Seabed Mining

Impacts from seabed mining fall into two categories, biological and physical.

Physical: Benthic and Erosionary Impacts

Go down to the beach and dig a hole in the wet sand. It doesn’t take long for other sand to replace it. Applied on a large scale, the principle will be the same. Seabed mining sites drag sand to infill themselves, that might otherwise form part of existing, sustainable sand movements. The complex erosionary tendencies and pressures created by removing any large volumes of sand from an inshore area are barely understood by the few so called experts in the field, and much debate still rages over the various models of sand movement proposed.

The Pakiri case study is a classic local example of dissent between parties, yet clearly the beach changed since the introduction of seabed sand mining. KASM believes, large scale mining of the Tasman seabed will cause increased coastal erosion both up and downstream from where any mining takes place. Erosion is already rife on the West Coast. Port Waikato has lost 20 metres of dunes in the last 20 years. The cliffs of South Taranaki have been receding dangerously for many years. Marokopa has fought a long battle to maintain a dune system that protects its river estuary.

In the case of the West Coast Ironsands, there is no precedent anywhere in the world to match these proposals in scale. Any speculation by related parties about how much erosion would be created by any of the various proposals would be just that; speculation.

Anecdotal evidence from existing seabed mining operations suggests far higher levels of damage than predicted. This is where the supporting science is at its weakest, exacerbated by the dynamic nature of this particular marine environment.

At risk from erosion is a fantastic coastline, stacked with some of NZ’s most loved, and commercially valuable surf-breaks, plus a host of spectacular swimming beaches that are slowly gaining the recognition they deserve.

This reef break north of Aotea Harbour requires proper sand formation for optimum wave shape
This reef break north of Aotea Harbour requires proper sand formation for optimum wave shape
Taranaki Foodweb

Biological Impacts

The seafloor supports a wide variety of organisms including mussels, worms and other bi-valves, plus a range of crustaceans, which in turn support an extremely healthy fishery (see food chain diagram above).

Suction dredging is akin to open-cast mining, where the entire top surface of the seabed is removed to depths of up to 20 metres. Every living thing in the sand is killed in the process, turning both the mined areas plus a significant area around the mining sites, into a dead-zone.

Then there are the plumes created at the time of mining, plus the plume blanket when the unwanted silica is replaced into the ecosystem. To quote from NIWA’s website, “Next to the collector system tracks, sediment will be piled up. Small areas may remain undisturbed by these actions, but they will most certainly receive a cover of sediment from the plume. 

Sediment surface feeding fauna will die from food shortage if these manage to survive the direct mining impact. Some chance of survival remains only for stalked organisms penetrating high above the blanketing layer. Their food sources, drifting plankton or other particles, will pass by with the currents, after the plume has disappeared. In total the community will be tremendously altered and recolonization will be a very slow process. The re-establishment of a balanced community may finally take decades. 

It is too early yet to say how serious the environmental consequences would be. Refer NIWA presentation on Mining”. The following is a list of potential disturbances in scientific terms, with a simple summary, also taken from the NIWA website:

  • Physical disturbance and destruction of benthic habitat
  • Modification to diversity and assemblage structure in benthic communities (including demersal fish)
  • Alteration of biogeochemical processes in the water column and on the seafloor
  • Downstream sediment plumes potentially affecting water column organisms and productivity and seabed fauna
  • Surface noise and light affecting seabirds
  • Subsurface noise affecting marine mammals and fish
  • Any semi-permanent structures may act as artificial reefs
  • Modification of the natural wave and current regime through removal or addition of substrate
  • Modification of the coastal sand budget and shore mobility
  • Risks associated with increased infrastructure, e.g. oil spills or processing vessels

Summary

  • Disturbances from seabed mining have the potential to effect the benthos and the water column as well as more distant habitats
  • Impacts are dependent on the scale (magnitude and frequency) of disturbance
  • Habitats will vary in their vulnerability to the same disturbance regime
  • Current levels of ecological knowledge are generally poor, especially for deep slope and abyssal areas
  • Presently working in a policy and regulatory vacuum – difficult for all concerned”.

The extent to which the local ecology is affected depends on how large an area is mined, the intensity of the dredging, the sediment type and how much the local area is exposed to natural disturbance from currents and wave action.