Effects of Hydrologic Variability on Macroinvertebrate-based Biological Assessments of Streams in Austin, TX




Scoggins, Matthew

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The City of Austin, Texas, has been using Rapid Biological Assessments (RBA’s) in urban and sub-urban streams for the last seven years in an effort to expand and improve its environmental monitoring programs. Central Texas weather is characterized by flashy spates, long dry periods and is distinct from the temperate climates where the RBA's were developed. In addition to these naturally dramatic hydrological cycles, urbanization and its high levels of impervious cover further exaggerate stream flow patterns, producing greater runoff volumes, higher peak flows and less baseflow. Eleven hydrologic statistics were calculated using historical USGS flow data for 11 study streams and compared to available City of Austin benthic macroinvertebrate data using analysis of variance and multiple regression. A field study was also conducted to evaluate the effects of antecedent hydrologic conditions on biological assessments of three streams of differing development condition (high, medium, low) during a 6-month spring flow season. Results show that both long-term hydrologic character of streams in this area as well as immediately antecedent hydrologic conditions have a significant affect on the results of RBA’s, which is compounded in urbanized streams. Hydrologic variability should be utilized as a template in interpreting biological assessments using RBA metrics.



water quality, rivers, hydrology, biological assessment


Scoggins, M. (2001). Effects of hydrologic variability on macroinvertebrate-based biological assessments of streams in Austin, TX (Unpublished thesis). Southwest Texas State University, San Marcos, Texas.


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