Bioavailability Of Dissolved Organic Matter Research Articles

Karenia brevis and Pyrodinium bahamense Utilization of Dissolved Organic Matter in Urban Stormwater Runoff and Rainfall Entering Tampa Bay, Florida

This study investigated how nitrogen and dissolved organic matter (DOM) from stormwater runoff and rainfall support the growth of Karenia brevis and Pyrodinium bahamense. Excitation–emission matrix spectroscopy coupled with parallel factor analysis tracked changes in the optical properties of DOM in each bioassay, revealing greater reactivity of terrestrial humic-like DOM. Significant increases in cell yield and specific growth rates were observed upon additions of runoff for both species, with significant increases in specific growth rates upon the addition of a 2 in simulated rain event for P. bahamense only. By hour 48, 100% of the dissolved organic nitrogen (DON) in each treatment was utilized by P. bahamense, and by hour 72, over 50% of the DON was utilized by K. brevis. The percentage of bioavailable dissolved organic carbon (DOC) was greater for P. bahamense compared to K. brevis, suggesting a greater affinity for DOC compounds by P. bahamense. However, the bioavailability of DOM for each species could be owed to distinct chemical characteristics of labile DOM conveyed from each site. This study demonstrates that stormwater runoff and rainfall are both sources of labile DOM and DON for K. brevis and P. bahamense, which has implications for blooms of these species in Tampa Bay waters.

Quantity and quality characteristics of DOM loss in sloping cropland under natural rainfall in Southwestern China

Rainfall events lead to dissolved organic matter (DOM) loss in sloping cropland, resulting in a high risk of soil carbon emissions and water pollution. However, limited studies have concentrated on the quality of DOM during different loss pathways in sloping cropland. In this study, the characteristics of DOM loss were explored during different loss pathways (surface runoff, interflow (0–20 cm), interflow (20–40 cm), and sediment) under different slope gradients (10° and 15°), based on natural rainfall. The results showed that surface runoff was the primary carrier of DOM in the sloping cropland, occupying 33 %-43 % of the total loss flux. The slope gradient significantly increased the DOM loss flux of surface runoff and sediment (p < 0.05). Parallel factor analysis (PARAFAC) analyses indicated that four fluorescent components of DOM were detected in both the runoff and sediment. The humic-like components (C1 and C2) accounted for higher than 70 % of the DOM in surface runoff. The protein-like components (C3 and C4) tended to dominate the DOM in the sediment and accounted for 63.02 %-66.93 %. An increased slope gradient exacerbated hydrophobic carbon loss in runoff. The hydrophobicity and aromaticity of DOM in sediment were higher than those in surface runoff. The molecular weight and bioavailability of DOM in sediment were lower than those in surface runoff. The range of humification index (HIX) was 0.63–0.70, indicating a low degree of DOM humification in sloping cropland. Our study clarified the differences between DOM quantity and quality during different loss pathways, which can provide a theoretical foundation for the effective prevention and control of DOM loss and the sustainable agricultural development of sloping cropland.

Dynamic Changes of Dissolved Organic Matter Derived from Algal Decomposition and the Environmental Effects in Eutrophic Lakes

The global occurrences of lake eutrophication have led to algal bloom and the subsequent algal decomposition, releasing high amounts of algae-derived dissolved organic matter (DOM) into the lake water. Algae-derived DOM could regulate the quantity and composition of DOM in lake water and further impact the biogeochemical cycles of multiple elements. In this study, the dynamic changes in the quantity and quality of DOM during algal decomposition under different eutrophic scenarios (e.g., from oligotrophication to severe eutrophication) were monitored, and the corresponding environmental effects (e.g., microbial responses and greenhouse gas emissions) caused by algal decomposition were further explored. The results showed that algal decomposition significantly increased the DOM levels, bioavailability, and intensities of fluorescent components in the water. The total DOM levels gradually decreased, whereas the average molecular weight increased along the decomposition process. Furthermore, unsaturated hydrocarbon and aliphatic compounds were preferentially utilized by microorganisms during algal decomposition, and some refractory molecules (e.g., lignin, condensed hydrocarbons, and tannin with high O/C values) were synchronously generated, as evidenced by the results from ultra-high-resolution mass spectrometry. The dominant bacterial species during algal decomposition shifted from Proteobacteria (46%) to Bacteroidetes (42%). In addition, algae addition resulted in 1.2-5 times the emissions of CO2 and CH4 from water, and the emission rates could be well predicted by the optical index of a254 in water. This study provides comprehensive perspectives for understanding the environmental behaviors of aquatic DOM and further paves the ways for the mitigation of lake eutrophication.

