Discharges and Sediments as Sources of Extracellular Alkaline Phosphatase in a Shallow Chinese Eutrophic Lake

Total alkaline phosphatase activity (APA) and soluble reactive phosphorus (SRP) concentrations were measured in municipal wastewater, and a shallow Chinese freshwater lake receiving it. Activities of Dissolved alkaline phosphatase (ADAP) in overlying and interstitial water were also analyzed monthly at three sites for several years. The lake was enriched with SRP and alkaline phosphatase by discharge of the wastewater, indicating that the inclusion of APA for estimating water pollution was reasonable. Annual data showed that APA in coarser fraction was significantly higher at the site receiving more wastewaters, both in surface and overlying water, suggesting that resuspension of enzyme most likely occurred in the basin heavily discharged. ADAP was an order of magnitude higher in the wastewater than those in lake waters, and was generally higher in interstitial water, a feature more striking at the site receiving more discharges. Besides, it was irrespectively inhibited by Na₂WO₄, L-cysteine and EDTA-Na, but stimulated by Cu²⁺, Zn²⁺, CTAB and Triton X-100 in interstitial, overlying and surface waters. This similarity of responding patterns to the stressors indicated an analogy between dissolved alkaline phosphatase in water column and that in interstitial water, supporting the hypothesis that the polluted sediments act as source of dissolved alkaline phosphatase in eutrophic lakes.