Phosphorus uptake and retention in headwater streams of the Fox River Basin

Abstract

Anthropomorphic input of phosphorus into lakes and rivers can lead to harmful effects including eutrophication, algal blooms, and changes in community structure. Small order streams in agricultural and urban watersheds could potentially limit phosphorus loading to lakes through biotic and abiotic nutrient uptake and retention. In this study, we conducted sustained releases of potassium phosphate and Rhodamine WT to examine phosphorus retention and cycling in small order streams in the Fox River Basin in eastern Wisconsin. Stream characteristics measured included stream discharge, average width and depth, and background phosphorus concentration. Transient storage and phosphorus uptake metrics were determined using a solute transport model based on solute releases. Phosphorus background concentration was positively related to areal uptake (U) and negatively related to uptake velocity (Vf). Akaike Information Criterion was used to select linear models that best predicted transient storage and phosphorus uptake with the least amount of information loss. A model with stream velocity as the dependent variable was selected for predicting transient storage (Fmed200) and a model with the percentage of forested landuse as the dependent variable was selected for predicting Vf. We did not observe a strong relationship between transient storage and nutrient uptake. Additionally, our results suggest that streams in agricultural watersheds have limited capacity to reduce the loading of phosphorus to downstream lentic systems.