Ecological Costs of Streamflow Regulation
Public demands of regulated flows include both the needs of ecosystems and society. A key question is how much natural hydrology can be altered before measurable declines in biological integrity occur. Biological integrity is how community composition and native species richness in a stream segment differs from regional reference conditions. Similarly, hydrological alteration is the degree to which various streamflow characteristics 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(including flow and temperature)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.
This study is intended to be an additional exploration (see Project ID 6188) 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. While the previous study in this area focused on flow, results point to the additional importance of temperature in modification of biotic communities.
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 hyrological alteration at regional scales are necessary to establish goals for water management that balance ecosystem and societal needs. Ultimately it is also important to associate specific stressors, such as degree of regulation, with a particular alteration in a macroinvertebrate community. This would increase the ability to diagnose issues that might arise below a specific reservoir. It is expected that this study would provide information of specific seasons of flow and effects on macroinvertebrate communities. This may allow for fine-tuning of ecological flows.
Aquatic macroinvertebrates may also play a critical role in management for protected fishes, such as some salmon, where they provide food for juvenile salmon and are potential predators of eggs/alevins during early life-history stages. Understanding the degree of alteration in macroinvertebrate communities could underpin efforts to recover endangered fishes.
We expect to publish the results as a journal article. The article will be among the first to quantify the relationship between biological integrity and hydrological alteration, which is a topic of great interest to water resource managers. If a model can be reliably fit to this relationship, it could be used to guide the establishment of instream minimum and maximum flows, along with timing of flows required for the protection of aquatic life within the ecoregion studied. Such a model would also aid researchers and managers in predicting the ecological consequences of streamflow alteration expected under various scenarios of climate change, especially given the likelihood of required changes in water management if long-term precipitation and runoff patterns change. If we can develop a model that relates bug impairment to flow, it would be limited in scope to the Sierras, and would be included in the peer-reviewed manuscript.