Factors Governing Site and Charge Density of Dissolved Natural Organic Matter

Abstract

Rising organic charge in northern freshwaters is attributed to increasing levels of dissolved natural organic matter (DNOM) and changes in water chemistry. Organic charge concentration may be determined through charge balance calculations (Org.−) or modelled (OAN−) using the Oliver and Hruška conceptual models, which are based on the density of weak acid functional sites (SD) present in DNOM. The charge density (CD) is governed by SD as well as protonation and complexation reactions on the functional groups. These models use SD as a key parameter to empirically fit the model to Org.−. Utilizing extensive water chemistry datasets, this study shows that spatial and temporal differences in SD and CD are influenced by variations in the humic-to-fulvic ratio of DNOM, organic aluminum (Al) complexation, and the mole fraction of CD to SD, which is governed by acidity. The median SD values obtained for 44 long-term monitored acid-sensitive lakes were 11.1 and 13.9 µEq/mg C for the Oliver and Hruška models, respectively. Over 34 years of monitoring, the CD increased by 70%, likely due to rising pH and declining Al complexation with DNOM. Present-day median SD values for the Oliver and Hruška models in 16 low-order streams are 13.8 and 15.8 µEq/mg C, respectively, and 10.8 and 12.5 µEq/mg C, respectively, in 10 high-order rivers.

UV/Advanced Oxidation Process for Removing Humic Acid from Natural Water: Comparison of Different Methods and Effect of External Factors

“…As the concentration of organic matter increases, HA and its degradation byproducts compete for SO 4 − • and •OH radicals [49]. 2 ⃝ The augmentation of HA concentration results in a visual darkening of the solution, thereby diminishing its transparency. UV radiation is subsequently obstructed and assimilated by HA molecules and their decomposition intermediates, thereby impeding the activation of PMS [50].…”

“…In China, water resources are significantly contaminated, primarily by organic pollutants, with natural organic matter (NOM) serving as a major pollution source. NOM constitutes a crucial element of aquatic ecosystems and is commonly present in natural water sources, with levels typically varying between 0.1 mg/L and 20 mg/L, demonstrating a progressive escalation [1,2]. Elevated concentrations of NOM impose significant challenges on nearby water treatment plants and ecosystems.…”