Displays

Dissolved organic carbon (DOC) represents an important component of the terrestrial and fluvial carbon cycle as it represents a flux from terrestrial carbon stores and while it transfers through the fluvial network it can be processed to release greenhouse gases to the atmosphere. Furthermore, DOC is a major water resource limitation as the dissolved organic matter has to be removed prior to treatment. Therefore, we need to understand the concentration and fluxes of DOC and they change across a landscape between the terrestrial source and the tidal limit.

Our ability to understand the processing of terrestrial and fluvial carbon has been limited by the range of catchments that have been considered and the time scale over which they have been considered. Studies focused on similar catchment types and very little means of comparing between catchments. However, if we can access and understand large datasets we can find general principles which control DOC and the relative importance of these controls. In this study we use two datasets. The first, is a dataset sampled across the UK for major rivers (270 catchments) from 1974 and this dataset is ideal for understanding flux to the continental shelf and this dataset has over 50000 datapoints. Secondly, many of these sites are monitored for a rang e of other parameters that are related to the composition of the dissolved organic matter. The important covariates for DOM composition are BOD, which is a measure of DOM decomposition, and COD which is measure of the oxidation state of the DOM. All the study catchments could be characterised by a range of covariate information, eg. soil cover, land use, hydro-climatology. To make maximum use of this data the dataset was considered within a Bayesian hierarchical framework.

The concentrations of DOC from the UK rose for the 1974 on to the late 1990s before a decline to 2007-08. The decline was driven by changes in urban sources, particular by improvements in sewage treatment. The DOC flux from the UK has declined since a peak in 2000 and in 2017 was 767 ktonnes C/yr (95% credible interval 644 – 909 ktonnesC/yr). Modelling composition turnover gives the DOC flux from source as 3.5 Mtonnes C/yr with 2.6 Mtonnes C/yr lost to atmosphere (14 Mtonnes CO_2eq/yr = 59 tonnes CO_2eq/km2/yr).

How to cite: Worrall, F., Howden, N., and Burt, T.: Understanding the long-term concentration, flux, composition and processing of dissolved organic carbon in UK rivers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6885, https://doi.org/10.5194/egusphere-egu2020-6885, 2020.

Biodegradability of DOM is controlled by both external environmental factors and by DOM character itself. Currently in the literature, more emphasis is being placed on the role of environmental parameters, and the idea of refractory molecules is being challenged. Biodegradation is the most important transformation process for DOM in lakes and has implications such as fuelling the lower food-web with energy/carbon and producing greenhouse gases. To be able to predict ecological responses to future climatic conditions, a better understanding of the controlling factors of DOM biodegradability is needed.  

Here, we present a unique dataset on lake DOM characteristics from an extensive land-covering survey form Norway. The total of 333 different lakes included cover different catchment types such as lowland boreal forests, coastal impacted areas, alpine mountains, and arctic conditions, and with a wide range in catchment-to-lake ratios. The samples were collected using helicopter during the autumn of 2019, just after water mixing, and the samples were analysed immediately upon arrival at the laboratory. The lakes range in TOC concentration from 0.25 to more than 25 mg L^-1.

Principal DOM characterisation methods included the acquisition of fluorescence excitation-emission matrices in combination with parallel factor analysis (EEM-PARAFAC) and the assessment of intrinsic DOM biodegradability. The latter was determined by measuring O₂ consumption during 24 h using a batch experimental setup, after re-inoculating filtered (0.2 µm) lake DOM samples with a standard environmental inoculum.

The aim of this study is, by contributing with unique spatial data, to reveal the controlling factors of DOM biodegradability in lakes. The measured DOM biodegradability will be linked to structural information of the DOM molecules, extracted from the EEMs, and to environmental parameters such as water chemistry, local climatic conditions, and other catchment characteristics.

How to cite: Brecke Gundersen, C., Crapart, C. M., Garmo, Ø. A., Austnes, K., Vogt, R. D., and de Wit, H.: DOM biodegradability assessed in a land covering lake survey in Norway: does DOM character dominate environmental controls?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18118, https://doi.org/10.5194/egusphere-egu2020-18118, 2020.

Hydrological events mobilize chemically diverse dissolved organic matter (DOM) from soils to streams. Further, such events can also cause an influx of soil microbial life into fluvial systems. Here we present results from the HYDRO-DIVERSITY project, which aims to investigate the dynamic transfer of DOM and microbial life from catchment soils to streams, as well as their downstream fate. We studied the microbial community composition and DOM quality using 16S Illumina sequencing and fluorescence and absorbance spectroscopy. Data from small streams showed strong changes in DOM composition and in the microbial community delivered from soils during hydrological events. Moreover, we performed a flume experiment, in which soil microbial inoculation and the processing of DOM across different biofilm ages were evaluated. As such, biofilm age did not directly affect the establishment of soil microbes in the stream ecosystem. However, in-stream processing of soil DOM appeared to be affected by the inoculation event. This poses the fundamental question, if the processing of DOM in streams and rivers depends on the transient presence of specific soil microbes in stream ecosystems. Overall our results show that soils provide a dynamic and relevant influx of microbes and DOM to first order streams and that this dynamic influx likely affects microbial community dynamics of downstream fluvial networks as well as in-stream DOM processing. 

How to cite: Schelker, J., Caillon, F., Besemer, K., Peduzzi, P., and Harjung, A.: The effect of stream microbial inoculation on in-stream carbon processing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20555, https://doi.org/10.5194/egusphere-egu2020-20555, 2020.

