Preliminary investigation on the enrichment of heavy metals in marine sediments originated from intensive aquaculture effluents

In the last decades, marine aquaculture has experienced an important development around the world. One of the main environmental impacts of these activities is the high amount of particulate matter discharged, which comes from uneaten food and faeces. Although the concentration of heavy metals in these particles is relatively low, the total amount of solids is so high that the accumulation of metals in the sediments may become an important problem. This fact has been mentioned in previous works, but it was not studied in depth. In this work, we demonstrate the accumulation of selected heavy metals (Cu, Zn, and Pb) and organic matter (estimated as Loss on Ignition, LOI) in marine sediments as a consequence of intensive marine aquaculture.The study was carried out in an arm-of-the-sea of the Bay of Cádiz (SW Spain) where several intensive marine aquaculture facilities are located. The data obtained were statistically treated to determine whether the spatial and temporal gradients in heavy metals and organic matter in sediments were related to aquaculture. Although the area is relatively pristine in regards to heavy metals, aquaculture activities have increased metals (Zn, Cu, Pb) and organic matter concentrations significantly. The average enrichments were: 140%, 362%, 97% and 445%, respectively. The results suggested that trace metals' enrichment in the sediments may be attributed to the fish farm effluents, although metal concentrations are not likely to cause harmful effects in the marine ecosystem.