Martin Suchy, M.Sc. Candidate

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TRACING GROUNDWATER RECHARGE THROUGH CULTIVATED FIELDS USING VARIOUS ENVIRONMENTAL ISOTOPES

The use of both manufactured fertilizers and manures as sources of nutrients in agricultural watersheds has the potential to impact groundwater and surface water quality. 

In this study, environmental isotopes and nutrient analysis are used to determine agro-contaminant pathways, transformation and attenuation in the subsurface within the intensively cultivated Raisin River watershed of eastern Ontario.  To assess the significance of direct infiltration through cultivated corridors, versus regionally recharged groundwater, this research hopes to determine rates of seasonal mixing.  Monthly monitoring of key geochemical and isotopic parameters will establish temporal variations, and allow a reconstruction of the seasonal variations of biogeochemical reactions involving DOC and nitrogen species as they recharge through cultivated landscapes.  Naturally occurring stable isotopes (δ18O and δ2H), which are sensitive to seasonality of recharge, are being used to examine seasonal variations and to provide an estimate of recharge and mass loading to the aquifer. δ13CDIC is used to distinguish water infiltrating through fields where corn is grown (C4 vegetation), and natural vegetation (C3 vegetation) predominant in the headwater environments. δ15N and δ18O in nitrate and δ15N in ammonium provide insight into denitrification processes.  Water levels were monitored and groundwater samples collected from a network of multi-level suction-lysimeters, piezometers, dug and drilled wells, and tile drains, all located within or in close proximity to three cultivated fields and one naturally vegetated control site.  The significance of this investigation is that it may be used as an analogue for other drainage basins in areas of intensive agriculture. 

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