This research explores the in-situ bacterial production of aquatic fluorescent organic matter (AFOM) under controlled laboratory conditions. Whilst fluorescence techniques have long been used to monitor AFOM distribution, origin and dynamics within aquatic systems, the extent to which AFOM characteristics are defined by microbial processing in surface freshwaters has largely been overlooked. Current convention champions the assumption that humic-like (Peak C) and protein-like (Peak T) fluorescence signatures are exclusively derived from terrestrial (allochthonous) or microbial (autochthonous) origins respectively, with Peak T having been directly correlated with microbial enumeration. Under intensifying anthropogenic perturbations and changing catchment characteristics, the complexities associated with bacterial-organic matter (OM) interactions in freshwater systems are increasing, challenging our understanding as to the origin and fate of aquatic OM. To what extent the observed AFOM in freshwater systems is defined by bacterial processing and how such processing may be influenced by nutrient availability are key knowledge gaps that need to be addressed. Previous research has observed the in-situ bacterial production of humic-like compounds in a laboratory model system with a high-nutrient and high-carbon content synthetic growth medium. This work describes a non-fluorescing, simulated freshwater matrix which is low in both nutrient and organic carbon concentrations. Using this model, growth curve incubation experiments have been undertaken over a 48-hour period with a monoculture laboratory strain of Pseudomonas aeruginosa. Microbiological and fluorescence analyses undertaken at regular time intervals demonstrate the bacterial production of humic-like OM (Peak C) under oligotrophic (after 8hrs) and simulated high-nutrient conditions (after 6hrs). These findings, albeit under laboratory conditions, are important as they show that this fluorescence region, currently viewed as allochthonous in origin, can also represent labile OM generated in-situ by bacteria and, furthermore, that this bacterial production increases as a function of nutrient loading. In addition, the data quantitatively demonstrates that fluorescence intensities increase independently of cell density. These results challenge the assumption that humic-like AFOM is exclusively terrestrial in origin and suggest that bacteria may “engineer” OM in-situ that gives rise to these fluorescence characteristics as a function of metabolism. Importantly, nutrient availability is a key driver of metabolic activity, outlining the potential for the use of fluorescence as a marker for stream metabolism as opposed to a measure of bacterial numbers. Further development of the laboratory model via the utilisation of environmentally-sourced bacterial communities is required. Ultimately, this laboratory model will inform field studies that look to improve our understanding of how microbial communities respond to catchment stressors, and how these responses influence AFOM fluorescence signatures and ultimately the origin and fate of OM in freshwater systems.

How to cite: Perrin, E., Attridge, J., Thorn, R., Sargeant, S., and Reynolds, D.: Investigating the in-situ bacterial production of aquatic fluorescent organic matter using a freshwater laboratory model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8466, https://doi.org/10.5194/egusphere-egu2020-8466, 2020.

River water quality models offer studying spatio-temporal variation and processes of nitrogen (N) turnover. However, the infrequent temporal resolution of monitoring data commonly limit the reliability of modeling instream N processing. These limitations of the temporal data resolution can result in equifinality of model parameter sets and considerable uncertainties due to insufficient ability of validating internal turnover processes. The combination of emerging high frequency monitoring techniques and water quality modeling may support continuous quantification of instream N processing pathways with higher reliability.

In this study, we set up a hydrodynamic and river water quality model (WASP 7.5.2) in the 27.4-km reach of the 5^th order river Bode in Central Germany for a 5-year period (2014-2018). High frequency data (15-min interval) of discharge, nitrate, dissolved oxygen (DO) and Chlorophyll-a (Chl-a) at the upstream and downstream station were used as model inputs and for model testing, respectively. Chl-a and DO data were used for disentangling uptake via phytoplankton and benthic algae. Furthermore we identified the most important N-removal and release processes including denitrification, excretion from phytoplankton and benthic algae at daily, seasonal and annual scales.

The PBias of lower than 20% between the simulated and measured high-frequency values for the four variables showed general good performance of the model. Results showed that on an annual scale, net N uptake efficiency ranged from 0.2-17.2% and increased with decreasing discharge resulting in highest value for the extreme low-flow year 2018. Among seasons, net uptake efficiency was found to be the highest in summer. Over 50% of the N loading was taken up at the extreme low flow in the summer of 2018. The contributions of each pathway to total N uptake decreased from assimilatory uptake via benthic algae, denitrification, and assimilatory uptake via phytoplankton. However, in the extreme low-flow summer of 2018, the importance of denitrification was largely increased compared to former years. Besides, in autumn, the reach became a net N source, because remineralization of N from benthic algae surpassed uptake processes.

Our study highlights the value of high frequency data to support river water quality modeling allowing continuous quantification of whole-stream N uptake and release pathways.

How to cite: Huang, J. and Rode, M.: River water quality modeling using continuous high frequency data allows disentangling whole-stream nitrogen uptake and release pathways, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9292, https://doi.org/10.5194/egusphere-egu2020-9292, 2020.

Controls on the degradation of dissolved organic matter (DOM) in freshwaters play a major role in the global carbon cycle. Under the changing climate, the aquatic systems are exposed to increasing terrestrial OM load due to changes in precipitation and air temperature. However, little is known about how the source and composition of this DOM influence its microbial processing in receiving waters.

In this study, we aimed to determine the composition of riverine DOM at a molecular level to gain a more comprehensive understanding on how the quality and quantity of DOM reflect its microbial degradability. Our objectives were to determine how the DOM decay patterns differ between brown-water and clearwater river and how these further regulate the potential greenhouse gas production (carbon dioxide, CO₂ and methane, CH₄) in these waters.

