Assessing seasonal dynamics of sediment legacy phosphorus in the Grand River watershed, Ontario

Session: Poster Session

Lance Ouellette, University of Guelph, [email protected]
Paul Voroney , University of Guelph, [email protected]
Ivan O'halloran , University of Guelph, [email protected]

Abstract

Recent studies have attempted to quantify the external P loads from the Grand River watershed to Lake Erie; however, few studies have looked into the impact of seasonal dynamics of sediment legacy P on such loads. The objectives of this study were, 1) to characterize P forms that contribute to legacy P in stream sediments, 2) to assess the temporal, spatial, vertical distribution of P species, and 3) to predict the rate of P release from the legacy P pool under varying water chemistries. Five sites were sampled for sediments in the months of May (2016), June, August and October (2017). Cores were sectioned by depth and analysed by sequential fractionation. Organic P was further analyzed by solution 31P NMR spectroscopy. Results suggest a decrease of mobile P over the four sampling dates, from 38% in May to 24% in October. The organic P pool made up the majority of the loss in mobile P, as the size of the organic pool decreased significantly from 66% in May to 25% in October, and attributed to mineralization. The ratio of orthophosphate monoester/diester, however, only ranged from 3 to 7 on a monthly basis, suggesting replenishment of labile P in the fall.