2000 Progress Report: Biogeochemical Indicators of Watershed Integrity and Wetland Eutrophication

EPA Grant Number: R827641
Title: Biogeochemical Indicators of Watershed Integrity and Wetland Eutrophication
Investigators: Reddy, Konda R. , DeBusk, William F. , Fisher, M. M. , Graham, William M. , Keenan, L. W. , Lowe, E. F. , Ogram, A. , Prenger, Joseph P.
Institution: University of Florida , St. Johns River Water Management District
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1999 through September 30, 2002
Project Period Covered by this Report: October 1, 1999 through September 30, 2000
Project Amount: $639,410
RFA: Ecological Indicators (1999) RFA Text |  Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Ecosystems


The purpose of this research project is to develop sensitive, reliable, rapid, and inexpensive indicators of ecological integrity for use in large-scale ecosystem management and restoration. In many areas, wetlands will more efficiently indicate the ecological integrity of the entire watershed than will any other portions of the landscape, for the following reasons:

  • Wetlands are critical areas of the landscape. Many species depend upon wetlands for successful completion of their life cycle and most species require, or benefit from, nearby aquatic habitat. If the integrity of a wetland decreases, the effects on the biota eventually will be far-reaching.

  • Wetlands, as low lying areas in the landscape, receive inputs from all adjacent uplands. If the integrity of an upland area is compromised, it is likely that it will soon be reflected in the integrity of the associated wetlands.

  • The response of a wetland to inputs from the uplands is patterned, indicating areas within the landscape which are experiencing degradation or improvement. Unlike lakes, which will show a generalized response to inputs due to mixing, or streams, which rapidly transport materials to other areas, wetlands absorb inflowing pollutants and nutrients proximal to the points of inflow.
Biogeochemical processes are good indicators of ecological integrity because they are potentially very sensitive. They also are likely to be highly reliable in the sense that ecological changes at such a fundamental level will affect all species utilizing the ecosystem. Changes at higher levels (e.g., population changes) may be due to factors that affect only a small portion of the biota, whereas changes in biogeochemical processes portend comprehensive alteration of the biota.

The central hypothesis of this research is that rates of biogeochemical cycling of carbon, nitrogen and phosphorus (C, N, and P) in wetlands can be used to indicate the ecological integrity of wetlands, and that the concentrations of certain forms of these elements can accurately predict the rates of ecologically important processes. The objectives of this research are to: (1) identify the key biogeochemical processes impacted by nutrient loading and measure the rates of these processes along the nutrient gradient; (2) develop relationships between a process and its related easily measurable indicator; (3) determine the spatial and temporal distribution of easily measurable indicators for a test wetland ecosystem; (4) determine the spatial variations in biogeochemical processes, and develop spatial maps for various processes to determine the extent of impact and risk assessment; and (5) validate the predictability of empirical relationships by making independent measurements of biogeochemical processes in different wetland ecosystems.

We will test the hypotheses presented above in the Blue Cypress Marsh Conservation Area (BCMCA) located within Upper St Johns River Basin, Florida. Some areas of the BCMCA have been impacted by nutrient loading from adjacent uplands, resulting in distinct nutrient and vegetation gradients. The BCMCA provides the benefit of established gradients of high nutrient (impacted) to low nutrient systems (unimpacted), to test our hypotheses. Specific tasks and progress are listed below.

Progress Summary:

A preliminary sampling was performed in January 2000, to delineate the areas of impact and to determine those areas most appropriate for comparison of spatial variability. This sampling was done along transects originating at the approximate source of nutrient impacts in the northeast and southwest areas of the marsh. Sediment cores were obtained at 40 sites and divided into plant litter and soil samples (0-10 cm). Total phosphorus analyses were performed on these samples and the results plotted. These data were used to determine placement of the sampling grid for determination of spatial variability and inter-relationships of biogeochemical processes and efficient indicators.

Due to drought conditions in the headwater region of the St. Johns River, it was not possible to obtain access to selected sampling sites until late summer. Final sampling for the first task was accomplished on September 11-26, 2000. Based on the results of phosphorus analyses of soil cores from the preliminary sampling, a nested sampling plan was repeated in three areas within BCMCA for a total of approximately 120 samples. The sampling grid was designed to provide information for the spatial and geostatistical analyses. The regions were selected to provide a range of soil properties and include impacted and non-impacted areas. Approximately 40 soil samples were collected from each region and each sample was the composite of two soil cores. Two samples from each sample node were composited for analysis. These samples were taken with a 10 cm ID stainless steel core tube and samples were subdivided into litter and 0-10 cm. Samples were stored in sealed containers for use in batch incubation experiments and for routine soil analysis.

