Porirua Harbour A sensitive receiving environment A sensitive receiving environment Juliet Milne, 21 October 2009
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