Sediment Dissolved Organic Matter Research Articles

Occurrence of dissolved organic matter in storm-drain inlet sediments and its implication for urban stormwater infrastructure sustainability

In the context of climate change, the effective management of carbon in urban stormwater infrastructure (USI) become increasingly crucial. Research indicates that dissolved organic matter (DOM) plays a significant role in the carbon cycle within USI. However, there is a lack of comprehensive information regarding the occurrence of DOM in urban storm-drain inlet (SDI) sediments. This study was undertaken to examine the land use type-related distribution of DOM in SDI sediments, and then provide the suggestion for urban infrastructure sustainability. There are three findings: (1) The characteristics of DOM in SDI sediments, including content, hydrophilicity, molecular weight, and functional groups of aromatic rings, exhibited variation with land functional type; (2) Urban SDI DOM had low humification, and was primarily originated from autochthonous sources, with the proportion of humic-like components close to or exceeding 50%; and (3) SDI sediment DOM was likely to have different characteristics from road dust and stormwater due to microbial activities over dry season. Based on these findings, measures for urban stormwater infrastructure sustainability are proposed, including properly road sweeping, frequently SDI sediment dredging, decreasing in emission from industrial activities, promoting local educational practices, and limiting improper organic waste disposal. These results have implications for the management of stormwater-related carbon and provide valuable insights for the development of sustainable practices for urban ecosystems.

Strong associations between dissolved organic matter and microbial communities in the sediments of Qinghai-Tibetan Plateau lakes depend on salinity

In aquatic ecosystems, dissolved organic matter (DOM) plays a vital role in microbial communities and the biogeochemical cycling of elements. However, little is known about the associations between DOM and microbial communities in lake sediments. This study investigated the composition of water-extractable organic matter and microbial communities in surface sediments of lakes with different salinities on the Qinghai-Tibet Plateau. Ultrahigh-resolution mass spectrometry and high-throughput microbial sequencing techniques were employed to assess the associations between molecular diversity and microbial diversity and the effects of salinity in 19 lakes spanning a salinity range from 0.22 ‰ to 341.87 ‰. Our results show that increasing salinity of lake water led to higher molecular diversity of DOM in surface sediments. High-salinity lakes exhibited distinct DOM characteristics, such as lower aromaticity, smaller molecular weight, and higher oxidation degree, compared to freshwater lakes. The complexity of the microbial network composition of sediments first increased and then decreased with the increase of salinity. Moreover, as salinity increases, the dominant species transitioned from Gammaproteobacteria to Bacteroidia, and this transition was accompanied by a decrease in microbial diversity and an increase in molecular diversity. Microbial factors accounted for 34.68 % of the variation in the molecular composition of DOM. Overall, this study emphasizes the significant effects of salinity on both molecular and microbial diversity in lake sediments. Furthermore, our findings underscore the importance of microbes in controlling the range of organic compounds present in lakes and deepen our knowledge of the biogeochemical cycling of DOM.

Linkages Between Mineral Element Composition of Soils and Sediments With Hyporheic Zone Dissolved Organic Matter Chemistry Across the Contiguous United States

AbstractThe hyporheic zone is a hotspot for biogeochemical cycling where interactions with mineral metals preserve the release and biodegradation of organic matter (OM). A small fraction of OM can still be exchanged between localized sediments and the overlying water column, and recent evidence suggests there exists a longitudinal structuring in sediment dissolved OM (DOM) chemistry across the continental United States (CONUS). In this study, we tested a hypothesis that water extractable sediment DOM chemistry could be explained by sediment metal contents and integrative watershed scale features at the CONUS scale. Crowdsourced samples were characterized for high resolution mass spectrometry and coupled with sediment metals determined via x‐ray fluorescence as well as with land cover and soil elemental information obtained from national databases. Our results highlight weak relationships between DOM chemistry and elemental composition at the CONUS scale indicating limited transferability of organo‐metal linkages into multi‐scale hydrobiogeochemical models.