The diversity and composition of key assemblages of prokaryotes responsible for important steps in the carbon cycle, particularly those involved in methanogenesis, sulfate reduction, and nitrification may undergo changes due to environmental impacts. As a first step towards investigating this possibility, the diversity and composition of periphytic bacterial communities from low nutrient (unimpacted) and high nutrient areas were examined. Periphyton are algal communities associated with substrates such as plants and sediment surfaces in the photic zone. Bacteria associated with these communities would be expected to respond rapidly to changes in water quality. Diversity and community composition were analyzed by Polymerase Chain Reaction (PCR) amplification of 16S rDNA, cloning and sequencing, and by Terminal Restriction Fragment Length Polymorphism (T-RFLP) of 16S rDNA PCR products. Periphyton samples were collected from unimpacted (central marsh) and impacted (canal adjacent to marsh receiving agricultural runoff) areas. Impacted samples were collected separately from sand surface and plant material. DNA was purified from these samples and 16S rDNA amplified using bacterial- and archaeal- specific primers. Unique PCR products were cloned and sequenced, and a phylogenetic tree constructed with all sequences. Analysis of these results is ongoing. However, obvious differences in the three communities are observed.

Future Activities:

We will continue to investigate the diversity and composition of prokaryotic groups related to C, N, and P cycling in wetlands. Numerous species responsible for a particular process may be present at a site; if one of these species is particularly sensitive to some aspect of eutrophication, another species may be present to carry out the process. We intend to investigate the diversity and composition of key assemblages of prokaryotes responsible for important steps in the carbon cycle, with particular attention paid to those prokaryotes involved in methanogenesis, sulfate reduction, and nitrification. This will be accomplished by denaturing gradient gel electrophoresis (DGGE) utilizing PCR primers directed toward group-specific16S rRNA gene sequences, T-RFLP analysis, and through cloning and sequencing of 16S rDNA.

Biogeochemical processes and microbial functional groups and activities related to C, N, and P cycling will be measured in litter and surface soils from the current set of samples. Multivariate statistical procedures will be used to evaluate relationships among sensitive biogeochemical indicators, and between indicators and biogeochemical processes. Geostatistical analysis techniques will be used to develop preliminary information about the pattern of spatial variation of the biogeochemical indicators and processes. Based on the results obtained from the spatial variability studies, one station in each region (total of three stations, each with three 2 x 2 meter plots) will be instrumented for continuous monitoring of water depth, soil temperature, and redox potential. Four soil cores per plot will be obtained once every two months for one year. Detritus and soil will be characterized for selected biogeochemical processes and indicators. In the final phase, a large-scale monitoring network will be developed to characterize the spatial distribution of biogeochemical indicators in water, litter and soil throughout the study site. Approximately 300 additional sample locations will be identified, and litter and soil samples will be obtained from each for analysis of indicators. It is anticipated that different regions within BCWMA will have differing levels of soil heterogeneity, thus dictating an irregular, most likely nested, sampling scheme. Geostatistical analyses will be conducted as outlined above.

The predictive relationships between the biogeochemical processes and parameters will be evaluated in a variety of ways. First, as indicated above, a snapshot including 120 sets of processes and parameters have been collected over the site. From this data, 60 sets of measured processes and parameters will be used to develop the empirical relationships, while the remaining 60 will be used to evaluate the accuracy of using the relationship at different sites within the same wetland. As a second measure of the robustness of the predictive relationships, the temporal biogeochemical data to be collected in the next phase will be used to test the models developed from the initial sampling. This analysis will test the applicability of extending the model to predict biogeochemical processes using biogeochemical indicators measured at different times and over different seasons of the year. A final measure of the validity of the relationships developed between the processes and parameters will be determined by sampling 12 sites in selected wetlands in the southeastern United States. Site selection will be made after discussion with the Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP) wetland resource group. At each site a minimum of three stations will be sampled. Both the processes and the soils parameters listed above will be determined at these locations. This should demonstrate that the biogeochemical process and parameter relationships are valid and that the magnitude of the processes measured can be used as a reliable indicator of the extent to which a wetland has been impacted by nutrient loading. Sampling methods, data analysis, and modeling will be similar to that outlined previously.

Journal Articles:

No journal articles submitted with this report: View all 26 publications for this project

Supplemental Keywords:

watersheds, soil, sediments, ecological effects, sensitive populations, enzymes, stressor, bacteria, ecosystem, indicators, scaling, terrestrial, aquatic, habitat, biogeochemistry, ecology, modeling, monitoring, southeast, Florida, FL, EPA Region 4, research., RFA, Scientific Discipline, Geographic Area, Water, Ecosystem Protection/Environmental Exposure & Risk, Nutrients, Environmental Chemistry, Ecosystem/Assessment/Indicators, Ecosystem Protection, State, Ecological Risk Assessment, Ecology and Ecosystems, Ecological Indicators, aquatic ecosystem, eutrophication, nutrient supply, nutrient transport, risk assessment, wetlands, wetland vegetation, biogeochemical indicators, watersheds, nutrient gradiants, ecosystem indicators, soil, vegetation gradients, nutrient cycling, water quality, aquatic ecosystems, GIS, nutrient fluxes, spatial and temporal patterns, Florida, nitrogen, statistical evaluation

Relevant Websites:


Progress and Final Reports:

Original Abstract
  • 2001 Progress Report
  • Final Report