Bacteria Affect the Distribution of Soil-Dissolved Organic Matter on the Slope: A Long-Term Experiment in Black Soil Erosion

Soil erosion results in dissolved organic matter (DOM) loss and is one of the main paths of soil carbon loss. Bacteria affect the generation and transformation of DOM. However, the effect of bacteria on the composition and slope distribution of DOM has rarely been investigated under field conditions. Based on a long-term experiment of three gradients (3°, 5°, 8°) in a black soil erosion area of Northeast China, the content, composition, and source of DOM were studied. The results showed that the DOM of the 3° and 5° slope was enriched midslope, and the DOM of the 8° slope was enriched downslope. Parallel factor (PARAFAC) analysis indicated that the main substances in DOM were fulvic-like acid, humic-like acid, tryptophan-like protein, and soluble microbial metabolites. The upslope and downslope soils of 3° and 5° slopes showed high DOM bioavailability, while the downslope soil of the 8° slope showed high DOM bioavailability. The content of new DOM in downslope soil increased with the gradient. Bacteria played an important role in the synthesis and transformation of DOM and affected its composition and slope distribution. Verrucomicrobiota, Firmicutes, Planctomycetota, and Gemmatimonadota were the main factors affecting soil DOM. The results could be helpful in understanding the loss mechanism of DOM in eroded black soil and provide support for soil carbon sequestration.

Insights into priming effects of dissolved organic matter degradation in urban lakes with different trophic states

Priming effect (PE) is recognized as an important potential mechanism for dissolved organic matter (DOM) degradation in aquatic ecosystems. However, the priming effects (PEs) of various priming substances on the degradation of DOM pools in urban lakes along diverse trophic states remain unknown. To address this knowledge gap, the PEs and drivers of glucose and plant leachate of lake water with three trophic states were investigated. We reveal differences in the bioavailability of DOM in lake water, glucose, and plant leachate. The PE of the same priming substance was significantly higher in highly-eutrophic lake water than in mesotrophic lake. The priming intensity induced by glucose was significantly higher when compared to plant leachate. Regarding the addition of glucose, humic-like components (C1 and C3) showed slight PE, while the tyrosine-like component C2 showed negative PE. However, the positive PEs were observed on three components after adding plant leachate. The driver of PE by glucose shifted from nutrients to DOM components with increasing trophic levels. The PEs induced by plant leachate were affected by nutrients, chlorophyll-a (Chl-a), water chemistry, and DOM components in lightly/moderately-eutrophic lake water. This study revealed the intensities, directions, and drivers of PEs, providing essential insights into uncovering the DOM biogeochemical process in urban lakes.

Urbanization influences dissolved organic matter characteristics but microbes affect greenhouse gas concentrations in lakes

Recognition and prediction of dissolved organic matter (DOM) properties and greenhouse gas (GHG) emissions is critical to understanding climate change and the fate of carbon in aquatic ecosystems, but related data is challenging to interpret due to covariance in multiple natural and anthropogenic variables with high spatial and temporal heterogeneity. Here, machine learning modeling combined with environmental analysis reveals that urbanization (e.g., population density and artificial surfaces) rather than geography determines DOM composition and properties in lakes. The structure of the bacterial community is the dominant factor determining GHG emissions from lakes. Urbanization increases DOM bioavailability and decreases the DOM degradation index (Ideg), increasing the potential for DOM conversion into inorganic carbon in lakes. The traditional fossil fuel-based path (SSP5) scenario increases carbon emission potential. Land conversion from water bodies into artificial surfaces causes organic carbon burial. It is predicted that increased urbanization will accelerate the carbon cycle in lake ecosystems in the future, which deserves attention in climate models and in the management of global warming.

