Quantifying Stream Ecosystem Resilence To Identify Thresholds For Salmon Recovery

EPA Grant Number: R832439
Title: Quantifying Stream Ecosystem Resilence To Identify Thresholds For Salmon Recovery
Investigators: Merenlender, Adina , Kondolf, Matt , Moyle, Peter , Resh, Vincent
Institution: University of California - Berkeley
EPA Project Officer: Hiscock, Michael
Project Period: July 1, 2006 through June 30, 2007 (Extended to August 31, 2008)
Project Amount: $299,922
RFA: Exploratory Research: Understanding Ecological Thresholds In Aquatic Systems Through Retrospective Analysis (2004) RFA Text |  Recipients Lists
Research Category: Aquatic Ecosystems , Ecosystems , Water


Most of the precipitation in coastal California occurs opposite the growing season, so humans must rely on alternative sources such as direct diversion from streams to meet agricultural and residential water needs. Depending on their magnitude and timing, small-scale diversions have the potential to alter the natural hydrologic regime during peiods when water levels are already naturally low, challenging the capacity for the stream ecosystem to maintain important organizing processes and support aquatic biota. The goal of the proposed research is to use historical data to link signals of changes in ecological resilience to estimates of stream flow available for environmental needs to identify when and where the remaining water for environmental needs has dropped below a threshold that results in a change in ecosystem resilience. Thresholds have been crossed where and when biological data indicate that (1) streams that once supported salmonids through the summer are now no longer able to do so; or (2) the macroinvertebrate community composition reflects a species assemblage better adapted to lentic environments. We hypothesize that interactions among the following driver and response variables operating at different temporal scales can result in the systen to cross the thresholds described above. Slow variables incude residential and agricultural development as primary drivers of water use, and populaton trends of endangered salmonids as a primary response variable to altered stream flows. The annual hydrologic cycle and changes in the aquatic macroinvertebrate assemblages are intermediate variables. Stream levels can drop quickly, depending on the magnitude of the diversion and antecedent flow conditions, resulting in a fast response to water use. As a result, salmonid and macroinvertebrate mortality can occur quickly if water levels cross a threhold required for survival.


Retrospective data describing rainfall, stream flow, land cover, and permitted stream diversions will be used to develop baseline stream flow models and spatially explicit estimates of water demand and use; and a comparison of these results will provide estimates of remaining environmental flows. In order to establish flow thresholds, these estimates of flow for environmental needs will be compared with existing biological data for anadromous fish and aquatic macroinvertebrates over time in streams throughout the study region to determine if they can explain the decline in salmon populations and changes to the macroinvertebrate community in upland streams.

Expected Results:

The proposed research will identify those sites where resilience thresholds have been crossed, as well as those sites which may be close to crossing these thresholds in order to prioritize alternative water management strategies, allocation of existing and future water rights, and delivery of alternative water sources to protect endangered species. The research proposed here wil serve as an essential first step for State and Federal agencies committed to salmon recovery to ensure that the necessary flow levels exist for fish survivorship prior to expending additional funds on stream habitat enhancement.

Publications and Presentations:

Publications have been submitted on this project: View all 10 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 5 journal articles for this project

Supplemental Keywords:

watershed, geographic informtion system, regression analysis, time-series, salmonids, ecosystem threshold, environmental stream flows, water diversion, Calfiornia,, RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Aquatic Ecosystem, Environmental Monitoring, Ecology and Ecosystems, Ecological Risk Assessment, anthropogenic stress, estuarine research, species interaction, ecological thresholds, salmon recovery, anthropogenic impact, ecosystem indicators, modeling ecosystem change, stream habitat, aquatic ecosystems, water quality, ecosystem stress, riverine ecosystems, trophic interactions, aquatic ecosystem restoration, ecosystem response

Progress and Final Reports:

  • 2007 Progress Report
  • 2008 Progress Report
  • Final Report