Roles of Wetlands at Multiple Scales: Biological, Geochemical, and Hydrological Interactions II
Presiding: A Worman, Swedish University of Agricultural Sciences (SLU); A Ward, University of Alabama
NB43D-01 INVITED 13:30h
Scale Dependence of Measurements of Surface-water and Groundwater Interactions in Everglades Wetlands
The Everglades is an outstanding example of a subtropical peatland with a distinctive plant community adapted to the low-nutrient, calcium bicarbonate-type water. Interactions between surface water and groundwater were fundamental in developing the hydrological and chemical signatures that define the Everglades habitat. One of the changes resulting from decades of Everglades management for flood control is believed to be increases in recharge and discharge fluxes in the Everglades. Resulting effects that may need to be addressed by the Everglades restoration include increased rates of storage of contaminants (phosphorus, sulfur, mercury) in peat soils that could prolong the legacy of water-quality contamination, as well as increased discharge from deeper parts of the aquifer of dissolved salts emerging near canal and levee systems that move into the wetlands to influence plant community structure in profound ways. The present research compared results from several independent methods, including estimation of recharge and discharge fluxes from (1) hydraulic-head gradients and hydraulic conductivity in peat; (2) rates of vertical movement in the subsurface based on bromide tracer injections, and (3) rates of vertical movement in the subsurface based on modeling the subsurface distribution of naturally occurring isotopes (224Ra, 223Ra, 3H, and 3H/3He). The measurements revealed that surface-water and groundwater interactions are best described as bi-directional, with both recharge and discharge occurring within relatively close proximity. Most of the surface water that is recharged remains within peat porewater or the top 7 m of the underlying aquifer for variable periods or time (ranging from weeks to centuries) before being returned by discharge back to surface water. Inherent differences were found in the sensitivity of each method to different timescales of surface-subsurface water exchange. For example, tracer measurements in peat were sensitive to the relatively large component of recharge and discharge fluxes driven by high-frequency (weekly to monthly) reversals in the hydraulic gradient that result from heavy precipitation and/or sudden surface-water releases through water-control structures. In contrast, tritium modeling was not sensitive to those high-frequency signals, and was instead sensitive to the much smaller component of recharge and discharge fluxes that are driven deeper into the aquifer (limit of approximately 8 m) by lower frequency fluctuations in hydraulic gradient resulting from longer term (interannual to decadal) variations in the Everglades water balance. Use of complementary measurement approaches therefore revealed a "scale-dependence" of measurements of surface-water and groundwater interactions in the Everglades that must be considered for specific applications. For example, rates of recharge and discharge based on fast-timescale exchanges between surface water and peat porewater are appropriate for problems involving the possible remobilization of very high levels of nutrients stored in areas of the Everglades that were previously enriched by drainage from agricultural areas.
http://water.usgs.gov/nrp/jharvey/site/index.html
NB43D-02 13:45h
Linking Lesser Scaup Population Decline To The Environment:Issues Of Time, Space And Scale
Continental breeding populations of Lesser scaup(Aythya affinis)have been declining since the 1980's. The most comprehensive explanation for this is the Spring Condition Hypothesis (SCH),which predicts that female lesser scaup are arriving on breeding/nesting areas in poorer condition than they did historically, possibly due to lack of sufficient forage along spring migration routes. Diet analyses of lesser scaup have shown aquatic macroinvertebrates to be their primary food, inferring that prey availability is a key factor influencing body condition and reproductive success, however, factors affecting macro invertebrate abundance in the prairie pothole region (PPR)and their relationship to lesser scaup are not well known. Although lesser scaup surveys span several years, lack of long-term macroinvertebrate data raises critical questions about linking their population decline to changes in macroinvertebrate abundance. The aim of this study is to test the viability of the SCH by collating literature from previous and current research, combining field data, microcosms and remote sensing to investigate both the causes as well as the mechanisms behind of the problem and to use this as the basis for predicting long term trends and possible remediation.
NB43D-03 14:00h
Wetland Macroinvertebrates: Do They Respond to Human-Induced Changes in the Environment?
