Dr. David O'Connell, a Research Associate in the Ecohydrology Research Group in the Earth and Environmental Science Department, University of Waterloo, installs and programs a surface water sampler on Spencer Creek, just downstream from the Valens Reservoir in Ontario. With him is masters student Sana Louie. They are studying the mobilization of nutrients during a flood pulse event, such as when a reservoir is emptied, which is scheduled to happen on Tuesday.Peter Power/The Globe and Mail