We collected water samples during two sampling occasions (June and October 2018) from two pristine subarctic rivers in Finnish Lapland and conducted 21-day incubation studies to follow the changes in the concentration and molecular composition of DOM, as well as the changes in the CO₂ and CH₄ concentrations. The molecular characterization of DOM was carried out using electrospray ionization (ESI) coupled to high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS).

Both rivers acted as a source of CO₂ and CH₄. Our preliminary results show that river water surrounded by peatlands contained a higher number of compounds such as condensed aromatic structures and lignin-like molecules, which led to slower decomposition rates compared to DOM in clearwater river. Overall, the decomposition of DOM was higher during spring flow than during fall due to recently released fresh DOM in the water.

How to cite: Saarela, T., Jäntti, H., Ohashi, M., Ide, J., Berninger, F., Ojala, A., and Pumpanen, J.: The molecular composition of dissolved organic matter (DOM) and its effects on the greenhouse gas production in pristine subarctic rivers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7936, https://doi.org/10.5194/egusphere-egu2020-7936, 2020.

Dissolved organic matter (DOM) plays important roles in aquatic ecosystems but can interfere with drinking water production. However, its highly complex composition and chemical diversity makes it difficult to understand molecular reactivity in natural systems. Here we used ultra-high resolution mass spectrometry (FT-ICR-MS) and data from two independent studies (a lake monitoring and a photo-irradiation experiment) to disentangle DOM reactivity based on photochemical and microbial induced transformations.

Monitoring in Germany’ largest drinking water reservoir (Rappbode reservoir, Harz Mountains) was conducted over one year on seven dates using water from nine depths. Water chemistry and limnological parameters, including chlorophyll a (chl a) concentration were determined. Stratification of the lake allowed to determine depths and periods, where an accumulation of chl a corresponded with an accumulation of DOM compounds. Chl a served as a surrogate for microbially (i.e. primary) produced DOM. In addition, we used data from a photodegradation experiment using river water from a catchment with similar land use (tributary to Muldenberg reservoir in the Ore Mountains, Germany). The water had been irradiated for 6 days in triplicates using natural sunlight. Thirteen time points had been sampled and used to determine the photochemical reactivity of DOM compounds.

We used robust rank correlations to establish relationships between predictor (chl a concentration or cumulated sunlight irradiation) and response variables (normalized FT-ICR mass peak intensities) for each dataset. Combining the resulting data further allowed for an orthogonal classification of 1277 molecular formulas, which were present in all samples. Using this approach, we could identify 11 reactivity groups and attributed chemical properties to these groups based on molecular information. Photodegradation was observed for high molecular weight molecules - similar to microbial degradation - whereas photo products were aliphatic and oxygen rich. We found that in the lake studied, DOM turnover was dominated by photochemical processes. Exclusively microbial products were comparably low in number and of small molecular weight compounds.

Based on the molecular-property-reactivity-relationships, we trained a random forest model and predicted the molecular reactivity for the remainder of molecular formulas, for which insufficient data were initially available.

The approach presented here offers an expandable tool to integrate reactivity of DOM from specific environments and link it to its molecular properties and chemistry. This will lead to enhanced understanding of the ecological function and biogeochemical cycling of DOM.

How to cite: Lechtenfeld, O., Wentzky, V., Rinke, K., Kamjunke, N., von Tümpling, W., Wilske, C., Friese, K., Böhrer, B., Reemtsma, T., and Herzsprung, P.: Shedding light into the forest: improved understanding of DOM processing in freshwater using complementary experimental and machine learning approaches, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7437, https://doi.org/10.5194/egusphere-egu2020-7437, 2020.

Little is known about dissolved organic matter (DOM) in thermal springs. To fill this gap, this study describes the quantity, optical and molecular properties of dissolved organic matter (DOM) in two geothermal springs located in the East African rift valley a region extremely rich in geothermal phenomena such as hot springs, fumaroles, geysers and spouting springs and solfataras. The two sampled hot springs are located at the south of Elmentatia soda-saline lake and at the Ol Njorowa gorge. Results evidenced the abundance of reduced, saturated, little aromatic compounds that might reflect DOM altered by high temperature and pressure. Beside that, the two hots springs showed very clear distinctive signatures. At Ol Njorowa the most abundant molecules are oxygen poor and sulphur bearing like molecules which might reflect abiotic sulfurization from geo fluids rich in H₂S. In contrast Elmentatia hot spring is characterized by abundant nitrogen bearing aliphatic and protein-like molecules probably mirroring perfusion of geo-fluids through organic rich sediments located below the Elmentaita lake bottom.

How to cite: Butturini, A., Herzsprung, P., Lechtenfeld, O., Venturi, S., Amalfitano, S., Olaka, L., Pacini, N., Harper, D., Tassi, F., and Fazi, S.: Dissolved organic matter in two thermal springs of East African rift valley, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2586, https://doi.org/10.5194/egusphere-egu2020-2586, 2020.

Florida Bay is subtropical embayment characterized by dense Thalassia testudinum seagrass meadows, the prevalence of carbonate-rich sediments, and relatively long residence times (~1 yr). Florida Bay seagrass meadows store appreciable quantities of allochthonous and autochthonous organic matter (OM) as so-called ‘blue carbon’, the fate of which is therefore tied to that of the carbonate minerals it is bound to.  Dissolved organic carbon (DOC) concentrations are also relatively high (~7-12 mg/L), despite potential photo-oxidative loss in this shallow and long residence time system, as well as low internal DOC production due to the ecosystem’s documented oligotrophy.  These carbonate sediments can dissolve through net acid production via sediment heterotrophic processes as well as sulfide oxidation, processes which may be enhanced via O₂ pumping through seagrass roots.  

