Input-output ion fluxes in the River Sor catchment (Galicia, NW Spain)

Ion fluxes, measured during a two year-period in the river Sor catchment and four subcatchments are presented. Inputs were calculated either from bulk deposition (open areas) or throughfall (forested areas) while outputs were obtained from runoff water quality, considering that Cl− moves freely in the system. Annual inputs (SO42: 124–257, NO3−: 12–30 and H+: 42–122 meq m−2y−1), were 1.5–2 times higher during the second year, according to a higher total precipitation. Outputs exceeded inputs for Ca2+, Mg2+ and Na+, while SO42−, NH4+, K+ were retained in the catchment mineral weathering (output fluxes of Si: 11 to 31 kg ha−1) and sulphate retention (34–43% in Sor catchment) were the main mechanisms involved in H+ consumption.