While the specific article titled "Coupled Carbonate Equilibrium and Metabolic Fractionation Drive δ¹³C-DIC Variability in Freshwater Ecosystems - ESS Open Archive" could not be directly located or verified through Google Search, the scientific concepts it addresses are well-established and actively researched within environmental science. Dissolved inorganic carbon (DIC) and its stable isotopic composition (δ¹³C-DIC) are critical tracers for understanding carbon cycling in freshwater environments. Research indicates that δ¹³C-DIC variability in freshwater ecosystems is primarily influenced by two major mechanisms: carbonate equilibrium and metabolic fractionation. Carbonate equilibrium reactions play a significant role in determining the fluxes and spatiotemporal patterns of CO2 and the isotopic composition of DIC. For instance, carbonate buffering reactions can contribute substantially to CO2 emissions in high-alkalinity systems, and alkalinity dramatically increases isotope equilibration timescales, complicating carbon source identification. Metabolic processes, such as photosynthesis and respiration by aquatic organisms, also profoundly affect δ¹³C-DIC. Photosynthesis preferentially utilizes lighter carbon isotopes (¹²C), leading to an enrichment of ¹³C in the remaining DIC. Conversely, the decomposition of organic matter releases ¹²C-depleted carbon, thus decreasing δ¹³C-DIC values. These biological activities can cause significant diurnal and seasonal variations in DIC concentration and its isotopic signature. High-resolution studies reveal that such biological processes can lead to substantial changes in carbon dynamics over short timescales, with implications for estimating CO2 evasion rates. Understanding these intricate controls—from geological and atmospheric sources to biological transformations—is crucial for accurately quantifying carbon fluxes from continents to oceans and their contribution to the global carbon cycle. This field of study uses stable isotopes as a valuable tool to trace carbon origins and transformations, providing insights into complex ecological processes in rivers, lakes, and other freshwater bodies.