Variations in high-latitude riverine fluorescent dissolved organic matter: A comparison of large Arctic rivers

Given the pace of climate change, it is important to better understand dissolved organic matter (DOM) storage and cycling in high-latitude rivers and its subsequent export to the Arctic Ocean. To address this concern, excitation/emission matrix spectroscopy and parallel factor analysis (PARAFAC) coupled with optical indices were used to characterize the optical properties of fluorescent DOM (FDOM) and colored DOM (CDOM) in five large Arctic rivers over two seasonal cycles. Five PARAFAC components were identified and proved useful indicators for the quantitative and qualitative descriptions of DOM sources and modification processes within Arctic watersheds. In comparing Pan-Arctic relationships between the optical properties and chemical properties of DOM, three components traced terrigenous biomarkers and two components are introduced as potential indicators for microbial processing. Conversely, no individual PARAFAC component could be directly linked to a specific plant source or river and simpler absorbance indices (i.e., a(350)) proved to be better suited to quantify dissolved organic carbon and lignin phenol concentrations. Differences in FDOM character between the rivers could be explained by general watershed characteristics, including vegetation, topography, and hydrology. Based on these differences, the influence of coniferous vegetation on DOM character is most apparent in the Lena and Yenisei Rivers and bog-derived FDOM sources are more important in the Ob River. This study illustrates how increased hydrological connectivity in the Ob catchment and the abundance of lakes within the Mackenzie watershed may influence FDOM concentrations and the microbial processing of DOM within these watersheds.