Effects of Phragmites Management on the Ecology of a
Wetland
Amy Krzton-Presson, Brett Davis, Kirk Raper, Katlyn Hitz, Christopher Mecklin, and Howard Whiteman
Northeastern Naturalist, Volume 25, Issue 3 (2018): 418–436
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22001188 NORTHEASTERN NATURALIST 2V5(o3l). :2451,8 N–4o3. 63
Effects of Phragmites Management on the Ecology of a
Wetland
Amy Krzton-Presson1,*, Brett Davis1, Kirk Raper1, Katlyn Hitz1,
Christopher Mecklin1,2, and Howard Whiteman1
Abstract - Effective management of wetlands often involves the suppression of invasive
species, and understanding the ecological consequences of management efforts is
an important goal. A non-native strain of Phragmites australis (Common Reed; hereafter
Phragmites) is aggressively invading North American wetlands, and the species has been
shown to alter hydrology and impact aquatic organisms. Clear Creek Wildlife Management
Area, in Kentucky, is heavily impacted by Phragmites invasion. Portions of the Wildlife
Management Area with Phragmites were treated with herbicide to restore wetland flora, and
in this study, we evaluated the effects of both the presence and management of Phragmites
on wildlife populations and ecosystem function. We selected 3 locations (treated Phragmites,
untreated Phragmites, and Phragmites-free) and surveyed each for water chemistry,
wildlife populations, and stable-isotope signatures over a 2-y period. Water chemistry
varied with the presence or absence of Phragmites, suggesting differences in nutrient cycling.
Fish diversity did not differ among sites, but individual species varied in distribution
and abundance between the Phragmites sites and the Phragmites-free site. Turtles showed
significant differences in both diversity and body size based on the presence or absence of
Phragmites, but not herbicide treatment. We detected no significant differences in frog diversity
across treatments. We recorded 8 Kentucky Species of Greatest Conservation Need,
but there were few differences in the distribution of these species across sites. Stable-isotope
analysis revealed variation in food-web structure based on the presence of Phragmites.
These results indicate that herbicides had little effect on fish and herpetofaunal communities
in the short term, but potentially significant ecological changes may occur if Phragmites
were eradicated. Our conclusions highlight the importance of monitoring habitat restoration
to guide future management. A holistic, ecosystem-level approach is necessary to understand
the impacts of both invasive species and their management.
Introduction
Invasive species have been severely impacting habitats and communities worldwide
for decades (Gratton and Denno 2006, Simberloff 1996). Wetland ecosystems
are particularly susceptible to invasion because they accumulate water, nutrients,
and sediment from disturbances to both terrestrial and aquatic systems, providing
ample resources for invasive plants to thrive (Zedler and Kercher 2004). One of the
best-known and aggressively managed invasive wetland plants in North America is
Phragmites australis (Cav.) Trin. ex Steud. (Common Reed; hereafter Phragmites)
(Rogalski and Skelly 2012).
1Watershed Studies Institute and Department of Biological Sciences, Murray State University,
Murray, KY 42071. 2Department of Mathematics and Statistics, Murray State University,
Murray, KY 42071. *Corresponding author - amy.krztonpresson@gmail.com.
Manuscript Editor: Robert Bertin
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Phragmites is a coarse, perennial, wetland grass with several haplotypes including
1 native to North America. However, a Eurasian haplotype is rapidly
invading wetlands of North America via high seed-production and vegetative
propagation, often forming dense monocultures (Ailstock et al. 2001, Saltonstall
2002). This invasive strain of Phragmites can replace more diverse floral communities,
as well as alter structural habitat complexity and wetland functioning.
Communities consisting of monocultural stands of Phragmites are often considered
poor wildlife habitat with low faunal diversity (Paxton 2007, Roman et al.
1984). Invasive Phragmites alters hydrologic and chemical cycles in wetlands
where it becomes monotypic, replacing the more diverse native flora; thus, changing
the structure, and also the function of the wetland (Meyerson et al. 2000).
For example, Armstrong and Armstrong (1988) found that Phragmites limits the
cycling of phosphorus and other nutrients by increasing rhizosphere oxidation,
which binds these elements in the sediments.
The documented and deleterious ecological effects associated with Phragmites
invasion warrant the control and eradication of this plant to restore affected wetlands
to their pre-invasion state. Options for Phragmites reduction and/or removal
include chemical, mechanical, and biological controls (Ailstock et al. 2001, Haslam
1971). Regardless of the method used, the destruction of a plant that has such a
large presence in a community is likely to have an impact on the surrounding fauna
by simply changing community composition and habitat structure.
