenfeld2003;
Wi ndham and Meyerson 2003). In the present study we
did not detect significant differences in nutrients from soil
water of vegetation (total nitrogen and SRP) between
Phragmites and non-Phragmites stands. T his could be due
to the fact that the invasion process is in its early stages
(some of the sites were invaded in periods as short as
2 years) and it is too early to detect any changes.
On Lake Erie, Phragmites increased in cover at Presque
Isle, Otter Creek, Bay Creek, and Little Lake Creek,
remained unchanged at Toledo Beach, and decreased in
cover at Kelly Doty Drain. All of our Lake Erie sites with
the exception of Presque Isle were located at the western
end of Lake Erie, which has been altered by construction of
dikes for wetland water level control (Johnston et al.
2007b). These structures disrupt the natural flow and water
level fluctuations and may have influenced changes in
Phragmites cover at these sites.
Phragmites did not change in cover at our sites located
on Lake Ontario. This is one of the Great Lakes where
water level did not drop between 1999 and 2001, and our
findings show that Phragmites expanded more at Great
Lakes coastal wetlands where there was a drop in water
levels early in the decade. Lake Ontario sites had primarily
organic and clay soils (Johnston et al. 2009b). The GLEI
project showed that the invasive Typha X glauca is an
indicator species of organic soil and a common species on
Lake Ontario wetlands (Johnston et al. 2009b
; Vaccaro et
al. 2009). Typha spp. could also generate their own organic
matter substrate, as they are known to form floating mats of
organic matter (Hogg and Wein 1988). The competition
between the two species might prevent Phragmites from
invading those wetlands.
Although Phragmites tolerates most soil conditions
(Global Invasive Species Database), we found that Phrag-
mites occurred predominantly on sandy soils (60% of the
plots where it occurred), similar to our previous study
(Tulbure et al. 2007). This could also be due to the fact that
Phragmites invades newly exposed substrates where sandy
soils are prevalent.
Our focus on wetlands that already contained Phrag-
mites in 20012003 was intentional, because those wet-
lands would be expected to experience more rapid invasion
by Phragmites than wetlands lacking an internal source of
Phragmites propagules. However, the exclusion of Phrag-
mites-free wetlands from our sample design means that
these findings cannot be extrapolated to all Great Lakes
coastal wetlands without further research.
The fact that none of the samples we analyzed in this
present study came from native Phragmites populations
suggests that non-native genotypes are common in wetlands
Table 4 July Great Lakes water level from 19992006 (USCOE,
http://www.lre.usace.army.mil/greatlakes/)
July water level (meters above IGLD 1983)
Year Michigan/Huron Erie Ontario
1999 176.40 174.23 74.81
2000 176.13 174.27 75.24
2001 176.05 174.04 74.97
2002 176.33 174.25 75.19
2003 176.04 174.19 75.05
2004 176.37 174.35 75.09
2005 176.19 174.23 74.95
2006 176.14 174.29 74.98
Record High 177.39 175.03 75.66
Record Low 175.78 173.45 74.14
Long term average 176.60 174.32 74.99
584 Wetlands (2010) 30:577587
of the southern Great Lakes coast. The non-native genotype
displays an aggressive behavior and has a greater ability to
ventilate the root system with atmospheric oxygen (Tulbure
2008). To our knowledge, there is no evidence to suggest
that the native Phragmites inhabited the wetlands that were
sampled in this study. However, there still are native
Phragmites populations in the region, at Bark Bay (Lynch
and Saltonstall 2002) and other Lake Superior wetlands
(Natalie Wright, Univ. of Minnesota, personal communica-
tion),andinOhio(JohnMack,OhioEPA,personal
communication). This underlies the need to identify the
origins of populations especially in areas where they are
sympatric (Saltonstall 2003).
Mixed model results showed that a combination of plot
and site level variables were the most useful predictors of
Phragmites change. Decreases in bare soil at plots with
high increase in Phragmites suggest that the bare substrate
was colonized by Phragmites rather than other species.
