The effect of suspended bentonite and kaolinite clay on phosphorus uptake and release by lotic periphyton.

Lotic systems act as nutrient buffers to receiving lentic systems. As streams transport allochthonous phosphorus through a watershed, the loads are modified in quantity and quality through biotic and abiotic mechanisms. Lotic systems are frequently dominated by periphyton, the attached benthic community consisting mainly of algae and bacteria. This community exhibits the ability to buffer phosphorus loads to receiving waters through several mechanisms including: biotic uptake, chemical precipitation, and mechanical filtration. Stream sediments, including clays, influence dissolved phosphorus concentrations primarily through equilibrium-driven sorption/desorption reactions. Additionally, suspended clays in aquatic environments are known to: modify food webs, influence species composition, and affect biotic integrity by altering the physical and chemical conditions. Given the influence that suspended clays exert upon aquatic systems, it was hypothesized that suspended clays would modify, either positively or negatively, phosphorus uptake and/or release by lotic periphyton. Experiments were conducted using two clay minerals, dissolved reactive phosphorus, and cultivated periphyton communities. Bentonite and kaolinite were selected to represent two clay types commonly found in aquatic systems. Standardized laboratory procedures were utilized to describe the physical characteristics and phosphorus sorption behavior of the clays. An artificial stream system was designed, tested, and operated to control water conditions necessary to cultivate periphyton communities, support suspend clays, and conduct clay-phosphorus-periphyton interaction studies. Periphyton communities were subjected to different clay and phosphorus concentrations under controlled conditions in artificial streams and laboratory microcosms. Phosphorus uptake rates were unaffected by the presence of clays at several different concentrations in artificial stream settings. Periphyton exposure to heavy clay loads in lotic microcosms, under laboratory conditions, had no effect on the ability of the periphyton to uptake or release phosphorus. The results may be helpful to water resource managers working with water quality issues and researchers interested in basic ecosystem function.