Characterizing the Impacts of Seismic Exploration Lines on the Hydrology and Vadose Zone for a Watershed in West-Central Alberta
Creators: Kononovs, Daniels
Publisher: name: University of Alberta Library
Year: 2023

<p>Seismic lines are long linear cut lines through forests created for hydrocarbon exploration and comprise over 50 % of all linear disturbances in the Canadian Boreal Forest. They are known to impact local eco-hydrological conditions and show minimal regeneration back to pre-disturbance conditions. This thesis aims at assessing the effects of seismic exploration lines on the eco-hydrology and vadose zone of a 700 km2 forested watershed located near Fox Creek in west-central Alberta. This region has been one of the most active areas for hydrocarbon production in Canada for the past 50 years, having a mean density of 3.3 km/km2 of seismic lines. Here, the impacts of seismic exploration lines on soil-water content (SWC), the hydrological cycle using a 1-D model known as the Simultaneous Heat and Water (SHAW) model, and the physio-chemical properties of the vadose zone are examined using paired sites in disturbed and undisturbed areas.<br>
SWC measurements indicated that seismic lines do not always have a higher moisture content. During the fall season, SWC measured at 15 cm depth were significantly higher on the seismic line due to the faster dormancy and reduced water usage of grasses and understory species that are dominant on seismic lines, in contrast to the trees and shrubs that are dominant in the adjacent undisturbed area. In the spring, SWC was significantly higher on the adjacent undisturbed area, due to delayed snowmelt on the seismic line. SWC measured during the summer and winter seasons was more variable among study sites and shallow soil layers (15 cm and 30 cm), which experience more seasonal SWC variations than deeper (60 cm) soil layers.<br>
Using the SHAW model, an annual water budget was estimated for a 60 cm soil profile. The simulations revealed that undisturbed areas have a higher annual evapotranspiration (ET), by up to 117 mm/year, as compared to undisturbed areas. Consequently, the higher ET rates on undisturbed areas lead to a larger depletion (up to 126.0 mm) of soil water storage. Simulated percolation at the bottom of the profile ranged from 0 to 47.8 mm/year, and was preferentially observed in the undisturbed areas, whereas seismic lines contributed to enhanced runoff.<br>
Soil-water sampled using suction lysimeters was mainly of the CaHCO3 type which is like the shallow (within 30 – 40 m) groundwater in the region. Measured δ18O and δ2H isotopic signatures of soil-water samples (n=154) indicate water of meteoric origin that has undergone minimal evaporation as they align with the local meteoric water line (LMWL). Soil bulk density (BD) values were all &lt; 1.7 g/cm3, thus within the range of typical mineral soils (1.0 to 1.8 g/cm3). BD values for the upper 15 cm were higher by 8 to 65 % on the seismic lines compared to the undisturbed areas, showing that the soils were not significantly compacted by machinery. The soils were acidic with a mean pH of 4.9 (n = 30) and soil samples from seismic lines had a lower cation-exchange capacity (CEC) and higher concentrations of base ions (e.g., Ca2+, Mg2+) in the soil solution compared to undisturbed areas. The reduced CEC on seismic lines indicates a lower buffering capacity of the soil, increasing its vulnerability to acidification and potential contamination by metals compared to undisturbed areas.</p>