State of the Bay Report 2010-Final - Anchor Environmental

State of the Bay 2010: Saldanha Bay and Langebaan Lagoon
Anchor Environmental
reduced production of mussels in the Bay during the course of 2009 (see section §4.2 for more
details on this). The noticeable decline in POC at the Yacht Club basin over the decade is
encouraging and may indicate recovery of sediment health at this site. In addition, POC levels
recorded in 2010 at the Channel end of the ore jetty, North Channel small bay and Big Bay are lower
than in 2009, and are close to those measured prior to development. This is indicative of improved
environmental health.
No historical percentage organic nitrogen (PON) data were attainable for the purposes of
this report, however, data from 1999 to 2009 of the PON measured at selected sites within Small
and Big Bay indicates that the highest levels of organic nitrogen in Saldanha Bay were recorded at
the Yacht Club basin and near the Mussel rafts (Figure 6.9). This is predicted to be as a result of fish
factory waste discharge and faecal waste accumulating beneath the mussel rafts. The
concentrations of PON in the sediments of the Yacht Club basin and Multi-purpose Quay have
increased steadily over the last decade, which indicates long term deposition of nitrogen-rich
matter. Only in the 2009 survey was a reduction in PON observed at the Yacht Club basin. This site
has also shown a reduction in mud content as well as POC content, suggesting improved health of
the sediments possibly linked to increased flushing or water movement. The nitrogen content of the
sediments at all other sites remained fairly constant between 2008 and 2009. Sources of organic
nitrogen in Small Bay include fish factory wastes, biogenic waste from mussel and oyster culture,
sewage effluent from the waste water treatment works and leaking of sewage from septic tanks.
The high organic loading at these sites has had a detrimental impact on marine benthic fauna as is
evident from the macrofauna survey results (see §8). An increase in the organic loading of the
sediments generally results in hypoxic conditions, which are unsuitable for most life forms.
A slightly elevated concentration of organic content in the sediments in Salamander Bay was
noted in July 2010 following the dredging of the shallow subtidal zone for the construction of the
boat park (Robinson 2010). The results of the 2010 State of the Bay survey indicated that there were
no notable increases in the percentage POC or PON in the sediments at sites BB29 or LL38 (closest
sampled sites to Salamander Bay) between 2009 and 2010 (Figure 6.10). This suggests that the
impact of the dredging on the organic content of the sediments was limited to a small area.