Change in water depth was another predictor of Phragmites
increase in cover, with a greater increase in Phragmites
cover at plots where there was a decrease in water level.
Phragmites is generally found in shallower water or areas
not permanently inundated, but it is also favored by wide
water-level fluctuations and is known to survive in water as
deep as 2 m (Squires and van der Valk 1992; Herrick and
Wolf 2005).
Phragmites invades and spreads when water levels drop
and temperatures rise in Lake Erie (Wilcox et al. 2003) and
Lake Michigan-Huron (Pengra et al. 2007; Tulbure et al.
2007). Recently, Brisson et al. (2008) found evidence of
sexual reproduction in the non-native Phragmites at sites
with newly exposed substrate of eastern Canada. The
authors attributed the phenomenon to the recent climate
change towards warmer years (Brisson et al. 2008). The
substrate exposed by declining water levels in the Great
Lakes provi des new germi nation opportunities for rapid
colonization by invasive wetland plant species. Under
most climate models Great Lakes water levels are
projectedtodecline(Chaoetal.1999). Stream runoff will
also drop (International Joint Commission 2003). Water
level in Lake Michigan-Huron Basin is anticipated t o drop
by as much 1.38 m due to decreased precipitation and
increased air temperature and evapotranspiration (Lofgren
et al. 2002). The frequency and duration of low water
levels could increase, dropping water levels below historic
lows (International Joint Commission 2003). Given these
projections it is very likely that Phragmites is going to
expand and thrive at most Great Lakes coastal wetlands
where water levels drop, adding to the multiple stresses
that these ecosystems are facing. Once established,
Phragmites populations cause biodiversity loss and are
extremely difficult to eradicate (Havens et al. 1997).
Monitoring coastal wetlands where water level has
dropped and controlling Phragm ites at early stages of
invasion are essential for maintaining healthy wetlands
along the Great Lakes coast. Our work underscores the
need to collect baseline vegetation data and revisit sites
often to monitor Phragmites invasion.
In contrast to previous studies of
Phragmites invasion in
individual wetlands, this study is, to our knowledge, the
first to investigate rates and causes of Phragmites invasion
in multiple Great Lakes wetlands spanning a large range of
geographic and abiotic conditions. Understanding how
natural and anthropogenic abiotic factors drive changes in
coastal wetlands is important and can help managers focus
their efforts in areas where they are needed the most.
Documenting vegetation shifts in time is especially impor-
tant in dynamic systems such as Great Lakes coastal
wetlands that experience water level fluctuations and
changes in emergent vegetation.
Acknowledgments We thank the associate editor and two anony-
mous reviewers for helpful comments on an earlier draft. This research
has been supported by a grant from the United States Environmental
Protection Agencys Science to Achieve Results Estuarine and Great
Lakes (EaGLe) program through funding to the Great Lakes
Environmental Indicators Project, US EPA Agreement EPA/R-
828675. Although the research described in this article has been
funded wholly or in part by the U.S. Environmental Protection
Agency, it has not been subjected to the Agency s required peer and
policy review and therefore does not necessarily reflect the views of
the Agency and no official endorsement should be inferred. We thank
Dr. Donald Auger for help with the genetic analysis. We thank Heidi
Walking, Lynn Vaccaro, Christin Frieswyk DeJong, Michael Aho,
Kathy Bailey Boomer, Michael Bourdaghs, K. Cappillino, Randy
Clark, Spencer Cronk, D. James, Angie Marsh, and Cindy Williams
for field assistance.
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... Schoenoplectus is typically found in water, whereas Typha and Phragmites colonies may only have a portion of the stand in water and thus accessible to fish. Phragmites grows best on sandy substrates, while Typha prefers nutrient-rich organic and clay soils, and Schoenoplectus prefers low nutrient environments (Svengsouk & Mitsch, 2001;Tulbure & Johnston, 2010). In terms of how they grow, both Phragmites and invasive Typha rapidly colonize exposed substrates where they can outcompete native emergent vegetation species through the formation of dense monocultures (Shih & Finkelstein, 2008). ...
