State of the Bay Report 2010-Final - Anchor Environmental

percentage of mud compared to Langebaan Lagoon. This higher proportion of fine grained particles
enhances the level of trace metals accumulated in the sediments. This is clearly seen at site SB1,
which had the highest mud content and the highest concentrations of trace metals. The benthic
community composition at this site was a clear outlier.
Site SB1 represents an impoverished community with a very low abundance and diversity of
benthic macrofauna (only 4 species and 14 individuals found). This site was also identified as
impoverished in 2008 and 2009, most likely owing to the high concentrations of organic matter and
anoxic conditions within the sediments. This site also has an extremely elevated concentration of
cadmium relative to all the other sites sampled. In addition it has relatively high concentrations of
lead, copper, nickel, organic nitrogen (PON), organic carbon (POC) and mud. Any further distinction
between the other sites sampled in Saldanha Bay according to benthic macrofauna community
composition does not clearly correlate with any of the other environmental variables measured. It is
likely that natural community interactions and possibly other environmental variables not measured
in this report are having an influence on the community composition in Big Bay and Small Bay.
Figure 8.17. MDS of Saldanha Bay and Langebaan Lagoon benthic macrofauna abundance (2010) with
superimposed circles representing depth (Increasing circle size = deeper)
Figure 8.18, Figure 8.17 and Figure 8.19 clearly shows that Langebaan Lagoon is
characterised by shallow water depths, and sediments with low mud, particulate organic carbon,
particulate organic nitrogen compositions and no or very low to negligible concentrations of trace
metals. This suite of abiotic factors clearly correlates with the cluster of Langebaan sites that have
been grouped according to benthic macrofauna community structure. This indicates that this
particular suite of abiotic factors strongly influences the benthic macrofauna communities. More
fine scale differences between the benthic communities within the lagoon are clearly not shaped by
the abiotic variables considered here and it is likely that other factors such as water circulation and
vegetation cover as well as community interactions influence the species composition within the
lagoon.
State of the Bay 2010: Saldanha Bay and Langebaan Lagoon 181