| Zhelin Bay with water area of 68~70 km2 is one of the most important estuaries for mariculture in the east of Guangdong, China. There were more than 40,000 net-cases of fishery culture and approximately 20 km2 of shellfish area in Zhelin Bay. In addition, there were about 3,000 net-cases of fishery culture and approximately 6.1 km2 of oyster culture in Shen'ao Bay located on Nan'ao Island, where is about 10 km away from Zhelin Bay. With constantly increasing in fishery culture and nutrient input to the estuaries within decades, the ecological environment has been significantly changed, resulting in red tide hitting this area frequently and the ecosystem being seriously affected. For this reason, we investigated the temporal and spatial distribution of temperature, salinity, dissolve oxygen, nutrients, phytoplankton, biomass, chlorophyll a in Zhelin Bay and Shen'ao Bay from May 2000 to May 2001. The thesis presents the investigated results and the relationship between phytoplankton and nutrients.Water samples were collected from eight stations in Zhelin Bay and three stations in Shen'ao Bay weekly (March~November) or biweekly (December-February). Sampling was scheduled to cover the period around high tide (?.5hr). Samples for phytoplankton were fixed with acid lugol solution in situ and analyzed with the microscope in laboratory. Samples for nutrients were filtered with 0.45um Millipore filter in situ, then transported in ice to the laboratory within 2hr. The NO3-N, NO2-N, NH4-N and PO4-P were analyzed by the SKALAR Channel Seawater Segmented Flow Nutrient Analyzer. The SiOs-Si, Fe and Chlorophyll a were analyzed by the SHMADZU UV-2501 PC.In both bays, the contents of dissolved inorganic nitrogen, phosphate and silicate decreased gradually from inner bay to outer bay, descent from nearshore to offshore. The significant inverse correlations were found between dissolved nitrogen and salinity (r=-0.511,p<0.0001) and between silicate and salinity (r=-0.600, p<0.0001) in Zhelin Bay. This indicates that nutrient loads in Zhelin Bay were mainly originated from Huanggang river and discharge of industrial, domestic and mariculture waster around the bay. The inverse correlation between dissolved nitrogen andsalinity(r=-0.266,p<0.01) and between silicate and salinity (r=-0.444, p<0.01) in Shen'ao Bay indicated that discharge of mari culture and domestic waster were the mainly nutrient source of the bay. Because a phosphate "buffer" from exchange between particulate and dissolved phases influenced phosphate concentrations, the phosphate-salinity relationship indicated the non-conservative in both bays. The iron-salinity relationship also indicated the non-conservative, displaying both strong biological removal and input signals.The annual average of dissolved nitrogen, phosphate, silicate and iron concentration were 25.2 umol/1, 2.14 umol/1, 65.2 umol/1 and 71.1 ug/1, respectively, in Zhelin Bay. Compared with most estuaries in world, the nitrogen concentration was not so much in Zhelin Bay, whereas the phosphate, silicate and iron concentration were much higher. The contents of nitrogen and phosphate were 1.18 and 1.84 times the third-class seawater standard in China, respectively. The annual average of dissolved nitrogen, phosphate, silicate and iron concentration were 15.2 umol/1, 1.63 umol/1, 39.6 umol/1 and 66.2 ug/1, respectively, in Shen'ao Bay. The contents of nitrogen and phosphate were higher than the second-class and the third-class seawater standard in China, respectively. All of those indicated that eutrophication caused by overload of mariculture have made great pressure on both bays.According to the stoichiometric limitation standard of Justic (1995) and Dortch et ai, (1992), the plots of atomic DIN: P, Si: P and Si: DIN ratios in the water column of Zhelin Bay displayed the stoichiometric limitation of 41.8% in DIN, 22.9% in P and 2.36% in Si. In Shen'ao Bay, the stoichiometric limitations were 42.9% in DIN, 21.0% in P and 4.76% in Si. This result showed that N limitation might be more prevalent...
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