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Issue: Pressures on biodiversity - Changed hydrology

This is an issue under the Biodiversity theme of the Data Reporting System.

Why we need to know about this issue

Hydrology broadly describes the properties, distribution, and effects of water on the earth's surface, in the soil and underlying rocks, and in the atmosphere. Impacts of changed hydrology on biodiversity include deteriorating water quality, reduced water availability, altered flow regimes in waterways, and the rising of water tables due to clearing of native vegetation and the movement of salts to surface layers of soil and waterways.

In urban and other cleared areas, reduced infiltration may lead to lowering of the water table and drying of wetlands. Clearing of areas adjacent to or above wetlands may result in stormwater being channelled into creeks rather than infiltrating the soil and recharging the groundwater feeding the wetlands. Vegetation clearing is also responsible for significant areas of land becoming saline. In 2000 the National Land and Water Resources Audit estimated that 631 000 ha of remnant native vegetation and associated ecosystems were at risk from dryland salinity. This area was projected to increase by up to 2 000 000 ha over the next 50 years.

Other types of changed hydrology include altered flow regimes and deteriorating water quality. River and stream flows are affected by weirs and dams and water diversions. Water quality is reduced following runoff from land subjected to fire and pollution. Aquatic biodiversity and species that rely on water resources for food, such as waterbirds, are affected by the reduced availability of water or a reduction in its quality.

Indicators

• BD-14 Examples of impacts of changed hydrology on biodiversity 
  In the absence of comprehensive data on the impacts of changes in hydrology on biodiversity, some examples of the impacts on particular species, and on particular places where species are likely to be vulnerable, provide insights into this pressure.
• LD-06 Area and proportion of land affected by dryland salinity and acidity 
  Area of land affected by dryland salinity is a surrogate indicator for extent of disturbance of biodiversity by dryland salinity.
• IW-05 Average annual groundwater depth 
  In urban and other cleared areas, reduced infiltration may lead to lowering of the water table and drying of wetlands. Clearing of areas adjacent to or above wetlands may result in stormwater being channelled into creeks rather than infiltrating the soil and recharging the groundwater feeding the wetlands.
  Aquatic biodiversity and species that rely on water resources for food, such as waterbirds, are affected by the reduced availability of water or a reduction in its quality.
  Rising groundwater can also place pressure on biodiversity as salt is drawn to the surface where it may contaminate soil and surface water and kill remaining vegetation and biodiversity.
  In the absence of data on groundwater depth, estimates of sustainable yield provide little insight into this issue.
• IW-06 Average annual groundwater pressure 
  Reduced groundwater pressure can lead to insufficient water available to sustain groundwater dependent ecosystems such as mound springs.
• IW-10 Assessment of river condition indices 
  River and stream flows are affected by weirs and dams and water diversions. Aquatic biodiversity and species that rely on water resources for food, such as waterbirds, are affected by the reduced availability of water. The component parts of this indicator provide a broad insight into the condition of river systems in respect to several aspects of flow regimes, and therefore into these pressures on biodiversity.
• IW-26 Forested streamlength 
  Riparian zones are sensitive environments - important for biodiversity in themselves - and with potentially significant effects on instream characteristics such as nutrient levels and turbidity. Protection and enhancement of natural values along water frontages will contribute to overall conservation management objectives.
• IW-27 Extent of significant wetlands (incl. Ramsar) 
  Although extent of wetlands is to some extent seasonal, long term trends in extent of wetlands is a surrogate indicator for condition of wetlands, and both extent and condition of wetlands are in turn indicative of changes in hydrology more generally.
• IW-28 Number of effective fishways 
  Barriers to fish passage is one reason for a decline in fish abundance and distribution. Fishways can address this problem. Number of effective fishways would be indicative of improvements in the management of this pressure on biodiversity.
• IW-33 Abundance and distribution of waterbirds 
  The distribution and abundance of waterbirds is closely connected to the occurrence of floods and wetland inundation during wet years. Severe reductions in wetland extent in Australia have reduced the available habitat as well as the numbers and breeding success of native waterbirds. Changes in the abundance and distribution of species could therefore also be indicative of changes in wetland hydrology.
• IW-46 Implementation of COAG principles 
  The COAG framework includes provisions for allocating water for the environment, which should have a positively effect on some pressures on biodiversity over the long term. Monitoring of their implementation should provide critical indicators of the effectiveness of environmental flows allocation and management, and should ultimately result in improved hydrological and ecological condition of river systems.

Related issues

• Biodiversity - Species, habitats and ecological communities - Conservation status of species and ecological communities 
• Land - Land condition - Hydrology 
• Inland Waters - Catchment scale influences - Hydrological condition- Surface-water availability and human use 
• Inland Waters - Catchment scale influences - Hydrological condition- Ground-water availability and human use 
• Inland Waters - Catchment scale influences - Hydrological condition- Ecological aspects of river flow regimes 
• Inland Waters - Catchment scale influences - Hydrological condition- Connectivity - dams, weirs, regulators and levees