Determination of Ecological Thresholds Through an Historical Perspective of Trophic Dynamics

EPA Grant Number: R832442
Title: Determination of Ecological Thresholds Through an Historical Perspective of Trophic Dynamics
Investigators: Delong, Michael D. , Anderson, Jeffrey R. , Thorp, James
Institution: Winona State University , University of Kansas
EPA Project Officer: Hiscock, Michael
Project Period: September 1, 2005 through August 31, 2007
Project Amount: $297,489
RFA: Exploratory Research: Understanding Ecological Thresholds In Aquatic Systems Through Retrospective Analysis (2004) RFA Text |  Recipients Lists
Research Category: Ecosystems , Water , Aquatic Ecosystems


This project will define the nature of alternative stable states derived as responses to anthropogenic disturbances in river ecosystems. Many changes to enhance human use of rivers act on the major driving variable – the hydrological regime. Hydrological processes shape the physical, chemical, and biological attributes of such rivers, creating a dynamic ecosystem of tremendous temporal, spatial, and biological complexity. Dams and levees temper or eliminate the dynamics of rivers by reducing temporal variability in annual high- and low-discharge periods, and decrease connectivity to slackwater areas and to periodically connected floodplain habitats. These changes reduce biocomplexity and alter temperature, sediment, and nutrient regimes in rivers; therefore it is reasonable to assume that rivers will shift to alternative states reflective of the current status of their key drivers.


An essential component of identifying the existence of altenative stable states is the availability of long-term data. Species compositional and water quality data for rivers are limited and rarely cover the time-frame over which these anthropogenic disturbances occurred. Resources that are available over these periods, however, are museum specimens of fish and mollusc. Stable isotopes from tissues of museum specimens have recently been shown to provide accurate historical perspectives of trophic dynamics for interpreting impacts of disturbance on ecosystems. We propose to apply this approach to develop a time-line of measures of trophic dynamics of river ecosystems and to ascertain if shifts in stable states occur in response to human-related disturbances. Specifically, the objectives of this study are to:

  1. Develop a time-line for eight rivers that have experienced different human-linked disturbances and obtain trophic data reflective of the time line using stable isotope analysis of museum specimens.
  2. Generate models examining response of process variables, as reflected by food chain measures and the contribution of pelagic and benthic energy sources, over the time-line to assess presence of state shifts.
  3. Assess linkages between state shifts and timing/magnitude of disturbance through the application of appropriate models.

Expected Results:

This approach will provide insights into the response of fast, intermediate, and slow process variables to disturbance, and be used to produce models promoting a better understanding of how these process variables respond to changes in key drivers. This study could serve as a predictive tool to enhance assessment and rehabilitation of these biologically dynamic ecosystems.

Supplemental Keywords:

aquatic, ecology, mathematics, modeling indicators, restoration, decision-making, hydrologic regime, dams, isotopic analysis,, RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Aquatic Ecosystem, Environmental Monitoring, Ecological Risk Assessment, Ecology and Ecosystems, anthropogenic stress, estuarine research, species interaction, ecological thresholds, anthropogenic impact, ecosystem indicators, modeling ecosystem change, aquatic ecosystems, water quality, ecosystem stress, riverine ecosystems, trophic interactions, ecosystem response

Progress and Final Reports:

  • 2006
  • Final