State of the Bay Report 2010-Final - Anchor Environmental

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AOU (ml/l) AOU (ml/l) 5 4 3 2 1 0 -1 -2 -3 -4 2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 -2.5 -3 -3.5 Increasing oxygen deficit Oct-79 Jul-79 Apr-79 Jan-79 Sep-78 Jun-78 Mar-78 Dec-77 Oct-77 Aug-77 Jun-77 Mar-77 Dec-76 Sep-76 Jun-76 Mar-76 Jan-76 Oct-75 Jul-75 Apr-75 Mar-75 Feb-75 Jan-75 Dec-74 Oct-74 Sep-74 Aug-74 Jul-74 May-74 Apr-74 Oct-79 Jul-79 Apr-79 Jan-79 Sep-78 Jun-78 Mar-78 Dec-77 Oct-77 Aug-77 Jun-77 Mar-77 Dec-76 Sep-76 Jun-76 Mar-76 Jan-76 Oct-75 Jul-75 Apr-75 Mar-75 Feb-75 Jan-75 Dec-74 Oct-74 Sep-74 Aug-74 Jul-74 May- Apr-74 Small Bay Big Bay Anchor Environmental Figure 5.4. Apparent oxygen utilization (AOU) time series Small Bay and Big Bay, Saldanha Bay. (Note: Positive values in red indicate an oxygen deficit). There is no clear trend evident in the AOU time series, low oxygen concentrations (high AOU values) occur during both winter and summer months (Figure 5.4). Small Bay does experience a fairly regular oxygen deficit during the winter months, whilst Big Bay experiences less frequent and lower magnitude oxygen deficits. Monteiro et al. (1990) attributed the oxygen deficit in Small Bay largely to anthropogenic causes, namely reduced flushing rates (due to the causeway and ore jetty construction) and discharges of organic rich effluents. The most recent data (September 1999- February 2000) indicate a persistent and increasing oxygen deficit as summer progresses (Figure 5.4). It is clear that oxygen levels within Small Bay are very low during the late summer months, State of the Bay 2010: Saldanha Bay and Langebaan Lagoon 90 Oct-82 Jul-82 Apr-82 Jan-82 Oct-81 Jul-81 Apr-81 Jan-81 Oct-82 Jul-82 Apr-82 Jan-82 Oct-81 Jul-81 Apr-81 Jan-81 Jul 88 Feb-00 Jan-00 Dec-99 Nov-99 Oct-99 Sep-99 Jul 88
Anchor Environmental likely as a result of naturally occurring conditions, however, the ecological functioning of the system could be further compromised by organic pollutants entering the Bay. There is evidence of anoxia in localised areas of Small Bay (e.g. under the mussel rafts, within the yacht basin) that is caused by excessive organic inputs. Monteiro et al. (1997) identified the effluent from a pelagic fish processing factory as the source of nitrogen that resulted in an Ulva seaweed bloom in Small Bay. 5.4 Currents and waves Circulation patterns and current strengths prior to the development (1974-75) in Saldanha Bay were investigated using several techniques (drogues, dye-tracing, drift cards and sea-bed drifters). Surface currents (within the upper five meters) are complex and appeared to be dependent on wind strength and direction as well as the tidal state. Within Small Bay, currents were weak (5-15 cm.s -1 ) and tended to be clockwise (towards the NE) irrespective of the tidal state or the wind (Figure 5.5A). Greater current strengths were observed within Big Bay (10-20 cm.s -1 ) and current direction within the main channels was dependent on the tidal state (Figure 5.5A). The strongest tidal currents were recorded at the mouth of Langebaan Lagoon (50-100 cm.s -1 ), these being either enhanced or retarded by the prevailing wind direction (Figure 5.5A). Currents within the main channels in Langebaan Lagoon were also relatively strong (20-25 cm.s -1 ). Outside of the main tidal channels, surface currents tended to flow in the approximate direction of the prevailing wind with velocities of 2-3 % of the wind speed (Shannon and Stander 1977). Current strength and direction at 5 m depth was similar to that at the surface, but was less dependent on wind direction and velocity and appeared to be more influenced by the tidal state. Currents at 10 m depth at the mouth of the Bay were found to be tidal (up to 10 cm. s -1 , either eastwards or westwards) and in the remainder of the Bay, a slow (5 cm.s -1 ) southward or eastward movement, irrespective of the tidal state, was recorded. The currents and circulation of Saldanha Bay subsequent to the construction of the Marcus Island causeway and the iron ore/oil jetty were described by Weeks et al. (1991a). Historical data of drogue tracking collected by the Sea Fisheries Research Institute during 1976-1979 were analysed in this paper. This study confirmed that wind is the primary determinant of surface currents in both Small Bay and Big Bay; although tidal flows do influence currents below the thermocline and are the dominant forcing factor in the proximity of Langebaan Lagoon. Weeks et al. (1991a) noted that because much of the drogue tracking was conducted under conditions of weak or moderate wind speeds, the surface current velocities measured (5-20cm.s -1 ), were probably underestimated. The authors concluded that the harbour construction had constrained water circulation within Small Bay, enhancing the general clockwise pattern and increasing current speeds along the boundaries, particularly the south-westward current flow along the iron ore/oil jetty (Figure 5.5B). More recent data collected during strong NNE wind conditions in August 1990 revealed that greater wind velocities do indeed influence current strength and direction throughout the water column (Weeks et al. 1991b). These strong NNE winds were observed to enhance the surface flowing SSW currents along the ore jetty in Small Bay (out of the Bay), but resulted in a northward replacement flow (into the Bay) along the bottom, under both ebb and flood tides. The importance of wind as the dominant forcing factor of bottom, as well as surface, waters was further confirmed by Monteiro and Largier (1999) who described the density driven inflow-outflow of cold bottom water into Saldanha Bay during summer conditions when prevailing SSW winds cause regional scale upwelling. State of the Bay 2010: Saldanha Bay and Langebaan Lagoon 91
