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projects > application of stable isotope techniques to identifying foodweb structure, contaminant sources, and biogeochemical reactions in the everglades > work plan
U.S. Geological Survey Greater Everglades Science Initiative (Place-Based Studies)
Fiscal Year 2004 Project Work Plan
A. GENERAL INFORMATION:
Project Title: Application of Stable Isotope Techniques to Identifying Foodweb Structure, Contaminant Sources, and Biogeochemical Reactions in the Everglades
A first step of the Everglades restoration effects is "getting the water right." However, the underlying goal is actually to re-establish, as much as possible, the "pre-development" spatial and temporal distribution of ecosystems throughout the Everglades. Stable isotope compositions of dissolved nutrients, biota, and sediments provide critical information about current and historical ecosystem conditions in the Everglades, including temporal and spatial variations in contaminant sources, biogeochemical reactions in the water column and shallow subsurface, and trophic relations. Hence, the scientific focus of this project is to examine ecosystem responses (especially variations in foodweb base, trophic structure, and marsh biogeochemistry) to variations in hydroperiod and contaminant loading, and how ecosystem restoration steps may affect spatial/temporal changes in foodwebs and MeHg bioaccumulation.
This is the largest isotope foodweb study ever attempted in a marsh ecosystem, and combines detailed, long-term, trophic and biogeochemical studies at selected well-monitored USGS/SFWMD-FGFFC sites with limited synoptic foodweb data from over 300 sites sampled during 1996 and 1999 by a collaboration with the EPA/REMAP program. The preliminary synthesis of the biota isotopes at USGS and 1996 REMAP suites provides a mechanism for extrapolating the detailed foodwebs developed at the intensive USGS sites to the entire marsh system sampled by REMAP. Furthermore, this unique study strongly suggests that biota isotopes provide a simple means for monitoring how future ecosystem changes affect the role of periphyton (vs macrophyte-dominated detritus) in local foodchains, and for predictive models for foodweb structure and MeHg bioaccumulation under different proposed land-management changes.
Project Objectives and Strategy:
The major "long-term" objectives of this project have been to: (1) determine the stable C, N, and S isotopic compositions of Everglades biota, (2) determine the relative trophic positions of major organisms, (3) examine spatial and temporal changes in foodweb structures across the ecosystem, especially with respect to the effect of anthropogenically derived nutrients and contaminants from agricultural land uses on foodwebs, (4) evaluate the effectiveness of isotopic techniques vs gut contents for determining trophic relations in the Everglades, (5) evaluate the role of algae vs detrital/microbial foodwebs for the entire freshwater marsh part of the Everglades, and (6) work with modelers to correctly incorporate foodweb and MeHg bioaccumulation data into predictive models. We have generally completed the sample analysis parts of objectives #1-5, and are working on papers related to #1-5.
More recent and specific objectives include: (1) link our data on seasonal and temporal differences in foodweb bases and trophic levels with SFWMD, FGFFC, and USGS Hg datasets (first for large fish and, more recently, for lower trophic levels), (2) investigate the effects of seasonal/spatial changes in nutrients, water levels, and reactions on the isotopic compositions at the base of the foodweb (that affect our interpretation of relative trophic positions of organisms), and (3) continue our efforts to link our foodweb isotope data from samples collected at USGS-ACME and EPA-REMAP sites with the spatial environmental patterns observed by the REMAP program.
