Wetlands in farmland are at risk of contamination by fertilizers and pesticides. One recommendation for reducing wetland contamination is to maintain a buffer of contiguous uncropped land around the wetland (a wetland buffer). Many agricultural water protection policies around the world recommend 5 to 50‐m wide uncropped buffers around water bodies, but it is unclear how large wetland buffers must be to effectively protect against these chemicals. In addition, it is unclear whether wetland buffers have similar—or stronger—effects on fertilizer and pesticide contamination than reducing the amount of cropped land within the larger landscape context around wetlands. Our study, conducted across 37 wetlands in eastern Ontario, Canada, addressed the following questions: (1) Does increasing buffer width, or increasing the amount of contiguous uncropped land within recommended buffer width guidelines, reduce nutrient and pesticide levels in agricultural wetlands? (2) Does increasing uncropped land cover in the broader landscape reduce nutrient and pesticide levels in agricultural wetlands? and (3) What is the relative importance of buffer size and landscape‐scale uncropped cover for reducing nutrient and pesticide levels in agricultural wetlands? A rigorous site selection process was employed to minimize the correlation between buffer size and landscape‐scale uncropped cover, minimize spatial gradients in these predictor variables, and minimize variation in potentially confounding variables. We obtained nutrient and pesticide data by collecting water samples from each wetland under similar weather conditions in June–July 2015. Nitrate concentrations were measured using ion chromatography, and atrazine and neonicotinoid (pesticide) concentrations using a combination of high‐performance liquid chromatography and mass spectrometry. We found that nitrate, atrazine, and neonicotinoid concentrations in study wetlands were unaffected by wetland buffer size. However, concentrations of each chemical decreased with uncropped land cover in the surrounding 150 to 300‐m radius landscapes. To effectively protect water in agricultural wetlands from contamination by nitrate‐based fertilizers and atrazine or neonicotinoid pesticides, we recommend either increasing the policy‐recommended width of wetland buffers to at least 150 m, or abandoning the buffer paradigm in favor of landscape‐scale conservation.
OverviewPonds in agricultural areas can be important havens for wetland-dependent wildlife, especially in regions with high rates of wetland loss. However, diverse wildlife can only persist in these agricultural wetlands if the water is of sufficient quality and if wetlands are surrounded by enough terrestrial habitat for semi-aquatic taxa such as anurans (frogs and toads). Most recommended protection measures for agricultural wetlands fall into one of two categories: (i) conserving a certain percentage of natural vegetation (undisturbed land) in the landscape surrounding each wetland, or (ii) retaining or implementing vegetated buffers between wetlands and adjacent crop fields (Castelle et al. 1992; Findlay and Houlahan 1997). Landscape-scale conservation of undisturbed land is known to increase anuran species richness in most types of wetlands (e.g. Houlahan and Findlay 2003; Herrmann et al. 2005), but its role in protecting the water quality of small, lentic water bodies is less well-established. Vegetated buffers along streams have been shown to intercept contaminants from runoff (Castelle et al. 1994), but multiple aspects of their role in aquatic habitat improvement and terrestrial habitat provisioning around non-riparian agricultural wetlands remain unclear.The following work is divided into two chapters. The first chapter, Wetland Buffers Are No Substitute for Landscape-Scale Conservation, examines the roles of landscape-scale conservation and wetland buffers in protecting water quality of agricultural wetlands. It addresses the following questions:(1) Does increasing undisturbed land cover in the landscape reduce nutrient and pesticide levels in agricultural wetlands? (2) Does complying with buffer guidelines reduce nutrient and pesticide levels in agricultural wetlands? If so, how large should wetland buffers be? ii (3) What is the relative importance of landscape-scale undisturbed land conservation and compliance with buffer guidelines for reducing nutrient and pesticide levels in agricultural wetlands? The second chapter, Do Wetland Buffers Work for Frogs and Toads? examines the role of wetland buffers in promoting anuran species richness and abundance. It focuses less on landscape composition than the first chapter does, because anurans are already known to respond to landscape composition, usually at scales of 500 to 3000 m (Hecnar and M'Closkey 1998; Houlahan and Findlay 2003; Price et al. 2005). The second chapter addresses the following questions:(1) Can wetland buffers increase anuran species richness and abundance? If so, (a) how should they be vegetated, and (b) how large should they be?(2) How strong are wetland buffer effects on anuran species richness and abundance in agricultural wetlands, relative to the effects of landscape composition (woodland cover, road density, and water cover)?Our 1 research findings show that landscape-scale land management is key to protecting water quality and anuran diversity in agricultural wetlands, and that for buffers to be effective, they must be larger th...
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