EXPLORING SULFATE CYCLING IN A MINERAL-SOIL WETLAND RESTORED WITH WASTEWATER

Sulfate pollution is contributing to the salinization of surface waters worldwide. Wetlands are natural filters on the landscape that remediate surface water by retaining and processing various pollutants. However, the capacity for wetlands to process excess sulfate from wastewater is poorly understood, especially for natural (as opposed to constructed) wetlands. Here, we explore the sulfate remediation capacity of Frank Lake, a restored, multi-basin wetland complex in southern Alberta, Canada, that is used to treat effluents from municipal and beef slaughterhouse sources. Using a combination of approaches, we show limited sulfate processing throughout the wetland. Mass balances constructed for two distinct hydrologic periods showed that Frank Lake shifted from a sulfate source during wet years (2013 - 2015) to a sink during drought years (2021 - 2022). Yet we found little evidence of active sulfate processing in surveys conducted during drought years. Stable isotope (³⁴S and ¹⁸O) analysis showed limited enrichment across the basins of the wetland, implying limited transformation of sulfate via microbial reduction. Sediment incubations confirmed the patterns observed for stable isotopes. We hypothesize that the preferential reduction of nitrate and other more energetically favourable constituents of effluent may restrict the rate of microbial sulfate reduction. The limited extent of emergent and submerged vegetation may also limit sulfate uptake by plants. Given the limited sulfate processing in Frank Lake, and the headwater position of this wetland complex in the broader watershed, our work provides context on previous reports of increasing salt concentrations documented in rivers throughout the South Saskatchewan River watershed.

Primary Presenter: Mariya Denny, University of Lethbridge (avemaria9513@gmail.com)

Authors:

Mariya Denny, University of Lethbridge  (mariya.denny@uleth.ca)

Laura Logozzo, University of Lethbridge  (laura.logozzo@uleth.ca)

Xingzi Zhou, University of Lethbridge  (xingzi.zhou@uleth.ca)

Matthew Bogard, University of Lethbridge  (matthew.bogard@uleth.ca)