Chromophoric dissolved organic matter in the Athabasca Oil Sands Region, Canada, and its association to lake acid sensitivity

Chromophoric dissolved organic matter (CDOM) represents a broad class of organic compounds that absorb visible and ultraviolet light and can influence numerous aquatic system functions. The Athabasca Oil Sands Region (AOSR) in Alberta, Canada, contains an abundance of boreal lakes suspected to possess high quantities of CDOM. However, CDOM within these lakes has never been investigated; moreover, the potential impact of shifting acid-base chemistry (possibly linked to industrial acid deposition) is largely unknown. This study characterized CDOM within fifty acid sensitive lakes in the AOSR using fluorescence spectroscopy and parallel factor analysis (PARAFAC) to ultimately identify the sources and processes acting on organic matter, and to explore the potential link between CDOM and lake water acid-base chemistry. Four fluorescent components including two humic-like (C1, C2) and two amino acid-like (C3, C4) compounds were identified through PARAFAC. Multivariate analysis indicated that C1 and C2 likely originated from surrounding peatlands and were associated with lake water colour and dissolved organic carbon, respectively (Spearman correlation coefficient [RS] > 0.7). Strong associations with metals and variables reflective of irradiation (RS > 0.65) suggested that the comparatively aromatic C1 formed CDOM–metal complexes that were vulnerable to photodegradation. Both C3 and C4 remained largely unresolved due to limited associations with the available data; however, C3 spectra were similar to anthropogenic fluorescent species reported in the literature. Weak associations were observed between CDOM variables and pH and alkalinity, providing limited evidence to suggest that CDOM and acid-base chemistry shared a direct relationship within AOSR lakes.