GDEs

Groundwater Dependent Ecosystems

Subterranean water occurring in aquifers constitutes approximately 97% of all the unfrozen freshwater reserves on earth and sustains a remarkable diversity of ecosystems and species. These ecosystems occur from the sub–polar regions to the equator, from mountain ranges to below sea level and are the largest, and possibly, most diverse of all freshwater ecosystems. The study of these environments is a rapidly burgeoning field in Australian and globally that is being used to effectively describe, understand and manage groundwater resources for the benefit of society and the environment.

In Australia, there is a broad range of ecosystems that are dependent on groundwater. These are called Groundwater Dependent Ecosystems or GDEs and they have their species composition, natural ecological processes and, in most case their survival, determined by the presence and quality of groundwater. They are a diverse, distinct and significant component of all landscapes and include six major types of ecosystems.
These are:

•  Aquifer ecosystems (subterranean ecosystems)
•  Karst and Cave ecosystems
•  River Baseflow Ecosystems (groundwater fed rivers and streams)
•  Groundwater fed Wetlands
•  Terrestrial and Riparian Vegetation or Phreatophytes
•  and Marine Ecosystems.

Groundwater ecosystems are a vital component of most landscapes because they provide a range of ecological services to other environments (both surface and subsurface) and possess unique values within themselves as well. These values can include:

Biodiversity and Conservation values

Contain high numbers of short range endemic, rare, vulnerable and threatened fauna and flora species and communities

Many species of flora and fauna are classic 'living fossils' that have remained relatively unchanged since well before the time of the dinosaurs. Many can be traced back over 300 million years and have linkages to other continents.

Many are now restricted to remnant, small pockets of these ancient habitats because of climate and landscape changes.
Ecological Functions
Provide water quality/carbon cycle/nutrient transformation functions including acting as filters of nutrients, sediment and pollutants.

Provide habitat for endangered flora and fauna.

Act as refuge environments during drought by providing food, water and shelter due to access to shallow water tables and river baseflows.

As being increasing used as bioindicators of groundwater quality. Groundwater typically is very constant both in water levels and water quality which has resulted in the many dependent ecosystems and species adapting to narrow environmental ranges. This is particularly the case among the groundwater invertebrates known as stygofauna. (See "Stygofauna", also "Troglofauna" and "Hyporheic fauna").