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State of the Bay 2010: Saldanha Bay
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TABLE OF CONTENTS Anchor Environmen
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11 BIRDS 234 Anchor Environmental 1
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LIST OF FIGURES Anchor Environmenta
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Anchor Environmental Figure 4.27. O
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Anchor Environmental Figure 7.3. Ch
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Anchor Environmental Figure 9.10. C
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Anchor Environmental Figure 12.1. N
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Anchor Environmental samples were c
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EXECUTIVE SUMMARY Anchor Environmen
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Anchor Environmental matter in the
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Anchor Environmental considered mos
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Anchor Environmental again in 2004,
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Anchor Environmental Populations of
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GLOSSARY Alien species An introduce
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1 INTRODUCTION Anchor Environmental
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2 STRUCTURE OF THIS REPORT Anchor E
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Anchor Environmental complicates ma
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Page 41 and 42: Anchor Environmental 4 ACTIVITIES A
Page 43 and 44: Fish factories Small craft harbour
Page 45 and 46: Anchor Environmental Aerial photogr
Page 47 and 48: Anchor Environmental interferes wit
Page 49 and 50: Anchor Environmental Figure 4.7. Nu
Page 51 and 52: o Decrease in oxygen concentrations
Page 53 and 54: Anchor Environmental Upgrades to th
Page 55 and 56: Anchor Environmental Figure 4.9. A)
Page 57 and 58: Anchor Environmental (possibly link
Page 59 and 60: Anchor Environmental Prestedge Reti
Page 61 and 62: Anchor Environmental the constructi
Page 63 and 64: Number and types of vessels enterin
Page 65 and 66: Anchor Environmental is contained b
Page 67 and 68: Anchor Environmental include the be
Page 69 and 70: o 33 3’S o 33 10’S Saldanha Bay
Page 71 and 72: Anchor Environmental (1956) UNDER T
Page 73 and 74: Free ACtive Chlorine (mg/l) Amonia
Page 75 and 76: Faecal coliforms (org/100 ml) Chemi
Page 77 and 78: 4.3.7 Storm water Anchor Environmen
Page 79 and 80: Anchor Environmental sites (concent
Page 81 and 82: Anchor Environmental Discharges fro
Page 83 and 84: Anchor Environmental Table 4.9. Det
Page 85 and 86: 5 WATER QUALITY Anchor Environmenta
Page 87 and 88: Anchor Environmental Stander (1977)
Page 89: Anchor Environmental coast, result
Page 93 and 94: Anchor Environmental Construction o
Page 95 and 96: Anchor Environmental Table 5.2. Per
Page 103 and 104: Counts per 100ml of sample Counts p
Page 105 and 106: Counts per 100ml of sample 10000 10
Page 107 and 108: 5.6 Trace Metal Contaminants in the
Page 109 and 110: State of the Bay 2010: Saldanha Bay
Page 111 and 112: Lead(mg/kg) Mercury (mg/kg) Cadmium
Page 113 and 114: 6 SEDIMENTS 6.1 Sediment particle s
Page 115 and 116: 6.1.2 Sediment Particle size result
Page 119 and 120: 100% 90% 80% 70% 60% 50% 40% 30% 20
Page 125 and 126: % POC 18 16 14 12 10 8 6 4 2 0 % PO
Page 127 and 128: Percentage Percentage 1.8 1.6 1.4 1
Page 129 and 130: o 33 3’S o 33 10’S Yacht Club B
Page 131 and 132: Figure 6.12. Variation in the conce
Page 133 and 134: The concentrations of metals in sed
Page 135 and 136: concentrations are 56 and 29 times
Page 137 and 138: threshold of 1.2 mg/kg established
Page 139 and 140: Cadmium (mg/kg) 8 7 6 5 4 3 2 1 0 C
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Copper (mg/kg) 45 40 35 30 25 20 15
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16000 14000 12000 10000 8000 6000 4
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In summary, elevated trace metal co
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6.5 Summary of sediment health stat
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7.1 Long term changes in seagrass i
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7.2 Long term changes in Saltmarshe
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Figure 8.1. Benthic macrofauna samp
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Table 8.1. Depth at each of the sit
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these species usually provide the l
