Straw mulching alters the composition and loss of dissolved organic matter in farmland surface runoff by inhibiting the fragmentation of soil small macroaggregates

Straw mulching is a widespread practice for reducing the soil carbon loss caused by erosion.However,the effects of straw mulching on dissolved organic matter(DOM)runoff loss from black soil are not well studied.How straw mulching affects the composition and loss of runoff DOM by changing soil aggregates remains largely unclear.Here,a straw mulching treatment was compared to a no mulching treatment(as a control)on sloping farmland with black soil erosion in Northeast China.We divided the soil into large macroaggregates(>2 mm),small macroaggregates(0.25-2 mm),and microaggregates(<0.25 mm).After five rain events,the effects of straw mulching on the concentration(characterized by dissolved organic carbon(DoC)and composition(analyzed by fluorescence spectroscopy)of runoff and soil aggregate DOM were studied.The results showed that straw mulching reduced the runoff amount by 54.7%.Therefore,although straw mulching increased the average DOc concentration in runoff,it reduced the total runoff DOM loss by 48.3%.The composition of runoff DOM is similar to that of soil,as both contain humic-like acid and protein-like components.With straw mulching treatment,the protein-like components in small macroaggregates accumulated and the protein-like components in runoff declined with rain events.Fluorescence spectroscopy technology may help in understanding the hydrological paths of rain events by capturing the dynamic changes of runoff and soil DOM characteristics.A variation partitioning analysis(VPA)indicated that the DOM concentration and composition of microaggregates explained 68.2%of the change in runoff DOM from no mulching plots,while the change in runoff DOM from straw mulching plots was dominated by small macroaggregates at a rate of 55.1%.Taken together,our results demonstrated that straw mulching reduces the fragmentation of small macroaggregates and the loss of microaggregates,thus effecting DOM compositions in soil and reducing the DOM loss in runoff.These results provide a theoretical basis for reducing carbon loss in sloping farmland.

Impacts of Water-Sediment Regulation Scheme on Chromophoric Dissolved Organic Matter in the Lower Yellow River

As a river with more than 3000 reservoirs in its watershed,the Yellow River has been affected by dams not only on the sediment load,but also on the water quality.Water-sediment regulation scheme(WSRS),which has been carried out annually in the Yellow River since 2002,is a typical human activity affecting river water quality.Chromophoric dissolved organic matter(CDOM)in river is susceptible to changes in ecological and environmental conditions as well as human activities.Here,we report variations in dissolved organic carbon concentrations,compositions and sources of CDOM in time series samples in the lower Yellow River during WSRS.In addition,a parallel factor fluorescence analysis(PARAFAC)method is applied to identify different fluorescent components in water samples during WRSR,showing four major components including tryptophan-like component(C1),microbial humic-like component(C2),terrestrial humic-like component(C3)and tyrosine-like component(C4).In general,C1 increased after water regulation,while C2 and C3 increased after sediment regulation,indicating that the water and sediment released by the dam have different effects on CDOM compositions.Under the impacts of the dam,source of CDOM in the lower Yellow River is mainly autochthonous related to microbial activities,and is regulated by the terrestrial input during WSRS period.Sediment resuspension inhibits microbial activities and reduces the production of autochthonous CDOM.Overall,human activities especially WSRS,as exemplified here,significantly alter the quality and quantity of CDOM in the lower Yellow River,affecting CDOM dynamics and biogeochemical processes in the estuarine environment.

Spatiotemporal characteristics and remote sensing estimation of colored dissolved organic matter around the Leizhou Peninsula