Deciphering the bioavailability of dissolved organic matter in thermophilic compost and vermicompost at the molecular level

Studies on compost dissolved organic matter (DOM) previously focus on its composition and humification, without considering DOM bioavailability to understand compost fertility. To decipher the fertility basis of compost, DOM bioavailability in thermophilic compost (TC) and vermicompost (VC) was investigated and linked with its molecular composition. Results showed that DOM bioavailability of VC (36 % BDOC) was generally higher than that of TC (22 % BDOC) due to containing more tannin-like substances. Inversely, only lipid-/carbohydrate-/protein-like substances contributed to DOM bioavailability in TC. Moreover, these differences of bioavailability expanded with C/N decreased in composting materials. Specifically, the %BDOC of VC with N-rich materials (C/N < 25) was 2.1–3.0 times higher than that in TC, while it was only 1.2–1.4 times for C-rich materials (C/N < 25), because N-surplus facilitated the formation of O-/N-containing aromatics (e.g., CHON and tannin) in VC, but inhibited the decomposition of organic materials into small bioactive molecules in TC.

Seasonal dynamics of dissolved organic matter bioavailability coupling with water mass circulation in the South Yellow Sea

As a typical shelf-marginal sea, the South Yellow Sea (SYS) is significantly influenced by various factors such as land-based inputs and water mass movements, leading the complex biogeochemical processes of dissolved organic matter (DOM) to become highly dynamic. However, the bioavailability of dissolved organic matter (DOM) coupled with water mass circulation has not been accurately assessed, despite being crucial for understanding the source-sink pattern of organic carbon in marginal sea. In this study, four cruises were conducted in the SYS to analyze the spatial and temporal distribution characteristics of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and total dissolved amino acids (TDAA). Combined with the bioassay experiments, TDAA carbon normalized yield [TDAA (%DOC)] and TDAA degradation index (DIAA) were used as indicators to explore the bioavailability of DOM across different water masses. Results show that the DOC of the SYS exhibits higher average value in late autumn and early winter, and lower value in spring and summer due to the seasonal alternation of water mass and biological activities. The collective results indicate that DOM bioavailability is higher in the Changjiang River diluted water (CDW) and lower in the Yellow Sea warm current (YSWC) and the Yellow Sea cold water mass (YSCWM). Approximately 20 % of DON can be degraded in the YSCWM during autumn. Notably, although the YSCWM constitutes merely constitutes 10 % of the SYS volume, it stores 18.1 % dissolved inorganic nitrogen (DIN) and 23.9 % PO43− of total nutrients, indicating that the YSCWM is a significant nutrient reservoir within the SYS.

Performance of gravity-driven membrane filtration for treatment of low-temperature and low-turbidity water: Effect of coagulation pretreatment

As a promising technology for decentralized drinking water treatment, performance of gravity-driven membrane (GDM) filtration for low-temperature and low-turbidity water purification and effects of coagulation pretreatment were investigated in this study. Flux development and permeate water quality of three GDM systems, i.e., control GDM without pretreatment, GDM with in-line coagulation (IC) pretreatment (IC-GDM), GDM with coagulation-sedimentation (CS) pretreatment (CS-GDM), were compared. Moreover, composition and morphology of bio-cake layer were characterized to explain underlying mechanisms for performance improvement by coagulation pretreatment. Results suggested that permeate flux of control GDM stabilized at ∼4.0 L/(m2·h) for raw water with relatively low temperature (8.1– 10.8 °C) and turbidity (1.15– 2.47 NTU). IC pretreatment increased stable flux by 65 %, although the bio-cake layer thickness in IC-GDM was increased by 71.7 %, probably due to a significant reduction (57.1 %) in extracellular polymeric substances (EPS) in the bio-cake layer. Meanwhile, CS pretreatment increased stable flux by 87.5 %, which can be attributed to 63.3 % reduction in EPS and 47.0 % decrease in bio-cake layer thickness. As for permeate water quality, dissolved organic matter (DOM) was significantly reduced by both IC and CS pretreatments, mainly due to transformation from dissolved state to particulates. Compared with control GDM, both IC and CS pretreatments resulted in decrease in microbial abundance and activity and changes in microbial community, probably due to decrease in bioavailable phosphate and DOM. This study suggested that both IC and CS pretreatments can be integrated with GDM filtration for efficient purification of low-temperature and low-turbidity water.