Phragmites is considered one of Kentucky’s most noxious invasive wetland
species, with prevalent populations throughout the western part of the state and
along the Ohio River (Mahala 2008). Invasive Phragmites has been particularly
successful in establishing a dominant monoculture at the Clear Creek Wildlife
Management Area (CCWMA), a property in Hopkins County, KY, managed by
Kentucky Department of Fish and Wildlife Resources (KDFWR). In an effort
to increase access to this public area and begin restoration of this wetland ecosystem,
the KDFWR and Ducks Unlimited collaborated to manage 121 ha of
Phragmites on CCWMA. Our goal was to study the effects of herbicide management
on the fish and herpetofaunal communities and develop recommendations
for future management of Phragmites. Due to limited management funding, the
CCWMA was the only Phragmites-invaded wetland in the area being managed
at this scale. Thus, we were unable to replicate this study with additional sites.
Although our results must be interpreted cautiously, we thought it prudent to take
advantage of the unique situation provided and document observations through
the early stages of the management effort.
In this study, we focused on 2 questions: (1) What effect does Phragmites and
its management have on fish, reptile, and amphibian populations and Species of
Greatest Conservation Need (SGCN)? and (2) What impact does Phragmites and its
management efforts have on the ecosystem as a whole? Our efforts were aimed at
monitoring the effects of Phragmites, as well as herbicide treatment of Phragmites,
on fish and herpetofaunal diversity, the presence of SGCN, water quality, and ecosystem
function. Previous research suggested that Phragmites has a negative effect
on wetland fauna, and that vegetation removal results in an alteration of the fish
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and herpetofaunal communities (Able et al. 2003, Fell et al. 2003, Meyer 2003).
Therefore, we hypothesized that areas impacted by Phragmites represented lowerquality
habitat for SGCN and would have reduced diversity and altered community
structure. We also hypothesized that Phragmites management would increase
species richness and abundance in the fish and herpetofaunal communities when
compared with unmanaged Phragmites-dominant areas. Finally, we hypothesized
that the high growth rate of Phragmites would impact the entire ecosystem by lowering
nutrient availability.
Field-Site Description
Clear Creek is a low-gradient, 5th-order stream (~51 km long) that drains 15,661
ha, of which 347 ha make up the CCWMA (Fig. 1). Since the 1850s, timber removal,
a lack of effective soil-conservation techniques in agriculture, and intensive
coal mining operations have caused extreme sedimentation, hydrologic alterations,
and acid-mine drainage (AMD) in Clear Creek (Hill 1983, Leuthart 1975, Neichter
1972). Prior to these disturbances, Clear Creek had defined banks surrounded by
bottomland hardwood forests; however, it is now a broad, permanently inundated
wetland (Hill 1983, Leuthart 1975, Neichter 1972). Before reclamation, abandoned
mine sites leached AMD into Clear Creek until at least the early 1980s (Hill 1983),
with pH measurements in the main channel recorded as low as 2.8 (Niechter 1972).
Concentrated sulfate, heavy-metal loads, and acidic water conditions rendered the
creek channel depauperate of all but the most tolerant wildlife (Hill 1983). No fish
species were observed at all in Clear Creek during research from 1969 to 1974
(Leuthart 1975).
Phragmites was not present in plant community descriptions from previous research
at Clear Creek, although Hill (1983) noted a dense Phragmites stand about
48 km north near Smith Mills, KY. Thus, Phragmites likely invaded Clear Creek
within the last 30 y and has since come to dominate the system. Concurrent genetic
analysis of Phragmites specimens from Clear Creek WMA revealed this population
to be the exotic, more invasive genotype (Croteau et al. 2013). At the time of
this study, the Phragmites in CCWMA had established dense stands throughout the
inundated wetland, except for areas where the water deepened, typically near the
stream thalweg. There was shallow, slow-moving water inundating the dead Phragmites
mulch within the Phragmites stands. The rest of the wetland community
was comprised primarily of native plants, including Lemna minor L. (Duckweed),
Ceratophyllum demersum L. (Coontail), Peltandra virginica (L.) Schott (Arrow
Arum), Potamogeton spp. (pondweeds), and Typha sp. (cattail).
As part of this study, we surveyed an adjacent Phragmites-free wetland as a
comparison to Clear Creek (Fig. 1). Weir Creek is a 3rd-order stream and tributary of
Clear Creek. It drains an area of ~6133 ha and is 18 km long. The predominant plant
species included Nuphar advena (Ait.) Ait. f. in Ait. & Ait. f. (Immigrant Pond-lily),
Duckweed, Cattail, and Coontail. Weir Creek was characterized by low-gradient,
tea-colored water, and a loose bottom consisting of detritus, vegetation, large
woody debris, and silt.
