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Integrating tidal freshwaters into conceptual frameworks for how hydrology structures benthic communities in wetlands [ABSTRACT]

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wetland science
practice
Vol. 32, No. 4 Dec 2015
published by the Society of Wetland Scientists
metabolites while the bacterial community will be analyzed
for changes in community structure. Serial dilutions will be
employed to detect shifts in the soil microbial community
populations. This research will shed light on the role of
these mechanisms for treatment of TCE in wetland systems.
The overall hypothesis is that the degradation of TCE in
wetland systems is done through the interaction between
abiotic, microbial and plant activities. n
Integrating tidal freshwaters into conceptual frameworks for
how hydrology structures benthic communities in wetlands
Jack McLachlan,
University of Maine
jack.mclachlan@maine.edu
Tidal freshwater wetlands (TFWs)
are not well integrated into
conceptual wetland ecology. Benthic
communities in TFWs are apparently
depauperate, but the mechanisms
driving community structure are poorly understood. Twice-
daily water level changes allow close examination of how
hydroperiod structures wetland communities. Integrating
TFWs with community models of seasonal inland wetlands
provides an excellent framework for reconciling tidal and
non-tidal wetland community ecology. Drying and inunda-
tion cycles exert a strong selective pressure on the traits of
benthic wetland invertebrates. In ephemeral wetlands that
dry and rell predictably, and remain inundated for longer
than invertebrate generation time, taxa will have niche-
specic life history adaptations that maximize tness, such
as seasonal emergence cues. In non-seasonal wetlands,
that dry and rell unpredictably, taxa will have physiologi-
cal tolerances against desiccation that allow persistence in
sporadic habitats. When wetland permanence is sufcient
for sh persistence, predation pressure will surpass abiotic
stressors as the driver of benthic community structure. How
the predictable high-frequency tidal cycles of TFWs might
inuence community structure is not clear. I hypothesize
that the low benthic diversity of TFWs results from the dual
pressures of twice daily wetting and drying, and preda-
tion by sh that can follow tides. Alternatively, variation
in hydroperiod associated with tidal height may promote
beta-diversity in TFWs, with uneven marsh topography
providing refugia from desiccation and predation. I will
manipulate drying frequency and predators in articial
mesocosms to identify shifts in community structure based
on species’ traits. This manipulation will be paired with
multi-season surveys of benthic communities along tran-
sects of tidal-marsh height in Merrymeeting Bay, Maine – a
nationally important wetland conservation area and one of
the largest contiguous TFW areas in the northeast. Results
from these approaches will be combined in conceptual
and statistical models of how spatiotemporal variation in
wetland hydroperiods inuence broader scale patterns of
benthic community diversity. My results will 1.) advance
current understanding of how abiotic and biological drivers
interact to structure communities in dynamic wetlands, 2.)
help predict wetland communities responses to forecasted
environmental change (e.g. sea-level rise), and 3.) unify
community ecology theory across wetland types. n
Identifying source water contributions to floodplain
forest vegetation across seasonal and hydrological
connectivity gradients
Mary Grace Lemon,
Louisiana State University
mlemon7@tigers.lsu.edu
Floodplain wetlands are com-
monly recognized as high
diversity ecosystems that provide
many services such as wildlife
habitat and nutrient retention. In
oodplain wetlands, surface water, soil water, and aquifers
form an interconnected system that varies temporally and
spatially, affecting the sources of water available in the soil
for vegetation use. Continued degradation of oodplain
river connectivity through river modication and increased
human water use can signicantly alter these existing
hydrological networks. In southeastern bottomland hard-
wood forests (BLH) of the US, there is a lack of process
understanding of how the composition of vegetation source
water changes through time and space across a oodplain.
In order to maintain ecosystem integrity under further water
resource development, the temporal and spatial variation
of soil moisture source water must be further investigated.
We propose to test the following hypotheses (1) the inu-
ence of ood recharge on soil moisture and xylem water
decrease through the growing season as soil water becomes
dominated by rainfall and groundwater; and (2) the domi-
nant hydrological processes controlling soil moisture and
xylem water vary by reach, which differ in degree of river
entrenchment. We will test these hypotheses by measuring
the sources of water to the rooting zone and xylem using
stable isotopes at White River National Wildlife Refuge
(NWR). White River NWR provides a unique setting to
look at the effects of degraded connectivity on subsurface
hydrology due to its location within a large regulated water-
shed. Spatial and temporal variations in the relative impor-
tance of various sources of water (precipitation, surface
ooding, groundwater) to the rooting zone and in the xylem
will provide information about potential threats of further
water development to oodplain vegetation. n
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