Eutrophication (the condition whereby a river or estuary has very high concentrations of nutrients present) can be either natural or caused by human impact. When humans alter the landscape by clearing vegetation for agriculture or urban development the way water moves through the landscape changes. 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.
The two most common types of nutrients that cause problems in Western Australia are nitrogen and phosphorus. Whilst these nutrients are not toxic at the concentrations typically found they can have a large impact on the health of rivers and estuaries. For example, high concentrations of nutrients can encourage algal growth which may result in nuisance or toxic algal blooms. Eventually these blooms will collapse and the resulting decomposition of the algal cells strip oxygen out of the water, potentially resulting in fish kills. Nutrients will also be stored in the sediments of rivers and estuaries where they can become available again under certain environmental conditions such as low oxygen levels.
Long term monitoring of nutrients allows us to assess trends in waterways over time which tells us if they are improving or degrading. We can also use this data and our knowledge of land use to construct models, which help us predict where in the landscape the nutrients are being exported from. They also allow us to target remediation works to ensure the best results are obtained.