The influence of agricultural land-use on plant and macroinvertebrate communities in springs

  • Knysh K
  • Giberson D
  • van den Heuvel M
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Abstract

Many freshwater cool springs can be characterized by nearly constant temperatures and chemical composi-tion. Agricultural activities may leach nutrients to the groundwater, add sediment and nutrients from over-land flow, and change the cover of the riparian area surrounding springs, all factors that influence aquatic invertebrate and plant communities. Twenty limnocrene springs in Prince Edward Island, Canada (10 sur-rounded by and within 20 m of agricultural land, and 10 located in forested areas with < 5% agriculture within 1 km) were studied to determine effects of agricultural activities on invertebrate and plant community structure. Chemical, flow, sediment, and cover variables were examined in all 20 springs, and invertebrates and macrophytes were evaluated in a subset of four agricultural and four forested springs. Although nutrients (particularly nitrate) were higher in agricultural springs than in forested ones, and plant communities dif-fered between springs in the two land use types, light level (relating to the riparian canopy in the two land-use types) was a stronger predictor of aquatic plant community composition than nutrients. Plant diversity was highest in open agricultural sites. Overall invertebrate richness and abundance were higher in forested sites than agricultural sites, but invertebrate community composition differed between the two land-use types, and was primarily related to aquatic plant composition. Few taxa responded directly to elevated nutrients. The composition of the riparian area may be more important than direct inputs of nutrients and sedimentation when assessing agricultural impacts on springs. Springs have long been considered as natural laboratories to examine questions of basic and applied ecology (Odum 1957) due to their constancy in many physical variables (e.g., temperature and water chemistry; van der Kamp 1995), and their relatively low species diversity (Williams and Williams 1998). Springs are transition habitats between groundwater or subsurface water and surface water (Barquin and Scarsbrook 2008), but are dominated by local ground-water conditions (van Everdingen 1991). The constant, relatively low, temperatures found in many cool-springs (Cantonati et al. 2012) restrict species diversity as many insect species require warm temperatures for development, and greater fluctuating temperatures to regulate their life-cycles (Williams 1991; Barquin and Death 2011). Most previ-ous study of spring organisms, including invertebrates, has focused on biodiversity and ecological differences between

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Authors

  • Kyle KnyshUniversity of Prince Edward Island Department of Biology

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  • Donna J. Giberson

  • Michael R. van den Heuvel

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