LAUSR

This study evaluated three biochars derived from bioenergy by-products - manure-based anaerobic digestate (DIG), distillers' grains (DIS), and a mixture thereof (75G25S) - as amendments to stabilize Hg in contaminated floodplain soil under long-term saturated (up to 200 d) and cyclic drying and rewetting conditions. Greater total Hg (THg) removal (72 to nearly 100%) and limited MeHg production (<65 ng L-1) were observed in digestate-based biochar-amended systems under initial saturated conditions. Drying and rewetting resulted in limited THg release, increased aqueous MeHg, and decreased solid MeHg in digestate-based biochar-amended systems. Changes in Fe and S chemistry as well as microbial communities during drying and rewetting potentially affected MeHg production. Digestate-based biochars may be more effective as amendments to control Hg release and minimize MeHg production in floodplain soils under long-term saturated and drying and rewetting conditions compared to distillers' grains biochar.