... More than 80 species of fish rely on the coastal wetlands of the Laurentian Great Lakes during at least one part of their life cycle (Jude & Pappas, 1992) and a diverse community of emergent, submergent, and floating wetland vegetation provide essential feeding, spawning, and nursery habitat for these fishes (Croft & Chow-Fraser, 2007;Cvetkovic et al., 2010). A period of prolonged low water levels in the Great Lakes (1998-2014Norton et al., 2019) has enabled the expansion of Phragmites on exposed lake bottom sediment (Wilcox et al., 2003;Whyte et al., 2008;Tulbure & Johnston, 2010) and this expansion is expected to continue during low water level years (Jung et al., 2017). Water levels within the Great Lakes rose in 2015 and remained high during the sampling year for the present study. ...
... From a habitat perspective, the measured environmental metrics only reflect a subset of potential differences that may exist and shape fish habitat among the three emergent vegetation types. For example, it is well established that emergent species prefer specific types of substrate (Svengsouk & Mitsch, 2001;Tulbure & Johnston, 2010); however, this information was not collected during this study, so potential linkages between substrate composition and fish community assemblages (like those identified in Trebitz et al., 2009) could not be explored. Additionally, the age of the vegetation stand was not estimated, but older stands will have increased live biomass and litter accumulation, which could lead to sediment accretion and the loss of fish habitat (Rooth et al., 2003). ...
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Invasive species can significantly impact native wildlife by structurally altering habitats and access to resources. Understanding how native species respond to habitat modification by invasive species can inform effective habitat restoration, avoiding inadvertent harm to species at risk. The invasive graminoids Phragmites australis australis (hereafter Phragmites ) and Typha × glauca are increasingly dominating Nearctic wetlands, often outcompeting native vegetation. Previous research suggests that turtles may avoid invasive Phragmites when moving through their home ranges, but the mechanisms driving avoidance are unclear. We tested two hypotheses that could explain avoidance of invaded habitat: (1) that stands of invasive macrophytes ( Phragmites and Typha x glauca ) impede movement, and (2) that they provide inadequate thermal conditions for turtles. We quantified active-season movements of E. blandingii (n = 14, 1328 relocations) and spotted turtles ( Clemmys guttata ; n = 12, 2295 relocations) in a coastal wetland in the Laurentian Great Lakes. Neither hypothesis was supported by the data. Phragmites and mixed-species Typha stands occurred within the home ranges of mature, active E. blandingii and C. guttata , and were used similarly to most other available habitats, regardless of macrophyte stem density. Turtles using stands of invasive macrophytes did not experience restricted movements or cooler shell temperatures compared to other wetland habitat types. Control of invasive macrophytes can restore habitat heterogeneity and benefit native wetland species. However, such restoration work should be informed by the presence of at-risk turtles, as heavy machinery used for control or removal may injure turtles that use these stands as habitat.
... australis) (Martin & Blossey, 2013;Saltonstall, 2002) was introduced to North America from Europe prior to 1900 and has been aggressively disrupting and displacing native plant communities (Mozdzer et al., 2013;Saltonstall, 2002) and altering wildlife habitat and ecosystem properties (Perez et al., 2013;Rogalski & Skelly, 2012). The invasive subspecies occurs throughout the contiguous United States (U.S.) and the entire Laurentian Great Lakes basin (Bourgeau-Chavez et al., 2013;Saltonstall, 2002;Tulbure & Johnston, 2010) (Figure 1b) and is one of the most problematic invasive plant species in wetland habitats in eastern North America, with millions of dollars per year invested in control efforts (Kowalski et al., 2015;Meyerson et al., 2016). It co-occurs with the native subspecies in many areas (Figure 1c) but exhibits more robust growth (Figure 1d,e) with larger inflorescences, leaves, and height (Figure 1f,g). ...