This study investigated the impact of carbonate dissolution on the release of sediment-associated OM to surface waters, and the relative contribution of this process to surface water DOC quantity and quality.  We undertook a three-part experimental approach, with analyses including EEMs, δ13C-DOC, and FT-ICR-MS, to better understand the sources and fate of DOC in Florida Bay. 1) We conducted a spatial survey of surface waters, pore waters, and acid-leachable (representing the ‘carbonate-bound’ OM fraction) sedimentary OM.  2)  We conducted a DOM photodegradation study using two potential source surface waters, from a main tributary (Taylor Slough) and a central mangrove island.  3) We conducted benthic flux experiments using intact sediment cores facilitating direct measurements of the quality and quantity of DOC release from sediments. The flux information was placed into the context of sediment dissolution rates, estimated from coinciding determinations of alkalinity and inorganic carbon.

While analyses are ongoing, our initial results indicate a high degree of similarity between the fluorescence signature (PARAFAC components and fluorescence indices) of acid-leachable sedimentary OM, and that of DOC in pore water and surface water throughout Florida Bay.  Taken together, our study points to sediment dissolution as an important, yet understudied, process affecting organic carbon cycling in carbonate-dominated systems like Florida Bay.

How to cite: Zeller, M., Van Dam, B., Lopes, C., Smyth, A., Osburn, C., and Kominoski, J.: Is carbonate sediment dissolution a significant source of dissolved organic matter to Florida Bay?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-812, https://doi.org/10.5194/egusphere-egu2020-812, 2020.

Natural organic matter (NOM) played an important role in the riverine and global carbon cycle. In order to evaluate the impact of river discharge and anthropogenic activities on the spatio-temporal variability of NOM content and sources in Lancang River, China, a comprehensive study was conducted in two years from the head to the leave-boundary section. As results, the DOC value ranged among 0.91-2.80 mg/L, with sharp decrease in the middle reaches and downstream. While the SOC value significantly enhanced along the water flow, varied from 0.06% to 3.54%. The isotopic composition of organic carbon (δ13C) suggested that predominant contribution of NOM is C3 plants in the upper reach, algae and soil organic matter in the middle reach, and aquatic plants in the downstream. EEM-PARAFAC results proved that NOM in Lancang River is mainly terrestrial organic carbon, while in situ microbial transformed NOM is very low. Moreover, the sharp increase of dissolved CO2 concentration in the lower reaches confirmed the strong respiration of microorganisms due to the higher DO and water temperature, thus resulted in the significantly different fluctuations of DOC and SOC.

How to cite: Wang, T.: Spatio-temporal variability of natural organic matter in Lancang River: concentration, sources and destination, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3186, https://doi.org/10.5194/egusphere-egu2020-3186, 2020.

Sediments represent a large reservoir of nutrients and natural organic matter (NOM) from diverse inputs in various proportions. Indeed, sedimentary OM is derived from bacteria or plankton formed in situ, but also receives allochthonous OM from the upstream catchment. Soil OM is a representative allochthonous OM source and it is easily transported into the rivers and ends up in sediments through hydrological processes (Briand et al., 2015; van der Meij et al., 2018). Sediments are also a reactive compartment where diagenetic processes occur inducing changes.  Among the diagenetic processes, biodegradation plays a key role as it is one of the main processes causing changes in the amount, composition and properties of OM in sediment (Arndt et al., 2013; Guenet et al., 2014).

In this study, we decided to examine the molecular changes under early diagenesis on sedimentary OM.  In this context, we designed a controlled degradation experiment at laboratory scale using organic-rich sediments artificially composed of two contrasting OM end-members (i.e., soil and algae) at known mixing ratios. The incubations were performed under oxic and anoxic conditions in the dark at 25°C for 60 days. The sediment samples were collected on day 0 (e.g., the day where the samples were inoculated) and day 60 and were directly analyzed by laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (LDI FT-ICR MS). LDI permits molecular analysis of the sediment to be achieved without any sample pre-treatment step and consequently limits the inherent problems related to the extraction (Aubriet and Carré, 2019).

The results allowed us, first, to identify (i) which molecules or groups of molecules are the most affected by the biodegradation processes and then, to examine (ii) the potential effect of the absence and/or occurrence of oxygen and (iii) the potential effect of the OM sources on the molecular composition during biodegradation. Finally, this study provides insights into the responding features of sedimentary OM to one of the main biogeochemical processes.

Arndt, S., Jørgensen, B.B., LaRowe, D.E., Middelburg, J.J., Pancost, R.D., Regnier, P., 2013. Quantifying the degradation of organic matter in marine sediments: A review and synthesis. Earth-Science Rev. 123, 53–86. https://doi.org/10.1016/J.EARSCIREV.2013.02.008

Aubriet, F., Carré, V., 2019. Fourier transform ion cyclotron resonance mass spectrometry and laser: A versatile tool. Fundam. Appl. Fourier Transform Mass Spectrom. 281–322. https://doi.org/10.1016/B978-0-12-814013-0.00010-7

Briand, M.J., Bonnet, X., Goiran, C., Guillou, G., Letourneur, Y., 2015. Major Sources of Organic Matter in a Complex Coral Reef Lagoon: Identification from Isotopic Signatures (δ(13)C and δ(15)N). PLoS One 10, e0131555. https://doi.org/10.1371/journal.pone.0131555

