Groundwater: out of sight, but vital for life

Posted 26 July 2007

Although groundwater is out of sight beneath the earth, many plants and animals that live on the surface depend on it for their existence.

Some trees, for example, can send their roots deep into the soil to reach the water table and so thrive in dry places where other plants find it hard to survive at all.

These special relationships may not always be apparent to see but they are vital to consider when we make decisions about how to manage our groundwater resources.

Take out too much groundwater to irrigate crops or water livestock, for example, and you may put such trees and shrubs under stress and weaken them, or even make them more likely to die in times of drought.

In a recent journal article, Derek Eamus, of the Institute for Water and Environmental Resource Management, University of Technology, Sydney, and Ray Froend, of the School of Natural Sciences and Centre for Ecosystem Management, Edith Cowan University, note that these issues are long overdue for attention.

"With increasing demand for water and a changing climate regime, the need to mitigate the environmental impacts of groundwater development is increasing," say Eamus and Froend.

"Current borefield operation in Australia is largely responsive to consumption demand and often in conflict with environmental needs for groundwater, resulting in drought stress and sometimes death of phreatophytic vegetation and other impacts on groundwater-dependent ecosystems."

When water managers make allocations of groundwater for human use, they must try to balance the social and economic uses to which that water will be put along with an ecological water requirement (EWR), which may not be well known.

"Poorley defined EWRs, often the result of insufficient data and time, lead to `technical' breaches of environmental conditions (without obvious ecological impact) or understated water requirements, resulting in unexpected environmental impacts," the authors say.

They recommend that more effort be put into determining EWRS, noting that not all living things in an ecosystem will respond in the same way to a reduction in groundwater levels, and that the length of time that a given area is flooded or dry may also be highly significant.

Earlier research has shown, for example, that phreatophytic plants use groundwater most heavily during dry times, and that life in many wetlands is well adapted to experience periods of drying out.

In short, groundwater-dependent ecosystems (GDEs)are complex, so simplistic assessments of EWRs that assume all plants and animals will respond in the same way in all conditions simply won't assure that groundwater is being used sustainably - we need more information and better understanding of the role of groundwater in these ecosystems to be able to manage them well in the long term.

The authors point out that three fundamental questions challenge managers of water and GDEs:

  • which attributes of the groundwater regime are important to the GDE (e.g. pressure, flow rate, depth);
  • what are the safe limits to changes in groundwater regime;
  • which features of vegetation can be measured to monitor ecosystem function?

"It isn't until we have identified the location of GDEs and the groundwater regime required to maintain them, that protection of these important ecosystems can be realistically attempted," they conclude.

[Note: The scientific term for groundwater-dependent plants is "phreatophytic", meaning an association with a well or a spring.]

Article source: Eamus, D. and Froend, R. "Groundwater-dependent ecosystems: the where, what and why of GDEs", Australian Journal of Botany, 2006, 54, 91-96.

www.publish.csiro.au/journals/ajb

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