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Figure 1. Clear Creek Wildlife Management Area (CCWMA; outlined area that includes
treated sites) and associated study sites. Sampling locations are represented by filled
circles. Dead Phragmites, the result of herbicide application, is apparent in the treated
area. Phragmites-free reference sites located on Weir Creek located in upper left, outside of
CCWMA. Map created by Jane Benson, Mid-American Remote-sensing Center (MARC),
Murray State University.
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On 22 August 2009, KDFWR and Ducks Unlimited carried out a chemical
treatment of Phragmites on a section of the CCWMA. They undertook an aerial
application of a glyphosate herbicide (AquaMaster®) via helicopter on ~121 ha
of the 347-ha site at a rate of 15.3 L/ha (E. Williams, KDFWR, Drakesboro, KY,
pers. comm.). We collected data in 2 Phragmites-dominated sites on the CCWMA:
1 treated with herbicide, and 1 untreated. The Weir Creek wetland served as our
Phragmites-free reference site (Fig. 1).
Methods
We conducted all statistical analyses in the software R, version 2.10 (https://
cran.r-project.org/).
Water chemistry
To evaluate water quality, we collected 1–3 replicate water samples from each
site every month. We analyzed these samples for nitrogen (nitrate + nitrite), soluble
reactive phosphorus (SRP), total phosphorus (TP), and total nitrogen (TN) using
a Lachat Quick Chem 8000 Flow Injection Analyzer at the Hancock Biological
Station (HBS), Murray, KY. We filtered dissolved organic carbon (DOC) water
samples through Whatman GF/F glass-microfiber filters with a nominal pore size
of 0.7 mm. We recorded turbidity, temperature, pH, conductivity, and dissolved
oxygen (DO) during each sampling event using a YSI 6600 multi-parameter sonde
(YSI, Inc., Yellow Springs, OH) and YSI 650MDS hand-held data display system
(YSI). We employed MANOVA to compare overall water-quality across sites and
individual ANOVAs for each parameter.
Faunal sampling
We sampled fish at 6 locations per site at least every 3 weeks from September
2009 until August 2010, except during duck-hunting season (October 2009–March
2010). We collected fish by seining and electrofishing according to the standardized
methods of the Kentucky index of biotic integrity (KIBI; Kentucky Department of
Fish and Wildlife Resources 2008); identifications were to the species level. We
conducted ANOVA to evaluate differences in KIBI and Shannon diversity among
sampling locations and dates. We used the JACCARD index to compare fish community
similarity and analyzed the data via a permutational MANOVA to test for
significance among sample locations and dates.
We used hoop traps to sample turtles at the same 6 locations per site throughout
the summers of 2009, 2010, and early summer 2011. We checked traps daily and
removed them from the water at the end of a trap period to prevent mortality. Information
we recorded for captured turtles included sex, carapace length, carapace
width, carapace height, plastron length, and mass. We marked each adult turtle
with a unique code composed of holes drilled in marginal scales on the carapace
(Dustman 2010, Gibbons 1990). We used turtle-capture data to analyze movement
patterns, size–density relationships, and species diversity. We employed the
Shannon diversity index and an ADONIS analysis of similarity to compare turtle
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diversity between study sites, followed by a Tukey’s HSD test to identify which
sites differed significantly in diversity. Excluding juveniles, we compared turtle
measurements across sites using MANOVA.
We trapped Siren intermedia (Goin) (Western Lesser Siren, hereafter Siren),
an SGCN within Kentucky, at each site in the spring, fall, and summer. We set,
baited with sardines, and checked daily 6 modified trashcan traps (Luhring and
Jennison 2008) at each site (n = 18). We opened and upended traps after each
trap period to allow captured organisms to escape and prevent mortality. Snoutto-
vent length, total length, and mass were measured for each captured Siren.
At each site, we set and baited with dry dog food 24 minnow traps. We identified
to the lowest taxon possible and released all other organisms (snakes, frogs,
tadpoles, fish, and invertebrates) captured in the minnow and trashcan traps. All
SGCN that were captured or casually observed during fish and herpetofaunal
sampling were also recorded.
We utilized a Song Meter1® (Wildlife Acoustics Inc., Maynard, MA) automated
recording device (ARD) that recorded ambient sound for 2 min every hour to estimate
relative densities of frog and toad species. One ARD was placed at each
site and data were regularly downloaded. We identified species using the songs of
breeding males. We estimated semi-quantitative densities using the North American
Amphibian Monitoring Program (NAAMP) ranking system (Bridges and Dorcas
2000, Royle and Link 2005). We employed a Gower’s measure of dissimilarity to
statistically measure the level of dissimilarity of both species richness and ordinal
densities, and performed an ADONIS analysis to identify significant dissimilarities
in the Gower’s results.
