Good water quality is fundamental requirement for the health of aquatic ecosystems and the diversity of plants and animals they sustain. Good water quality is also important to maintain the numerous benefits that streams provide to us: we store their waters for drinking, eat fish and shellfish obtained from them, recreate within them, and water our livestock and crops with their waters.
With severe declines in populations of most native fish, massive increases in sedimentation and turbidity, loss of riparian vegetation, alienation of floodplain wetlands, increasing salinity, alteration in flow and flooding patterns, and increasing instances of toxic blue-green algae blooms, there is little doubt that many, perhaps the majority, of Australia's rivers and streams are seriously degraded.
In 1995 the Environment Protection Authority (RACAC1996c) undertook a systematic sampling of water quality across the Northern Rivers (Tweed, Brunswick, Richmond and Clarence). For low flow conditions most sites were ranked very poor for potable (drinking) water, with only one site ranking as high as poor on the Tweed and 19% on the Clarence qualifying as poor. For aquatic ecosystem protection 54-100% of sites on the three northern rivers were ranked poor-very poor, with only the Clarence River having the majority of sites (58%) with a fair-good ranking. For edible seafood 60-100% of sites on the three northern rivers were ranked poor-very poor, with only the Clarence River having the majority of sites (66%) with a fair-good ranking. For primary contact recreation (ie swimming) 57-80% of sites were ranked poor-very poor.
Under high flow conditions following heavy rainfall water quality deteriorated dramatically, with no sites in the Tweed, Brunswick, Richmond or Clarence River catchments passing the criteria for potable water, aquatic ecosystem protection, edible seafoods, or primary contact recreation (with the exception of one site on the Brunswick passing for primary contact, which was attributed to sampling before significant runoff had affected the site). There were large increases in suspended sediments and nutrients, with over 20,000 tonnes of suspended sediments, 179 tonnes of nitrogen and 17 tonnes of phosphorous per day moving down the Clarence River through Grafton.
A s noted by the EPA (RACAC1996c):
Land use practices that that involve the removal of vegetation and/or disturbance of soils, including cropping, grazing, logging and urban development, will increase the export of suspended sediments and nutrients from the catchment during heavy rainfall events. ...
Vegetation plays an essential role in limiting erosion and transport of material from the catchment, slowing the movement of water across the catchment surface, allowing for increased infiltration and lower erosion energy.
When we think of catchments it is often the large rivers which come to mind, though it is along the smallest streams and drainage lines where most of the interaction between terrestrial and aquatic environments occurs. Small headwater streams generally drain catchments smaller than two square kilometres and can constitute over 75 per cent of the stream length in a drainage basin (Barmuta et. al. 2009). Restoration of catchment health must start in the headwaters and expand downstream.
In a natural forest most water movement occurs as subsurface flows seeping through the ground. In logging operations the removal of vegetation cover, soil disturbances and roading create and channel overland flows, which erode soils and nutrients, transporting them into streams (see Logging impacts on streams). Forestry is largely focussed on the smaller headwater streams and thus can have a disproportionate affect on stream health.
An important part of the solution to restoring stream health is to establish wide buffers along streams and around wetlands to protect riparian habitat and exclude cattle and logging (see The Need for Stream Buffers). While adequate buffers can protect streams from direct impacts they can only modify sediment and nutrient inputs from overland flow, so it is important to apply rigorous erosion mitigation measures outside buffers and to ensure the impacts of road crossings are minimised.
The suspended sediment added to the streams is like a dust storm on dry land – fish can be suffocated, vegetation smothered, and sediment can permeate into all the homes and nurseries of invertebrates hidden away in nooks and crannies between rocks and in gravel beds. As the velocity of the water begins to slow the larger soil particles are progressively deposited. At their worst, sediments can completely cover the natural substrate, filling pools and turning the stream beds into the equivalent of biological deserts.
All forests are important for water supply, though this importance increases in relation to the numbers of people and the value of industries a catchment supplies. For the more significant catchments water supply should be a “primary consideration in decision-making affecting the catchment” and not an incidental consideration as it often is now. The Sydney Water Inquiry was established following the 1998 Sydney water contamination crisis, in part it concluded (McClellan 1998):
“The health of the catchment is a fundamental responsibility of our community, both for this, and subsequent generations. I have concluded that immediate action must be taken to establish appropriate management and regulatory structures to ensure the catchment is not further compromised and, if possible, existing problems minimised or removed. … We must not allow vested interests to inhibit the creation of effective planning, regulatory and management structures for the catchment.
“The problems of the catchment demand a strong and effective response. A modern treatment plant is not a substitute for proper catchment management. Protecting the catchment provides the best long-term protection for Sydney’s drinking water. …
“Under the current arrangements, the catchment is managed to allow a range of activities. Water quality considerations may be diminished in favour of agricultural, urban and rural residential, forestry, mining and other developments. …
“In my view, this situation cannot be allowed to continue. … From now, water quality should be the primary consideration in decision-making affecting the catchment. This has significant implications for proposed future developments in the catchment. …
“There is a need to develop directions, catchment wide strategies and water quality objectives to guide management activities and development decisions in the catchment. …
McClellan, P. (1998) Assessment of the contamination events and future directions for the management of the catchment. Sydney Water Inquiry, Third Report, NSW Premier’s Department.
RACAC – Resource and Conservation Assessment Council (1996) Regional Report of Upper North East New South Wales, Volume 3, Water Attributes. RACAC, Sydney.