Streams can be contaminated by a range of material from adjacent land. This can include soil particles (sediment), nutrients such as nitrogen and phosphorus, salt, plant material from crops, chemicals, and microbes. In rural regions, eroding soil and associated nutrients are the most important and widespread causes of reduced water quality.
Sediment and some nutrients, particularly phosphorus, are carried to streams primarily in the overland flow of water. This flow can range from thin threads to broad sheets of water, and may be concentrated in dips and gullies in the landscape. Dissolved nutrients such as nitrogen, salt, and other materials (including dissolved organic carbon) can also move through the soil in underground flows and contaminate streams as they enter them as base flow.
The clearing of catchments for agricultural land, soil disturbance during forestry operations or urban development, and bare areas such as gravel roads and stock tracks, have led to substantial increases in the amounts of sediment (gravel, sand, silt and clay) entering ours streams and rivers. This sediment and its associated nutrients and chemicals can contaminate human and stock water supplies, smother breeding sites for fish and other in-stream animals and, by filling up stream pools, deprive these animals of the deeper waters that are a vital refuge in dry seasons and prolonged droughts. Whatever the specific impact, the end result is likely to be significantly decreased water quality.
How a riparian buffer strip functions to protect the
stream from contaminants. Illustration Carolyn Brooks.
The full fact sheet is available in Adobe Acrobat format:
Fact Sheet 3 - Improving water quality (facts03.pdf, 340Kb)
Topics covered
- How does riparian vegetation affect water quality?
- Do riparian buffer strips work?
- Designing an effective riparian filter strip
- Other ways of limiting stream contamination
- Timing and placement of fertiliser
- Managing stock access
- For further information
This Fact Sheet is the third in a series dealing with the management of riparian land.
