Rep. 3.10 - Partitioning of Solutes from Agricultural Fields within the Hydrologic System

Research Report 3.10

Partitioning of Solutes from Agricultural Fields within the Hydrologic System at Two Sites in Southern Ontario and the Subsequent Impact on Adjacent Aquatic Ecosystems

Dr. David Rudolph and Dr. Gary Parkin (Kachanoski, Barton),
Waterloo Centre for Groundwater Research,
University of Waterloo, Waterloo, ONT N2L 3G1

COESA Report No.: RES/MON-010/97

Objectives & Expected Outputs
Executive Summary
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Objectives and Expected Outputs
Objectives:	To construct a sufficient data base which will represent annual variations in the agricultural cycle by quantifying the contaminant flux distribution over the annual cycle though a hydrologic water balance focusing on water partitioning between the unsaturated zone, saturated zone, tile drainage and surface water systems; by evaluating the significance of spatial positioning within the field; by documenting subsurface geochemical conditions that control the nitrification-denitrification processes in relation to the spatial positioning; by assessing the health of the aquatic ecosystem in the surface water drains compared to systems not impacted by similar toxins and finally, to employ newly-developed mathematical models to develop predictive capabilities for agricultural land-use impact assessment.
Expected Outputs:	Documentation of the annual variability in water flux as a result of seasonal variation and during specific hydrologic events such as large rain storms will be provided. In addition the spatial and temporal variability of nitrogen compounds including ammonia and nitrate will be tracked. Additional chemical parameters will included dissolved oxygen, dissolved organic carbon and pH. The combination of the water balance and nitrogen balance measurements will provide a fairly detailed view of contaminant flux partitioning between soil water, shallow groundwater, tile drainage, deep ground water and surface water. Non-reactive tracers will be used at both sites to provide additional information for calibration and interpretation of contaminant transport observations.
Type:	Contribution Agreement, University
Spending Profile:	93-94: $54.4 K, 94-95: $201.0 K, 95-96: $173.5 K, 96-97: $164.5 K, Total: $593.5 K
Status:	Available March 1998

Executive Summary

Measurements of the hydrologic water balance of two agricultural field sites in southern Ontario (a hillslope comprised of loam soils near Kintore and a clay plain near Woodslee) were undertaken to determine the major transport pathways of contaminants (including nitrate, chloride, and atrazine) below the root zone. As well, a numerical model of two-dimensional water flow which includes tile drains was developed and tested at the Woodslee site. At the Kintore field site only, we investigated potential impacts of the contaminants on the biological health of a drainage ditch located near the perimeter of the study field.

The study fields were instrumented with meteorological stations and time domain reflectometry probes to measure potential and actual evapotranspiration, water flow metering systems at all tile drainage outlets and at upstream and downstream ditch stations (Kintore only), and groundwater monitoring wells to measure hydraulic heads below the water table.

To quantify the contaminant flux soil samples were collected from the A horizon and water samples were collected at all tile and drainage ditch monitoring stations and from all monitoring wells. Water and soil samples were analysed mainly for nitrate, ammonium, and chloride content; however, a limited number of samples were analysed for a standard suite of anions and cations, isotopes (¹⁵N and ¹⁸O), and atrazine.

Results at the Woodslee clay plain site suggest that up to 20% of infiltration may bypass the tile drains and recharge deep groundwater. Preliminary results from the numerical model agree quite well with the measured quantity of tile drain effluent; however, the model overpredicts the quantity of runoff and underestimates the amount of deep groundwater flow. One explanation for the discrepancies between model results and measurements is that the point measurements of soil hydraulic conductivity used in the model do not include macro-features such as fractures and are probably too low.

Based on an investigation of biological effects on the drainage ditch at Kintore, each of the biotic indices. (EPT richness index, Hilsenhoff BI) showed that water quality declined downstream. The Hilsenhoff BI indicated some organic pollution at all of the study sites in Logan Drain, but water quality was still considered to be good.

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