What lives beneath

New Zealand researchers are looking at how the microbes that exist in underground aquifers can help keep groundwater supplies healthy.

ESR scientist Louise Weaver says the ecosystem in groundwater plays a vital role in processing contaminants such as nitrates that end up there from a range of land uses.

‘‘The perception is that groundwater is a sterile environment. However, there are organisms there that form a complex ecosystem that can protect the water as part of nutrient cycling.’’

But these natural underground communities of organisms are coming under stress from the cumulative effects of a range of contaminants coming from the land.

Weaver says that by looking at the whole range of organisms that are there and how they change in response to contaminants, scientists can start building a picture of the stress a groundwater environment is under.

Changes in water quality will be seen in changes to biological diversity.

She says changes in aboveground ecosystems are well understood because they have been studied intensively for so long.

‘‘Take for example the African plains – we know what the lions and zebras do and how they interact. By comparison some of the macro-invertebrates and micro-organisms in groundwater systems have yet to be identified.’’

Macro-invertebrates are organisms that lack a spine and are large enough to be seen with the naked eye.

A paper published last year by researchers at the British Geological Survey found vast quantities of nitrate stored in rocks above drinking water resources.

The authors of that report estimated up to 180 million tonnes of nitrates are stored in rocks worldwide, perhaps twice the amount stored in soils.

New Zealand’s groundwater

‘‘There are organisms that form a complex ecosystem that can protect the water as part of nutrient cycling.’’ Louise Weaver, right

resources extend beneath about a quarter of our landmass. They are made up of extensive systems of saturated rock and sediment, which sustain flows in 80 per cent of our rivers and streams.

Weaver says one of the challenges has been identifying the organisms that play a part in removing the nitrates.

‘‘At the moment there is so much fundamental research we don’t know. There is a whole range of organisms that have specific functions, habitats and inter-relationships, which are currently poorly understood.’’

The project is part of wider research looking to develop an index, similar to the macroinvertebrate community index which is used in surface water, to get an indication of the health of the groundwater resource.

She says New Zealand scientists are at an early stage of developing that groundwater index, and refining systems for getting accurate samples of the vast array of macroinvertebrates and microbial organisms that are there.

The challenge is coming up with techniques to ensure that the samples will be representative of what is underground.

With larger macroinvertebrates researchers use nets. With smaller organisms they pump large volumes of water from the ground and filter it, extract the DNA and see what is present.

Aside from the inherent conservation values in the array of organisms present in groundwater, Weaver says research to identify and characterise what is there would have another benefit.

‘‘If we understand the processes and the organisms involved in more detail then there’s the potential to actually use them for bio-remediation.

‘‘In the future you could put in some of these organisms into the system to drive the removal of contaminants even further.’’