Influence of transient storage on stream nutrient uptake based on substrata manipulation.

Quantification of the transient storage zone (A) has become critical in stream biogeochemical studies addressed to examine factors controlling nutrient uptake. It is expected that higher A may enhance the interaction between nutrients and biota and thus, increase nutrient uptake. However, results from the literature are controversial. We hypothesized that besides of the size of A, the intrinsic physical and biological characteristics of stream structures that generate A are also relevant for nutrient uptake. We performed 24 additions of phosphate, ammonium, and chloride in four reaches of a man-made channel where we introduced three types of naturally colonized substrata packs (mud, sand and cobbles) to modify A. We estimated ammonium and phosphate uptake coefficients in both the main channel and A using a solute transport model (OTIS-P) and compared the results among reaches with different substrata types. The introduction of substrata packs decreased water velocity and increased A similarly among treatments. Nutrient uptake coefficients in the main channel were similar among reaches with different type substrata packs; however, nutrient uptake coefficients measured in A differed among them as well as the ratio between ammonium and phosphorus uptake coefficients in A, which were 1.6 in reaches with mud packs and 0.02 in reaches with sand or cobble packs. Results obtained in this study suggest that the contribution of A in nutrient uptake not only depends on the size of A but on the type of materials used to increase A, and thus, have biogeochemical implications on restoration projects aimed to modify channel morphology. [ABSTRACT FROM AUTHOR]