Potential Impacts and Major Products:
Biota isotopes provide a map of the current spatial distributions of the extent of several biogeochemical reactions (esp. sulfate reduction) affecting nutrient and Hg uptake. (2) By comparing the spatial patterns in the biota with those in the shallow sediments, recent anthropogenic changes in biogeochemical processes at the landscape scale can be demonstrated and dated. (3) Isotopes provide detailed information about temporal and spatial changes in trophic relations that complements traditional gut-contents analyses used by the FGFWFC (and others) for understanding foodwebs and the bioaccumulation of contaminants. (4) The preliminary synthesis of the biota isotopes at USGS and 1996 REMAP sites provides a mechanism for extrapolating the detailed foodwebs developed at the intensive USGS sites to the entire marsh system sampled by REMAP. (5) Biota isotopes provide a simple means for monitoring how future ecosystem changes affect the role of periphyton (vs. macrophyte-dominated detritus) in the gambusia foodchain, and for predictive models for MeHg bioaccumulation under different proposed land-management changes. (6) Since the REMAP spatial data are likely to be an important "benchmark" for assessing ecosystem changes, it is critical that these data be critically evaluated in the context of data generated by the USGS and local FL agencies; we are among the few scientists who are trying to "justify" the different perspectives and data generated by the USGS and EPA teams.
Recent products include 6 GEER presentations, posters on SOFIA, and two publications (Rumbold et al., 2002; Havens et al., 2003). In progress this FY: Bemis et al. (Hg paper, in review by co-authors); Kendall et al. (mini-synthesis, USGS report waiting for editor); Rawlik et al. (temporal foodwebs, being revised per journal reviewers comments for resubmission); Wankel et al. (WCA2, to co-authors 9/03); McLaughlin et al. (phosphate 18O method, to authors 8/03); Kendall et al. (synthesis, to co-authors 11/03); Bemis and Kendall isotope data & plots (http://wwwrcamnl.wr.usgs.gov/isoig/projects/Everglades under construction). Planned for FY04: Another Kendall et al. foodweb/biogeochemistry synthesis; another Bemis et al. foodweb Hg synthesis (lower trophic levels); and maybe a Kendall-Trexler paper related to my recent talk at GEER. Planned for FY05: Science Report; Kendall et al. REMAP synthesis paper (comparison of 1996 and 1999 data); Wankel et al. paper (how nutrients affect 15N-13C at base of foodwebs).
Collaborators: Dave Krabbenhoft, Bill Orem, Paul McCormick (USGS); Ted Lange (FGFWFC); Peter Rawlik, Scot Hagerthey, Darren Rumbold, Karl Havens, Larry Fink (SFWMD); Joel Trexler (FIU); Jerry Stober (EPA).
Clients: Government and private agencies involved in the CERP.
B. WORK PLAN
Title of Task 1: Continued evaluation and publication of data generated in previous collaborations with ACME, EPA, FGFFC, SFWMD, and FIU
Task Summary and Objectives: Our isotope study in the Everglades is the largest marsh foodweb isotope study ever attempted in terms of samples analyzed, size of the field area, and number of sites sampled. Our challenge was to link the detailed foodweb and process information available at the USGS-ACME sites (where we had data at some 15 sites, many sampled 2-3 times per year for several years) with the wealth of synoptic data but limited foodweb samples (mainly just periphyton and gambusia) collected by the EPA-REMAP program in their 1996 and 1999 field campaigns. It took 6 years and >7000 samples for us to develop and integrated and coherent model for major controls on spatial and temporal variations in foodwebs and foodweb bases, and we have started the time-consuming task of dividing up the many complicated stories into publishable units. With the large amount of data we have available both our isotope data and the ancillary geochemical, hydrological, or gut contents data provided by our collaborators data interpretation and paper writing go very slowly.
Work to be undertaken during the proposal year and a description of the methods and procedures:
Planned Outreach: A fact sheet about the use of isotopes in ecological studies in the Everglades will be prepared. I understand that one of our isotope foodweb diagrams, available on a poster on SOFIA, is the most requested item from the help desk. We have put a lot of isotope information on SOFIA and on a web site connected to our IsoIG web page this would make a good start on a fact sheet.
Title of Task 2: Investigation of the effects of temporal and spatial changes in nutrients, water levels, and reactions on the isotopic compositions at the base of the foodweb.
