Effects of electron acceptors on soluble reactive phosphorus in the overlying water during algal decomposition

Wang, Jinzhi; Jiang, Xia; Zheng, Binghui; Niu, Yuan; Wang, Kun; Wang, Wenwen; Kardol, Paul

Effects of electron acceptors on soluble reactive phosphorus in the overlying water during algal decomposition

2015

Endogenous phosphorus (P) release from sediments is an important factor to cause eutrophication and, hence, algal bloom in lakes in China. Algal decomposition depletes dissolved oxygen (DO) and causes anaerobic conditions and therefore increases P release from sediments. As sediment P release is dependent on the iron (Fe) cycle, electron acceptors (e.g., NO₃ ⁻, SO₄ ²⁻, and Mn⁴⁺) can be utilized to suppress the reduction of Fe³⁺ under anaerobic conditions and, as such, have the potential to impair the release of sediment P. Here, we used a laboratory experiment to test the effects of FeCl₃, MnO₂, and KNO₃ on soluble reactive phosphorus (SRP) concentration and related chemical variables in the overlying water column during algal decomposition at different algal densities. Results showed that algal decomposition significantly depleted DO and thereby increased sediment Fe-bound P release. Compared with the control, addition of FeCl₃ significantly decreased water SRP concentration through inhibiting sediment P release. Compared with FeCl₃, addition of MnO₂ has less potential to suppress sediment P release during algal decomposition. Algal decomposition has the potential for NO₃ ⁻ removal from aquatic ecosystem through denitrification and by that alleviates the suppressing role of NO₃ ⁻ on sediment P release. Our results indicated that FeCl₃ and MnO₂ could be efficient in reducing sediment P release during algal decomposition, with the strongest effect found for FeCl₃; large amounts of NO₃ ⁻ were removed from the aquatic ecosystem through denitrification during algal decomposition. Moreover, the amounts of NO₃ ⁻ removal increased with increasing algal density.

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