Colored dissolved organic matter(CDOM)is an important optically active substance in marine environment.Its biochemical conservatism makes it an important indicator to offshore pollution process.Monitoring the content,composition,and diffusion process of CDOM is a good approach to analyze the terrestrial input,optical properties,and ecological environment of offshore areas.The spatiotemporal characteristics of CDOM around the Leizhou Peninsula were analyzed based on field observation data collected in the autumn 2020 and spring 2021,and an empirical inversion model of the ag(355)(absorption coefficient at 355 nm)and spectral slope(Sg)(g stands for gelbstoff/gilvin,which is called CDOM)based on Sentinel-3A ocean and land color instrument(OLCI)images was constructed.The results show(1)the order of average ag(355)value around the Leizhou Peninsula was east coast(0.503/m)>Qiongzhou Strait(0.502/m)>west coast(0.365/m);(2)the best band combinations of CDOM inversion in spring and autumn were(B4+B11)/B3 and(B7-B1)/B6(B stands for the band of spectral images),and the final inversion results are close to the measured results,indicating that the model has good accuracy;(3)the S_(g)value of the CDOM absorption spectrum was fitted to the hyperbolicexponential model.The fitting accuracy of the model was higher than those of the exponential model and the hyperbolic model,and the best S_(g)inversion model was constructed by selecting Sg(275-295)and Sg(250-295)in spring and autumn;(4)the spatial distributions of ag(355)and S_(g)were inverted,and CDOM in the waters around the Leizhou Peninsula originated from terrestrial organic matter carried by coastal aquaculture zones and runoff in the northeast Zhanjiang and the northern Beibu Gulf.

Seasonal Distribution of Observed Colored Dissolved Organic Matter(CDOM)in the Eastern Indian Ocean

Colored dissolved organic matter(CDOM)is a crucial constituent that affects the optical absorption properties of seawater.Owing to the relatively limited measured data on the spatial distribution characteristics of CDOM in the tropical eastern Indian Ocean,this study analyzes the optical absorption characteristics of CDOM in the southeast Indian Ocean using the data collected during four seasons from 2013 to 2017.This work also systematically describes the seasonal horizontal and vertical distribution characteristics of CDOM in this area and conducts a preliminary analysis of the relevant factors affecting CDOM absorption characteristics in this region.Results indicate that the CDOM ag(440)during summer was remarkably lower than that in the coastal waters of Europe and coastal waters of China but slightly higher than that in the western and southeast Pacific.The spatial distribution of surface CDOM shows remarkable seasonal differences,and the spatial distribution characteristics of CDOM in the 5°S,92°E region differ between spring/summer and autumn/winter.The values of ag(400)and ag(440)are weak/strong at a surface/subsurface level of 100 m,with differences found between summer and winter.The correlation of CDOM with temperature,salinity,and chlorophyll-a concentration is relatively low,indicating that CDOM is an independent driving mechanism influenced by phytoplankton degradation,photobleaching,and water mixing.

Effect of dissolved organic matter on adsorption and desorption of mercury by soils

Effects of dissolved organic matter (DOM) on adsorption and desorption of Hg were investigated in two kinds of soils, Xanthi-Udic Ferralosols (XUF) and Typic Purpli-Udic Cambosols (TPUC). The DOM was obtained from humus soil (DOMH), rice straw (DOMR), and pig manure (DOMP). The presence of DOM obviously reduced Hg maximum adsorption capacity with up to 40% decreases over the control, being an order of DOMH (250.00 mg/kg)< DOMR (303.03 mg/kg) < DOMP (322.58 mg/kg) < CK (control 416.67 mg/kg) for the XUF and DOMH (270.27 mg/kg) < DOMR (312.50 mg/kg) < DOMP (324.23 mg/kg) < CK (476.11 mg/kg) for the TPUC, respectively. The inhibition of DOM on Hg adsorption was slightly weaker in XUF than in TPUC. Meanwhile, the DOM promoted Hg desorption from the soils. The kinetic models, the Two-constant equation and Elovich equation, were applicable to describe the adsorption and desorption processes of Hg in soils. The speed of Hg adsorption was consistently slowed down by the existence of DOM.

