Subterranean wetlands include all underground areas containing water, including caves and aquifers. Subterranean cave systems are groundwater dependent ecosystems. Subterranean cave systems with large void sizes are part of ‘karst landscapes’ often characterised by sinkholes and springs. Karst landscapes are commonly found in regions where carbonate rocks are abundant. Carbonate rock may be fractured and/or dissolved by mechanical weathering and chemical weathering from contract with water (e.g. rain and soil water naturally containing weak acids). Subterranean cave ecosystems can be divided into four zones (shown as focal circles in the conceptual model):

• Entrance zone – this is where the surface and subterranean environments connect.
• Twilight zone – in this zone light from the surface progressively diminishes. Flora (e.g. ferns, mosses and algae) can grow in areas of this zone where light from the surface is able to penetrate.
• Transition zone – in this zone light is unable to penetrate from the surface. However other surface environmental conditions, including temperature fluctuations and moisture content, influence the conditions in the transition zone.
• Deep zone – in this zone light is unable to penetrate from the surface. Relative humidity is high and evaporation is low. Temperature is relatively constant throughout the year. Fauna found in the deep zone (i.e. stygofauna and troglofauna) are adapted to the subterranean environment.

Subterranean cave systems may store and transmit groundwater through the void spaces created through the interaction of carbonate rocks and water over time. Groundwater in these subterranean cave systems may support plant and/or animal communities, ecological processes and delivery of ecosystem services.  Subterranean cave systems may support stygofauna (aquatic fauna that depend on groundwater for all or some of their life cycle) and troglofauna (terrestrial, air-breathing fauna for which groundwater provides a humid environment and transmits nutrients from the surface environment).

The discharge of groundwater from cave systems may also support:

• Palustrine (e.g. swamps), lacustrine (e.g. lakes) and riverine (e.g. streams and rivers) wetlands located near springs fed by groundwater in cave systems.
• Terrestrial vegetation accessing groundwater from cave systems through their root zone.
• Aquifer ecosystems by recharging overlying aquifers.
• Estuarine ecosystems located at or down-gradient of springs fed by groundwater in cave systems.
• Near-shore marine ecosystems located at or down-gradient of submarine springs fed by groundwater in cave systems, although this is less common in Queensland landscapes.

Pictorial conceptual model PDF

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