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The rapid invasion of the non‐native Phragmites australis (Poaceae, subfamily Arundinoideae) is a major threat to native wetland ecosystems in North America and elsewhere. We describe the first reference genome for P. australis and compare invasive (ssp. australis) and native (ssp. americanus) genotypes collected from replicated populations across the Laurentian Great Lakes to deduce genomic bases driving its invasive success. We report novel genomic features including a Phragmites lineage‐specific whole genome duplication, followed by gene loss and preferential retention of genes associated with transcription factors and regulatory functions in the remaining duplicates. Comparative transcriptomic analyses revealed that genes associated with biotic stress and defense responses were expressed at a higher basal level in invasive genotypes, but native genotypes showed a stronger induction of defense responses when challenged by a fungal endophyte. The reference genome and transcriptomes, combined with previous ecological and environmental data, add to our understanding of mechanisms leading to invasiveness and support the development of novel, genomics‐assisted management approaches for invasive Phragmites.
... Native Phragmites has a smaller stature and generally does not form dense monotypic stands. Invasive Phragmites is spreading quickly in Minnesota and will likely see an expansion of its distribution [14]. ...
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Invasive plant species are an increasing worldwide threat both ecologically and financially. Knowing the location of these invasive plant infestations is the first step in their control. Surveying for invasive Phragmites australis is particularly challenging due to limited accessibility in wetland environments. Unoccupied aircraft systems (UAS) are a popular choice for invasive species management due to their ability to survey challenging environments and their high spatial and temporal resolution. This study tested the utility of three-band (i.e., red, green, and blue; RGB) UAS imagery for mapping Phragmites in the St. Louis River Estuary in Minnesota, U.S.A. and Saginaw Bay in Michigan, U.S.A. Iterative object-based image analysis techniques were used to identify two classes, Phragmites and Not Phragmites. Additionally, the effectiveness of canopy height models (CHMs) created from two data types, UAS imagery and commercial satellite stereo retrievals, and the RADARSAT-2 horizontal-horizontal (HH) polarization were tested for Phragmites identification. The highest overall classification accuracy of 90% was achieved when pairing the UAS imagery with a UAS-derived CHM. Producer’s accuracy for the Phragmites class ranged from 3 to 76%, and the user’s accuracies were above 90%. The Not Phragmites class had user’s and producer’s accuracies above 88%. Inclusion of the RADARSAT-2 HH polarization caused a slight reduction in classification accuracy. Commercial satellite stereo retrievals increased commission errors due to decreased spatial resolution and vertical accuracy. The lowest classification accuracy was seen when using only the RGB UAS imagery. UAS are promising for Phragmites identification, but the imagery should be used in conjunction with a CHM.
... In the Laurentian Great Lakes, the largest system of freshwater lakes on Earth, climate change is increasing the frequency and amplitude of extreme water level events, with higher highs, lower lows, and more rapid rates of water level change expected in the next century (Gronewold and Rood, 2019). Large-amplitude swings in water levels coupled with increased nutrient loading from agriculture and urban watersheds promotes invasion by dominant macrophytes (e.g., Phragmites australis, Typha × glauca) into freshwater coastal wetlands (Lishawa et al., 2010;Tulbure and Johnston, 2010;Woo and Zedler, 2002). Increased water level variability and invasive species dominance alter wetland vegetation structure, and in turn can dramatically affect wetland C dynamics (Duke et al., 2015;Liao et al., 2008). ...
