Differential influence of landscape features and climate on nitrogen and phosphorus transport throughout the watershed

Abstract

Anthropogenic activities have led to increased transfers of nitrogen (N) and phosphorus (P) to surface waters where changes in the absolute amounts of N and P delivery, and in N:P ratios, threaten water quality. While models of riverine fluxes are increasingly good at predicting total annual nutrient loads, our understanding of which features of a watershed differentially affect N and P transport downstream is still limited. In this study, we used linear mixed models to quantify the relative transport of N and P through different landscape and limnoscape compartments (e.g. hill slopes, lakes, reservoirs,) under a variety of climate regimes over 26 years in 18 watersheds of the St. Lawrence Basin. Water retention capacity and precipitation patterns were the features that most strongly influenced nutrient export from land to water, where P was preferentially retained in the landscape over N when water retention capacity was highest. Lakes and reservoirs also emerged as features that influenced nutrient fluxes, where lakes preferentially retain more P over N and reservoirs tended to export N. Factors that favor erosion, such as flashiness of precipitation and land-use change also alter N:P ratios in receiving waters, largely by mobilizing legacy sources of P.