Effects of submerged macrophytes on kinetics of alkaline phosphatase in Lake Donghu—I. unfiltered water and sediments

The impacts of submerged macrophytes on kinetics of alkaline phosphatase were studied in two 680 m2 enclosures in a shallow Chinese freshwater lake (Donghu Lake) from April to October 1996, and two experimental pools (120 m2) built inland in 1998. The submerged macrophytes were Vallisneria sp, Potamogeton crispus. In the presence of macrophytes, the concentration of orthophosphate was significantly lower, coupled with the decreasing function of organic P hydrolysis, in terms of lower Vmax and higher Km values of alkaline phosphatase in water, filtered and unfiltered (0.45 μm); in the interstitial water, the Vmax values of the enzyme in sediments were significantly lower, exhibited by a spatial and vertical profile. The results implied the key role of submerged macrophytes was the retention of P nutrients.