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Project Summary Sheet

U.S. Geological Survey, Greater Everglades Science Program: Place-Based Studies

Fiscal Year 2002 Project Summary Sheet

Project: Developing a ATLSS/ELM Lower Trophic Level Model

Web Sites: ATLSS.ORG

Location (Subregions & Counties): The total system

Funding (Source): USGS Place-Based Studies

Principal Investigator: Quan Dong, Southeast Environmental Research Center, OE 148, University Park, Florida International University, Miami, FL 33199, USA

Project Personnel: Donald L. DeAngelis, Phone: 305-284-1690 e-mail: ddeangelis@umiami.ir.miami.edu

Supporting Organizations: USGS/BRD, NPS, ACE, EPA

Associated / Linked Projects: Component of ATLSS Program

Overview and Status: This project is part of the ATLSS Program and focuses on the lower trophic levels of food web in the freshwater marshes of the Everglades; in particular, primary producers and primary consumers. These lower trophic levels provide both food and physical structures of habitats for the more conspicuous, higher trophic level species of the Everglades. Hydrology, nutrient supply, and other environmental forces drive the food web dynamics through bottom-up processes. The lower trophic levels are important for the integrity and health of ecosystems and can serve as important performance measure for the Everglades restoration.

Needs & Products: Two models were developed for ATLSS. The first was a periphyton model, constructed in order to understand the interactive relationship between periphyton and phosphorus dynamics. The understanding is critical for identification of the phosphorus threshold of ecological imbalance, the design of the periphyton based storm-water treatment areas, the design of dosing studies, and the design of a phosphorus reduction plan. The second was a lower-trophic-level model designed to link hydrological conditions and nutrient supply to the upper trophic levels studied by the ATLSS Program. This model incorporates the periphyton model. In addition to periphyton, the lower trophic levels comprise of five other functional groups: macrophytes, detritus, herbivores, detritivores, and predators. All of the consumers here are aquatic micro- and mesofauna. The lower-trophic-level model synthesizes information and describes dynamics of the trophic interactions. The trophic structure of lower trophic levels can serve as a specific performance measure.

Several major conclusions have derived from the lower trophic level model: 1) more than one steady state may exist, 2) changes to the system may not be reversible without hysteresis (that is, it may take a greater decrease in phosphorus to reverse the changes caused by the previous increase in phosphorus), 3) energy flowing up the detritivorous food chain may support higher level consumers that produce a trophic cascade in the grazing chain, 4) omnivory is common, and 5) phosphorus enrichment may lead to changes in the trophic structure of food web, 6) greatest variability in the trophic groups occurs for hydroperiods of intermediate length, and 7) nonlinearities in the interactions between trophic levels interact with the periodic hydrologic pulsing to create peaks in production of some consumers that have multi-year periods.

Application to Everglades Restoration: The lower trophic level model has been delivered to The University of Tennessee for incorporation into the ATLSS model for freshwater fish, ALFISH. ALFISH will be used in CERP evaluations.

Study Milestones
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
Familiarity         x            
Design         x            
Field Work         NA NA          
Data Analysis         x x          
Initial Reporting         x            
Quality Assurance           x          
Results Published               x      
Synthesis               x      
Note: "x" indicates task completed during quarter, and "o" indicates task planned, but not completed

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