[Influences of Potamogeton crispus population on the lake water quality distribution]

A continuing 26-hour monitoring is given on the physical and chemical indicators of the water around the Potamogeton crispus population in Xuanwu Lake, Nanjing City to study the consequent environmental effects. The result shows that both the highest (11.85 mg/L) and the lowest (9.90 mg/L) DO concentrations occur in the population, while the DO concentration decreases with increasing distance from the population. The DO concentration difference of the surface and bottom waters within the population and the open waters is slight, yet it is more obvious in the junction between the population and the open waters. The pH value declines from the population to the open waters. The maximum pH value of the surface water within the population is 10.3, and the minimum value outside the population is 9.2. The pH value of surface water is higher than the bottom within the population, but there is no such difference in the open waters. The TDS content increases with increasing distance from the population, which shows the maximum is 216.9 mg/L of the surface water and the minimum is 177.7 mg/L outside the population. The TDS value of the surface is lower than that in the bottom. The TN, NO2(-) -N, NO3(-) -N contents also increase with the increasing distance from the population, in that the TN content is lower than 2.00 mg/L within the population while the outside is higher than 2.00 mg/L; the NO2(-) -N content is less than 0.026 mg/L within the population while the outside is higher than 0.026 mg/L; the NO3(-) -N content is lower than 1.25 mg/L within the population while the outside is mostly higher than 1.25 mg/L. The TN, NO2(-) -N, NO3(-) -N contents of the surface water are lower than those in the bottom, but the difference is insignificant (p > 0.05). There is no significant difference of the NH4(+) -N content between the inner population and the external and the surface and the bottom. The TP and PO4(3-) -P contents of the surface water are lower than those in the bottom within the population, in that the TP, PO4(3-) -P contents of the highest point of the surface water within the population are 90.9% and 69.64% higher than the lowest point outside the population. The TP and PO4(3-) -P contents of the bottom water are significantly higher than those of the surface within the population, but the difference is slight from outside the population. Therefore, the Potamogeton crispus population plays an important role in improving the lake water quality.