Distinguishing between Sources of Natural Dissolved Organic Matter (DOM) Based on Its Characteristics

Abstract

Increasing levels of dissolved organic matter (DOM) in watercourses in the northern hemisphere are mainly due to reduced acid rain, climate change, and changes in agricultural practices. However, their impacts vary in time and space. To predict how DOM responds to changes in environmental pressures, we need to differentiate between allochthonous and autochthonous sources as well as identify anthropogenic DOM. In this study we distinguish between allochthonous, autochthonous, and anthropogenic sources of DOM in a diverse watercourse network by assessing effects of land cover on water quality and using DOM characterization tools. The main sources of DOM at the studied site are forests discharging allochthonous humic DOM, autochthonous fulvic DOM, and runoff from urban sites and fish farms with high levels of anthropogenic DOM rich in protein-like material. Specific UV absorbency (sUVa) distinguishes allochthonous DOM from autochthonous and anthropogenic DOM. Anthropogenic DOM differs from autochthonous fulvic DOM by containing elevated levels of protein-like material. DOM from fishponds is distinguished from autochthonous and sewage DOM by having high sUVa. DOM characteristics are thus valuable tools for deconvoluting the various sources of DOM, enabling water resource managers to identify anthropogenic sources of DOM and predict future trends in DOM.

Factors Governing Site and Charge Density of Dissolved Natural Organic Matter

“…Changes in climate may have had a similar effect by enhancing the influx of humic rich allochthonous DNOM to surface waters. Terrestrial material typically exhibits a higher humic character than autochthonous material [15]. This shift is likely the cause for the strong decline in CD observed at the less acid-sensitive and acid rain loaded site of Kårvatn in mid-Norway.…”

“…Aromatic compounds, rich in conjugated double bonds, absorb UV light and wavelengths (λ) into the visible (VIS) light spectrum. λ of 254 and 410nm are thus widely used as proxies for DNOM, and their specific absorbencies (sUVa and sVISa) are positively correlated to DNOM aromaticity and, consequently, to the ratio of humic to fulvic fractions in the DNOM ( [15] and references therein). Based on this conceptual framework, one could hypothesize that the SD of DNOM decreases with increasing sUVa and sVISa.…”

Factors Governing Site and Charge Density of Dissolved Natural Organic Matter

“…Aromatic compounds, rich in conjugated double bonds, absorb UV light and wavelengths (λ) into the visible (VIS) light spectrum. Wavelengths of 254 and 410 nm are thus widely used as proxies for DNOM, and their specific absorbencies (sUVa and sVISa) are positively correlated to DNOM aromaticity and, consequently, to the ratio of humic to fulvic fractions in the DNOM ( [16] and references therein). Based on this conceptual framework, one could hypothesize that the SD of DNOM decreases with increasing sUVa and sVISa.…”

“…This suggests that in areas where the influence of acid rain has been minimal, the SD and thus the CD have decreased with increasing DNOM, as observed in Kårvatn with low median sulphate levels (Table 2). Additionally, runoff from catchments with high biomass (forests) tends to have higher sUVa [16], resulting in lower SD. Furthermore, increased runoff and its intensity, especially through the forest floor containing DNOM with higher sUVa [31], could influence these trends.…”

“…− ) normalized to the concentration of total organic carbon (TOC), is a conceptually important factor for understanding the solubility of DNOM and its function as a counter ion in the leaching of base cations and thus in the recovery from acid rain [7], as well as its role in the complexation and detoxification of heavy metals and aluminum (Al) [8]. For drinking water treatment plants that need to remove DNOM from their raw water, the CD of the DNOM plays a key role in governing treatability and Water 2024, 16, 1716 2 of 17 coagulant dose requirements [9]. Additionally, organic charge plays an important role in the quality control of major anion and cation data, as it significantly contributes to charge balance control, especially in dystrophic waters.…”