Sedimentary Environment Characteristics And Benthic Habitat Quality Assessment Of Xiaoqing River Estuary And Its Adjacent Sea

Laizhou Bay, which situates at the south of Bohai Sea, China, is an important fishing-spawning-feeding ground. Xiaoqing River is among the major rivers which flow into Laizhou Bay. And Xiaoqing River Estuary, lying in the southwest of Laizhou Bay, is a typical representative of severely polluted small and middle-sized estuaries. Being the primary pollution source of Laizhou Bay, Xiaoqing River will definitely influence the sustainable development of biological resources of this area. Macrobenthic invertebrates can make predictable responses to changes in marine environment caused by natural or anthropogenic disturbances, so using benthic invertebrates as indicators of marine ecosystem monitoring for ecological system quality assessment has been widely recognized. Based on surface sediment and macrofauna data in Xiaoqing River Estuary and its adjacent sea from 2008 to 2013, the concentration and spatial distribution characteristics of sedimentary factors, including grain size, sulfide, total organic carbon, total nitrogen and heavy metals； were studied to analyse sedimentary environment characteristics of the study area. Meanwhile, the Shannon-Wiener index (H’), the AZTI Marine Biotic Index (AMBI) and Multivariate AMBI (M-AMBI) were used for benthic habitat quality (BHQ) assessment here. Based on the relationships between the three indices and hydrochemical and sedimentary chemical parameters, the suitability of the indices for BHQ assessment in the study area was discussed. Results showed that:Redox potential (Eh) of sediment was relatively low while sulfide concentration was high in stream channel and estuary, indicating the strong reducing sedimentary environment characteristic of this region. Moreover, total organic carbon (TOC), total nitrogen (TN) and heavy metals (Cu, Zn, Pb, Cd, Hg) here had rather higher concentrations than coastal area, where the salinity was over 24. In the area of stream channel and estuary, TOC concentration and TN concentration of some samples exceeded the lowest safety level which could cause toxic effect on benthic assemblage. Pb was the primary pollution factor of the study area, reaching ’Moderate’ pollution level. While the other heavy metals were all at ’Low’ pollution level. Comprehensive potential ecological risk of the study area was at ’Moderate’ or ’Low’ level, and the relatively high potential ecological risk of Cd, Hg and Pb led to the ’Moderate’ level of some stations. Moreover, risk index values of the estuary were significantly higher than those of coastal area.In the study area,120 species of macrobenthos were identified in the 8 cruises, including 46 species of polychaetes,35 species of mollusks,34 species of crustaceans and 5 other species. The numbers of species in the estuary and coastal area were significantly larger than those in stream channel. Benthic assemblage was mainly composed of EGⅡ and EGⅤ in stream channel, with mainly EGⅡ and EGⅣ in estuary; whereas for coastal area, EGⅠ and EGⅡ accounted for the most. BHQ presented an obvious trend of improvement along the direction of stream channel, estuary and coastal area, but the three areas all suffered from different levels of disturbances. Assessment results of Shannon diversity were that:the averages of H’ were respectively 1.14,1.75 and 1.70 for stream channel, estuary and coastal area, so BHQs of the three areas were all assigned ’Moderate’; yet BHQs of estuary and coastal area were better than that of stream channel. Assessment results of AMBI showed that:the averages were 3.44,3.56 and 1.86 for stream channel, estuary and coastal area respectively, so BHQs of stream channel and estuary were assigned ’Moderate’ with that of coastal area being ’Good’;BHQ of coastal area was significantly better than those of stream channel and estuary. And assessment results of M-AMBI were that:the averages were 0.29,0.40 and 0.48 respectively for stream channel, estuary and coastal area, so BHQs of estuary and coastal area were assigned ’Moderate’ while that of stream channel was assigned ’Poor’; BHQs of estuary and coastal area were significantly better than that of stream channel. BHQ of estuary was assigned ’Moderate’ by all the three indices; In stream channel, M-AMBI gave lower BHQ level than H’and AMBI did; while in coastal area, AMBI gave higher BHQ level than H’and M-AMBI did.Through comparison and analysis of the relationships between the three indices and hydrochemical and sedimentary chemical factors, the sensitivity and stability of the indices for BHQ assessment of the study area were systematically verified. Results of correlation analysis showed that AMBI and M-AMBI were significantly related to salinity, dissolved oxygen, COD, dissolved inorganic nitrogen, chlorophyll a and sedimentary chemical factors (sulfide and TOC); whereas H’was not. Xiaoqing River Estuary and its adjacent sea suffered from relatively serious pollution, which could cause the loss or even extinction of species of weak tolerance to chemicals with a few species of strong tolerance striving to live. In the calculation of H’, all the species were considered the same in conveying information of benthic assemblage structure and effect upon it, and this led to the result that there was no significant difference between different areas. Therefore, AMBI and M-AMBI might be more suitable for BHQ assessment of this area than H’.In this paper, pollution characteristics of sedimentary environment of Xiaoqing River Estuary and its adjacent sea were described; potential ecological risk of estuarine ecosystem and BHQ of this area were also evaluated to provide basic data of sedimentary environment pollution for ecological management of this area, to offer scientific basis for enhancing marine environment management, as well as to provide reference data and early warning for further governance of Xiaoqing River and fishery production and aquaculture of Laizhou Bay.