Oases of the desert
Groundwater dependent ecosystems (GDEs) are plants, animals or ecosystems that are partially or totally dependent on the presence and quality of groundwater below the surface. Shallow groundwater is critical for the survival of many groundwater dependent ecosystems, whether that is for example trees, soaks, springs or wetlands.
In the arid and semi-arid lands, groundwater dependent ecosystems function as oases of the desert. These shallow groundwater environments are the most biodiverse, complex and climate resilient habitat across the arid and semi-arid lands. That presence of shallow groundwater has literally transformed parts of the arid lands into woodlands and wetlands, which are sites of biodiversity and abundance.
Groundwater dependent ecosystems are often also places of significant cultural values, whether that is sacred trees, soaks, springs or wetlands, or as social or cultural meeting places.
Types of Groundwater Dependent Ecosystems
There are three main groups of groundwater dependent ecosystems (GDEs),
1. Terrestrial groundwater dependent ecosystems
These are trees and other plants that rely on shallow groundwater just below the surface to survive. Trees that are groundwater dependent are larger, create more complex habitat (e.g. hollows) and may live for a very long-time. For example river red gums may be able to live for one thousand years.
In the arid zone, when suddenly there are heavily wooded areas with unevenly spaced large trees, it is very likely there is shallow groundwater below the surface. There is underground water sustaining these large trees, which are the homes for many of the bees, bats, birds, frogs, reptiles, mammals and insects.
What are some different examples of groundwater dependent trees?
River red gum in the Lhere Mparntwe in Alice Springs
Inland tea, ghost gum, smooth-barked coolibah, northern corkwood and bloodwood near Singleton Station
2. Aquatic groundwater dependent ecosystems
They rely on surface expression of groundwater - may include rivers, wetlands, springs and soaks.
3. Subterranean groundwater dependent ecosystems
They include cave and aquifer ecosystems, e.g. stygofauna
How are groundwater dependent ecosystems at risk?
GROUNDWATER MINING
If the shallow groundwater table is lowered and mined, then the groundwater dependent, trees, soaks, springs and wetlands will die and disappear.
Adapted from Rohde et al (2017) here.
CATTLE, HORSES, DONKEYS & CAMELS
Cattle and other feral mega-fauna stop the recruitment of groundwater dependent trees, they graze young sapplings and their hooves destroy young trees.
Cattle and other feral mega-fauna degrade groundwater dependent soaks, springs and wetlands during dry times. They cause significant damage to these ecosystems.
CONTAMINATION, POLLUTION & SPILLS
Mining, the gas industry and large-scale agribusiness may contaminate and pollute the quality of groundwater. This may be through spills of heavy metals or nuclear material (e.g. what has occurred at McCarthur River’s zinc and lead mine, Rum Jungle Uranium mine or Redbank Copper mine. Conversely, agribusiness’ use of groundwater may be a salinity risk to the groundwater resource which may also impact land condition. Similarly, agricultural run-off of chemicals may impact groundwater quality.