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Invasive species management typically aims to promote diversity and wildlife habitat, but little is known about how management techniques affect wetland carbon (C) dynamics. Since wetland C uptake is largely influenced by water levels and highly productive plants, the interplay of hydrologic extremes and invasive species is fundamental to understanding and managing these ecosystems. During a period of rapid water level rise in the Laurentian Great Lakes, we tested how mechanical treatment of invasive plant Typha × glauca shifts plant-mediated wetland C metrics. From 2015 to 2017, we implemented large-scale treatment plots (0.36-ha) of harvest (i.e., cut above water surface, removed biomass twice a season), crush (i.e., ran over biomass once mid-season with a tracked vehicle), and Typha-dominated controls. Treated Typha regrew with approximately half as much biomass as un-manipulated controls each year, and Typha production in control stands increased from 500 to 1,500 g-dry mass m⁻² yr⁻¹ with rising water levels (~10 to 75 cm) across five years. Harvested stands had total in-situ methane (CH4) flux rates twice as high as in controls, and this increase was likely via transport through cut stems because crushing did not change total CH4 flux. In 2018, one year after final treatment implementation, crushed stands had greater surface water diffusive CH4 flux rates than controls (measured using dissolved gas in water), likely due to anaerobic decomposition of flattened biomass. Legacy effects of treatments were evident in 2019; floating Typha mats were present only in harvested and crushed stands, with higher frequency in deeper water and a positive correlation with surface water diffusive CH4 flux. Our study demonstrates that two mechanical treatments have differential effects on Typha structure and consequent wetland CH4 emissions, suggesting that C-based responses and multi-year monitoring in variable water conditions are necessary to accurately assess how management impacts ecological function.
... australis) 13,14 was introduced to North America from Europe around 1900 and has been aggressively disrupting and displacing native plant communities 13,15 and altering wildlife habitat and ecosystem properties 16,17 . The invasive subspecies occurs throughout the contiguous United States (U.S.) and the entire Great Lakes basin 13,18,19 (Fig. 1b). It is one of the most problematic invasive plant species in wetland habitats in eastern North America, with hundreds of millions of dollars per year invested in control efforts 20,21 . ...
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The rapid invasion of the non-native Phragmites australis (Poaceae, subfamily Arundinoideae) is a major threat to native ecosystems in North America. We describe a 1.14 Gbp reference genome for P. australis and compare invasive (ssp. australis ) and native (ssp. americanus ) genotypes collected across the Laurentian Great Lakes to deduce genomic bases driving its invasive success. We report novel genomic features including a lineage-specific whole genome duplication, followed by gene loss and preferential retention of genes associated with transcription factors and regulatory functions in the remaining duplicates. The comparative transcriptomic analyses revealed that genes associated with biotic stress and defense responses were expressed at a higher basal level in invasive genotypes, but the native genotypes showed a stronger induction of defense responses following fungal inoculation. The reference genome and transcriptomes, combined with previous ecological and environmental data, support the development of novel, genomics-assisted management approaches for invasive Phragmites .
... Water level fluctuations also disrupt native cattail (Typha latifolia) marshes and promote invasive European common reed (Phragmites australis) (Wei and Chow-Fraser, 2006), which in turn reduce herpetofauna recruitment, available habitat and threaten to strand smaller turtles such as painted turtles Misfud, 2014;Bolton and Brooks, 2010). European common reed has been expanding rapidly in Lake Ontario wetlands (Tulbure and Johnston, 2010;Wilcox et al., 2003,) and was a dominant species in many wetlands we surveyed and is of great concern to local conservation authorities (Bourgeau-Chavez et al., 2013). Anecdotally, at one of the specific wetlands within our study sites, Cell-1 of Tommy Thompson Park, visual surveys had documented annual sightings of painted turtles from 2004 to 2012, but none in 2013, one in 2014, and none in 2015 (Dupuis-Desormeaux et al., 2018). ...