Characteristics of dissolved organic matter in lakes with different eutrophic levels in southeastern Hubei Province,China

Dissolved organic matter(DOM)plays a crucial role in both the carbon cycle and geochemical cycles of other nutrient elements,which is of importance to the management and protection of the aquatic environments.To achieve a more comprehensive understanding the characteristics of DOM in the Changjiang(Yangtze)River basin,water samples from four natural lakes(Xiandao,Baoan,Daye,and Qingshan)in southeastern Hubei Province in China with different eutrophication levels were collected and analyzed.The optical characteristics were analyzed using ultraviolet-visible spectrophotometry and excitation-emission matrix spectroscopy coupled with parallel factor analysis.The results show that:(1)two humic-like components(C1 and C2)and two protein-like substances(C3 and C4)of DOM were identified in all waterbodies;(2)C3 originated primarily from the degradation of microalgae and contributed substantially to humic-like components during transformation.C4 was widely present in the Changjiang River basin and its formation was related to microbial activity,rather than algal blooms or seasons.Influenced by the water mixing,the protein-like components were more likely to be transformed by microorganism,whereas humic-like components were more easily to be photobleached;(3)the concentration of DOM and the fluorescence intensity of humic-like components gradually increased with rising lake eutrophication levels.With respect to protein-like components,only C3 showed changes along the eutrophication gradients;(4)DOM showed a high affinity with permanganate index(COD Mn)and chlorophyll a(chl a)while the relationship was variable with phosphorus.This study helps us systematically understand the DOM characteristics,microbial activities,and pollutant transformation in the Changjiang River basin and provides reference to the ecological restoration of aquatic environments.

Variation in spectral characteristics of dissolved organic matter derived from rape straw of plants grown in Se-amended soil

Straw return is an effective management practice. It not only utilizes agricultural waste but also introduces dissolved organic matter(DOM) into the soil. Selenium(Se) is an essential trace element in the human diet and contributes to the popularity of Se-enriched agricultural products in the Chinese market. Moreover, there are still some Se-enriched agricultural products that have yet to be utilized. This study investigated whether Se addition in soil caused component changes in the DOM extracted from rape straw. DOM extracted from rape straw grown in soil with four Se levels(0, 0.1, 0.5 and 1.0 mg Se kg-1 soil) was characterized by UV-Visible spectroscopy, fluorescence spectroscopy and FTIR spectroscopy. The UVvisible spectra revealed that 0.1 mg Se kg-1 soil reduced the molecular weight of DOM and caused the presence of more irreplaceable aromatic structures in the substituent groups of the DOM, while 0.5 and 1.0 mg Se kg-1 soil only reduced the DOM molecular weight. Fluorescence spectroscopy indicated that Se improved the humification degree but reduced the aromaticity of DOM. FTIR spectra proved that Se altered the contents of carboxylic acids, amino acids, alcohols and aromatic heterocycles in DOM, which were maximized in the 0.5 and 1.0 mg Se kg-1 treatment groups. We concluded that Se application could change the composition of DOM extracted from rape straw, potentially impacting the nutrient bioavailability in soil. This study provides basic data on Se-enriched rape straw utilization for eco-agriculture.

Chemical composition and Pb(II)binding of dissolved organic matter in a hypersaline lake in China

Dissolved organic matter(DOM)plays a vital role in promoting carbon and nutrient cycling.It is a food source for organisms and controls the migration and transformation of trace metals and other contaminants in aquatic systems.The contributions of aquatic DOM to the environment and ecology of a system are closely related to its abundance and chemical structure.In this study,the chemical composition and binding properties of DOM in a hypersaline lake watershed were investigated for the fi rst time using dissolved organic carbon(DOC)analysis,absorption spectroscopy,Fourier transform infrared spectroscopy,pyrolysis-GC-MS(Py-GC-MS),and fl uorescence parallel factor(PARAFAC)analysis combined with Pb(II)titration techniques.The results showed that DOM from the tributaries that fl owed into the lake had a lower DOC content,higher molecular weight,and higher specifi c UV absorbance than the DOM in lake water.Protein-like fl uorophores were mainly found in tributary and lake surface water DOM(LSDOM)and humic-like substances were abundant in lake groundwater DOM(LGDOM).Using this multi-methodological approach,we found that the DOM from the hypersaline lake watershed was mainly from microbial origins,and consisted of aromatics,carbohydrates,and aliphatics.The results from quantitative analysis showed that DOM from the infl owing tributaries contained more aromatics,lower carbohydrates,and lower aliphatics than DOM in the lake.Monocyclic aromatic hydrocarbons and carbohydrates were more abundant in LSDOM than LGDOM.The results from the Pb(II)titration technique coupled with PARAFAC analysis suggested that PARAFAC-derived components had relatively low condition stability constants(log K_(M)<2).Of the two types of lake DOM,the LGDOM had a higher Pb(II)binding potential than the LSDOM.From this study we have improved our understanding of how DOM within a hypersaline lake watershed varies in its composition and potential to bind with metals.

