Abstract
BackgroundWater level management has been suggested as a potential tool to reduce malaria around large reservoirs. However, no field-based test has been conducted to assess the effect of water level management on mosquito larval abundance in African settings. The objective of the present study is to evaluate the effects of water level drawdown rates on mosquito larval abundance.MethodsTwelve experimental dams were constructed on the foreshore of the Koka Dam in Ethiopia. These were grouped into four daily water drawdown treatments, each with three replicates: no water-level drawdown (Group 1; Control), 10 mm.d-1 (Group 2), 15 mm.d-1 (Group 3) and 20 mm.d-1 (Group 4). Larval sampling was conducted weekly for a period of 6 weeks each in the main malaria transmission season (October to November 2013) and subsequent dry season (February to March 2014). Larval densities were compared among treatments over time using repeated measures Analysis of Variance (ANOVA).ResultsA total of 284 Anopheles mosquito larvae were collected from the experimental dams during the study period. Most (63.4%; n = 180) were collected during the main malaria transmission season while the remaining (36.6%; n = 104) were collected during the dry season. Larvae comprised four Anopheles species, dominated by Anopheles arabiensis (48.1% of total larval samples; n = 136) and An. pharoensis (33.2%; n = 94). Mean larval density was highest in control treatment dams with stable water levels throughout the study, and decreased significantly (P < 0.05) with increasing water drawdown rates in both seasons. During the main transmission season, anopheline larval density was generally lower by 30%, 70% and 84% in Groups 2, Group 3 and Group 4, respectively, compared with the control dams (Group 1). In the dry season, larval density was reduced by 45%, 70% and 84% in Groups 2, Group 3 and Group 4, respectively, when compared to the control dams.ConclusionIncreased water drawdown rates were associated with lower mosquito larval abundance. Water level management could thus serve as a potential control measure for malaria vectors around reservoirs by regulating the persistence of shallow shoreline breeding habitats. Dam operators and water resource managers should consider incorporating water level management as a malaria control mechanism into routine dam operations to manage the risk of malaria transmission to human populations around reservoirs.
Highlights
Water storage can help safeguard livelihoods and reduce rural poverty [1]
Mean larval density was highest in control treatment dams with stable water levels throughout the study, and decreased significantly (P < 0.05) with increasing water drawdown rates in both seasons
Increased water drawdown rates were associated with lower mosquito larval abundance
Summary
Construction of dams has been widely advocated to help ensure food security and promote economic development in Africa [2]. In recognition of this fact, the Program for Infrastructure Development in Africa (PIDA), endorsed in 2012 by the continent’s heads of state and government, has laid out an ambitious long-term plan for closing Africa’s infrastructure gap [3]. In the water and power sector, PIDA calls for an expansion of hydroelectric power generation capacity by more than 54,000 megawatts (MW) and that of water storage capacity by 20,000 cubic km To meet these goals, Africa has entered a new era of dam building, with over 200 large dams currently under construction or planned for the near future [4]. The objective of the present study is to evaluate the effects of water level drawdown rates on mosquito larval abundance
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