Nutrient flows following changes in source strengths, land use and climate in an urban catchment, Råcksta Träsk in Stockholm, Sweden

Abstract

Managing nutrient flows to urban lakes is one of the main challenges to environmental sustainability in cities. Considering that future urban and climate changes may increase the challenge of handling future eutrophication, prediction of future nutrient loadings to aquatic environments in urban catchments has become increasingly important. Based on a new, innovative, structured Substance Flow Analysis (SFA) approach, where a source model was coupled to a Generalised Watershed Loading Functions (GWLF) model, this study investigated nutrient (nitrogen and phosphorus) delivery from sources to a water recipient for an urban catchment, using the case of Råcksta Träsk in Stockholm, Sweden, as an example. Potential effects from future changes in atmospheric deposition, vehicle volume and land use and from climate change (temperature and precipitation) were examined by comparing model scenarios in two periods (2000⿿2009 and 2050⿿2059). Model results suggested that climate change may have a greater impact on nitrogen loading to Råcksta Träsk lake than increasing vehicle volume and land use change. In addition, the results suggested that nitrogen loading to the lake may increase taking into account all changes examined, despite the expected decrease in background atmospheric deposition of nitrogen. In contrast, a marginal impact was found for phosphorus loading to the lake under all scenarios examined, resulting in only a slight increase in the combined scenario. From a nutrient pathways perspective, the results suggested that major pathways of nutrient loadings to the lake may not be much affected under most future scenarios examined, although groundwater was found to be a potentially sensitive pathway of nitrogen transport in the climate scenario. The model results provided important information for managers who need to plan for future nutrient handling in urban catchments, and the coupled SFA-GWLF model was suggested to be worthy of further testing at other sites and conditions.