The effect of seasonal drying on sulphate dynamics in streams across southeastern Canada and the northeastern USA

Within the southeast Canada and northeast USA region, a peak in sulphate (SO4 ) concentration has been reported for some streams following periods of substantial catchment drying during the summer months (ON, Canada; VT, NH and NY, USA). However, it is currently unclear if a SO4 2response to seasonal drying is widespread across the broader region, or to what extent the level of response varies among catchments. In our study, SO4 2response to seasonal drying was compared in 20 catchments from 11 locations across southeastern Canada (ON, QC and NS) and northeastern USA (NH, NY, VT, WV and ME). Using long-term monitoring data of stream discharge and chemistry, the number of days for each month of the dry season (# d) when discharge (Q) was below a threshold level (25th percentile; Q25) was calculated for each catchment to give a measure of ‘seasonal dryness’ (# d Q \ Q25). A SO4 2response J. G. Kerr (&) M. C. Eimers Department of Geography, Trent University, Peterborough, ON K9J 7B8, Canada e-mail: [email protected] I. F. Creed Department of Biology, University of Western Ontario, London, ON, Canada M. B. Adams USDA Forest Service, Parsons, WV, USA F. Beall Natural Resources Canada, Canadian Forest Service, Sault Ste. Marie, ON, Canada D. Burns US Geological Survey, Troy, NY, USA J. L. Campbell US Forest Service, Durham, NH, USA S. F. Christopher Virginia Water Resources Research Center, Virginia Tech, Blacksburg, VA, USA T. A. Clair Water Science and Technology Branch, Environment Canada, Sackville, NB, Canada F. Courchesne Département de Géographie, Université de Montréal, Montreal, QC, Canada L. Duchesne Forêt Québec, Ministère Des Ressources Naturelles, Québec, QC, Canada I. Fernandez Department of Plant, Soil, and Environmental Sciences, University of Maine, Orono, ME, USA D. Houle Ministère Des Ressources naturelles et de la Faune, Québec, QC, Canada D. S. Jeffries Aquatic Ecosystems Research Impacts Division, National Water Research Institute, Environment Canada, Burlington, ON, Canada 123 Biogeochemistry (2012) 111:393–409 DOI 10.1007/s10533-011-9664-1