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

State of Saldanha Bay & Langebaan Lagoon 2011
Executive Summary
the fish factories and faecal waste from the mussel rafts. Accumulation of organic waste, especially
in sheltered areas where there is limited water flushing, can lead to anoxic conditions and negatively
impact on the marine environment as has been seen from the species composition and abundance
of the benthic communities inhabiting the sediments in the affected areas. Data collected between
1999 and 2011 indicate generally low organic matter concentrations occurring in Saldanha Bay,
except at the Yacht Club Basin, Multipurpose Terminal and the Mussel Farm sites. Organic levels
should thus continue to be monitored on a regular basis, especially in Small Bay.
Contaminants (metals and toxic pollutants) are commonly associated with fine sediments
and mud. In areas of the bay where fine sediments tend to accumulate, these contaminants
sometimes exceed acceptable threshold levels. This is believed to be due either to naturallyoccurring
high levels of the contaminants in the environment (e.g. in the case of cadmium) or due to
impacts of human activities (e.g. lead, copper and nickel associated with ore exports). While such
trace metals are generally biologically inactive when buried in the sediment, they can become toxic
to the environment when re-suspended as a result of mechanical disturbance. On average, the
concentrations of all metals were highest in Small Bay, lower in Big Bay and below detection limits in
Langebaan lagoon. Following the major dredging event in 1999, cadmium concentrations in certain
areas in Small Bay exceeded internationally accepted safety levels, while concentrations of other
trace metals (e.g. lead, copper and nickel) approached threshold levels. Subsequent to this time,
there have been a number of smaller spikes in trace metal levels, mostly as a result of dredging
operations. For example, trace metals in the entrance to Langebaan Lagoon were significantly
elevated in 2011 following dredging operations that were conducted as part of the expansion of the
Naval Boat Yard in Salamander Bay. Currently, trace metal levels are well within safety thresholds at
most sites owing to the fact that fine sediments, along with the associated contaminants, have
either been flushed out of the bay or have been reburied. Key areas of concern regarding heavy
metal pollution within Small Bay include the Yacht Club basin and the multipurpose terminal where
levels of cadmium, copper and lead are still in excess of internationally-accepted guidelines. Regular
monitoring of trace metal concentrations is strongly recommended to provide an early warning of
any future increases.
Hydrocarbons measured in the sediments of Saldanha Bay in 1999 were reported to be very
low and not considered an environmental risk. No poly-cyclic, poly-nuclear compounds or pesticides
were detected in sediments of Saldanha Bay. Sediment samples from the vicinity of the ore terminal
were collected and tested for hydrocarbon contamination again in 2010 and 2011. The total
petroleum hydrocarbon contamination for all sites, with the exception of one in 2010, fell below the
level where toxic effects on marine organisms is expected (the latter site fell exactly on this limit).
Hydrocarbons are thus not considered to be of major concern at present, but it is recommended
that petroleum hydrocarbons in the vicinity of the ore terminal continue to be monitored in future.
Aquatic macrophytes (eelgrass and saltmarshes)
Three distinct intertidal habitats exist within Langebaan Lagoon: seagrass beds, such as those of the
eelgrass Zostera capensis (a type of seagrass); saltmarsh dominated by cordgrass Spartina maritime
and Sarcocornia perennis; and unvegetated sandflats dominated by the sand prawn, Callianassa
krausii and the mudprawn Upogebia capensis. Eelgrass and saltmarsh beds are extremely important
as they increase habitat diversity in the lagoon, provide important an food source, increase sediment
stability, provide protection to juvenile fish and invertebrates from natural predators and generally
support higher species richness, diversity, abundance and biomass of invertebrate fauna compared
to unvegetated areas. Eelgrass and saltmarsh beds are also important for waterbirds which feed
directly on the shoots and rhizomes, forage amongst the leaves or use them as roosting areas at high
tide. Recent studies show that the aerial extent of seagrass beds in Langebaan Lagoon has declined
by an estimated 38% since the 1960s, this being more dramatic in some areas than others (e.g.
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