Teacher background information
Our rivers and estuaries are under increasing pressure from land use change, altered aquatic habitat, competition from exotic species, changes to flow regime, pollution and a changing climate.
What are nutrients?
Nutrients are elements or compounds including nitrogen, phosphorus and organic carbon. They enter rivers from catchments through drains, surface runoff and groundwater. The most common sources of nutrients entering our rivers include fertilisers, plant matter (e.g. grass clippings, leaves), detergents, sewage and animal waste.
Eutrophication (high concentrations of nutrients) can be either natural or caused by human impact. When humans alter the landscape by clearing vegetation there may no longer be enough vegetation around rivers and estuaries to absorb excess nutrients before they enter these waterways. This problem is exacerbated by the addition of extra nutrients onto the land in the form of fertilisers and animal manure and by changing the types of plants present.
What is the problem with nutrients?
Nutrients are essential for plant growth, including algae. However excess nutrients fuel algal blooms and can promote harmful algae. When an algal bloom collapses, the algal cells fall to the riverbed. Here, bacteria break down the algal organic matter from the catchment. This process takes oxygen out of the water and the greater the amount of organic matter in the system, the greater the amount of oxygen that is removed from the water. This can result in low oxygen conditions.
Low oxygen conditions can result in nutrient release from the river sediments, which can favour toxic algal blooms. Low oxygen conditions and toxic algal blooms may result in fish deaths.
What can we do to help?
- Fertilise wisely by limiting fertiliser application and only applying a river-friendly variety. Ensure that you never overwater.
- Do not dispose of items in drains, as these lead to our waterways.
- Wash your car on the lawn to keep detergents out of the stormwater drainage system.
- Grow local native plants, which need less water and fertiliser.
- Take your rubbish home when you are out enjoying the rivers.
- Pick up your dog’s waste and put it in a bin.
- Check with your local council where to dispose of paint, oil and chemicals.
- Use phosphorus-free detergents when washing clothes or dishes.
- Compost your leaves and grass clippings.