2001 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. , Graham, William M. , Lowe, E. F. , Ogram, A. , Prenger, Joseph P.
Current 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, 2000 through September 30, 2001
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: (1) 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. (2) 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. (3) The response of a wetland to inputs from the uplands is patterned, indicating areas within the landscape that are experiencing degradation or improvement. Unlike lakes that will show a generalized response to inputs due to mixing, or streams that 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:

Based on preliminary data from January 2000, soil-sampling grids were established in one reference and two impacted areas. Soil sampling for the first task was planned for June 2000; however, due to drought conditions in the headwater region of the St. Johns River, this sampling was not accomplished until September 11?26, 2000. Samples were obtained from a grid that will provide maximum information for spatial and geostatistical analyses. Each sample was the composite of two soil cores and detritus samples were collected at each coring site. Approximately 120 soil and detritus samples were obtained for use in batch incubation experiments and for routine soil analysis. Biogeochemical processes related to carbon, nitrogen, and phosphorus cycling were measured in plant litter and soil samples; all samples were characterized for basic physicochemical properties, and a subset of samples were analyzed for microbial indicators. These analyses indicate a substantial difference between soil and detritus in the various areas and vegetation communities.

Multivariate statistical procedures were used to evaluate relationships among sensitive biogeochemical indicators, and between indicators and biogeochemical processes. These results indicate that soil biogeochemical measurements can be used to discriminate between low impact and high impact regions, and vegetation type (which can be used as a measure of ecosystem disturbance). The establishment of discriminant functions for these groups makes it possible to assign new samples to membership in these groups. Additionally, geostatistical analyses can extend such information over space. However, further work is needed to refine the present results, especially focusing on the comparison of appropriate approaches in clustering variables and validation of the discriminant function analysis using an independent data set.

Based on the results obtained from the first task, two stations in each area (total of six stations) were established to determine temporal variability of key biogeochemical processes and associated indicators. At each station, three plots (2 x 2 m area) were established in March 2001, and will be monitored every 2 months for 1 year. The plots were instrumented for continuous monitoring of soil temperature, and redox potential will be measured at four depths (5, 10, 20, and 30 cm) each sampling period. Water level is continuously monitored at two recording stations within the marsh. Soil cores (one composite sample of four cores/plot) and detritus samples are obtained once every 2 months, and all samples will be characterized for selected biogeochemical processes and indicators.

Although the focus of Task 3 is the diversity and composition of soil bacterial communities, as a first step in this investigation we have examined the diversity and composition of periphytic bacterial communities from low nutrient (unimpacted) and high nutrient areas. Periphyton are algal communities associated with substrates such as plants and sediment surfaces in the photic zone. Bacteria associated with these communities would be directly exposed to water quality changes and therefore, expected to respond rapidly to these changes. Diversity and community composition were analyzed by Polymerase Chain Reaction (PCR) amplification of 16S rDNA, cloning and sequencing, followed by phylogentic analysis and by Terminal Restriction Fragment Length Polymorphism (T-RFLP) analysis of 16S rDNA PCR products.

Periphyton samples were collected from unimpacted (BCM1?central marsh) and impacted (BCM3?canal adjacent to marsh receiving agricultural runoff) areas. Samples from impacted areas were collected separately from sand surface (episammic) and plant material (epiphytic). 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 was constructed with all sequences. Analysis of these results is ongoing; however, obvious differences in the three communities are observed.

Future Activities:

Temporal sampling will continue on a 2-month schedule until February 2002. Biogeochemical processes related to C, N, and P cycling will be measured in plant litter and soil samples), and all samples will be characterized as above. This sampling will provide information on seasonal variation in the biogeochemical parameters being developed as indicators of impact.

We intend to investigate the diversity and composition of key assemblages of prokaryotes responsible for important steps in the carbon cycle. This will be accomplished by T-RFLP analysis utilizing PCR primers directed toward group-specific 16S rRNA and/or functional gene sequences (e.g., ammonia monooxygenase, nitrite reductase) and by cloning and sequencing of the respective 16S rDNA of identified groups. Particular attention will be paid to those prokaryotes involved in methanogenesis, sulfate reduction, and nitrification. Shifts in composition within these assemblages will be investigated, and phylogenetic groups or species identified as being particularly sensitive to eutrophication will be investigated in detail.

Due to expected redundancy of bacterial species capable of performing processes related to C, N, and P cycling in wetlands, the overall rates of these processes may be more insensitive to eutrophication than would abundance of individual species responsible for the processes. It is expected that clear relationships between diversity of indicator groups and nutrient loading will be observed, and that microbial diversity of specific groups will be affected by nutrient input in regions before their respective processes will be affected. Soil samples collected from three stations will be used to determine the diversity and composition of selected microbial groups. This analysis will be performed during four times a year to determine the temporal variability in microbial groups. Results obtained from this will be correlated with the process rates measured.

Based on the results obtained from the preliminary geostatistical analyses in the first task, a large-scale monitoring network will be developed in spring 2002 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 BCMCA will have differing levels of soil heterogeneity, thus dictating an irregular, most likely nested, sampling scheme. Geostatistical analyses will be conducted as outlined in the first task. This will yield a map of percentage impacted, or the excess of a particular process over the background level of that process for a specific area of the marsh. The final outcome will be a landscape-scale representation of the dominant biogeochemical processes within the BCMCA.

The predictive relationships between the biogeochemical processes and parameters will be evaluated in a variety of ways. First, a snapshot including approximately 120 sets of processes and parameters has been collected over the site in Task 1. From these data, 60 sets of measured processes and parameters have been 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 collected in Task 2 will be used to test the models developed in Task 1. 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 U.S. Environmental Protection Agency's EMAP wetland resource group. At each site, a minimum of three stations will be sampled. Both the processes and the soils parameters listed in Task 1 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 in Task 1.

Journal Articles:

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

Supplemental Keywords:

geostatistical analyses, nutrient cycling, microbial, diversity, landscape scale., 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:

http://wetlands.ifas.ufl.edu/eutro.htmExit EPA icon

Progress and Final Reports:

Original Abstract
  • 2000 Progress Report
  • Final Report