The freshwater phosophorus cycle and the fate of water-borne pathogens

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During the tenure of the proposed NSERC Discovery Grant, three PhD students will conduct research on the phosphorus cycle in lakes and rivers, and one will work on the persistence of pathogenic microbes in rivers.  At the Dorset Environmental Science Centre we will use new techniques developed with previous NSERC DG funding to determine what environmental factors determine the concentration of phosphate available to bacteria and algae in the plankton, and hence their productivity.  Initially, we will address the hypothesis that food web structure and light (determined by mixing depth and water transparency) are the key variables.  The second fundamental problem we will address at DESC is the residence time of P in the epilimnion of lakes and therefore the total amount of biomass that will be present for a given nutrient loading.  To do this we will exploit naturally occurring radioisotopes that can be used to measure the age of P in the epilimnion.   A major environmental problem for eutrophic rivers is excess biomass of aquatic plants caused by high phosphorus loading from sewage and agriculture, leading to low dissolved oxygen at night.  To understand phosphate concentration available to plants during summer low flow periods, when nutrients likely control plant growth, we will estimate how much of the P at summer low flow is sequestered in different communities, and we will determine whether each of these is a net source or sink for phosphate as a function of phosphate concentration.  This research will lead to a model predicting phosphate concentrations at low flow for rivers with different relative abundances of these communities.   Concentrations of pathogens in surface waters are determined by both loading and persistence. We will study the removal of pathogens by different aquatic communities, including seston, sediments, biofilms on hard surfaces, and biofilms associated with macrophytes.  This information will inform as to how river communities interact with pathogen loading to determine pathogen levels.