Assessing the Ecological Costs of Streamflow Regulation

Project ID: 6188
Principal Investigator: Mark Nelson
Research Topic: Ecosystem Needs
Priority Area Assignments: 2011 (Climate Adaptation)
Funded Fiscal Years: 2010 and 2011
Keywords: None

Research Question

There is growing public demand that riverflows should be managed to balance the needs of ecosystems and society. A key question is the degree to which natural hydrology can be altered before there are measurable declines in biological integrity. Biological integrity is how community composition and native species richness in a particular stream segment differ from regional reference conditions. Similarly, hydrological alteration is the degree to which various streamflow characteristics (e.g., characteristics of annual minimum flows) differ from expected natural conditions (usually based on regional or nearby unregulated streams).

The objective of this study is to evaluate the relationship between the severity of hydrological alteration and biological integrity. We propose to conduct biological assessments of macroinvertebrate communities in a set of rivers with varying degrees of hydrological alteration. Hydrological alteration will be quantified with recently developed models that make predictions of site-specific, average streamflow magnitudes expected in the absence (natural) of human activities. Biological integrity will be quantified using methods developed by the State of Utah, Department of Environmental Quality.

This study is intended to be a preliminary exploration of the range of biological integrity--as represented by macroinvertebrate communities--encountered over a wide range of hydrological alteration. Alteration of natural streamflows is a multidimensional phenomenon affecting frequency, duration, and timing of various streamflow magnitudes. In addition, altered flows affect stream ecosystems through habitat modification, temperature modification, desiccation, and sheer stress. Future studies should focus on these other dimensions of natural streamflows, as well as the mechanisms by which biological communities and their habitats are subsequently affected as hydrological characteristics are altered by water management activities.

Need and Benefit

A critical need in managing water resources for society and ecosystems is an understanding of how alteration of natural streamflow dynamics alters biological communities and ecosystem functioning. Unfortunately, the limits of hydrological alteration that protect biological communities are largely unknown beyond a few case studies. In the absence of site-specific studies, associations between biological integrity and hydrological alteration at regional scales are necessary to establish goals for water management that balance ecosystem and societal needs.

Contributing Partners

Contact the Principal Investigator for information about partners.

Research Products

Independent Peer Review

The following documents were reviewed by qualified Bureau of Reclamation employees. The findings were determined to be achieved using valid means.

By Dr. Daren M. Carlisle
Report completed on September 12, 2012

We assessed macroinvertebrate community condition in 25 mountain streams representing a large gradient of streamflow alteration, which we quantified as the departure of observed flows from natural expectations.Biological condition, as measured by richness of sensitive taxa (Ephemeroptera,Plecoptera and Trichoptera) and taxonomic completeness (O/E), was strongly and negatively related to the severity of depleted flows in winter.

By Dr. Daren M. Carlisle, Dr. Ken Eng and Mr. S. Mark Nelson
Publication completed on November 12, 2012

Natural streamflows play a critical role in stream ecosystems, yet quantitative relations between streamflow alteration and stream health have been elusive. One reason for this difficulty is that neither streamflow alteration nor ecological responses are measured relative to their natural expectations. We assessed macroinvertebrate community condition in 25 mountain streams representing a large gradient of streamflow alteration, which we quantified as the departure of observed flows from........

Last Updated: 9/19/16