Zika virus is a risk in border regions (Arizona Daily Star, July 11)
Since construction of the Sweetwater Wetlands began in 1996, the City of Tucson has significantly reduced the mosquito population. The site includes 17.5 acres of constructed wetlands, 14 acres of recharge basins, and a recurring mosquito problem. The Wetlands was initially constructed to treat filter backwash water from the City's Reclaimed Water Treatment Plant.
The treatment plant, built in 1984, used to produce reclaimed water by filtering secondary effluent from the Roger Road Water Reclamation Facility through granular silica/carbon filters. The filters plugged up periodically and plant operators had to backwash the filters to clean them. The Wetlands was originally designed to receive and treat the backwash water produced during this process. The backwash water, high in suspended solids, drained by gravity into settling basins, wetland ponds, and eventually adjacent recharge basins. Since 2014, the Wetlands is no longer needed to treat backwash water because the tertiary effluent from the new Agua Nueva Water Reclamation Facility does not need to be filtered.
The wetland ponds contain areas of deep, open water alternating with zones of shallow water planted with bulrush and cattail. Over the years, the shallow vegetated zones have been prone to produce mosquitoes which are potential carriers of the West Nile virus and the Zika virus.To avoid a potential public health risk, the City has a mitigation program to control the mosquito population.
Currently, Tucson Water staff uses a few different methods to control and limit the population growth of mosquitoes at the Sweetwater Wetlands to protect visitors and ultimately the city from potential threats. The staff applies bacterial larvicide to the ponds to stop mosquito larvae from growing into adults on a regular basis. This larvicide is specific to mosquito larvae and does not harm any of the other wildlife or the habitat itself. To kill adult mosquitoes, Water staff implements fogging, especially during the monsoon season since mosquitoes thrive in higher humidity. Every spring, Tucson Water and the Tucson Fire Department conduct a controlled burn that reduces mosquito habitat.
Every week from March to October, a Tucson Water staff member sets six carbon dioxide traps around Sweetwater Wetlands. The trapped mosquitoes are then sent to University of Arizona entomologists for counts at the various locations and species identification. It can be concluded from the data that total mosquito populations have been consistently declining since the beginning of the Mosquito Abatement Program.