Analysis of hydrologic time series and fish community data across the Tennessee River Valley identified three hydrologic metrics essential to habitat suitability and food availability for insectivorous fish communities in streams of the Tennessee River Valley: constancy (flow stability or temporal invariance), frequency of moderate flooding (frequency of habitat disturbance), and rate of streamflow recession. Initial datasets included 1100 fish community sites and 300 streamgages. Reduction of these datasets to sites with coexisting data yielded 33 sites with streamflow and fish community data for analysis. Identification of critical hydrologic metrics was completed using a multivariate correlation procedure that maximizes the rank correlation between the hydrologic metrics and fish community resemblance matrices. Quantile regression was used to define thresholds of potential ranges of insectivore scores for given values of the hydrologic metrics. Increased values of constancy and insectivore scores were positively correlated. Constancy of streamflow maintains wetted perimeter, which is important for providing habitat for fish spawning and increased surface area for invertebrate colonization and reproduction. Site scores for insectivorous fish increased as the frequency of moderate flooding (3 times the median annual streamflow) decreased, suggesting that insectivorous fish communities respond positively to less frequent disturbance and a more stable habitat. Increased streamflow recession rates were associated with decreased insectivore scores. Increased streamflow recession can strand fish in pools and other areas that are disconnected from flowing water and remove invertebrates as food sources that were suspended during high-streamflow events. Published in
We examined associations of fish assemblages and fish traits with urbanization and selected environmental variables in nine major United States metropolitan areas. The strongest relations between fishes and urbanization occurred in the metropolitan areas of Atlanta, Georgia; Birmingham, Alabama; Boston, Massachusetts; and Portland, Oregon. In these areas, environmental variables with strong associations (r s ≥0.70) with fish assemblages and fish traits tended to have strong associations with urbanization. Relations of urbanization with fish assemblages and fish traits were weaker in Denver, Colorado; Dallas-Fort Worth, Texas; Milwaukee-Green Bay, Wisconsin; and Raleigh, North Carolina. Environmental variables associated with fishes varied among the metropolitan areas. The metropolitan areas with poor relations may have had a limited range of possible response because of previous landscape disturbances. Given the complexities of urban landscapes in different metropolitan areas, our results indicate that caution is warranted when generalizing about biological responses to urbanization.
We investigated the relations among 83 hydrologic condition metrics (HCMs) and changes in algal, invertebrate, and fish communities in five metropolitan areas across the continental United States. We used a statistical approach that employed Spearman correlation and regression tree analysis to identify five HCMs that are strongly associated with observed biological variation along a gradient of urbanization. The HCMs related to average flow magnitude, highflow magnitude, high-flow event frequency, high-flow duration, and rate of change of stream cross-sectional area were most consistently associated with changes in aquatic communities. Although our investigation used an urban gradient design with short hydrologic periods of record (B1 year) of hourly cross-sectional area time series, these five HCMs were consistent with previous investigations using long-term daily-flow records. The ecological sampling day often was included in the hydrologic period. Regression tree models explained up to 73, 92, and 79% of variance for specific algal, invertebrate, and fish community metrics, respectively. National models generally were not as statistically significant as models for individual metropolitan areas. High-flow event frequency, a hydrologic metric found to be transferable across stream type and useful for classifying habitat by previous research, was found to be the most ecologically relevant HCM; transformation by precipitation increased national-scale applicability. We also investigated the relation between measures of stream flashiness and land-cover indicators of urbanization and found that land-cover characteristic and pattern variables, such as road density, percent wetland, and proximity of developed land, were strongly related to HCMs at both a metropolitan and national scale and, therefore, may be effective land-use management options in addition to wholesale impervious-area reduction.
The Chattahoochee River National Recreation Area (CRNRA) attracted approximately 2.9 million visitors in 1999 with nearly 30 percent of the visitors participating in water-based activities such as fishing and boating (William J. Carroll, National Park Service, oral commun., 2000). The CRNRA contains about three-fourths of all public green space in a 10-county area of Metropolitan Atlanta (Kunkle and Vana-Miller, 2000). 20 85 B u fo rd D a m
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