Groundwater is a significant component of the world's water balance and accounts for
>90 % of usable freshwater. Around the world groundwater is an important source of
water for major cities, towns, industries, agriculture and forestry. Groundwater plays a
role in the ecological processes and 'health' of many surface ecosystems, and is the
critical habitat for subterranean aquatic animals (stygofauna). Over-abstraction or
contamination of groundwater resources may imperil the survival of stygofauna and
other groundwater-dependent ecosystems (GDEs). In two karst areas in Western
Australia (Yanchep and Leeuwin-Naturaliste Ridge), rich stygofauna communities
occur in cave waters containing submerged tree roots. These aquatic root mat
communities were listed as critically endangered because of declining groundwater
levels, presumably caused by lower rainfall, groundwater abstraction, and/or forest
plantations. Investigation of the hydrology and ecology of the cave systems was
considered essential for the conservation and recovery of these threatened ecological
communities (TECs). This thesis investigated the hydrology and ecology of one of the
TECs, located in the Jewel Cave karst system in the Leeuwin-Naturaliste Ridge. A
multi-disciplinary approach was used to explore aspects pertinent to the hydrology and
ecology of the groundwater system.
Thermoluminescence dating of the limestone suggested that development of the karst
system dates from the Early Pleistocene and that caves have been available for
colonisation by groundwater fauna since that time. Speleogenesis of the watertable
maze caves occurred in a flank margin setting during earlier periods of wetter climate
and/or elevated base levels. Field mapping and leveling were used to determine
hydrologic relationships between caves and the boundaries of the karst aquifer.
Monitoring of groundwater levels was undertaken to characterise the conditions of
recharge, storage, flow and discharge. A hydrogeologic model of the karst system was
developed.
The groundwater hydrograph for the last 50 years was reconstructed from old
photographs and records whilst radiometric dating and leveling of stratigraphic horizons
enabled reconstruction of a history of watertable fluctuations spanning the Holocene to
Late Pleistocene. The watertable fluctuations over the previous 50 years did not exceed the range of fluctuations experienced in the Quaternary history, including a period
11,000 to 13,000 years ago when the watertable was lower than the present level.
The recent groundwater decline in Jewel Cave was not reflected in the annual rainfall
trend, which was above average during the period (1 976 to 1988) when the major drop
in water levels occurred. Groundwater abstraction and tree plantations in nearby
catchments have not contributed to the groundwater decline as previously suggested.
The period of major watertable decline coincided with a substantial reduction in fire
frequency within the karst catchment. The resultant increase in understorey vegetation
and ground litter may have contributed to a reduction in groundwater recharge, through
increased evapotranspiration and interception of rainfall. To better understand the
relationships between rainfall, vegetation and fire and their effects on groundwater
recharge, an experiment is proposed that involves a prescribed burn of the cave
catchment with before-after monitoring of rainfall, leaf-area, ground litter, soil moisture,
vadose infiltration and groundwater levels.
Molecular genetic techniques (allozyrne electrophoresis and mitochondria1 DNA) were
used to assess the species and population boundaries of two genera and species of cave
dwelling Amphipoda. Populations of both species were largely panrnictic which was
consistent with the hydrogeologic model. The molecular data supported the conclusion
that both species of amphipod have survived lower watertable levels experienced in the
caves during the Late Pleistocene. A mechanism for the colonization and isolation of
populations in caves is proposed.
Multi Dimensional Scaling was used to investigate patterns in groundwater biodiversity
including species diversity, species assemblages, habitat associations and biogeography.
Faunal patterns were related to abiotic environmental parameters. Investigation of
hydrochemistry and water quality characterized the ecological water requirements
(EWR) of the TEC and established a baseline against which to evaluate potential
impacts such as groundwater pollution.
The conservation status of the listed TEC was significantly improved by increasing the
number of known occurrences and distribution range of the community (from 10 m2 to >
2 x lo6 m2), and by showing that earlier perceived threatening processes (rainfall
decline, groundwater pumping, tree plantations) were either ameliorated or inoperative
within this catchment. The GDE in the Jewel Cave karst system may not have been
endangered by the major phase of watertable decline experienced 1975-1987, or by the
relatively stable level experienced up until 2000. However, if the present trend of
declining rainfall in southwest Wester,,Australia continues, and the cave watertable
declines > 0.5 m below the present level, then the GDE may become more vulnerable to
extinction.
The occurrence and distribution of aquatic root mat communities and related
groundwater fauna in other karst catchments in the Leeuwin-Naturaliste Ridge is
substantially greater than previously thought, however some of these are predicted to be
threatened by groundwater pumping and pollution associated with increasing urban and
rural developments. The taxonomy of most stygofauna taxa and the distribution of root
mat communities is too poorly known to enable proper assessment of their conservation
requirements. A regional-scale survey of stygofauna in southwest Western Australia is
required to address this problem. In the interim, conservation actions for the listed TECs
need to be focused at the most appropriate spatial scale, which is the karst drainage
system and catchment area. Conservation of GDEs in Western Australia will benefit
fi-om understanding and integration with abiotic groundwater system processes,
especially hydrogeologic and geomorphic processes.
| Identifer | oai:union.ndltd.org:ADTP/221670 |
| Date | January 2004 |
| Creators | Stefan@calm.wa.gov.au, Stefan Eberhard |
| Publisher | Murdoch University |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.murdoch.edu.au/goto/CopyrightNotice, Copyright Stefan Eberhard |
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