Impacts on seafloor organisms arising from mining on the Chatham Rise- Dr Judith Hewitt Presentation to the EPA DMC – Chatham Rock Phosphate 3 October 2014
Impacts from mining on seafloor organisms My evidence discussed the potential for impacts associated with 1. Increased sediment deposition 2. Enhanced suspended sediment concentrations Looking at available international and New Zealand literature Importantly, no information was available about the sensitivities of dominant species of communities described in Appendix 15 of the EIA to either sedimentation or suspended sediments 2
Sensitivity information • Information on taxa in the same order was available from the MarLin database – At least one dominant species in each epifaunal community was • highly or very highly sensitive to smothering, with the exception of community H from video transects • highly sensitive to increased suspended sediments, with the exception of community H from video transects – infaunal communities were comparatively less sensitive to smothering, but just as highly sensitive to suspended sediment 3
Sensitivity information • MarLin thresholds – an increase in deposited sediment of 5 cm, lasting for one month – an increase in suspended sediment concentrations of 100 mg/L lasting for 1 month • Caveats – A number of international and New Zealand studies document impacts below these levels – For sediment deposition, the size of the organism, or location and mobility of feeding apparatus is a critical factor – Biological responses to stressors usually get worse with repeated events 4
Sediment deposition • International studies on corals report death with complete burial for time periods as short as one week • 2 New Zealand studies have found that of 12 tested taxa – 5 could not move up through 3 cm of deposited sediment – 2 could not move up through < 1cm • Another New Zealand study found high mortality of an urchin and reduced condition of a bivalve, sponge and ascidian at 3 mm • The encrusting bryozoans (Escharella spinosissima, Chaperia sp., Fenestrulina n. sp) described in Appendix 15 of the EIA protrude no more than 0.5 mm 5
Suspended sediment • International studies on corals report variable mortality thresholds from – 20% at 54 mg/L – 100% >25 mg/L for >10% of the time over a period of several months or >10 mg/L for >25 % of the time • A New Zealand study found horse mussel feeding affected at 80 mg/L • Another New Zealand study observed significant drops in condition after 13 days for: – a mussel 26 – 100 mg/L – an oyster 15 -26 mg/L – a sponge <15 mg/L for the sponge 6
Predicted areas associated with these levels • Chatham Rock Phosphate Ltd (2014) Tables 2 and 3 predict with release at the seafloor that the area covered b – 1 – 5 cm will be 13-18 square km per mining block – 1 mm – 1 cm will be 18 - 61 square km per mining block • Tables 4 and 5 (Chatham Rock Phosphate 2014) similarly predict that for durations of 1 week to 1 month the area covered by – >50 mg/L is 12- 22 square km – >30 mg/L is 15 -33 square km – >10 mg/L is 47 – 124 square km 7
Summary • There are likely to be some impacts on seafloor organisms beyond the area physically mined • TSS and sedimentation will decrease with distance from the area being mined • The impacts of TSS and sedimentation are likely to also form a gradient (with distance) depending on benthic species/communities present at any point • The exact nature of these impacts and how extensive they would be can not be reliably assessed at present 8
Sensitivity definitions from MARLIN Sensitivity Explanation and rationale Category Very High "Very high" sensitivity is indicated by the following scenario: o The habitat or species is very adversely affected by an external factor arising from human activities or natural events (either killed/destroyed, "high" intolerance) and is expected to recover only over a prolonged period of time, i.e., >25 years or not at all (recoverability is "very low" or "none"). o The habitat or species is adversely affected by an external factor arising from human activities or natural events (damaged, "intermediate" intolerance) but is not expected to recover at all (recoverability is "none"). High "High" sensitivity is indicated by the following scenarios: o The habitat or species is very adversely affected by an external factor arising from human activities or natural events (killed/destroyed, "high" intolerance) and is expected to recover over a very long period of time, i.e., >10 or up to 25 years ("low" recoverability). o The habitat or species is adversely affected by an external factor arising from human activities or natural events (damaged, "intermediate" intolerance) and is expected to recover over a very long period of time, i.e., >10 years (recoverability is "low", or "very low"). o The habitat or species is affected by an external factor arising from human activities or natural events (reduced viability **, "low" intolerance) but is not expected to recover at all (recoverability is "none"), so that the habitat or species may be vulnerable to subsequent damage. 9
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