Quality of dissolved organic matter affects planktonic but not biofilm bacterial production in streams

Microbial community structure and diversity attached to the periphyton in different urban aquatic habitats

Periphyton is a complex community composed of diverse prokaryotes and eukaryotes; understanding the characteristics of microbial communities within periphyton becomes crucial for biogeochemical cycles and energy dynamics of aquatic ecosystems. To further elucidate the community characteristics of periphyton across varied aquatic habitats, including unpolluted ecologically restored lakes, aquaculture ponds, and areas adjacent to domestic and industrial wastewater treatment plant outfalls, we explored the composition and diversity of prokaryotic and eukaryotic communities in periphyton by employing Illumina MiSeq sequencing. Our findings indicated that the prokaryotic communities were predominantly composed of Proteobacteria (40.92%), Bacteroidota (21.01%), and Cyanobacteria (10.12%), whereas the eukaryotic communities were primarily characterized by the dominance of Bacillariophyta (24.09%), Chlorophyta (20.83%), and Annelida (15.31%). Notably, Flavobacterium emerged as a widely distributed genus among the prokaryotic community. Unclassified_Tobrilidae exhibited higher abundance in unpolluted ecologically restored lakes. Chaetogaster and Nais were enriched in aquaculture ponds and domestic wastewater treatment plant outfall area, respectively, while Surirella and Gomphonema dominated industrial sewage treatment plant outfall area. The alpha diversity of eukaryotes was higher in unpolluted ecologically restored lakes. pH and nitrogen content (NO 2 - - N ,NO 3 - - N , and TN) significantly explained the variations for prokaryotic and eukaryotic community structures, respectively. Eukaryotic communities exhibited a more pronounced response to habitat variations compared to prokaryotic communities. Moreover, the association networks revealed an intensive positive correlation between dominant Bacillariophyta and Bacteroidota. This study provided useful data for identifying keystone species and understanding their ecological functions.

Molecular-level insights into the transformation and degradation pathways of dissolved organic matter during full-scale swine wastewater treatment

The rapid development of swine farming has resulted in the generation of a large amount of swine wastewater (SW), and dissolved organic matter (DOM) has a crucial role in determining the efficiency and safety of SW treatment. In this study, the transformation and influential mechanisms of DOM on the quality of SW effluent during full-scale SW treatment in actual engineering were systematically investigated using multispectral analysis and the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) technique. The results showed that S-containing, reduced, saturated, and less aromatic molecules were preferentially removed in the C-AF, while C-S preferentially removed reduced, unsaturated, and aromatic molecules, as well as molecules with large molecular weights. And in the two-stage A/O, the degradation of organic matter and DOM transformation occurred mainly in the A/O-1, with the A/O-2 acting as a supplement to further enhance the humification of DOM. Furthermore, the AOP preferentially removed lignin-like and highly unsaturated compounds, replacing them with a new generation of substances such as proteins and tannins with low aromaticity and unsaturation. More deeply, oxygen addition reactions dominate in both A/O and AOP. Specifically, the most common types of reactions in the A/O were the corresponding potential precursor-product pairs based on methyl to carboxylic acid (-H2 + O2) and alcohol to carboxylic acid (-H2 + O), while tri-hydroxylation (+O3) and di-hydroxylation (+H2O2) reactions were predominant in the AOP. Finally, the study's findings might suggest improving the actual engineering by prioritizing the AOP before the A/O-2 and using the C-S for safeguard treatment of the A/O-2 effluent. It is reliable that this kind of adjustment guarantees safe drainage indications and raises each process unit's efficiency in purifying.

Comprehensive assessment of dissolved organic matter processing in the Amazon River and its major tributaries revealed by positive and negative electrospray mass spectrometry and NMR spectroscopy

Rivers are natural biogeochemical systems shaping the fates of dissolved organic matter (DOM) from leaving soils to reaching the oceans. This study focuses on Amazon basin DOM processing employing negative and positive electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI[±] FT-ICR MS) and nuclear magnetic resonance spectroscopy (NMR) to reveal effects of major processes on the compositional space and structural characteristics of black, white and clear water systems. These include non-conservative mixing at the confluences of (1) Solimões and the Negro River, (2) the Amazon River and the Madeira River, and (3) in-stream processing of Amazon River DOM between the Madeira River and the Tapajós River. The Negro River (black water) supplies more highly oxygenated and high molecular weight compounds, whereas the Solimões and Madeira Rivers (white water) contribute more CHNO and CHOS molecules to the Amazon River main stem. Aliphatic CHO and abundant CHNO compounds prevail in Tapajos River DOM (clear water), likely originating from primary production. Sorption onto particles and heterotrophic microbial degradation are probably the principal mechanisms for the observed changes in DOM composition in the Amazon River and its tributaries.

