The Preliminary Study On The Influence Of Enteromorpha On Water-quality Of The Northern Jiangsu Nearshore Sea Area

The phenomenon of a large number of green marine macroalgal proliferation is called'Green Tide'. Generally, green tide occurs in spring or summer and end in summer when temperature is high, but sometimes extended to the fall. In recent years, frequency and biomass of green tide are rising totally, it has become a major concern of the international community to marine environmental problems and ecological disasters. Green tide occurs in the south Yellow Sea of China from 2007 to 2008, which bring about significant losses to coastal fisheries, aquaculture and tourism, causing significant impact on the natural landscape too.At present, Enteromorpha has been researched more, but mostly focus on ecological characteristics of Enteromorpha, algae composition and Enteromorpha competion with microalgae, less focus on the influence of Enteromorpha on water-quality. Three problems is studied in the thesis: (1) stude on the influence of Enteromorpha on nutrients in water in lab; (2) based on the survey data of the Jiangsu coastal and surrounding sea area from March to June, 2010, analyze the influence of Enteromorpha on water-quality of the Northern Jiangsu nearshore sea area; (3) analyze the influence of different stages of green tide on water-quality of the Northern Jiangsu nearshore sea area; Conclusions were summarized as follows:1. The experiment of concentration variation of NO₃-N, PO₄-P, DO and pH in Enteromorpha culture medium shows that, In the beginning of five days, the higer density algae the concentration of culture medium reduce the more obvious in the same interval; The same density and interval, Enteromorpha on the nutritional needs of NO₃-N is greater than PO₄-P, within the experimental time, when the concentration of NO₃-N, PO₄-P reduced to the lowest value and then rose slightly after. In the eighth day of the experiment,concentration of DO in culture medium reaches the highest value and then decreases to the end of the experiment, pH has increased during the experiment. 2. Based on the survey data of the Jiang Su coastal and surrounding sea area from March to June, in 2010, shows that temperature increases from 8.77℃to 21.61℃, from the first voyage to the fifth, In the third voyage, whose temperature is 14.58℃, salinity is 31.62, floating Enteromorpha appears;temperature and salinity are suitable for the growth of Enteromorpha, which provide green tide bloom with some important foundation;Concentration of dissolved oxygen is oversaturation and decreases from the first voyage to the fifth, mostly, pH is lower 8.0 in the whole survery area. Survery area locates in northern Jiangsu culture zone, terrestrial runoff brings many nutrients to this area, which causes higher concentration of DIN(23.04μmol/L), PO₄-P(0.55μmol/L), SiO₃-Si(15.85μmol/L), respectively. Phyto-plankton bloom and nutrients absorbed by Enteromorpha causes concentration of NO₃-N, PO₄-Pand DIN is decreasing from the first voyage to the fifith, trends of nutrient distribution is concentration become lower from coast to offshore.3. The influence of different stages of green tide on water-quality shows that, temperature and salinity are suitable for the growth of Enteromorpha in June 2010, whose temperature is lower than voyage of July 2006, but salinity is higer than that, concentration of NO₃-N and SiO₃-Si is higher than July 2006, while concentration of PO₄-P is similar to July 2006; Different stages of green tide have different impact on the concentration variation and distribution of nutrients.In pre-green tide(June 2010), trends of NO₃-N, PO₄-P, SiO₃-Si distribution is that concentration become lower from coast to offshore. In mid-green tide (July 2008), some yellow algae began to die, concentration of NH₄-N is higher but PO₄-P and SiO₃-Si is lower in the sea area of floating Enteromorpha;In the sea area of no floating Enteromorpha, concentration of PO₄-P and SiO₃-Si is higher but NH₄-N is lower. In the end of green tide(August 2008), the average concentration of NH₄-N is lower than the former voyage, trends of NO₃-N, PO₄-P and SiO₃-Si distribution is that concentration become lower from coast to offshore, N/P becomes lower and closes to 16:1.