|Title||In situ manipulations of two factors affecting a lentic periphyton community: effects of nutrients and disturbance|
|Year of Publication||1990|
|Degree||Doctor of Philosophy|
|Number of Pages||184 pp.|
|University||Bowling Green State University|
|City||Bowling Green, OH|
This study was designed to determine the response of a lentic periphyton community to the individual and simulataneous manipulations of nutrient ratio, nutrient concentration, and small scale (localized) disturbance. In situ manipulations of nutrient regimes employed nutrient leaching substrates containing one of seven N:P ratios at three absolute concentrations. Algal biovolume generally increased with nutrient additions whereas diversity decreased relative to controls. The green alga, Stigeoclonium tenue responded positively to nutrient additions and accounted for a major portion of the algal biovolume. In contrast, Achnanthes minutissima responded to specific N:P ratios. Most taxa exhibited varying responses to treatments. Addition of N and P appears to stimulate one or a few species that are poor nutrient competitors, but superior competitors for space. To determine the response of periphyton to localized disturbance, communities were allowed to develop for 14 days on substrates consisting of petri plates containing clay tiles embedded in a sand-agar matrix. Communities were exposed to disturbance every 3, 6, or 9 days. Fine scale analysis (SEM) indicated that disturbance locally altered community physiognomy and species composition. The community reformed by lateral growth of the remaining undisturbed community. Coarse scale analysis (light microscopy) did not detect changes due to localized disturbance. In comparison to previous studies, the disturbance regime used for this study was of low intensity. However, the ability to detect effects of disturbance appears to depend on the scale of the disturbance and analyses. The response of the periphyton to the simultaneous manipulation of nutrients and disturbance was determined at two levels of resolution using SEM and light microscopy. Light microscopy did not detect changes due to local disturbance, nutrients, or the interaction of factors. A few taxa did exhibit significant responses to treatments. Nutrient additions did not magnify the affects of localized disturbance. SEM revealed that disturbance changed community physiognomy, species composition, and biomass on a local scale. Additional information is needed to define the interaction of environmental variables, particularly when factors function at different levels. Furthermore, the relationship between the scale of analyses and the scale that an environmental factor functions at should be considered in studies of periphyton communities.