Urban and agricultural land use regulates the molecular composition and bio-lability of fluvial dissolved organic matter in human-impacted southeastern China

Abstract

Urbanization and agricultural land use can increase the transport of nutrients to fluvial ecosystems; yet, the overall impact of urban and nonpoint agricultural inputs on the composition, bio-lability, and the fate of fluvial dissolved organic matter (DOM) remains poorly understood. We investigated the optical and molecular composition and bio-lability of DOM in 76 streams and rivers with varying sizes of catchment area (1 ~ 4850 km2) along large gradients of urban and agricultural land use. Optical spectroscopy and Fourier transform ion cyclotron mass spectrometry (FT-ICR MS) were used to determine the chemical composition of DOM, and laboratory bio-incubations were used to assess DOM bio-lability. We found that urban and agricultural land use intensification was associated with the reduced relative contribution of DOM from pristine soils, enriched dissolved organic carbon (DOC), and higher contributions of aliphatic and peptide-like DOM, as well as enrichment of N- and S-containing molecular formulae. Specifically, FT-ICR MS revealed that the relative abundance of CHO-containing formulae decreased while that of CHOS-containing formulae increased with increasing urban land use. DOM bio-availability was higher in rivers draining urbanized and agricultural landscapes and was related to decreased DOM aromaticity and increased proportions of energy-rich aliphatic formulae. Our results suggested that DOM from urbanized and agricultural catchments significantly altered the chemical composition and bio-availability of DOM with potential effects on ecosystem metabolism and the fate of organic carbon in the downstream-linked streams and rivers. Anthropogenic disturbances may thus boost the microbial processing of organic carbon, including uptake, retention, and outgassing in the impacted ecosystems. Graphical Abstract

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.…”

Selective Exclusion of Aromatic Organic Carbon During Lake Ice Formation

“…This is supported by higher mean apparent retention factors of protein‐like than that of humic‐like components in both the field observations and experimental results (Figure 3b). The protein‐like components are typically associated with transparent DOM that is produced aquatically, and are often associated with higher bioavailability (Fellman et al., 2010; Hu et al., 2022; Kothawala et al., 2015). Thus, we can speculate that the bioavailable fraction of DOM is potentially selectively frozen, but further studies using water from freshwater systems with bioassays would be required to fully address this question.…”

Geospatial Variability of Fluorescent Dissolved Organic Matter in Urban Watersheds: Relationships with Land Cover and Wastewater Infrastructure

“…To differentiate DOM sources, some have adopted parallel factor analysis (PARAFAC) of excitation–emission matrices (EEMs) to identify unique components that can be collectively used to model the fluorescence signatures of environmental samples . Using EEM-PARAFAC, previous studies have evaluated the composition of fluorescent DOM (FDOM) in aquatic environments influenced by agriculture, forests, wastewater effluent, sewer leaks, − and septic systems…”