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(clustering of similar groups) (Meg
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The Big Bay samples BB 25 and BB29
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2007/08 dredging. Other signs of th
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Wet mass per m² Wet mass per m² 4
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Big Bay Crustaceans and polychaetes
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Average number of individuals per m
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Number Individuals per m² Number I
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8.4.2 Abundance Biomass Indices 8.4
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and percentage organic nitrogen (PO
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Table 8.5. W statistics at all stat
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Figure 8.15: Variation in the diver
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percentage of mud compared to Lange
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Cu (mg/kg) Cd (mg/kg) Ni (mg/kg) Pb
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contaminants. Furthermore dredging
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areas even 5 months after the clear
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Brittle star ( Ophiuroidea spp) Sea
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9.2 Approach and Methodology 9.2.1
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cover data for both mobile and sess
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9.2.3 Data Analysis The similaritie
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40%, co-occurring with sponges espe
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stands of the kelp Ecklonia maxima
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Plocamium spp. Ecklonia maxima Scut
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20 40 A Group 1 B 60 Similarity C G
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Percentage Cover 80 70 60 50 40 30
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Evenness Shannon Wiener 0.9 0.8 0.7
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2005 2008 2009 2010 Dive School Jet
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Table 9.5. Results from the SIMPER
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In general, the inter-annual differ
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The temporal distribution of M. gal
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Consistent with the previous years,
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Saldanha and Langebaan. Results fro
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The average abundance of the four m
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Anchor Environmental Figure 10.5. A
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Anchor Environmental Figure 10.7. A
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Anchor Environmental Within Big Bay
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Anchor Environmental 2008 and 2009
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Anchor Environmental the islands, b
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Anchor Environmental at Saldanha ar
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their main prey species, sardines a
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Anchor Environmental 2009). The eff
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Anchor Environmental attributed to
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Number of breeding pairs 800 700 60
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11.3 Birds of Langebaan Lagoon 11.3
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Anchor Environmental Figure 11.11.
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Anchor Environmental for the gannet
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Taxon Anchor Environmental Occurren
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Taxon Anchor Environmental Occurren
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Anchor Environmental 13 MANAGEMENT
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Anchor Environmental their operatio
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Anchor Environmental concentrations
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Anchor Environmental changes that p
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Anchor Environmental and slight imp
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Birdlife International. 2010. URL w
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Anchor Environmental penguins Sphen
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Anchor Environmental Game, E.T., Gr
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Anchor Environmental Kerwath, S. E.
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Anchor Environmental Moldan, A. 197
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Anchor Environmental Robinson, T.B.
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Anchor Environmental Tunley KL, Att
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