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The aim of this study was to provide a baseline assessment of the turtle community in the coastal wetlands of the Greater Toronto Area. We documented turtle species diversity, abundance, reproductive classes, sex-ratios, and evidence of inter-wetland movement. Our study consisted of a series of mark-recapture surveys across eleven Lake Ontario coastal wetland complexes of the Greater Toronto Area performed between 2016 and 2019. We captured and marked 532 individual turtles of four native species (298 midland painted, Chrysemys picta marginata; 180 snapping, Chelydra serpentina; 7 Blanding's, Emydoidea blandingii, and 5 map, Graptemys geographica) and three non-native species (40 red-eared sli-der, Trachemys scripta elegans; 1 false map, Graptemys pseudogeographica, and 1 Chinese softshell, Pelodiscus sinensis). Of note was the capture of an exceptionally large male snapping turtle, one of the largest recorded in Canada for both length and mass. The age classes of both snapping and midland painted species presented large proportions of breeding-sized adults, yet midland painted turtles showed a potential low recruitment with an underrepresentation of non-reproductive females. The sex ratios of both midland painted and snapping turtles across the whole waterfront did not differ from the expected 1:1 ratio. We also recaptured 198 turtles (135 midland painted, 53 snapping, 6 Blanding's and 12 red-eared Sliders). The recaptured turtles revealed inter-wetland movements of 12 km over a two-year span for a midland painted turtle and an 8 km journey for a snapping turtle, potentially demonstrating some connectivity between geographically separate wetland complexes.
... The potential effects of climate change on Great Lakes coastal wetland ecosystems have been discussed for more than three decades (Hartmann, 1990;Magnuson et al., 1997;Meisner et al., 1987;Mortsch and Quinn, 1996, and others). Projections of future lake levels vary widely (Gronewold et al., 2013), but the combined effects of changes in precipitation, water temperature, evaporation rate, and vulnerability to invasive species (Tulbure and Johnston, 2010) almost certainly will affect the dynamics of coastal wetlands. If lake levels decrease in the future, our results suggest that local populations of many marsh-obligate bird species will decrease in the Great Lakes coastal zone, although populations of several others may increase. ...
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Coastal wetlands in the Laurentian Great Lakes undergo frequent, sometimes dramatic, physical changes at varying spatial and temporal scales. Changes in lake levels and the juxtaposition of vegetation and open water greatly influence biota that use coastal wetlands. Several regional studies have shown that changes in vegetation and lake levels lead to predictable changes in the composition of coastal wetland bird communities. We report new findings of wetland bird community changes at a broader scale, covering the entire Great Lakes basin. Our results indicate that water extent and interspersion increased in coastal wetlands across the Great Lakes between low (2013) and high (2018) lake-level years, although variation in the magnitude of change occurred within and among lakes. Increases in water extent and interspersion resulted in a general increase in marsh-obligate and marsh-facultative bird species richness. Species like American bittern (Botaurus lentiginosus), common gallinule (Gallinula galeata), American coot (Fulica americana), sora (Porzana carolina), Virginia rail (Rallus limicola), and pied-billed grebe (Podilymbus podiceps) were significantly more abundant during high water years. Lakes Huron and Michigan showed the greatest increase in water extent and interspersion among the five Great Lakes while Lake Michigan showed the greatest increase in marsh-obligate bird species richness. These results reinforce the idea that effective management, restoration, and assessment of wetlands must account for fluctuations in lake levels. Although high lake levels generally provide the most favorable conditions for wetland bird species, variation in lake levels and bird species assemblages create ecosystems that are both spatially and temporally dynamic.
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Wetland restoration often involves invasive-plant suppression to encourage the recovery of native-dominated vegetation communities. However, assessment of recovery is usually focused only on vegetation, and the response of other critical wetland biota, such as macroinvertebrates, is seldom assessed. We characterized the aquatic, semi-aquatic, and terrestrial macroinvertebrate communities in remnant, uninvaded marsh to identify restoration targets and compared this to the communities in Phragmites australis-invaded marsh and in formerly invaded marsh that was treated with the herbicide glyphosate in 2016 to simultaneously evaluate the effects of invasion and of invasive-species suppression. We sampled invertebrates in 2017 and 2018 to track two years following herbicide treatment. The invertebrate community composition was similar between P. australis invaded and remnant marsh, suggesting invasion has little effect on macroinvertebrate community structure. There was also high concordance between the aquatic and emerging invertebrate communities in the invaded and uninvaded habitats. In contrast, herbicide-treated sites had a unique community composition, characterized by very high densities of Chironomidae (Diptera) and low taxa richness and evenness. Herbicide-treated sites also exhibited low concordance between the aquatic and emerging invertebrate communities, potentially attributable to the sparse, emergent-vegetation cover providing limited substrates for emergence. Herbicide-based, invasive-species control resulted in considerable changes to the macroinvertebrate community in freshwater marshes for at least two years after treatment, which may have consequences for aquatic food webs and species that rely on macroinvertebrates as prey. This article is protected by copyright. All rights reserved.