Stable-isotope analysis
We collected samples for stable isotope analysis from the wetland substrate
on 24–28 May 2010 and 6–10 June 2011. We also collected samples from dominant
primary producers (Phragmites, Duckweed, cattail, Immigrant Pond-lily,
Zygnematales [green algae]), invertebrates (Belostoma [hemipterans], Dytiscus
[predaceous diving beetles], Ranatra [water scorpions], Odonata [dragonflies
and damselflies], Decapoda [crustaceans], Notonecta [backswimmers], and
Gastropoda [molluscs]), turtles (Trachemys scripta elegans [Wied-Neuwied]
[Red-eared Slider] Chelydra serpentina L. [Common Snapping Turtle]), frogs
(Rana and Pseudacris), and fish (Lepomis [sunfish], Gambusia [mosquitofish],
Noturus [madtoms], Esox [pike], and Aphredoderus [perch]). We placed on ice
and stored samples in either Whirl-Paks® or scintillation vials until they could be
transferred to a freezer. We dried samples at 55 °C for 72 h and then ground them
to a fine powder using a ceramic mortar and pestle. Small organisms and small
tissue-samples of the same species were combined to provide an adequate mass
as a composite sample. We placed 0.05–3.00 mg of each sample in an 8 x 5 mm
Elemental Microanalysis Ltd. (Devon, UK) tin capsule. The sample capsules were
analyzed in a Finnigan Delta Plus XP mass spectrometer (Thermo Fisher Scientific,
Waltham, MA).
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Results
Water chemistry
Five of the 11 water-quality parameters varied significantly among sites. DOC,
SRP, TP, and TN were significantly higher at the Phragmites-free reference site
than at either Phragmites-dominated site (all F2,38 > 8.0, all P < 0.01). In contrast,
conductivity was significantly lower at the reference site than the other 2 sites
(F2,38 = 76.3, P < 0.01). The treated Phragmites site never differed significantly
from the untreated Phragmites site. DOC, TP, turbidity, ORP, TN, and conductivity
showed significant seasonal variation (F1,38 ≥ 4.7, P < 0.05), but only conductivity
exhibited a significant interaction between site and month (Fig. 2). This interaction
inversely correlated with discharge data at the 2 Phragmites-dominated sites, while
conductivity at the Phragmites-free reference site remained stable throughout rain
events and a drought (Fig.2). Nitrogen, temperature, pH, and DO did not differ
significantly across treatments or over time (all P > 0.06).
Fish
Over the course of this study, we captured and recorded a total of 26 species of
fish representing 14 families and 2525 individuals. Fifteen fish species were each
represented by more than 15 total individuals captured. Of these well-represented
species, 12 had similar capture numbers at the Phragmites-dominated sites, but
were substantially different at the Phragmites-free reference (χ2 = 5.4, P = 0.02,
df = 1; Fig. 3). The permutational MANOVA of the Jaccard similarity index
Figure 2. Specific conductivity in microsiemens/cm over time at each of the 3 sites: treated
Phragmites (diamonds), Phragmites-free (squares), and untreated Phragmites (triangles).
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Figure 3. Total number of individuals captured across 25 fish species per sample site. See
Appendix 1 for authorities and common names of fish species.
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showed significant dissimilarity between the 2 Phragmites-dominated sites and the
reference site (both Phragmites sites F1,12 > 2.4, both P < 0.001), but not between
the treated and untreated sites (F1,12 = 0.77, P = 0.75). Shannon’s diversity index
showed no differences across sites, including when controlling for time (both F <
0.5, both P > 0.61).
Of particular interest among the fish samples was the distribution of Erimyzon
sucetta (Lake Chubsucker). The Lake Chubsucker is threatened in the state of
Kentucky, is an SGCN, and was found at all 3 sampling locations. We captured a
total of 477 Lake Chubsuckers during this study, the second-highest abundance of
any species; the majority of these individuals (57%) were collected at the untreated
Phragmites-dominated site.
Turtles
Over 2 field seasons, we trapped each site for 288 trap days, resulting in 661
turtles captured, consisting of 328 Common Snapping Turtles, 330 Red-eared
Sliders, 2 Sternotherus oderatus (Latreille in Sonnini & Latreille) (Musk Turtle),
and 1 Chrysemys picta margenata Agassiz (Midland Painted Turtle). The
ADONIS analysis showed a significant difference in turtle biodiversity across
sites (F2,106 = 3.2, P = 0.01). The subsequent Tukey’s test showed diversity was
significantly lower at the Phragmites-free reference site than either of the 2
Phragmites-dominated sites (P < 0.02). The 2 Phragmites-dominated sites did not
differ significantly (P > 0.7).
