Urban wetland restoration : what about mosquito threats?

Sweetwater Wetland, Tucson, Arizona – Photo by Sara Grimm. Source: http://tucsonaudubon.org/go-birding/get-started-with-birding/great-places-to-bird/sweetwater-wetlands/

When they come to restore or plan wetlands in urban areas, environmental managers are sometimes rejected for good reason. Wetland restorations are always linked to an aspect that urban dwellers are familiar with: it creates good habitats for mosquitoes. This is an inescapable result of urban wetland planning projects (1).

Wetlands play a valuable role in providing numerous economic, ecological, and wellbeing benefits (2). During storms, they can absorb excess rainfall, reduce flooding and economic damage. They can also act as a filter for pollution, improve water and air quality, moderate extreme city temperatures, and provide habitat for many species. Urban wetland are essential for the development of urban and peri-urban agriculture, and of course they have aesthetic value that adds to quality of life. However, they have traditionally been undervalued. This, in combination with agricultural development, urbanisation, pollution, and the introduction of dams and canalizations, has resulted in widespread ecological loss and degradation. Scientists estimate that 64 % of the world’s wetlands have disappeared since 1900. Urban wetlands need to be conserved, restored, and managed to maintain the multiple services they provide. There is still important work to do for a better integration of wetlands in urban planning decisions.

Even so, it must be acknowledged that people will be more exposed to mosquitoes after a wetland restoration project. In fact, “several obstacles block people from frankly discussing mosquito problems.” (1) Sometimes this problem is simply not treated by planners because they prioritize other objectives, and undervalue the issue. Mosquito problems are not included in urban planning as they are considered a perception from the population, who is not aware of the value of wetland for cities. Eliminating this lack of knowledge through education could be the solution: people will accept mosquitoes if they know the role of wetlands.

But sometimes the problem perceived by the population is real. Yes, there used to be an ignorance of the preciosity of wetlands, which led to their destruction. Still, there was an important reason why wetlands were drained: in the 19th century, many wetlands were drained to help control mosquito-borne diseases such as malaria or encephalitis. There is no way to say whether malaria or yellow fever will ever return to historic levels: today, houses are better built and we have better medical treatments. However, reviewing history should remind us that nature contains threats.

When we say that we desire to experience nature in cities, we want to experience selected  aspects of nature and not serious illness. We need to be aware of what has happened and what threats we could potentially face due to mosquitoes. We must have foresight, since there could be new viruses that we won’t be able to control. We need to measure if there is a significant threat and if it is appropriate to take some control

A large range of tactics to manage mosquito populations exists, such as choosing a particular vegetation or a particular design, using biological insecticides or using bio-control by introducing mosquito predators. But these practices also show weaknesses. Sweetwater Wetland in Tucson, Arizona, is a good example of a well-managed wetland. This area is monitored regularly for mosquitoes by managing the vegetation and using biological insecticides, which are applied every week to keep mosquito populations down. Nevertheless, this suggests that mosquitoes can be a significant problem unless continuously managed. Then, the short-term nature of funding for these controls is a problem and depends on the uncertainty of politics. Bio-control methods also show their limits: one of the most introduced fish that predates mosquitoes, Gambusia, turned out to be an invasive species.

Gambusia or Western Mosquitofish – Illustration by Joseph Tomelleri. Source: https://biodiversity.utexas.edu/news/entry/campus-biodiversity-western-mosquitofish

Finally, forgetting or minimizing this threat and its treatment may hamper the attempt to reconnect cities with nature. When we restore or plan natural space in urban areas, we need to consider that it is not just about changing nature, but also particular social contexts. We also need to keep in mind, beyond the benefits urban wetlands can provide, how mosquitoes can be managed effectively depending on location features.

This article was written by Suzy Pensuet in collaboration with Mariem El Harrak, Tristan Macadre, and Benjamin Terrasse, all Master’s students in the Museum’s “Society and Biodiversity” specialization.

Bibliography:

(1) Willott, E. (2004). “ Restoring Nature, Without Mosquitoes? Restoration Ecology”, 12(2), 147–153. doi:10.1111/j.1061-2971.2004.00392.x

(2) Ramsar Convention on Wetlands (2015). “ Ramsar fact sheet 3. Wetlands: a global disappearing act” https://www.ramsar.org/sites/default/files/documents/library/factsheet3_global_disappeazing_act_0.pdf

Dale, Pat & Knight, Jon. (2008). Wetlands and mosquitoes: A review. Wetlands Ecology and Management. 16. 255-276. 10.1007/s11273-008-9098-2