Nutrient and light effects on productivity, respiration, and standing crop on sand riffle communities in two northern Michigan streams.

Abstract

The effects of light and shade on algal sand communities in two branches of the Maple River were studied. A secondary objective was to test an experimental method using dissolved oxygen measurements to assess respiration and net primary productivity. Glass jars set in light and dark areas of the stream reach were used to measure net primary productivity and respiration. Standing crop was determined with chlorophyll a and ash-free dry mass analysis of sand samples. Respiration was higher in the West Branch, but there was no significant difference between light conditions. Net primary productivity, chlorophyll a values and ash-free dry mass were all significantly higher in the East Branch. Chlorophyll a had significantly greater amounts in shaded areas, as did ash-free dry mass. Higher standing crop in the East Branch may be due to richer substrates surrounding the site and to algal drift. Lower light intensities in the shaded areas probably account for higher chlorophyll a concentrations than in light.