Final Report: 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: Packard, Benjamin H
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


The objective of this study was to determine the long-term resilience of aquatic communities in mediterranean-climate streams. In particular, we aimed to identify stream flow thresholds, influenced by drought and water withdrawals for agricultural production, beyond which changes in macroinvertebrate community structure and decline in salmonid survivorship may result.  To do this we used retrospective data to develop models based on the relationship among physical and biological variables that interact on different temporal and spatial scales in California’s North Coast mediterranean-climate watersheds.

Long-term data are needed to assess spatial and temporal variability of communities and their resilience to natural and anthropogenic disturbances, particularly in climatic regions marked by high interannual variability (e.g. mediterranean-climate). Despite the need for and insights gained from a long-term perspective, most ecological studies are short, with a few notable exceptions.  For example, a survey of the recent stream ecology literature (1999-2005) revealed that 83% of studies were less than three years in duration, and only ~7% exceeded 10 years.  So, our research findings provide important insights from long-term dataset that continue to be difficult to obtain.  Our macroinvertebrate data span 20 years (from 1982 to 2002); and salmonid data span ten years (from 1994 to 2003).  Biotic community data were not augmented, but streamflow data were modeled for the Russian River tributaries to fit the period of salmonid data based on historical precipitation and streamflow data collected from 1960 to 1980.

It is important to note that extreme climatic events are expected to increase as a result of global climatic change, including an increase in drought frequency, duration, and/or intensity in many regions of the world.  For example, some temperate regions are predicted to become more “mediterranean” in climate, i.e. with more seasonal and interannual variation in precipitation.  In another example, the proportion of precipitation occurring as snowfall is predicted to decrease (as rainfall remains unchanged or decreases) in the western US; simultaneously, snowmelt is expected to occur earlier in the year with rising temperatures.  These changes will also result in increased prevalence of seasonal and interannual drought that are characteristic of mediterranean-climate regions.  Thus, understanding the effects of climatic variability on mediterranean-climate ecosystems may lead to a better understanding of potential future impacts of climate change in other climatic regions.

We tried to identify streamflow thresholds that, when crossed, lead to changes in macroinvertebrate community structure and salmonid persistence/survivorship.  Aquatic communities in our study region must withstand the drought conditions that occur each summer (wherein flows typically approach or reach intermittence) to persist in these environs; but particularly harsh conditions driven by prolonged drought or water removal for agricultural and other uses may cause re-structuring of ecosystems to an alternative regime. 

Summary/Accomplishments (Outputs/Outcomes):

To quantify the human impacts on the natural hydrologic regime and identify resilience thresholds we proposed the following methods: (I) creating models of natural flow regime on a daily-scale by using historical stream flow and  rainfall data; (II) creating spatially explicit estimates of water demand in each stream in the study region over time; (III) identifying reaches where stream flow may be adversely affected by human water extraction and evaluating trade-offs among water management options; and (IV) exploring the potential impacts that spring and summer stream flow dynamics have had on stream biota, evaluated using long-term fish and macroinvertebrate monitoring data.  We have made progress on all four tasks listed above for several upstream tributaries in North Coast California.  We are studying stream ecosystems in tributaries to the Russian River and Putah Creek in northern coastal California.  These streams provide habitat for a complex and diverse macroinvertebrate community throughout the drainage network; and anadromous salmonids use the Russian River tributaries for spawning in winter and juvenile rearing in summer. 

The models we developed support an integrated approach to water management by accounting for the spatial and temporal variability in water availability, human water needs and environmental flow requirements. In addition, the model allows for cumulative impacts analysis, which is often difficult to quantify but may be significant cause of ecosystem degradation in decentralized, water management systems. Furthermore, the approach can help to prioritize freshwater conservation efforts by evaluating the impacts and benefits of changes in water management practices on environmental flows. Finally, this approach is makes it possible to assess the consequences of alternative policy scenarios and supports integrated decision-making by institutions responsible for water and freshwater ecosystem management.

From retrospective analysis of macroinvertebrate and fish data we found that temporal synchrony in the effects of prolonged drought on community composition changes was observed across the study sites (i.e. the periods representing before/early drought, late drought, and post-drought were identified at all sites in multivariate ordination).  Because the prolonged drought resulted in directional change in community composition, there was no evidence of invertebrate “recovery” from drought (i.e. no return to a pre-drought community composition).  Overall, the results indicate that there were stable, but different, community compositions between pre- and post-drought periods.

Responses to prolonged drought for fish were species and site-specific, with effects being positive (green sunfish), neutral (sucker), or negative (roach).  In the case of roach, recovery was relatively rapid (1-2 years) in the permanent sites, but was delayed or non-existent in the ephemeral and intermittent sites, respectively.  During drought, roach survival and reproduction are likely to be affected by increased competition, predation, and dry-season habitat loss.  The delayed drought recovery of roach may be a result of the cumulative effect of drought over time, where already low summer flows are increasingly diminished as drought continues because of reduced recharge.  However, unless populations are extirpated (as in the ephemeral site), or habitat is irrevocably altered (as in the intermittent site), fishes are expected to recover quickly from drought once adequate flows resume.

