What kind of environmental impacts can we expect from the dredging operations of the phosphate sands and will it affect tourism and whale watching?
Dredging of phosphate sands by Trailer Suction Hopper Dredger will have a strictly local effect on the seabed biology under the immediate path of the dredge-head (‘draghead’) within an active dredge zone of up to 3km in length and about 300m in width. The dredging vessel and associated ore-processing vessel will be operating at a distance of about 23 km from the coast and will not be visible from the shoreline. There will be no visual effects that might intrude on the amenities of the adjacent coastline, neither will there be shore-based facilities which might affect the Leisure & Tourism industry of the Baja California Sur area.
Will the turtles and whales be threatened or injured by the dredging?
The protection of whales and turtles is a priority for any infrastructure project in the California Sur area. Pacific gray whales (Eschrichtius robustus) have calving areas within the coastal lagoons far outside any impacts of dredging. Dredging at the “Don Diego” site will also not affect the north-south migration routes of other whale species. The humpback whale (Megaptera vaeangliae) migrates close to the shore whilst the blue whale (Balaenoptera musculus) migrates well to the west of any potential impacts of dredging.
The protection of turtles (particularly the loggerhead turtle Caretta caretta) is also a high priority for the design and operation of dredging at the “Don Diego” site. Losses of turtles are of serious concern in Mexico, and have been mainly attributed to ‘by-catch’ from fishing as well as possibly more complex environmental factors. Whatever the causes of current turtle mortality, Exploraciones Oceánicas is committed to active prevention and monitoring of any impacts on the occasional turtles that may occur at the dredge site. Given the depth at which the site is located (60-90 meters) and the fact that turtles need to come up to the surface in order to breathe, almost no turtles have been spotted in the dredging area. They are not normally found at such depths.
It should be pointed out that few turtles spend a significant time on the seabed at 80 meters depth compared with the shallow coastal deposits to the east where light penetration and associated biological communities are favorable as turtle feeding areas. Nevertheless well-tried turtle exclusion devices (‘tickler chains’) and deflection equipment on the draghead, as well as rigorous management of dredging operation forms an integral part of the dredging operation. These measures are proven to keep losses of turtles by ‘entrainment’ into the draghead to an absolute minimum in shallow waters elsewhere worldwide where turtle densities are high. By way of comparison, turtle losses by entrainment in shallow water maintenance dredging operations are recorded as less than 5 turtles per year in the USA, and this is to be compared with estimated losses attributed to fishing by-catch amounting to several thousand per year. The effectiveness of turtle exclusion devices and deflection equipment will be rigorously monitored and any entrainment of individual turtles will be recorded and reported as part of the proposed monitoring procedure specified in the dredging proposal.
Will you release chemicals or foreign substances into the ocean?
Material dredged from the seabed contains a mixture of phosphate sands and other material including silica sands, shells and fine silty material. The dredged deposits will then be separated by strictly mechanical means using sieves and water (hydrocyclones) to obtain a more concentrated ore cargo. Residual non-phosphate material will be returned to the seabed through so-called ‘green valves’ located in the lower hull of the processing vessel. This ensures that any plume of material settling to the seabed disperses below the surface waters where primary production by the plant cells (phytoplankton) occurs. No chemicals are used in the mechanical extraction process, and the material returned to the seabed is strictly the original seabed deposits from which phosphate rich component sands have been extracted mechanically.
What parts of the world currently use these same dredging methods and what have been their experiences?
Trailer suction hopper dredging (TSHD) similar to that which is proposed for the “Don Diego” site has been carried out for many decades elsewhere worldwide for aggregate extraction, capital dredging and maintenance dredging. In Mexico alone, more than 220 dredging projects of this kind have taken place. The UK is the second largest aggregate producer after Japan and invested a sum in excess of $50 million between 2002 and 2011 on a major research program to study the impacts of TSHD on the marine environment, and how impacts can be managed and minimized. This program was funded through the UK Government Department of Environment, Food and Rural Affairs and was supported through a levy on the aggregates industry known as the ‘Aggregate Levy Sustainability Fund (ALSF)’.The results and experience from this program have been brought to bear in the design and interpretation of data relevant to the “Don Diego” dredge site.
The nature and scale of potential impacts of TSHD, and the rates or recovery of biological resources on the seabed are well-understood and fully reported in the international literature. They have also recently been summarized in a book ‘Aggregate Dredging and the Marine Environment: An overview of recent research and current industry practice’ (Newell & Woodcock, 2013). This work shows that the physical ‘footprint’ of aggregate dredging is generally less than 3 km from the point of discharge of excess material from the dredger, and that the biological impact is confined to this zone. It is has been shown that recolonization and recovery of biological communities can occur rapidly in fine sands and muds (for review, see Newell et al., 1998; Foden et al., 2009). A recovery time of 2-3 years is not uncommon for sandy deposits, and in some cases significant recolonization can take place within months of dredging cessation.
Will the project affect the local fishing industries?
The dredge site is well outside any of the fishing concession areas that are located along the coastline of Baja California Sur. There are very few seabed resources that comprise a significant food source for demersal (bottom dwelling) fish and the area is of low value for fishing. There will be no impact on local fisheries from the proposed dredging operation at the “Don Diego” site.
Is there much vegetation and sea dwelling creatures where the phosphate is?
All vegetation is dependent on light for active photosynthesis to occur. Light is rapidly absorbed by seawater and rarely penetrates to depths of more than 30 meters, even in clear oceanic waters such as occur at the “Don Diego” site. This means that the only places where plant life can thrive is in the upper 30 meters of water which is known as the ‘Euphotic Zone’. Below this the waters are dark and there is no plant life. The waters at the “Don Diego” site are at a depth of between 60 and 90 meters – at which light penetration is minimal and there is therefore no plant life on the seabed.
There are, however, seabed animals that can occur in abundance in deeper water deposits. These animals are all dependent on dead material settling to the seabed from the plant and animal life in the surface waters, and from material (including small animals) in the water column. In the case of the “Don Diego” deposits, the phosphatite sands have a texture which appears to be unsuited to support the burrowing animals that live on the seabed. There is a community of small oligochaete and polychaete worms and also nematode worms that colonize the superficial muddy sand, but surveys of the area suggest that the deposits of phosphate-rich material are unsuited to supporting a rich community of animals.
Will the existing flora and fauna recover after the dredging and if so in how long a time period?
The rates of recovery of the community in seabed deposits following dredging have been well-studied worldwide. As a generalization, fine deposits (such as occur at the “Don Diego” site) support a relatively low biodiversity of animals that are capable of rapid recolonization and recovery. These communities are known as ‘opportunistic’ species that can rapidly colonize a habitat that has been vacated by other species – such as occurs under the path of a dredge area).
Based on the type of community recorded from the surface deposits at the “Don Diego” site, and the type of silty sand that occurs at the site, studies elsewhere worldwide suggest that a major recovery of biodiversity is likely to occur within months of cessation of dredging. Some of the larger mollusk species would take longer to recolonize and grow to maximal size, so for this reason we have made a conservative estimate of 2-3 years for full recovery to take place.
Will the dredging release any toxic elements that might affect the environment?
Detailed analyses of the chemistry of the seabed deposits has been carried out at part of the science base that underpins the EIA for this project. Part of the analytical work was aimed at establishing whether there is any possibility of chemical components in the dredged material being released into the water column following separation and processing of the deposits.
The ecotoxicology tests show that the elements found in the sands to be dredged are not dissolved in the water when the dredger is used to extract the sands. The results show that there is no significant release of contaminants from the dredged material during any of the processing stages.