Effect of Dissolved Organic Matter on Titanium Dioxide Nanoparticles in Aquatic Environment:Molecular Weight Fractions

At present,a growing number of consumer products contain engineered nanoparticle TiO2(nano⁃TiO2),which has resulted in the consequences of nano⁃TiO2 entering the aquatic environment directly or indirectly at some stage.The fate of nano⁃TiO2 in the aquatic environment has become the key factor which affects its safety application and nanoecotoxicology.This paper aims to investigate how the dissolved organic matters(DOM),especially the molecular weight fractions in the aquatic environment,affect the aggregation,stability,and fate of nano⁃TiO2,and the interaction mechanism of DOM and nano⁃TiO2.Results of dynamic light scattering(DLS)showed that the molecular weight of DOM molecules caused different aggregation rates of nano⁃TiO2 in aqueous solution.Fourier Transform infrared spectroscopy(FTIR)results indicated the molecular structure is characteristics of DOM fractions and the mechanisms of bonds formation between DOM and nano⁃TiO2.Results of three⁃dimensional excitation⁃emission matrices(3D⁃EEM)confirmed the FTIR results and implied the increase of the stability of theπ-πconjugated system in the presence of DOM.In addition,low molecular weight of DOM fractions appeared to show more affinity with nano⁃TiO2 than high molecular weight fractions.

Optical Characteristics of Chromophoric Dissolved Organic Matter(CDOM)in Upstream and Downstream Lakes of Taihu Lake Basin:New Insights for Water Environmental Management

Chromophoric dissolved organic matter(CDOM)is a key component of organic matter that contributes to the ecological functioning of lakes.The lakes in Taihu Lake Basin play an important role in maintaining regional ecological stabilities;however,the optical characteristics of the CDOM in the upstream and downstream lakes in this basin have not yet been systematically studied.Here,the optical characteristics of CDOM in ten lakes of upstream and downstream of the Taihu Lake Basin were studied using UV-Visible and excitation-emission matrix spectroscopies.Three different fluorophores consisting of two humic-like components(C1,C2)and one protein-like component(C3)were identified by parallel factor analysis.Soil or surface erosion was responsible for the higher abund-ance of C1 in the upstream lakes,and increased biological activities accounted for the higher abundance of C3 in the downstream lakes.Rainfall erosion in the wet season led to an increase in CDOM.We also found that the photodegradation and flocculation degree,which played a significant role in reducing CDOM,were higher in downstream lakes than in upstream lakes.Optical analysis of CDOM provides a promising method for monitoring water qualities(e.g.,total phosphorus and potassium permanganate index)in each lake.Re-ductions in soil or surface erosion in the upstream are needed to improve water quality.

Seasonal variations in dissolved organic matter concentration and composition in an outdoor system for bank filtration simulation

Dissolved organic matter(DOM)in surface waters can vary markedly in character depending on seasonal variations such as rainfall intensity,UV radiations and temperature.Changes in DOM as well as temperature and rainfall intensity over the year can affect the biochemical processes occurring in bank filtration(BF).Identification and characterization of DOM in the surface water could help to optimize the water treatment and provide stable and safe drinking water.This study investigated year-long variations of DOM concentrations and compositions in a surface water of a circulated outdoor pond(research facility)connected to a BF passage.DOM was dominated by humic substances and a changing pattern of DOM in surface water was observed throughout the year.A significant increase of DOM(~38%)in surface water was noted in August compared to November.The fluorescent DOM showed that DOM in summer was enriched with the degradable fraction whilst non-degradable fraction was dominated in winter.A constant(1.7±0.1 mg/L)effluent DOM was recirculated in the system throughout the year.DOM removal through BF varied between 4%to 39%and was achieved within a few meters after infiltration and significantly correlated with influent DOM concentration(R^(2)=0.82,p<0.05).However,no significant(p>0.05)change in the removal of DOM was observed in two subsurface layers(upper and lower).This study highlights the presence of a constant non-degradable DOM in the bank filtrate,which was not affected by temperature,redox conditions and UV radiations.

