Nutrients and urbanisation
What are the potential sources of nutrients from urbanisation?
Urban lakes, rivers, and streams often receive untreated (i.e., from stormwater) and treated discharges (i.e., from wastewater processing plants). Discharges may contain chemical contaminants and nutrients from surrounding land use activities including roads, building sites, residential areas, and waste treatment facilities.
Waterways in urban areas can be very polluted, giving them a milky, oily, or murky brown, turbid appearance. Nutrients in overland flow can be intercepted by planting riparian vegetation. For nutrients that enter streams and lakes from stormwater pipes, constructed wetlands can be designed to receive discharges and absorb nutrients that would otherwise end up in waterways.
Potential impacts of high nutrients on water quality and mahinga kai
- Eutrophication - excess nutrients in lakes, estuaries, or slow-moving streams and rivers can lead to an increase in primary productivity which stimulates excessive plant growth (algae, nuisance plants, and weeds), thereby degrading water quality. This process is called eutrophication.
- Loss of species - an increase in plant growth, sometimes called an algal bloom, reduces dissolved oxygen (DO) in the water when the plants die and decompose, and can cause organisms (fish and invertebrates) to die.
- Loss of habitat - eutrophication of the water can kill off plants that fish depend on for their habitat.
- Increase in turbidity and a decrease in visibility - when the phytoplankton community increases in response to nutrients this reduces water clarity, visibility, and recreational suitability. It also reduces the ability of some fish to see prey or predators.
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