Author(s):
Santos, Cristina 
; Barreiros, Maria Alexandra ; Pestana, Pilar ; Cardoso, Ana ; Freire, Alexandre
Date: 2011
Persistent ID: http://hdl.handle.net/10400.9/1335
Origin: Repositório do LNEG
Subject(s): Submarine outfall; Receiving waters; Sediments; Monitoring; Emissário submarino; Meio receptor; Monitorização; Sedimentos
Description
The sea along the western coast of Portugal presents hydrodynamic conditions that place it among the most favourable of European coastal waters for dilution and dispersion of waste water. Thus it is an appropriate zone for the location of submarine outfalls. According to the European Union Directives and Portuguese Regulations the waste waters produced by this densely populated coast should be treated, therefore 18 wastewater treatment plants with submarine outfalls were built along the coast. Between 2002 and 2004, five sampling campaigns were performed in seven outfalls that were selected to participate in water and sediment quality surveys supported by INAG (Portuguese Water Institute), and performed by the Hydrographic Institute of the Portuguese Navy. The water quality assessment was based on 10 chemical and physical parameters, including heavy metals. The results were compared with reference values and data from the largest flow outfall located at Guia, which has an autonomous monitoring program. In order to evaluate significant differences in water quality between years and sampling sites, statistical analyses were performed. S ediments were evaluated for grain size, heavy metals, PAH, hydrocarbons, chlorinated pesticides and PCB. In order to evaluate the level of pollution of the different areas where the outfalls are located, the concentration factor (CF) (sediment/water elemental concentration ratio) was calculated and compared with the recommended values for the CF of each element. The water sampling program did not allow identifying a clear seasonal evolutionary pattern. The environmental status of the waters surrounding the outfalls discharges comply, to a great extent, with the reference values proposed by INAG and did not revel high levels of contaminants. Due to the low sorptive capacity of the sediment for contaminants, trace metals, hydrocarbons and PAHs have a low environmental impact. The values of the concentration factors for metals are below the recommended values.
