Nutrient uptake length, the distance traveled by a nutrient atom before being biotically or abiotically removed from solution, provides an index of stream retention and therefore has implications concerning production and efficiency. Previous studies found an inverse relationship between quantity of course particulate organic matter (CPOM) in the stream and nutrient uptake length. It is hypothesized that in addition to CPOM quantity, microbial colonization patterns and breakdown rates of CPOM are also important in regulating uptake length. This hypothesis will be tested by constructing nine artificial streams and conducting two 6-8 month long experiments. In experiment 1, three leaf types with different microbial colonization patterns and breakdown rates will be used. One leaf type will be placed in each stream (three replicates of each leaf type) and nutrient uptake length will be measured biweekly for several months. In experiment 2, a mixture of leaf types will be placed in each stream. Leaf shredding invertebrates will be placed in some streams and excluded from others to determine how shredding affects nutrient uptake through its impact on microbial activity and breakdown rates. A lab experiment will be done concurrent with field work to determine the relative importance of biotic and abiotic uptake.
