Molecular Composition of Dissolved Organic Matter in the Changjiang (Yangtze River) – Imprints of Anthropogenic Impact

Abstract

Understanding the biogeochemical transformation of dissolved organic matter (DOM) across fluvial networks will ultimately help to predict anthropogenic influences. To date, few studies have evaluated the anthropogenic impact on the spatial and temporal changes of DOM composition in large river systems. Here, FT-ICR-MS combined with excitation-emission matrix spectroscopy (EEMs) and biomarkers were applied to resolve chemical differences of DOM collected from the Changjiang basin at different hydrological and environmental conditions. PCA and cluster analysis illustrated that samples collected from lake systems and northern and southern tributaries differed from the two batches of main stream samples, particularly due to higher contribution of nitrogen and sulfur containing compounds. Correlation of land-use information along the tributaries with different PCA loadings indicated that agricultural, forest and wetland areas and wastewater discharge control the composition of DOM within these subregions. Higher heteroatom content (especially CHONx) in the low discharge period ( 2009) may be contributed by paddy soil leaching into groundwater. The relative peak magnitude of sulfur containing formulas was elevated during flood season (2010), which may be related to pollutions in areas of high population density. In addition, lignin phenol concentrations were higher in the flood season because of elevated soil erosion. Consequently, land use and human activities can strongly alter the quality and composition of DOM in watersheds flowing through densely populated regions, which may also impact or influence the riverine carbon flux in anthropogenically disturbed river systems.

Anthropogenic Disturbance Stimulates the Export of Dissolved Organic Carbon to Rivers on the Tibetan Plateau

“…In detail, N-containing and S-containing formulas were more abundant in samples with aged DOC (Figure ). Compared with pristine forest catchments, the molecular composition of riverine DOM in urban or agricultural catchments was also richer in N-containing or S-containing formulas. ,, Therefore, riverine aged DOC in the BLR catchment may be directly affected by the release of anthropogenic pollution and indirectly influenced by agricultural activity.…”

Source, distribution, and transformation of dissolved and particulate organic matters in Qinzhou Bay, Northern Beibu Gulf

“…Unlike the dominance of dissolved OM (DOM) in reduced carbon pools of open ocean (Gardner et al, 2006, Hansell et al, 2009, particulate OM (POM) accounts for a considerable proportion of total OM in coastal regions due to large external inputs and substantial in situ phytoplankton production (Ji et al, 2021). Focusing on either the DOM or POM in coastal regions, with respect to its composition, sources, and sinks has led to them to being well understood, largely by applying key techniques such as elemental analyses, isotopic data and analysis (Sarma et al, 2014;Huang et al, 2020), optical properties (Stedmon et al, 2000, Guo et al, 2014, and molecular characterization (Wu et al, 2022). Yet, studies that simultaneously investigate POM and DOM in coastal ecosystems are still rare despite their likely active linkages, for example, regarding their sources, composition, and transformation (Li et al, 2018).…”