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What is the minimum number of sites needed for precisely assessing the ecological status of mainstem rivers?
Citation:
HUGHES, R. M. AND P. R. KAUFMANN. What is the minimum number of sites needed for precisely assessing the ecological status of mainstem rivers? Presented at North American Benthological Society, Salt Lake City, UT, May 25 - 30, 2008.
Impact/Purpose:
We evaluated the number of sites that would yield relatively precise estimates of physical, chemical, and biological condition for six raftable rivers 100-200 km long and 20-120 m wide.
Description:
We evaluated the number of sites that would yield relatively precise estimates of physical, chemical, and biological condition for six raftable rivers 100-200 km long and 20-120 m wide. We used a probability design to select 20 sites on each of two rivers in Washington and four in Oregon. The rivers included those draining cold deserts, dry and wet forests, and agricultural plains. All sites were sampled by a four person crew from two rafts. Crews collected physical and chemical habitat and fish, algae and macroinvertebrate assemblage data at each site through use of USEPA’s EMAP-West methods. The reach length for each site was 50 times the mean wetted width of the channel, totaling 1000 channel widths per river. The data indicate considerable longitudinal ecological change in some rivers but little in others, as well as local variability in biological assemblages associated with local changes in macrohabitat types. Based on preliminary analyses on these rivers, our data suggest a high degree of spatial autocorrelation between sites that are < 10-40 km apart, and we observed no marked changes between sites within this distance range. This autocorrelation needs to be considered in designing regional or river monitoring surveys and research projects.