Effects of Phosphorus Limitation on the Bioavailability of DOM Released by Marine Heterotrophic Prokaryotes.

Heterotrophic prokaryotes (HP) contribute largely to dissolved organic matter (DOM) processing in the ocean, but they also release diverse organic substances. The bioavailability of DOM released by HP under varying environmental conditions has not been fully elucidated. In this study, we investigated the bioavailability of DOM released by a single bacterial strain (Sphingopyxis alaskensis) and 2 natural HP communities grown under P-replete and P-limited conditions. The released DOM (HP-DOM) was used as a substrate for natural HP communities at a coastal site in the Northwestern Mediterranean Sea. We followed changes in HP growth, enzymatic activity, diversity, and community composition together with the consumption of HP-DOM fluorescence (FDOM). HP-DOM produced under P-replete and P-limited conditions promoted significant growth in all incubations. No clear differences in HP-DOM lability released under P-repletion and P-limitation were evidenced based on the HP growth, and P-limitation was not demonstrated to decrease HP-DOM lability. However, HP-DOM supported the growth of diverse HP communities, and P-driven differences in HP-DOM quality were selected for different indicator taxa in the degrading communities. The humic-like fluorescence, commonly considered recalcitrant, was consumed during the incubations when this peak was initially dominating the FDOM pool, and this consumption coincided with higher alkaline phosphatase activity. Taken together, our findings emphasize that HP-DOM lability is dependent on both DOM quality, which is shaped by P availability, and the composition of the consumer community.

Key factors driving dissolved organic matter composition and bioavailability in lakes situated along the Eastern Route of the South-to-North Water Diversion Project, China

The Eastern Route of the South-to-North Water Diversion Project (SNWDP-ER) is a large scale multi-decade infrastructure project aiming to divert substantial amounts of water (≈45 billion m3 yr−1) to alleviate water shortage in comparatively arid regions of northern China. The project has ramifications for hydrological connectivity and biogeochemical cycling of dissolved organic matter (DOM) in regional lakes affected by the project. We carried out an extensive field sampling campaign along the SNWDP-ER in different hydrological seasons of 2018 and monthly observations in Lake Hongze and Lake Luoma from April 2018 to June 2021. We found the lakes connecting to the SNWDP-ER had higher mean DOC, specific UV absorbance, higher ratio of humic-like to protein-like fluorophores (Humic : Protein), and shallower spectral slope (S275–295) in the wet season compared to the wet-to-dry transition, and dry seasons. The southern lakes and Yangtze River had lower DOC concentration, bioavailable DOC (BDOC), and higher DOM aromaticity compared to the northern two downstream lakes. Ultrahigh-resolution mass spectrometry (FT-ICR MS) revealed higher relative abundance of CHO-containing and aromatic compounds in the Yangtze River and the southern three upstream lakes compared to the northern two lakes. The data from Lake Hongze and Lake Luoma, studied in different hydrological seasons, suggest that water delivery had high consistency in DOM composition and BDOC over the season. We conclude that positioning along the watercourse and seasonally variable hydrological conditions play an important role in influencing the DOM composition and bioavailability of key lakes connecting to the SNWDP-ER. Our results indicated that the water diversion project delivers water with low DOC concentration and higher aromaticity and thus is of higher quality since it has higher DOM removal potential during drinking water treatment.