New insights into the distribution and interaction mechanism of microplastics with humic acid in river sediments

Information on the distribution and interaction of microplastics (MPs) and humic acids (HAs) in river sediment has not been fully explored. This study assessed the distribution and interaction of MPs with HAs at different depths in river sediments. The results delineated that the average abundance of MPs in the 0-10 cm layer (190 ± 20 items/kg) was significantly lower than that in the 11-20 cm and 21-30 cm layers (211 ± 10 items/kg and 238 ± 18 items/kg, respectively). Likewise, the large MP particles mainly existed in the 0-10 cm layer (31.53%-37.87%), while small MP particles were found in the 21-30 cm layers (73.23%-100%). Moreover, HAs in MPs showed a transformation from low molecular weight to high molecular weight with an increase in depth from 0-10 cm to 21-30 cm, which may contribute to the distribution of MPs in the river sediments. These results provide new insight into the migration of MP pollution in river sediments, but further research needs to assess the interaction of MP with HA for mitigating MP pollution in river sediment.

Investigating the Evolution of Structural Characteristics of Humic Acid Generated during the Continuous Anaerobic Digestion and Its Potential for Chromium Adsorption and Reduction

Humic acid (HA), as an important by-product, has been demonstrated to affect anaerobic digestion performance and subsequent land application of digestate via the batch anaerobic digestion process. However, the knowledge about the evolution of structure and function of HA during continuous anaerobic digestion (AD) is still unclear. Therefore, the current study examined the structural changes in HA produced during the continuous AD process and its metal-adsorption-reduction abilities. The results of three-dimensional fluorescence spectroscopy showed a general upsurge in humic-like components’ abundance (70–77%), with an increase in humification index (2.56–3.43). Likewise, the content of HA increased from 4.8 g L−1 to 6.9 g L−1 in the continuous AD process. The evolution of C-H, O-H, C=O, C=C, and C-O functional groups of HA was observed via the 2D COS FTIR analysis. Moreover, the concurrent dynamics of functional groups contributed to the higher adsorption (255.2 mg g−1) of Cr (VI) and reduction (60.3 mg g−1) of Cr (VI) to Cr (III) after 168 days of the continuous AD process. The findings of the current study not only advanced understanding of the evolution of HA during continuous anaerobic digestion and its metal remediation potential but also support further research toward developing an eco-friendly and innovative strategy for the remediation of heavy metals contaminated soils employing anaerobic digestate as an auxiliary agent.

Lagrangian profiles of riverine autotrophy, organic matter transformation, and micropollutants at extreme drought

On their way from inland to the ocean, flowing water bodies, their constituents and their biotic communities are exposed to complex transport and transformation processes. However, detailed process knowledge as revealed by Lagrangian measurements adjusted to travel time is rare in large rivers, in particular at hydrological extremes. To fill this gap, we investigated autotrophic processes, heterotrophic carbon utilization, and micropollutant concentrations applying a Lagrangian sampling design in a 600 km section of the River Elbe (Germany) at historically low discharge. Under base flow conditions, we expect the maximum intensity of instream processes and of point source impacts. Phytoplankton biomass and photosynthesis increased from upstream to downstream sites but maximum chlorophyll concentration was lower than at mean discharge. Concentrations of dissolved macronutrients decreased to almost complete phosphate depletion and low nitrate values. The longitudinal increase of bacterial abundance and production was less pronounced than in wetter years and bacterial community composition changed downstream. Molecular analyses revealed a longitudinal increase of many DOM components due to microbial production, whereas saturated lipid-like DOM, unsaturated aromatics and polyphenols, and some CHOS surfactants declined. In decomposition experiments, DOM components with high O/C ratios and high masses decreased whereas those with low O/C ratios, low masses, and high nitrogen content increased at all sites. Radiocarbon age analyses showed that DOC was relatively old (890-1870 years B.P.), whereas the mineralized fraction was much younger suggesting predominant oxidation of algal lysis products and exudates particularly at downstream sites. Micropollutants determining toxicity for algae (terbuthylazine, terbutryn, isoproturon and lenacil), hexachlorocyclohexanes and DDTs showed higher concentrations from the middle towards the downstream part but calculated toxicity was not negatively correlated to phytoplankton. Overall, autotrophic and heterotrophic process rates and micropollutant concentrations increased from up- to downstream reaches, but their magnitudes were not distinctly different to conditions at medium discharges.

Benthic Biofilm Bacterial Communities and Their Linkage with Water-Soluble Organic Matter in Effluent Receivers

Benthic biofilms are pioneering microbial aggregates responding to effluent discharge from wastewater treatment plants (WWTPs). However, knowledge of the characteristics and linkage of bacterial communities and water-soluble organic matter (WSOM) of benthic biofilms in effluent-receiving rivers remains unknown. Here, we investigated the quality of WSOM and the evolution of bacterial communities in benthic biofilm to evaluate the ecological impacts of effluent discharge on a representative receiving water. Tryptophan-like proteins showed an increased proportion in biofilms collected from the discharge area and downstream from the WWTP, especially in summer. Biofilm WSOM showed weak humic character and strong autochthonous components, and species turnover was proven to be the main factor governing biofilm bacteria community diversity patterns. The bacterial community alpha diversity, interspecies interaction, biological index, and humification index were signally altered in the biofilms from the discharge area, while the values were more similar in biofilms collected upstream and downstream from the WWTP, indicating that both biofilm bacterial communities and WSOM characters have resilience capacities. Although effluent discharge simplified the network pattern of the biofilm bacterial community, its metabolic functional abundance was basically stable. The functional abundance of carbohydrate metabolism and amino acid metabolism in the discharge area increased, and the key modules in the non-random co-occurrence network also verified the important ecological role of carbon metabolism in the effluent-receiving river. The study sheds light on how benthic biofilms respond to effluent discharge from both ecological and material points of view, providing new insights on the feasibility of utilizing benthic biofilms as robust indicators reflecting river ecological health.