Mechanisms of cadmium release from manganese-rich sediments driven by exogenous DOM and the role of microorganisms

Dissolved organic matter (DOM) is a crucial component of natural sediments that alters Cd sequestration. Nevertheless, how different types of DOM fuel Cd mobilization in Mn-rich sediments has not been elucidated. In the present study, four typical DOM, fluvic acid (FA), bovine serum albumin (BSA), sodium alginate (SA), and sodium dodecyl benzene sulfonate (SDBS), were used to amend Cd-contaminated sediment to study their effects on Cd/Mn biotransformation and microbial community response. The results demonstrated that different DOM drive microbial community shifts and enhance microbially mediated Mn oxide (MnO) reduction and Cd release. The amendment of terrestrial- and anthropogenic-derived DOM (FA and SDBS) mainly contributed to enriching Mn-reducing bacteria phylum Proteobacteria, and its abundance increased by 38.16–74.47 % and 56.41–73.98 %, respectively. Meanwhile, microbial-derived DOM (BSA and SA) mainly stimulated the abundances of metal(loid)-resistant bacteria phylum Firmicutes. Accompanied by microbial community structure, diversity, and co-occurrence network shifts, the DOM concentration and oxidation-reduction potential changed, resulting in enhanced Cd mobilization. Importantly, FA stimulated Cd release most remarkably, probably because of the decreased cooperative interactions between bacterial populations, stronger reduction of MnOs, and higher aromaticity and hydrophobicity of the sediment DOM after amendment. This study linked DOM types to functional microbial communities, and explored the potential roles of different DOM types in Cd biotransformation in lake sediments.

Adsorption and thermal stability of dissolved organic matter on Ca- and Mg-exchanged montmorillonite: Implications for persistence in soils and sediments

Dissolved organic matter (DOM) represents a vital and highly dynamic component of organic matter in the environment. Despite its significance, there is still limited knowledge regarding how different base cations and chemical conditions influence the preservation of complex natural DOM through adsorption. This study aimed to investigate the adsorption of natural DOM onto montmorillonite (Mt) by systematically exploring the effects of exchanging cations (Ca2+ and Mg2+), pH levels (4 and 7), and DOM molecular weight (< 10, 10–100, and > 100 kDa) on the mechanisms and thermal stability of adsorbed DOM. To this end, we conducted a series of adsorption experiments, complemented by spectroscopic and thermal analyses. Our results revealed that lower pH and higher DOM molecular weight enhanced adsorption, with affinity for carbohydrate-like compounds. Notably, changes in d001 spacing and peak broadening indicated intercalation of DOM into the interlayer space of Mt, which was positively correlated with the amount of DOM adsorbed. Conversely, increased adsorption was found to negatively correlate with thermal stability. This was attributed to the prevalence of weaker DOM-DOM interactions occurring at higher DOM weight and lower pH, owing to reduced repulsion among protonated organic molecules, in contrast to stronger electrostatic interactions near the Mt surface that appeared to dominate at lower DOM weight and higher pH conditions. Intriguingly, no clear preference for DOM adsorption on Ca- or Mg-exchanged Mt was observed, suggesting similar efficiencies of these cations in stabilizing DOM through cation-bridging. Our findings provide significant insights into the mechanisms involved in mineral-organic associations and have implications for understanding the persistence of DOM in soils and sediments.

Molecule-based quantification of dissolved organic matter sources in high-arsenic groundwater

Compositions of dissolved organic matter (DOM) in high-arsenic groundwater are usually sourced from the recharged groundwater DOM and the in-situ mobilized organic matter (OM) from aquifer sediments. However, relative importance of the two sources in DOM remains unclear. To quantify sources of DOM, Fourier transform ion cyclotron resonance mass spectrometry was used to analyze molecular characteristics of groundwater DOM and water-soluble organic matter (WSOM) in sediments along an inferred groundwater flow path in the Hetao Basin, China. Results showed that dissolved arsenic concentrations gradually increased from 1.92 to 402 μg/L along the flow path, being mainly due to the DOM degradation-triggered Fe(III) oxide reduction. The DOM molecules being unique to the background groundwater represented the in-situ mobilized OM, which showed the similar abundance to the DOM molecules being common to its depth-matched WSOM. An increasing trend of the relative abundance of the in-situ mobilized OM to the total DOM molecules along the flow path was recognized (from 0 % to 44.5 %). This suggests that the relative contribution of the in-situ mobilized OM to the groundwater DOM increased along with dissolved arsenic concentration. Furthermore, the biodegradable pool among the in-situ mobilized OM was significantly positively correlated with dissolved arsenic, indicating that this in-situ mobilized OM exhibited a dominant role in groundwater arsenic enrichment. The study provides novel insights into contribution of the in-situ mobilized OM to DOM and arsenic mobility in groundwater systems.

