An Integrated Marine Sediment Quality Assessment Framework Based On The Coupling Relationships Between Benthic Community Alterations And Toxic Metals

Marine sediments are main sinks for terrigenous materials, which play a critical rolein the marine biogeochemical cycles of matters. The environmental quality ofsediment is closely correlated with the water column and the benthic invertebratesinfaunal in particular. Thus a scientifically robust quality assessment framework isvital for marine sediments, since the latter ones are essential component of marineecosystem. Based on systematic study of coupling relationships between toxicmetals and benthic community structure in typical estuarine and marine sediments inBohai Sea, a novel integrated sediment quality assessment framework wasestablished including chemical measurement endpoints, chemical screening values,and an integrated sediment quality index. The main conclusions are as follows:1. The benthic community structures were closely correlated with the toxicmetal in the sediment of Bohai Sea. There were enormous regional variations onthe influences of metals on benthic community structures. Our results indicatedthat As in sediments of Bohai Bay was significantly correlated with the benthiccommunity alteration, providing key evidences in community levels in terms ofecological relevance. In case of Laizhou Bay, a trend of increasing species withincreasing proximity to stations with high concentration of Zn, which wassuggested by positive and significant correlations them. In respect of JinzhouBay, sediments were heavily contaminated by Cu, Pb, Zn and Cd, where onlyfew individuals on very occasional locations were found, indicating hardship forsurvival of benthos. Variations of toxic metals in sediment from Bohai Bay revealed the significantanthropogenic stressors from the coast. The benthic community structures wereapparently influenced by the toxic metals in the southern portion of Bohai Bay, withthe overwhelming predominance of Mollusca species and low diversity subsequently.Canonical correspondence analysis (CCA) results showed the benthic distribution inthe near shore stations was significantly influenced by Zn. For benthic community inthe southern portion of the Bay, CCA also suggested As and Hg were the mostinfluential stressors. Further, As was significantly correlated to the difference ofbenthic community structure at stations in the surveyed area implied by Monte Carlopermutation test (F=1.988, P=0.0260), which provides key evidences of ecologicalrelevance in the community level.For Laizhou Bay, trace metals in this area originate from both the natural andanthropogenic processes, with the riverine inputs predominated. There were alsopossible common sources of Cu and As indicated by significant positive correlations.The major axes of heavy metals (Metals-PC1) and benthic community structure(DIM1) were weak and insignificant correlated, indicating that metals may not be theprimary explanatory factors for benthic alterations. There were significantcorrelations (rs=0.646, P<0.01) between benthic abundance and Zn, which indicateda trend of increasing species with increasing proximity to stations with highconcentration of Zn. In respect of Huanghe River Estuary, the overall metalcontamination level was relatively low. The presence of larger size species (Mollusca)with increasing proximity to stations with higher metal contamination level wasinferred from Pearson correlation analysis between benthic data and chemical data.The Jinzhou Bay ecosystem has been severely degraded. Sediments in the surveyedregion were heavily contaminated by Cu, Pb, Zn and Cd, which poses highecological risks. Our results showed that the higher concentrations of metals werefound in the sediments located near the Wulihe River and Huludao Zinc Smelter,which indicated massive influences of the source locations. Benthic investigationrevealed that there were very few individuals on very occasional locations, which further indicated that the Jinzhou Bay ecosystem were seriously impaired.2. Integrated sediment quality assessment was performed in light of thecoupling relationships between benthic community structure alterations andtheir possible explanatory factors, usually toxic metals. The resulting pictures ofsediment quality in the Bohai Sea (excluding Jinzhou Bay) however showed thatlevels of metal contamination were minor-than-expected.In the study areas, unimpaired sediments were mainly rested far from the rivermouth, including the central portion of Bohai Bay and Bohai Sea, the western part ofLaizhou Bay. Impaired sediments however mainly distributed near the HuangheRiver mouth, Xiaoqinghe River mouth and northern portion of Laizhou Bay.Sediment degradation in southern portion of Bohai Bay was mainly resulted from Hg,while Cu and As may be the caused for sediment impairment in central north ofLaizhou Bay. For sediments in the Huanghe River Estuary and parts of Laizhou Bay,sediment impairment was mainly explained by river dominated stressors such asphysical habitat alteration rather than toxic metals. The overall results of integratedsediment quality assessment showed that the majority of sediment locations were notthe impaired ones. Additionally, Decades records of heavy metals in variouspublication results also suggested a mitigation trend of metals. Therefore, theenvironment quality of sediments in Bohai Sea (except Jinzhou Bay) wasminor-than-expected.3. In light of the coupling relationships between toxic metals and benthiccommunity alterations, a novel marine sediment quality assessment frameworkincluding18measurement endpoints in5categories and10backupmeasurements of emerging contaminants, chemical screening values, and anintegrated quality index was established.A selection of18traditional chemical endpoints distributed in5chemical groups and10backup measurements of emerging contaminants on the basis of the ecologicalsignificances. The geochemical background values for metals were calculated and summarized from the concentrations of metals in deep layers of core sediments formBohai Bay, Laizhou Bay and Jinzhou Bay, respectively. Further, the toxicitythreshold for metals were also derived from9single TECs and8single PECs(including TEL-PEL in China) by the method of consensus-based sediment qualityguidelines. Based on the integrated assessment results of Bohai Sea, an integratedquality index (IQI) was condensed form benthic community structure, predictedtoxicity and sediment contamination through a weight of evidence method.