Microbial biofilm community dynamics in five lowland streams

Stream biofilms are complex aggregates of diverse organism groups that play a vital role in global carbon and nitrogen cycles. Most of the current studies on stream biofilm focus on a limited number of organism groups (e.g., bacteria and algae), and few have included both prokaryote and eukaryote communities simultaneously. In this study, we incubated artificial substrates in five Danish lowland streams exhibiting different hydrological and physico-chemical conditions and explored the dynamics of community composition and diversity of the benthic biofilm, including both prokaryotes and eukaryotes. We found that few phyla in the prokaryote (Gammaproteobacteria and Bacteroidetes) and eukaryote (Cercozoa) communities accounted for over two-thirds of the total abundance at most of the sites. Both prokaryotic and eukaryotic diversity displayed the same temporal patterns, i.e., diversity peaked in July and January. We also found that hydrological and physico-chemical variables significantly explained the variation in the community composition at phylum level for both prokaryotes and eukaryotes. However, a large proportion of variation remained unexplained, which can be ascribed to important but unmeasured variables like light intensity and biological factors such as trophic and non-trophic interactions as revealed by network analysis. Therefore, we suggest that use of a multitrophic level perspective is needed to study biofilm i.e., the "microbial jungles", where high occurrences of trophic and non-trophic interactions are expected.

Revealing the characteristics of dissolved organic matter in urban runoff at three typical regions via optical indices and molecular composition

Dissolved organic matter (DOM) plays a major role in ecological systems and influences the fate and transportation of many pollutants. Despite the significance of DOM, understanding of how environmental and anthropogenic factors influence its composition and characteristics is limited, especially in urban stormwater runoff. In this article, the chemical properties (pollutant loads, molecular weight, aromaticity, sources, and molecular composition) of DOM in stormwater extracted from three typical end-members (traffic, residential, and campus regions) were characterized by UV-visible (UV-vis) spectroscopy, excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC), and ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS). There are three findings: (1) The basic properties of DOM in stormwater runoff varied obviously from three urban fields, and the effect of initial flush was also apparent. (2) The DOM in residential areas mainly came from autochthonous sources, while allochthonous sources primarily contributed to the DOM in traffic and campus areas. However, it was mainly composed of terrestrial humic-like components with CHO and CHON element composition and HULO and aliphatic formulas. (3) The parameters characterizing DOM were primarily related to terrestrial source and aromaticity, but their correlations varied. Through the combination of optical methods and UPLC-Q-TOF spectrometry, the optical and molecular characteristics of rainwater are effectively revealed, which may provide a solid foundation for the classification management of stormwater runoff in different urban regions.

Molecular structure and evolution characteristics of dissolved organic matter in groundwater near landfill: Implications of the identification of leachate leakage

Landfills can cause groundwater contamination, the pollution characteristics in groundwater near landfill sites have been extensively investigated, while the rapid identification of leachate leakage remained unclear. Comprehensively characterizing dissolved organic matter (DOM) is crucial for tracing the source, species, and migration of contaminants within groundwater and protecting groundwater sources. Here, we showed that DOM composition from newer landfills was mainly composed of newly-produced tryptophan and tyrosine, and protein-like and humic-like substances were more abundant in landfills that were relatively older. DOM in landfill groundwater was initially dominated by outputs from microbial activities, followed by terrigenous input. Leaked leachate contained an additional dye-derived fluorescent matter at the excitation/emission wavelength of 240-260/440-460 nm that was absent in uncontaminated groundwater. Leachate leakage increased the concentrations of humic-like substance, DOM molecular weight, and microbial activity in the downstream groundwater, resulting in the microorganisms rapidly multiply and secrete large amounts of microbial metabolism by-products, making them suitable indicators of groundwater pollution. Three criteria were proposed to establish an interpretable fluorescence method to identify leachate pollution. The obtained results provide a novel insight into not only the monitoring, early warning, and identification but also the transport, fate and removal or transformation of groundwater leachate in landfills.

