Porirua Harbour

A sensitive receiving environmentA sensitive receiving environment

Juliet Milne, 21 October 2009

Outline• The harbour is an

estuary

• Common estuary issues

• Monitoring results

• Management issues

Porirua Estuary• The harbour is an actually

an estuary

• Estuaries are sensitive to a number of issues:– habitat loss– sedimentation– eutrophication (enrichment)– contamination

• Monitoring & management need to target these issues

[ Sedimentation monitoring site

Recreation monitoring site

Intertidal monitoring site

Subtidal monitoring site

Stream monitoring site

Habitat loss• Broad-scale mapping

of intertidal substrate & vegetation– % cover of mud,

saltmarsh, seagrass, vegetated terrestrial buffer, nuisance algae

• December 2007 base-line (5-yearly mapping)

Rushland, Pauatahanui arm

2007 survey results

“Invasive species”

Invasive kelp (Undaria pinnatifida)

“Invasive species”

Plastica fizzii

Roadus tyrus

Shoppin trolleri

Roadus conerii

Sedimentation• Sedimentation plates installed in 2007/08

• Depth to plates measured annually

Eutrophication• Annual monitoring at 4 intertidal sites

– fine-scale sediment condition indicators – benthic (sediment-dwelling) fauna

• Annual mapping of macroalgal cover

Measuring the depth of oxygenated sediment

“Healthy”

Anoxic

Macroalgae cover

Sea lettuce (Ulva)

Eel grass (Zostera)

January 2009 – more than 50% coverage of nuisance algae in some areas

Identification of benthic fauna

Cockle

Wedgeshell

Mudflat whelk

Capitella capitata

Polychaete worms

Benthic fauna photos: Cawthron©

Contaminants – Part I Disease risk

• Water quality tested at 6 recreational sites weekly during summer

• Not always safe for swimming

– avoid after rain

1

10

100

1,000

10,000

Jul-2007 Dec-2007 Jun-2008 Dec-2008 Jun-2009

Ent

eroc

occi

(cf

u/10

0 m

L)

Action guideline

Alert guideline

Paremata Bridge, 2007-2009

Porirua Harbour rowing club, 2001-2009

1

10

100

1,000

10,000

Nov-2001 Nov-2002 Nov-2003 Nov-2004 Nov-2005 Nov-2006 Nov-2007 Nov-2008 Nov-2009

Ent

eroc

occi

(cf

u/10

0 m

L)

Action guideline

Alert guideline

unsafe

Contaminants – Part I cont.Disease risk

• Shellfish flesh (cockles) tested periodically

• Lack of guidelines for many contaminants

• Avoid streams & stormwateroutfalls

Contaminants – Part II Toxicants

• Five subtidalmonitoring sites sampled in 2004, 2005 & 2008

• Lead, zinc & DDT main contaminants of concern– elevated, persistent & toxic

• No clear evidence of significant ecological effects

Total zinc concentrations

ANZECC ISQG-low

Total DDT concentrations (at 1% TOC)

PAH1 PAH2 PAH3 POR1 POR2Site

0

1

2

3

4

5

6

7

8

9

10

DD

T (

ng/g

@ 1

%T

OC

)

ANZECC ISQG-Low = 1.6 ng/g

ARC ERC:red = 3.9 ng/g

ANZECC ISQG-low

ARC ERC red

Toxicants - intertidal “hotspot” study• Targeted stream outflows,

and stormwater outfalls– southern end of harbour– streambed sediments

• Clear evidence of stormwater-derived contamination

• Zinc , lead, PAHs, DDTabove guidelines in surface sediments

Semple St outfall

Management issues• Sensitive receiving

environment in an urban setting

• Sediment & nutrient inputs – control at source

• Transport of contaminants– stormwater-derived

inputs are ongoing

Management issues• Existing contamination

• Future development?

• Whole of catchment approach needed

Everyone has a role to play