Guenet, B., Danger, M., Harrault, L., Allard, B., Jauset-Alcala, M., Bardoux, G., Benest, D., Abbadie, L., Lacroix, G., 2014. Fast mineralization of land-born C in inland waters: first experimental evidences of aquatic priming effect. Hydrobiologia 721, 35–44. https://doi.org/10.1007/s10750-013-1635-1

van der Meij, W.M., Temme, A.J.A.M., Lin, H.S., Gerke, H.H., Sommer, M., 2018. On the role of hydrologic processes in soil and landscape evolution modeling: concepts, complications and partial solutions. Earth-Science Rev. https://doi.org/10.1016/j.earscirev.2018.09.001

How to cite: Derrien, M., Hur, J., and Kim, S.: How do early diagenetic processes affect the molecular composition of the sedimentary organic matter?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6552, https://doi.org/10.5194/egusphere-egu2020-6552, 2020.

Photochemical processing is a major transformation pathway for allochthonous and autochthonous dissolved organic matter (DOM). DOM consists of thousands or even millions of different molecules and the isomer-resolved identification molecular structures is still far from any analytical realization. The highest analytical resolution of DOM can be achieved on a molecular mass basis via Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). With this technique, the molecular elemental compositions of thousands of DOM components can be assessed, given that they are extractable from water (via e.g. solid phase extraction, SPE-DOM) and ionizable (e.g. via electrospray ionization).

Increasing levels of DOC in drinking water reservoirs pose serious challenges for drinking water processing. Photochemical processes potentially influence the DOM quality in the reservoir water. The photo degradation and / or the photo production of DOM components in surface freshwater as function of cumulated radiation was rarely investigated. In order to fill this gap we performed an irradiation experiment with water from a shaded forest stream flowing into a large reservoir (Muldenberg, Germany). DOC concentration, UV absorption, excitation-emission-matrices (EEMs) including calculated PARAFAC components and fluorescence indices, and FT-ICR MS derived molecular formulas of SPE-DOM were recorded at 13 different time points. The cumulated radiation was recorded during six days of solar irradiation (sunny days in August at 50.401847 deg. latitude and 12.380528 deg. longitude). Changes in relative peak intensity of DOM components as function of cumulated radiation were evaluated both by Spearman`s rank correlation and linear regression.

We found components with different types of photo reaction behavior. Relative aliphatic components like C₉H₁₂O₅ were identified as photo products showing a monotonous mass peak intensity increase with irradiation time. Highly unsaturated and oxygen-rich components like C₁₅H₆O₈ showed a more or less monotonous intensity decrease indicating photo degradation. Many similar components were positively correlated to the humic-like fluorescence intensity and the humification index (HIX). The strong degradation of these components can explain the high loss of fluorescence intensity and the drop of the HIX in our experiment. As a result of the high temporal resolution in our experiment (i.e. intensity change as function of cumulated irradiation) we found another type of photo reaction. Components like C₁₅H₁₆O₈ showed first increasing and then decreasing intensity indicating the formation of intermediate products.

In general, the river DOM from the forested catchment area showed high potential for photochemical transformations which probably occur in the sunlight exposed predam of the drinking water reservoir.

How to cite: Herzsprung, P., Wilske, C., von Tümpling, W., Kamjunke, N., and Lechtenfeld, O. J.: Resolution of photo chemically induced changes of dissolved organic matter as function of cumulated radiation in a sample of a humic-rich and forested stream, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5145, https://doi.org/10.5194/egusphere-egu2020-5145, 2020.

Information about hydrocarbons (HCs) distribution in components of geological environment (including aromatic (Ar) compounds) allows to estimate relative amounts of both natural and anthropogenic components and reveal sources of contamination. HCs are widely spread in lithosphere and create stable geochemical background. Variations in their composition attest to the specificity of initial organic matter, conditions of its accumulation and transformation.
The studied samples of soils and surface bottom sediments were collected during the research expedition in July, 2019 (supported by RFBR №18-54-20001 and NFR №280724). On the Norwegian coast of the Barents Sea the area of study included: salt marshes of Tana and Varanger fjords, littoral zone of rocky shores around Kiberg. In the Russian part of the Barents Sea samples were taken from the shallow water area of the Eastern coast of the Kola Bay. All samples were taken along the sublittoral – littoral – supralittoral transects appropriate for a detailed study of the organic matter (OM) spatial distribution. Study of the group composition of ArHCs in the extractable part of soil and sedimentary OM were performed using spectrofluorimetry.
 The method is based on the ability of ArHCs to fluoresce under the influence of ultraviolet emitting in narrow spectral ranges determined by their molecular structure. This allows us to characterize the nature of ArHCs and determine possible sources of their input.
The spectrum characteristics of samples from intertidal zone of the Tana fjord salt marshes reflect the input of fresh unoxidized petroleum products such as diesel fuels and engine oils. The significant increase of ArHCs fluorescence intensity in surface sediments may testify to recent pollution accidents.
The spectrum traditionally associated with the estuarine-delta and lacustrine and swampy facies and characteristic for the post-sedimentation and early diagenetic stage of OM transformation was detected in samples from the salt marshes of Varanger fjord. 
ArHCs of mixed origin (natural and anthropogenic) are identified in samples from the littoral zone of rocky shores of Kiberg. The spectral data of littoral sediments are typical for the polluted areas with high input of petroleum products. The specific maxima in the long wavelength region of spectrum that is characteristic for the high molecular weight aromatic compounds from the land plants is also detected in these samples. 
Spectral characteristics of ArHCs of bottom sediments and soils collected from the shallow water area of the Russian part of the Barents Sea point to the presence of both low molecular weight benzene HCs (high volatile components of flammable liquids) and high molecular weight compounds (oil fuel, gas oil). The detailed study of these anthropogenic HC components seems to be very important given the fact of their detection in all littoral samples.
The further detailed study of the molecular markers and biomarkers (n-alkanes, isoprenoids, cyclanes, terpanes, PAHs) will increase our knowledge about HC sources, efficiency of their microbial and chemical degradation, allow to estimate human impacts on the environment of the region and draw up the regional “geochemical passport”.