Disentangling multiple chemical and non-chemical stressors in a lotic ecosystem using a longitudinal approach

Meeting ecological and water quality standards in lotic ecosystems is often failed due to multiple stressors. However, disentangling stressor effects and identifying relevant stressor-effect-relationships in complex environmental settings remain major challenges. By combining state-of-the-art methods from ecotoxicology and aquatic ecosystem analysis, we aimed here to disentangle the effects of multiple chemical and non-chemical stressors along a longitudinal land use gradient in a third-order river in Germany. We distinguished and evaluated four dominant stressor categories along this gradient: (1) Hydromorphological alterations: Flow diversity and substrate diversity correlated with the EU-Water Framework Directive based indicators for the quality element macroinvertebrates, which deteriorated at the transition from near-natural reference sites to urban sites. (2) Elevated nutrient levels and eutrophication: Low to moderate nutrient concentrations together with complete canopy cover at the reference sites correlated with low densities of benthic algae (biofilms). We found no more systematic relation of algal density with nutrient concentrations at the downstream sites, suggesting that limiting concentrations are exceeded already at moderate nutrient concentrations and reduced shading by riparian vegetation. (3) Elevated organic matter levels: Wastewater treatment plants (WWTP) and stormwater drainage systems were the primary sources of bioavailable dissolved organic carbon. Consequently, planktonic bacterial production and especially extracellular enzyme activity increased downstream of those effluents showing local peaks. (4) Micropollutants and toxicity-related stress: WWTPs were the predominant source of toxic stress, resulting in a rapid increase of the toxicity for invertebrates and algae with only one order of magnitude below the acute toxic levels. This toxicity correlates negatively with the contribution of invertebrate species being sensitive towards pesticides (SPEAR_pesticides index), probably contributing to the loss of biodiversity recorded in response to WWTP effluents. Our longitudinal approach highlights the potential of coordinated community efforts in supplementing established monitoring methods to tackle the complex phenomenon of multiple stress.

Structural Characterization of Dissolved Organic Matter in Permafrost Peatland Lakes

Thermokarst lakes result from the thawing of ice-rich permafrost and are widespread across northern landscapes. These waters are strong emitters of methane, especially in permafrost peatland regions, where they are stained black by high concentrations of dissolved organic matter (DOM). In the present study, we aimed to structurally characterize the DOM from a set of peatland thermokarst lakes that are known to be intense sites of microbial decomposition and methane emission. Samples were collected at different depths from three thermokarst lakes in the Sasapimakwananisikw (SAS) River valley near the eastern Hudson Bay community of Kuujjuarapik–Whapmagoostui (Nunavik, Canada). Samples were analyzed by spectrofluorometry, Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), and elemental analysis. Fluorescence analyses indicated considerable amounts of autochthonous DOM in the surface waters of one of SAS 1A, indicating a strong bioavailability of labile DOM, and consequently a greater methanogenic potential. The three lakes differed in their chemical composition and diversity, suggesting various DOM transformations phenomena. The usefulness of complementary analytical approaches to characterize the complex mixture of DOM in permafrost peatland waters cannot be overlooked, representing a first step towards greater comprehension of the organic geochemical properties of these permafrost-derived systems.

Quality of Dissolved Organic Matter Driven by Autotrophic and Heterotrophic Microbial Processes in a Large River

Rivers are regarded as important sites for processing of dissolved organic matter (DOM) from terrestrial sources on its way to the ocean. However, little is known about the longitudinal change of DOM molecular composition in large rivers. Here we performed a Lagrangian sampling in the lower part of the Middle Elbe at low discharge conditions to test how DOM composition changes along the river stretch and how this is related to microbial processes. The concentration of dissolved organic carbon and fluorescence indices showed only subtle longitudinal differences. In contrast, ultra-high-resolution mass spectrometry analysis of riverine DOM detected pronounced changes in molecular composition. Also, chlorophyll a concentration, bacterial abundance, and bacterial production all increased downstream. The three microbial parameters were positively related to intensities of CHO and CHNO molecular formulas with high hydrogen/carbon and low oxygen/carbon ratios but negatively to several CHOS surfactants. To disentangle the role of autotrophic and heterotrophic processes, we developed a new approach and compared slopes from linear regression of DOM compound intensities versus chlorophyll a concentration and bacteria abundance. As a result, most of the positive related DOM compounds were produced by bacteria. In conclusion, longitudinal changes of river DOM seemed to be largely driven by microbial processes.

Photochemically Induced Changes of Dissolved Organic Matter in a Humic-Rich and Forested Stream

Photochemical processing is an important way to transform terrestrial dissolved organic matter (DOM) but was rarely investigated by ultra-high resolution mass spectrometry. We performed an irradiation experiment with water from a shaded forest stream flowing into a lit reservoir. Bacterial activity explained only 1% of dissolved organic carbon (DOC) decline in a combined bacterial and photodegradation approach. Photodegradation decreased the DOC concentration by 30%, the specific ultraviolet (UV) absorption by 40%–50%, and fluorescence intensity by 80% during six days. The humification index (HIX) decreased whereas the fluorescence index (FI) did not change. Two humic-like components identified by parallel factor analysis (PARAFAC) of excitation–emission matrices followed the decrease of fluorescent DOM. Changes of relative peak intensities of Fourier transform-ion cyclotron resonance mass spectroscopy (FT-ICR MS) elemental formula components as a function of cumulated radiation were evaluated both by Spearman’s rank correlation and linear regression. The FT-ICR MS intensity changes indicate that high aromatic material was photochemically converted into smaller non-fluorescent molecules or degraded by the release of CO2. This study shows the molecular change of terrestrial DOM before the preparation of drinking water from reservoirs.