Spatial heterogeneity and compositional profiles of dissolved organic matter in farmland soils across China' Mainland

Dissolved organic matter(DOM) plays an essential role in many geochemical processes,however its complexity, chemical diversity, and molecular composition are poorly understood. Soil samples were collected from 500 vegetable fields in administrative regions of China' Mainland, of which 122 were selected for further investigation. DOM properties were characterized by three-dimensional excitation-emission matrix(3D-EEM) fuorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry(FTICRMS)(field intensity is 15 Tesla). Our results indicated that the main constituents were UVA humic-like substances, humic-like substances, fulvic acid-like substances, and tyrosine-like substances. A total of 10,989 molecular formulae with a mass range of 100.04 to 799.59 Da were detected, covering the mass spectrometric information of the soil samples from 27 different regions. CHO and CHON molecules were dominant in DOM, whereas lignin, tannins,and aromatic substances served as the main components. The results of cluster analysis revealed that the soil properties in Jiangxi Province were considerably different from those in other regions. The key backgrounds of the DOM molecular characteristics in the vegetablefield soil samples across China' Mainland were provided at the molecular level, with large abundance and great variability.

Effects of acid mine drainage on photochemical and biological degradation of dissolved organic matter in karst river water

Dissolved organic matter(DOM)can be removed or transformed by photochemical and biological processes,producing the negative effect of transforming organic carbon into inorganic carbon,which plays a vital role in the karst carbon cycle.However,acid mine drainage(AMD)will affect this process,so the degradation of DOM in karst river water(KRW)needs to be studied in this context.In this study,to reveal the evolution processes of DOM under photochemical and biological conditions in AMD-impacted KRW,AMD and KRW were mixed in different ratios under conditions of visible light irradiation(VL),biodegradation(BD),ultraviolet irradiation(UV)and ultraviolet irradiation+biodegradation(UV+BD).The average DOC concentrations in samples after mixing AMD and KRW in different proportions decreased significantly(by 23%)in UV+BD,which was 1.2–1.4 times higher than under the other conditions and would lead to a significant release of inorganic carbon.Further analysis of the fluorescence parameters via parallel factor analysis(PARAFAC)revealed that the DOM fluorescence components in AMD comprised mainly protein-like substances derived from autochthonous components,while the DOM fluorescence components in KRW were mainly humic-like substances with both autochthonous and allochthonous sources.Therefore,AMD could promote both the photochemical and biological degradation of DOM in karst receiving streams,resulting in the conversion of DOC to inorganic carbon.The results showed that the synergistic effects of UV+BD and AMD accelerated the degradation of DOM and the release of inorganic carbon in KRW,thus affecting the stability of the karst carbon cycle.

Dissolved organic matter accelerates microbial degradation of 17 alpha-ethinylestradiol in the presence of iron mineral

Dissolved organic matter(DOM)and iron minerals widely existing in the natural aquatic environment can mediate the migration and transformation of organic pollutants.However,the mechanism of interaction between DOM and iron minerals in the microbial degradation of pollutants deserves further investigation.In this study,the mechanism of 17 alphaethinylestradiol(EE2)biodegradation mediated by humic acid(HA)and three kinds of iron minerals(goethite,magnetite,and pyrite)was investigated.The results found that HA and iron minerals significantly accelerated the biodegradation process of EE2,and the highest degradation efficiency of EE2(48%)was observed in the HA-mediated microbial system with pyrite under aerobic conditions.Furthermore,it had been demonstrated that hydroxyl radicals(HO·)was the main active substance responsible for the microbial degradation of EE2.HO·is primarily generated through the reaction between hydrogen peroxide secreted by microorganisms and Fe(II),with aerobic conditions being more conducive.The presence of iron minerals and HA could change the microbial communities in the EE2 biodegradation system.These findings provide new information for exploring the migration and transformation of pollutants by microorganisms in iron-rich environments.

