Bacteriological study of seawater for the culture of bivalve molluscs in Baja California

During critical seasons of environmental pollution, bacteriological samplings were made in Willard Bay and Los Angeles Bay, Baja California, in 1985-1987, and in Falsa Bay and Todos Santos Bay, B.C., in 1991-1993. The objective of this study was to determine the quality of the water for culturing bivalve molluscs. Bacteriological faecal indicators (total coliforms and faecal coliforms) were determined by MPN technique, according to standard methods. Except for summer 1985 in Willard Bay, when a significant amount of organic material was introduced by fishing boats, and winter 1992 in Falsa Bay and Todos Santos Bay, when there was an important input of bacteria due to rainfall, the bacteriological quality of the water was acceptable for culturing bivalve molluscs in the four locations, since the values were below the limit established by legislation

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 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

Macrobenthic community response to copper in Shelter Island Yacht Basin, San Diego Bay, California

We examined Cu contamination effects on macrobenthic communities and Cu concentration in invertebrates within Shelter Island Yacht Basin, San Diego Bay, California. Results indicate that at some sites, Cu in sediment has exceeded a threshold for “self defense” mechanisms and highlight the potential negative impacts on benthic faunal communities where Cu accumulates and persists in sediments. At sites with elevated Cu levels in sediment, macrobenthic communities were not only less diverse but also their total biomass and body size (individual biomass) were reduced compared to sites with lower Cu. Cu concentration in tissue varied between species and within the same species, reflecting differing abilities to “regulate” their body load. The spatial complexity of Cu effects in a small marina such as SIYB emphasizes that sediment-quality criteria based solely on laboratory experiments should be used with caution, as they do not necessarily reflect the condition at the community and ecosystem levels

Spatial distribution of copper in relation to recreational boating in a California shallow-water basin

The overall effect of the number of boats on the copper (Cu) levels in the water column and sediment, along with their spatial variability within Shelter Island Yacht Basin (SIYB), San Diego Bay, California was examined. We identified a horizontal gradient of increasing dissolved Cu and Cu in sediment from outside to the head of SIYB which was coincident with the increasing number of boats. Spatial models of Cu distribution in water and sediment indicated the presence of ‘hotspots’ of Cu concentration. From outside to the head of SIYB, dissolved Cu ranged from 1.3 µ g L-1 to 14.6 µ g L-1 in surface water, and 2.0 µ g L-1 to 10.2 µ g L-1 in bottom water. Cu in sediment exceeded the Effect Range Low of 34 mg kg-1 (i.e. where adverse effects to fauna may occur), with a peak concentration of 442 mg kg-1 at the head of the basin. Free Cu++ in surface water was several orders of magnitude higher than in sediment porewater. High-resolution data of Cu species together with probability maps presented in this paper will allow managers to easily visualise and localise areas of impaired quality and to prioritise which areas should be targeted to improve Cu-related conditions

Mytilus californianus transplanted as upwelling bioindicators to two areas off Baja California, Mexico

 To study the spatial and temporal variability of bioavailable Cd, mussels (Mytilus californianus) were transplanted from a control zone to two upwelling areas off the northwestern coast of Baja California, Mexico. The mussels were placed at 5 and 15 m depth on buoy systems, at two sites selected for their different upwelling intensity. Punta Banda is characterized by intense upwelling events, with mean monthly temperatures of 13.00 ± 1.83ºC and abrupt drops in temperature to 9.7ºC, whereas upwelling off the Coronado Islands is less intense and mean monthly temperatures are 16.33 ± 2.15ºC, with abrupt drops in temperature to 11.0ºC. Mussel samples were collected regularly during upwelling (April to September) and non-upwelling periods (January to March). Mean Cd concentrations in soft tissue of transplanted mussels were higher at Punta Banda (17.23± 1.89 ∞g g|–1 dry weight) than at Coronado Islands (9.86 ± 1.37 ∞g g–1 dry weight). The analysis of correlation showed that the concentration of Cd in mussels from Punta Banda (r = 0.91) and Coronado Islands (r = 0.75) is related to the Bakun upwelling index. These results suggest that upwelling plays an important role in controlling Cd content in M. californianus from northwestern Baja California. Transplanted mussels proved to be excellent bioindicators of upwelling

Atmospheric input and concentration of dissolved iron in the surface layer of the Gulf of California

A survey was conducted to determine the atmospheric input of particulate iron (Fep) and the factors and processes controlling the concentration and distribution of dissolved iron (Fed) in surface water (200 m) of the central Gulf of California. Atmospheric fluxes of Fep (7.0–90.4 µmol m–2 d–1) were of the same order of magnitude as those reported for the Red Sea (1.5–116 µmol m–2 d–1) and the northeastern Pacific Ocean (24 µmol m–2 d–1), but higher than the fluxes registered for the northwestern Mediterranean Sea (0.25–0.49 µmol m–2 d–1). According to the Fed concentration in surface water, three different zones were identified in the study area: a northern zone with Fed surface enrichment (5.57–7.21 nM) due to atmospheric input, a central zone with dilution of the Fed-enriched surface water by enhanced vertical mixing (0.07–0.59 nM), and a southern zone showing low Fed concentrations (less than 1 nM) due to biological uptake. Two types of vertical profiles were observed: (1) the typical nutrient-like distribution (with low concentrations at the surface and subsequent increase with depth) in the southern zone, and (2) mixed distribution (surface enrichment, decrease at subsurface level, and increase with depth) in the northern zone. The northern profile was 23.5 times more enriched than the adjacent Northeastern Pacific. Results indicate that Fed distribution in the surface layer of the central Gulf of California is controlled by complex interactions involving atmospheric input, biological uptake, and in situ removal-remineralization of particles, coupled with physical transport and vertical mixing

Phosphate balance and spatial variability on the continental shelf off the western US-Mexico border region

 A cruise was conducted along the northwestern coast of Baja California, off the US-Mexico border region, to determine the physical, biological and anthropogenic factors affecting the concentration and distribution of phosphates (PO43–). The vertical distribution of temperature and PO43– showed isograms (13ºC and 0.75 µM, respectively) rising towards the shore. Although this phenomenon was observed in all the study area, it was more abrupt in the southern part than in the northern, resulting in lower phosphate concentrations in the north (0.50 µM) associated with high chlorophyll a concentrations (10.0 mg m–3). A principal components analysis indicated that the PO43– concentrations were related to upwelling (51%) and phytoplankton biomass (23%). A PO43– mass balance indicated that sewage discharge had a very local effect, contributing 3.0 ± 0.12 t d–1 (5%), while horizontal advection contributed 20.0 ± 2.2 t d–1 (32%) and upwelling supply was 41.1 ± 2.3 t d–1 (63%). If the PO43– sewage contribution trend does not change, we predict that in 2035 the anthropogenic contribution will be as high as the amount delivered to the area by the Californian Current. Conversely, if Mexico´ s sewage treatment systems improve to a level similar to that in the USA, we estimate that by 2012 the anthropogenic sources will be insignificant