Molecular change of dissolved organic matter and patterns of bacterial activity in a stream along a land-use gradient

Fluvial networks are globally relevant for the processing of dissolved organic matter (DOM). To investigate the change in molecular DOM diversity along the river course, high-field FTICR mass spectrometry and NMR spectroscopy of riverine DOM as well as bacterial abundance and activity were measured in a third order stream along a land-use gradient from pristine, agricultural to urban landscapes. DOM composition showed a clear evolution along the river course with an initial decrease of average oxidation and unsaturation followed by an increased relative abundance of CHNO and CHOS compounds introduced by agriculture and waste water, respectively. DOM composition was dominated by rather unsaturated CHO compounds (H/C ≤ 1) in headwaters and by more aliphatic molecules at downstream sites. Oxygenated functional groups shifted from aromatic ethers and hydroxyl groups to aliphatic carboxylic acids and aliphatic hydroxyl groups. This massive dislocation of oxygen significantly increased the diversity of atomic environments in branched aliphatic groups from headwater to downstream DOM. Mass spectra of DOM enabled the detection of compositional relationships to bacterial abundance and activity which was positively related to more aliphatic components (H/C > 1) and negatively related to unsaturated components. FTICR mass and NMR spectra corroborated the initial decline in DOM molecular diversity predicted by the River Continuum Concept (RCC) but demonstrated an anthropogenic increase in the molecular diversity of DOM further downstream. While the high DOM molecular diversity in first order headwater streams was the result of small scale ecosystem plurality, agriculture and waste water treatment introduced many components in the lower reaches. These anthropogenic influences together with massive bacterial oxidation of DOM contributed to a growth of molecular diversity of downstream DOM whose composition and structure differed entirely from those found in pristine headwaters.

Transformation of dissolved organic matter during full-scale treatment of integrated chemical wastewater: Molecular composition correlated with spectral indexes and acute toxicity

As one of the key economic modes in China, chemical industry park (CIP) has made great contribution to the Chinese rapid economic growth. Concomitantly, how to effectively and safely dispose of the CIP wastewater (CIPWW) has been an unavoidable issue. Molecular transformation of dissolved organic matter (DOM) in CIPWW treatment is essential to optimize the employed process and to provide solid basis for risk evaluation of the discharged effluent as well. In this study, electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) was used to characterize the molecular transformation of DOM during full-scale treatment of integrated chemical wastewater in a centralized wastewater treatment plant (CWWTP), where the combined process follows hydrolysis/acidification (HA)-flocculation/precipitation (FP)-A²/O-membrane bioreactor (MBR)-ultrafiltration (UF)-reverse osmosis (RO). Compared to municipal wastewater, DOM in CIPWW exhibited higher unsaturation degree, lower molecular weight, and higher toxicity. In FP unit, DOM of C_<24 and higher nominal oxidation state of carbon (NOSC) values was preferentially removed. The HA and anaerobic units are capable of significantly degrading DOM, resulting in great changes in molecular composition of DOM. However, the anoxic, oxic, and MBR units only lead to a slight change of the molecular formulae. The terminal units of UF and RO can remove most DOM, with the concentration of dissolved organic carbon (DOC) declining by 19.2% and 94.6% respectively. The correlation between spectral indexes and acute toxicity with the molecular formulae of DOM suggested that polyphenols and highly unsaturated phenols were positively correlated with the specific UV absorbance at 254 nm (SUVA₂₅₄). In addition, both compounds (0.32 < O/C < 0.63) as well as the aliphatic ones (0.22 < O/C < 0.56) presented positive correlation with acute toxicity. Further, the pairwise correlation analysis illustrated that SUVA₂₅₄, O/C_wa, double bond equivalence (DBE_wa), and NOSC_wa were positively correlated with each other, whereas the acute toxicity was positively correlated with humification index (HIX), O/C_wa, and DBE_wa.

Going with the flow: Planktonic processing of dissolved organic carbon in streams

A large part of the organic carbon in streams is transported by pulses of terrestrial dissolved organic carbon (tDOC) during hydrological events, which is more pronounced in agricultural catchments due to their hydrological flashiness. The majority of the literature considers stationary benthic biofilms and hyporheic biofilms to dominate uptake and processing of tDOC. Here, we argue for expanding this viewpoint to planktonic bacteria, which are transported downstream together with tDOC pulses, and thus perceive them as a less variable resource relative to stationary benthic bacteria. We show that pulse DOC can contribute significantly to the annual DOC export of streams and that planktonic bacteria take up considerable labile tDOC from such pulses in a short time frame, with the DOC uptake being as high as that of benthic biofilm bacteria. Furthermore, we show that planktonic bacteria efficiently take up labile tDOC which strongly increases planktonic bacterial production and abundance. We found that the response of planktonic bacteria to tDOC pulses was stronger in smaller streams than in larger streams, which may be related to bacterial metacommunity dynamics. Furthermore, the response of planktonic bacterial abundance was influenced by soluble reactive phosphorus concentration, pointing to phosphorus limitation. Our data suggest that planktonic bacteria can efficiently utilize tDOC pulses and likely determine tDOC fate during downstream transport, influencing aquatic food webs and related biochemical cycles.

