EFFECT OF WASTE-WATER DISCHARGE ON NUTRIENT CONTAMINATION OF MANGROVESOILS AND PLANTS

The ecological impact of sewage discharges to a mangrove wetland in Fu tian National Nature Reserve, the People's Republic of China was asses sed by comparing the plant community, plant growth and nutrient status of soils and vegetation of a site treated with settled municipal wast ewater (Site A) with those of a control adjacent site (Site B) which d id not receive sewage. During the one year study, the total and availa ble N and P, and organic carbon concentrations of mangrove soils in Si te A did not significantly differ from those of Site B. In both sites, the soil organic C, total N, NH4+-N and total P content exhibited a d escending trend from landward to seaward regions, with the lowest meas urements obtained from the most foreshore location. Seasonal variation in N content of soil samples was more obvious than any difference bet ween wastewater treated and the control sites. The soil N content was lower in spring and summer. This was attributed to the higher temperat ure in these seasons which facilitated degradation of organic matter a nd absorption of nitro en by the plants for growth. No significant dif ference in plant community structure, plant growth (in terms of tree h eight and diameter) and biomass was found between Sites A and B. Leaf samples of the two dominant plant species, Kandelia candel and Aegicer as corniculatum collected from Site A had comparable content of organi c carbon, N, P and K to those of Site B. These preliminary results ind icated that the discharge of a total volume of 2600 m(3) municipal was tewater to an area of 1800 m(2) mangrove plants over the period of a y ear did not produce any apparent impact on growth of the plants. The s oils and plant leaves of Site A were not contaminated, in terms of nut rient content, by the discharged sewage.