Grant: Discovery Grants Program - Individual

We believe that increases in agricultural fertilization needed to feed 3 billion more people by 2050 will saturate soils with phosphorus (P) and create conditions in which subsequent influx of nitrogen (N) regulates water quality in developed regions. However, unlike during the Green Revolution, future N fertilization will be carried out with urea. Rarely used prior to 1960, urea now accounts for >50% of global N fertilizer, is ubiquitous in lakes worldwide, and has detrimental but incompletely understood effects on aquatic ecosystems. Given that ~1 billion people lack clean water, we seek to develop a predictive understanding of the consequences of these global changes for humans and freshwaters. Our program will advance this paradigm for future water quality degradation by conducting 3 projects. First, we will combine explicit land-use models with biweekly determinations of aquatic and biological parameters in lakes and streams to quantify how urea is created, destroyed and transported to prairie aquatic ecosystems. Second, we will use ~60,000-L experiments and paleoecological (fossil) analyses to identify chemical thresholds for N effects on P-rich lakes. Here open- and closed-bottom enclosures in lakes of contrasting P content will be fertilized with N to both refine understanding of thresholds to N effects, and evaluate the role of sediments in regulating water quality. The relevance of these thresholds to entire lakes will be tested by replicated fossil analysis of the past relationship between N influx and algal abundance in 20 lakes along a gradient of P content. We expect that N influx will predict historical changes in water quality only when P concentrations exceed thresholds. Third, we will take advantage of the forthcoming City of Regina wastewater treatment upgrade to test the effects of elimination of N pollution. Here we will use mass balances of N, P and carbon measured as part of our 2 decades of prairie lake research to determine whether N diversion will return P-rich lakes to natural, baseline water quality. Together these projects will provide managers, scientists, governments, and the public with a means to better understand and avoid future water-quality loss.