New report highlights human impacts on Wellington Harbour health

A comprehensive report from Greater Wellington, in partnership with Wellington Water, on the ecological health of the region’s largest harbour, Te Whanganui-a-Tara (Wellington Harbour) has just been published.

Every four years, data is analysed from over twenty strategically placed monitoring sites, including several control sites in the depths of the harbour. The findings look to understand the impact that human activity and subsequent sediment contamination have had over time.

Two key findings are the high amounts of muddy sediments at all sites barring Evan’s Bay and high concentrations of copper, lead, and legacy concentrations of mercury at some sites.

“This hasn’t happened overnight, rather over decades or longer” said Megan Melidonis, GW Senior Environmental Scientist, referring to the metal concentrations.

“Left untouched this industrial legacy often has limited effect on the marine environment, but when disturbances shift sediment, toxic effects can be felt both within localised bottom dwelling animal communities and within the wider aquatic environment.

Such a disruption of the natural food chain may deter visiting marine life such as dolphins, orcas and seabirds but may also affect important aquatic habitats including recently discovered beds of red seaweed, an important habitat in Wellington Harbour that provides refuge for an abundance of sea life including the elusive decorator crab”. 

“Potential degradation of the harbour is not confined to industrial sites as monitoring areas further afield are vulnerable to sediment, nutrients and contaminants from rivers and paved areas.

“Being a deep basin harbour, Te Whanganui-a-Tara encourages the retention of fine sediment, while the activity of waves and wind fetch over its great expanse can shift sediment and associated contaminants from point source stormwater discharges, industrial sites, and areas focused around port activities.

Wellington Water are required to monitor sites within Wellington Harbour as a condition of the consent granted to them to allow discharges to the marine environment.

“With numerous outfalls located around the Harbour, we not only need to be aware of what’s entering our harbours through stormwater but also ensuring we’re not inadvertently contributing to the deterioration of our marine and coastal environments” said Melidonis, referring also to over 700 litter items recorded in an area only the length of a rugby field, during quarterly Litter Intelligence surveys at 11 sites around Te Whanganui-a-Tara coastline.

“Common household rubbish from plastic bags through to more unusual items like bikes and scooters are occasionally found, with our Harbours patrol vessel also pulling out odd bits of discarded household items from time to time.

Greater Wellington Climate Committee Chair and Regional Councillor, Thomas Nash said there is a lot that people and organisations and businesses in Wellington can all be consciously doing to dispose of their waste and to do more to help the plants and animals – precious local taonga – to thrive.

Washing your vehicles and equipment in places where the runoff will be contained onto land rather run straight down a stormwater drain and into the sea, replace parts when you can with more environmentally sound components and use fewer herbicides and pesticides in your garden, it all helps. Whatever you do, always report any pollution incidents to us for investigation on 0800 496 734. 

“Human activity in and around this wāhi tapu (sacred area) determines the harbour’s health.

“We want to help people and organisations understand the impact of our activity and recognise the intrinsic link between our actions on land and the impacts on water. Doing this will help us all minimise the harmful impacts we have, adopt an environmentally conscious outlook for our activities and allow our harbour to flourish with abundant native life and wider climate benefits”.

As part of Greater Wellington’s Whaitua programme, documents have recently been published featuring recommendations, information on issues affecting water quality in the Wellington and Hutt Valley catchment, and pathways to wai ora (healthy water).

The full technical report and findings are available for members of the public at gw.govt.nz/harbour-reporting.