Wetlands and Human Health: Hydrology, Biogeochemistry, and West Nile Virus.

Wetlands have long been associated with societal benefits such as water filtration and hydrologic stabilization. This positive perspective contrasts sharply with earlier views of these ecosystems as threatening reservoirs of risk for humankind. Some concerns about wetlands were (and remain) justified from the standpoint of diseases like malaria which prevailed within the southern United States through the early 1950s and remain an enormous threat in many parts of the world. However, as a result of the hydrologic stability and water filtration afforded by wetlands, these systems serve as a buffer against some arboviruses such as West Nile virus (WNV). A high proportion of green space and particularly wetlands within watersheds reduces the occurrence of storm surges which, when combined with stormwater – sewer overflows, create ideal conditions for reproduction of Culex sp. mosquitoes, the main vector of WNV. Similarly, variation in carbon sources and elevated NO₃, PO₄, and NH₄ concentrations drive changes in Culex larvae and pupae that could elevate risk of WNV incidence within 2 km of stream locations. Specifically, increasing NO₃ in streamwater from 1 to 10 mg/l was associated with more rapid pupation times (reduction from 60 to 50 days) of female Culex, larval success was increased by a factor of 4.5 when PO₄ concentrations rose from 0.1 to 10 mg/l, and PO₄ increases from 0-6 mg/l were linked with a 57% increase in numbers of adults. Also, conversion of native forests to lawns (and associated export of lawn clippings into breeding pools) increased numbers of pupae 10-fold as a result of higher litter quality in the grasses. Inverse linkages between WNV incidence and presence of wetlands and natural vegetation suggest that wetlands help regulate the WNV transmission cycle and provide an additional societal benefit related to public health.