MANOVA comparisons of overall body sizes showed significant differences
among both Common Snapping Turtles and Red-eared Sliders. Turtles of both species
were significantly larger at the Phragmites-free reference site than either of the
2 sites with Phragmites (both F > 3.4, both P < 0.01); the Phragmites-dominated
treated site did not differ significantly from the untreated Phragmites site (both F >
1.6, both P > 0.1).
Sirens and other SGCN
We monitored trash-can traps at each site for ~654 days over the 2-y period for
Siren. Trapping resulted in 7 Sirens captured within the Phragmites sites, only 1
of which was at the treated site. In addition to Sirens, we occasionally captured
Nerodia rhombifer Hallowell (Diamondback Water Snake), Nerodia erythrogaster
neglecta (Conant) (Copperbelly Water Snake), and Agkistrodon piscivorus leucostoma
(Troost) (Western Cottonmouth) in these traps. We captured or observed
Sirens and Western Cottonmouths only at the Phragmites-dominated sites; the 6
other recorded SGCN were observed at all 3 sites.
Anurans
The ARDs recorded for 10 months at each site, which provided over 360 h of
sound for analysis. We identified 12 anuran species across the 3 sites including 3
SGCN: Hyla avivoca Viosca (Bird-voiced Tree Frog), Lithobates areolata circulosa
(Rice and Davis) (Crawfish Frog), and the Lithobates sphenocephala Cope
(Southern Leopard Frog). Gower’s measure of dissimilarity showed no trends,
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and the subsequent ADONIS analysis showed no significant differences in anuran
biodiversity across sites (F2,21 = 0.54, P > 0.05).
Stable-isotope analysis
Only 3 organisms showed variation between sites in δ 15N (Fig. 4). One fish
(Esox) and 1 invertebrate (Dytiscus) displayed an increase of 2.5‰ and 4‰ δ 15N,
respectively, in the Phragmites-free reference site as compared to both Phragmites
sites (Fig. 4). Another fish (Noturus) had a heavier δ 15N in both Phragmites sites
than in the reference site by 2.5‰.
The majority of the observed variation in stable isotopes was in the δ 13C signatures.
Noturus exhibited enriched levels in its δ 13C signature at both Phragmites
sites in comparison to the reference site’s more negative signature. Notonecta, Odonata,
Ranatra, and Trachemys showed the opposite result, with heavier δ 13C levels
at the reference site than both Phragmites sites. This shift led to reduced variation in
δ 13C in the Phragmites-free reference site (most organisms between -32‰ to -24‰)
when compared to both Phragmites (-35‰ to -25‰). We observed a difference in
the δ13C signatures of Phragmites between the treated and untreated Phragmites
sites. The treated site showed a lighter mean δ 13C value (-29‰) as compared to the
untreated (-26‰) site.
Discussion
Overall, we detected no differences between the treated and untreated Phragmites-
dominated sites, with exception to the δ 13C signature of the Phragmites itself.
All statistically significant differences found were between the Phragmites-free
site and the Phragmites-dominated sites. These dissimilarities are complex due to
a broad range of dynamic environmental variables and should therefore be interpreted
cautiously.
Water chemistry
All significant differences in the water-chemistry analysis paralleled the presence
or absence of Phragmites, suggesting that this plant may be directly impacting
nutrient cycling in Clear Creek. The land use surrounding all 3 sites is similar—
historical agricultural activity and coal mining adjacent to every site (Davis 2011,
Hill 1983, Neichter 1972). The differences across sites included the major nutrients
involved in aquatic ecosystems.
An increase in DOC can reflect the faunal community that the ecosystem can
support. Sources of DOC include excretion of waste materials by animals, cell
breakdown, and microbial decomposition (Lampert and Sommer 2007). An increase
in DOC, as well as other more limiting nutrients, such as phosphorus and
nitrogen, can indicate an increased trophic state of an aquatic habitat and even
increased species diversity (Lampert and Sommer 2007). Our data contradict this
trend, with the Phragmites-free reference site having higher nutrient availability
and lower faunal diversity.
Reactive phosphorus (SRP) is typically the most limiting nutrient in a wetland
(Cole 1994). More available phosphorus can benefit algal communities at the base
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Figure 4. Stableisotope
analysis for
each site. Nuphar
was sampled at the
Phragmites-free site
in the absence of
Phragmites.
