Roles of Wetlands at Multiple Scales: Biological, Geochemical, and Hydrological Interactions I Posters
Presiding: A Worman, Swedish University of Agricultural Sciences (SLU); A Ward, University of Alabama
NB33C-01 1330h
Nitrogenase and Alkaline Phosphatase Activity in Wetland Metaphyton: Implications for Primary Production and CNP Composition
Longitudinal gradients of nutrient availability often occur along the flow path of water in freshwater wetlands. Differential removal efficiencies of water column nitrogen (N) and phosphorus (P) may increase the severity of nutrient deficiency and possibly change the nutrient that limits primary production. A previous study demonstrated that periphyton in the Lake Waco Wetlands (LWW), near Waco, Texas, USA, are generally more P limited near the inflow and become increasingly N limited as distance from the inflow increases. Therefore, spatial heterogeneity in nutrient availability likely influences both the structure and function of periphyton assemblages within this system. In this ongoing study, we are evaluating the relationships between metaphyton primary production, nitrogenase activity, alkaline phosphatase activity, and CNP stoichiometry in areas of differing nutrient limitation within the LWW. As expected, primary production is generally greatest in areas where nitrogenase and alkaline phosphatase activities are minimal. However, expected increases in C:N ratios in areas of greatest nutrient deficiency have not been frequently observed. Decreased primary production and increased enzyme mediated nutrient uptake appear to balance metaphyton nutrient content in these areas.
NB33C-02 1330h
Seasonal Phosphorus and Nitrogen Trends During Restoration of the Wood River Wetland, Klamath Falls, Oregon
From 1985-1994, the 3200 acre Wood River Wetland (WRW) was managed as irrigated pasture for beef cattle production. In 1996, a project to restore the historical wetland was initiated to provide long-term improvement in water quality and quantity entering Agency/Klamath Lake. Presently, the WRW is managed for seasonal wetland habitat (1600 acres) and more permanent marsh/open water habit (1400 acres). Between May and August 2003, TP increased from 4 to 19 mg P/L. TP was significantly higher in the wetland than in source waters, including artesian groundwater and surface streams. TP increased at the same rate as specific conductance, suggesting that the increase resulted from water evaporation rather than biological or geochemical processes. Approximately 75-95 percent of the TP was soluble inorganic P. TKN, like TP, increased from 7 to 19 mg N/L and was significantly higher in the wetland than in any potential source. TKN, unlike TP, consisted mainly of an organic form of N, with 10 percent or less composed of ammonium and nitrate. Since SRP dominated the TP pool, and concentrations were exceedingly high, there was little biological impact on the P cycle. The low concentrations of bioavailable N indicated a significant biological impact on the inorganic N cycle.
NB33C-03 1330h
Factors affecting macroinvertebrate assemblages in autumnal wetlands at Mammoth Cave National Park, Kentucky.
Temporary wetlands exhibit many between- and within-pond environmental gradients. Most research on macroinvertebrate communities of forested temporary wetlands has cited pond size and two corresponding effects, hydroperiod and habitat complexity, as important factors regulating biotic diversity and density. However, additional variables (e.g., dissolved oxygen, life history strategies) can override the effects of wetland size. We investigated the potential relationships between chemical and biotic parameters and macroinvertebrate communities of 10 temporary, forested autumnal wetlands in Mammoth Cave National Park, Kentucky. The ponds were small (< 0.5 ha) and varied along several environmental gradients, most notably pH, maximum depth, dissolved oxygen content, temperature, hydroperiod, and size. Preliminary data analyses revealed (a) each pond generally supported a similar number of species, and (b) the diversity and abundance of macroinvertebrates could not be explained by pond size, hydroperiod, or habitat diversity. A second set of data analyses will be performed by partitioning the ponds into shallow and deep zones, and assessing macroinvertebrate communities separately according to functional groups and life history characteristics.
