INTERACTIVE EFFECTS OF CLIMATE VARIABILITY ON HEAVY METAL SPECIATION, BIOAVAILABILITY, AND TROPHIC TRANSFER IN FRESHWATER ECOSYSTEMS

Abstract

The convergence of climate variability and legacy heavy metal contamination is reshaping the behavior of potentially toxic elements in freshwater ecosystems worldwide. This review synthesizes current scientific understanding of how changing temperature regimes, hydrological extremes, and biogeochemical alterations influence metal speciation, bioavailability, and trophic transfer across multiple ecological scales. At the global scale, climate-driven hydrological variability and permafrost thaw enhance the mobilization of trace metals from terrestrial reservoirs, while at the environmental scale, shifts in pH, dissolved organic matter, and redox conditions modify chemical speciation and toxicity. At the organismal level, physiological stress and climate-induced toxicant sensitivity amplify metal uptake, disrupt metabolic pathways, and increase susceptibility to bioaccumulation and biomagnification through food webs. Emerging evidence indicates that traditional equilibrium-based models such as the biotic ligand model may underestimate exposure risks under rapidly fluctuating environmental conditions associated with climate change. Furthermore, processes such as mercury methylation, brownification, and acid rock drainage amplify ecosystem-level risks and alter contaminant pathways across freshwater and boreal systems. Integrating multi-scale observational studies with advanced modeling approaches, including kinetic and GIS-based frameworks, is essential for improving prediction and management of metal contamination in a changing climate. Overall, the interaction between climate variability and heavy metal dynamics represents a critical challenge for freshwater ecosystem resilience and requires adaptive, bioavailability-based regulatory frameworks.