Importance of diffusion and resuspension for phosphorus cycling during the growing season in large, shallow Lake Peipsi

Our study aimed at elucidating the role of internal loading in the budget of phosphorus (P) and assessed the importance of resuspension and diffusive fluxes for P cycling in large, shallow Lake Peipsi. The internal loading of P was quantified by a mass balance approach that considered the gross sedimentation of P as a component. The gross sedimentation of P was measured with sediment traps during May-October 2011. Additionally, we followed the monthly dynamics of diffusive fluxes and resuspension of P within this time period. The gross sedimentation of P dominated the mass balance calculations in Lake Peipsi. The resuspension of P constituted 62-68% of the gross sedimentation of P, and thereby accounted for the bulk of the total internal P load. Until late July, the release of P by diffusion was similar in magnitude to that of resuspension. Since August, resuspension was of governing importance for P cycling: the release of P by resuspension at that time was about 40-fold higher than that of the diffusion. Therefore, diffusion and resuspension provided a continuous supply of P to the water column during the growing season.