Understanding sources of streamflow to the Wasi watershed using stable water isotopes and hydrogeochemistry

This thesis / dissertation was completed and submitted at Nipissing University, and is made freely accessible through the University of Toronto’s TSpace repositoryThe Wistiwasing (Wasi) watershed (235 km2) is a major source of water and nutrients to Callander Bay, Lake Nipissing, Ontario. Within the watershed stream phosphorus concentrations regularly exceed provincial water quality objectives. To better understand source water contributions to streamflow, a tracer-based study was performed using stable water isotopes (deuterium and oxygen-18) and a preliminary end-member mixing analysis (EMMA). In this study, 38 tracers, including stable water isotopes, major and trace elements, and in situ water characteristics were used to hydrochemically fingerprint water and its sources. Biweekly sampling of groundwater, surface water and precipitation was conducted between May to September 2012, with 332 stable water isotope samples and 293 hydrochemical samples collected to determine source water spatiotemporal influences on streamflow. Samples were analyzed for deuterium and oxygen-18 using a Picarro L2120-i, whereas cations and anions were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS) and ion chromatography (IC), respectively. Regions of strong groundwater influence, inferred by deuterium and oxygen-18 signatures, were particularly identifiable during low-flow, late summer conditions and corresponded with coarse-grained sediments. High flow, early period isoscapes (contoured maps of surface water isotope signatures) featured smaller spatial variation in surface water isotope signatures, with more negative values resembling long-term groundwater recharge, a mix of snowmelt and spring/fall rains; late period low flow isoscapes indicated larger spatial variability due to changing influences of groundwater and upstream surface water undergoing summertime evaporative enrichment of heavier isotopes. Hydrochemical analysis revealed the majority of surface water and groundwater could be classified as a calcium bicarbonate (Ca-HCO3) water type. In cases where groundwater shifted between water types, dug-well groundwaters shifted more often than for drilled wells, with some dug wells exhibiting potential influence from human landuse activities (e.g. road salt, agricultural use). Principle component analyses of hydrochemical data suggested that four end-members would be required to explain mainstem hydrochemistry (a mixing space dimensionality of 3). Monte Carlo Parallel Analysis estimated a smaller mixing space dimensionality than the rule of one, with mixing space dimensionality relatively independent of the number of tracers included. This case study maps the dynamics of source water contributions to late spring-summer baseflow in the Wasi watershed and contributes preliminary analysis of major and trace element hydrochemistry towards a future end-member mixing analysis.M.Sc