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of the aquatic food web. Phragmites has higher net primary-productivity and
plant biomass than the native plants it displaces (Ehrenfeld 2003), and thus could
have sequestered much of the phosphorus at the Phragmites-dominated sites,
limiting available phosphorus for other autotrophs. At the treated Phragmitesdominated
site, we observed a decrease in living Phragmites shoots. If Phragmites
management had any effect on nutrients such as SRP, it was not detected during
this short-term study. However, nutrient cycling in a stream ecosystem has a longitudinal
(downstream) element (Newbold 1992); unmanaged Phragmites existed
upstream and may have impacted the influx of nutrients to the ar ea.
Conductivity varied significantly over time at both Phragmites sites, while
levels at the Phragmites-free site were much more stable. This finding suggests
that the flow of minerals into Weir Creek was much more constant and stable than
that entering Clear Creek. High mineral-content in watersheds is often a result of
the erosion of rocks and soils (Golterman 1975). Although the historical coal mining
in Hopkins County increased erosion in both streams, Clear Creek was more
severely impacted than Weir Creek (Neichter 1972). This situation could explain
the higher and more-variable conductivity levels found at the Clear Creek sites in
the current study (Fig. 2). Additionally, Clear Creek is a higher-order stream with
more exposure to potential drainage sources across a larger watershed. Drainage
from strip mines is often characterized by a low pH and increased heavy metals
(Robb and Robinson 1995). Phragmites has been shown to increase sediment deposition
(Rooth and Stevenson 2000), which may have affected the transport of
conductive dissolved solids in Clear Creek. The pH levels during this study were
relatively neutral for all 3 sites. Considering the historical documentation of very
acidic conditions in Clear Creek (Niechter 1972) and research findings that indicate
that Phragmites has the capacity to increase the pH of runoff from mines by adding
alkalinity through gas exchange in the substrate (Robb and Robinson 1995), it is
plausible that Phragmites has stabilized the pH at CCWMA. Other water-chemistry
parameters showed seasonal effects, but no variation across sites.
Alternatively, the differences seen in conductivity across sites could be sitespecific
characteristics, independent of the presence of Phragmites. For example,
drainage from strip mines that increased conductivity may have degraded Clear
Creek, making it difficult for native plants to survive, thereby reducing competition
for Phragmites and making it easier for this species to invade CCWMA. Peverly
et al. (1995) documented Phragmites thriving and expanding in high concentrations
of metal leachate from an adjacent strip mine, with its roots acting as filters
to absorb metals while the rhizosphere released oxygen to form metal precipitates.
If this is the case at our sites, Clear Creek may be more difficult to restore because
Phragmites is providing an ecological buffer for strip-mine drainage. Even after
the invasive plant is removed, native species may have difficulty reestablishing in
a degraded habitat. Further monitoring would provide insight into this question.
Faunal population effects
Our results do not support the hypothesis that the CCWMA fish community was
affected by Phragmites management. The lack of difference between the treated and
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untreated Phragmites sites could be attributed to the structurally similar habitat that
still exists at these 2 locations. Although the treatment of Phragmites resulted in the
elimination of green plant tissue in adult individuals, we observed that throughout
this study the dead plant stems remained standing and the amount of open-water
habitat remained essentially the same as before the herbicide application. The short
duration of the present study may not reflect long-term changes in the fish community
that could result from continued Phragmites management. For example, the
fish community at the Phragmites-free reference site was made up of a significantly
different assemblage than those at either of the Phragmites locations. This finding
supports the hypothesis that the native plant community at the Phragmites-free site
provides habitat for a different fish community than those sites dominated by Phragmites.
As the remaining Phragmites stems decompose and active management of
Phragmites presumably continues, open-water habitat and native species may yet
increase at the CCWMA, with the caveats described above.
Phragmites presence, but not management, also affected turtle species. We
captured more large turtles of the 2 most-dominant species at the Phragmites-free
site than at either of the 2 Phragmites sites. There were large numbers of native
Immigrant Pond-lily and Duckweed at the non-Phragmites site, both of which are
commonly consumed by Red-eared Sliders (Gibbons 1990). Although Common
Snapping Turtles are much more carnivorous than Sliders, both species are omnivorous.
Our observation that large turtles of both species were more common at
the Phragmites-free reference site indicates habitat selection according to age and
size. Invasion by an exotic plant such as Phragmites lowers plant diversity (Warren
et al. 2001), and Phragmites may have outcompeted more palatable plants at our 2
Phragmites sites. Our fish-community results revealed no significant differences in
overall prey availability for turtles among sites. Thus, all 3 areas had adequate food
for younger and smaller turtles that typically have a more protein-based diet, suggesting
that larger turtles may have been more concentrated in the non-Phragmites
site because of the vegetation differences.
