THE DEVELOPMENT AND USE OF BIOLOGICAL INDICATORS TO ADDRESS TMDL LISTING AND DELISTING DECISIONS
Abstract:This paper presents the approach used in the technical development of assemblage-level biological indicators in two widely disjunct areas of the United States (the ecoregions of Wyoming, and the Chattooga River Watershed in Georgia), and how they have been, or will be, used. The State of Wyoming has been sampling benthic macroinvertebrate, physical habitat quality, and selected field chemistry across the state since 1992. The 301 sites that have been sampled include a range of conditions, from near-natural or essentially undisturbed to heavily degraded. They are distributed throughout the seven Level III ecoregions of Wyoming: the Snake River Basin/High Desert, the Middle Rockies, the Wyoming Basin, the Wasatch and Uinta Mountains, the Southern Rockies, the Western High Plains, and the Northwestern Great Plains. In this study, seven basic steps were used to develop a regionally-calibrated biological index and included determining the appropriate geographic stratification, establishing numeric criteria for reference and degraded streams, determining bioregional delineations, and constructing a biological index. The final biological index (called the “Wyoming Stream Integrity Index” [WSII]) is segregated into two indices, one for relatively high gradient streams (WSII-H, discrimination efficiency 85.3%) and relatively low gradient (WSII-L discrimination efficiency 97.0%). That is, it correctly detects physical and chemical stressors at that rate. The index results in numerically-based biological condition narratives of “very good”, “good”, “fair”, “poor”, or “very poor”. Precision of individual metrics and the overall index is represented by root mean square error, and produced a 90% confidence interval of ±3.3 index units. Application of the index to the 301 sites is leading to reconsideration of previous listing decisions, and selected site de-listing.
The Chattooga River Watershed had experienced elevated sediment input to its streams apparently due to small-scale increases in silvicultural activities, which led to several segments being placed on the State of Georgia's 303(d) list. In response to the listings, field sampling of stream biota (benthic macroinvertebrates), physical habitat quality, selected sediment measures, and field chemistry was undertaken at 59 channel reaches throughout the watershed. Because the state is in the process of developing and calibrating ecoregional-based reference conditions, it was, thus, necessary to develop them for the Chattooga River Watershed using this dataset. Using the multimetric approach to developing biological indicators, those assemblage-level metrics (biological measures) that showed the clearest response to stressors were selected for use in a final index. The results of the data analysis showed a majority of the sites with little or no impairment; this information did, however, lead to several reaches being listed.
Document Type: Research Article
Publication date: 2000-01-01
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