Impact of Mining on Primary Producers Dr Emily Roberts Scientific - - PowerPoint PPT Presentation

Impact of Mining on Primary Producers

Dr Emily Roberts Scientific Officer – Marine Ecologist Taranaki Regional Council

Primary Producers

Introduction

• Euphotic zone
• Benthic microalgae
• Phytoplankton

Concerns

• Scale
• Nutrient versus light limitation

Suggestions

• Scale of risk assessment
• Adaptive management
• Monitoring

Intro: Euphotic Zone

Definition:

• Euphotic Zone Depth: light declined to 1% of surface value
• Compensation depth:
• 24h mean photosynthesis = 24h mean respiration

Pinkerton (2014) Predicting the effects of ironsand mining on optical properties of the STB

Intro: Euphotic Zone

Pinkerton (2014) Predicting the effects of ironsand mining on optical properties of the STB

Intro: Euphotic Zone

Natural Mining

Intro: Phytoplankton

Compensation irradiance: ~1% Relative average (2 year) light in water column: (% of surface?)

Natural Mining: Site A Mining: Site B

Pinkerton (2014)

Intro: Benthic Microalgae

Compensation irradiance: 0.4 mol photons m-2 d-1 Average (2 year) light @ seabed: mol photons m-2 d-1

Natural Mining: Site A Mining: Site B

Pinkerton (2014)

Intro: % Decrease over South Taranaki Bight

Average Mining Site A Mining Site B Benthic microalgae: Light @ seabed 51% 59% Phytoplankton: Light in water column 8% 15% Phytoplankton primary production 4% 8% Total (B+P) primary production 5% 12% Energy flow to benthos 9% 16%

Pinkerton (2014)

Concern 1: Scale

STB: 12,500 km2 Plume: ~800 km2 Plume = <7% STB

Concern 1: Scale

Consent Condition (April 2014):

9 (f) vii. No more than minor impact on STB phytoplankton abundance and distribution attributable to optical property changes arising from TTR’s operations.

• High uncertainty
• More variable pulses of phytoplankton

Concern 1: Scale

• Plume shifting
• Operations
• Water masses
• Seasonal
• Nutrient limitation

Require: Conditions minimize knock on food web effects

Concern 2: Nutrient vrs Light

Discussion: Nutrient limitation, e.g.:

• McClary, Statement of Evidence, p33, Point 168
• Pinkerton, Optical Properties Report, Point 14
• Huber, Hearing Transcripts, p637
• Venus, Hearing Transcripts, p1883

Clarify: Nutrient and light limitation of phytoplankton growth

Concern 2: Nutrient vrs Light

Do not know:

• Extent: phytoplankton growth limited by N?
• Extent: phytoplankton rely on NH4

+?

• Point: growth switch from nutrient to light limitation?
• Area of plume: nutrient to light limitation?

Some of year: Phytoplankton growth N limited When phytoplankton N limited: decrease light without effecting growth

Concern 2: Nutrient vrs Light

N limitation of phytoplankton growth: important Current lack of info: Cannot use to imply plume minor impact on primary productivity Requires robust approach: assess impacts of plume:

• Risk assessment
• Consent conditions
• Adaptive management
• Monitoring

Suggestion 1: Scale of Risk Assessment

Provide comparative estimates of primary productivity values over median footprint

• f plume: mining vrs non-mining
• Required: assess/manage potential foodweb impacts
• Values: inform monitoring effort & design

Suggestion 2: Adaptive Management

Use adaptive management approach: manage potential impacts mining on PP

• Model: management tool
• Validated: appropriate monitoring
• Model output: development trigger values (SSC & optical)
• Spatial scale

Develop robust monitoring programme: enable management risk in relation to primary producers

• Currently: plan proposed monitoring phytoplankton &

benthic microalgae = limited:

• Benthic microalgae chlorophyll a: Condition 79
• Primary productivity (incl. light) – Conditions 83 & 131

(Venus, p1884: only light?)

• Joint Expert Reports ‘Optical’ & ‘Benthic 2’: Macrofauna:
• Valuable: detecting when impact occurred
• Limited: confirms impact in hindsight

Suggestion 3: Monitoring

Develop predictive model:

• Forecast risk
• Inform implementation of appropriate trigger values
• Validated during baseline monitoring
• Monitoring: determine:
• Effects of SSC on primary productivity
• Switch nutrient to light limitation of phytoplankton growth
• Phytoplankton physiologist/modeller on TPRG

Suggestion 3: Monitoring

Thank You

Dr Emily Roberts Scientific Officer – Marine Ecologist Taranaki Regional Council