[Vertical distribution of species of nitrogen and phosphorus in the sediments of Lake Donghu].

Vertical distributions of species of nitrogen and phosphorus in the sediments of three sampling sites in Lake Donghu were examined and analyzed. pH was combined to be studied at the same time. The results showed that the pH values in sediments were lower than those in overlying water and decreased with depth. The highest concentration of TN and TP occurred in Station 1, where suffered from heavy domestic sewerage. The lowest concentration of TP and TN presented to Station 2, which is located at the center of Lake Donghu. The concentrations of dissolved ammoniac nitrogen (DAN) and dissolved nitrate nitrogen (DNN) of station 1 were higher than the other stations. In recent years, along with the pollution treatment measures, the concentration of TN and TP in station 1 presented a trend of decline. However, the concentration of TN and TP ascends very fast in station 3 and it has been as high as station 1 on the surface sediments. Although phosphorus is the most restricting nutritious element all the same, the concentration of TN descended greatly in the last two decades because of the combined effect of nitrification, denitrification and phosphorus removing bacteria. As a result, the N/P ratio is only about 3.

[Chemical characteristics of nitrogen and phosphorus in the sediments of the typical bays in Dianchi Lake and calculation of their dredging layers].

The sediments of Haidong bay and Macun bay in Dianchi Lakes' experimental area were studied. The sediment column was cut in every 3cm, and the following items are tested, such as total phosphorus, phosphorus species, which include labile phosphate, Fe,Al-P, Ca-P and residual-P, total nitrogen, nitrate nitrogen, nitrite nitrogen, ammonium nitrogen. The results showed that the loads of nitrogen and phosphorus of these two bays increased quickly in recent years. The Fe, Al-P was the largest component in all the P-forms and the content of ammonium nitrogen in these two bays less than that of other lakes. The layer of 9 to 12 centimeters of the two bays was polluted less than the rests. It indicated that these years more and more wastewater was inflow in these two bays. At the same time, the distribution of each testing items showed another low value between 24 to 39 centimeters. So considering feasibility and economic restriction, we can set the 24 - 39 centimeters depth as a dredging layer.

[Method of algae-bacterium biofilm to improve the water quality in eutrophic waters].

The quality of eutrophic waters was improved by the algae-bacterium biofilm, which covered over the artificial aquatic mat made from a kind of mend macromolecule material. Two series of experiments show that using the artificial aquatic mat technique, algae bloom was inhibited markedly. At the eleventh day, the transparency was increased from 6 cm to 62 cm; and the concentrations of COD(Mn), TP, TN and NH4(+) -N were decreased to 92.89%, 49.25% , 94.97% and 70.15% respectively. The DO concentration also kept in certain satisfied level for using the algae-bacterium biofilm method. The suitable and economical density was about 8 - 16 bunchs/m(2) when the ratio of the artificial aquatic mat length to water depth was 0.7.