Stream aufwuchs accumulation

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Virginia Polytechnic Institute and State University


I investigated the Aufwuchs accumulation process on glass slides (chlorophyll, adenosine triphosphate, and diatoms) in experimental streams near Glen Lyn VA (Phase I) and in Stroubles Creek near Blacksburg VA (Phase II). Depopulation experiments carried out during Phase I supported my hypothesis that accumulation rates are greater in reference than in depopulated streams. The effects of depopulation on Aufwuchs biomass accumulation disappeared in about two weeks indicating the rapidity of recovery from short-term catastrophic events. Variability anong replicate slides was generally lower after shorter submergence times than after longer times.

In disturbance frequency experiments carried out during Phase I, Aufwuchs accumulation depended on the frequency of copper disturbance. Accumulation was faster in the low stress streams (LSS) than in the high stress streams (HSS) • Resistance of Aufwuchs conununities to an additional Cu disturbance was greater in HSS than in LSS. Resilience of Aufwuchs biomass to the additional disturbance was lower in the LSS than in HSS. Stress resistance tended to be an inverse function of community age and to be greater in HSS than in LSS. Diatom species and diversity were greater in LSS than in HSS.

In Stroubles Creek I tested the effect 6f five factors on the Aufwuchs accumulation process and found biomass accumulation was greater in summer than in fall, in riffles than in pools, and in open than in shaded sites. Accumulation differences were not significantly different between upstream and downstream locations or between depopulated and reference areas. Biomass accumulation rates decreased inversely with submergence time. Biomass variability tended to be lower for shorter submergence times and in riffles than in pools. The autotrophic ratio decreased with submergence time. Diatom species number and diversities increased with submergence time.