INFLUENCES OF SUBMERGED MACROPHYTES DISTRIBUTION PATTERN ON NITROGEN AND PHOSPHOROUS FACTORS OF WATER ENVIRONMENT IN LAKES

Baoan Lake is one of typical shallow lakes along middle reach of the Yangtze River. In August 2001, submerged macrophytes were investigated in Baoan Lake by setting up 103 sampling sites with assistant of a GPS setting. Water samples were collected simultaneously for chemical analysis. Under the support of GIS software ArcView 3.2, we established two GIS databases, including the database of mycrophytes and the database of physicochemical factors, and the data source comes respectively from the field sampling and chemical analysis. Then the database was applied to simulate macrophytes distribution and ecological factor fields in the lake. Based on the technique of GIS spatial analysis, different parts of N and P factor fields were selected spatially according to distribution areas of four dominant submerged macrophytes ( Ceratophyllum demersum L ., Myriophyllum spicatum L .,Potamogeton maackianus A. Benn. and Vallisneria spiralis L.), and the non macrophyte distribution area. By characterizing these selected fields with the grid statistic method, we analyzed the influence of each macorphyte distribution pattern on the levels of N and P factors in the water environment. The results implied significant impact of each macrophyte distribution on N and P factors concentration in their surrounding water environment, moreover impact effect and intensity has varied according to the mycrophyte species. As far as the concentration of TN and TP in surrounding water is concerned,TN: M. spicatum (0.774mg稬-1 )> V. spiralis (0.714mg稬-1 )> C.demersum (0.701mg稬-1 )> P. maackianus (0.695mg稬-1 );TP: M. spicatum (0.123mg稬-1 )> P. maackianus (0.118mg稬-1 ) > C.demersum (0.107mg稬-1 )> V. spiralis (0.079mg稬-1 ). The results also demonstrated C.demersum, P.maackianu and V.spiralis are unable to change the TN concentration in the water phase by comparing with the non mycrophyte distribution area. The influence on N factor is just to regulate and control the N circle among different inorganic compounds. In addition, P. maackianus and C. demersum presented the potential on organic pollutants degradation. M. spicatum is quite different from other macrophytes. TN concentration in water increases sharply because of M. spicatum distribution. The increased N is mainly emitted from M. spicatum individuals. As to TP concentration in water environment, the four macrophytes have the same effect. They are all able to absorb P directly from surrounding water, decreasing observably the TP concentration in water. It suggested that the water phase is playing a role in the nutrition of these species in the eutrophic waters. It is different from the in oligotrophic waters in which macrophytes acheive P requirements by direct uptake from the sediments. In condusion submerged macrophytes have ability to reduce TP concentration and stabilize TN concentration in waters. Macrophytes help to reduce the trophic level of water expcept that M. spicatum accelerate the eutrophication.