The community values of a waterway can be strongly influenced by issues other than water quality. These non-water quality related stressors can either impact directly on the community values of a waterway or indirectly by affecting water quality itself.
When assessing water quality, you need to consider whether and how non-water quality related pressures and stressors might be contributing to or even driving changes to the system, particularly to biodiversity.
Considering pressures and stressors other than those related to water quality is critical so you can attribute measured responses of indicators to the correct cause.
How this is achieved will be reliant on:
- identifying and incorporating the direct and indirect influences of these stressors in the conceptual model for the issue (in
Step 1 of the Water Quality Management Framework)
- considering the range of lines of evidence and associated indicators needed to
- determine the causes of water quality changes
- distinguish the effects of water quality and non-water quality stressors on the community values.
This can be done using a quality of evidence assessment as described in
Weight of evidence. These quality of evidence examples indicate that having insufficient lines of evidence and associated indicators to distinguish the effects of water quality and non-water quality stressors can provide poor quality inference across the weight-of-evidence assessment.
Examples of non-water quality stressors to consider
Alteration to aquatic habitats, such as de-snagging, ponding, rock removal, bank erosion, loss of riparian vegetation and substratum smothering, can have profound effects on the composition and functioning of aquatic ecosystems. A number of established habitat quality assessment schemes have demonstrated ability to relate aquatic ecosystem health to habitat features, including:
They focus particularly on characteristics such as riparian vegetation structure and composition, which can directly affect water quality parameters such as temperature, due to reduced shading. An example of the application of this approach to distinguish between water quality and habitat alteration impacts on ecosystem health is Sudaryanti et al. (2001).
Both habitat availability and organism movements can be affected by flow alteration caused by impoundments, diversions and water extraction for other uses.
Water quality impacts are also commonly associated with flow alterations, particularly where the base flow is substantially reduced. These are primarily physical changes initially, but can progress to ecological impacts as a result of both the water quality and quantity changes.
Where flow alteration affects key ecosystem processes, substantial ecological change can readily result, and this has been the focus of considerable policy and management action by states and catchment management authorities. Examples of these include:
Changes to water flow, particularly those leading to the absence of water, reduction in flood pulses or reduced baseflow, will exert strong control on the status of aquatic ecosystems, availability of water for agricultural, recreational or drinking water source use, and to cultural and spiritual values. This will be particularly so for
water bodies in the semi-arid and arid regions that have shorter, less frequent flow periods, but will hold for all aquatic ecosystems. Often there are linkages between water flow or quantity and water quality, and these should be identified in the conceptual model for the issue being considered. A good discussion of the relationships between alteration of water quantity and water quality is provided in SKM (2013), along with conceptual models for systems from each climatic zone in Australia.
Organism passage barriers
The prevention of movement of aquatic organisms, like fish, through watercourses can affect their distributions and those of their prey and predators. There are also substantial state and local management and research efforts into the impacts of ecosystem status and function from alteration of aquatic organism movement patterns, particularly fishes. Examples of these include:
The introduction of exotic species can have profound impacts on the structure and composition of an aquatic ecosystem. This includes the translocation of otherwise native species outside their normal ranges with and between catchments.
Unusual or strong climate events, such as floods, droughts, cyclones, fires, can greatly influence the condition of aquatic ecosystem and other community values. Usually, using a referential approach will allow for consideration of the effects of such events on condition status in the area of interest.
Characterising the Relationship Between Water Quality and Water Quantity, Australian Government Department of Sustainability, Environment, Water, Population and Communities, Canberra.
Sudaryanti S, Trihadiningrum Y, Hart BT, Davies PE, Humphrey C, Norris R, Simpson J & Thurtell L 2001,
Assessment of the biological health of the Brantas River, East Java, Indonesia using the Australian River Assessment System (AUSRIVAS) methodology, Aquatic Ecology 35: 135–146.