The Establishment Of Evaluation Index System Based On The Macrobenthos In The Sediment Environment Of Xiaoqing River Estuary

Abundant researches have demonstrated that macrobenthos communities responds relatively rapidly to natural and man-induced changes in water and sediment quality, so benthic communities are used frequently as bio-indicators of marine monitoring and biotic indices of assessing the marine ecosystem health. Based on the data obtained from 5 cruises in May and November, 2008, August, 2009, May and September, 2010, the paper analyzed the physical and chemical indexes and distribution characteristics of the macrobenthos in the sediment environment of the Xiaoqing River estuary and its adjacent sea waters, and screeninged the polluted factors which indicated the characteristic of sediment environment. The pollution conditions of the sediment environment in the Xiaoqing River estuary and its adjacent sea waters were preliminary evaluated by the Shannon-wiener diversity index and A Marine Biotic Index(AMBI) which could better reflect the sediments quality status of this region. Moreover, AMBI was corrected by the selected indexes including sulphide, organic pollution index and organic nitrogen. The evaluation index system based on the macrobenthos in the sediment environment of the Xiaoqing River estuary was established. The main conclusions were as follows:The characteristics of the sediment environment in the Xiaoqing River estuary and adjacent sea waters were as follows: The granularity of the sediments was dominanted by sand and silt, the percent of clay was lower. Along the stream channel, estuary to coastal waters, the content of sulphide was reduced gradually, which was between 6.96 and 1231.58 mg/kg. The content of sulphide was badly exceeded nearby the stream channel and the estuary, the sulphide pollution in 27% and 51% sites exceeded the third and the first class of GB18668-2002 separately. While the content of sulphide in the coastal waters was in the range of the first class of GB18668-2002. The contents of total nitrogen and organic carbon were higher in the stream channel and the estuary, while lower in the coastal waters. The content of total nitrogen was between 0.14 and 1.06 mg/g, and the content of organic carbon ranged from 1.57 to 13.47 mg/g.Except for in September, 2010, the content of total phosphorous was between 0.42 and 0.87mg/g, and no significant variation.The content of total nitrogen and phosphorous exceeded the scope of the security level nearby the stream channel and the estuary, where were badly polluted. Though the content of organic carbon didn't reach the first class of GB18668-2002, the organic pollution index was higher and the content of organic nitrogen was close to the level of organic pollution in the stream channel and estuary, where existed the eutrophication. Except for Cu, the average contents of other heavy metal were lower than the first class of GB18668-2002. The results showed a lower pollution degree and a lower potential ecological risk assessment in the Xiaoqing River estuary.The distribution characteristics of macrobenthos in the Xiaoqing River estuary and adjacent waters were as follows: A total of 97 macrobenthos species were identified in the study, which were dominanted by polychaetes (46.39%), mollusks (28.86%) and crustaceans (20.62%); Along the stream channel, estuary and the coastal waters, the species and abundance of polychaetes reduced gradually. While the species and abundance of mollusks and crustaceans increased gradually. As for seasonal distribution, the species and abundance were higher in spring, lower in autumn and lowest in summer.Compared with other macrobenthic species, mollusks are in the majority of biomass, while polychaetes and crustaceans took the second place. The biomass was higher in spring relatively, while lower in summer and autumn.The macrobenthos which appeared frequented were as follows: Potamocorbula laevis, Potamilla acuminate, Eteone longa, Mediomastus sp.and Glycinde gurjanovae. Compared with contemporaneous Laizhou Bay, Yellow River Delta and Bohai Bay, the abundance and biomass in the Xiaoqing River estuary were highest, while lower in the Laizhou Bay and Bohai Bay, lowest in Yellow River Delta. Xiaoqing River estuary was dominanted by polychaetes, while others were dominanted by mollusks.By means of the correlation analysis among species, abundance, biomass and factors of sediments, combined with the pollution characteristics of surface sediment in Xiaoqing River estuary, the indexes of sulphide, the organic pollution index and organic nitrogen were selected as the indicate factors of sediment environment of the Xiaoqing River estuary. The evaluation results of diversity index and AMBI (A Marine Biotic Index) showed that the values of the two indexs increased at first and then decreased along the stream channel, estuary and the coastal waters, which reached the maximum in the estuary. There were obvious differences in the results between diversity index and AMBI Index in the coastal waters. The values of diversity index were lower in the coastal waters compared with the stream channel and estuary.And the evaluation results were two to three times higher than the AMBI index, consequently, which didn't correspond with the pollution characteristics of the sediment environment.So AMBI could better reflect the characteristics of sediment environment than diversity index.The indicate factors of sulphide, the organic pollution index and organic nitrogen were used to correct the ecological levels of macrobenthos. With regard to not assigned species, determine the initial levels according to the approximate species existing in the list of ecological groups and then correct the levels of macrobenthos combined with the indicate factors. As for identified species, levels were corrected combined with the indicate factors directly. The evaluation results of AMBI based on the corrected ecological groups of macrobenthos showed that the value of the stream channel was between 3.3 and 7.0, where the macrobenthos community health was in the status of heavily disturbed, the sediment environment condition was a poor status; the value of the estuary was between 3.3 and 4.3, where the macrobenthos community health was in the status of moderately disturbed, the sediment environment condition was a moderate status; the value of the coastal was about 2, where the macrobenthos community health was in the status of slightly disturbed, the sediment environment condition was a good status. The correlation among AMBI and the indicate factors of sulphide, the organic pollution index and organic nitrogen reached to significant positive correlation at the level of 0.0001. Therefore, the establishment of evaluation index system based on the macrobenthos applied to evaluate the sediment environment of Xiaoqing River estuary,which could reflect the pollution condition of the sediment environment in the research areas objectively.