Ecological analysis in a polluted area of Algeciras Bay (southern Spain): External ‘versus’ internal outfalls and environmental implications

The effects of organic effluents both inside and outside the Saladillo Harbour (Algeciras, southern Spain) are investigated. Although the external outfall has a greater rate of discharge, the low levels of hydrodynamism inside the harbour create an area of relatively stagnant water, with markedly different environmental conditions. A clear gradient of decreasing pollution levels was observed from the interior to the exterior of the harbour. This was reflected both in the physicochemical water and sediment parameters and in their respective microbiological parameters. Macrobenthic species also mirrored the pollution gradient, as did the applied analysis. The effects of the external outfall are seen to dissipate and clear much closer to the external pollution source than in the internal, enclosed harbour area.