Status Quo Of The Water Pollution Of The Creeks In Suburban Shanghai And The Countermeasures

Water quality of the middle and small creeks in Xianghuaqiao town, suburban Shanghai has been monitored for more than one year. It indicates that: (1) the creeks are under heavy eutropic condition, with high loadings of nitrogen, phosphorus and organic pollutants. KN, TP and COD of the surface water of them are several times greater than the critical values of Types V, the worst level of water. (2) Spatial variations of N and P pollution have been observed, as the creeks in different places accepted different types and amounts of pollutants. Affected by domestic sewage, the creeks nearby residential areas were often heavily polluted by NH4+ and P. The creeks in agricultural fields were more easily polluted by NO3- than by NH? and phosphorus. The creeks nearby livestock farms often witnessed sudden soaring of NH4+ and P. (3) N and P loadings of the creeks are also affected by the seasonal evolvement of ecological environment. With the increase of temperature and biomass, NH4+ and NO3-in the surface water were largely consumed and decreased as a result; while organic N and particle P increased as the enhancement of suspending biological particles. NO2- in the surface water increased with temperature as nitrifying bacteria became active. Total P and water soluble P also showed the trend of enhancement with the intensification of biological activities, however, they were also controlled by the condition of pH and DO in the water. (4) At the height of the summer, the surface and bottom water of the creeks differed in N and P loadings. NH4+, soluble P and total reactive P in the bottom water were higher than those in the surface; while NO3- and NO2- in the surface were higher than those in the bottom. Such water-quality stratification inevitably resulted from the enhancement of phytoplankton in the surface water and intensified release of NH4+and P from the sediments. In the autumn, as the temperature decrease, such phenomenon declined gradually.High loads of nitrogen and phosphorus were found in the sediments, obtained from the middle and small creeks, outskirts of Shanghai. A laboratory study was conducted to observe the release of nitrogen and phosphorus from the sediments under both anaerobic and aerobic conditions. The sediment from a fish pond was also used as an experimental material. The results were as follows: (1) The anaerobic ammonia releases from the sediments were greater and quicker than the aerobic releases. Furthermore, high levels of ammonia concentrations in the anaerobic waters were maintained; in the aerobic waters, however, ammonia concentrations decreased sharply after reaching the peaks because of strong nitrification. (2) The anaerobic phosphorus releases were greater than aerobic and the released ortho-phosphate was mainly from Fe-bound phosphorus. (3) The potential of nitrogen and phosphorus releases from the sediments of dredged creeks was relatively weak. (4) Ammonia and phosphorus release from the fish pond sediment was greater than that from the creek sediments, though its K-nitrogen and total phosphorus was not the highest. High content of easily degraded organic matter in the fish pond sediment was responsible for this.The contaminant-resist aquatic plants, duckweed, Alternanthera philoxeroides and Eichhornia crassipes, are popular in the middle and small creeks. Contents of Cd, Pb, Cu and Zn in duckweed and Alternanthera philoxeroides there were determined. As a result, high loadings of Zn and Cu in both plants were found; in the duckweed, high content of Pb was also observed. The contents of heavy metals in different parts of plants are different. Higher content of heavy metals was accumulated in the roots of Alternanthera philoxeroides than that in the leaves and stems. The amounts of heavy metals accumulated in the aquatic plants were also related to the types and degrees of the pollution of the creeks. The sequence was as followings: heavy metal accumulations in aquatic plants in the creeks nearby industrial areas>that in township-level resident areas> that in village-level resid...