Impact of transparent exopolymer particles on the dynamics of dissolved organic carbon in the Amundsen Sea,Antarctica

The Southern Ocean is an important carbon sink pool and plays a critical role in the global carbon cycling.The Amundsen Sea was reported to be highly productive in inshore area in the Southern Ocean.In order to investigate the influence of transparent exopolymer particles(TEP)on the behavior of dissolved organic carbon(DOC)in this region,a comprehensive study was conducted,encompassing both open water areas and highly productive polynyas.It was found that microbial heterotrophic metabolism is the primary process responsible for the production of humic-like fluorescent components in the open ocean.The relationship between apparent oxygen utilization and the two humic-like components can be accurately described by a power-law function,with a conversion rate consistent with that observed globally.The presence of TEP was found to have little impact on this process.Additionally,the study revealed the accumulation of DOC at the sea surface in the Amundsen Sea Polynya,suggesting that TEP may play a critical role in this phenomenon.These findings contribute to a deeper understanding of the dynamics and surface accumulation of DOC in the Amundsen Sea Polynya,and provide valuable insights into the carbon cycle in this region.

Ultraviolet humic-like component contributes to riverine dissolved organic matter biodegradation

Biological degradation of dissolved organic matter(DOM)regulates its structure and fate in river ecosystems.Previous views suggested that labile components were dominantly consumed by microbial metabolism.Here we provide new observations that a part of recalcitrant compounds largely contribute to riverine DOM biodegradation.The excitationemission matrix fluorescent spectroscopy combined with peak picking and parallel factor analysis are used to explore component variability during DOM incubation.Humic-like and tryptophan-like DOM are the primary components of riverine DOM,with proportion contributions of 39%–82% and 16%–61% for % of the maximumfluorescence intensity,respectively.After 56 days of aerobic incubation in the dark,large amounts of tyrosine-like DOM generation are observed.Elevated temperature enhances the decomposition of ultraviolet humiclike substance and further stimulates labile DOM bio-mineralization into carbon dioxide.Meanwhile,averaged proportions of amino acid compositions(peak B and T)markedly increase(p<0.05)as the humic-like compositions(peak A,M and C)decrease after DOM incubation,suggesting incomplete degradation of refractory DOM from high-molecular to low-molecular weight compounds.The findings support the new notion of the continuous DOM biodegradation in a mode as“steps by steps”,contributing to a new understanding of carbon cycling for the UN Sustainable Development Goal.

Refractory humic-like dissolved organic matter fuels microbial communities in deep energy-limiting marine sediments

Humic-like dissolved organic matter(DOM),usually regarded as refractory,is a major component of DOM in marine sediment pore waters.However,its bio-reactivity remains poorly explored in natural environments,which makes its roles in supporting subsurface microbial communities and regulating long-term carbon cycling elusive.Here,the bio-reactivity of humiclike DOM was evaluated by modeled reaction rates together with its interactions with microbial communities in five sediment cores collected from the eutrophic Pearl River Estuary to the oligotrophic deep-sea basin in the northern South China Sea.We revealed contrasting relationships between humic-like DOM and microbes in the coastal and deep-sea sediments.In eutrophic coastal sediments,specific microbial groups enriched in the deep layers co-varied with humic-like DOM,while most microbial groups were significantly correlated with protein-like DOM,microbial transformation of which likely resulted in the production of humic-like DOM.On the contrary,in energy-limiting deep-sea sediments,over 70%of the microbial groups were found closely correlated with humic-like DOM,a net consumption of which was demonstrated in deep layers.The consumption of humic-like DOM in deep-sea sediments reduced its total production flux in the uppermost~5-meter layer to about one-tenth of that in coastal sediments,which could consequently decrease the refractory DOM flux to the overlying seawater and influence long-term oceanic carbon cycling.

