Land use and stream ecosystem functioning: nutrient uptake in streams that contrast in agricultural development

Abstract

Rates of nutrient uptake were measured in streams with varying amounts of agricultural development in their catchments. We conducted short-term (1- 3 h) relea- ses of nitrate and phosphate in seven streams in summer and five streams in winter, measuring uptake from downstream changes in nutrient concentrations after correction for dilution. Nitrate (NO3 - ) uptake lengths varied from 45 to 3560 m across sites and seasons, and soluble reactive phosphorus (SRP) uptake lengths from 80 to 1310 m. In streams monitored in both seasons, uptake lengths were generally longer in winter, when discharge was higher and temperatures were lower. Uptake lengths of both nutri- ents were positively related to discharge. NO3 - uptake velocity was related to nitrate concentration and benthic chlorophyll standing stock, which together explained 55 % of its variation. SRP uptake velocity was related to chlorophyll standing stock, and a multiple regression that included SRP concentration and chlorophyll concentration ac- counted for 34 % of the variation in uptake velocity. There was no clear evidence of saturation of nutrient uptake at high background concentrations in the streams. Nutri- ent uptake in these streams was not closely related to estimates of transient storage of water. Catchment land use influenced streamwater concentrations of nutrients and to a lesser extent chlorophyll standing stocks, and these two stream characteristics affected nutrient uptake in these streams.