These findings emphasizes that the severity and duration of drought is important in determining the outcome on aquatic communities.  When drought is  combined with increasing human demand for water exacerbated by climate change, droughts may have increasingly dramatic effects on freshwater ecosystems and other closely coupled ecosystems (e.g. estuaries, riparian zones, etc.).  

From a long-term salmon survivorship dataset in Russian River tributaries, we observed high variability in fish counts both temporally and spatially. Despite the high variability, the long term record make it possible to assess how the various flow, habitat and landuse variables explain the observed patterns in both initial counts and over-summer survival.

Median spring flows observed at the study reaches did not explain variation in juvenile salmonid recruitment, but was a significant predictor of over-summer survival. The regression model indicates that an increase of median spring flows by 10 percent is associated with a 26 percent increase in over-summer survival, averaged across all sites. The relationship between flows and fish survival did not appear to conform to a threshold pattern that was consistent across all sites. Rather, flow generally had a linear positive relationship to juvenile survival across the range of observed conditions. Our findings indicate that stream flow is critical to the survival of rearing juvenile salmonids during the dry season and suggest that changes in water management practices and restoration programs to increase flows could improve fish survival, even in streams that are highly impaired.

Despite the high variability in juvenile salmonid recruitment and survival between sites and years, the long-term record make it possible to assess quantify the effects of several relevant environmental variables operating at different temporal and spatial scales. Agricultural and land use development in proximity to the sampling reaches have negative effects on both recruitment and survival. The vineyard cover and road density variables used in the model likely served as proxies for other disturbances, such as sediment delivery and water diversions, but the findings nevertheless consistent with the well-documented adverse effects of land use on aquatic ecosystems. The regression models reveal (see Table 1)  that juvenile fish survival is highly sensitive to landuse activities, indicating that a 1 unit increase in vineyard cover and road density are associated with 20 to 25 percent declines in fish survival. In contrast, riparian vegetation cover had a significant positive effect on recruitment and survival. As with the landuse variables, riparian cover may have captured other unobserved yet important habitat variables, such as water temperature.

Our research also can inform how and where ecosystems could be recovered by reducing the stress human systems place on stream flow; and where restoration practices are likely to achieve desired results.  Working with stakeholders, we are using this information to help develop best management guidelines so that vineyard managers can minimize the impacts of pumping stream water during the dry season.  Since increasing water storage during the winter is often the only alternative to removing stream water during the dry season, we are also examining the potential consequences of appropriating additional winter storage on winter flows that can impact the ability for salmonids to move up to their spawning grounds.

Journal Articles on this Report : 5 Displayed | Download in RIS Format

Other project views: All 10 publications 5 publications in selected types All 5 journal articles
Type Citation Project Document Sources
Journal Article Beche LA, McElravy EP, Resh VH. Long-term seasonal variation in the biological traits of benthic-macroinvertebrates in two Mediterranean-climate streams in California, U.S.A. Freshwater Biology 2006;51(1):56-75. R832439 (2006)
R832439 (2008)
R832439 (Final)
  • Abstract: Wiley Online
  • Journal Article Beche LA, Resh VH. Short-term climatic trends affect the temporal variability of macroinvertebrates in California 'Mediterranean' streams. Freshwater Biology 2007;52(12):2317-2339. R832439 (2007)
    R832439 (2008)
    R832439 (Final)
  • Abstract: Wiley Online-Abstract
  • Journal Article Beche LA, Resh VH. Biological traits of benthic macroinvertebrates in California mediterranean-climate streams:long-term annual variability and trait diversity patterns. Fundamental and Applied Limnology/Archiv fur Hydrobiologie 2007;169(1):1-23. R832439 (2007)
    R832439 (2008)
    R832439 (Final)
  • Abstract: IngentaConnect-Abstract
  • Other:
  • Journal Article Deitch MJ, Kondolf GM, Merenlender AM. Hydrologic impacts of small-scale instream diversions for frost and heat protection in the California wine country. River Research and Applications 2009;25(2):118-134. R832439 (2007)
    R832439 (2008)
    R832439 (Final)
  • Full-text: University of California-PDF
  • Abstract: Wiley Online-Abstract
  • Journal Article Merenlender AM, Deitch MJ, Feirer S. Decision support tool seeks to aid stream flow recovery and enhance water security. California Agriculture 2008;62(4):148-155. R832439 (Final)
  • Full-text: University of California - full text HTML
  • Abstract: University of California
  • Other: University of California - full text PDF
  • Supplemental Keywords:

    environmental flow, ecological resilience, anadromous salmonids, threshold, surface water abstraction, inter-annual variability, benthic macroinvertebrate, water management, nonlinear ecosystem dynamics, aquatic ecology, coupled human and natural systems, cumulative watershed effects, 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, 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

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    Progress and Final Reports:

    Original Abstract
  • 2007 Progress Report
  • 2008 Progress Report