Temporal and spatial studies of organic phosphorus cycling in sediments of a eutrophic bay in Lake Champlain (USA)

Lake sediments represent a potentially significant internal source of phosphorus (P) in eutrophic freshwater systems during periods of high temperature, biological activity, and oxygen depletion. This work describes the contribution of organic P (Po) to the internal cycling of sediment P during multiple algal bloom stages in Lake Champlain, VT USA (2007-2008) using solution 31-P NMR spectroscopy and enzymatic hydrolysis (EH) to assess P forms and latent bioavailability. Sediments collected during bloom onset and peak bloom stages contained the largest proportion of enzyme-labile-P, whereas pre- and post-bloom sediments where primarily composed of non-labile-P. 31P NMR tracked decreasing monoester: diester ratios with respect to depth, particularly during peak bloom conditions, as well as evidence for the deposition of myo-IHP and subsequent epimerization to alternate stereoisomeric forms. Large enzyme-labile and Po species proportions corresponded to increases in sediment phosphate flux and the presence of reduced iron and manganese species in porewater. On-going studies of the Missisquoi Bay system (2012-2014) will assess the spatio-temporal variability of enzyme-labile P in sediments, as well as employ a delta18O-PO4 methodology for tracking internal and external contributions to surface water phosphates. Sediment Po appears to be a significant and potentially bioavailable nutrient source in aquatic systems, which should be considered to understand the environmental impacts of P on water quality.