Characterizing photochemical production carboxyl content of dissolved organic matters using absorbance spectroscopy combined with FT-ICR MS

Irradiation can significantly impact the structure, reactivity and environmental behavior of dissolved organic matter (DOM). The extent of these processes remains to be ascertained in more detail but the heterogeneity and site-specificity of DOM, and the lack of methods to characterize DOM at its environmentally-relevant concentrations make it a challenge. In this study, the differences of DOM response to photodegradation in four typical origins (i.e., surface water, sediment and intracellular and extracellular algal DOM) were tracked on the molecular-level using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). Changes of the carboxyl and phenolic DOM moieties induced by irradiation were quantified by spectroscopic titrations, and the mechanism of functional groups affecting the changes of specific molecular composition was qualitatively proposed. The results demonstrated that intracellular algal organic matter (I-DOM) was most susceptible to photodegradation (ca. 63% DOM loss), then came extracellular algal organic matter (E-DOM) and surface water DOM (W-DOM) (ca. 15% DOM loss). Sediment DOM (S-DOM) was most resistant to irradiation, with a very small level of its mineralization. Lipids, lignin-like compounds and tannin-like compounds in I-DOM and E-DOM were relatively photo-labile. The photodegradation of lipids was related to the decarboxylation of carboxyl functional groups, while the photodegradation of tannin-like compounds was related to the rupture of phenolic functional groups. In comparison, the molecular composition of W-DOM and S-DOM was less affected by irradiation, which was also reflected in the fact that the carboxyl and phenolic functional groups were highly photo-resistant. This study showed that the photoactivity of DOM in surface water was closely related to the abundance of algae, so controlling the excessive reproduction of algae may have a positive effect on stability of quality and quantity of organic matter in surface water.

Effects of dissolved organic matter from sediment and soil samples on the growth and physiology of four bloom-forming algal species

Algal blooms negatively impact the water quality of reservoirs; however, the role of dissolved organic matter (DOM) in bloom formation in reservoirs has not been investigated. Therefore, we assessed the compositions of sediment- and soil-derived DOM and their effects on the growth, physiology, and photosynthetic activity of Microcystis aeruginosa, Anabaena sp., Chlamydomonas sp., and Peridiniopsis sp. (bloom-forming species). Sediment DOM promoted the growth of all algal species, whereas soil DOM significantly promoted the growth of Chlamydomonas sp. and Peridiniopsis sp.; this effect was due to enhanced stress tolerance and photosynthetic efficiency exhibited by these algae under DOM treatment. However, soil DOM slightly inhibited the growth of Anabaena sp. by increasing reactive oxygen species levels and inactivating some photosystem II reaction centers. The tyrosine-like substance, humic acid-like substances, and unsaturated aliphatic compounds were the main DOM components that affected algal growth. The findings of this study will provide a theoretical foundation for the development of bloom-prevention strategies for river-type reservoirs.

Niche differentiation of microbial community shapes vertical distribution of recalcitrant dissolved organic matter in deep-sea sediments

Sedimentary organic matter provides carbon substrates and energy sources for microorganisms, which drive benthic biogeochemical processes and in turn modify the quantity and quality of dissolved organic matter (DOM). However, the molecular composition and distribution of DOM and its interactions with microbes in deep-sea sediments remain poorly understood. Here, molecular composition of DOM and its relationship with microbes were analyzed in samples collected from two sediment cores (∼40 cm below the sea floor), at depths of 1157 and 2253 m from the South China Sea. Results show that niche differentiation was observed on a fine scale in different sediment layers, with Proteobacteria and Nitrososphaeria dominating the shallow sediments (0–6 cm) and Chloroflexi and Bathyarchaeia prevailing in deeper sediments (6–40 cm), indicating correspondence of microbial community composition with both geographical isolation and the availability of organic matter. An intimate link between the DOM composition and microbial community further indicates that, microbial mineralization of fresh organic matter in the shallow layer potentially resulted in the accumulation of recalcitrant DOM (RDOM), while relatively low abundance of RDOM was linked to anaerobic microbial utilization in deeper sediment layers. In addition, higher RDOM abundance in the overlying water, as compared to that in the surface sediment, suggests that sediment might be a source of deep-sea RDOM. These results emphasize the close relation between the distribution of sediment DOM and different microbial community, laying a foundation for understanding the complex dynamics of RDOM in deep-sea sediment and water column.

