Trends in Total Phosphorus Concentrations in Urban and Non-Urban Environments

Abstract

A study of lake trends was conducted across Minnesota and Wisconsin to determine the effects of actions to improve water quality. A comparison between urban and non-urban environments helped determine drivers of change, as many factors contribute to water quality and they differ between environments. Though evidence of both increasing and decreasing trends in phosphorus were observed, there were more lakes with decreasing trends than increasing trends, especially in the urban environment. Similar trend patterns were not found with nitrogen. Trends in nitrogen were more often positive, and trends in N:P were generally strongly positive. Climatic and morphometric factors were not significantly related to trends, but there was a connection between the amount of lawn at lake edge and phosphorus reduction. The results indicate that phosphorus concentrations in the study lakes are improving more frequently than not. This may be due to the adoption of phosphorus control measures.