Research On Nitrogen Forms In Typical Eutrophication Lakes And Reservoirs In The Pearl River Delta Region

With the acceleration of the process of industrialization, surface water pollution problems nutrient pollution have become increasingly prominent, especially organic pollution and nutrient pollution in landscape lakes and drinking water sources have attracted much attention. Therefore, on the basis of domestic and foreign studies, typical small and medium-sized reservoirs and urban landscape lakes in Pearl River Delta were selected as research objects in this paper. Firstly, the characteristics of nitrogen forms in typical eutrophic lakes and reservoirs have been discussed by sampling analysis in the field. Secondly, with the help of fuzzy mathematics comprehensive evaluation method, the eutrophication evaluation of improved fuzzy comprehensive evaluation method was established. At last, the effects of temperature, p H and dissolved oxygen to different forms of nitrogen have been explored, and the effects of the different forms of nitrogen to eutrophication of lakes and reservoirs were analyzed. Then the specific research results are as follows:(1)As to the randomness of weight assignment and inaccuracy of subordinate function in the process of traditional fuzzy comprehensive evaluation method, improved fuzzy comprehensive evaluation method with simple and practical has been constructed,which can be applied for eutrophication status evaluation in lakes and reservoirs.(2) The improved fuzzy comprehensive evaluation method was validated and applied to evaluate degrees of eutrophication of typical small and medium-sized reservoirs and urban landscape lakes in Pearl River Delta, and evaluation results were close to the reliability. The eutrophication status of these lakes and reservoirs were covered light eutropher, middle eutropher, and hyper eutropher.(3) The exploration results about the characteristics of different nitrogen forms in typical eutrophication lakes and reservoirs show that there are some rules about different forms of nitrogen proportion of total nitrogen in the different trophic levels. From light to hyper eutropher, inorganic nitrogen ratio gradually increased, the organic nitrogen ratio gradually decreased, and inorganic nitrogen ratio exceeded 50%, the specific performance: ammonia nitrogen, nitrite nitrogen ratio of total nitrogen and the ratio of ammonia nitrogen and nitrate nitrogen increased, but nitrate nitrogen total nitrogen ratio decreased with the increasing of the eutrophication level.(4) Nitrogen forms were affected obviously by temperature and p H, however, there are differences between lakes and reservoirs: total nitrogen and organic nitrogen concentration increased with the increasing of temperature in lakes, but it reduced with the increasing of temperature. Ammonia nitrogen and organic nitrogen reduced with the increasing of p H both in lakes and reservoirs, but nitrate nitrogen increased. The effects of dissolved oxygen to the transformation among nitrogen forms were not significant.(5) The effects of different forms of nitrogen to eutrophication show that there is a significant positive correlation between ammonia and chlorophyll a, and the increasing of ammonia can contribute to the growth of algae in water investigated. There is a significant negative correlation between nitrate nitrogen and chlorophyll a, and the increasing of nitrate nitrogen can suppress the growth of algae in water investigated. There is a negative correlation between organic nitrogen and chlorophyll, and the correlation is significant in lakes. Besides, there is a significant positive linear correlation when N/P about 12 to 25, and N is the limiting factor for the growth of algae, while, there is a significant negative linear relationship when N/P at about 25 or more, P is the limiting factor for algae growth.