Microcosmic experimental comparison of ecological and physicochemical characters between macrophytic and algal lakes

In order to study differences between a macrophytic and an algal lake,6 micro-simulation systems of shallow lakes were established with different nutrition levels and macrophytes in September,2006,and water plants adopted are Potamogeton crispus Linn and Potamogeton malaianus Miq. During the 15-month experimental period,the conclusions are drawn based on the regular measured data regarding the appearance characteristics and the water quality of the simulation systems. They can be addressed as follows:(1) A macrophytic lake and a algal lake are in the clear water state and the turbid water state respectively characterized by the individual appearance characteristics. (2) The macrophytes play a crucial role in maintaining a clear lake ecosystem,and they can maintain a eutrophicated lake in the clear water state under some conditions. However,decomposition of the massive macrophtes may deteriorate water quality rapidly,and sometimes results in the change of a lake state. The important thing is that whether the macrophyte can grow healthfully in the changing environment. (3)There is almost no change of the water quality over time in a oligotrophic lake because of the poor production and the nutrition limitation. Regardless of the macrophyte growth,the oligotrophic system is in the clear water state all the time. The extent of DO in the oligotrophic macrophytic and algal systems are 8.1～14.4 mg·L-1,7.5～11.6 mg·L-1 respectively; pH 8.71～9.89,8.25～9.22; TP 0.006～0.012 mg·L-1,0.006～0.053 mg·L-1; TN 0.11～0.71 mg·L-1,0.10～0.83 mg·L-1; NH4+-N 0.01～0.17 mg·L-1,0.01～0.26 mg·L-1; PO43--P 0.002～0.012 mg·L-1,0.000～0.008 mg·L-1. (4) Daily change curves of DO,pH,water temperature and NH4+-N present ⌒ shape because of the abundance in macrophyte and al-gae in the mestrophic or eutrophic lakes,and the water quality varies seasonally. Compared to the algal lakes,the concentration of PO43-P is higher,while the concentrations of TP,TN and NH4+-N are lower in the macrophytic lakes due to the growth of the macrophytes. The average TP concentrations in the macrophytic and the algal systems are 0.16 and 0.51 mg·L-1 respectively,TN 1.30,8.32 mg·L-1; NH4+-N 0.19,0.43 mg·L-1; PO43--P 0.07,0.01 mg·L-1.