How to age water & why it’s important
New science is telling us about the age of the water in our lakes and rivers, and it explains why things may get worse before they get better.
Akey challenge for resource managers and communities is predicting how the world might look 10, 20 or even 50 years from now. Decisions we make and actions we take all lead to outcomes, some that can be difficult to foresee or predict.
Striking the balance between enabling growth and protecting the environment generates tension within communities. Many appear to be striving toward the same goal, but in recent years we have seen disagreements arise over the pace or scale of change, or the mechanisms required for us to reach a common end. Social, economic and cultural values that we hold dear also come into play and add further complexity to decision making.
However, challenge is often accompanied by opportunity. Advances in science and technology continue to provide new tools and techniques that can improve our understanding of our environment and help us manage our natural resources in a sustainable way.
One group leading the way is the dedicated team of scientists at Te Pu Ao, GNS Science, which has developed one of the most accurate age dating laboratories in the world.
Water dating is emerging as an important tool for water management in New Zealand. Novel techniques using isotopes and tracers found in water have a range of applications. They can help us understand natural and human impacts on water quality, identify areas where groundwater systems are replenished, and how long water takes to travel to lakes, rivers or the sea. These techniques can also help us identify areas of interaction between ground and surface water. This is important for managing the effects of land use on water quality.
One example is radon which is now being used to map areas of groundwater inflow into waterways in NZ.
Radon is a radioactive gas that occurs naturally in rocks and soils. It is transported by water underground, deteriorating quickly when it is exposed to the atmosphere. The presence of radon tells us where groundwater is entering waterways. This is important for tracking the flow of water through a catchment, and also the nutrients and contaminants that can accompany it.
Radon Tritium is an isotope of hydrogen that forms in the atmosphere and is transported via rainfall onto land and into our rivers, lakes and groundwater systems. Tritium isotopes decay at a known rate, which means that the amount of tritium in a sample can be used to calculate the average age of the water. Tritium is measured in surface and groundwater, and interpreted by scientists using flow models to establish the average age of the water.
Age and chemistry can tell us about the journey of water: where it has come from, how far it has travelled, and how long it will take to see water quality respond to management interventions.
Water dating has become an important technique in developing management approaches for water resources in NZ. In Lake Rotorua, water can take around 60 years to travel from the surrounding catchment, through large volcanic aquifers, and into the lake.
By contrast, groundwater discharging into gravel-bed rivers such as the Mangatainoka River near Pahiatua (20km east of Palmerston North) can be very young, just a year or two old. The difference between the two travel times highlights the important role that geology plays in the transport of water and nutrients, particularly nitrogen which can contribute to algal growth in rivers and lakes.
In time, improvements may be seen, but in some catchments water quality is likely to get worse before it gets better, even when improvements are being made. In others, positive change will be more immediate.
There is no one-size-fits-all management approach that is appropriate for all our rivers, lakes, estuaries and aquifers. Catchments are unique and the best solutions can only be developed with a sound understanding of the environment around us. There’s increasing pressure on our waterways and that means a need for new and novel approaches to fill the gaps in our knowledge. By investing in techniques such as age dating, we can ensure that catchment management decision-making is informed by science.
The more advanced our scientific tool box, the better equipped we are to manage our environment sustainably.
ABBY MATTHEWS is an environmental scientist, and the science and innovation manager for Horizons Regional Council.