Task Summary and Objectives: The main objective of this study (which will be part of Scott Wankels dissertation at Stanford) is to test several hypotheses generated during our earlier studies (and papers) about how temporal and spatial changes in nutrients, water levels, and biogeochemical reactions affect the isotopic compositions of the algae, macrophytes, and bacteria at the base of Everglades foodwebs. This validation is a critical "missing link: between our biota isotope data and the chemical and hydrological data (and models!) generated by ACME, EPA, SFWMD, and FGFWFC teams. Without these data, our "mechanistic" interpretations of spatial and temporal changes of foodwebs and foodweb bases rest largely on statistical correlations make possibly by our huge dataset at hundreds of sites and dates, and will not be easily related to actual variations in nutrient sources and environmental sources at specific locations. However, we want to have more than just statistical data and arguments to support our process-based interpretation of how the temporal and spatial biota isotope patterns are established. In other words, we want to better establish exactly how spatial and temporal differences in the isotopic compositions of periphyton and macrophytes are established from the temporally and spatially varying isotopic compositions of dissolved carbon, nitrogen, and sulfur in the environment (which are directly linked to nutrient sources and biogeochemical processes). We absolutely need these data to correctly interpret how the foodweb isotope data link to environmental conditions and proposed ecosystem restoration changes. It is unfortunate that we didnt get these data years earlier, but we only just solved the analytical problems in FY03. Everglades waters are very tricky to analyze for isotopes, especially since we needed methods that would be easy enough that field folks in FL (i.e., SFWMD) would be able to collect and transport the samples for us. I sure wish we had had the methods available when the REMAP folks were samplingwhat a dataset that would have been!
Work to be undertaken during the proposal year and a description of the methods and procedures: We tried several times in 1998 to connect the isotopic compositions in the water column to those of plants, but failed to get reliable 13C of DIC and 15N of nitrate and ammonium because of the high DOC concentrations. We also tried to assemble collaborations with SFWMD personnel 1999-2001 that visited selected sites monthly, but once McCormick left, we never succeeded. His replacement, Scot Hagerthey, is very interested in collaboration since he views that our isotope data will provide valuable data on the extent of N recycling along the nutrient gradient in WCA2 (and at other SFWMD sites) that will help them understand processes that affect P concentrations in water. Furthermore, after a lot of hard work in FY03 by Scott Wankel on developing and automating a new nitrate 15N- 18O method, and by Dan Doctor (an NRC postdoc working on C cycling at the Sleepers River Watershed) who got our new automated DIC/DOC- 13C device working, we now have the methods we need to see how temporal and spatial variability in the water column solutes are established, and how they affect the 13C and 15N in plants (and microinvertebrates) at the base of the foodweb. We will also analyze a small number of samples for phosphate- 18O, organic matter 34S, and water 18O/ D. Hagerthey has a number of sites in WCA2 and elsewhere across the Everglades that he samples monthly, and he will collect us water samples, macrophytes, floc, periphyton, and (we hope) microinvertebrates from some 10-15 sites, several times during the year. We are in the process of developing a similar but smaller collaboration with Paul McCormick for sampling at WCA1. Our nitrate and DIC isotope preparation units are extremely well automated, so these samples will not require much manpower to analyze. We hope these data will provide an adequate test of the hypotheses we will be describing in our papers written as part of task 1. A journal paper describing this study will be written in FY05.
Planned Outreach: Results will be presented to our colleagues and collaborating agencies through talks and posters at meetings. Data and information will be make available on the SOFIA web site. Peer-reviewed papers will follow, detailing the methodology, data, and interpretations.
C. BRIEF DESCRIPTION OF HOW PROJECT TASKS SUPPORT THE DOI AND USGS EVERGLADES RESTORATION SCIENCE PLANS
Specific USGS Science Objectives to be addressed:
Specific DOI Everglades Science Prioritization Needs to be addressed:
U.S. Department of the Interior, U.S. Geological Survey
This page is: http://sofia.usgs.gov/projects/workplans04/stable-isotopes.html
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Last updated: 04 September, 2013 @ 02:08 PM(TJE)
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