The Spatial Distribution Characteristics of Dissolved Organic Matter (DOM) in Sediments and Water Quality of Wuli Lake, Taihu Lake Basin, China

Based on a field investigation conducted in May 2019, the spatial distribution characteristics of dissolved organic matter (DOM) in sediments of Wuli Lake in the Taihu Lake basin were analyzed using ultraviolet-visible (UV-Vis) absorption spectroscopy and three-dimensional fluorescence spectroscopy. The results showed that: (1) The overall water quality of West Wuli Lake was significantly better than that of East Wuli Lake. The water transparency, measured in Secchi depth (SD), of West Wuli Lake was higher than that of East Wuli Lake, while the suspended solids (SS), total nitrogen (TN), total phosphorus (TP) and chlorophyll a (Chl-a) were higher in East Wuli Lake than in West Wuli Lake. (2) The spatial distribution of a(350), M and SR values of DOM in surface sediment in Wuli Lake differed; a(350) values were highest in the northwestern part of Wuli Lake, while M and SR values were highest in the eastern part. The mean value of SR in Wuli Lake was 2.12 ± 0.67, indicating that the DOM contained more authigenic humus; the mean M value was less than 3.5, indicating that the proportion of humic acid was higher than that of fulvic acid. (3) The ranges of the biogenic index (BIX), the humic index (HIX) and the fluorescence index (FI) of surface sediments in Wuli Lake were 0.64~0.85, 3.79~4.84 and 1.72~1.84, respectively, indicating that surface sediments in Wuli Lake were characterized by authigenic sources, and the humic components of DOM in sediments were characterized by a dual contribution from terrestrial and endogenous sources.

Potential linkage between WWTPs-river-integrated area pollution risk assessment and dissolved organic matter spectral index.

The direct discharge of wastewater can cause severe damage to the water environment of the surface water. However, the influence of dissolved organic matter (DOM) present in wastewater on the allocation of DOM, nitrogen (N), and phosphorus (P) in rivers remains largely unexplored. Addressing the urgent need to monitor areas affected by direct wastewater discharge in a long-term and systematic manner is crucial. In this paper, the DOM of overlying water and sediment in the WWTPs-river-integrated area was characterized by ultraviolet-visible absorption spectroscopy (UV-vis), three-dimensional excitation-emission matrix combined with parallel factor (PARAFAC) method. The effects of WWTPs on receiving waters were investigated, and the potential link between DOM and N, P pollution was explored. The pollution risk was fitted and predicted using a spectral index. The results indicate that the improved water quality index (IWQI) is more suitable for the WWTPs-river integration zone. The DOM fraction in this region is dominated by humic-like matter, which is mainly influenced by WWTPs drainage as well as microbial activities. The DOM fractions in sediment and overlying water were extremely similar, but fluorescence intensity possessed more significant spatial differences. The increase in humic-like matter facilitates the production and preservation of P and also inhibits nitrification, thus affecting the N cycle. There is a significant correlation between DOM fraction, fluorescence index, and N, P. Fluorescence index (FI) fitting of overlying water DOM predicted IWQI and trophic level index, and a(254) fitting of sediment DOM predicted nitrogen and phosphorus pollution risk (FF) with good results. These results contribute to a better understanding of the impact of WWTPs on receiving waters and the potential link between DOM and N and P pollution and provide new ideas for monitoring the water environment in highly polluted areas.

Chemodiversity of Dissolved Organic Matter Is Governed by Microbial Biogeography in Inland Waters.