The Phragmites-free reference site had lower turtle diversity than either of the
2 Phragmites sites, primarily because of low species evenness. The 2 Phragmites
sites did not differ significantly from each other. The ratio of Common Snapping
Turtles to Red-eared Sliders was much higher in the Phragmites-free site, as opposed
to either the treated or untreated Phragmites sites (~4:1 at Phragmites-free
versus ~1:2 for both Phragmites sites). These results suggest Phragmites has
species-specific effects on turtle distribution and population size. It is possible that
turtle species differ in habitat selection, either preferring or avoiding Phragmitesdominant
habitats. Alternatively, the species that are more aggressive, such as
Common Snapping Turtles, may outcompete those that are less aggressive, such
as Red-eared Sliders, for access to the high-quality resources at the Phragmites-free
locality. Further research will be required to evaluate these disparate hypotheses.
We found no significant difference in anuran diversity based on either species
richness or ordinal densities using the NAAMP ranking. This result supports the
null hypothesis that anurans are not affected by the presence of Phragmites and may
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therefore show little reaction to Phragmites management. Although Phragmites
does not grow in deep water, there was standing water throughout the stands of
Phragmites in Clear Creek during our study. Our results suggest that Phragmites
provides adequate habitat for the frog species of this area. This result is congruent
with the findings of Mazerolle et al. (2013).
We confirmed the presence of Sirens at both the treated and untreated Phragmites
sites. Although Sirens were not captured at the Phragmites-free site, we found
a Farancia abacura (Holbrook) (Western Mud Snake), a Siren-specialist predator
(Petranka 1998) and an SGCN, nearby, suggesting both species are present in that
area. Of the 10 aquatic reptile and amphibian SGCN that are listed as confirmed in
Hopkins County, KY (Kentucky Department of Fish and Wildlife Resources 2010),
we observed 8 at or directly adjacent to the study sites. The presence of these species
suggests that Clear Creek has high-quality habitat for herpetofaunal SGCN,
despite the invasion of Phragmites. Some of these species, particularly the Siren,
were rare and might benefit from the successful management of this invasive plant.
Other SGCN at our sites may have been affected by anthropogenic disturbance. For
example, the Phragmites-free reference site is heavily trafficked by the landowner,
and the treated Phragmites site is open to public use, and we observed relatively
few Western Cottonmouth snakes at both sites. Based on personal communications
with individuals in the local community, the Western Cottonmouth is likely affected
by human-induced mortality at these 2 sites. Frequent observations of this species
at the untreated Phragmites site suggest the Phragmites is not responsible for lower
numbers of Western Cottonmouths at the treated and reference site.
Ecosystem effects
The stable-isotope results provide insight into the food-web dynamics at each
of the 3 study sites. The stable-isotope signatures of the organisms at the treated
and untreated Phragmites sites resemble one another overall. However, the signatures
of the organisms at the Phragmites-free site show a slightly different food
web, particularly in δ13C levels (Fig. 4). Emergent plants that grow in littoral
zones in aquatic systems tend to have a less-negative carbon signature than do
algae and organisms that feed on algae (Post 2002). The lack of Phragmites at the
reference site may have allowed herbivores to feed on the more available native
macrophytes within this community, such as Immigrant Pond-lily and Duckweed.
In a similar study, Gratton and Denno (2006) found the food web at their
control treatment (Spartina [cordgrass]-dominated wetland) to be trophically
linked to the dominant macrophyte, while Phragmites-invaded areas had isotopic
signatures linking the food web to algal resources. This result corresponds to the
greater range of δ13C values at both Phragmites-dominated sites. For example, 3
invertebrates (backswimmers, damselflies/dragonflies, and water scoprions) and
1 turtle (Red-eared Slider) showed a heavier δ 13C signature at both Phragmites
sites as compared to the reference site. If the reference site has more palatable
macrophytes, then consumers will not need to rely so much on algal resources.
However, the isotopic signature of backswimmers contradicts this hypothesis
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with a lighter δ13C signature at the Phragmites-free site, suggesting that it consumes
more algae or more organisms that eat algae there. One potential effect of
management efforts can be observed in the δ13C signature of Phragmites. The live
Phragmites analyzed from the treated site exhibited a more negative signature
than that from the untreated Phragmites site by approximately 4‰. Despite no
significant differences in water-sample nutrient levels between the Phragmites
sites, the δ13C signatures potentially reflect a difference in the microbial community
in the substrate. Wang et al. (2017) found a negative correlation between
microbial biomass and the δ13C levels of the associated plant community. It is possible
that either an increase in decomposing Phragmites mulch due to herbicide
application or direct effects of the herbicide itself might have impacted the microbial
community and thereby may have subsequently altered nutrient availability
to the remaining live Phragmites plants. The nutritional state of plants can impact
isotopic signatures (O’Leary 1981). Neither site had atypical δ13C signatures for
Phragmites nor high variation among sample replicates (~0.7‰ for both), indicating
the higher signature at the treated site is unlikely due to temporal variation.
