Display omitted
•Hg and DOM concentrations increased dramatically during snowmelt.•Clockwise C-Q hysteresis for filtered THg concentrations.•Hg was predominantly in the dissolved fraction.•DOM was ...dominated by humic and fulvic acids from soils.•Most Hg and DOM export occurred during the snowmelt period by soil water flushing.
The mechanisms of Hg and dissolved organic matter (DOM) transport from watersheds to streams remain unclear, especially in snowmelt dominated montane systems. We characterized total Hg concentrations and DOM characteristics during snowmelt by weekly and/or monthly sampling at three locations in the upper Provo River, northern Utah, over two water years (2016 and 2017). Total Hg concentrations increased from <1 ng/L during baseflow to >7 ng/L during the snowmelt period (April–June), with decreasing concentrations from upstream to downstream. Filtered THg concentrations accounted for 65–75% of the unfiltered concentrations, suggesting that Hg is primarily transported in the dissolved phase. Annual THg loading in the upper Provo River was approximately 1 kg/yr, with ~90% of the flux occurring during the snowmelt period. Filtered THg concentrations were strongly correlated with in-situ fluorescence DOM (fDOM) measurements, allowing for the development of high-resolution proxy THg concentrations. Further, DOM characteristics, evaluated using excitation-emission matrices (EEMs) and parallel factor analysis (PARAFAC), identified the dominance of soil humic and fulvic acid fractions of DOM during runoff. Total Hg concentrations were low in snowpack but elevated in ephemeral streams during snowmelt runoff, indicating that Hg originated from shallow soil water rather than snow. Concentration—discharge relationships revealed clockwise hysteresis patterns, suggesting that Hg was flushed from soils on the rising limb of the hydrograph. Our results demonstrate that a majority of Hg transport occurs with a flux of DOM during the short snowmelt season as shallow soils are flushed by meltwater. The snowmelt-driven Hg pulse is a substantial source to downstream reservoirs and potentially contributes to a fish consumption advisory.
The molecular-level interactions between phytoplankton-derived dissolved organic matter (DOM) and heterotrophic prokaryotes represent a fundamental and yet poorly understood component of the marine ...elemental cycle. Here, we investigated the degradation of
-derived organic matter (SynOM) by coastal microorganisms using spectroscopic and ultrahigh-resolution mass spectrometry analyses coupled with high-throughput sequencing. The added SynOM showed a spectrum of reactivity during a 180-day dark incubation experiment. Along with the decrease in DOM bioavailability, the chemical properties of DOM molecules overall showed increases in oxidation state and aromaticity. Both the microbial community and DOM molecular compositions became more homogeneous toward the end of the incubation. The experiment was partitioned into three phases (I, II, and III) based on the total organic carbon consumption rates from 7.0 ± 1.0 to 1.0 ± 0.1 and to 0.1 ± 0.0 μmol C L
day
, respectively. Diverse generalists with low abundance were present in all three phases of the experiment, while a few abundant specialists dominated specific phases, suggesting their diverse roles in the transformation of DOM molecules from labile and semilabile to recalcitrant. The changes of organic molecules belonging to CHO, CHNO, and CHOS containing formulas were closely associated with specific microbial populations, suggesting close interactions between the different bacterial metabolic potential for substrates and DOM molecular compositional characteristics. This study sheds light on the interactions between microbial population succession and DOM molecular changes processes and collectively advances our understanding of microbial processing of the marine elemental cycle.
Phytoplankton are a major contributor of labile dissolved organic matter (DOM) in the upper ocean, fueling tremendous marine prokaryotic activity. Interactions between microorganisms and algae-derived DOM regulate biogeochemical cycles in the ocean, but key aspects of their interactions remain poorly understood. Under global warming and eutrophication scenarios,
blooms are commonly observed in coastal seawaters, and they significantly influence the elemental biogeochemistry cycling in eutrophic ecosystems. To understand the interactions between
-derived DOM and heterotrophic prokaryotes as well as their influence on the coastal environment, we investigated the degradation of DOM by coastal microbes during a 180-day dark incubation. We showed substantial DOM compositional changes that were closely linked to the developments of microbial specialists and generalists. Our study provides information on the interactions between microbial population succession and DOM molecular changes, thereby advancing our understanding of microbial processing of the marine DOM pool under the influence of climate change.
