TEMPORAL AND SPATIAL VARIATIONS OF NUTRIENT AND TRACE METALS IN A EUTROPHIC LAKE, MISSISQUOI BAY, LAKE CHAMPLAIN

To understand the seasonal and spatial drivers of nutrient loading and eutrophication, nutrient (N and P) and trace metal (Al, Ca, Fe, Mn) distribution and sediment flux were studied in a eutrophic arm of Lake Champlain (USA), Missisquoi Bay from June to September 2013. In August 2013 when the water column TN/TP ratio was very low (< 15) we observed the maximum density of cyanobacteria, probably related to the abilities of nitrogen fixation and/or vertical migration of cyanobacteria. Seasonal variations of TN/TP ratio increased over time due to both increasing P and decreasing N. Based on temperature, pH, DO as well as surface-bottom concentration contrasts, and cumulative fluxes in the sediments and river, the seasonal variation of nutrients and metals were influenced mainly by river inputs and local benthic remobilization. Spatial distribution of sedimentary P and metal fluxes exhibited significant to temporal and spatial variation due to hydrodynamic and biogeochemical drivers. Overall, our study suggests that the temporal and spatial variation of nutrients should be considered for lake monitoring system for better water quality management.