Phosphorus and Glucose Uptake by Seston and Epilithon in Boreal Forest Streams

Factors affecting phosphate and glucose uptake by seston and epilithon in a pristine boreal forest stream system in north-eastern Quebec were investigated using 6-L recirculating laboratory chambers. The rate of phosphate uptake by the epilithon was highest at 20°C; light intensity had no effect between 0 and 500 μE m-2 s-1. Phosphate uptake rates on colonized rock surfaces, normalized for surface area, organic matter, or chlorophyll a, showed no direct relationship with stream order but were highest in middle-order streams. Uptake rates on colonized glass slides were considerably lower. In contrast, phosphate uptake rates by stream seston increased with stream order, except for one anomolously high rate in a highly organic fifth-order stream. Size fractionation experiments revealed the greatest uptake was by seston particles in the 0.2-1.0-μm size range. Epilithic glucose uptake was apparently unconnected with stream order but was correlated with organic carbon. Phosphate uptake by the epilithon in these phosphorus-limited streams apparently is not directly linked to the ecosystem-level continuum of organic carbon retention and use, but is more likely related to environmental and physiological factors at a finer scale.