Organic matter cycling in a model restored wetland receiving complex effluent

Wetlands have been used to treat anthropogenic effluents for decades due to their intense biogeochemical processes that transform and uptake nutrients, organic matter, and toxins. Despite these known functions, we lack generalizable knowledge of effluent-derived dissolved organic matter (DOM) cycling in wetlands. Here, we quantify the cycling of DOM in one of Canada’s more economically important wetland complexes (Frank Lake, Alberta), restored to hydrologic permanence in the 1980s using urban and agro-industrial effluents. Optical analyses and PARAFAC (parallel factor analysis) modelling showed a clear compositional change from more bioavailable and protein-like DOM at effluent input sites to more aromatic and humic-like at the wetland outflow, likely due to DOM processing and inputs from marsh plants and wetland soils. Microbial incubations showed that effluent DOM was rapidly consumed, with the half-life of DOM increasing from as low as 35 days for effluent, to 462 days at the outflow, as a function of compositional shifts toward aromatic, humic-like material. Long-term averaged dissolved organic carbon (DOC) export was low compared to many wetlands (10.3 ± 2.0 g C m−2 yr−1). Consistent with predictions based on water residence time, our mass balance showed Frank Lake was a net source of DOM across all measured years, but shifted from a source to sink among wet and drought years that respectively shortened or lengthened the water residence and DOM processing times. Overall, Frank Lake processes and transforms effluent DOM, despite being a longer-term net source of DOM to downstream environments.

Molecular level characterization of the biolability of rainwater dissolved organic matter

The atmospheric wet deposition has been recognized as a significant allochthonous source of dissolved organic carbon (DOC) to the ocean. However, few studies have examined the biolability of rainwater dissolved organic matter (DOM) at the molecular level. Rainwater samples were collected and incubated with ambient microbes. DOC, UV–vis spectroscopy, formic acid (FA), acetic acid (AA), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS) were applied. Approximately 50 ± 16 % of rainwater DOC and ~90 % of FA and AA were bioconsumed within 28 days. The contribution of FA and AA to the total BDOC was ~30 %, which was the largest known biolabile fraction in rainwater DOC. In contrast, only approximately 15 % of formulae identified by FT-ICRMS were consumed, which were characterized by higher saturation, higher heteroatom content and lower modified aromaticity. Among the major high molecular weight secondary organic carbon (HWW-SOC)-like compounds, organosulfate contained the largest fraction of consumed formulae, while biogenic volatile organic-derived CHO compounds had the lowest. Our study for the first time provided both quantitative and qualitative understanding of the bioavailability of rainwater DOM, which is essential for understanding their effects on the biogeochemical cycles and the environmental health in the receiving waters.

Zooplankton‐derived dissolved organic matter composition and its bioavailability to natural prokaryotic communities

AbstractZooplankton grazing onphytoplankton promotes the release of particulate and dissolved organic matter (DOM) into the water column and therefore plays a key role in organic matter cycling in aquatic systems. Prokaryotes are the main DOM consumers in the ocean by actively remineralizing and transforming it, contributing to its molecular diversification. To explore the molecular composition of zooplankton‐derived DOM and its bioavailability to natural prokaryotic communities, the DOM generated by a mixed zooplankton community in the coastal Atlantic off Spain was used as substrate for a natural prokaryotic community and monitored over a ~ 5‐d incubation experiment. The molecular composition of solid‐phase extracted DOM was characterized via Fourier‐transform ion cyclotron resonance mass spectrometry. After ~ 4 d in the zooplankton‐derived DOM amended incubation, the prokaryotic community demonstrated a 17‐fold exponential increase in cell number. The prokaryotic growth resulted in a reduction in bulk dissolved organic carbon concentration and the zooplankton‐derived DOM was considerably transformed at molecular and bulk elemental levels over the incubation period. The C : N ratio (calculated from the obtained molecular formulae) increased while the functional diversity decreased over the incubation time. In addition, molecular indices pointed to a reduced bioavailability of DOM at the end of the experiment. These findings show that zooplankton excreta are a source of labile organic matter that is quickly metabolized by the prokaryotic community. Therefore, a fraction of carbon is shunted from transfer to secondary consumers similarly to the viral shunt, suggesting that the zooplankton–prokaryotic interactions play an important role in the ocean's carbon cycle.

