Estuaries are coastal waterbodies where freshwater mixes with seawater. Many estuaries in Aotearoa New Zealand have been impacted by pollutants and contaminants entering via freshwater.
Regional councils are developing coastal environmental plans to comply with New Zealand's National Policy Statement for Freshwater Management, which requires sustainable care of natural and physical resources and must give regard to estuaries.
Estuaries are an integral part of the coastal environment, but the policy for freshwater management does not yet include clear direction on how to assess the health of estuaries.
Councils need guidance to determine the impact of interacting contaminants delivered to estuaries from streams and rivers. Councils must also consider within-estuary activities such as dredging and fishing and overarching effects of climate and ocean change.
Considering the interconnectedness of all things is central in Te Ao Māori, and holistic ki uta ki tai (mountains-to-sea) management is required to restore the mauri (life force) of the nation's estuaries, according to a 2020 Parliamentary Commissioner for the Environment report.
To address this need, NIWA is leading research as part of a joint initiative funded by two National Science Challenges and the Ministry for the Environment (MfE).
The challenge
Researchers from Sustainable Seas and Our Land & Water National Science Challenges are involved in a two-year project called Ki uta ki tai: Estuaries, thresholds and values, which includes interwoven critical steps funded by MfE.
NIWA's new Coasts & Estuaries Centre is also allocating significant strategic science investment funding to estuarine research and management.
"It is wonderful to see so much focus and attention on estuaries at present. Estuaries have fallen through the cracks for too long," said lead researcher and NIWA marine ecology specialist Dr Drew Lohrer.
Ki uta ki tai researchers are working with whānau, hapū, iwi and community groups to identify aspirations for their estuaries.
The researchers are also estimating freshwater contaminant loads in 12 case study estuaries from Northland to Southland, from now, in the past, and in the future (in an altered climate).
The study sites: Whangarei Harbour; Mahurangi Harbour and Okura Harbour in Auckland; Tairua Estuary and Raglan Harbour in Waikato; Tauranga Harbour and Waihi Estuary; Ahuriri Estuary in Napier; Porirua Harbour; Kaipara Harbour; Avon-Heathcote Estuary in Canterbury and New River Estuary in Southland.
The team will relate those loads to measures of ecological health in estuaries to determine critical stressor thresholds.
Combined, the findings will be used to guide limit-setting for freshwater contaminants in estuaries which the ministry can use to set policy for regional councils to follow.
Estuary types
The 12 study sites being investigated in detail represent different estuary types and sizes with different surrounding land uses and climates.
Councils in those areas have supplied data collected from their estuaries, some dating back 10 to 15 years.
"The data will help us calculate the loadings of sediments, nutrients, and E. coli to each estuary."
"We are also able to use macrofauna assemblages and kaimoana abundance data as indicators of estuary health because we know a lot about how these organisms respond to contaminants."
Lohrer said larger councils with more resources can gather data more often while smaller councils might struggle to provide the same level of detail on their estuaries.
NIWA freshwater modelling experts will help develop tools that all councils can use to determine the exposures of ecological sampling sites to multiple stressors in different parts of their estuaries.
These tools can be used to calculate exposures in specific areas of estuaries, rather than averaged across entire estuaries.
Lohrer said this was important because estuaries came in all shapes and sizes and were complicated, spatially variable environments.
For example, large estuaries can have dozens of streams emptying into them, each delivering differing amounts of contaminants. Catchment size, freshwater volume, land use, adjacent ocean characteristics and climate regimes can also play varying roles.
"This research will incorporate mātauranga Māori and western science to take a holistic approach to managing the entire catchment, from the mountains to the sea, in keeping with the ki uta ki tai concept.
"It's about understanding the types and levels of stressors that are most damaging to estuaries, then taking steps, either on land or in the estuaries themselves, to improve their health."
High valued but highly stressed
Lohrer said there was keen interest in the project among councils, with whom he has been communicating regularly. The joint initiative is expected to be completed in late 2023.
"The people of Aotearoa New Zealand are very coastally orientated. Coasts and estuaries are where we interact with the marine environment the most."
"Estuaries are highly valued culturally, socially and environmentally. They have multiple uses but because of that they are also highly stressed.
"They are important because they trap sediment and remove nutrients delivered by freshwater. They benefit us in many ways and so we really need to look after them."
