NAMAGROEN EMPR Amendment.pdf - DLIST Benguela

Addendum to EMPR for Concessions 8(a), 9(a) and 8(b) 31sediment suspension, reduced trailing speed, use of underwater pumps to maximise solidconcentration, and/or avoidance of use of draghead water jets (ABP Research 1999).Management actions include avoiding dredging in the immediate vicinity of reefs.Furthermore, under no circumstances are overburden spoils to be dumped on, or in the vicinityof, reef habitats.Target areas to be dredged in Concessions 8(a), 9(a) and 8(b) should preferably be mined tocompletion, and then not be visited for at least five years, to allow communities to recover.The successful coverage of a specific mining area should thus be determined before moving toa new target area. Efficient, high intensity mining methods are thus preferable to repeated,smaller scale operations, provided that the larger scale operations do not cause unacceptableimpact on adjacent sensitive rocky outcrop areas.4.3.2 Chemical Effects of Sediment Resuspension and DepositionThere are several indirect effects of mining associated with sediment disturbance andincreased suspended sediment concentrations in the water column. Marine biogeochemicalprocesses may be affected by mining-induced sediment re-suspension, with potential cascadeeffects through the marine food web.The Namaqualand coastline is frequently exposed to natural hypoxic conditions owing toextremely high primary production and subsequent oxidative degeneration of organic matterbelow the thermocline (Weeks et al. 2004). During the dredging process particulate organicmatter previously associated with the sediments is re-suspended, and both the suspension andthe subsequent re-deposition thereof may lead to further reduction in near-bottom dissolvedoxygen concentrations, thereby aggravating already hypoxic conditions near the seabed (seealso Herrmann et al. 1999). However, in comparison with the high natural organic deposition,and periodic and often extensive low-oxygen events characteristic of the Benguela region, thecontribution by organic material re-suspended and deposited during dredging, and thelikelihood of this resulting in substantial hypoxia or anoxia is negligible. In the highly turbulentnearshore zone, where the surface waters down to ~25 m depth are usually well saturated,mining-induced organic enrichment are not likely to affect near-bottom oxygen concentrations,and the associated impacts are thus of low significance.Several studies have suggested that recently deposited sediments in specific areas on thecontinental shelf off the Southern African West Coast may be characterised by high levels ofheavy metals of marine and/or terrestrial origin (Calvert & Price 1970; Chapman & Shannon1985; Bremner & Willis 1990). The re-suspension of sediments during dredging can releasethese trace metals into the water column. Metal bio-availability and eco-toxicology is complexand depends on the partitioning of metals between dissolved and particulate phases and thespeciation of the dissolved phase into bound or free forms (Paulson & Amy 1993; Rainbow 1995;Galvin 1996). Although dissolved forms are regarded as the most bio-available, many of theseare not readily utilisable by aquatic organisms. Consequently those forms that are ultimatelybio-available and potentially toxic to marine organisms usually constitute only a fraction of thetotal concentration. However, such contaminants have only been occasionally foundassociated with muds. The constant turnover of sediments in the wave-influenced inshoreareas will ensure rapid diluted of any contaminants that may be present, and theirconcentrations in the water column will thus be very low. The impacts associated with therelease of contaminants from disturbed sediments is therefore considered of low significance.Namagroen Prospecting & Investments October 2008