NB33C-04 1330h
The Potential Role of Secondary Circulation, Nutrient Transport, and Peat Accretion in Wavelength Evolution of the Ridge and Slough Landscape, Everglades, FL
The ridge and slough landscape is a crucial ecosystem that has been deteriorating since the drainage of the Everglades in the early 1900s. The landscape is characterized by interconnected open-water sloughs interspersed among sawgrass ridges, which are 2-3 feet higher than the bottom of the sloughs and elongated parallel to the pre-drainage flow. The self-organized patterning of this landscape features a characteristic wavelength of approximately 50 meters. An understanding of the mechanisms responsible for landscape creation and maintenance is currently lacking but necessary for effective restoration planning. In exploring the mechanisms potentially responsible for formation of the ridge and slough landscape, it is noteworthy that the heads of ridges are indistinguishable from the tails; that is, landforms do not take on the lemniscate-shaped, minimum drag form associated with formation through nutrient or sediment transport via the mean flow. Rather, ridges and sloughs, though larger in scale, are more similar in form to longitudinal furrows and bars, which, in rivers and tidal flats, are generated by secondary circulation. However, bedforms generated by secondary circulation would be expected to scale at a maximum with flow depth, which in the Everglades would result in an initial wavelength an order of magnitude smaller than the current wavelength of the landscape. In this poster, the possibility of wavelength evolution resulting from preferential nutrient transport towards transpiring sawgrass colonists on ridges and differential peat accretion is explored through a combined finite difference/cellular automata model. The model is initialized with topography corrugated at the expected scale of secondary circulation cells. At each time step, the probability of sawgrass colonization, based on ridge height, porewater nutrient content, and proximity to surrounding sawgrass stands, is calculated. Based on the resulting distribution of plants and the state of plant growth, surface and porewater flow fields are determined, and a phosphorus balance is performed on each cell. Calculation of peat accretion and oxidation based on plant biomass and distance to the water table determines the new topography, and the model advances to the next time step. Results of the effect of this process on biogeomorphic evolution of the ridge and slough landscape are presented.
NB33C-05 1330h
The Effect of Flow on Periphyton Structure and Nitrate Removal
High nutrient levels in surface waters are a persistent worldwide problem. Natural and constructed wetlands are frequently employed to reduce nutrients levels from non-point sources, such as agriculture activity. However, there is little understanding of the variation in nitrate removal with flow conditions, and it is difficult to control peaks of nitrogen, especially in the spring when flows tend to be high and there is substantial agricultural nutrient input. Observations of nitrogen transformations in the Des Plaines River Wetland Demonstration Project (Wadsworth, IL) indicate that the emplacement of benthic mesh netting increases the rate of denitrification by providing a favorable and uniform substrate for thick periphyton growth, which, in turn, promotes a superior habitat and carbon source for denitrifying bacteria. We are evaluating this hypothesis in a series of studies designed to improve understanding of the interplay between periphyton assemblage characteristics, overlying flow conditions, and the rate of denitrification. We are conducting laboratory experiments in a model wetland system (250 cm long and 20 cm wide). Nitrate removal is evaluated by monitoring changes in the concentrations of nitrate, nitrite, ammonium and total nitrogen in the system under different fluid velocities (0.05, 0.5 and 5 cm/s). Temporal changes in the periphyton assemblage characteristics are quantified using a combination of confocal microscopy, algal identification, and microbial enumeration. We also utilize micro-profiling with oxygen and nitrate micro-sensors to evaluate chemical heterogeneity in the periphyton and sediments. Combined knowledge of the response of the microbial system and bulk denitrification rates to the system geometry and flow conditions will support the development of improved strategies that rely on periphytic growth to enhance denitrification rates in natural and constructed wetlands.
NB33C-06 1330h
Coastal forest productivity and wetland hydrology: A dendrochronological study
Modified river flows and subsidence of deltaic sediments have caused many coastal swamp forests in Louisiana to become subject to greatly modified flooding and sediment and nutrient regimes. Many areas have become inundated at greater depth, duration, and frequency, and either receive drastically increased sediment and nutrients or have been disconnected from inputs. To better understand how these changes are affecting ecosystems, we used dendrochronology of baldcypress (Taxodium distichum L. Rich.) at two contrasting sites to compare the historical relationship of hydrology and productivity. Both sites are adjacent to long-term records of water levels, and are in similar topographic positions near lakes in backswamps of the Atchafalaya River distributary basin, but have strongly contrasting hydrological conditions. The first site is near Grand Lake, where diversion of Mississippi River water into the Atchafalaya Basin Floodway has drastically increased flooding and inputs of sediment and nutrients. The second site is near Lake Verret, where flood control levees have eliminated seasonal riverine flooding but inundation has increased because of subsidence, impeded drainage, and backwater flooding from the outlet of the Atchafalaya Basin. We compare the historical responses of baldcypress radial growth to varying depth, duration, and timing of flooding at these two sites. Further development of this tool will also be useful as an indicator of historical hydrology in forests where historical hydrological conditions are unknown.
