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Groundwater Dependent Ecosystems (GDEs)

Groundwater Dependent Ecosystems (GDEs) are ecosystems that are partially or completely dependent on underground water for their existence or health. When groundwater is close to the surface, plant roots can access it as a steady water supply so they can thrive in times of low rainfall.

The plants then support the animal communities. When groundwater discharges to the surface it supports wetland and stream ecosystems. Underwater springs at the coast and in estuaries can provide nutrients for sea grasses and aquatic species. There are even some animal species that only live underground in the groundwater system aquifers.

In addition to the intrinsic importance of maintaining the biodiversity of GDEs, they provide important resources for rural lifestyle. GDEs support fishing, bird watching, and other recreation. The locations of GDEs provide valuable insight to the hydrologic system within catchments and understanding GDEs is important to water resource, environmental, and agricultural management.

Groundwater Dependent Ecosystem
A digital representation of potential Groundwater Dependent Ecosystem (Condah Drain) showing levels of species tolerance

The study of GDEs is complex and requires an understanding of hydrogeology, surface water hydrology, and ecology. Some of the signs of the presence of a possible GDE are: water logging at or near the surface that persists through long dry periods, vegetation that is much greener in dry periods than surrounding vegetation, vegetation that stays nearly as green in the summer and winter, and species known for their ability to use groundwater.

GDEs can be threatened by over- use of groundwater that causes the water table to decline to a point that it won’t support the ecosystem. Draining land can also cause water table declines that affect GDEs. They may also be threatened by changes to salinity or by extreme climate stress changes such as long droughts.

The former DPI prepared maps of potential GDEs across Victoria and developed methods to evaluate the areas most likely to be dependent to groundwater and sensitive to changes in the groundwater system. Work is continuing to refine and apply these methods across Victoria, especially in groundwater resource areas where over-extraction of groundwater may threaten GDEs.
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