| Zhelin Bay is a famous estuary for large-scale mariculture in the eastern Guangdong, China. With constantly increasing in fishery culture and nutrient input to the estuaries within decades, the ecological environment has been significantly changed, resulting in harmful algal blooms hitting this area frequently damage to the ecosystem. Therefore, It is necessary to find out the source and distribution rules of some important elements and the relationships between physical, chemical and biological factors. In the present study, I investigated the spatial and temporal distributions of temperature, salinity, dissolved oxygen, nutrients, trace element, Chl a, COD, TSM and alkaline phosphatase activity in Zhelin Bay from July 2001 to July 2002.Water sampals were collected from nineteen stations in Zhelin Bay twice each month. Sampling was scheduled to cover the period around high tide (±1.5 hr). Water samples were filtered with 0.45 μm Millipore filter in situ, and then transported by a cooler with ice to the laboratory within 2 hr. The inorganic nitrogen, phosphorus, total dissolved nitrogen and phosphorus were analyzed by the SKALAR Channel Seawater Segmented Flow Nutrient Analyzer. The SiO3-Si, Fe and Chl a were analyzed by the SHMADZU UV-2501 PC. Water samples were filtered with Whatman GF/C filter and analyzed by analytical balance (METTLER TOLEDOU) for the determination of total suspended material (TSM). Used alkali potassium permanganate to determinate COD. Alkaline phosphorus activity was determined with fluorometry (PerkinElmer LS55) by using 3-o-methylfluorescein phosphate (Sigma) as the substrate.In Zhelin Bay, the contents of dissolved inorganic nitrogen (DIN), phosphorus (DIP) and silicate (SiO3-Si) decreased gradually from inside of the bay to outside of the bay, and were greater in outer and eastern boundaries of the bay than in inner and western boundaries. Such distribution pattern was mainly affected by the capacity of water exchange, sewage discharge from terrestrial, the distribution and species of mariculture.The annual average of DIN, DIP and SiO3-Si concentration were 27.38, 1.26, 44.06 μmol/L. Compared to the results of previous investigation in the same area (May 2000-May 2001), the concentration of nitrogen increased 20.9 %, while phosphate dropped 35.4 % andsilicate dropped 26.2 %. The decrease of phosphate and silicate was due to the reduction of river flux, which in turn resulted from the low precipitation in the spring of 2002 associated with the El Nino event in 2001-2002. Increase of DIN might be a kind of reflection of nitrogen enrichment in the world. However, NH4-N increased 182 % compared with the previous investigation, which was partly resulted from faster rates of bodies decomposed and excretion to aminated due to high temperature and low rainfall, and partly from slower dilution of NH4-N due to weaker river flux.The result also showed that phosphorus (39.1 %) was the limiting factor for phytoplankton growth in Zhelin Bay during the present investigation, but the limiting factor was nitrogen (41.8 %) in the previous investigation. In such case, harmful algal blooms would break out if high phosphate was input. Expect for nutrients, TSM might be a factor to cause sharp decline of phytoplankton density in the present study.The annual average of dissolved organic nitrogen, phosphate (DON, DOP) concentration were 50.32 and 0.98 μmol/L. DON and DOP was mainly originated from Huanggang river, but discharge of mariculture waster and biological activity might also be important factors. DON occupied 65.1 % of TDN, and NO3-N, NH4-N occupied 49.7 % and 44.8 % of DIN, respectively. DIP occupied 56.1 % of TDP.The annual average of dissolved iron (Fe) was 0.165 mg/L, which much higher than those other estuaries in China. Iron ore located near Zhelin Bay might be the reason. Dissolved iron in Huanggang River and outside of the bay was higher than that inside of the bay, which might be affected by resuspending of sediments. Because the TSM outside of the bay was also higher...
|
PDF Full Text Request