NB33C-07 1330h
The Diverse Bacterial Community Associated with Fine Particulate Organic Matter in Wetland Sediments
Fine particulate organic matter (FPOM) is one of the dominant forms of organic material in aquatic systems, although few studies have characterized the microbial community associated with this material, particularly in wetlands. We used molecular techniques to examine the bacterial community associated with two sizes of FPOM collected from a Louisiana coastal wetland. Sediment was sieved into two size ranges: 0.25-1 mm (primary FPOM), and 0.038-0.25 mm (secondary FPOM). DNA was extracted from the microbial community associated with each size range, and the 16S rRNA genes amplified using conserved bacterial-specific primers. The amplified 16S rRNA genes were cloned and sequenced to determine the identity and frequency of each sequence type. The majority of sequences obtained were unique, suggesting that both primary and secondary FPOM harbored diverse bacterial communities. Most of the 16S rRNA sequences showed low similarity to known bacteria, suggesting the presence of many undescribed bacterial populations. There was little similarity in the gene sequences obtained from each size range suggesting significant differences in bacterial community composition with particle size. These findings suggest that wetland FPOM contains diverse bacterial communities and that differences in particle size result in different bacterial communities associated with this FPOM.
NB33C-08 1330h
Microhabitat Use by Trichoptera in a Lake Erie Coastal Wetland
We examined the differences in microhabitat use by caddisfly (Trichoptera) adults at a Lake Erie coastal wetlands complex in northwestern Ohio. Light traps were employed in three vegetative zones; a Pontedaria stand, a submerged willow/cottonwood forest, and an adjacent open water area. We used concealed UV lights inside of replicate traps (n = 4 per habitat), attracting only caddisflies near the habitat, that were run May, June, and September 2004. Analysis of the data revealed differences in adult abundance between habitats and months for some taxa. Principal components analyses run at the level of genera and species showed that sites cluster by habitat type and by month, suggesting differences occur temporally and spatially but not exclusively of each other. ANOVA reveals statistical differences between habitats and months for the most common taxa. Hydroptilidae, including Agraylea multipunctata, Orthotrichia aegerfasciella, and Oxyethira pallida, were the most abundant taxa contributing approximately 90% of samples depending on vegetative zone. Information on the microscale preferences of adult caddisflies indicates potential habitat specificity. This may aid managers who decide which habitats within wetlands to conserve based on productivity and unique potential contribution of insect taxa.
NB33C-09 1330h
Bottle Traps and Dipnetting: Evaluation of two Sampling Techniques for Assessing Macroinvertebrate Biodiversity in Depressional Wetlands.
Dipnet (DN) sampling is routinely employed for macroinvertebrate bioassessments, however it has been shown that some taxa are more effectively sampled with activity traps, commonly called Bottle Traps (BT). In 2001, the Minnesota Pollution Control Agency used both DN and BT sampling in nine depressional wetlands in the North Central Hardwood Forest Ecoregion to evaluate macroinvertebrate biodiversity for the purpose of assessing water quality and developing biological criteria. Both methods, consisting of five bottle trap samples and two dip net samples per wetland, were collected from each of two sites in each wetland. To determine the performance of each method in documenting biodiversity, we compared taxa and their abundances by wetland, for each type of sample. DN sampling was more effective, with 44 of 140 macroinvertebrate taxa only identified from DN, compared to 14 only from BT. By contrast, BT more effectively collected leeches and beetles, especially active swimmers such as Tropisternus and several genera of Dytiscidae. However, taxa richness patterns for BT and DN were not strongly correlated. Consequently, we conclude these two sampling methods complement each other, providing a better overall picture of macroinvertebrate biodiversity, and should be used jointly when investigating macroinvertebrate biodiversity in depressional wetlands.
NB33C-10 1330h
Modification of the 3H-leucine Incorporation Technique for Quantifying Rates of Bacterial Secondary Production on Decaying Wetland Plant Litter: Effectiveness of Microdialysis.
The radiolabelled 3H-leucine incorporation technique for quantifying rates of bacterial production has increased in popularity since its original description for bacterioplankton communities. Prior studies addressing incorporation conditions (e.g., substrate saturation) for bacterial communities in other habitats, such as decaying plant litter, have reported a wide range of final leucine concentrations (400nM to 50,000nM) to achieve saturation-level uptake. We assessed the application of the 3H-leucine incorporation procedure for measuring bacterial production on decaying wetland plant litter. Substrate saturation experiments (9 concentrations, 10nM to 50,000nM final leucine) were conducted for bacterial communities colonizing submerged litter of three emergent plant species (Typha angustifolia, Schoenoplectus validus, and Phragmites australis). A modified 3H-leucine protocol was developed by coupling previously described incubation and extraction protocols with microdialysis (500MWCO) of the final radiolabelled protein extract. Incorporation of 3H-leucine into protein exhibited a biphasic saturation curve, with lower Km values ranging from 400nM to 1200nM depending on the plant species studied. Upper Km values ranged from 4000nM to 6000nM. Dialysis of the crude protein extract significantly improved counting precision and the signal-to-noise ratio. These results suggest differential uptake by litter associated microbial assemblages, with lower Km values possibly representing bacterial uptake and higher Km values representing non-bacterial uptake.
