Something in the water

Under the Wairau Plain, within the tiny pores of our aquifers, lives a subterranean colony of blind, colourless and, for humans, largely mysterious creatures.

The minuscule invertebrates, ranging from less than 1mm to 8mm in size, are rarely seen, but may in future play a big part in understanding the health of Marlborough’s aquifers.

Marlborough District Council groundwater scientist Peter Davidson says the invertebrates respire and feed on organic matters, ‘‘so if there’s waste coming down from the surface then the benefit for us as humans is that they probably tidy that for us’’.

In his book Groundwaters of Marlborough (2011), Peter wrote that the creatures are ‘‘potentially bio-indicators of aquifer water quality and indirectly the impacts of overlying land-uses.’’

They were first discovered in New Zealand in the 1880s, but their function is largely unknown. ’’To manage them and know what to do with them we need more knowledge. It’s fascinating that there’s a whole community of life there.’’

Peter says scientists agree there is a need for a New Zealand-wide benchmark study about the invertebrates to discover what they can tell us about the state of, and human impact on, our aquifers and waterways.

A national initiative is underway to seek funding for such a study across New Zealand’s major economic aquifers, including Marlborough, but this was in the initial stages, says Peter.

What is known is that the invertebrates are present in the transitional zones between aquifers and spring-fed streams, as some have been found in stream samples, and past studies have identified about a dozen different species in Marlborough, though there are likely more.

Peter says the invertebrates are most likely to be found in porous gravels which exist northwest of Renwick, and less likely towards the coast of the lower Wairau Plains where the aquifer is deeper and there is less oxygen and food.

Council freshwater ecologist Peter Hamill happened upon some of the invertebrates a few years ago when they blocked up a landowner’s wellwater filter. Many look like tiny white or transparent sandhoppers.

The challenge to studying the invertebrates was retrieving them from a well without the pump mushing them up like the filter had, which required specialist equipment that only went to a certain depth in the ground, he says.