Burial rates and stoichiometry of sedimentary carbon, nitrogen and phosphorus in Midwestern US reservoirs

Lakes and reservoirs bury large quantities of organic carbon (C) and nutrients (nitrogen, N; phosphorus, P) in their sediments, especially when expressed relative to the small area they occupy. Global estimates of C and nutrient burial rates in reservoirs require a quantitative understanding of the wide variation in the rates and ratios at which C, N and P are sequestered in sediments. We examined how catchment and reservoir characteristics relate to sediment organic C, N and P concentrations, stoichiometric burial ratios (C : P, C : N, N : P) and burial rates in 13 small reservoirs across a catchment land use gradient in the Midwestern United States. Sediment P concentrations were positively correlated with urban catchment land use and negatively correlated with agricultural catchment land use. Stoichiometric burial ratios varied with catchment land use. Both N : P and C : P were positively correlated with agricultural land use, while these ratios were negatively correlated with urban land use and forested land use. In general, rates of C, N and P burial per unit lake area were not related to land use in the catchment, but were all positively correlated with catchment area to lake area ratios. Results from our study reservoirs suggest that reservoir burial rates are more tightly coupled with morphometric catchment characteristics than with land use. Our results suggest that small reservoirs are regionally and globally significant for biogeochemical processing. However, regional variation requires that much more comprehensive sampling is needed for accurate estimates of global element burial rates.