Greater Wellington and Wellington City Councils are surveying the harbour for the second time to find how healthy it is for the animals that live in the sediment on the sea floor.
The first survey five years ago showed that urban stormwater — which can contain toxic chemicals such as paint and oil, copper from vehicle brake pads and zinc from unpainted galvanized roofs — is a major cause of the contamination.
While some contamination occurred in the past (such as lead from leaded petrol), the contaminants are persistent and toxic. Meanwhile, they continue to enter the harbour in streams and stormwater outfalls.
The present survey, which runs through this month, follows a base-line assessment in 2006 and will assess how urban stormwater is affecting the quality of the sediment and the health of the benthic (bottom-dwelling) invertebrates.
The sediment samples will be analysed for a range of contaminants, including heavy metals, polycyclic aromatic hydrocarbons (PAH’s — which are byproducts of fuel burning) and pesticides.
The 2006 assessment showed that heavy metals, PAHs and pesticides have accumulated, with the highest concentrations found in inner Lambton Basin and Evans Bay where there is less flushing of contaminants.
It reported a moderately healthy 101 species of invertebrates living in the harbour’s sediments, but also found that the abundance and diversity of these species was higher in areas with less contamination.
Additional sites to be surveyed
The present survey will sample additional sites closer to shore to make clearer this impact on invertebrate communities.
The Wellington City Council is required to check sediment quality at five-yearly intervals at several sites, as part of a consent granted earlier this year which covers all of the city’s stormwater discharges into the harbour.
Greater Wellington regional councillor Chris Laidlaw, Chair of Te Upoko Taiao – Natural Resource Management Committee – says:
“We’re aiming to see steady improvements in the quality of stormwater discharges into the harbour over the 10-year term of WCC’s consent because water quality is crucial to the survival of marine life in the harbour.
“We cannot afford to compromise here.”