Future-proofing Groundwater SystemsBuffering climate change effects on water availability and quality

Researchers will use an innovative tracer technique to identify where the groundwater has come from and how long it has been underground. One of the tracers used is Tritium, a radioactive isotope of hydrogen produced in the atmosphere by nuclear reactions between cosmic rays and atmospheric gases. After Tritium combines with oxygen forming water molecules, it becomes part of the water cycle. As part of the rainwater, it enters groundwater systems and there it can be used as a 'radioactive clock'. When the rainwater infiltrates into the ground and becomes separated from the atmosphere, the clock starts to tick, with the Tritium concentration decreasing. This decrease can be measured and the age of the groundwater calculated.

The groundwater age data is used to provide information about the dynamics of groundwater flow, storage volumes of the aquifer, along with data from airborne electromagnetic surveying.

In a world-first, the team will measure groundwater denitrification at the catchment scale, using Earth Science New Zealand’s new state-of-the-art noble gas facility. Nitrate (NO₃) is a chemical compound that occurs naturally, but the use of fertilisers and waste from animals adds to the amount of nitrate in the environment. When there is too much nitrate it can leach from the soil and contaminate our groundwater and surface water.

Microbial denitrification is a naturally occurring process, which under the right conditions can reduce nitrate (NO₃) contamination in groundwater into inert harmless N₂ gas. This ‘excess-nitrogen’ accumulates in the groundwater along its flow path. The amount of excess-nitrogen can be measured at springs or a wells where the groundwater discharges.  Noble gas analysis allows the team to calculate the amount of ‘intrinsic’ nitrogen in the groundwater (atmospheric N₂ that has been dissolved in rainwater and infiltrated the groundwater system) to then quantify how much denitrification has occurred in the groundwater system. 

Through this improved understanding of where denitrification is taking place, and the conditions under which denitrification occurs, the programme will identify strategies to enhance mitigation of excess nitrate loads.

A national groundwater model will be extended to extract information from available and new data, including groundwater isotope and geophysical data, to understand how groundwater vulnerability to land use and climate change impacts vary spatially. 

Model simulation outputs will show how water availability and water demand relationships vary across New Zealand currently, and how they will change given climate projections. This will support the exploration of climate change implications for freshwater availability for communities, the environment and the economy. 

Simulation outputs will also map where land use presents a higher and a lower risk of nitrate contamination of freshwater systems.  This will harness the information from the new noble gas analyses, to map where denitrification is occurring.  This will support explorations of how changing land use at a location would increase or decrease impacts on freshwater.

Researchers will develop tools to guide adaptive management decision making processes for communities.  These tools are designed to be used iteratively, in contexts where there is significant uncertainty, and where decision relevant information is increasing over time as early warning (sentinel) monitoring data is collected.  

These modelling tools will be designed to be computationally efficient, and able to navigate water allocation and land use decision trade-offs and synergies across a range of values and aspirations in a community. They will be capable of identifying the most reliable early warning monitoring systems, which will be used to determine whether a change to the adaptation management pathway is required.  The tools will rapidly process new monitoring data as soon as it becomes available, to assess if freshwater responses to management are as expected, or whether the management pathway must be reconsidered.

Adaptation pathways is a flexible, long-term approach to managing climate-related risks and opportunities. It involves identifying different actions that can be taken over time in response to changing environmental conditions and uncertainty. Pathways planning helps communities and decision-makers stay flexible and avoid being locked into plans that may no longer work. 

The team will work alongside iwi and hapū in Hawke’s Bay and Northland, to explore and understand their values, aspirations, economic drivers, and decision-making processes. 

They will work together to co-design adaptation pathways to help maintain and enhance groundwater resources, combining new knowledge about groundwater resources, with place-based insights, and mātauranga Māori. These plans will provide practical, long-term guidance to enhance drought resilience and manage nitrate loads in freshwater systems. 

The case study adaptation pathways will be designed so they can be applied more widely, and the findings will be shared through stakeholder engagement, public outreach, workshops, and hui across Aotearoa.