How to cite: Kursheva, A., Morgunova, I., Petrova, V., Batova, G., Litvinenko, I., Granovitch, A., and Renaud, P.: Aromatic hydrocarbons in components of geological environment of the Norwegian and Russian parts of coastal zone of the Barents Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7519, https://doi.org/10.5194/egusphere-egu2020-7519, 2020.

Ireland has a far greater number of regulatory exceedances for trihalomethanes (THMs) in public water supplies than the next highest European Union member state. In Ireland, 82% of public water supplies originate from surface water catchments which require disinfection to inactivate pathogens and prevent the spread of waterborne diseases. Since the 1970s, it has been known that the use of chlorine for disinfection leads to the formation of potentially harmful disinfection byproducts (DBPs) of which some are suspected carcinogens. THMs are one prominent class of at least 700 potentially harmful disinfection byproducts (DBPs) produced after chlorination of dissolved organic matter (DOM) present in source water which is not removed prior to disinfection.

We introduce a new research project, funded by the Irish Environmental Protection Agency entitled PRODOM: PRoactive Optical monitoring of catchment Dissolved Organic Matter for drinking water source protection. The overall aim of the research is to develop an integrated catchment-level understanding of the spatiotemporal dynamics of DOM precursors and associated DBP formation risk. The project will explore the relationship between optically-active DOM precursors and laboratory formation potentials for key DBPs including emerging classes of potentially more harmful nitrogenous DBPs. Through high-resolution spatial sampling we will develop geospatial DBP formation risk maps and identify risk-driving point and diffuse precursor sources. We will evaluate the potential of state-of-the-art UV fluorescence sensor technology to act as an early warning tool for proactive management of source water at sub-catchment scale. Using high-frequency time series monitoring of fluorescent precursors, we will identify high-risk periods in the catchment hydrograph and evaluate critical precursor sources and pathways to inform a series of catchment management measures designed to reduce DBP formation risk. 

How to cite: Weatherill, J., Fernandez-Pascual, E., O'Dwyer, J., Gilchrist, E., Harrison, S., Goslan, E., Khamis, K., and O’Driscoll, C.: Proactive optical monitoring of catchment dissolved organic matter for drinking water source protection, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9932, https://doi.org/10.5194/egusphere-egu2020-9932, 2020.

Forested watersheds are a major source of drinking water for more than two thirds of Canadians. However, drinking water security is increasingly pressured by the combination of higher demands resulting from population growth and industrial development and climate change-exacerbated landscape disturbances (e.g., wildfires, hurricanes). These may lead to deteriorated, more variable source water quality that can challenge treatment operations beyond their response capacities and have the potential to cause service disruptions. The character and concentration of dissolved organic matter (DOM), as well their shifts in response to seasonal and event-based changes in streamflow, make DOM a key driver of drinking water treatment infrastructure needs and operational challenges. As part of the forWater NSERC Network, which seeks to evaluate the impacts of pre-emptive forest management approaches on drinking water treatability in Canada, the objective of this study is to characterize differences in DOM concentrations and composition in headwater streams in different forested regions, including both undisturbed and disturbed catchments, and to evaluate the implications for drinking water treatability.

Our pan-Canadian study was conducted using existing long-term research sites, which span an area from 48.5° to 63° N between Canada’s east and west coasts, and represent six major forested ecozones. These ecozones exhibit significant differences in soils, vegetation, hydrological systems, and consequently surface water chemistry. At each research site, 2 to 6 headwater streams were sampled several times in 2019 and 2020 to characterize seasonal and spatial variations in water chemistry. Where relevant, both disturbed (harvested or burned) and undisturbed catchments were sampled.

The spatial and temporal variability in DOM characteristics, including the effects of disturbances, were evaluated, and the links between DOM characteristics and drinking water treatability were explored. Distinct regional differences in the concentrations of major ions, dissolved organic carbon and nutrients were observed. Variations in DOM composition, as assessed through UV-vis absorbance and excitation-emission matrix (EEM) fluorescence spectroscopy, Fourier-transform ion cyclotron mass spectrometry (FT-ICR-MS), and asymmetric flow field-flow fractionation (AF4), were also detected. To characterize drinking water treatability, relative implications to coagulant demand, membrane fouling, and distribution system stability were evaluated. The true disinfection by-product formation potential for trihalomethanes and haloacetic acids after complete oxidation resulting from chlorination was also assessed. Collectively, the results of this study underscore the importance of better understanding and anticipating natural variations in stream DOM as well as the impacts of landscape disturbance to ensure the uninterrupted supply of safe drinking water.

How to cite: Orlova, J., Olefeldt, D., Amiri, F., Bourgeois, A., Buttle, J., Cherlet, E., Emelko, M., Floyd, B., Foster, D., Hutchins, R., Jamieson, R., Johnson, M., McSorley, H., Qi, N., Silins, U., Tank, S., Thompson, L., and Williams, C.: Regional variability in stream dissolved organic matter characteristics across forested regions of Canada, and its implications for drinking water treatability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12327, https://doi.org/10.5194/egusphere-egu2020-12327, 2020.

