Estimates of Detrltal and Epllithon Community Metaboilsm from Particle-Sized Riffle Sediments of a Woodland Stream

ABSTRACT

Estimates of net community productivity (NCP) and community respiration (CR) were made with a Gilson respirometer at levels of light-saturated photosynthesis (15000 lux) and darkness for particle-sized detrital and inorganic fractions of riffle sediments from five sites (first to third order) of Augusta Creek, Michigan. Sediments were separated into detrital and inorganic fractions and particle-sized into >4mm, lmm, 250um, 75um and 0.45um fractions. NCP as ulO₂g⁻¹h⁻¹ ash free dry weight (AFDW) of detritus ranged from −319.7 to 1687.6; both values were on 0.45um fractions. Epilithon NCP ranged from −321.0 to 421.2 ulO₂g⁻¹h⁻¹ on 75um particles. Detrital CR ranged from 15.1 ulO₂g⁻¹h⁻¹ on 4mm pieces to 738.8 ulO₂g⁻¹h⁻¹ on 0.45um fractions, while epilithon CR ranged from non-detectable amounts for 250um sands to 241.9 ulO₂g⁻¹h⁻¹ for 75um sands.

Expressed on an areal basis to analyze the ecological impact of each particle size, detrital fragments were generally lower in all rates except CR of ultrafine particulate organic matter. Little autotrophic potential existed in detrital communities at all sites, except where algal sloughing into detrital pools occurred. Epilithon rates were dominated by larger particles. Areal trends for sites mirrored in situ values of NCP and CR. The importance of the epilithon community in dictating the autotrophic-heterotrophic nature of riffle sections and the importance of measuring community metabolism on intact sediments were reinforced.