Two predators (predaceous diving beetles and pike) existed at an increased trophic
level (mean δ15N value) at the Phragmites-free reference site as compared to
either Phragmites site, suggesting the reference site supported a longer food chain.
In a bottom-up–controlled ecosystem, a longer food chain is supported by increased
biomass in the preceding trophic levels (Campbell and Reece 2002). An increase in
biomass on all trophic levels means there would be an increase in faunal excretory
waste and cellular decomposition, which corresponds to increases in DOC (Lampert
and Sommer 2007) as found at our Phragmites-free reference site. Again, this
finding was not supported by the nitrogen signature of madtoms, which showed an
enriched δ15N in both Phragmites sites (+~3‰) as compared to the reference site.
Neither the carbon nor the nitrogen signature of madtoms corresponds to the more
positive trends seen in other organisms in the Phragmites-free site, but this is not
entirely unexpected. Other studies regarding Phragmites’ effect on fish have shown
mixed results (Able and Hagan 2000, Davis 2011, Fell et al. 2003), and it is not
surprising that species react differently to resource alterations.
Conclusion
This study demonstrates the complex and variable nature of invasive species
treatment in a wetland ecosystem. Plant invasions generally affect all levels and
processes within an ecosystem; thus, multi-disciplinary and cross-taxa monitoring
research is important for understanding the ecological implications of invasive species
management (Blossey 1999). This interdisciplinary approach is reflected in the
management goals and monitoring strategies at Clear Creek WMA. Replicating this
study in conjunction with continued management efforts could tease out nuances in
how different populations of flora and fauna react to invasive plant ma nagement.
The ability of Phragmites to quickly dominate marsh-plant communities (Roman
et al. 1984) makes possible the alteration of wetlands on an ecosystem level.
Our results illustrate the complexities of wetland dynamics and fluxes, some of
which originate from the bottom of the food web and manifest in top predators. The
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successful management of Phragmites and any subsequent effects on the wetland
community may not be apparent without long-term monitoring in conjunction with
continued management. Successful habitat restoration in this context can be defined
as an attempt to re-establish communities to a state that is both physically and
functionally similar to the pre-invasion habitat (Palmer et al. 1997). Complementing
management efforts with thorough biological monitoring allows for a deeper
understanding of how this invasive plant and its management can affect wetlands,
and thus provides guidance for future restoration efforts.
Acknowledgments
This research was funded by a State Wildlife Grant from the Kentucky Department
of Fish and Wildlife Resources. We thank the Hancock Biological Station for logistical
support and B. Kik for access to the Clear Creek Wildlife Management Area and for lodging.
We are grateful to E. Dustman, Dr. G. Kipphut, T. Johnson, T. Flynt, K. Johnston, G.
Harris, J. Benson, S. Roach, T. Anderson, and others for their valuable guidance and assistance.
Finally, we thank 2 anonymous reviewers for their helpful suggestions on an earlier
version of this manuscript.
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Appendix 1. The following are the scientific names, authorities, and common names of fish
species captured during this study at CCWMA as seen in Figure 3.
Scientific name Authority Common name
Amia calva L. Bowfin
Lepisosteus oculatus Winchell Spotted Gar
Lepisosteus osseus (L.) Long-nose Gar
Esox americanus Gmelin Grass Pickerel
Dorosoma cepedianum (Lesueur) Eastern Gizzard Shad
Erimyzon sucetta (Lacepède) Lake Chubsucker
Cyprinus carpio L. Common Carp
Notemigonus crysoleucas (Mitchill) Golden Shiner
Labidesthes sicculus (Cope) Brook Silverside
Ameiurus melas (Rafinesque) Black Bullhead
Ameiurus natalis (Lesueur) Yellow Bullhead
Noturus gyrinus (Mitchell) Tadpole Madtom
Fundulus olivaceus (Storer) Blackspotted Topminnow
Gambusia affinis (Baird & Girard) Mosquito Fish
Aphredoderus sayanus (Gilliams) Pirate Perch
Centrarchus macropterus (Lacepède) Flier
Lepomis cyanellus Rafinesque Green Sunfish
Lepomis gulosus (Cuvier) Warmouth
Lepomis macrochirus Rafinesque Bluegill
Lepomis megalotis (Rafinesque) Longear Sunfish
Micropterus salmoides (Lacepède) Largemouth Bass
Pomoxis annularis Rafinesque White Crappie
Pomoxis nigromaculatus (Lesueur) Black Crappie
Elassoma zonatum Jordan Banded Pygmy Sunfish
Etheostoma squamiceps Jordan Spottail Darter