This study investigates the efficacy of microbial (bioremediation) materials by exploring the kinetics of the removal of pollutants in polluted surface water bodies representing real world conditions. The experiments were performed in three sets for three commercially available microbial materials viz. Enbiozyme Aqua-S (EAS), Bacta cult (BC) and NatureVel-WWB (NVWWB). All the experiments were carried out under controlled conditions of pH (7.0 ±0.5), dissolved oxygen (4±0.5 mg/l), Mix Liquor Suspended Solid (2500-3000 mg/l) and temperature (25 ±5 ºC). For bench scale studies, the laboratory reactors were used for the degradation experiments at variable hydraulic retention time (HRTs) ranges from 6-72 h along with control (without addition of biomaterial) reactor for each study.

The samples were collected from a nearby polluted tributary (Solani) of River Ganges. During remediation experiments, the raw and treated samples were characterized for Biochemical Oxygen Demand (BOD), Chemical oxygen demand (COD), Total Suspended Solid (TSS), Colour, Total & Fecal Coliform (TC and FC), Total nitrogen (TN) and Total phosphates. Adenosine triphosphate (ATP) quantification for the evaluation of microbial biomass was performed by using luminometer (ATP Analyzer), which involves the determination of intracellular (inactive ATP) and extracellular (active ATP) ATPs. Among the mentioned biomaterials, the Bacta cult (BC) was examined higher microbial viability as compared to those of Enbiozyme Aqua-S (EAS) and NatureVel-WWB (NVWWB). Furthermore, this biomaterial (BC) was also found to be lower percentage of Biomass Stress Index (BSI).

The maximum pollutant removal  in Control after 72 h of treatment for BOD-77 %, COD-71%, TSS-71 %, Colour- 64 % ,TN-55 % and TP-15 %  respectively while  using BC  increased with a percentage of 12% for BOD, 15% for COD, 15% for TSS, 25% for Colour, 10% for TN and 1% for TP. A remarkable degradation rate of organic pollutants was examined up to 24 h, 24 h and 48 h for BC, NVWWB and EAS, respectively. The nutrient (TP and TN) removal rate was observed to be 24 h for BC and NVWWB while 36 h for EAS. The study concludes that the Bacta Cult (BC) is efficient in removing the pollutants except TC and FC under optimum conditions. Moreover, the performance of biomaterial NVWWB was found to be fairly good, whereas, the efficiency of EAS was insignificant under the same controlled conditions. [HJ1]  The Biomass Stress Index (BSI) was calculated to be < 30 % BC and NVWWB, whereas, it was > 50 % for EAS.

The present investigation will help in selective utilization of bioremediation materials for their application in real world and synthesis of robust and frugal bioremediation material. It will also lead to addition to the existing knowledge base on bioremediation will enable and promote further research in this area at various levels. Furthermore, ATP analysis (microbial viability analysis) might play an important role in field screening and monitoring of bio-remediation based efforts.

Keywords: Commercial bio-materials, bioremediation, pollutants, surface water, bio-preparation.

How to cite: Simon, M. and Joshi, H.: Performance appraisal of bioremediation materials for polluted surface water treatment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13998, https://doi.org/10.5194/egusphere-egu2020-13998, 2020.

Natural organic matter (NOM) is commonly contained in surface water bodies, including those that serve as sources for drinking water treatment plants (DWTPs). The composition of NOM may be very diverse, and can be further divided into humic substances (HS) and algal organic matter (AOM). Recently, increasing content of AOM is becoming a challenge for many DWTPs, owing to the global proliferation of cyanobacteria and algae. This phenomenon is most often attributed to climate changes and enhanced input of nutrients to aquatic environments.

We investigated the evolution of NOM character in a selected water reservoir (located in the Vysočina Region, Czech Republic), that serves as an irreplaceable drinking water source, for a period of 12 years (starting in the year 2006). Besides the quantitation of NOM, it was divided into fractions according to its character, i.e., VHA (very hydrophobic acids), SHA (slightly hydrophobic acids), CHA (charged hydrophilics), and NEU (neutral hydrophilics). Within the observed timescale, the relative proportion of VHA and SHA (that both belong to HS) decreased, while CHA and NEU (associated to AOM) significantly increased and comprised majority since 2016. Additionally, seasonal variations were also observed. This points out to the rising occurrence of phytoplankton in the reservoir, while its seasonal dynamic must not be neglected.

To elucidate the dependence of AOM properties on the species and the growth phase, we investigated the composition of AOM produced by green alga, diatom, and cyanobacteria. They were grown under laboratory conditions and harvested at different growth phases; extracellular and cellular AOM (EOM and COM, resp.) was investigated separately. The distinct AOM fractions were analysed in terms of peptide-protein and non-proteinaceous content, hydrophilicity/hydrophobicity, specific UV absorbance (SUVA), and molecular weights (MW). In general, both EOM and COM of all the species was mainly hydrophilic and had low SUVA values; however, the proportions of peptides-proteins and non-proteinaceous fraction and MW distribution greatly differed. For example, EOM and COM of the cyanobacteria (Microcystis aeruginosa and Merismopedia tenuissima) contained larger portions of peptides-proteins and had wider MW distributions than the green alga (Chlamydomonas geitleri) or the diatom (Fragilaria crotonensis). Changes were observed also along their growth phase.

