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Assessment of temporal variance components and implications for trend assessment in biological monitoring programs
Citation:
Gurtz, M. E., D. E. Carlisle, S. G. PAULSEN, AND J. VAN SICKLE. Assessment of temporal variance components and implications for trend assessment in biological monitoring programs. Presented at 2010 NABS and ASLO Joint Meeting, Santa Fe, NM, June 06 - 11, 2010.
Impact/Purpose:
Assessment of temporal trends in biological monitoring programs is often undertaken without an understanding of temporal variability of biological communities.
Description:
Assessment of temporal trends in biological monitoring programs is often undertaken without an understanding of temporal variability of biological communities. Typically, the within-site variance is unknown and included as part of sampling error. This investigation – designed jointly by the U.S. Geological Survey (National Water-Quality Assessment Program) and the U.S. Environmental Protection Agency (Office of Research and Development) – compared the relative magnitude of short-term (within-year) variability to long-term (between-year) variability in biological indicators of water quality. A total of 33 sites (9 urban, 6 agricultural, and 18 relatively undisturbed streams distributed throughout the U.S.) were sampled in two consecutive years, and twice in a 10-week index period during one of those years; as many as 10 additional annual samples collected in previous years also were used to characterize interannual variability. Four sources of variance were calculated for invertebrate indicators (IBI and O/E) – within-site in a single year, among years, among sites, and interaction between years and sites. Results of this study will provide information on the importance of understanding temporal variability for interpreting long-term (multi-year) trends, and designing future trends sampling.