Relative effects of wetland buffers and landscape composition on water quality and anuran diversity in agricultural wetlands

Abstract

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...

Wetland buffers are no substitute for landscape‐scale conservation

“…One June water sample and the July water sample from each wetland were analyzed for nitrate within 5 d of sampling using ion chromatography with chemical suppression of eluent conductivity. This work was conducted by Laboratory Services at the City of Ottawa using an ion chromatograph (ICS-1000; Dionex, Sunnydale, California, USA) interfaced with Chromeleon analytical software (version 6.8; Dionex 2006;details in Haas et al 2015, Sawatzky 2016. The lower detection limit for nitrate was 0.04 mg/L, which is <1% of the minimum concentration at which nitrate is thought to be detrimental to the long-term health of freshwater organisms (CCME 2014).…”

“…The second June water sample from each wetland was analyzed for atrazine and neonicotinoids (acetamiprid, clothianidin, imidacloprid, and thiomethoxam) in September-October 2015 using solid phase extraction followed by highperformance liquid chromatography-mass spectrometry (HPLC-MS; details in Prosser et al 2016, Sawatzky 2016, Robinson et al 2017). This work was conducted by Laboratory Services at Environment Canada's National Wildlife Research Centre.…”