Design and management of free water surface constructed wetlands to minimize mosquito production

Constructed wetland technology has broad applications for the treatment of many types of wastewaters and provides an ecological approach to mitigate the release of nutrients and toxic materials into the environment. However, design features, maintenance activities and the characteristics of the wastewater undergoing treatment contribute differentially to potential levels of mosquito production and, consequently, to threats to human and animal health from mosquito-borne pathogens. Of the variables typically considered when designing free-water surface constructed wetlands for the improvement of water quality of municipal and agricultural wastewaters, organic loading (i.e., biochemical oxygen demand, total suspended solids), nutrients (nitrogen and phosphorus), and the configuration and maintenance of emergent vegetation can have strong effects on mosquito production. The production of Culex vectors of encephalitides and filarial worms is directly related to loading rates of organic matter and bottom-up enrichment of larval mosquito resources and their interaction with design features and management practices that reduce the physical and biological factors causing mortality of immature mosquitoes. As loading rates of organic matter and nutrients decline, the diversity of mosquitoes produced by treatment wetlands tends to increase and the relative abundance of Anopheles species, which are capable of vectoring the causative agents of malaria, increases in temperate man-made wetlands. Habitat features and management practices that create intermittently inundated substrate can lead to the production of other mosquitoes (i.e., Aedes, Psorophora) with floodwater life histories. Constructed wetland technology is expected to play an increasing role in water treatment and reclamation in tropical and subtropical countries where virulent mosquito-borne pathogens already cause significant levels of morbidity and mortality.