Roles of Wetlands at Multiple Scales: Biological, Geochemical, and Hydrological Interactions III
Presiding: A Worman, Swedish University of Agricultural Sciences (SLU); A Ward, University of Alabama
NB44C-01 INVITED 15:30h
Seed Bank Contribution to Vascular Plant Richness on Temporary Floating Islands
Fluctuating water levels create opportunities for recruitment of new individuals from wetland seed banks. In this study, floating island formation functioned similarly to drawdowns in water level by creating patches of sediment that were less inundated than the surrounding, undisturbed deep-water marsh. To examine if and how seed banks contributed to temporary formation of distinct plant assemblages on these islands, field surveys of plant percent cover on and off of islands were conducted over two years, along with a controlled greenhouse experiment in which inundation was manipulated. Plant assemblages differed significantly on and off of floating islands. Floating-leaved perennials dominated undisturbed deep-water marsh, while emergent species dominated floating islands. Moreover, species richness was greater on islands than in the undisturbed deep-water marsh. Plant assemblages in the greenhouse experiment also differed among inundation treatments in a manner consistent with differences observed in field surveys. These results demonstrate that floating island formation temporarily altered levels of inundation favoring the germination of a more species-rich, emergent plant assemblage. Because these islands persisted long enough for several species to set seed, their formation may contribute to the maintenance of the seed bank and help maintain populations of otherwise rare species within the deep-water marsh.
NB44C-02 INVITED 15:45h
Effects of Dissolved Organic Matter Source on Wetland Bacterial Metabolism
Wetlands are rich environments for organic matter production from a variety of wetland plant types. Investigations of the Talladega Wetland Ecosystem (TWE) in the southeastern U.S. show that bacterioplankton productivity is driven by dissolved organic carbon derived from wetland plants. The TWE is formed from a small coastal plain stream that has been dammed by beaver activity and resides in a forested catchment. In this study, bacterioplankton communities sampled from the wetland were amended with leachate from two different plants common in the TWE, the soft rush, Juncus effusus, and hazel alder, Alnus serrulata, and compared to unamended controls. The bacterioplankton response was examined by measuring bacterial carbon productivity and by an array of fluorescent microscope techniques used to distinguish metabolically active and non-active cells. Both plant leachates elicited rapid and significant increases in productivity and numbers of metabolically active bacterial cells. However, the timeframe of response, the magnitude of response, and the bacterial morphotypes varied depending on the leachate source. This study suggests that wetland bacterial communities contain different sub-component populations that may generally occur in low numbers, but that can adapt and respond rapidly to different sources of organic matter native to the wetland.
NB44C-03 16:00h
Ibero Atlantic Forested Wetlands: Plant-Abiotic Interactions at a Regional Scale
In biogeographical terms, forested wetlands are considered azonal ecosystems due to their special edaphic conditions. Duration of waterlogging decreases the effect of regional climate in vegetation communities. In this work we test this hypothesis by studying the relative contribution of spatial and environmental variation. Plant community composition and vertical structure were inventoried in inland forested wetlands along the Atlantic coast of the Iberian Peninsula. The study area ranges from latitude N 44° to 38° and includes Temperate and Mediterranean climate. Forested wetlands area was delimitated and sampled using plots where all the vascular plants and bryophytes were registered and their percentage cover estimated. Collected environmental regional variables included geographic, climatic, geologic and hydro geomorphologic data. Multivariate analysis was used to interpret species abundance data to assess the relative weight of environmental conditions and the spatial structure in the species data variation. Results of species-environment treatment revealed that tree overstorey species were determinant for vegetation types and that hydroperiod was the key abiotic variable classifying forested wetlands.
NB44C-04 16:15h
Tracer experiment and flow modelling applied to Ekeby treatment wetland, Sweden.
The use of treatment wetlands have come to play an important role in reducing nutrient content in wastewater and in run-off water from agricultural areas. It is of interest to optimize the nutrient removal efficiency. In order to do so hydrological and geochemical processes, and the coupling between them, must be known in greater detail than is currently the case. One way of investigating this matter is to perform tracer experiments and evaluate the results using computer simulations. In November 2002 a simultaneous tracer experiment was performed in a treatment wetland, using tritiated water, P-32 and N-15. The wetland is situated 120 km west of Stockholm in Sweden, and the basin where the experiment was performed has an area of 2,6 ha. The simultaneous use of conservative tracer and reactive tracers enables a fair evaluation of both hydraulic processes and biochemical reactions. In this presentation evaluation of the hydraulic matters will be in focus, the geochemical issues will be described in companion presentations. In order to evaluate the hydraulic behaviour and the fate of tritium through the wetland, a two-dimensional flow model was developed in a MATLAB environment. The model is able to deal with variations in shape, bottom topography and friction factors. It was used to simulate flow of inert particles through the wetland. Breakthrough curves of tritium and simulation results were studied and compared for different setups of friction parameters. The simulations show that bottom topography and shape of basin alone are not enough to explain the spreading of water residence times in the wetland. Distribution and density of vegetation, simulated as friction factors, are shown to be crucial when it comes to reproducing the residence time distribution from the experiment.
NB44C-05 16:30h
Relationships Between Litter Processing and Impervious Surface Cover in Headwater Tributaries of the St. Johns River, Florida
We investigated relationships between land-use and litter processing in 18 tributaries of the St. Johns River, Florida. The percent total impervious area (PTIA) of these catchments ranged from 0-66%. We measured mass loss and fungal biomass (as ergosterol) and associated macroinvertebrate biomass for 2 litter species (red maple [Acer rubrum] and sweetgum [Liquidambar styraciflua]). Processing rates ranged from 0.010-0.046d-1 for maple and 0.006-0.018d-1 for sweetgum. The fastest processing occurred at intermediate PTIA. Fungal biomass peaked at 24 days with the lowest biomass occurring in the low PTIA stream. Rates of processing were positively related to both mean macroinvertebrate biomass and taxa richness. Shredder biomass was not related to maple, but was negatively related to sweetgum processing. Scraper biomass peaked at intermediate PTIA, and was positively related to processing rates for both leaf species. We reduced correlated physicochemical, land-use and biological variables to several orthogonal variables using principle components analysis. Regression models based on these variables accounted for 70% of the variance in processing rates for both leaf species. Collectively, these results demonstrate that PTIA and other land-use indicators are associated with differences in stream ecosystem patterns and processes between low gradient, subtropical streams.
NB44C-06 16:45h
The effects of a Cattail invasion on a Great Lakes coastal marsh
Great Lakes coastal marshes have been increasingly invaded by aggressive exotic plant species, such as the cattail Typha x glauca. T. x glauca has replaced much of the native plant community in Cheboygan Marsh, a coastal marsh on Lake Huron. Investigations done in this marsh during Summer 2004 addressed the T. x glauca invasion impacts on several ecosystem attributes. Multiple physical, chemical, and biological parameters were measured along transects extending from the native community through the T. x glauca-dominated vegetation zone. As expected, species diversity was much lower in the T. x glauca stands (d=0.14) than in the native community (d=0.82). The T. x glauca zone was found to have 2.2 times higher aboveground biomass and large accumulations of dead plant litter averaging 1.25m deep. Light intensities decreased 3-fold, and temperature at the sediment-water interface fell 5°C under these litter masses. T. x glauca was also found to retain 2 to 7 times higher levels of nitrogen in its associated sediments than the native community. Further research is being conducted to determine how nitrogen accumulates in the T. x glauca zone and if this change in nitrogen cycling dynamics facilitates its invasion success.