| The analysis of the eutrophication characteristics in some typical Chinese coastalareas were carried out. In these coastal areas, the nutrient enrichment status and thespatial and temporal characteristic of some eutrophication symptoms such as HarmfulAlgal Blooms (HABs) were analyzed. Based on the analysis of the eutrophicationcharacteristics, an integrated model for assessment of eutrophication status, whichwas based on both water quality and ecological response, was described. The―PhaseII‖assessment model structure and previous assessment model for Changjing rivereustuary were referred to in the construction of the integrated model. The integratedmodel was then applied to some typical Chinese coastal areas, hoping to provide someimplications for eutrophication management. Comparison works, such as thecomparison between the integrated method and the nutrient index method, and thecomparison between the integrated method and other multi-parameter assessmentmodel, were also carried out for improvements of current methods. The mainconclusions are as follows:The analysis of the eutrophication characteristics of the typical coastal areasindicated that: for a long-term time series, the trend of nutrient concentrations showedan increasing trend in typical coastal areas which means a nutrient enrichmentconditions. The trend of nutrient concentrations is in accordance with the trend ofoccurrences of HABs. Previous research indicated that the increases in nutrientconcentrations had a good correlation with the frequency of occurrences of HABsevents especially in the Changjiang river estuaries. For spatial characteristic ofeutrophication, nutrients inner the bays and in the nearshore areas were usually high.And the areas with high concentrations of nutrient were almost areas with highfrequency of HABs, just as the case in the southwest Bohai Sea, the Xiangshan Bayand the nearshore areas of Xiangshan Bay. For a small proportion of areas, thedistribution of high nutrient concentrations and HABs were not in consistency. Justlike the case in Changjiang river estuary and the Hangzhou Bay, the area of high nutrient concentrations (inner the estuary and the Hangzhou Bay) was not areas whereoccurrences of HABs were frequent. In the offshore area of the Changjiang riverestuary and outside the Hangzhou Bay where nutrient was relatively low, highfrequency of HABs occurred. This is mainly due to the expressions of eutrophicationsymptoms were influenced by the regional characteristics or system-specific attributes.This had provided good implications that when assessing the trophic status of coastalareas, nutrient enrichment factors, eutrophication symptoms such as HABs, high-levelbiomass and hypoxia, e.g. should all be considered.The results of the application of the integrated model to three typical coastalareas indicated that: Among the three typical coastal areas in different geographicallocations (southwest Bohai Sea, coastal areas in Shandong Peninsula and Changjiangriver estuary and Hangzhou Bay), the Changjiang river estuary and Hangzhou Baywere areas with most serious eutrophication problems. The trophic status in a fairlylarge area of Changjiang river estuary and Hangzhou Bay ranged from the―Poor‖category to the―Bad‖category. Following the Changjiang river estuary and HangzhouBay, the eutrophication problem in the north Bohai Bay, especially in the Haihe riverestuary was also very serious. The trophic status in most coastal areas and bays inShandong Peninsula did not follow in the―Bad‖category, indicating the least seriousproblem in the three geographical regions. The trophic status inner the Xiangshan Bay,the Laizhou Bay, the Jiaozhou Bay, the Dingzi Bay and the Sishili Bay was not good.In general, eutrophication problems inner the Bays were more serious than that in theopen sea areas. The trophic status in the coastal areas of Shandong Peninsula, thecentral open sea of Bohai Sea was almost―Moderate‖category or―Moderate Low‖category, which may be attributed to the lower riverine input of nutrients and goodhydrodynamic conditions. There was good relationship between the trophic status andthe characteristics of the estuaries. The trophic status was worse in the offshore areasthan that inner the estuaries if the river discharge was large and carried a large amountof suspended solids, since the eutrophication symptoms were not easily expressedinner the estuaries due to the high turbidities. These areas included the Changjiangriver estuary and the Hangzhou Bay. For low-discharge and low-turbidity rivers, such as the Haiher river in north Bohai Bay, Xiaoqing river in west Laizhou Bay and Haiporiver in the Jiaozhou Bay, eutrophication symptoms were easily expressed near theriver estuary and showed a Bad tophic status as soon as nutrients was delivered to thebays.In the comparisons of different assessment methods, both the integrated methodand the―NOWPAP‖common procedure identified that there was high degree ofnutrient enrichment problem inner the Jiaozhou Bay. For primary ecological responseor symptom (e.g. Chl-a), the integrated method identified the―High‖category whilethe―NOWPAP‖identified―Low‖category, partially due to the way the monitoringdata were processed (90thpercentile-based approach for the indicators of theintegrated method while the average or maximum value for―NOWPAP‖method) andpartially due to the threshold used by different methods. For secondary ecologicalresponse, different time-scale data were used by the two methods according to theavailability of data collected. And HABs events showed a decreasing trend from theyear2004to2009, so the secondary ecological response became better in the―NOWPAP‖method, which resulted in a better final trophic status. For comparisonsof the integrated method and the traditional nutrient index method, the integratedmethod obtained more reasonable results. Inclusion of both causative factors andeffect factors, combination of concentration, spatial coverage and frequency ofindicators, and usage of a multi-season monitoring datasets in the methodology resultin a more accurate and representative assessment. Nutrient-based EI method obtaineddeclining gradient of trophic status as water depth increases simply because the EImethod assumes that eutrophication problems are only reflected as changes innutrients and fail to reflect the changes in the ecological response or impairments ofthe system. |
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