Spatial and temporal variations in water quality of Todos Santos Bay, northwestern Baja California, Mexico

Coastal pollution levels in Todos Santos Bay (TSB) recreational beaches have increased in recent years due to the uncontrolled disposal of wastewater and pollutants to the coast by human activities (urbanization and tourism). In this work, the concentration of water quality parameters along the coast of TSB was evaluated from February 2012 to January 2013. Sampling was carried out at monthly intervals on 29 beach locations. Results showed that the maximum values of all parameters were always found close to the treated wastewater discharge area at Arroyo El Gallo station. Temporally, both nutrients and biochemical oxygen demand reached notably high levels in winter-spring and close to wastewater discharges. During summer, maximum counts of total coliforms and parasite eggs were detected close to wastewater discharges. Overall, our study provides a diagnostic approach on the spatiotemporal variability of water quality parameters for future studies along the coastal waters of TSB. •A baseline on the spatiotemporal variability of water quality parameters was provided.•Vulnerable zones affected by the discharge of treated wastewater were detected.•Maximum values of water quality parameters were found at the main municipal beaches.•Fluvial runoff in winter and upwelling during spring, provide nutrients to the coast.•Coastal currents influence the distribution of contaminants across the coast.