Porirua Harbour health under the spotlight

Greater Wellington and the Porirua City Council are taking a closer look at the health of the Porirua Harbour and Pauatahanui Inlet.

The monitoring, which has been partly funded by Porirua City Council's Porirua Harbour Programme, follows a review last year which identified excess sediment inputs, contaminants, nuisance algal growths and habitat loss as key risks to the health of the harbour.

Excess sediment entering the Harbour, particularly the Pauatahanui Inlet, has been highlighted in recent months, with one earthworks contractor fined $10,000 in November for an unauthorised sediment discharge from the Silverwood subdivision site.

The two councils have commissioned Wriggle Coastal Consultants to take field measurements and samples within Porirua Harbour and Pauatahanui Inlet.

Fieldwork kicked off in December, with mapping of the dominant vegetation and sediment types in the tidal areas of the harbour and inlet - including the extent of sea lettuce, which is a common indicator of estuary condition. Sediment plates were also installed in each arm to help measure the rates of sedimentation over time.

The scientists were back in the water last weekend, taking a closer look at what lives in and on the sediments. Sediment samples were also collected and will be tested for a range of contaminants, including nutrients and heavy metals.

"All of this information helps contribute to our understanding of the health of this highly valued ecosystem" says Greater Wellington's Environmental Science team leader Juliet Milne.

"On first glance, it appears that the estuary is highly productive, even by national standards. While this may be a good thing, it could also indicate signs of nutrient enrichment from agricultural runoff or urban storm water," she says.

Ms Milne says a report on the fieldwork's findings is expected in early June, once all of the samples have been processed. The information gained will feed into the development of a long-term monitoring programme for the Porirua Harbour.

"Long-term monitoring is an essential part of sustainably managing this valuable coastal ecosystem for present and future generations," she says.

ENDS