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:
o 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
Relative average (2 year) light in water column: (% of surface?)
Natural
Compensation
irradiance:
~1%
Pinkerton (2014)
Mining: Site A
Mining: Site B
Intro: Benthic Microalgae
Average (2 year) light @ seabed: mol photons m-2 d-1
Natural
Compensation
irradiance:
0.4 mol photons
m-2 d-1
Pinkerton (2014)
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%
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.
Concern 1: Scale
• Plume shifting
• Operations
• Water masses
• Seasonal
• Nutrient limitation
• High uncertainty
• More variable pulses of phytoplankton
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
Some of year: Phytoplankton growth N limited
When phytoplankton N limited: decrease light without
effecting growth
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?
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
of 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
Suggestion 3: Monitoring
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:
o Valuable: detecting when impact occurred
o 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:
o Effects of SSC on primary productivity
o Switch nutrient to light limitation of phytoplankton growth
• Phytoplankton physiologist/modeller on TPRG
Thank You
Dr Emily Roberts
Scientific Officer – Marine Ecologist
Taranaki Regional Council