Tailings reclamation is a significant challenge facing the oil sands industry. There are 1.4 billion m 3 of fluid fine tailings (FFT), a slurry waste stream generated from oil sands surface mining, awaiting reclamation. Pit lakes may be a suitable reclamation option, however further evaluation is required before pit lakes receive regulatory approval as an FFT reclamation method. FFT destined for pit lakes may be treated (with alum and polyacrylamide) and contain residual hydrocarbons. This study is the first publicly available comparison of the behavior of untreated versus treated FFT in pit lakes. Forty columns were monitored for 540 d under anaerobic conditions to evaluate the effects of tailings treatment, hydrocarbon amendments, and temperature (10 °C and 20 °C) on the biogeochemical and geotechnical behavior of FFT in pit lakes. Although tailings treatment aims to improve dewatering performance, this study found that treatment significantly reduced dewatering and consolidation. This highlights challenges in achieving optimal flocculation conditions, even in a controlled laboratory setting. Tailings treatment and hydrocarbon amendments significantly enhanced sulfate reduction, which was the dominant microbial process. Treated FFT had a greater abundance of known sulfate reducing bacteria and more extensive sulfate reduction than untreated FFT, while hydrocarbon amendments quickly led to >99% sulfate reduction. Sulfate reduction generated dissolved sulfide species throughout the columns and led to significant increases in alkalinity and CO 2(g) . Divalent cations were subsequently impacted and presumably precipitated as carbonate minerals. These pore water chemistry changes resulted in higher tailings solids contents, leading the authors to propose a new bioconsolidation pathway for FFT via sulfate reduction. • Coagulation/flocculation treatment decreased tailings dewatering and consolidation • Sulfate reduction was significantly enhanced by tailings treatment and hydrocarbons • Treated tailings had a greater abundance of sulfate reducing bacteria • Hydrocarbon amendments led to rapid and > 99% sulfate reduction • Sulfate reduction increased alkalinity and CO 2 and decreased cation concentrations

Over the last decades, the use of boron stable isotopes has steadily increased in the Earth Science literature, including hydrological studies. This paper presents “IsoBorDat”, a global open-access database containing boron stable isotope ratios (expressed as permil δ 11 B) measured in various hydrologic reservoirs such as groundwaters, surface waters, and rainwaters. The repository includes B contamination-related samples that have been (i) characterized in their isotopic signature as raw material or (ii) identified as potential sources of pollution in hydrological systems. IsoBorDat provides information on B content and B isotope ratios, water type, analytical methods, sampling time, and location. Data are available in open, structured .ods format, adhering to the FAIR principles. The database is hosted by the National Research Council of Italy (CNR) and is openly accessible at https://isobordat.cnr.it . We also present a quantitative and qualitative explorative approach applied to the statistical distribution of boron concentrations and isotope compositions across the four water types (meteoric, river, lake, and groundwater) and diverse water contamination sources of IsoBorDat. The statistical analysis reveals general distribution patterns and highlights differences among reservoirs, offering insights into geochemical processes influencing boron behaviour. This work supports the integrated use of isotopic data to better understand natural and anthropogenic influences on hydrological systems. IsoBorDat will be integrated within the ISOTOPE VRE, a Virtual Research Environment dedicated to environmental isotopes. • IsoBorDat is a global open-access database of boron concentrations and δ 11 B in waters • The dataset covers meteoric, river, lake, groundwater and contaminated waters • B and δ 11 B distributions show non-linear and multimodal behaviour • IsoBorDat supports isotope-based interpretation of hydrological systems