Impact of land use on the DOM composition in different seasons in a subtropical river flowing through a region undergoing rapid urbanization

Abstract

The dissolved organic matter (DOM) composition in river ecosystems could reflect the human impacts on the river ecosystem, and plays an important role in the carbon cycling process. We collected water and phytoplankton samples at 107 sites in the Dongjiang River in two seasons to assess the impact of the sub-catchments land use structure on the DOM composition. The results showed that (1) the forested subcatchments had higher humic-like C1 (16.45%) and C2 (25.04%) and lower proteinlike C3 (22.57%) and C4 (35.95%) than urbanized and mixed forest-agriculture subcatchments, while the urbanized sub-catchments showed an inverse trend (4.54%, 15.51%, 33.97% and 45.98%, respectively). (2) The significant variation in the proportion of C1 and C4 between the dry and rainy seasons was recorded in both the forested and the mixed forest-agriculture sub-catchments (p<0.01), but only C4 showed an obvious seasonal variation in the urbanized sub-catchments (p<0.01). While the DOM composition was mainly related to the proportion of urbanized land and forested land year-round (p<0.01), it had stronger correlation with forested land in the dry season and urbanized land in the rainy season.(3) No significant correlation between the DOM composition and the agricultural land proportion was found in either season (p>0.05).Our findings indicated that the DOM composition was strongly dependent on the land use structure of the sub-catchments and varied seasonally, but the seasonal variation pattern could be disturbed by human activities in the extensively urbanized catchments.Notably, the higher C4 proportion compared with those in temperate rivers implied a larger amount of CO2 released from the subtropical rivers into the atmosphere when considering bioavailability.

Spectroscopic and Molecular-Level Characteristics of Dissolved Organic Matter in a Highly Polluted Urban River in South China

“…For example, Meng et al found that the levels of dissolved organic carbon (DOC) and tryptophan- and tyrosine-like fluorescent DOM components were significantly elevated in the Guangzhou section of the Pearl River in China. Similarly, Liu et al showed that urbanized subcatchments had notably high abundance of protein-like components but low abundance of humic-like components relative to those of forested subcatchments in Dongjiang River of the Pearl River. These studies primarily focused on the properties and fluorescent components of DOM by means of ultraviolet–visible spectroscopy, fluorescent spectroscopy, and parallel factor analysis (PARAFAC).…”

Dissolved Metal(loid) Concentrations and Their Relations with Chromophoric and Fluorescent Dissolved Organic Matter in an Urban River in Shenzhen, South China

“…This phenomenon could be explained by the negative correlations between the Fmax/DOC for humic-like FDOM and the Fmax/DOC for protein-like FDOM within the mainstream samples. In other words, in the disturbed mainstream river, the anthropogenic protein-like proportion in DOM increased while the natural humic-like proportion decreased with increasing disturbance [28,33]. This phenomenon also implies that the dominant ligands for dissolved metal(loid)s in the mainstream could shift from natural sources (such as humic-like FDOM) to anthropogenic sources (such as protein-like FDOM from the WWTP).…”

“…For example, wastewater effluents from WWTPs can contribute high loads of Zn, Cu, and their complexes with effluent organic matter to urban rivers [4,54,55]. The DOM impacted by WWTPs in urban river was found to have more protein-like, polysaccharide-like, and surfactant-like DOM components, with lower molecular size, aromaticity, and HIX, but higher FI and BIX than natural DOM [28,33,34]. In addition, two-dimensional correlation spectroscopy (2D-COS) analysis has previously indicated that the protein-like and polysaccharide-like organic matter had a higher susceptibility and preferential binding with Cu(II) than did humic-like substances [17].…”

“…In addition, various anthropogenic sources of metal(loid)s, such as industrial and domestic wastewater discharge and urban runoff [30,31], may further complicate the metal(loid) composition and distribution and alter the metal(loid)-DOM equilibrium. Urbanization significantly influences DOM characteristics, such as composition, aromaticity, molecular size, and functional groups [28,29,32,33], which inevitably alter metal(loid) affinity [15]. For example, while the DOM in a peri-urban river exhibited significant positive correlations with Mn, Pb, and Cu, the DOM in an urban river had significantly positive correlations with Cr, Mn, As, Zn, and Pb [34].…”

Spatiotemporal variations of DOM in a typical multi-source watershed in northern China: A fluorescent evidence

“…However, with the rapid economic development and the intensi cation of human activities, water pollution in the North Canal River watershed has become increasingly serious. In recent years, researches on the North Canal River watershed have focused on the concentration and risk of heavy metals, pharmaceuticals, and personal care products, polycyclic aromatic hydrocarbons, microbial diversity, and different nitrogen and phosphorous in water and sediment (Dai et al, 2015;Guo et al, 2020;Liu et al, 2019a;Qiao et al, 2020;Zhang et al, 2020). For all this, the composition and source of DOM in the North Canal River watershed and its relationship with water quality are still lacking.…”