Surface water quality in a contrasted land-use river catchment

Abstract

To evaluate the current state quality of the surface water resources in a river catchment near the city of Leiria (Central Portugal), a water sampling programme was designed and has been carried out since September of 2017. The land uses of the basin area were also studied. The three sampling sites are located in the river Lis catchment, downstream from the river spring to the city of Leiria, and in the Ribeira do Sirol tributary. The sampling programme was performed according to ISO 5667 standards. At each sampling site and twice a year, the field parameters, the concentration of dissolved gases (O2 and CO2) and the alkalinity were measured in the water. As the Lis river discharge is widely variable, flow parameters were also measured. The composition of surface water was determined in dissolved and particulate material, being the samples filtered at site. The major and minor constituents, cations (Ca, Mg, Na, K, NH4 and Fe) and anions (HCO3, Cl, SO4, PO4, F, NO3 and NO2) were analysed. Data of the winter campaign show that the hydrochemical facies of Lis River water are mainly Ca-HCO3. The chemical species are in dissolved forms and there is no evidence of nitrites, phosphates or fluoride in the surface waters. The concentration of Na, K and Cl, Mg and SO4, increase downstream, after the Ribeira do Sirol tributary, whose basin is mainly of agricultural land use. The water of River Lis in the urban area of Leiria shows evidence of a mixture of the spring water and of the Ribeira do Sirol water, with little contributions of other water sources in the urban area, pointing to a greater concern with respect to sanitation and good environmental practices in the city of Leiria.