Dissolved organic matter (DOM) is crucial for the carbon biogeochemical cycle and has a close link with microbiome in aquatic ecosystems; however, the causal relationship between DOM and microbial diversity in inland waters is not very clear so far. Therefore, a national survey of China's inland waters was conducted, and the DOM chemical composition and microbial community composition were determined by Fourier transform ion cyclotron resonance mass spectrometry and high-throughput sequencing to clarify the abovementioned question. Here, we found that DOM chemodiversity was governed by microbial community assembly in inland waters, not vice versa. Under the control of microbial biogeography, DOM chemodiversity showed a clear geographical distribution difference. Water DOM chemodiversity was mainly constrained by bacterial and archaeal community composition, whereas sediment DOM chemodiversity was mainly controlled by eukaryotic and fungal community composition. In addition, the sediment DOM chemical composition was also affected by the interaction of different microbial groups between waters and sediments. The study is the first to clarify the causal relationship and proposes a microbial regulatory mechanism on the geographical distribution pattern of DOM chemodiversity, thus further deepening the understanding of the DOM biogeochemical cycle.

Electrokinetic remediation leads to translocation of dissolved organic matter/nutrients and oxidation of aromatics and polysaccharides

Dissolved organic matter (DOM) in the sediment matrix affects contaminant remediation through consumption of oxidants and binding with contaminants. Yet the change in DOM during remediation processes, particularly during electrokinetic remediation (EKR), remains under-investigated. In this work, we elucidated the fate of sediment DOM in EKR using multiple spectroscopic tools under abiotic and biotic conditions. We found that EKR led to significant electromigration of the alkaline-extractable DOM (AEOM) toward the anode, followed by transformation of the aromatics and mineralization of the polysaccharides. The AEOM remaining in the cathode (largely polysaccharides) was resistant to reductive transformation. Limited difference was noted between abiotic and biotic conditions, indicating the dominance of electrochemical processes when relatively high voltages were applied (1–2 V/cm). The water-extractable organic matter (WEOM), in contrast, showed an increase at both electrodes, which was likely attributable to pH-driven dissociations of humic substances and amino acid-type constituents at the cathode and the anode, respectively. Nitrogen migrated with the AEOM toward the anode, but phosphorus remained immobilized. Understanding the redistribution and transformation of DOM could inform studies on contaminant degradation, carbon and nutrient availability, and sediment structural changes in EKR.

Optical and molecular diversity of dissolved organic matter in sediments of the Daning and Shennong tributaries of the Three Gorges Reservoir

Introduction: Damming significantly modifies the function of natural river networks and influences sediment dynamics with a reservoir’s operation. The dissolved organic matter (DOM) in reservoir sediments severely affects carbon flow from land to sea. However, the properties of DOM (e.g., quantity and quality) in reservoir sediments and their relationship with carbon cycling remain unclear as complex reservoir construction interrupts the environmental processes.Methods: This study characterizes the optical and molecular properties of sediment water-extractable organic matter (WEOM) in the Daning and Shennong tributaries of the world’s largest reservoir—the Three Gorges Reservoir (TGR)—by applying optical techniques and ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS).Results and Discussion: We first assessed the link between light-absorbing components and the individual molecules in WEOM, which were significantly different than DOM in water and indicated that there might be an intrinsic variation between DOM in sediment and in water. Then, with the unique optical–molecular property linkage assessed, multiple sources (autochthonous and terrestrial) were identified, and a declining trend of terrestrial and recalcitrant WEOM was revealed from the tributaries upstream to downstream. Finally, through covariance analysis of the properties between WEOM and sediment particles, we demonstrated that the WEOM dynamic was most likely regulated by hydrologic sorting-induced particle size and mineral composition variations of sediment. Moreover, assessment between lability and WEOM molecular properties suggested that the WEOM dynamic likely contributes to carbon burial in the reservoir. This study emphasizes the influence of dam construction on organic matter accumulation and riverine carbon cycling.

