Subterranean (groundwater or aquifer) wetlands

What are subterranean wetlands?

The definition used in this section is the one used in the Draft Australian National Aquatic Ecosystem (ANAE) Classification which is:

Subterranean - (Fractured, Unconsolidated and Cave/Karsts – determined by void size) – include all underground areas containing water, including ice caves.  Australia supports a rich array of these subsurface aquatic environments ranging from the aquifers of the Great Artesian Basin to the karst system in Ida Bay, Tasmania (Boulton et al., 2003) The Subterranean Class includes some coastal hypogean habitats which are influenced by the presence of sea water. These include anchialine caves (such as the Bundera Sinkhole in Cape Range Peninsula, WA; Humphreys, 1999), groundwater estuaries (seawater-groundwater interface; Hancock et al., 2005) and sea caves (littoral caves; Halliday, 2004). The Sixth Conference of the Contracting Parties to the Convention on Wetlands (Ramsar) agreed to include subterranean karst wetlands as a wetland type under the Ramsar Wetland Classification System.

The Subterranean Class does not include the endogean (edaphic) environment, which is the soil zone separating the soil surface (epigean) from the hypogean (subsurface saturated) environment (Sket, 2004).

The following definitions taken from Tomlinson and Boulton (2008) provide additional clarity:

• Unconsolidated Aquifers - Unconsolidated aquifers consist of particles of gravel, sand, silt or clay that are not bound by mineral cement, by pressure or by thermal alteration of the grains (Freeze and Cherry 1979).  On a larger scale, alluvial aquifers represent an interstitial highway linking spatially discontinuous subterranean ecosystems with surface waters (Ward and Palmer 1994).
• Fractured Rock Aquifers - Fractured rock aquifers occur in rocks of sedimentary, igneous or metamorphic origin.
• Karst - Karst is a term describing subterranean systems with a large void size. Karst is a terrain characterised by sinkholes, caves and springs developed most commonly in carbonate rocks where significant solution of the rock has occurred due to flowing water. (Bakalowicz 2005).

Subterranean wetlands are aquatic systems

Subterranean wetlands :

• have a diversity of habitats (sand, gravel, fractured rock, karst, calcrete)
• are home to a vast diversity of microorganisms, invertebrates and even some vertebrates
• deliver ecosystem services (breakdown of organic carbon, nitrate reduction, containment attenuation)
• support terrestrial and other aquatic ecosystems
• provide approximately 20% of water used in Australia
• are largely unresearched compared to other areas water management

Ecological function in subterranean wetlands

Subterranean wetland biodiversity

• Low number of lineages
• high endemism
• relict taxa
• phreatomorphies

Subterranean fauna: stygofauna or trogofauna

Troglofauna are terrestrial, air-breathing fauna that do not rely directly on groundwater, although groundwater provides a humid environment and carries food from the surface. Stygofauna is all aquatic fauna in groundwater. Stygofauna can be classified depending on how much of the life cycle is spent in groundwater (see diagram below).

Diagram shows different types of fauna and where they live.

What stygofauna can tell us

• Indicator of surface water connectivity
• Indicator of water quality
• Presence of functioning groundwater dependent ecosystem
• Baseline data for effectiveness of water management strategies
• Biodiversity value

Additional information

Subsurface Groundwater Dependant Ecosystems: a review of their biodiversity, ecological processes and ecosystem services

Bibliography