| Bay has unique natural conditions and a variety of marine resources that provides the survival and development of material basis for the people along coast.Maintaining the bay ecosystem health is the fundamental guarantee for the sustainable development of coastal society.However,the bay ecosystem health status in China is degrading severely due to the rapid coastal development and overwhelming pollutant discharge.The protection and restoration of the bay ecosystem is an urgent task for the bay ecosystem management.The understanding and evaluation of bay ecosystem health is the scientific basis of protection and restoration of the bay ecosystem.However,the current research on marine ecosystem health assessment in China is still in the infant stage;especially the quantitative health assessment is scarce.This study is aimed to enrich the research on bay ecology,to improve the method for bay ecosystem health assessment,and also to provide technical supports for ecological protection and restoration of bays.Five representative bays in Fujian Province(Shacheng Harbour,Sansha Bay,Luoyuan Bay,Quanzhou Bay and Dongshan Bay)were chosen to conduct case studies.The main results of this study are presented in the below.1.The development of bay ecosystem health assessment method(1)The development of assessment index system and weighting methods18 indicators are selected in the index system covering water quality,sediment quality,biological quality and biology,which is developed based on the ecosystem's structure-function in reference to the coastal ecosystem health evaluation system most used in home and abroad and in combined with the characteristics of Fujian bay ecosystem and its data availability.The weight value of the indicators are estimated and analyzed comparatively using subjective weights(analytic hierarchy process),objective weights(improved entropy method)and compromise weight coefficient methods(the combination of subjective and objective weights),respectively.The weight of each indicator determined by the subjective weight factor showed that marine biotic index dominates in the bay ecosystem health assessment index,accounting for about 60%of the full index,such as the weight of indicators in primary productivity,benthic biodiversity,nutrient level,fish eggs&larvae density and heavy metals in organism contribute 0.1456,0.0929,0.0884 and 0.0798,respectively.The indicators with higher weights basically indicate the major environmental problems in Fujian coastal ecosystem.The marine biotic index determined by the objective weighting methods also dominates in each bay system,ranging from 0.4859 to 0.5526,which is close to the subjective weighting results of 0.5981.The objective weights of organic pollution,nutrient level,fish eggs and larval density index is relatively low,which does not match the real situation of bays in Fujian Province.The weight estimated by compromise weight coefficient method varies in bays,and the benthic biodiversity index has the highest weight(from 0.0837 to 0.0869),fish eggs and larvae density index(from 0.0729 to 0.0769)and nutrient level(from 0.0685 to 0.0753)comes next.In addition,the index of zooplankton diversity(from 0.0662 to 0.0756),phytoplankton diversity(from 0.0653 to 0.0738),organic pollution(from0.0520 to 0.0598)and the heavy metal in sediments index(from 0.0543 to 0.0608)are also relatively high.This is consistent with the main environmental problems and ecological characteristics of the bay.(2)The standard value of Fujian Province bays ecosystem health assessment indexWater environmental chemistry parameters' assessing standards are determined in reference to the current standard and research literatures.Reference value of marine biological Shannon Weaver diversity index H' is determined mainly by the sequence analysis of the historical and present data in reference to the research literatures and expert judgment.Reference value of marine biological quantity(density)is determined mainly by the statistical average of historical and present data in reference to the research literatures.Reference value of phytoplankton,zooplankton and macrofaunal Shannon Weaver diversity index H' in Fujian Province bays are 3.5,3.2 and 4.2,respectively.The standard of the indicators is divided into 5 levels:grade 1(excellent),grade 2(good),grade 3(moderate),grade 4(poor)and grade 5(bad).(3)Bay ecosystem health index calculation based on variable fuzzy evaluation modelBay ecosystem health index is calculated through data normalization and the relative membership degree model.The grade eigenvalue H of the bay ecosystem health comprehensive evaluation results is calculated,and the judgment criteria regarding the level of bay ecosystem health is divided into eight grades.2.Case study in Fujian Province baysThe health status of representative bay ecosystems in Fujian Province was evaluated based on variable fuzzy evaluation model,and the credibility of results are validated by fuzzy comprehensive evaluation model.The results show that:The bay ecosystem health grade(eigenvalue H)of Shacheng Harbor,Sansha Bay,Luoyuan Bay,Quanzhou Bay and Dongshan Bay are averaged as 3.11±0.11,3.03±0.15,305±0.12,3.13±0.14 and 2.55±0.12,respectively.The ecosystem health level of Dongshan Bay is classified as "between moderate and good,mostly good",and the other four bays' ecosystem health level are classified as "between poor and moderate,mostlypoor".H values in all stations of Shacheng Harbour,Sansha Bay,Luoyuan Bay,Quanzhou Bay and Dongshan Bay ranged from 2.93 to 3.25,from 2.79 to 3.22,from 2.88 to 3.29,from 2.79 to 3.23 and from 2.33 to 2.74,respectively.The distribution characteristics of H value is similar to that of the organic pollution and nutrient level index,which is decreased from the top to the mouth of the bay or from inshore to offshore.The ecosystem health levels of runoff,land-based sewage outfall,port and aquaculture sea areas are generally inferior to other sea areas,with the H value ranging from 3.01 to 3.29(Shacheng Harbour,Sansha Bay,Luoyuan Bay,Quanzhou Bay)and from 2.49 to 2.74(Dongshan Bay),judging the ecosystem health level as"between moderate and good" or "between poor and moderate"(Dongshan Bay).Marine nature reserve ecosystems,such as mangrove coral and large yellow croaker marine protected area,have better ecosystem health level than other areas,with the H value ranging from 2.33 to 2.88,judging the ecosystem health level as "between moderate and good" or "between poor and moderate".The indicators that have adverse impact on the level of the bay ecosystem health(value of ecosystem health index is greater than 3.5)include organic pollution index(5.00),nutrient index(5.00),primary productivity(4.90),benthic biomass(4.81),benthic diversity index(3.88),zooplankton diversity index(3.59)and fish eggs and larvae density(3.57)in Shacheng Harbour,organic pollution index(4.77),primary productivity(4.68),zooplankton biomass(4.64),nutrient index(4.54),the benthic biomass(3.78)and zooplankton diversity(3.61)in Sansha Bay,organic pollution index(5.00),nutrient index(4.17),heavy metals in organisms index(4.17)and zooplankton biomass(4.01)in Luoyuan Bay,fish eggs and larvae density(4.98),organic pollution index(4.61),benthic biomass(4.23),nutrient level index(4.13)and primary productivity(4.09)in Quanzhou Bay,fish eggs and larvae density(4.01)and benthic diversity index(3.57)in Dongshan Bay,respectively.The bay ecosystem health evaluation results are basically stable within a narrow range and generally classified as one level calculated by different combinations of criterion parameters a and distance parameter p in variable fuzzy evaluation model.The health index value ranges from 0.13 to 0.34 in Shacheng Harbour,from 0.10 to 0.33 in Sansha Bay,from 0.07 to 0.23 in Luoyuan Bay,from 0.15 to 0.28 in Quanzhou Bay,and from 0.33 to 0.51 in Dongshan Bay,respectively.The results of variable fuzzy evaluation model are basically consistent with that of the fuzzy comprehensive evaluation model,which are more close to the real situation of the bays and therefore should be more objective,accurate and reasonable. |
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