Effects of Fe(III) and quality of humic substances on As(V) distribution in freshwater: Use of ultrafiltration and Kohonen neural network

Humic substances (HS) are ubiquitous organic compounds able to affect mobility and availability of arsenic (As) in aquatic systems. Although it is known that associations between HS and As occur mainly via iron (Fe)-cationic bridges, the behaviour and distribution of this metalloid in HS- and Fe-rich environments is still not fully understood. In this paper, the quality of HS from different rivers in Brazil and Germany and its influence on the behaviour of As(V) under different Fe(III) concentrations were investigated. HS were extracted from four different rivers (Cascatinha, Holtemme, Selke and Warme Bode), characterised and fractionated into different molecular weight sizes (10, 5 and 1 kDa). Complexation tests were performed using an ultrafiltration system and 1 kDa membranes. All data was analysed using the Kohonen neural network (SOM - Self organising maps). All samples, except Selke, exhibited similar results of free As (<1 kDa). The results suggested that associations between HS, Fe and As were dependent on nitrogen (N)-aromatic carbon (C), amount of sulphur (S) and the molecular size of the HS. Although all HS appeared to be similar after looking at most variables analysed, the SOM could discriminate them into three different groups. Characterisation of the HS indicated that they had terrestrial material (from C₃ plants) as precursor material. Most of the As and Fe was distributed in the fractions of higher (>10 kDa) and lower (<1 kDa) size. HS quality is an important factor to take into account when studying the behaviour of As in HS-rich environments.

A new approach for evaluating transformations of dissolved organic matter (DOM) via high-resolution mass spectrometry and relating it to bacterial activity

Streams are important sites of transformation of dissolved organic matter (DOM). The molecular characterization of DOM-quality changes requires sophisticated analytical evaluation techniques. The goal of our study was to link molecular DOM transformation with bacterial activity. We measured the degradation of leaf leachate over a gradient of bacterial production obtained by different rates of percolation of sediments in seven experimental flumes on five sampling dates. We developed a new strategy for evaluating molecular formula data sets obtained by ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS), in which the time-dependent change of component abundance was fitted by a linear regression model after normalization of mass peak intensities. All components were categorized by calculating the slope (change of percent intensity per day) in each of the seven flumes. These slopes were then related to cumulative bacterial production. The concentration of DOM decreased quickly in all flumes. Bacterial activity was higher in flumes with percolated sediment than in those without percolation, whereas plankton bacterial activity was higher in flumes without percolation or without sediment. There were no differences in molecular-DOM characteristics between flumes, but there were distinct changes over time. Positive slopes, i.e. increasing intensities over time, were found for small molecules (MW < 450 Da) and high O/C ratios, whereas decreasing intensities were observed less often and only for large molecules and low O/C ratios. The positive slopes of produced components showed a positive relationship to bacterial production for small and for oxygen-rich components. The negative slopes of degraded components were negatively related to bacterial production for large and for oxygen-deficient molecules. Overall, the approach provided new insights into the transformation of specific molecular DOM components.

Deciphering biodiversity and interactions between bacteria and microeukaryotes within epilithic biofilms from the Loue River, France

Epilithic river biofilms are complex matrix-enclosed communities harboring a great diversity of prokaryotic and eukaryotic microorganisms. Interactions between these communities and the relative impacts of environmental factors on their compositions are poorly understood. In this study, we assessed the spatio-temporal variation in the diversity and composition of bacterial and microeukaryotic communities within biofilms in a French river. Significant changes were found in the composition of these microbial communities over the sampling period and between the upstream and downstream stations. In addition, the beta diversity of the bacterial community tended to decrease along the river, mostly as a result of turnover. These changes could be caused by the different water temperatures and geological and hydrological river contexts at the sampling sites (from karst landscape to river plain). Finally, our network analysis showed multiple correlations among dominant OTUs. Among them, negative correlations between Rhodobacteraceae and two other dominant groups of photosynthetic microorganisms (cyanobacteria and diatoms) were particularly interesting, which raises the question of what environmental factors trigger the changes occurring in benthic microbial photosynthetic communities.

