Monitoring coastal waters from Tijuana to Ensenada

by J. Vinicio Mac’as-Zamora, Universidad Autonoma de Baja California


he Bight of the Californias refers to the coastal waters and coastal water sheds that feed into the Southern California Bight the geographical feature characterized by the crecent shape of the coast from Point Conception in the Unites States to Cabo Colonet in Mexico. This region shares many oceanographic features, a unique marine ecosystem, similar terrestrial ecology and patterns of coastal development and marine uses that affect the quality of coastal water and the integrity of coastal and marine ecosystems.

    The Bight of the Californias is shared between two countries and has a rich and varied biology that is threatened by population growth that in 1990 exceeded 15 million inhabitants. Because of the variety of activities that take place in the coastal zone and watersheds that feed the Bight, these coastal waters receive industrial and municipal waste, and non-point source pollutants by way of both permanent and temporal streams along the entire coastline.

    In 1997, a group of scientists from the Instituto de Investigaciones Oceanológicas, in coordination with American colleagues, participated in a monitoring study using the same collection, preservation, selection and analysis methodologies. This article presents results from this joint effort of Mexican and US scientists working in close collaboration with the objective of determining the status of these coastal waters and the impact of human activities.

    This work is the Mexican component of the 1998 Shoreline Microbiology study, undertaken by the Southern California Coastal Water Research Project (SCCWRP.) The objective of this program is to monitor the Bight every four years in order to document changes associated with increased human activities as well as changes associated with the startup of new sewage plants (Binational, El Sauzal and El Naranjo).

    This is the first time that scientists from both nations have adopted the same methods for sampling and quality control. Measurements in the entire area can now be effectively compared. As a result of this study, we now have a regional perspective on water quality in this region for the first time. The Mexican component was financed by the Sistema de Investigación del Mar de Cortes (SIMAC), the North American Commission for Environmental Cooperation (NAECC), and the Algalita Foundation.

    Although this effort has provided a large amount of information, this study represents only one point in time. In order to understand environmental changes that take place in the coastal zone as a result of human activities, this effort will have to be repeated periodically. The results outlined in this document are preliminary and represent the first interpretation of this extensive effort. The work included sedimentary chemistry, bacteriology, hydrology and benthic studies.

 Sediment chemistry


    We determined concentrations for DDT and its derivatives, 24 compounds in the polyaromatic hydrocarbons (PAH) group, 41 congeners in the family of polychlorinated biphenyls (PCB), and linear alkylbenzenes (LAB). In addition, we measured a set of trace elements including lead, copper, nickel, chromium, zinc, cadmium and iron. These measurements were taken at 72 stations between 6 and 200 meters. An extensive inter-calibration exercise was conducted prior to the field and lab work.



    Bacterial indicators were measured weekly in 29 locations between Playas de Tijuana and Punta Banda for 5 consecutive weeks in the summer of 1998 and the winter of 1999. In addition, because winter storms are an important transport mechanism for contaminants, we conducted one winter monitoring exercise associated with stormy conditions in 2000.



    From the border to Punta Banda, we collected hydrological parameters with the goal of describing fresh water plumes and associated contaminants. We monitored the area between Tijuana and Ensenada, covering 65 stations in 23 transects in late January 1999 aboard the ROV Alguita from the Algalita Marine Research Foundation. The monitoring took place 2 days after a storm. In addition to salinity, temperature, pH, and dissolved oxygen, we measured organic nutrients, nitrogen, organic phosphorus, residual chlorine, and chlorophyll.



    The benthic monitoring took place in August and September 1999 simultaneously with sediment chemistry; 70 stations were monitored. All organisms, predominately macro-invertebrates, were identified to the lowest taxonomic level.


  • The entire area that was monitored appears to have had contact with wastewater. The gradients in concentrations for DDT and PCB appear to suggest that persistent organic pollutants associated with sediments are mobilized towards the south.
  • DDT and PCB are present in approximately 60 percent of the total area monitored. These compounds indicate a large influence of anthropogenic sources of contamination. However, the values measured for these compounds are still relatively low.
  • Trace metals were detected at levels consistent with natural biogeochemical processes. Anthropogenic effects are still not important in this area.
  • The levels for total and fecal bacteria that exceeded US legislation standards, and used here as a reference, were approximately 25 percent for summer measurements.
  • Bacterial levels on beaches were lower in the dry winter than in summer. However, during the wet winter (2000), higher levels of bacterial contamination associated with heavy rains were detected .
  • As was expected, areas nearest to point sources showed the highest bacterial counts.
  • The benthic analysis indicates these populations are still not stressed or impacted by human activities.

    Reprinted by permission of the Bight Bulletin, No. 2, July 2001, California Sea Grant College Program, and J. Vinicio Macias-Zamora, UABC, Mexico.

    Bight Bulletin/Boletín de la Cuenca. Working together to protect the waters we share/Trabajando juntos para proteger las aguas que compartimos