Effects of land use on periphyton chlorophyll a concentrations and biomass in Adirondack Upland Streams

Abstract

In this study we examined bottom-up (light, nutrient availability) and habitat (stream velocity, stream depth) factors affecting benthic chlorophyll a and periphyton biomass in logged and Forest Preserve watershed streams located in the Adirondack Uplands. Chlorophyll a concentrations and ash-free dry mass on ambient substrate were measured in six Preserve and six logged catchments, five samples were taken per site. In a nutrient amendment experiment, porous artificial substrates containing nutrient agar treatments (agar only, N, P, N+P) were secured to the bottom of two streams (one Preserve, one logged), and chlorophyll a concentrations measured after 19 days. Biomass was significantly higher (p=0.034) in streams located in the Preserve. Chlorophyll a was marginally higher (p=0.063) in the Preserve sites. Stream velocity and depth were significant covariables for both chlorophyll a concentrations and biomass. Light, while different between lands uses (p=0.045), was not a significant covariable of periphyton standing stock. In the nutrient amendment experiment, all treatments in the Preserve stream showed higher chlorophyll a concentrations than in the logged stream (p<0.001). Treatments within the logged stream showed higher chlorophyll a concentrations for the N+P treatment only, and treatments within the Preserve stream were not different (p=0.226). Higher ambient nutrient concentrations in the Preserve stream may explain these results.