RESEARCH BASED SOLUTIONS

The Motueka ICM Programme

The River Plume Ecosystem

Paul GillespieCommunity Reference Group

Presentation28 April 2009

INTEGRATED COASTAL MANAGEMENT

GOAL: to develop a “river plume ecosystem” (RPE) concept for evaluating and managing catchment-sea linkages

ICM frameworkLarge plume-affected areaRe-defined catchment areaExpansion of spatial scale to address multi-plume effects

173.00 173.10 173.20

41.15

41.05

40.95

40.85

Surface Salinity

173.00 173.10 173.20

41.15

41.05

40.95

40.85

Land-Sea Connections

• Fresh water

• Inorganic nutrients (C, N, P, Si)

• Organic matter

• Inorganic sediments

• Contaminants -Organic/inorganic-Microbes

• Water column structure (density stratification)

• Plant production

• Microbial processes (O2/nutrient flux, denitrification)

• Seabed habitat structure & composition (shellfish quality)

Catchment influences that define the RPE

Ecosystem features affected

Phytoplankton

Periodic development of east to west gradients of nutrients and chl a

173 173.1 173.2

9-10 May 2001

41.15

41.05

40.95

40.85

40.75

173 173.1 173.2

9-10 May 2001

41.15

41.05

40.95

40.85

40.75DRSi Chl a

Woodstock

Woodmans BendTasman Bay

Water Quality Monitoring Sites

Nutrient Loading to Tasman Bay (tonnes/yr)

122582969182293DRSiTPDRPNH4-NNO3-NTN

91323257212313DRSiTPDRPNH4-NNO3-NTN

90051746125190DRSiTPDRPNH4-NNO3-NTN

2005

2006

2007

2008

1131028610182295DRSiTPDRPNH4-NNO3-NTN

Nutrient Loading to Tasman Bay, (tonnes/month)

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Mas

s Lo

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TNNO3NH4

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Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

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TNNO3NH4

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2007

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Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Mas

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TNNO3NH42008

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Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Mas

s Lo

ad (t

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TNNONH4

2006

What effect is it having in Tasman Bay?

Motueka TN discharge (average 2005-2008) = ~269 t

Total freshwater TN discharge (including point source discharges) = ~900 t/ year

N loss via denitrification = ~1800 t/year

N Inputs ~50% of assimilation capacity

Problems associated with eutrophication unlikely

Nutrients probably having beneficial effects on productivity

But there still could be some effect on HAB incidence???

What effect is it having in Tasman Bay?

Sespended Sediment Discharge

~370,000 tonnes from the catchment annually

Les Basher (LCR), Murray Hicks (NIWA)

Motueka R. Susp. Sed. Plume6 Oct. 2007 - the day after a moderate flood event

Waimea River plume 25 Jan 2009 -no rain

Waimea/Maitaiplumes 25 Jan 2009 -no rain

Potential effects on shellfish resources in Tasman Bay

•Chronic condition of high near-bottom turbidity

Catchment susp. sed.

loads

Physical disturbance due to dredging & trawling

Deposition/ Resuspension

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89/90 91/92 93/94 95/96 97/98 99/00 01/02 03/04

Tasman Bay

Tasman Bay scallop catches 1989/90 – 2004/05 (tonnes)

Interference of scallop feeding

What do scallops eat?

Scallops more sensitive to inorganic SS than mussels

Phytoplankton Benthic diatoms

to pump

0.5m

1.0mScallops

CTDChl a

% Trans.

S4

Current meter11-25 Feb

Sediment Traps

Scallop feeding inhibited by high SS concentrations

Near-Bottom High Turbidity Layer

Suspended Solids content (mg/L) of near-bottom waters of the Motueka plume

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10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 23:00 1:00 3:00 5:00 7:00 9:00

Total Suspended solidsInorganicorganic

Tasman Bay LT in situ Data Collection FacilityDeployment of chl a / turbidity logging sensor

Physical seabed disturbancesHabitat alteration due to trawling/dredging

• Homogenisation/ loss of biodiversity

• Sediment anoxia

- Recovery

• Sediment stability

- 3D structure

- diatom film (glue-like)

Red Hills

Plume sediments- elevated Ni

Ni concentrations (mg/kg) in Tasman Bay sediments

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0 m 5000 m 10000 m 15000 m 20000 m

•Distinct plume area of elevated Ni concentraion

•ANZECC (2000) low 21 mg/kg

high 52 mg/kg

•Over 6 times greater than the level required to produce “probable” biological effects.

Plume sediments- elevated Cr

Cr concentrations (mg/kg) in Tasman Bay sediments

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0 m 5000 m 10000 m 15000 m 20000 m

•Similar distinct plume area

•ANZECC (2000) low 80 mg/kg

high 370 mg/kg

•Over 1.5 times greater than the level required to produce “possible” biological effects.

•Cu, Ba and V similar distribution

Motueka@Gorge

Riwaka@Hickmotts

Motueka@Woodmans

Graham R

Motueka@Woodstock

Stanley Brook

Motueka u/s WangapekaWangapeka@Walters Peak

Baton

Motueka u/s MotupikoMotupiko@Quinney Bush

1

23

4

56

78

Tadmore

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River Margin Sediments

Red Hills Mineral Belt

Ni up to 20x guideline levels for “probable”biological effects

ttp://icm.landcareresearch.co.nz/science_themes/Land/easter_flood_2005.htm

Conclusions

• SSs near the seabed can interfere with scallop feeding.

• Catchment erosion during heavy rainfall can result in extensive turbidity plumes in Tasman Bay.

• Wind & wave activity can also result in sediment plumes in the absence of rain.

•High SS concentrations can occur in near-bottom waters of the Bay (deposition & chronic resuspension).

•Seabed disturbance due to dredging and/or trawling activities may result in enhanced SS resuspension.

• A natural catchment source of heavy metals-enriched sediments results in a periodic discharge of Ni & Cr-contaminated sediments into the Bay.

- The plume area directly affects around 70-90 km2 of the seabed in the western Bay.

Considerations

• Long term cycles? e.g. weather, climate, flood frequency

• Mitigation? •Management of SS discharge (catchment land use)

•Stabilisation of sediment boundary layer

-Rahui, no trawl/dredge zones-Revised management regime (e.g. time allowance for benthic recovery)-Lessons from marine reserve and aquaculture monitoring

•Golden Bay?

•Similar high SS input from catchments•Similar shallow, mud-dominated seabed habitat•Higher phytoplankton biomass•Comparative investigation

ICM data buoy

ICM data buoy #2

Mussel cages moored at 3 m depth with salinity/temp loggers

Deploy droguesand sampling (x3)

CTD and water sampling transects

Woodman’s bend sampling

River plume FIO surveySalinity

TemperatureTurbidityCurrents

Light

Turbidity

MST Basics

Farming

Shellfish

MST

Urban

MST as a Tool

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General Bacteroides MarkerRuminant Bacteroides MarkerHuman Bacteroides MarkerHuman Enterococcus MarkerHuman Polyomavirus Marker

Water ColumnSediment Stormwater OutfallSaltwater Creek

Distribution of MST markers in the Maitai RiverDistribution of MST markers in the Maitai RiverDistribution of MST markers in the Maitai River