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Wednesday 24 April 2019
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Marine life recovers faster after phosphate dredging.

Unlike previous publications surrounding the dredging of marine phosphate, and its impact on the ecosystem on benthic. Most speculations has been hinged on the issue that marine life cannot recover after dredging.  The speculation is not true, because if you ask the Ministry of Fisheries and Marine Resources you will realise that the method of harvesting shell fish for more than 100 years on the shelf of Namibia has been dredging. Now if the ocean has been dredged off coast Namibia and today marine life is flourishing that in itself proves that dredging is not environmentally damaging as speculated.  Although the rate of recovery subsequent to dredging varies with habitat and sediment type, composition of the resident biological assemblage, and hydrodynamic attributes of the environment. Hence the method and management of the dredging operations are some of the factors, along with the use of sound practices, often mitigate impacts and accelerate ecological recovery of the benthic. In this light there is a strong evidence that phosphate dredging unlike fishing which is an annual dredging activity will have minimal environmental impact on the benthic. The scenario being that phosphate dredging is not a repetitive procedure unlike fishing method that has continuously dredged the same area continuously for more than 100 years.  It’s also important to note that dredging around the world is active apart from marine sand and gravel, phosphate is another mineral resource which has the potential to be exploited from the sea on a grand scale. Phosphate is mainly used as a feedstock for fertilizer production. Massive quantities are mined in West Africa and Tunisia, from where it is exported to many different countries. The importation and long-haul sea transportation are relatively expensive for distant nations, which would consequently prefer to make use of the marine resources off their own coasts.

Many research studies have examined the physical, biological and chemical effects of mechanical and hydraulic dregding on seafloor habitats. Field experiments have compared a variety of dredges, locations, substrates, and habitats at differing spatial and temporal scales. Understanding the effects of dredging requires knowledge of the gear-specific impacts on differing habitat types, the frequency and geographic extent of harvest disturbance, and the biological and physical attributes of affected habitats (Steele et al. 2005).  Although dredging initially disturbs benthic habitat, the rate and extent of ecological recovery vary widely. Although efficiency of mechanized dredging has been well described, the ecological effects on the benthic community are not as thoroughly understood (Thrush and Dayton 2002). Hence companies like Namibia Marine Phosphate may generate the data during the test mining.

Fisheries shell fish dredgers
Impacts of shellfish dredging can be contradictory when certain effects have both beneficial and detrimental consequences within the benthos (Dorsey and Pederson 1998). For example, while dredging may initially damage certain organisms, others, including scavengers and opportunistic predators, benefit by feeding on exposed prey or by colonizing newly exposed bottom surfaces (Rheault 2008). These complex factors have contributed to the variety of conflicting viewpoints associated with dredging impacts. Hence this is a similar process to phosphate dredging.  Fisheries dredgers vary in design, dimensions, and weight depending on target species, sediment type, and whether they are harvesting infauna or epifauna. Mechanical or dry dredges scrape the seafloor, while hydraulic dredges use pressurized water systems to first loosen sediments (Hawkins 2006).

Who is currently dredging the ocean ?Sand, gravel and phosphate from the sea
Europe’s second largest consumer of marine sand after the Netherlands is Great Britain. That nation used almost 12 million cubic metres in 2011, plus nearly 7 million cubic metres of gravel. Approximately 80 per cent of both products are used to manufacture concrete, particularly for construction work carried out in London and in southern parts of England. No other nations regularly extract sand and gravel to such an extent. However, in individual cases, large amounts are indeed needed for building projects such as the expansion of Hong Kong airport and the port of Singapore. What is more, despite the ready availability of desert sand, marine sand is also used to construct artificial islands such as the Palm Islands of Dubai. This is because the rounded grains of ocean sand are better for concrete production than the angular grains taken from the desert. Marine sand and gravel are used mainly where no suitable deposits can be found onshore. This is the case in both southern England and the Netherlands.
However, because it is generally substantially more costly to remove them from the sea, onshore deposits tend to be preferred worldwide. Sand and gravel are extracted by ships constructed specially for this purpose, which suck them from the ocean floor using a large pipe. This process is known as suction dredging. The pipes are up to 85 metres long and can have a diameter of up to 1 metre. As a rule, the dredging areas are around 3 kilometres long and several hundred metres wide. There are two different dredging processes. The first is static suction dredging during which the ship lies at anchor as it sucks up sand from a single spot. This produces pits of up to 10 metres in depth. The second process involves the ship pulling a suction pipe with a draghead behind it and slowly following a route through the dredging area. This method of material extraction removes a layer of sand 25 to 50 centimetres thick from the sea floor. The extent of the damage and destruction that is inflicted upon marine habitats by the large-scale extraction of sand and gravel has long been a subject of heated discussion.

Proof dredged marine can recover
Since the start of the new millennium, therefore, a whole raft of biological studies has been carried out with the aim of assessing the impact of suction dredging on the marine environment. These investigations have shown that dredging does indeed have an impact, but have also revealed that such effects are limited to relatively small areas. An English study, for instance, proved that after 25 years of sand dredging, an area needs about 6 years to completely repopulate. In an area dredged for only a brief period or just once, the original conditions are already restored after 1 or 2 years. A Dutch study even concluded that 2 years after dredging sand to expand the port of Rotterdam the fish biomass in the dredged area increased substantially.

Why this is, is unclear.
What is certain, however, is that extraction does change the composition of the seabed sediments. When gravel or coarse-grained sand is removed, the sites afterwards often fill with finer sand which is washed in by the current. Fine-grained areas attract different sea dwellers than coarse-grained areas. However, as relatively small areas covering only a few square kilometres are dredged, the studies conclude that there can be no question of major habitat change. Apart from sand and gravel, phosphate is another mineral resource which has the potential to be exploited from the sea on a grand scale. Phosphate is mainly used as a feedstock for fertilizer production. The importation and long-haul sea transportation are relatively expensive for distant nations, which would consequently prefer to make use of the marine resources off their own coasts like Namibia. There are thus plans to mine phosphate at Chatham Rise, a submarine ridge off the east coast of New Zealand. Although this is an issue of Environmental Management debate in Namibia.

Way for forward
Namibian government should allow NMP to dredge the sea floor in order to be used as an experimental ground in order to collect data that can be used in future for decision making. Hence, Impacts are often assessed by conducting experimental dredging and measuring the benthic community response.

Data are compared before and after disturbance, against an undisturbed control site, or by comparing experimental results to historical data for that area (Watling and Norse 1998; Johnson 2002; Løkkeborg 2005). There is need for a multi- sectoral  monitoring by both Ministries (Environment and Fisheries) during the experimental period while NMP will be dredging the ocean floor for phosphate.  The studies of dredging in Europe has shown that there is strong proof that marine ecosystem can recover backed by good environmental Management. In the case of NMP it has pledged its highest accountability to protect the environment in its EMP submitted to the Ministry of Environment and Tourism.  In comparison to fisheries dredging the ocean floor has never been subject to submit EMP in regard to seabed trawling of shell fish.
In fact may be its time Ministry of Fisheries educate the public how marine life has not been disturbed after dredging for shell fish. Such methods used to avoid disturbances could be used during phosphate dredging. Because both methods are the same. Its up to the nation to see the resource interest, because when an area is demarcated as mining no fishing is allowed. In conclusion this area where NMP will operate will allow fish stock to flourish because it won’t be fishing ground.




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