Differences in DOM of rewetted and natural peatlands - Results from high-field FT-ICR-MS and bulk optical parameters

Peatlands can be a potential source of dissolved organic matter (DOM) in fresh water catchment areas. The quantity and quality of DOM can differ between pristine, degraded and rewetted peatlands. Due to the large scale and continuing losses of peatlands, their conservation and restoration has been increasingly emphasized. Mostly rewetting measures are required to improve the hydrology of damaged peatlands, which is a precondition for the resettlement of peat-forming plant species. Thus, in term of DOM, there is a special need to understand how rewetting measures affect DOM characteristics and concentrations. To estimate the potential leaching of humic substances from rewetted areas two natural sites were compared with four artificially rewetted sites in a peatland area of the Harz Mountains National Park, Germany. This was done with regards to DOM quality by combining the results from Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS, measured at one time in Spring) and excitation-emission-matrix fluorescence spectroscopy (EEMF, measured monthly for the period of one year). The DOM quality was significantly less variable in the pristine peatland soil water compared to the rewetted peatland soil waters, from both a spatial and a seasonal perspective. The soil water from the rewetted peatland sites showed a higher degree of humification compared to pristine peatland. DOC concentration was mostly consistent in the pristine peatland over the year. The rewetted peatlands showed higher DOC levels in Summer months and lower DOC in Winter months compared to the pristine peatland. It can be concluded that the rewetting of peatlands is coupled with high concentrations of DOC in soil water and its quality is highly aromatic (as reflected by the observed values from the humification index) during times with elevated temperature. The results may have a significant input for dynamic catchment area studies with regards to rewetting peatland sites.

Land-based salmon aquacultures change the quality and bacterial degradation of riverine dissolved organic matter

Aquacultures are of great economic importance worldwide but pollute pristine headwater streams, lakes, and estuaries. However, there are no in-depth studies of the consequences of aquacultures on dissolved organic matter (DOM) composition and structure. We performed a detailed molecular level characterization of aquaculture DOM quality and its bacterial degradation using four salmon aquacultures in Chile. Fluorescence measurements, ultrahigh-resolution mass spectrometry, and nuclear magnetic resonance spectroscopy of the DOM revealed specific and extensive molecular alterations caused by aquacultures. Aquacultures released large quantities of readily bioavailable metabolites (primarily carbohydrates and peptides/proteins, and lipids), causing the organic matter downstream of all the investigated aquacultures to deviate strongly from the highly processed, polydisperse and molecularly heterogeneous DOM found in pristine rivers. However, the upstream individual catchment DOM signatures remained distinguishable at the downstream sites. The benthic algal biovolume decreased and the bacterial biovolume and production increased downstream of the aquacultures, shifting stream ecosystems to a more heterotrophic state and thus impairing the ecosystem health. The bacterial DOM degradation rates explain the attenuation of aquaculture DOM within the subsequent stream reaches. This knowledge may aid the development of improved waste processing facilities and may help to define emission thresholds to protect sensitive stream ecosystems.

Discharge determines production of, decomposition of and quality changes in dissolved organic carbon in pre-dams of drinking water reservoirs

Pre-dams are small reservoirs constructed upstream of the main drinking water reservoirs and are used for nutrient removal and sediment trapping. Little is known about the role of pre-dams regarding the production and decomposition of dissolved organic carbon (DOC) in relation to discharge and how this affects the quality of DOC in the water. We combined quantitative and qualitative investigations under different hydrological conditions at three pre-dams exhibiting a gradient from oligotrophic/high-DOC to eutrophic/low-DOC. All pre-dams were mainly autotrophic in their upper water layers. The ratio of OC production to total gained OC (i.e. OC import+OC production) decreased with increasing discharge. On average, 0-30% of the total gained OC was produced within the pre-dams. The amount of microbially decomposed DOC increased with the average water residence time (WRT) and with the trophic status of the pre-dams. Radiocarbon analyses of respired CO₂ revealed that heterotrophic bacteria preferentially utilized old DOC components (195-395years before present) under base flow conditions, whereas younger components (modern, i.e. OC produced after 1950) were utilized at high discharge. DOC quality changed significantly over the year within the pre-dams: High proportions of algae-derived DOC were observed during base flow in summer, and the freshness index (β/α ratio) decreased significantly with higher discharges. DOC production and quality changes in response to hydrological conditions should be considered for future water quality management in reservoirs, as climate scenarios for temperate regions predict decreased runoffs leading to longer WRT and increased eutrophication and production of algae-derived OC.

Comprehensive structure-selective characterization of dissolved organic matter by reducing molecular complexity and increasing analytical dimensions

Deciphering the molecular codes of dissolved organic matter (DOM) improves our understanding of its role in the global element cycles and its active involvement in ecosystem services. This study demonstrates comprehensive characterization of DOM by an initial polarity-based stepwise solid phase extraction (SPE) with single methanol elution of the cartridges, but separate collection of equal aliquots of eluate. The reduction of molecular complexity in the individual DOM fractions attenuates intermolecular interactions and substantially increases the disposable resolution of any structure selective characterization. Suwannee River DOM (SR DOM) was used to collect five distinct SPE fractions with overall 91% DOC recovery. Optical spectroscopy (UV and fluorescence spectroscopy), high-field Fourier transform ion cyclotron mass spectrometry (FTICR MS) and nuclear magnetic resonance (NMR) spectroscopy showed analogous hierarchical clustering among the five eluates corroborating the robustness of this approach. Two abundant moderately hydrophobic fractions contained most of the SR DOM compounds, with substantial proportions of aliphatics, carboxylic-rich alicyclic molecules, carbohydrates and aromatics. A minor early eluting hydrophilic fraction was highly aliphatic and presented a large diversity of alicyclic carboxylic acids, whereas the two late eluting, minor hydrophobic fractions appeared as a largely defunctionalized mixture of aliphatic molecules. Comparative mass analysis showed that fractionation of SR DOM was governed by multiple molecular interactions depending on O/C ratio, molecular weight and aromaticity. The traditional optical indices SUVA₂₅₄ and fluorescence index (FI) indicated the relative aromaticity in agreement with FTICR mass and NMR spectra; the classical fluorescent peaks A and C were observed in all four latter eluates. This versatile approach can be easily expanded to preparative scale under field conditions, and transferred to different DOM sources and SPE conditions.

