Distribution of BOD and bacteria along the coast of the US Mexico border

Biochemical oxygen demand (BOD) and total coliform bacteria (TCB) from the Tijuana municipal outfall were analyzed from six surface samplings (5-7 February and 30 June to 2 July 1987), conducted along the coast between the US-Mexico border and north of Rosarito, Baja California. This study was carried out under two oceanographic conditions: with a littoral transport towards the south (February) and north (July). Results indicate that BOD and TCB surface distribution patterns remained relatively constant during the sampling periods, indicating a short-term (three-day) stationary plume. However, spatial distribution showed seasonal differences, with the highest concentrations of BOD (55 mg l(-1)) and TCB (1,350,000 MPN 100 ml(-1)) occurring in summer. The surface distribution of the variables identifies a long- and offshore dispersion of matter, predominantly towards the south-southeast, indicating that the outfall is the principal source of BOD and TCB. Based on the physicochemical factors associated with the dispersion and degradation of the organic-bacteriological matter, it is unlikely that the surface outfall of the effluent from the San Antonio de los Buenos treatment plant, 9 km south of the border, affects the coasts of San Diego, California. The relatively high concentrations of BOD (2.0 mg l(-1)) and TCB (1,000 MPN 100 ml(-1)) at the US border are due to sources from the north and non-point outfalls along the coast of Playas de Tijuana.