Uptake of phosphorus by epilithon in three oligo- to mesotrophic post-mining lakes

Epilithon contributes to phosphorus (P) cycling in lakes, but its P uptake traits have been rarely studied. We measured the chemical composition of epilithon and its inorganic P uptake kinetics using isotope 33P in three deep oligo- to mesotrophic post-mining lakes in April, July, and October 2019. Over the sampling period, epilithon biomass doubled, while the P content in biomass dropped to 60% of the April values. High epilithic C:P molar ratios (677 on average) suggested strong P deficiency in all investigated lakes. Regarding the kinetic parameters of phosphorus uptake, maximum uptake velocity (Vmax, seasonal range 0.9–101 mg P g OM–1 h–1) decreased by an order of magnitude from April to October, while half-saturation constant (KS, 1.6–103 mg P L–1) did not show any consistent temporal trend. We found a general decrease in the specific P uptake affinity (0.1–2.2 L g OM–1 h–1) and the estimated in-situ P uptake (0.04–2.3 µg P g OM–1 h–1) of epilithon over the season, which might have resulted from changes in epilithon community composition, a decreasing ratio of living biomass to extracellular polymers and detritus, rapid internal recycling, and/or thickening of the epilithic biofilm. Additionally, we observed a phenomenon of reversible abiotic P adsorption on epilithon.