Controls on the Distribution, Enrichment, and Degradation of Dissolved Organic Matter in the Sea Surface Microlayer of the Yellow Sea and East China Sea

AbstractThe concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), total dissolved carbohydrates (TDCHO), and total hydrolyzable amino acids (THAA) in the sea surface microlayer (SML) and subsurface water (SSW) were measured in the Yellow Sea and East China Sea. Concentrations of DOC and TDCHO in the SML were correlated with their respective concentrations in the SSW (Pearson's correlations: DOC, r2 = 0.17, n = 45, p &lt; 0.01; TDCHO, r2 = 0.32, n = 45, p &lt; 0.01). In contrast, DON and THAA concentrations in the SML and SSW were not correlated, suggesting that processes other than exchange with SSW dominated their loss or gain in the SML. Both THAA and TDCHO were significantly enriched in the SML, with mean enrichment factors (EFs) of 2.24 ± 1.17 and 1.98 ± 1.08, respectively. The EFs of dissolved organic matter (DOM) were not correlated with wind speed under the influence of complex processes (e.g., bubbling and turbulence). THAA‐C% and TDCHO‐C% in the SML were 3.38 ± 1.71% and 8.49 ± 4.81%, respectively, which were significantly higher than those in the SSW (Mann‐Whitney U test, p &lt; 0.05), suggesting that DOM in the SML was fresher than that in the SSW. While the high bioavailability of DOM in the SML should be conducive to neuston proliferation in this unique environment, no significant correlations were observed between degradation indicators and neuston abundances. In contrast, the changes of temperature and pH may have an important impact on the degradation of DOM.

Bioavailability of dissolved organic matter varies with anthropogenic landcover in the Upper Mississippi River Basin

Anthropogenic conversion of forests and wetlands to agricultural and urban landcovers impacts dissolved organic matter (DOM) within streams draining these catchments. Research on how landcover conversion impacts DOM molecular level composition and bioavailability, however, is lacking. In the Upper Mississippi River Basin (UMRB), water from low-order streams and rivers draining one of three dominant landcovers (forest, agriculture, urban) was incubated for 28 days to determine bioavailable DOC (BDOC) concentrations and changes in DOM composition. The BDOC concentration averaged 0.49 ± 0.30 mg L−1 across all samples and was significantly higher in streams draining urban catchments (0.72 ± 0.34 mg L−1) compared to streams draining agricultural (0.28 ± 0.15 mg L−1) and forested (0.47 ± 0.17 mg L−1) catchments. Percent BDOC was significantly greater in urban (10% ± 4.4%) streams compared to forested streams (5.6% ± 3.2%), corresponding with greater relative abundances of aliphatic and N-containing aliphatic compounds in urban streams. Aliphatic compound relative abundance decreased across all landcovers during the bioincubation (average -4.1% ± 10%), whereas polyphenolics and condensed aromatics increased in relative abundance across all landcovers (average of +1.4% ± 5.9% and +1.8% ± 10%, respectively). Overall, the conversion of forested to urban landcover had a larger impact on stream DOM bioavailability in the UMRB compared to conversion to agricultural landcover. Future research examining the impacts of anthropogenic landcover conversion on stream DOM composition and bioavailability needs to be expanded to a range of spatial scales and to different ecotones, especially with continued landcover alterations.

Urban and agricultural land use regulates the molecular composition and bio-lability of fluvial dissolved organic matter in human-impacted southeastern China

AbstractUrbanization and agricultural land use can increase the transport of nutrients to fluvial ecosystems; yet, the overall impact of urban and nonpoint agricultural inputs on the composition, bio-lability, and the fate of fluvial dissolved organic matter (DOM) remains poorly understood. We investigated the optical and molecular composition and bio-lability of DOM in 76 streams and rivers with varying sizes of catchment area (1 ~ 4850 km2) along large gradients of urban and agricultural land use. Optical spectroscopy and Fourier transform ion cyclotron mass spectrometry (FT-ICR MS) were used to determine the chemical composition of DOM, and laboratory bio-incubations were used to assess DOM bio-lability. We found that urban and agricultural land use intensification was associated with the reduced relative contribution of DOM from pristine soils, enriched dissolved organic carbon (DOC), and higher contributions of aliphatic and peptide-like DOM, as well as enrichment of N- and S-containing molecular formulae. Specifically, FT-ICR MS revealed that the relative abundance of CHO-containing formulae decreased while that of CHOS-containing formulae increased with increasing urban land use. DOM bio-availability was higher in rivers draining urbanized and agricultural landscapes and was related to decreased DOM aromaticity and increased proportions of energy-rich aliphatic formulae. Our results suggested that DOM from urbanized and agricultural catchments significantly altered the chemical composition and bio-availability of DOM with potential effects on ecosystem metabolism and the fate of organic carbon in the downstream-linked streams and rivers. Anthropogenic disturbances may thus boost the microbial processing of organic carbon, including uptake, retention, and outgassing in the impacted ecosystems. Graphical Abstract

