Background
Sustaining aquatic ecosystems through drought
Australian river ecosystems are fully capable of surviving droughts when they and their surroundings are in a natural state and not also having to supply water for human uses. But there is real scientific concern that humans have modified much of the Australian environment to such an extent that we can no longer expect all freshwater ecosystems to survive and recover after drought.
Freshwater ecosystems appear to survive drought by taking refuge in 'refuge habitats'. These refuges may be sections of stream that continue to flow, or standing waters that only slowly lose volume, as well as small spaces that are able to remain moist for very long periods of time (see Refuge habitats and Planning ahead: Refuge identification and mapping).
Reactive
To help freshwater ecosystems through the crisis of drought, managers of rivers and catchments are reacting positively to protect refuge habitats, by:
- prohibiting pumping from refuge habitat areas, and nearby groundwater,
- providing targeted environmental flows, e.g. downstream of reservoirs, to refresh, dilute, and stir-up droughted streams and pools (refuge habitats), and maintain riverbank vegetation,
- prohibiting taking of fallen timbers (snags) from streams or pools, as these help to maintain bank and habitat structure and are refuge habitats in their own right during drought
- preventing free-ranging livestock and other sources of disturbance from accessing refuge habitats,
- preventing activities that would add nutrients to streams or pools that are refuge habitats,
- maintaining water quality in refuges by stirring the water periodically if it is tending to stratify,
- prohibiting infilling or ploughing or other activities that would convert dry streambeds or wetlands into arable land,
- not constructing culverts, bridges or other barriers between a refuge and adjacent habitats, that would impede recolonisation when the drought breaks.
Reactive actions tend to be short-term measures. For example, in upland streams when flow stops, the fauna needing flowing water, such as riffle-dwelling invertebrates (mussels and some caddis flies) and some specialist fish species, will decline in diversity and abundance. The pattern of drying will depend on the volumes of flow available and the shape of the channel. A reactive solution could be to provide a low-volume environmental flow downstream of dams or weirs by allowing a percentage of inflowing water to be released. Water quality issues might need to be considered, for example, thermal pollution and contaminants.
Proactive
Proactive measures focus on activities that rehabilitate freshwater ecosystems for the long term, not just for droughts. They can be similar to reactive measures in that they may focus on potential refuge habitats, but they are pursued as part of normal management practice, rather than being done 'for now'.
For their long-term protection, refuge habitats need to be sufficiently robust to withstand physical disturbance - both natural and artificial, now and in the future. Therefore, once management has identified and located the types of refuge habitats in its management area (see Planning ahead: Refuge identification and mapping), in many cases these places will need active protection, restoration and maintenance, as a proactive step towards dealing with future droughts.
In particular regions, the steps involved in protecting refuges will require:
- Firstly, determining the physical characteristics of refuges for a given river system or river type.
- Secondly, determining the location of such areas.
- Thirdly, prioritising protection based on conservation principles together with characteristics such as integrity, quality, connectivity.
- Finally, undertaking proactive measures to protect and, if necessary, strengthen the resistance and resilience of such habitats - both to drought itself and to other related threatening processes.
For example:
- restoring catchments and river banks and their vegetation, to minimise erosion and sedimentation, by removing barriers, replanting, etc.,
- protecting river-side (riparian) vegetation,
- preserving water quality (by limiting enriched runoff or sedimentation),
- restricting livestock access,
- reducing pumping from streams or pools and groundwater,
- providing protective (environmental) flows, as needed, in systems that have high rates of water extraction,
- constructing fish passes to help fish get around immovable barriers, especially during the recovery phase,
- identifying and protecting significant ecosystems and particular biota.
The challenge is to be better prepared for future droughts by adopting proactive strategies right now.
Modifications that can reduce the security of refuge habitats during drought, include:
- Excessive diversion of water from streams and standing waters - reducing the volume available to support life.
- Sedimentation infilling pools - sediment reduces water quality, covers up other features of the refuge such as logs and holes and resident plants or organic matter, and makes the pool shallower so it may dry up during drought.
- Clearing of bank vegetation - which leads to faster water loss by evaporation, as well as decreasing habitat quality by removing protective cover, letting in more light, removing inputs of organic matter, etc.
- Access by livestock - which trample banks and stream beds, leading to local erosion and increasing the turbidity of the water, affecting the soil structure of bank and bed, and adding nutrients from dung.
- Illegal fishing for fish or turtles.
- Prevention or diversion of environmental flows that would replenish the water volume and quality in the refuge and provide water to the bank vegetation.
- Taking of fallen timbers (snags) which, when left alone, help to maintain bank and habitat structure in the flowing stream between droughts, and are refuges in their own right during drought.
- Infilling or ploughing or other activities that convert dry streambed or wetland into arable land.
- Construction of culverts, bridges or other barriers that will impede access to the refuge as drought is setting-in, or prevent emigration by fish out of the refuge when the drought breaks.
Keywords:
Topics:
| Water supply | View Frequently Asked Questions | View Bibliography |
| Principels for protecting aquatic biodiversity | View Frequently Asked Questions | View Bibliography |
| Recovery from drought | View Frequently Asked Questions | View Bibliography |
| Drought impacts | View Frequently Asked Questions | View Bibliography |
| Ecological Responses | View Frequently Asked Questions | View Bibliography |
| Refuge habitats | View Frequently Asked Questions | View Bibliography |
