Effects of Diurnal Cycling on Metal(oid) Concentrations and Physicochemistry of a Small Stream in the Bathurst Mining Camp

Diurnal (diel) cycles continuously and predictably affect the world’s environmental spheres. Less is known about the intraday and seasonal impacts of diurnal processes on surface water hydrogeochemistry. This study presents diurnal physiochemical and hydrogeochemical data collected over 24 h from Forty Mile Brook in New Brunswick. Profound cycling is observed in the stream’s physiochemistry (pH, temperature, redox). There are clear changes in Al speciation as well as redox-sensitive elements Fe and Mn, which correspond to variation in trace metal(oid)s and REE. Large cycles in Zn concentrations are interpreted as predominantly due to photosynthesizing microbes in the water. The variation observed in this study best fits a model in which diurnal variation in air temperature and solar radiation (light) drives hydrogeochemical and biogeochemical reactions impacting metal(oid) aqueous solubility and mobility. This continuous and predictable diurnal rhythm observed in this study and elsewhere has potentially significant implications for water quality monitoring and data-interpretation protocols. Furthermore, given that the Canadian landmass is subject to seasonal swings in temperature and solar radiation, monitoring programs need to adopt appropriate strategies to ensure long-term environmental compliance and drinking water security.