Constructed wetlands and mosquitoes: Health hazards and management options—An Australian perspective

Constructed wetlands are increasingly being installed to ‘polish’ urban drainage and storm water by reducing contaminants before disposal into river systems. Unfortunately, they also provide habitat for mosquitoes that can be nuisance pests and transmit pathogens such as arboviruses and malaria. In Australia, Ross River virus is responsible for thousands of cases annually of a disease that is severely debilitating, has regional incidence rates often exceeding 1:1000, and costs millions of dollars in health and other impacts. Disease transmission depends on mosquito species and abundance, and extent of contact with humans; the characteristics and siting of wetlands determine hazards, and indicate risks for nuisance or disease. Mosquito control should not rely solely on chemical and biological agents. Design of wetlands is important: shallow water and dense vegetation promote mosquito production. Deeper habitats with cleaner steeper margins, and more open water, produce fewer mosquitoes. Water and vegetation management can reduce mosquitoes: aeration and sprinkler systems, and flooding and drainage regimes, can reduce larval densities; vegetation thinning can assist mosquito predators. Such measures may appear incompatible with objectives and operations of wetlands, but mosquito management must be an integral objective of modern wetland design and maintenance in order to minimise health hazards.