Nutrients, conductivity and plankton in a landscape approach to a Pampean saline lowland river (Salado River, Argentina)

Abstract

Nutrients, conductivity and other physical and chemical parameters were measured seasonally in the main channel and in tributaries of the Salado River basin during the period March 1997-June 1999. The sampling began in a low water period and later included flood events. High water events were associated with high proportions of allochthonous compounds (polyphenols, suspended solids and organic matter). Nutrients and conductivity were related to hydrological conditions and different land uses in the catchment. A relationship was found between the land-use and nutrient concentrations due to the inflow of diffuse sources from agricultural lands. High nutrient concentrations and conductivity recorded in the headwaters were, respectively, related to the intensive agriculture in this area and the inflow of saline groundwater, drained by canals from endorheic basin to the main channel. Their effects on the middle and lower reaches were related to the discharge and inputs of other sub-catchments. Nutrients, sulphates, alkalinity and conductivity declined downstream towards the river mouth. The consequences for the plankton community of these spatio-temporal changes in the chemical characteristics are discussed. The heterogeneity of the Salado River is related to seasonality, land use and the geomorphological features of the basin.