Analysis And Assessment Of The Trophic State In Jiulongjiang Estuary

Estuarine and coastal eutrophication has been one of the primary environmentalproblems worrying the coastal countries; it is also the hotspot of marine ecologicaland environmental researeh. Recently, Occident has developed Phase Ⅱmethodologies for estuarine and coastal eutrophication assessment based on thesymptoms of eutrophication. However, China’s actual eutrophication assessment forestuaries and coastal waters is still in Phase Ⅰ assessment systems which do notreflect the true states of eutrophication in waters. In addition, the current marineenvironmental monitoring system in China seems not to meet the requirements ofoccidental Phase Ⅱ methodologies well. Hence, it is in sore need of the developmentof the comprehensive assessment system for China’s estuarine and coastaleutrophication based on the PSR framework.In the dissertation, spatiotemporal variations of nutrients in Jiulongjiang Estuary wereanalyzed based on the survey data, including2cruises in2010, obtained from recent30years. Then the methodology for estuarine and coastal eutrophicationcomprehensive assessment was developed for China based on the PSR frameworkdrawing the advantages of occidental methods. And it was applied to assess theeutrophication state in Jiulongjiang Estuary. The main results are as follows:(1) Spatiotemporal variations of nutrients in Jiulongjiang EstuaryThe annual concentration of DIN and DIP tended to rise in recent30years while theDSi concentration increased recently and COD fluctuate in small amplitude. DIN washigher in the west than the east of the estuary with variations of DIP annually whileCOD and DSi concentration were high in the inner estuary and lower in the westernwaters of Xiamen and in the outer estuary. The N:P ratio did not rise significantly(N:P>22) while Si:N ratio decreased in recent years (Si:N>1). The phytoplankton growth was not limited potentially by phosphate or silicate or nitrate.(2) Development of methodology for estuarine and coastal eutrophicationcomprehensive assessment based on the PSR modelThe Pressure included anthropogenic influence index and system-specific attributesand features, which reflected the “filter” role of the estuarine and coastal systems.Base on analysis of applicability of indices in eutrophication assessment, the Statewas developed consisting of chlorophyll a concentration, phytoplankton cell density,dissolved oxygen concentration in bottoms, benthos abundance and red tidesconditions. The Response was based on the foreseeable evolution of DIN flux into thesea. Finally, the grade of each site and the whole area were obtained, respectively,which might fall into one of five categories: High, Good, Moderate, Poor or Bad.(3) Case study: comprehensive assessment of eutrophication in2010~2011inJiulongjiang EstuaryThe Pressure of Jiulongjiang estuary was moderate high. The State was moderate,which was worse in the inner estuary than the outter estuary. The Response wasmoderate high. Then the grade of the whole area fell into Poor. The grade of each sitewas Moderate or Poor, which was better in the outter estuary than the inner estuary.By comparing the grades with environmental elements, the index system seemedreasonable and the results reliable.The nutrient index methods could not provide a more detailed classification or anoverall value of system eutrophication status while the potential eutrophicationassessment method might have some flaws. These methods just reflected the pressureof nutrients in Jiulongjiang Estuary. The eutrophication symptoms, better in the outterestuary than the inner estuary, was the basis for the methodology for estuarine andcoastal eutrophication comprehensive assessment, which also made the results different between the methods.