Eutrophication (nutrient enrichment)
Eutrophication, is nutrient enrichment; it drives excess primary productivity in waterways. It can be either natural or caused by human impact.
Humans alter the way water moves through the landscape by clearing vegetation for agriculture or urban development and by constructing drainage that moves water quickly off the landscape into the receiving water bodies. These changes to the landscape mean that there is often insufficient vegetation around rivers and estuaries to utilise excess nutrients. This problem is exacerbated when extra nutrients are added onto the land in the form of fertiliser and animal manure, or also by changing the types of plants present.
Compounds that contain nitrogen and phosphorus are the most common culprits driving eutrophication. These nutrients are generally not toxic at the concentrations typically found in nature, however they can have a large impact on the health of rivers and estuaries. For example, high concentrations of nutrients may encourage algal growth and result in nuisance or toxic algal blooms.
Eventually these blooms will collapse and die and the resulting decomposition of the algal cells will strip oxygen out of the water, sometimes causing fish kill events.
Nutrients are also temporarily stored in the sediments of rivers and estuaries, but under certain environmental conditions, such as low oxygen, the nutrients can re-enter the overlying water and be available again to grow more algae.
The Department of Water assesses the concentrations of nutrients in a variety of water bodies including river and estuary systems, stormwater drains and groundwater. Understanding the concentrations of nutrients both within and entering our rivers and estuaries will assist the department in assessing the health of waterways and in determining management solutions for impacts such as algal blooms and fish kill events.
Long term monitoring allows us to assess trends in nutrients in our freshwater and estuarine systems. This allows us to assess and report whether nutrient conditions are improving or degrading (for example see catchment nutrient reports and the State-wide River Water Quality Assessment). We can also use this data and our knowledge of land use to construct models, which help us predict where nutrients are being exported from the landscape.
These models also allow us to target remediation works to ensure the best results are obtained and are an integral part of our water quality improvement plans.
The water quality information collected by the Department of Water and other organisations is available from the department's Water Information Reporting portal.
For further information see monitoring and assessing water quality and managing water quality and the following publications:
- Nitrogen and phosphorus cycles (River Science Issue 4)
- Sources of nutrients to the Swan and Canning rivers (River Science Issue 5)
- The delivery of nutrients to the Swan and Canning rivers has changed over time (River Science Issue 6)
- Seasonal nutrient dynamics in the Swan Estuary: 1995-2000 (River Science Issue 8)
- Seasonal nutrient dynamics in the Canning River and Estuary (River Science Issue 9)
- Field sampling guidelines : a guideline for field sampling for surface water quality monitoring programs
- Water quality monitoring program design: a guideline to the development of surface water quality monitoring programs