Laura Bony MSc Graduate Defense Seminar

Salt affected soils and their relationships with plant communities on reclamation well sites

Student: Laura Bony

Degree: MSc

Supervisor: Dr. M. Anne Naeth

Date: September 18, 2020

Time: 1:00 p.m.

Abstract: Salt affected soils are common around the world from natural causes or anthropogenic activities. Over 1030 million hectares of land worldwide are affected by salt or at risk of being affected. In Alberta, saline and sodic soils may occur with oil and gas production, increasing the risk of salinization on well sites due to waste water production. Those salts can have detrimental impacts on soil structure and impede vegetation growth and development. Land reclamation on these well sites follows provincial regulatory requirements that include thresholds for electrical conductivity (EC) and sodium adsorption ratio (SAR) to measure success. However, EC and SAR are not always representative of soil and vegetation recovery. This research assessed whether EC and SAR are the most scientifically appropriate indicators for salt affected soil reclamation.

Well sites were assessed in Dry Mixed Grass and Central Parkland ecoregions of Alberta. Soil was sampled from 0 to 1.5 m and analyzed for EC, SAR, pH, and individual ions including sodium, chloride, sulfate, calcium, magnesium, and potassium. Vegetation assessments included ground and canopy cover and diversity. Relationships between soil parameters and those between soil parameters and vegetation variables were determined using correlations, non-metric dimensional scaling, linear mixed model, hierarchical partitioning, and redundancy analysis.

Although EC and SAR gave good information on general soil health, they were not sufficient measures to determine salt impacts in reclaimed plant communities and to assess salt affected soils. EC and SAR did not always represent ion concentrations in the soil well, and were not a satisfactory measure to predict plant survival or general condition. Sodium, chloride, and sulfate, the most toxic salts for plants, are not always represented by EC and SAR. Magnesium and potassium were significantly impacting vegetation parameters, and are recommended to be added to reclamation criteria when EC and SAR do not meet criteria, but vegetation is healthy and productive. The upper 0.45 m of depth influenced the most vegetation parameters in both ecoregions; thus reclamation criteria is recommended to focus salt remediation at that depth.