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Wetland restoration often involves invasive plant species suppression to encourage the recovery of native-dominated vegetation communities. However, assessment of recovery is usually focused only on vegetation and the response of other critical wetland biota, such as macroinvertebrates, is seldom assessed. We characterized the aquatic, semi-aquatic, and terrestrial macroinvertebrate communities in remnant, uninvaded marsh to identify restoration targets and compared this to the communities in Phragmites australis-invaded marsh, and in formerly invaded marsh that was treated with the herbicide glyphosate in 2016 to simultaneously evaluate the effects of invasion and of invasive species suppression. We sampled invertebrates in 2017 and 2018 to track two years following herbicide treatment. The invertebrate community composition captured by the emergence traps was similar between P. australis and remnant marsh, suggesting invasion has little effect on macroinvertebrate community structure. There was also high concordance between the aquatic and emerging invertebrate communities in the invaded and uninvaded habitats. In contrast, herbicide-treated sites had a unique community composition, characterized by very high densities of Chironomidae (Diptera) and low taxa richness and evenness. Herbicide-treated sites also exhibited low concordance between the aquatic and emerging invertebrate communities, potentially attributable to the sparse emerging vegetation cover providing limited substrates for emergence. Herbicide-based invasive species control results in considerable changes to the macroinvertebrate community in freshwater marshes for at least two years after treatment, which may have consequences for aquatic food webs and species that rely on macroinvertebrates as prey.
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Key components of water availability in a hydrologic system4 are the amount of water in storage and the variability of that amount. In the Great Lakes Basin, a vast amount of water is stored in the lakes themselves. Because of the lakes’ size, small changes in water levels cause huge changes in the amount of water in storage. Approximately 5,439 mi3 of water, measured at chart datum, is stored in the Great Lakes. A change of 1 ft in water level over the total Great Lakes surface area of 94,250 mi2 means a change of 18 mi3 of water in storage. Changes in lake level over time also play an important role in human activities and in coastal processes and nearshore ecosystems, including development and maintenance of beaches, dunes, and wetlands. The purpose of this report is to present recorded and reconstructed (pre-historical) changes in water levels in the Great Lakes, relate them to climate changes of the past, and highlight major water-availability implications for storage, coastal ecosystems, and human activities. Reconstructed water-level changes have not been completed for all Great Lakes; consequently, this report presents these changes primarily for Lakes Michigan and Huron, with some reference to Lake Superior also.
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The seasonal contribution of living Typha components to the buoyancy of floating mats was investigated in a diked, freshwater impoundment near the head of the Bay of Fundy in New Brunswick, Canada. The objectives were (1) to examine the potential influence of a dominant, mat-building species on hydrologic conditions at the mat surface, and (2) to predict whether a complete killing of the dominant species could cause mats to sink. The Typha component contributing most to mat buoyancy was the rhizomes, which added a net buoyancy pressure of @?20 Pa throughout the growing season. The seasonal maximum buoyancy contribution of 28 Pa for all living Typha components combined was reached in spring, followed by a decline to 11 Pa in late summer as the aboveground shoots developed. This positive and seasonally variable contribution of Typha to mat buoyancy is expected to be most important during the early stages of mat development, when mats are thin and composed largely of living, belowground organs. However, on older and thicker mats the living Typha is less important because of the large volumes of gas bubbles from anaerobic decomposition that are trapped in the dead organic material. For the 50 cm thick floating mats under study, it is concluded that trapped gas is the main cause of buoyancy and would lead to the continued flotation of mats even if the living Typha were removed. Implications of the results are discussed in relation to the resiliency of floating mat systems.