Thesis Defence: Using biosolids to mitigate drought effects in a semi-arid grassland with and without grazing by cattle

Nikita Planz, supervised by Dr. Melanie Jones, will defend their thesis titled “Using biosolids to mitigate drought effects in a semi-arid grassland with and without grazing by cattle ” in partial fulfillment of the requirements for the degree of Master of Science in Biology.

An abstract for Nikita’s thesis is included below.

Examinations are open to all members of the campus community as well as the general public. Registration is not required for in-person defences.

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ABSTRACT

Climate extremes are becoming more common throughout semi-arid rangelands of British Columbia; therefore, finding climate mitigation techniques is paramount. Biosolids are an organic soil amendment made from treated municipal sewage that can be surface applied to grasslands to aid in reclamation and increase primary productivity. The purpose of this work was to examine the ability of a single application of biosolids to mitigate drought effects in a semi-arid, grazed and ungrazed, grassland 19 years after application. In 2002, biosolids were applied at a rate of 20 Mg ha-1 in two study sites, then one of these sites was fenced to create a grazing exclosure. In 2020 rainout shelters were constructed to a simulate growing season drought for approximately two years, where the experimental drought plots had a median 55% reduction in soil moisture. Before and after sampling included above and belowground biomass as well as plant community composition. Further, soil bulk density, pH, organic matter, total carbon and nitrogen, and soil water content were analyzed. Rainout shelters reduced root biomass but the biosolids treatment mitigated this loss. Additionally, biosolids significantly increased aboveground biomass and litter. Biosolids lowered diversity, whereas open grazing increased diversity. Biosolids also increased total carbon, total nitrogen, and soil organic matter. The only soil metric altered by the experimental drought treatment was soil water content, which was lowered. Overall, a single application of biosolids had lasting effects on the ecosystem nearly two decades later. Although some undesirable outcomes were observed, grazing may be used as a management tool, in combination with biosolids, to meet reclamation targets in a semi-arid rangeland. Further research is needed to understand the relationship between drought, biosolids, and grazing in semi-arid grasslands in British Columbia.