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A Comparison of Tension and Zero-Tension Lysimeter and PRS™ Probes for Measuring Soil Water Chemistry in Sandy Boreal Soils in the Athabasca Oil Sands Region, Canada

Watmough, S. A., I. Koseva and A. Landre. 2013. Water, Air, & Soil Pollution

Abstract

Because soil acidification models use soil solution chemistry as a critical endpoint for predicting adverse biological effects, it is essential that various options for measuring soil water chemistry are assessed. This is particularly true for the Athabasca oil sands region of Alberta, Canada, as widespread acidification impacts are predicted based on modelled soil solution chemistry, but no soil solution data are currently available to validate these estimates. In this study, tension and zero-tension lysimeters were compared over a 3-year period at a jack pine stand (Pinus banksiana Lamb.) established in an acidic, sandy brunisol adjacent (<2 km) to one of the largest mines in the region. During the final year, plant root simulator (PRS™) probes were also installed for comparative purposes as they are currently being used in the region to assess changes in soil chemistry. Despite the close proximity to the mine and high sulphur (S) and nitrogen (N) deposition, the annual average pH of the soil water collected by both lysimeter types was around 6.5 and NO3-N concentrations were negligible. Annual SO4 concentrations in tension lysimeters averaged 12-14 mg L-1 and were typically two to four times higher than in zero-tension lysimeters; similar differences between lysimeters were observed for divalent base cations (Ca and Mg). Values (ion supply rates) obtained by PRS™were affected by both the position of the probes (horizontal vs. vertical) and the duration of probe insertion (1, 2 and 5 months), such that higher values for most nutrients were obtained using probes that were installed vertically and for shorter periods of time. The Ca/Mg ratio in lysimeters and PRS™ probes were comparable, but other elemental ratios such as Ca/S or Ca/Al were much higher in PRS™ probes than in lysimeter water. Similar to lysimeter data, NO3-N values obtained by PRS™ probes were very low. PRS™ probes may be useful for assessing differences in nutrient availability among sites, but they do not reflect soil water chemistry that is used in geochemical acidification models.

Key Words

Soil solution chemistry PRS™ probes Acid deposition Alberta oil sands Lysimeters Base cation Aluminium