Thermal stratification often occurs in deep-water bodies, including oceans, lakes, and reservoirs. Dissolved organic matter (DOM) plays a critical role in regulating the dynamics of aquatic food webs ...and water quality in aquatic ecosystems. In the past, thermal stratification boundaries have been sometimes used exclusively to analyze the vertical distribution of DOM in thermally stratified water bodies. However, the validity of this practice has been challenged. Currently, there is limited understanding of the formation mechanism and stratification of the vertical distribution of DOM in thermally stratified water bodies, which hinders the analysis of the interactions between DOM and vertical aquatic ecological factors.
To address this gap, we conducted a comprehensive study to extensively collect the vertical distribution of DOM in thermally stratified water bodies and identify the primary factors influencing this distribution. We found that DOM was independently stratified in thermally stratified water bodies (including two cases in unstratified water bodies), and that the formation mechanisms and statuses of DOM stratification were different from those of thermal stratification. The boundaries and numbers of DOM stratification were generally inconsistent with those of thermal stratification. Therefore, it is more accurate to divide DOM into different layers according to its own vertical profile, and analyze DOM characteristics of each layer based on its own stratification instead of thermal stratification. This study sheds light on the relationship between DOM and thermal stratification and provides a novel approach for analyzing DOM vertical distribution characteristics and their impact on aquatic ecosystems. This finding also holds significant implications for the design and implementation of environmental management programs aimed at preserving the health and functionality of aquatic ecosystems.
Display omitted
•Analyzing DOM vertical distribution based on thermal stratification may be arguable.•DOM was found to be stratified independently in thermally stratified water bodies.•Some conformity existed between DOM and thermal stratification due to interaction.•DOM vertical distribution was primarily influenced by its sources and sinks.•DOM stratification's boundaries/numbers were different from thermal stratification.
Wastewater reuse for resolving water shortage is increasingly emphasized. The presence of DOM in wastewater is a main consideration for wastewater reuse. Therefore, systematic understanding of ...characteristic changes of DOM in different wastewater treatment processes is needed. As biotechnology together with disinfection operation has been used widely by WWTPs to treat wastewater, this review aims to introduce the recent advances in the effects of wastewater biological treatment and disinfection on the characteristics of DOM. Firstly, the composition of DOM in WWTPs is introduced. Then, the effects of wastewater treatments on hydrophobicity, MW distribution and optical characteristics of DOM and their correlations are reviewed. Also, the influences of wastewater treatments on biodegradability and biotoxicity of DOM are discussed. Finally, the environmental impact of effluent DOM is summarized. Since the discharge of wastewater effluent DOM to the environment not only influences nutrient uptake by bacteria, plankton and algae, and phototransformation rate of micropollutants in natural water, but also changes DOM level and physicochemical properties of soil.
•The changes of MW distribution, hydrophobicity and optical properties of DOM during wastewater treatment were reviewed.•The relationship between MW distribution, hydrophobicity and composition of DOM was analyzed by optical properties.•The transformation of DOM characteristics changed its biodegradability and biotoxicity.•Effluent DOM affected nutrient uptake, pollutant phototransformation in river, and physicochemical properties of soil.
