Artisanal gold mining can lead to contamination of soil and stream sediments, but the degree and extent of contamination varies widely. This study characterized Hg, As, Cd, Co, Cu, Mn, Ni, Pb, and Zn contamination in soils and sediments from two gold mines in Guyana. Soil sampled from the pit and overburden areas exhibited slightly higher concentrations of Co, Cu, Mn, Ni, and Zn, but below environmental guidelines. Similarly, stream sediments sampled within the mining area were not enriched relative to downstream areas. In contrast, soil and stream sediment was heavily contaminated with Hg, but the level of contamination was not higher within the mining area and was instead strongly related to organic matter content, which was much higher in soil at sites farther from the mines. These high organic matter soils father from the mining pits showed higher Hg concentrations (501-614 ng g-1). Leaching experiments showed that Hg leached from soil collected at distant (2-4 km) sites was as high as at sites close to mines, but the Hg/DOC ratio in leachate was much lower and Kd values (0.75-1.67 L mg-1) at all sites indicate that Hg is very loosely bound to soil.
Global climate change can alter the timing of migration for birds, and these temporal shifts can differ across species. There is little knowledge about whether these timing shifts could alter interspecific competition, with effects on reproductive success or interspecific interactions. Cackling geese (Branta hutchinsii) and Atlantic brant (Branta bernicla hrota) share similar coastal nesting habitat and may exhibit pre-emptive interference competition for nest sites. Thus, in early snow melt years when cackling geese can initiate nests 2 weeks sooner than brant, they may have a competitive advantage in finding optimal nesting sites that provide protection from Arctic foxes (Vulpes lagopus). In late melt years when both species initiate nests within a few days of each other, competitive advantages are less certain. Using a natural experiment driven by strong interannual variation in snow melt timing (early snow melt year of 2014 and the late snow melt year of 2015) on Southampton Island, Nunavut, Canada, we assessed whether snow melt timing affected nest site characteristics, brant behaviors, and nest success. Behavioral scans revealed that brant males and females altered their behavior between years that differed in cackling goose nest density, suggesting indirect exploitative competition for food resources. Apparent nest success varied between species and years, with brant nest success increasing in the late snow melt year of 2015. Our top model indicated that water levels surrounding nest sites limited arctic fox depredation, and brant nest success was higher in the years with later snow melt, which also had higher water levels during nesting. This study highlights the importance of considering interspecific competition in understanding the impacts of climate change on Arctic breeding bird populations.
Surges in gold prices coupled with socio-economic factors have increased small- and medium-scale gold mining in Guyana, which drives the emission of large quantities of mercury (Hg) into the atmosphere. Given the distribution of Hg through the atmosphere, reliable and affordable measurement of concentrations in the air is vital. Moss bags and Hg passive air samplers (MerPAS) were deployed to measure atmospheric Hg around a gold mine in Mahdia, Guyana over a 90-day period as well as a separate 2-day period that encompassed a periodic burn of Hg-gold amalgam (typically 2-h). Mercury in moss and MerPAS were positively correlated over both deployment periods, but Hg concentrations measured during the 2-day event were several-fold higher in both moss and MerPAS compared with the 90-day deployment. Using the 2-day deployment as an estimate of atmospheric Hg, Hg air concentrations around the burning station exceeded 100,000 ng m−3 averaged over a 48-h period, and moss Hg concentrations were greater than 250,000 ng g−1 around the burning station, although Hg concentrations in both media decreased rapidly with distance. There was no relationship between Hg in moss and soil Hg at the sampling sites; Hg in soil was instead positively associated with soil organic matter content. Overall, our study shows that Hg concentrations in air at artisanal gold mines in Guyana can exceed international health guidelines of 100,000 ng m−3 averaged over a 48-h period and that moss provides reliable estimates of relative Hg concentrations in air over both short-term and long-term exposures.
Mercury biomonitoring in freshwater fish is foundational for environmental science, public health, and Indigenous community well-being, given mercury's persistence and toxicity. Accurate characterization of length-mercury relationships is central to environmental monitoring, risk assessment, and the development of fish consumption guidelines. However, most monitoring programs rely on a single default model, typically a log-log or power regression, which may misrepresent true patterns across heterogeneous lake-species combinations. This study introduces a decision-based regression framework that evaluates multiple candidate models using predefined statistical criteria and incorporates sensitivity analyses to assess model stability. Applying this framework to community-based monitoring data from northern Ontario revealed substantial variability in the form and strength of length-mercury relationships. No model type was universally optimal; several lake-species groups exhibited weak or absent relationships, indicating that automatic regression-based approaches can produce misleading estimates. Sensitivity analyses (leave-one-out cross-validation and outlier diagnostics) identified model fragility in data-limited or biologically heterogeneous groups, highlighting the need for explicit uncertainty evaluation. This flexible and transparent approach improves methodological rigor, supports defensible ecological interpretation, and strengthens mercury exposure estimates. This framework reduces the risk of biased exposure estimates, strengthens the scientific defensibility of consumption guidelines, and provides a reproducible, adaptable modeling workflow that can be adopted across environmental monitoring programs, particularly those working in northern, remote, or community-led contexts.
Abstract Low concentrations of dissolved oxygen (DO) in hypolimnetic waters are becoming more common and could affect nutrient supplies available to phytoplankton communities in meso‐ and eutrophic lakes. We examined the connections among hypolimnetic DO, nutrient concentrations, and phytoplankton communities in 26 oligotrophic lakes in the Kawartha Highland region of south‐central Ontario, Canada. Lakes were divided into two categories based on their mid‐summer hypolimnetic DO concentration: oxic, >2.0 mg/L; anoxic, <2.0 mg/L. Despite differing in DO concentration, nutrient concentrations in surface or deep waters did not strongly differ between these two lake categories. Furthermore, we found no evidence that low hypolimnetic DO was linked to differences in phytoplankton communities either deep in the water column or in surface waters of these lakes. Our results show that low hypolimnetic DO, by itself, is insufficient to alter dissolved nutrient concentrations in hypolimnions and affect algal communities in oligotrophic lake ecosystems.
