CHANGES IN ABIOTIC AND BIOTIC PHOSPHORUS UPTAKE ACROSS A GRADIENT OF STREAM CONDITION

Degraded streams have been shown to retain fewer nutrients than un-modified streams. The aim of this project was to investigate the relative importance of abiotic and biotic pathways of phosphorus uptake by epilithic communities in un-modified and modified streams. This was investigated through a series of filterable reactive phosphorus (FRP)-uptake experiments in two streams of the Torrens River Catchment, South Australia. Total benthic FRP uptake was assessed as the loss of FRP to unsterilized epilithic communities (k(T)), abiotic uptake was the loss to sterilized epilithic communities (k(A)) and biotic uptake (k(B)) was the difference between total and abiotic uptake. It was hypothesized that un-modified reaches would have higher k(A) and k(B) than degraded and engineered reaches. Overall, k(T), k(A) and k(B) were greatest in un-modified reaches, but this pattern was not consistent across seasons. k(T) and k(B) were greatest in the un-modified reaches in autumn-winter and late spring, but not in winter-spring. Differences in k(B) were best explained by phosphorus availability in the water column and the period of continuous flow. k(A) was greatest in the un-modified reaches in autumn-winter, greatest in the degraded reaches in winter-spring, but similar in the un-modified reaches and degraded reaches in late spring. k(A) was most dependent upon the background FRP concentration, but also the attached organic matter in the un-modified reaches. The project demonstrated that several impacts of changes in land-use can alter the affinity of biotic and abiotic processes for phosphorus, which will have implications for in-stream nutrient availability and downstream ecosystems. Copyright (C) 2009 John Wiley & Sons, Ltd.