Properties and metal binding behaviors of sediment dissolved organic matter (SDOM) in lakes with different trophic states along the Yangtze River Basin: A comparison and summary

The nature of sediment dissolved organic matter (SDOM) can reflect the environmental background, nutritional status and human activities and is an important part of lakes. The differences in the binding capacity of heavy metals and organic matter in lake sediments with different trophic states at the catchment scale and the mechanism of the differences in binding are still unclear. To solve this problem, we collected bulk SDOMs (< 0.7 μm) from 6 respective lakes (from upstream to downstream) in the Yangtze River Basin (YRB) to qualitatively and quantitatively characterize their properties and metal binding behaviors using excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-FARAFAC) and two-dimensional correlation spectroscopy of synchronous fluorescence spectroscopy and Fourier transform infrared spectroscopy (2D-SF-COS and 2D-FTIR-COS). The results showed that sediment dissolved organic carbon (SDOC) was mainly enriched in low molecular weight (LMW: < 1 kDa) fractions. The total fluorescence intensity (Fmax) of SDOM from upstream was larger than that from downstream (p = 0.033), and humic-like fluorophores were dominant in these lakes. The Fmax of sediment humic-like components (C1+C2) was closely related to the trophic levels of the lakes. Protein-like substances and oxygen-containing functional groups (C−OH, C=O, and C−O) were preferred in the reaction between SDOM and copper (Cu2+) or cadmium (Cd2+), while a unique binding path was exhibited in the moderately eutrophic DCL. In terms of fluorophore types, higher Cu2+-binding abilities (LogKCu) were observed in the humic-like matter for the lakes in the upper reaches and tryptophan-like matter for the lakes from the midstream and downstream areas of the YRB. Although Cd2+ complexed only with humic-like matter, LogKCd was higher than LogKCu. In terms of molecular weight (MW), the LogKCu/Cd of components were enhanced after MW fractionation. The HMW (0.7 μm – 1 kDa) components possessed higher LogKCu in most lakes (except for CHL and C4). The different fluorophores and molecular weight fractions in SDOM make an important contribution to reducing the ecological risks of heavy metals in lakes.

Optical properties of sedimentary dissolved organic matter in intertidal zones along the coast of China: Influence of anthropogenic activities

The intertidal zone, due to its location in the transition zone of terrestrial and marine ecosystems, is seriously disturbed by anthropogenic activities such as fuel combustion and industrial production, causing significant increase in dissolved organic matter (DOM). However, the distribution and properties of DOM in intertidal sediments at the large scale and their correlations with local socio-economic indicators remain unclear. In this study, we collected sediment samples from 13 intertidal zones across 11 coastal provinces in China and analyzed optical properties and compositions of sedimentary DOM. The results showed that the physico-chemical properties of sediment, such as pH and texture, affected the content of organic matter, thereby influencing the concentration of sedimentary DOM indirectly. The contents of fulvic acid- and protein-like components were relatively higher than humic acid-like component at all sampling sites. Moreover, urbanization could lead to the release of aromatic and humified organic matters into intertidal zones. Unlike coal, oil consumption exhibited positive correlation with SUVA254, indicating that the combustion of oil released more aromatic compounds. These findings revealed the impact of anthropogenic activities on sedimentary DOM and provided theoretical basis for predicting and regulating intertidal carbon sink.

Geographical constraints on chemodiversity of sediment dissolved organic matter in China's coastal wetlands

Dissolved organic matter (DOM) plays an important role in wetland carbon cycle; however, the geographical pattern of DOM chemodiversity and controlling factors are not very clear for coastal wetland sediments, especially at large spatial scale. To this end, twenty China's coastal wetlands were surveyed on a national scale for their sediment DOM and related environmental parameters, and the DOM molecular compositions were resolved by Fourier transform ion cyclotron resonance mass spectrometry and relevant bioinformatics. The chemodiversity of a total of 14, 343 DOM molecular formulas showed a clear geographical pattern: a decrease with an increase in latitude. The moisture and organic matter contents of sediments were key factors controlling DOM chemodiversity and decreased with the increasing latitude. In addition, the sediment with higher DOM molecular chemodiversity contained more unsaturated compounds, and lignin-like and tannins increased with the decreasing latitude. This study highlights the molecular characteristics of sediment DOM in China's coastal wetlands and helps to deepen the geographical knowledge of coastal wetland DOM.

