| Zhelin Bay is a bay with the most large-scale marine culture in the Eastern of Guangdong, China. Recently, the increasing marine culture has made eutrophication of the bay becoming more and more serious and harmful algae blooms occurred frequently, which have given the great damage to local fisheries and ecosystem of the bay. To evaluate the environmental health of the bay and its change over time in the future and understand the primary factors of ecological degeneracy, we started a long-term systemic investigation and monitor on hydrological and chemical factors, macro-nutrients, plankton, microbe and heavy metals of the bay from May 2000, sponsored by a Grand Project for Technology on Marine Pollution Monitoring and Ecological Protection Along Guangdong Eastern Coast from Guangdong Marine and Fishery Bureau. The main objects of this thesis are to describe the spatial-temporal distributions and historical developmental tendency of nitrogen and phosphorus forms in the sediments at nine key sampling stations of Zhelin Bay.The surface sediments were collected in each month from July 2002 to July 2003, and the cores were obtained only on September 24, 2002. W% (water content) was estimated from a weight loss after drying of wet sediment at 105 C for 24 h, and TOM (total organic matter) from a weight loss after igniting at 550C for 5 h. TkN (total Kjeltec nitrogen) was determined by Tecator Kjeltec auto-analyzer. NH4+ (ammonium) was extracted with 2 M KC1, and OP (organic phosphorus) with acidic peroxide at high temperature and pressure. The sequential extraction procedure for inorganic phosphorus forms used in this study was created by Ruttenberg and modified by Jensen et al. A SKALAR analyzer was used to estimate the contents of NH4+ and orthophosphate after extraction.The results showed that TOM, TkN, NH4+ and phosphorus forms in the surface sediments were all positively significantly correlated with W%, indicating that the contents of these chemicals in the surface sediments can be simply evaluated by estimation of W%. There were positive significant correlations between TOM and nitrogen and phosphorus forms as well as phosphorus forms each other, indicating that TOM was a key factor in the distributions ofnitrogen and phosphorus in the sediment.Average TkN and TP (total phosphorus) in the surface sediments were 1113.1+382.5 g-g-1 and 564.9 + 219.4, respectively, during the investigation, which were significantly higher than those in many similar bays in the world. Generally, the annual averages of nitrogen and phosphorus forms were higher inside of the bay than outside of the bay and higher in the areas with large-scale cage-fish culture than those with oyster culture. Bio-detritus from decomposition of feed remainder and dead aquatic animals and terrestrial drainage were the main factors for such horizontal distributions of nitrogen and phosphorus forms in Zhelin Bay.Monthly averages of nitrogen and phosphorus forms increased in the summer (from July to August) and the averages of TOM, Ex-P (exchangeable phosphorus), De-P (detrital phosphorus) and OP were all in the peaks during the investigation in this season. It was not only because of high growing speed of fish in midsummer, more feed remained than any other time, but also the season of highest water temperature leading to more aquatic animals death, more bio-detritus were produced. And that organic nitrogen degraded fastest to create NH4+ as a result of high water temperature. In contrast with July 2002, the monthly averages of nitrogen and phosphorus forms were increased in July 2003. Furthermore, the sites that all targets increased most were presented to the areas with cage-fish culture (S2, S5, S6). These may suggest a eutrophic trend in Zhelin Bay and cage-fish culture act importantly in making water quality worse.Vertical profiles of TOM, TkN and phosphorus forms in all sites other than 82 and 85 suggested a significant three stages of "deposition-decomposition-accumulation", which resulted from diagenesis. Heavy pollution and weak water...
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