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DETERMINING THE MINIMUM NUMBER OF SITES FOR BIOASSESSMENT OF THE OHIO RIVER
Citation:
BLOCKSOM, K. A., E. EMERY, AND J. THOMAS. DETERMINING THE MINIMUM NUMBER OF SITES FOR BIOASSESSMENT OF THE OHIO RIVER. Presented at Association of Mid-Atlantic Aquatic Biologists 2007 Workshop, Berkeley Springs, WV, April 04 - 05, 2007.
Impact/Purpose:
The purpose of this research project is to provide methods, tools and guidance to Regions, States and Tribes to support the TMDL program. This research will investigate new measurement methods and models to link stressors to biological responses and will use existing data and knowledge to develop strategies to determine the causes of biological impairment in rivers and streams. Research will be performed across multiple spatial scales, site, subwatershed, watershed, basin, ecoregion and regional/state.
Description:
For wadeable stream bioassessment, much work has been done to determine the number of samples to composite or the appropriate reach length for obtaining an adequate sample. Proportions of stream miles in a given condition are then often reported at the watershed or ecoregion level so that each stream site represents a large number of stream miles of similar type. However, in larger systems like the Ohio River, it is often more desirable to report on the number or proportion of river miles in a given condition within that particular resource. In such cases, reach length may be fixed, with the premise that a large number of shorter reaches are more useful to represent the condition of a river than a few very long reaches. We used fish data collected systematically every 2-4 miles in the late 1990s and early 2000s to determine the number of sites necessary to characterize a single pool in the Ohio River. We examined IBI-based determinations of failing/passing in each pool to determine the number of sites necessary to adequately estimate the condition within a pool while achieving a minimum level of precision. Based on the precision level desired by ORSANCO, a sampling plan was developed that included an initial 15 sites per pool, with all pools being sampled over a 5-year period. Additional sampling within a pool was only necessary if attainment or nonattainment could not be determined with the desired level of precision.