Benthic algal community composition across a watershed: coupling processes between land and water

Abstract

One of the main goals of ecology is to understand how the abiotic environment influences the biotic characteristics of the ecosystem. Various processes at multiple scales interact to affect the physical and chemical environments that are experienced by organisms, which ultimately influence community composition. We aimed to understand the processes that control benthic algae community composition within a watershed. We investigated the impact of both land cover and physiochemical variables on benthic algal community composition. We sampled benthic algae along with multiple habitat and water chemistry parameters within three microhabitats across eight sites along the mainstem of the Kiamichi River in southeastern Oklahoma. We used the benthic light availability model to assess the amount of light reaching the bottom of the stream. Additionally, we conducted a GIS analysis of the watershed to determine the land cover affecting each of these sites. Several of the in-stream site-scale variables that were measured (e.g., conductivity, pH and canopy cover) were strongly correlated with both position within the watershed and percent agriculture within the watershed. The physiochemical parameters that were correlated with watershed position and land cover were then used to understand the linkage with algae community composition. Algae genera composition was strongly correlated with both light reaching the bottom of the stream and conductivity. Our results suggest a hierarchy of factors that determine species composition and show the dependence of community composition on differing light regimes.