Effective sediment depth for phosphorus release in a monomictic eutrophic lake

Sediments play an important role in phosphorus (P) dynamics in eutrophic lakes. P concentrations are higher in surface sediments compared to deeper layers, representing a pool of P that can be released into the water column. Effective sediment depth for P release is different among lakes and little is known about this depth. Through experimental evaluation of P release in sediment cores, characterization of sediment porosity and distribution of P fractions in the sediment profile from a monomictic eutrophic lake, we determined which sediment layers produce release of P. The release of P in sediment layers of different depths varied between 0.89 and 2.07 mg P/m2×d with the highest P flow found in the sediment layer of 0-15 cm. The porosity of the sediment strata varied between 68 and 80%, with higher porosity in the surface sediment and decreasing porosity with depth of the sediment profile. We found that P bound to Fe/Mn (BD-P), Al/Fe oxides (NaOH-SRP), and organic matter (NaOH-NRP) were higher in the layer of 0-15 cm than in deeper layers. Sediment porosity, P release, total P and concentrations of the different P species in the sediment profile declined with sediment depth, stabilizing at the depth of 15 cm in the sediment profile. Therefore, we conclude that the effective sediment depth for release of P in this monomictic eutrophic lake is found up to 15 cm.