Effect of water chemistry on nitrogen transformation, dissolved organic matter composition and microbial community structure in hyporheic zone sediment columns

Controlled surface water systems, including those with dams lead to dynamic stage changes that alter the fluctuation directions of flow exchange in the hyporheic zones (HZ). However, the nitrogen transformation, dissolved organic matter (DOM) composition, and microbial community responding to variable scenarios of water source and hyporheic exchange are poorly studied. The present work investigated nitrogen transformation in HZ sediments, focusing on how microbial community structure and biological functions related to nitrogen transformation and sediment-attached DOM compositions. Upwelling of synthesized groundwater, downwelling of synthesized river water and exchangeable elution of both feed water created distinct microbial zonation and N-transformation processes. Mixing of river water and groundwater enhanced microbial diversity, microbial co-occurrence network complexity and N-transformation functions. In terms of the sediment-attached DOM properties after hyporheic exchanges, humic fractions occupied the predominant chromophoric DOM. Correlation analysis implied that there were more DOM properties, e.g., tryptophan-like proteins, humic-like fractions, and the source of humic fractions, involved in affecting the microbial community under downwelling flow. Co-occurrence network analysis verified that fluorescent components, protein-like and lignin-like fractions in sediment-detached DOM were clustered with microbial communities in one module in downwelling column, implying closer interactions among microbial communities and DOM fractions. The strains of Nitrospinae, Dinghuibacter, and Lentimicrobium etc. were key species collaborating to metabolize both nitrogen and DOM in HZ sediments. The work provides insights into how the nitrogen transformation, DOM compositional changes, as well as the linkages between community structure and DOM factions, response to the changes in water chemistry, leading to valuable insights into hyporheic zone functions.

Spatial variability of dissolved organic matter in the water-sediment systems in the Baiyangdian Lake

Dissolved organic matter (DOM) is widespread in natural water bodies and plays an essential role in ecological processes of aquatic ecosystems. However, spatial variability of DOM in shallow lakes is still kept unclear. Surface water, overlaying water and sediment samples were collected at 61 sampling sites in the whole Baiyangdian Lake to investigate spatial variability and distribution patterns of organic matter contents in three environmental compartments using geostatistical analysis. Results showed that organic matter (OM) contents in sediments were higher with medium variability, and lower DOM content occurred in surface water, with medium variability in overlying waters and high variability in surface waters. The highest DOM contents in waters and OM in sediments appeared in Zaolinzhung (ZLZ) and Zaozhadian (ZZD), respectively, while a relatively low contents appeared in ZLZ sediments. DOM in surface water and overlying water were negatively correlated with OM in sediments. Semi-variance functions showed that a strong spatial autocorrelation for DOM in waters, while OM in sediments had a medium spatial correlation. The autocorrelation distance of DOM in waters was between 1.16 km and 11.70 km, and OM in sediments was 4.25 km. The findings of this work can contribute to better understanding spatial variability of OM, which would provide a guidance for the sampling optimization of waters and sediments in the Baiyangdian Lake and lake sustainable management.

Linking Bacterial Communities to Optical-Derived Properties of Porewater DOM in Sediments in the Coastal East China Sea

Bacterial communities and porewater dissolved organic matter (DOM) pool are intimately interactive in sedimentary environments. Estuarine coastal regions are an interactive area between terrestrial and marine influences in terms of DOM origins and freshness. Yet, we know little about the relationships between the bacterial communities and DOM in those regions. In this study, porewater DOM samples were collected from 42 sites in the coastal East China Sea. The porewater DOM optical properties were determined by fluorescence and absorption spectra, while the corresponding bacterial community compositions of those sediments were examined by 16S rRNA gene high-throughput sequencing. The results showed that bacterial species richness was positively correlated with multiple terrestrial indicators based on the optical properties of DOM, which implied that heterogeneous DOM from terrestrial origins might harbor a wider spectrum of bacterial taxa in marine sediments. The analysis of the co-occurrence network of the bacterial communities showed that the edges and density for samples with low DOM freshness were 3.4 times and 3 times those for the samples with high DOM freshness, respectively. This suggested that the connection among the bacterial taxa under the lower DOM freshness condition were enhanced and that reduced freshness of DOM may encourage more complimentary utilization of resources. The findings provide a new insight into such interactive processes of heterogeneous organic matter utilization meditated by microorganisms in coastal sediments.