Dissolved organic matter tracers reveal contrasting characteristics in the concentrated flow zone and matrix-with-fractures zone of a sulfate-contaminated karst aquifer in South China

Dissolved organic matter (DOM) is of great importance in biogeochemical processes, such as sulfate reduction, in groundwater. H2S is generated from microbial-mediated sulfate reduction fueled by DOM and erodes carbonate. However, understanding the transformation and fate of DOM in sulfated-contaminated karst aquifers is still poor. Here, fluorescence spectroscopy was used to characterize the DOM pool in the sulfate-contaminated (from human activities) karst aquifer of the Zengpiyan Site, South China, by investigating the groundwater flow system. A comparison of fluorescence DOM (FDOM) characteristics between the concentrated flow zone (CFZ) composed of highly permeable small conduits and fracture networks and the matrix-with-fractures zone (MFZ) made of low permeable fractures and matrix rock aquifers was done. The relative groundwater residence times for all sample sites were estimated using γCa/γMg, which are consistent with those of the groundwater tracer test. The FDOM in groundwater in the CFZ was composed mainly of terrestrial-derived fulvic acid (FA)- and humic acid (HA)-like components, with relatively small contributions of microbially derived tryptophan (TPH)-like components. Compared with CFZ groundwater, the MFZ groundwater showed a longer residence time and reducing conditions, more bioavailable DOM, dominant TPH-like components with relatively small contributions of FA-like components, and fewer humus and hydrophobic structures. Hydrogeological conditions indirectly altered DOM composition by altering the biotic and abiotic activity conditions. The coexistence of relatively strong reducibility conditions and the higher proportion of bioavailable DOM in the MFZ would promote sulfate reduction to H2S gas, possibly amplifying carbonate dissolution, leading to the erosion of cultural relics. It is hoped that this study will contribute to knowledge on DOM behavior in karst aquifers and provide a scientific basis for cave site protection.

New Insights into Microbial Degradation of Cyanobacterial Organic Matter Using a Fractionation Procedure.

Cyanobacterial blooms caused by phytoplankton Microcystis have occurred successively since 1980 in Lake Taihu, China, which has led to difficulty collecting clean drinking water. The effects of cyanobacterial scum-derived dissolved organic matter (DOM) on microbial population variations and of algal-derived filtrate and algal residual exudative organic matter caused by the fraction procedure on nutrient mineralization are unclear. This study revealed the microbial-regulated transformation of DOM from a high-molecular-weight labile to a low-molecular-weight recalcitrant, which was characterized by three obvious stages. The bioavailability of DOM derived from cyanobacterial scum by lake microbes was investigated during 80-d dark degradation. Carbon substrates provided distinct growth strategy links to the free-living bacteria abundance variation, and this process was coupled with the regeneration of different forms of inorganic nutrients. The carryover effects of Microcystis cyanobacteria blooms can exist for a long time. We also found the transformation of different biological availability of DOM derived from two different cyanobacterial DOM fractions, which all coupled with the regeneration of different forms of inorganic nutrients. Our study provides new insights into the microbial degradation of cyanobacterial organic matter using a fractionation procedure, which suggests that the exudate and lysate from degradation products of cyanobacteria biomass have heterogeneous impacts on DOM cycling in aquatic environments.

Linking Microbial Population Succession and DOM Molecular Changes in Synechococcus-Derived Organic Matter Addition Incubation.

ABSTRACTThe 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 Synechococcus-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−1 day−1, 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.IMPORTANCE 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, Synechococcus blooms are commonly observed in coastal seawaters, and they significantly influence the elemental biogeochemistry cycling in eutrophic ecosystems. To understand the interactions between Synechococcus-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.