Groundwater plays a vital role in sustaining both surface and subsurface ecosystems.
The ecosystems may rely on specific groundwater flows, or on specific ranges of fluctuations in level or pressure, or on specific groundwater quality parameters such as temperature or mineral content.
Groundwater dependent ecosystems represent a distinct and diverse component of the earth's biological diversity and as such they often have a high conservation value.
The major groundwater dependent ecosystem types that have been identified in Australia are as follows.
a) terrestrial vegetation
- vegetation communities and dependent fauna that have seasonal or episodic dependence on groundwater. Examples include paperbark or ti-tree swamps where the trees access groundwater with their root systems.
b) river base flow systems
- aquatic and riparian ecosytems that exist in or adjacent to streams that are fed by groundwater base flow during low rainfall periods. Many of Tasmania's rivers and streams are included in this category.
c) aquifer and cave ecosystems
- aquatic ecosystems that occupy caves or aquifers. These ecosystems include, for example, organisms that have specifically adapted to the darkness and constant temperature conditions typically found underground.
- aquatic communities and fringing vegetation dependent on groundwater fed lakes and wetlands.
e) estuarine and near-shore marine ecosystems
- coastal, estuarine and near shore marine plant and animal communities whose ecological function has some dependence on discharge of groundwater.
In Tasmania, the majority of our understanding of groundwater dependent ecosystems, being a relatively new area of research, is confined to those found in karst environments.
Aquatic ecosystems in karst environments support a specialised fauna that is often distinct from that of surface waters.
Species that live solely in these environments have curious morphologies including the degeneration or loss of eyes and body pigment, elongated antennae and legs, and enhanced sensory structures.
The invertebrate fauna in karst waters in Tasmania is quite diverse. The groups that have been recorded in caves include:
- roundworms (Nematoda)
- flatworms (Turbellaria)
- nemertine worms (Nemertea)
- segmented worms (Oligochaeta)
- water mites (Hydracarina)
- molluscs (Hydrobiidae)
- several orders of insects with aquatic larvae (caddisflies, mayflies, stoneflies and two-winged flies)
- a rich assemblage of crustaceans (copepods, ostracods, syncarids, isopods, amphipods and decapods).
The mollusc and crustacean groups include many rare, endemic and cave-limited forms, although much of this material remains undescribed.