Evolving characteristics of dissolved organic matter in soil profiles during 56 years of revegetation in Mu Us Sandy Land

Source, composition and molecular diversity determine the reactivity and stabilization of organic matter (OM, dissolved [DOM]/particulate [POM]), affecting its behavior and fate. Here, multiple spectral and mass spectrometry techniques were applied to examine how riparian land-use shaped the source, composition and molecular diversity of POM and DOM (HDOM) in adjacent headstreams. Compared to HDOM with abundant lignins, microbially-transformed heteroatoms and carboxyl-rich alicyclic acids (CRAMs), POM exhibited higher allochthonous characteristics and more bioactive components, but lower molecular weight and diversity in different land-use-dominated streams. Compared to wetland-dominated headstreams, both POM and HDOM exhibited more terrestrial origin and condensed aromatics/tannins molecules for agriculture-impacted headstreams and bio-labile lipids, proteins and carbohydrates for forest-impacted headstreams. Structural equation mode (SEM) showed that soil-derived DOM (SDOM) showed the most prominent influence on the source, composition and molecular diversity of POM and the source of HDOM. The molecular composition and diversity of HDOM were mainly influenced by soil properties/SDOM and aquatic microorganisms, respectively. Redundancy analysis (RDA) revealed that autochthonous, bio-labile compositions of POM in forest and wetland streams were positively related to aquatic Bacteroidetes/Cyanobacteria, and carbohydrates/biogenic index of SDOM, while that of HDOM were positively linked with aquatic Bacteroidetes/Cyanobacteria, and SDOM molecular diversity. Terrestrial and aromatic POM in agricultural headstreams were associated with aquatic total nitrogen/Actinobacteria, and humification degree, aromatic/phenolic substances of SDOM, while that of HDOM were mainly regulated by aquatic nitrate/total nitrogen/Actinobacteria, and aromatic/carboxylic-containing moieties of SDOM. Noteworthily, the molecular diversity of agricultural OM increased along the soil-stream continuum due to the input of soil condensed aromatics and tannins. The opposite trend was observed in forest and wetland streams due to the input of bioactive carbohydrates and the microbial-degradation in-stream. These results are helpful to predict the behavior and fate of OM and determine effective management strategies in tropical coastal regions undergoing intense anthropogenic alterations. 

Source, composition and molecular diversity of dissolved and particulate organic matter varied with riparian land use in tropical coastal headstreams.

This study investigates surface water contamination of Ben-Kazza River in Morocco, fed by effluents from an adjacent lagoon-based wastewater treatment plant (WWTP) and seasonally by industrial effluents, and which occasionally serves to irrigate agricultural fields. This study has two purpose: i) to track the main sources of contamination through the evolution of dissolved organic matter (DOM) characteristics along the watercourse, and ii) to characterize the WWTP influents and effluents with a focus on the efficiency of the lagoon treatment. We characterized a total of 495 water samples across the watercourse and from the inlet and outlet of the WWTP, using UV-visible absorption and excitation-emission fluorescence coupled with chemometric analyses. Absorption indicators and fluorescence indices were calculated and compared across sampling points. Results highlight spatial shifts together with temporal changes in DOM. PARAFAC identified components that varied between protein-like, humic-like and anthropogenic-like fluorophores along the river, permitted to trace the anthropogenic components and their sources. The lagoon treatment appeared to better remove fresh organic material than humic material: fluorescence intensity decreased by 68 % for peak T1 and by 22 % for peak C. Maximum fluorescence intensities (Fmax) decreased across all PARAFAC components, leading to more than 55 % reduction of ΣFmax. 

Identifying sources and distribution of organic pollutants in a Moroccan river: characterization of dissolved organic matter by absorption, excitation–emission fluorescence and chemometric analyses

Water pathways and water contamination in mixed land‐use catchments are complex to understand. Runoff‐generating sources can be numerous and water pathways modified by anthropogenic elements. Monitoring surveys considering geochemical and microbial parameters, are often carried out on such catchment, but are often simple in terms of studied parameters. Nonetheless, they can be helpful to identify the specific signatures of the main runoff‐generating sources and estimate their contribution to total runoff at the outlet of mixed land‐use catchments. Based on a monthly biogeochemical monitoring program conducted between 2017 and 2019 in the Ratier catchment (19.8 km2) near Lyon (France), a step‐by‐step approach was developed to: (1) identify the main runoff‐generating sources using a perceptual model of the Ratier catchment, (2) identify the respective biogeochemical signatures of each source using this biogeochemical dataset and hydro‐meteorological indicators and (3) estimate their contribution to the stream total runoff using an End‐Member Mixing Analysis method. We identified three main runoff‐generating sources outside of rainy periods: a colluvium aquifer, a fractured gneiss aquifer and a saprolite layer. The monitored geochemical datasets were found divided into three groups matching these sources. Contributions of these sources were estimated based on representative tracer concentrations. Microbial parameters showed a homogeneous agricultural and anthropogenic contamination among the catchment surface water, but also deeper into the fractured gneiss groundwater. This approach showed the potential of using simple monitoring datasets to identify runoff‐generating sources and estimate their contribution to total runoff.

Identification and estimation of hydrological contributions in a mixed land‐use catchment based on a simple biogeochemical and hydro‐meteorological dataset

Sampling terrigenous diffuse sources in watercourse: Influence of land use and hydrological conditions on dissolved organic matter characteristics

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Sampling terrigenous diffuse sources in watercourse: Influence of land use and hydrological conditions on dissolved organic matter characteristics