Wetlands provide many functions, both ecological (e.g., fish and wildlife habitat) and economical (e.g., flood prevention and recreation); however, they are continuously threatened by numerous human activities. These activities (e.g., agriculture, development) subsequently generate environmental stressors (e.g., nutrients, road salt) that can impact the physical, chemical and biological integrity of wetland ecosystems. The objective of this study was to identify relationships between human activities, stressors, and macroinvertebrate communities in wetland ecosystems, in order to identify macroinvertebrate response metrics to human-induced landscape changes. We predicted that macroinvertebrate taxa would show differentiated patterns along a human disturbance gradient. During the summer of 2002, macroinvertebrates were collected from multiple habitats (e.g., emergent vegetation, submergent vegetation) within 16 depression wetlands of the Muskegon River watershed (Michigan, USA). Preliminary data suggest that there are distinct shifts in macroinvertebrate taxa that represent biological responses along a human disturbance gradient. These shifts in taxa appear to vary between different wetland habitats. Knowledge of these relationships, between macroinvertebrates and human activity, could be utilized in assessments of wetland quality, predicting change in wetland structure, and in the establishment of biocriteria for the regulation and protection of wetland ecosystems.
NB43D-04 14:15h
Model evaluation of simultaneous injection of inert and reactive tracers in treatment wetlands
Treatment wetlands have shown to play an important role in reducing the nutrient content of recipient waters. The overall objective of this study is to evaluate simultaneous tracer experiment in Ekeby treatment wetland in Eskilstuna, Sweden, with tritiated water, nitrogen (N-15) and phosphorus (P-32). Particular modelling tools are essential to be able to understand the complexity of the wetland processes and to reveal the role underlying mechanisms. The model evaluation is based on a 2D physical description of stationary water flow and an uncoupled 1D formulation of the transport and transformation of nitrogen (N) and phosphorus (P). The overall N- and P- response of the wetland is obtained from averaging responses over the distribution of flow pathways. The flow modelling, described in a companion presentation, is thus a prerequisite for the interpretation of the P- and N-processes. Both P and N are affected by retention in the wetland, which is clear from comparing the slope of the tails of the breakthrough of P-32 and N-15 with tritium. The lower slopes of the reactive tracers compared to tritium indicate a slow wash-out for N and P. Nitrogen was also partly removed due to denitrification, which is evident from a larger degree of removal than phosphorus. A first-order loss rate coefficient, k, for N averaged for the entire wetland is about k = 0.12 1/days. The rate coefficient was defined from the expression Meff/Min=Exp(-k <T>), where <T> is the mean residence time, the effluent N-mass is Meff and the influent N-mass is Min. However, laboratory experiments indicate that the micro-biological activity in the bed sediment is generally much higher than the average for the wetland. Therefore, a consistent model interpretation of the denitrification process required that we accounted for both a rate-limited exchange with the hyporheic zone (sediments) and the first-order loss of N-2 from the hyporheic zone to the atmosphere.
NB43D-05 14:30h
Efficacy of Four Different Methods of Sampling Wetland Macroinvertebrates
Sampling of aquatic macroinvertebrates has become an important part of assessing water quality. Various samplers originally designed for sampling macroinvertebrates in aquatic ecosystems have been modified for use in wetlands with moderate success. Smaller, quantitative samplers often do not capture rare and mobile organisms whereas larger, qualitative samplers do not allow for density estimates. Sorting time is another important variable in deciding sampling regimes. This study examines the efficacy of four sampling devices in a permanent and two temporary wetlands.
NB43D-06 14:45h
Determining Reference Conditions in Western Iberia using Macrophytes
Are river plants linked with the human-disturbances to a point that they can be used to assess biotic integrity? If so, different groups of river plants should be related to river types and their reference conditions, something yet to be demonstrated, particularly in areas subjected to long-lasting human disturbance, such as the Iberian Peninsula (Western Europe). We analysed the floral variability from 197 least impacted sites and a sub-sample of 156 minimally disturbed, at two spatial scales, the river channel and the river corridor. We aimed to identify plant groups having a reliable ecological response to the hydrological and physical-chemical conditions. Correspondence analyses were applied to floristic data using the two reference-site groups and the two habitat type surveys according to diverse levels of life-form groups (e.g. all species, all waterlogged species, solely hydrophytes) and different alternatives of downscaling rare species. We found an overall weak cohesiveness of plant grouping, for all treatments. From the about 900 species recorded in the fluvial corridors, half were terrestrial species occasionally colonizing the riverbanks. Data treatment showed that in these Mediterranean-type streams, the fluvial corridor approach (discarding terrestrial and rare species) is the best option to establish plant groups and their ecological affiliations.