Variation in the delta15N and delta 13C composition of POM in the Lake Simcoe watershed

The purpose of this study was to quantify the variation of baseline carbon and nitrogen stable isotope signatures in the Lake Simcoe watershed and relate that variation to various physicochemical parameters. Particulate organic matter samples from 2009 and 2011 were used as representatives of baseline isotopic values. Temporal data from two offshore lake stations revealed that delta 15N of POM was lowest mid-summer and highest after the fall turnover. POM delta13C was variable throughout the summer before declining after fall turnover. Spatial data from the lake and the tributaries revealed that POM stable isotope signatures were highly variable. Various physicochemical parameters indicative of phytoplankton biomass were significantly positively correlated with POM delta15N and significantly negatively correlated with POM delta13C. The correlations were mostly significant in the tributaries, not the lake. Moreover, many of the correlations involving delta15N of POM were driven by extreme values in Cook's Bay and its tributaries. In general, it's likely that different processes or combination of processes were affecting the delta15N and delta 13C POM in the Lake Simcoe watershed as physicochemical parameters alone could not explain the variability. Measuring the delta15N of ammonium and nitrate, as well as the delta13C of DIC would help discern the dominant nitrogen and inorganic carbon cycling processes occurring in the Lake Simcoe watershed.