Integrative assessment of sediment quality in two littoral ecosystems from the Gulf of Cadiz, Spain

To evaluate sediment marine environmental quality in the Gulf of Cadiz, an integrative assessment approach was used-the sediment quality triad (SQT). Sediment samples were collected at seven stations in two littoral ecosystems and subjected to six separate, replicated sediment toxicity tests, comprehensive sediment chemistry analyses, and replicated benthic infaunal analyses. Chemistry analyses indicated that different contamination sources were associated with sediments highly contaminated with linear alkylbenzenesulfonates and some heavy metals associated with sewage discharges (Pb, and Ag), sediments with moderate levels of heavy metals associated with industrial activities (Hg, Cr, and As), and other sediments with slight or no contamination. Toxicity tests indicated that sediments close to the sewage discharges were most toxic, those associated with slight or no contamination were not toxic, and those associated with both sewage discharges and industrial sources of contamination were intermediate. Infaunal analyses indicated that communities at the salt-marsh of the Barbate River stations and CBZ station in the Bay of Cadiz were the most altered, whereas those at CB5 and CB3 in the Bay of Cadiz were slightly altered, relative to stations CB1 and CB4 in the Bay of Cadiz. A different methodology to calculate the ratio-to-reference and each composite SQT index value is proposed by adding to the classical normalization by using the reference clean station as a new normalization that includes a reference polluted station to establish a between-the-maximum and minimum level obtained in the area studied. We propose this new methodology to calculate weighted results based on the fact that they are obtained using two points of reference for comparison. The results show that sediment pollution is restricted to the vicinity of one untreated sewage discharge in the Bay of Cadiz.