EPS-Then and Now

“Slime” played a brief and spectacular role in the 19th century founded by the theory of primordial slime by Ernst Haeckel. However, that substance was never found and eventually abandoned. Further scientific attention slowly began in the 1930s referring to slime as a microbial product and then was inspired by “How bacteria stick” by Costerton et al. in 1978, and the matrix material was considered to be polysaccharides. Later, it turned out that proteins, nucleic acids and lipids were major other constituents of the extracellular polymeric substances (EPS), an acronym which was highly discussed. The role of the EPS matrix turns out to be fundamental for biofilms, in terms of keeping cells in proximity and allowing for extended interaction, resource capture, mechanical strength and other properties, which emerge from the life of biofilm organisms, including enhanced tolerance to antimicrobials and other stress. The EPS components are extremely complex and dynamic and fulfil many functional roles, turning biofilms into the most ubiquitous and successful form of life on Earth.

Bacterial production and their role in the removal of dissolved organic matter from tributaries of drinking water reservoirs

Enhanced concentrations of dissolved organic matter (DOM) in freshwaters are an increasing problem in drinking water reservoirs. In this study we investigated bacterial DOM degradation rates in the tributaries of the reservoirs and tested the hypotheses that (1) DOM degradation is high enough to decrease DOM loads to reservoirs considerably, (2) DOM degradation is affected by stream hydrology, and (3) phosphorus addition may stimulate bacterial DOM degradation. Bacterial biomass production, which was used as a measure of DOM degradation, was highest in summer, and was usually lower at upstream than at downstream sites. An important proportion of bacterial production was realized in epilithic biofilms. Production of planktonic and biofilm bacteria was related to water temperature. Planktonic production weakly correlated to DOM quality and to total phosphorus concentration. Addition of soluble reactive phosphorus did not stimulate bacterial DOM degradation. Overall, DOM was considerably degraded in summer at low discharge levels, whereas degradation was negligible during flood events (when DOM load in reservoirs was high). The ratio of DOM degradation to total DOM release was negatively related to discharge. On annual average, only 0.6-12% of total DOM released by the catchments was degraded within the tributaries.

Abundance and Diversity of CO2-Assimilating Bacteria and Algae Within Red Agricultural Soils Are Modulated by Changing Management Practice

Elucidating the biodiversity of CO(2)-assimilating bacterial and algal communities in soils is important for obtaining a mechanistic view of terrestrial carbon sinks operating at global scales. "Red" acidic soils (Orthic Acrisols) cover large geographic areas and are subject to a range of management practices, which may alter the balance between carbon dioxide production and assimilation through changes in microbial CO(2)-assimilating populations. Here, we determined the abundance and diversity of CO(2)-assimilating bacteria and algae in acidic soils using quantitative PCR and terminal restriction fragment length polymorphism (T-RFLP) of the cbbL gene, which encodes the key CO(2) assimilation enzyme (ribulose-1,5-bisphosphate carboxylase/oxygenase) in the Calvin cycle. Within the framework of a long-term experiment (Taoyuan Agro-ecosystem, subtropical China), paddy rice fields were converted in 1995 to four alternative land management regimes: natural forest (NF), paddy rice (PR), maize crops (CL), and tea plantations (TP). In 2012 (17 years after land use transformation), we collected and analyzed the soils from fields under the original and converted land management regimes. Our results indicated that fields under the PR soil management system harbored the greatest abundance of cbbL copies (4.33 × 10(8) copies g(-1) soil). More than a decade after converting PR soils to natural, rotation, and perennial management systems, a decline in both the diversity and abundance of cbbL-harboring bacteria and algae was recorded. The lowest abundance of bacteria (0.98 × 10(8) copies g(-1) soil) and algae (0.23 × 10(6) copies g(-1) soil) was observed for TP soils. When converting PR soil management to alternative management systems (i.e., NF, CL, and TP), soil edaphic factors (soil organic carbon and total nitrogen content) were the major determinants of bacterial autotrophic cbbL gene diversity. In contrast, soil phosphorus concentration was the major regulator of algal cbbL community composition. Our results provide new insights into the diversity, abundance, and modulation of organisms responsible for microbial autotrophic CO(2) fixation in red acidic soils subjected to changing management regimes.