The effects of petroleum exploitation on water quality bio-assessment and benthic macro-invertebrate communities in the Yellow River Delta wetland, Dongying

The major environmental risks associated with petroleum extraction(e.g.oil spills and leaks) are well known.There is a lot of information on the impacts of petroleum exploration on benthic communities in foreign studies.In this study,we probed the effects of petroleum exploration on macro-invertebrate assemblages,which are important components of benthic communities in this wetland ecosystem.The object of the investigation was to provide scientific data to guide the management,ecological restoration,conservation of biodiversity,and sustainable development of aquatic ecosystems.Physicochemical variables were measured at 34 sites in the Yellow River Delta wetland,Dongying,China,in October 2009,and benthic macro-invertebrate assemblages were collected using a D-frame net and a Peterson grab.The water body in the study area was oligohaline,its salinity ranging between 0.05 and 5 ppt.A total of 84 macro-invertebrate taxa,belonging to 70 genera,41 families,12 orders,6 classes,and 3 phyla,were collected.Insecta comprised 52.4% of all benthic invertebrate taxa,of which Odonata and Diptera accounted for 23% and 24%,respectively.The structure and diversity of macro-invertebrate assemblages were expressed using the Shannon-Wiener index,the Margalef index and the dominance index.Water quality was assessed by the Shannon-Wiener index and the biotic index.The dominant species at most of the sites were either Chironomus spp.or Glyptotendipes spp.with overall dominance indices of 0.0315 and 0.0522,respectively.Pearson correlation analysis showed that the Shannon-Wiener index was negatively correlated with total nitrogen(TN)(r=-0.446,P=0.02) but was not correlated with any of the other physicochemical variables measured.The biotic index was not correlated with any of the physicochemical variables.The numbers of molluscan taxa were negatively correlated with salinity(r=-0.422,P=0.028) and positively correlated with pH(r=0.435,P=0.023).Likewise,the percentages of individual Mollusca at the sites were negatively correlated with salinity(r=-0.395,P=0.041) and positively correlated with pH(r=0.565,P=0.002).The numbers of oligochaete taxa were significantly positively correlated with TN(r=0.524,P=0.005).The petroleum content of the water was not correlated with any of the biological indices and was not considered to be a major stressor.Canonical correspondence ordination analysis(CCA) showed that TN,pH,and salinity were the major contributors to the macro-invertebrate community structure,with 12.18% of species variation explained by these three variables.The substrate and hydrophytes also had effects on the structure of the macro-invertebrate communities.Cluster analysis and MDS ordination of sampling sites showed that all sites could be divided into 11 separate groups at the similarity level of 30%.Oligochaeta and Mollusca were the two main taxa responsive to environmental variables.The bio-assessment indicated that the Shannon-Wiener diversity index was a better indicator of water quality than the biotic index.Bio-assessment using the Shannon-Wiener index showed that the water quality of the Yihong River tributary,the Guangli River upstream,the Tiao River upstream,and the Dongzhang reservoir were clean,that nine sites were slightly polluted,and that the remaining sites were moderately to heavily polluted.We proposed that a comprehensive evaluation of water quality should ideally combine the Shannon-Wiener index,the biotic index,and physicochemical measurements.Additionally,other evaluation methods could be developed based on the biological indices for this region,taking into account the special characteristics of this native ecological environment.