Increasing sulfate concentrations result in higher sulfide production and phosphorous mobilization in a shallow eutrophic freshwater lake

• Algae decay induced sulfate reduction in water column of shallow lake mesocosms.
• Greater sulfide levels were linked to higher sulfate input during algae decay.
• High sulfate promoted P release from sediments during algae degradation.
• Enhanced sulfate reduction may promote black water formation in freshwater lakes.
• Control of sulfate input needs consideration for eutrophic shallow lake management.

Increasing sulfate input has been seen as an issue in management of aquatic ecosystems, but its influences on eutrophic freshwater lakes is not clear. In this study, it was observed that increasing sulfate concentration without additional cyanobacterial bloom biomass (CBB) addition did not have an obvious effect on element cycling during 1-year continuous flow mesocosm experiments in which water and sediments were taken from a shallow eutrophic lake with sulfate levels near 1 mM. However, following addition of CBB to mesocosms, sulfate-reducing bacteria (SRB) were observed in the water column, and increasing numbers of SRB in the water column were associated with higher sulfate input. Sulfate amendment (0–70 mg L−1) also resulted in a larger amount of total dissolved sulfide (peak values of 5.90 ± 0.36 to 7.60 ± 0.12 mg L−1) in the water column and acid volatile sulfide (1081.71 ± 69.91 to 1557.98 ± 41.72 mg kg−1) in 0–1 cm surface sediments due to sulfate reduction. During the period of CBB decomposition, increasing sulfate levels in the water column were positively correlated with increasing diffusive phosphate fluxes of 1.23 ± 0.32 to 2.17 ± 0.01 mg m−2 d−1 at the water-sediment interface. As increases in sulfide and phosphate release rates deteriorated the water quality/ecosystem and even spurred the occurrence of a black water problem in lakes, the control of sulfate input level should be considered for shallow eutrophic lake management, especially during cyanobacterial bloom periods.

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