Microbial degradation of various types of dissolved organic matter in aquatic ecosystems and its influencing factors

Interactions between chemodiverse dissolved organic matter(DOM)and biodiverse microbes are governed by a myriad of intrinsic and extrinsic factors which are not well understood.Here,we update and bridge the gap of this interdisciplinary theme comprehensively.At an ecosystem level,aquatic ecosystems dominated by algae-sourced DOM(e.g.,eutrophic lake or coastal upwelling areas)harbor more biolabile DOM,such as directly assimilable monomers and readily hydrolysable biopolymers.However,other ecosystems prevailed by DOM supply from soil and vascular plants(e.g.,river or wetland)have more biorefractory DOM,such as low molecular weight(LMW)residue of aliphatic C skeletons and geopolymers.A variety of heterotrophic bacteria,archaea,fungi,phagotrophic protists,and even photoautotrophic phytoplankton shows genomic and/or culturing experimental evidence of being able to process a diverse type of organics.The various biodegradable organics have different chemical structures and chemical bonds such as carbohydrates,amino acids,proteins,lignins,lipids,carboxylic acids,humic acids,hydrocarbons,and nanoplastics.Meanwhile,bio-production of metabolism intermediates and/or biorefractory organics(e.g.,carboxyl-rich alicyclic molecules,CRAM)is observed despite general decay of bulk dissolved organic carbon(DOC)during bioassay experiments.In particular,emerging evidence shows that archaea contribute significantly to biomass in the marine mesopelagic zone and subsurface environments and their abundance often increases with depth in sediments.Furthermore,not only intrinsic factors(e.g.,DOM composition and structure),but also extrinsic ones(e.g.,sunlight and dissolved oxygen)play important roles in interplays between DOM and microbes.

Spatiotemporal optical properties of dissolved organic matter in a sluice-controlled coastal plain river with both salinity and trophic gradients

Due to the combined effect of sluices and sea tide,the sluice-controlled coastal plain river would be characterized by both trophic state and salinity gradients,affecting the spatiotemporal optical properties of dissolved organicmatter(DOM).In this study,we investigated the spatiotemporal variation of water quality parameters and optical properties of DOM in the Haihe River,a representative sluice-controlled coastal plain river in Tianjin,China.A significant salinity gradient and four trophic states were observed in the water body of the Haihe River.Two humic-and one protein-like substances were identified from the DOM by the three-dimensional fluorescence spectra combined with the parallel factor(PARAFAC)analysis.Pearson’s correlation analysis and redundancy analysis(RDA)showed that the salinity significantly affected the abundance of chromophoric DOM(CDOM)but did not cause significant changes in the fluorescence optical characteristics.In addition,the effect of Trophic state index(TSI)on the CDOM abundance was greater than that on the fluorescence intensity of fluorescent dissolved organic matter(FDOM).In the water body with both salinity and trophic state gradients,TSI posed a greater influence than salinity on the CDOM abundance.Our results fill the research gap in spatiotemporal DOM characteristics and water quality variation in water bodies with both salinity and trophic state gradients.These results are beneficial for clarifying the joint influence of saline intrusion and sluices on the DOM characteristics and water quality in sluice-controlled coastal plain rivers.

Simultaneous degradation of sulfadiazine and dissolved organic matter based on low-impact development facilities

Sulfadiazine(SD)is a common antibiotic administered to treat bacterial infections in livestock,and its fate andmigration are greatly affected by dissolved organicmatter(DOM).The soil infiltration system[a typical low-impact development(LID)facility]can significantly alterDOMproperties during runoff pollution,thus affecting the complexation of SDwithDOM.Here,the binding characteristics of different DOM components and SD in the soil infiltration system were explored using spectroscopic techniques(excitation–emission matrices,parallel factor analysis,and synchronous fluorescence spectroscopy).Combined with the weakening of DOM fluorescence intensity and 78.63%reduction in mean SD concentration following treatment,synchronous degradation may have occurred.The binding sequence of SD and DOM fluorophores was further explored using two-dimensional correlation spectroscopy.Effluent DOM showed greater sensitivity to SD and more binding sites than influent DOM.Moreover,hydrophobic protein-like substances exhibited higher log K_(M) values than other fluorescent components,indicating that protein-like components play significant roles in SD complexation.The soil percolation system improved the complexation stability and binding sequence of fulvic-like substances.Thus,SD–DOM can be intercepted and degraded using LID facilities to reduce the risk of SD in aquatic environments.