Assessment of nutrients and material transport in the main tributaries of the Bahía Blanca Estuary (Argentina) and its relationships with hydrologic dynamics and land use

Context Land-based activities within a river basin alter nutrient and particle transport, affecting estuarine water quality and ecological health. Aim To assess spatial and seasonal dynamics of nutrients, particulate materials, and physicochemical parameters in Sauce Chico River (SCR), Napostá Grande Stream (NGS) and inner Bahía Blanca Estuary (BBE, Argentina) from autumn 2017 to summer 2018. Methods We analysed 14 sites located in freshwater bodies and within the estuary. Flows, pH, temperature, salinity, turbidity, ammonium (NH4⁺), chlorophyll a (Chl-a), phaeopigments (Phaeo), particulate organic carbon (POC) and suspended particulate matter (SPM) were determined. Key results Average flow rates reflected rainfall patterns. SCR acts as the primary driver of physical sedimentation, transporting significantly more SPM (3492 Mg year−1) than NGS. NGS exerted a stronger chemical influence, with sewage discharges triggering critical NH4+ spikes. Wide POC:Chl-a ratio range in BBE (94–595) and winter POC peaks from the NGS indicate seasonal shifts between terrestrial inputs and estuarine productivity. Conclusions BBE is subjected to dual, tributary-specific stressors – sediment loads from the SCR and nutrient pollution specially from the NGS. Implications Protecting of vulnerable ecosystems, as BBE, requires distinct, integrated watershed management strategies tailored to the unique anthropogenic pressures of each tributary.