δD and δ18O evidence for inputs to groundwater at a wetland coastal boundary in the southern Great Lakes region of Canada

摘要: Abstract The stable isotope compositions (δ18O and δD) of water have been used to determine the relative contributions different sources groundwater in a barrier sand-bar that separates coastal freshwater marsh from Lake Erie, Canada. An extensive study was initiated by Environment Canada at Point Pelee National Park after elevated nutrient concentrations were measured park’s marsh, located on spit land extends 15 km south into Erie. As part this larger study, which includes modelling, independently nature extent flow within sand deposits separate One two sites chosen for investigation is near large septic-system tile-bed receives human waste public toilet facility park, could potentially release nutrients via groundwater. Both transects studied are well suited isotopic because they between recharging surface bodies with temporally variable compositions, subject recharge local precipitation, exhibits seasonal variations. These differing when considered spatially temporally, make it possible establish source movement transects. oxygen hydrogen waters Erie lie an evaporation line slope 5.7. composition remained relatively over 21 months (δ18O=−7.5‰ −6.7‰) whereas exhibited considerable spatial temporal variability (δ18O=−8.4‰ −0.1‰). δD δ18O values precipitation samples vary seasonally temperatures, constitute meteoric δD=8.0(δ18O)+9.8. While influx evident similar upper metres both transects, contribution appears differ. average narrower transect −7.0‰ −54‰ respectively, reflect significant (∼67%) (∼28%). Precipitation constitutes primary wider transect, tile-bed, δ18O=−9.1‰ δD=−65‰. profile area very stable, depth time, contrasts sharply northern much more dynamic. findings suggest situated portion sand-bar, where head difference lake would be required produce equivalent observed transect. differences arise primarily width, account 2‰ 10‰ values, base-flow