State of the Bay Report 2011-Final.pdf - Anchor Environmental

State of Saldanha Bay & Langebaan Lagoon 2011
Water quality
4.4 Summary of Water Quality in Saldanha Bay and Langebaan Lagoon
There are no long term trends evident in the water temperature, salinity and dissolved oxygen data
series that solely indicate anthropogenic causes. In the absence of actual discharge of industrially
heated sea water into the Bay, water temperature is unlikely to show any change that is discernable
from that imposed by natural variability. Admittedly there is limited pre-development data (pre
1975), so although it is conceivable that construction of the causeway and ore/oil Terminal has
impeded water flow thus increasing residence time and increasing water temperatures, salinity and
likely decreasing oxygen concentration, particularly in Small Bay, there is little data to support this.
Given that cold, nutrient rich water influx during summer is density driven; dredging shipping
channels could have facilitated this process which would be evident as a decrease in water
temperature and salinity and an increase in nitrate and chlorophyll concentrations. Once again
there is little evidence of this in the available data series. Natural, regional oceanographic processes
(wind driven upwelling or downwelling and extensive coast–Bay exchange) rather than internal,
anthropogenic causes, appear to remain the major factors affecting physical and chemical water
characteristics in Saldanha Bay. The construction of physical barriers (the iron ore/oil Terminal and
the Marcus Island causeway) do appear to have changed current strengths and circulation within
Small Bay, resulting in increased residence time (decreased flushing rate), enhanced clockwise
circulation and enhanced boundary flows. There has also been an increase in sheltered and semisheltered
wave exposure zones in both Small and Big Bay subsequent to harbour development.
The microbiological monitoring program provides evidence that while many of the
monitoring sites in Small Bay still have faecal coliform counts in excess of the safety guidelines for
both mariculture and recreational use, there is a trend of improving compliance at many sites for
which the relevant authorities should be commended. However, the situation in Small Bay remains
a concern, with many sites exceeding levels for safe recreational activities. Given the current
importance and likely future growth of both the mariculture and tourism industries within Saldanha
Bay, it is imperative that whatever efforts have been taken in recent years (e.g. upgrading of sewage
and storm water facilities to keep pace with development and population growth) to combat
pollution by faecal coliforms in Small Bay should be increased and applied more widely. Continued
monitoring of bacterial indicators (intestinal Enterococci in particular), to assess the effectiveness of
adopted measures, is also required and should be undertaken at all sites on a bimonthly basis.
Large volumes of ballast water are discharged into Saldanha Bay on an annual basis. This
poses an enormous risks in respect of the introduction of alien species as well as contaminants in the
ballast water (trace metals, E. coli, etc.). Compliance with ballast water treatment requirements
(e.g. open ocean exchange, on-board treatment systems) designed to minimize the risks of alien
introductions should be rigorously enforced and voluntary compliance with any additional measures
strongly encouraged.
Data supplied by the Mussel Watch Programme (DEA) and mariculture operators in Saldanha
Bay suggest that concentrations of trace metals are high along the shore (particularly for Lead near
the multipurpose quay) and frequently or even consistently (in the case of Lead) above published
guidelines for foodstuff, concentrations offshore are clearly much lower and less of a concern. High
concentrations of trace metals along the shore is very clearly of concern and points to the need for
management intervention that can address this issue as it poses a very clear risk to the health of
people harvesting mussels from the shore. Regrettably no new data have been available from this
programme since 2007.
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