NB33C-11 1330h
The Effects of Ultraviolet Radiation on Attached Wetland Algae and Bacteria
Despite the well-known increases in ultraviolet radiation (UV-R) reaching the Earth's surface due to the destruction of the ozone layer, little is known about effects of UV-R on wetland periphyton. To study the effects of UV-R on wetland periphyton, artificial substrata were placed under acrylic mesocosms in the Paint Creek Wetland, Ypsilanti, MI. One treatment mesocosm excluded light in the UV range (<340nm) and the other allowed the passage of full light. Periphyton attached to artificial substrata was collected on 4 dates during August and September 2004 and analyzed for Chlorophyll a, ash-free dry mass (AFDM), bacterial density, colloidal extracellular polysaccharides (EPS) and algal community composition. Over the length of the experiment the proportion of dead to live bacteria (p<0.02), EPS accrual (Μgram glucose equivalents/cm2) (p=0.046), and the ratio of EPS to AFDM (p=0.027) were significantly greater in the UV-R-exposed treatment. These results suggest that ambient levels of UV-R damage periphytic bacteria and increase EPS production by periphyton.
NB33C-12 1330h
Topsoil Removal in a Restored Peat Wetland: an Experimental Study
Topsoil removal is a common practice in wetland restoration projects for eliminating the weed seed bank, any persistent herbicides or pesticides, as well as lowering the soil surface closer to the water table. In 2000, a peat wetland that was drained 85 years ago for agriculture was restored by removing 40-50 cm of topsoil, seeding wetland plants, and reestablishing wetland hydrology. In 2004, six 100m2 scraped plots and six adjacent 100m2 unscraped control plots were sampled in North and South fields. Plant percent cover and aboveground biomass was measured in each plot. Depth to the water table was greater in the North field because this field had a higher elevation than the South field, which was partially submerged. Total biomass was greater in the North field than in the South. In the North field, species diversity and richness were higher in treatment plots than control plots, but there was no difference in the South field. Dominant species were different between the control and treatment plots and between North and South fields. These results indicate that both water levels and topsoil removal have dramatic impacts on plant community establishment in restored wetlands.
NB33C-13 1330h
Implementation of Biotic Integrity Metrics to Identify the Effects of Land Use on the Diversity of Wetlands
To identify critical biological measures of wetland health, we studied twelve wetlands in north-central Tennessee and south-central Kentucky, six impacted by row crop agriculture and six unimpacted. Aquatic macroinvertebrate were collected using 10.2 cm clear PVC pipe funnel traps and wire minnow traps. Seven samples were collected from each site between May 19 and August 8, 2004. Qualitative samples (one person-hour) were collected with dip nets from each wetland to correspond with the early July trap samples. Water quality parameters measured included dissolved oxygen, pH, temperature, specific conductance, and turbidity with multiparameter aquatic probe and nephlometer. Macroinvertebrates from three sets of samples for each site were identified, when possible, to genus. The number of organism collected per trap-period per site ranged from 43 to 2224. Fifty-six taxa were identified. Generally, natural areas showed greater species richness, diversity and evenness than agricultural sites. Dipterans, primarily chironomids, were the most dominant assemblages. The three most abundant predatory orders, Coleoptera, Odonata and Hemiptera, showed alternating patterns of dominance. Habitat stability and greater vegetative complexity, which are impacted by surrounding agricultural practices, appear to be strongly related to higher species diversity.
NB33C-14 1330h
Macroinvertebrate Colonization of Leaf Litter Along a Wetland Habitat Gradient
Seasonal inputs of allochthonous material represent an important resource in aquatic systems and contribute to variability in invertebrate assemblages. Within wetlands, there are typically strong aquatic to terrestrial gradients associated with decomposition of terrestrially derived plant matter, which may influence patterns of invertebrate abundance and species composition. In this study, we examined overwinter (November-April 2003) patterns of leaf decomposition and associated macroinvertebrate abundance and diversity using leaf packs for two tree species (Quercus rubra and Liriodendron tulipifera). Leaf packs were placed along habitat transects spanning aquatic, semi-aquatic, and terrestrial habitats in a wetland. For both leaf species, decomposition rates were highest in aquatic habitats, but did not differ between semi-aquatic and terrestrial habitats. However, invertebrate abundance and diversity were significantly higher (P < 0.5) in semi-aquatic leaf packs than in aquatic or terrestrial leaf packs. Despite strong habitat effects, leaf species did not have a significant impact on patterns of invertebrate colonization. Overall, invertebrate abundance and diversity differed greatly along the aquatic-terrestrial transition, documenting the importance of habitat transition zones in wetland systems.
