DOM in the long arc of environmental science: looking back and thinking ahead

Abstract

Dissolved organic matter (DOM) is a heterogeneous mixture of organic compounds that is produced through both microbial degradation and abiotic leaching of solid phase organic matter, and by a wide range of metabolic processes in algae and higher plants. DOM is ubiquitous throughout the hydrologic cycle and plays an important role in watershed management for drinking water supply as well as many aspects of aquatic ecology and geochemistry. Due to its wide-ranging effects in natural waters and analytical challenges, the focal research questions regarding DOM have varied since the 1920s. A standard catchment-scale model has emerged to describe the environmental controls on DOM concentrations. Modest concentrations of DOM are found in atmospheric deposition, large increases occur in throughfall and shallow soil flow paths, and variable concentrations in surface waters occur largely as a result of the extent to which hydrologic flow paths encounter deeper mineral soils, wetlands or shallow organic-rich riparian soils. Both production and consumption of DOM occur in surface waters but appear to frequently balance, resulting in relatively constant concentrations with distance downstream in most streams and rivers. Across biomes the concentration and composition of DOM in flowing waters is driven largely by soil processes or direct inputs to channels, but high levels can be found in streams and rivers from the tropics to the poles. Seven central challenges and opportunities in the study of DOM should frame ongoing research. These include maintaining or establishing long-term records of changes in concentrations and fluxes over time, capitalizing on the use of sensors to describe short-term DOM dynamics in aquatic systems, integrating the full carbon cycle into understanding of watershed and aquatic DOM dynamics, understanding the role of DOM in evasion of greenhouse gases from inland waters, unraveling the enigma of dissolved organic nitrogen, documenting gross versus net DOM fluxes, and moving beyond an emphasis on functional ecological significance to understanding the evolutionary significance of DOM in a wide range of environments.

Differences in dissolved organic matter and analysis of influencing factors between plantations pure and mixed forest soils in the loess plateau

“…The DOC values of the soil at depths of 0-20 cm (22.07-46.32 mg/L) and 20-60 cm (9.47-11.15 mg/L) in the area were comparable to the values of subtropical forest tree species (0-20 cm:37.10-47.40 mg/L; 20-60 cm:4.80-9.50 mg/L) (Tu et al, 2011). DOC distribution and changes in soil profiles have certain regularities (McDowell and Likens, 1988;Gabor et al, 2014;McDowell, 2022), and the content of DOC in the surface soil layer is usually greater than that in the bottom soil layer. The elevated levels of DOC in the upper layers of forest soil mainly arise from the leachates of the canopy and litter; however, the decrease in DOC levels may be related to losses caused by adsorption and decomposition during downward migration in soil minerals, leading to a decrease in DOC levels with increasing depth (Tu et al, 2011).…”

Organic water features of three adjacent Eastern Mediterranean urbanized watersheds

“…Rivers have a major role in carbon cycles by transporting carbon from land to the seas representing a reactive ux and dissolved organic matter DOM is an inevitable carbon ux source. DOM is highly reactive in ecosystem processes such as bacterial respiration, photochemical oxidation and primary production (McDowell 2023). DOM are very dynamic, and they change by nature from upstream to downstream and even after entering the marine.…”

Dissolved organic carbon export in a small, disturbed peat catchment: Insights from long‐term, high‐resolution, sensor‐based monitoring

“…As a critical component of aquatic carbon (C) pools, accurate quantification and characterization of dissolved organic carbon (DOC) export is vital (Cole et al 2007; Vaughan et al 2019; McDowell 2022). Downstream export of DOC represents C not sequestered in terrestrial stocks and changes in DOC mobilization may represent destabilization of land in the catchment.…”