Abstract
Total and abiotic P-uptake rates and P-uptake capacities of seston suspended in the water column and of entrapped settling seston were measured by a radiotracer method in the moderately eutrophic Rímov Reservoir. The study was carried out over one seasonal cycle to investigate whether the settling seston was a sink or a source of dissolved orthophosphate. Total P-uptake rate and P-uptake capacity of both types of seston increased in the epilimnion during the summer months when dissolved reactive phosphorus (DRP) concentrations <3 μg l−1 and sestonic C:P ratios >180 (molar) indicated P-deficiency of phytoplankton. The P-uptake capacity within the flux of particles sinking from the epilimnion in this period corresponded to the removal of 1–4 mg P m−2d−1 from the lower, DRP-rich layers. During the remaining parts of the year and at other depths, the P-uptake rates and capacities were low but always positive. Abiotic uptake represented <10% of the total uptake in the summer epilimnion samples but nearly 100% in all others. This indicates that biotic P-uptake (apparently by living phytoplankton cells with a depleted cellular P-quota within the settling seston) was dominant in the epilimnion and upper metalimnion while abiotic processes prevailed in the lower layers. Based on these results and on information from the literature we suggest that settling seston possesses this biotic P-uptake capacity generally in all P-limited lakes and that this largely accounts for the observed decrease of sestonic C:P ratios with depth.
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Brzáková, M., Hejzlar, J. & Nedoma, J. Phosphorus uptake by suspended and settling seston in a stratified reservoir. Hydrobiologia 504, 39–49 (2003). https://doi.org/10.1023/B:HYDR.0000008506.29287.11
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DOI: https://doi.org/10.1023/B:HYDR.0000008506.29287.11