NB33C-15 1330h
Experimental verification of a mechanistic model of methane bubble formation in non-vegetated flooded rice field soil
Anoxic wetlands are an important source for the greenhouse gas CH4, much of which is emitted in form of gas bubbles. The conditions for formation of gas bubbles have recently been described by an analytical model, which allows the prediction of fluxes by first physical principles using the knowledge of gas concentration profiles and/or gas production rates. We verified parts of this model by experiments using microcosms of flooded, non-vegetated and homogeneous rice field soil incubated under different gas atmospheres and at different temperatures. In these experiments we determined rates of CH4 and CO2 production, upper boundaries of the bubble zone, gas-filled porosities and vertical profiles of dissolved CH4, CO2 and N2. Methane production rates were measured from slurry incubations and/or from CH4 emission rates by inhibition of CH4 oxidation with methyl fluoride. Vertical gas concentration profiles were measured by using gas diffusion probes and peepers. The vertical gas concentrations were used to determine the diffusive CH4 flux. The results of our experiments confirmed that by knowing only one of the following parameters, i.e. CH4 production, diffusive CH4 flux and depth of upper boundary of bubble zone, the remainder could be predicted from the model. In particular, we were able to predict the percentage of gas bubble flux from measured CH4 emission rates under the experimental conditions, which was on the order of 90 percent.
NB33C-16 1330h
Estimation of Biogenic Gas Distribution in a Northern Peatland Using Surface and Borehole Ground Penetrating Radar
A combination of borehole and surface ground penetrating radar (GPR), time domain reflectometry (TDR) and direct gas sampling was performed to detect biogenic gas accumulation areas in Caribou Bog, a multi-unit peatland in central Maine (Orono). Areas of electromagnetic (EM) signal scattering (or shadow zones, similar to those reported with the seismic reflection method) observed in the surface GPR coincide with sampled zones of high CH4 and CO2 concentration. Shadow zones also correlate with areas of high EM wave velocity detected in zero offset profiles (ZOP) conducted with the borehole GPR, and with areas of low water content inferred with TDR. Application of the Complex Refractive Index Model (CRIM) to the EM wave velocities implies that the anomalous high velocity zones results from a volumetric gas content of 7% and 10% for a peat soil porosity of 91% and 94% respectively. In the absence of gas, the CRIM model predicts a porosity value of only 84% to reach the maximum EM wave velocity recorded, a value not supported by our peat porosity measurements in the laboratory and inconsistent with the high porosity of peat recorded by others. Strong reflectors detected with the surface GPR are interpreted as confining layers acting as biogenic gas traps and inducing overpressurized biogenic gas pockets as postulated by others. Spatial gas distribution and volumetric gas content can be roughly estimated considering the areas affected by EM wave blanking. These findings also have implications for the monitoring of temporal behavior of biogenic gas emissions to the atmosphere from peatlands.
NB33C-17 1330h
Effects of Submerged Aquatic Vegetation on Macrobenthos in a Coastal Lagoon of the Southwestern Atlantic
The northern, freshwater-dominated, edge of Rocha coastal lagoon in Uruguay, South America, was invaded during recent years by submerged aquatic vegetation (SAV). To evaluate the effect of SAV on the composition and abundance of macrozoobenthos, I compared this assemblage between a site that was vegetated in summer-autumn (V) to another one that was always bare (N). Only station V often showed thermal stratification, due to a reduction in water circulation caused by the plants (Potamogeton, Cabomba, Myriophyillum, Ruppia). Both sites had similar water quality and sediment characteristics (70 % sand, 30 % silt). I found a total of 28 benthic taxa: 3 species of Polychaeta, 2 of Mollusca, 3 of Crustacea and 20 genera of Insecta. Taxon richness and total abundance of invertebrates, as well as individual abundance of amphipods, gastropods and chironomids were significantly higher at V compared with N. Conversely, the crustacean Tanais stanfordi, the clam Erodona mactroides and the polychaete Laeonereis culveri were significantly more abundant at the unvegetated site. Moreover, Shannon diversity was higher at N than at V. These results show that the colonization by plants may enhance the variety and the abundance of benthos.