Sediment organic carbon distribution in 4 small northern missouri impoundments: Implications for sampling and carbon sequestration

Four small impoundments (5-25 ha) in the Glacial Plains of the Midwestern USA were intensively sampled to determine the concentration and spatial distribution of sediment organic carbon (OC; 31-40 cores per reservoir, averaging 2.7 samples per hectare). Burial rates for sediment OC varied from 183 to 279 g OC m^-2 a^-1 over the lifetime of these reservoirs (about 50 years). Organic carbon averaged 39.4 mg per gram dry sediment (n = 137) and mean values varied from 20.3 to 54.8 mg OC per gram dry sediment among the reservoirs; these concentrations are within the mid-range of values reported from other lakes and reservoirs. Spatial distribution of OC generally showed an increase from the inflow to the dam and in some cases lateral gradients that varied by a factor of 2. Based on simple random sampling, 10 core samples provide relative precision of around 25% and equate to a mean of 0.8 samples per hectare. This analysis of sampling effort will be useful for global up-scaling of carbon sequestration in small impoundments.