To date, studies on the mobility of arsenic (As) in soil amended with biochar have primarily relied on broad empirical observations, resulting in a gap between the behavior of As in amended soil and ...the chemical mechanisms controlling that behavior. This study focuses on the influence of abiotic factors in As mobility in As-contaminated soils amended with biochar. In order to understand the leaching of DOC and phosphate across a range of biomass feedstock and pyrolysis temperature, rice straw and granular sludge from an anaerobic digester were pyrolyzed at 300, 550, and 700 °C, and subjected to leaching studies by mixing air dried soil with 10 wt% of biochar at a soil: water ratio of 1:1(w/v). The concentration of DOC in the presence of granular sludge biochar and rice straw biochar increased from 190 mg L−1 to 2605 mg L−1 and 1192 mg L−1, respectively, which considerable accelerated the mobilization of Fe and As. More specifically, DOC drove the reduction of Fe(III) to Fe(II). Our results suggest enhanced release of As via the reductive dissolution of iron oxides, including by the chelating-enhanced dissolution of Fe oxides, and competitive desorption by DOC and phosphate from biochar. The influence of DOC and phosphate was further evaluated using realistic application amounts (1, 3, and 5 wt%) of biochars derived from pyrolysis of granular sludge, rice straw and spent coffee ground at 300 and 550 °C. The results from these experiments further confirm that DOC is a key factor for influencing the mobility of As in the amendment of biochar to As-contaminated soil, which indicates that biochar having low levels of leachable carbon should be amended to As-contaminated soils, and with caution.
Display omitted
•Dissolved organic carbon from biochar increased mobility of As in soil.•Biochar enhanced reductive dissolution of Fe oxides in soil.•Dissolved organic carbons extract Fe via chelating enhanced dissolution.•Phosphate enhanced As mobility via competitive desorption
During leachate treatment, molecular information regarding the completely removed, partially removed, less-reactive, increased, and produced parts of dissolved organic matter (DOM) remains unknown. ...This study applied ESI FT-ICR MS to investigate the transformation characteristics of leachate nanofiltration concentrate (NFC) DOM during a combined flocculation–O3/H2O2 process. The NFC contained 5069 compounds in four main classes (CHO, CHON, CHOS, and CHONS compounds). The DOM number decreased to 4489 during flocculation and to 2903 after the O3/H2O2 process. During flocculation, the completely and partially removed DOM was mainly low-oxygen unsaturated and phenolic compounds. Saturated DOM was produced and remained in the flocculated effluent. During the O3/H2O2 process, the completely and partially removed DOM were mainly low-oxygen unsaturated and phenolic compounds that were mainly in a reduced state. Flocculation can remove many (condensed) aromatic compounds, and methylation and hydrogenation reactions occurred during flocculation. In the O3/H2O2 process, dearomatization, demethylation, carboxylation, and carbonylation reactions further achieved the degradation of DOM that was resistant to flocculation. Overall, the combined flocculation-O3/H2O2 process collectively eliminated a broader range of DOM than the single processes could achieve. The results of this study provide an in-depth understanding of DOM transformation in an NFC treatment.
Display omitted
•Transformation of NFC DOM in flocculation-O3/H2O2 process was studied by FT-ICR MS.•Removed, less-resistant, and produced parts of NFC DOM in flocculation-O3/H2O2 were determined.•A Kendrick mass defect theory was used to study DOM transformation of NFC.•Flocculation-O3/H2O2 collectively eliminated a broader range of DOM.
Landfill is an important method for the treatment of municipal solid wastes. Microbes play a central role in the biodegradation and stabilization of organic matter during landfill; however, the ...succession of microbial communities in landfills and their association with organic matter still remain unclear. This study investigated the succession and diversity of microorganisms in landfill depending on different depths and ages as well as its association with dissolved organic matter (DOM) and heavy metals. The results showed that the actinobacterial diversity and richness were high compared to bacteria in young landfill cells. The diversity and richness of bacteria and actinobacterial were the highest in the middle layer in the intermediate and old landfill cells. Firmicutes, Proteobacteria, and Actinobacteria were the most dominant phyla. Firmicutes were mainly affected by the humification degree, and the aromatic and protein-like substance content of the landfill-derived DOM. The phylum Proteobacteria was greatly affected by the lipid and humic-like substances content of the landfill-derived DOM, while the distribution of Actinobacteria was regulated by both aromatic and humic-like substances. The effect of dissolved heavy metals on the microbial distribution in landfill differed for the metals Cr, Ni, Pb, Mn, Cu, Zn, and Cd. Siderophile elements (Cr, Ni, and Pb) were necessary trace elements for Proteobacteria and Actinobacteria, and promoted their growth. Oxyphilic element (Mn) was an important factor promoting the growth of Actinobacteria. However, no apparent relationship was found between sulfurophile elements (Cu, Zn, and Cd) and microorganisms.
