Distribution of BOD and bacteria along the coast of the Us-Mexico border

Abstract

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 1^–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 1^–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.