Implications of water extraction on the low-flow hydrology and ecology of tropical savannah rivers: an appraisal for northern Australia

Abstract

Balancing the freshwater needs of humans and ecosystems is a fundamental challenge for the management of rivers worldwide. River regulation and water extraction can affect all components of the natural flow regime, yet few studies have investigated the effects on the low-flow end of the hydrograph. Low-flow periods are hydrologically distinctive and ecologically important, varying in nature among climatic zones. Tropical savannah rivers are characterized by highly seasonal and predictable flow regimes, but with high interannual variation in the magnitude, timing, and duration of low flows. Many tropical savannah rivers are relatively intact, especially in northern Australia, but many are now receiving increasing attention for water-resource development through surface-and groundwater extraction. We identified the hydroecological effects of water extraction on 3 phases of the seasonal flow regime: the wet-dry transition, dry season, and dry-wet season transition for perennial and intermittent rivers in tropical savannah climates. We propose a conceptual model and 7 predictions that describe the ecological implications of dry-season water extraction in tropical savannah river systems worldwide. The predictions address: 1) connectivity, 2) availability of in-stream habitat, 3) dry-season persistence of in-channel refugia, 4) water quality during dry-wet and wet-dry transition periods, 5) decoupling of wet-and dry-season flows, and the cumulative effects on 6) groundwater-dependent species and 7) whole-ecosystem shifts. We used northern Australia as a case study to review the current level of evidence in support of these predictions and their potential ecological consequences, and used this review to propose key priorities for future research that are globally applicable.

Flow‐mediated predator–prey dynamics influence fish populations in a tropical river

“…This supports previous work in the Daly River, which found that under water-extraction scenarios that reduced dry season flow magnitude, the probability that barramundi abundance would be extremely low increased by almost 20% (Chan et al, 2012). Furthermore, King et al (2015) suggest that dry season water extraction may lead to a de-coupling of the relationship between wet season flow and barramundi recruitment strength, potentially increasing densitydependent competition among juveniles. The alteration of dry season flows-which are critical for maintaining habitat availability and conditions for successful spawning and recruitment of many small-bodied prey fishes-could also compound these changes to barramundi populations.…”

Fish assemblage dynamics in an intermittent river of the northern Australian wet–dry tropics

“…() estimated that <1% of the total area of this region could be classified as perennial aquatic habitat. Not surprisingly, this annual wetting and drying exerts a dominant influence on the ecology of the region's rivers (King, Townsend, Douglas, & Kennard, ; Warfe et al., ).…”

A conceptual framework for ecological responses to groundwater regime alteration (FERGRA)

“…The first is the timing when a GDE is connected to groundwater. This is likely to be important in systems with strong seasonal and other temporal ecological cues (e.g., fish reproduction and migration; King et al, ). Timing of groundwater connections may also strongly influence the biota of GDEs subject to seasonal or supraseasonal precipitation droughts, especially when groundwater connections maintain drought refuges in GDEs (Barbeta et al, ) or favour particular taxa (e.g., the amphipod Gammarus pulex in a groundwater‐fed English stream; Stubbington et al, ).…”

“…Again, there are some major challenges to be considered when testing hypotheses about different GDEs' ecological responses to groundwater regime alteration. First, GDEs in the landscape are often affected by other stressors such as surface‐water regime alteration (e.g., King et al, ) and land uses such as grazing (Powell et al, ). Disentangling these effects from groundwater regime alteration is difficult but data on changes in surface water and land use can be incorporated into models of GDE responses (e.g., Korbel & Hose, ) to help establish potential sources of variance.…”