Display omitted
•The abundance of microbes in the upper and lower layers of landfills was high.•Firmicutes, Proteobacteria, and Actinobacteria were the dominant phyla in landfill.•Firmicutes played an important role in the synthesis of humic-like matter.•Proteobacteria facilitated to increase the content of aromatic compounds.•Actinobacteria could oxidize fatty chains into oxygen-containing functional groups.
Coastal marine ecosystems are strongly influenced by different occasional events, such as intense winds, mixing, rain and river discharges. These events can directly or indirectly cause changes in ...dissolved organic matter (DOM) quality through a cascade of different biotic and abiotic processes. Changes in DOM quality are often associated with changes in DOM optical properties. Thus, examining the dynamics of chromophoric DOM (CDOM) can provide valuable information about biological and physical processes that have occurred in the ecosystem. Episodic meteorological events, particularly in temperate areas, appear very abruptly and induce very rapid responses; therefore, high time-resolved measurements are needed to capture them. We used a weekly sampling scheme to characterize DOM and nutrient dynamics in the NW Mediterranean coastal station ‘SOLA’. From February 2013 to April 2014, we measured several physical and chemical variables including temperature, salinity, inorganic nutrients, chlorophyll a dissolved organic carbon (DOC), CDOM and fluorescent DOM (FDOM). During this period, two extremely high fresh water intrusions greatly influenced the dynamics of some DOM fractions, in particular the FDOM. Inorganic nutrients and chlorophyll a showed seasonal patterns: A winter period characterized by a high nutrient concentration in surface waters favored the phytoplankton spring bloom; then, summer stratification extended until autumn. This stratification led to nutrient depletion and, consequently, lower chlorophyll a values in the photic zone. The CDOM and FDOM optical active fractions did not follow temporal trends similar to total DOC. This was likely because the potential sources and sinks of these DOM pools are microbial activity and light exposure, and these were acting simultaneously but in opposite directions. Interestingly, DOC exhibited the highest concentrations in summer, coinciding with nutrient and chlorophyll a minima. To explain this mismatch, we propose a sequence of abiotic and biotic phenomena that drive DOC temporal dynamics.
Display omitted
•DOM composition monitored during 15 months in a NW Mediterranean coastal station.•Fluorescent DOM dynamics was influenced by freshwater intrusions.•A decrease in nutrients due to stratification promoted surface DOC accumulation.•A temporal mismatch was found between chlorophyll a and dissolved organic matter.
Dissolved organic matter (DOM) in the ocean accounts for nearly 662 Pg of carbon, most of which is formed into a long-lived carbon pool that plays an important role in carbon sequestration. This ...carbon resists rapid biological decomposition and is widely known as recalcitrant DOM (RDOM). The recalcitrant nature of deep-sea DOM has been addressed for more than half of a century, studies examining the chemical composition, production, distribution, and removal of RDOM are progressively increasing in recent decades and could add to our understanding of its cycling; however, they need to be better synthesized. A concept proposed over a decade ago, the microbial carbon pump (MCP), attributes the main mechanism of RDOM formation to successive microbial processing of organic matter. This ultimately leads to inaccessibility due to the intrinsic recalcitrant nature of DOM under certain environmental conditions, or to the organic concentration falling below the threshold for microbial reutilization, further explaining the recalcitrant nature of RDOM. This review focuses on those DOM molecules with intrinsic recalcitrant nature and collates studies on the following three aspects: (i) proxies of intrinsic RDOM, (ii) ecological processes that affect RDOM production within the conceptual framework of the MCP, and (iii) distribution and removal processes of RDOM in the ocean. Throughout this extensive review, we examine the vital role of microbes in the production and maintenance of RDOM in the ocean and conclude that the MCP is essentially associated with the sequestration of RDOM in the ocean.
•Proxies of intrinsically recalcitrant DOM were reviewed and suggested.•Several indices ready for evaluating recalcitrant state of DOM were collated.•Recalcitrance of deep-sea DOM could be explained by multi-mechanisms.•Microbial activities within the microbial carbon pump are vital in production and maintenance of marine recalcitrant DOM.
PDF