Additionally, we studied coagulation behaviour of the distinct NOM fractions (i.e., HS versus AOM, and also AOM peptides-proteins and non-proteinaceous fraction separately), since coagulation is an essential treatment steps at most DWTPs supplied by surface waters. It has shown that the non-proteinaceous fraction (corresponding to NEU) is the most difficult to coagulate (max. removal efficiency of 25%), while the removal of AOM peptides-proteins (corresponding to CHA) reached up to approx. 80%. HS were removed with 65% efficiency. It is of note that substantial optimization of coagulation conditions (especially the dose of coagulant and coagulation pH) was a nuisance, and that the coagulation optimums differed between the NOM fractions.

Thus, our results imply that continuous characterization of NOM is essential for an effective control over the processes at DWTPs.

How to cite: Cermakova, L., Novotna, K., Naceradska, J., and Pivokonsky, M.: Causes and consequences of the variations in natural organic matter properties, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14159, https://doi.org/10.5194/egusphere-egu2020-14159, 2020.

Chromophoric dissolved organic matter (CDOM) is an important optically active substance that might be used as an indicator of water quality. The study of CDOM characteristic and source identification in reservoirs is of great importance in decision- making for water quality protection.
Granting reservoir Beijing was selected as the case study, which was the drinking water source for Beijing, while it was ceased to supply water in 1997 because of water pollution. The water samples were collected from 37 sites in the reservoir. Three dimensional excitation-emission matrix (3DEEM) spectra combined with  parallel factor analysis (PARAFAC) was applied to investigate the fluorescence characteristics and sources of chromophoric dissolved organic matter (CDOM) in Guanting Reservoir. The results showed that: (1) four kinds of chromophoric dissolved organic matter (CDOM) was identified, which were the tryptophan-like component (C1) autochthonously, the humic-like component (C2) in the ultraviolet zone, the tryptophan-like component (C3) caused by photolysis reaction and the humic-like component (C4) in the visible light zone. (2) The tryptophan-like was the dominant fraction of CDOM in Guanting Reservoir. For the four component, C1 and C3 belong to humic-like; C2 and C4 belong to protein-like. The humic-like increases with the river flowing into the reservoir. the fluorescence intensity of humic-like and protein-like both was the highest in July. (3) the humic-like C2 and C4 were significantly correlated which might indicate they originated from the same source, while the protein-like C1 and C3 didn’t show the correlation that might indicate their source is different. (4)Fluorescence index(FI), biological index (BIX) and humification index (HIX) were also used to identify the source of different components. The FI ranged from 1.8 to 1.95 indicated that CDOM principally originated from microbially derived fulvic acids. The BIX ranged from 0.9 to 1.1 indicated that CDOM was strong autochthonous component and from biological or aquatic bacterial origin. The HIX ranged 1.3 to 3.5 indicated that CDOM was weak humic characteristic and important recent autochthonous component.

How to cite: Bai, Y., Ding, A., and Zhang, S.: Characterizing chromophoric dissolved organic matter in Guanting Reservoir Beijing using excitation-emission matrix fluorescence and parallel factor analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17510, https://doi.org/10.5194/egusphere-egu2020-17510, 2020.

Intensive monitoring data from the Danish National Monitoring programme (NOVANA) from 24 smaller catchments (mean: 14 km²) was used in a two layer cross-validation to establish a model for the annual diffuse phosphorus (P) flow-weighted concentration in Danish streams. A total of 196 monitoring years with data from automatic sampling (ISCO) of water from the 24 streams were used as a training dataset. Data in the training dataset covers the period 1994-2002.

Moreover, another dataset consisting of 108 agricultural mini-catchments with discrete water samples covering the period 1990-2017 was used as a control in the eight different georegions of Denmark. A total of four different models was established three models based on the intensive dataset and one model based on the larger dataset with discrete water sampling.

The best model established included eight explanatory parameters and explained 53 % of the variation in the annual flow-weighted total P concentrations in the training dataset. A validation of the four different models established showed that the best model has to be bias-corrected in some of the georegions. The result of the validation shows that the models generally overestimate the total P concentrations.   An overestimation of around 10-20% was to be expected as intensive automatic water sampling in streams has shown that the flow-weighted concentration of total P obtained from discrete sampling (monthly or fortnightly) is normally underestimated.

The validations of the three models based on intensive dataset showed an R-square between 0.08 and 0.12. The model based on the larger data with discrete samples had an R-square (0.29).

How to cite: Tornbjerg, H., Windolf, J., Thodsen, H., Kjeldgaard, A., Larsen, S. E., and Kronvang, B.: Modeling annual diffuse phosphorus concentrations in Danish mini-catchments , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18505, https://doi.org/10.5194/egusphere-egu2020-18505, 2020.

Oxygen dynamics in lakes and reservoirs are changing worldwide due to human activities. Changing hypolimnetic oxygen conditions will substantially alter carbon cycling in aquatic ecosystems, as oxygen dynamics near the sediment-water interface regulate whether carbon inputs will be buried, respired as carbon dioxide, or respired as methane. At the decadal scale, warming temperatures and increased nutrient loads are increasing the prevalence and duration of anoxia. Conversely, at the daily scale, mixing due to more powerful storms may periodically increase hypolimnetic oxygen availability. It remains unclear, however, how carbon quantity and quality will respond to these changes in oxygen at different time scales. Our team used unprecedented whole-ecosystem manipulations of hypolimnetic oxygen concentrations in a eutrophic reservoir to identify how changes in oxygen at different time scales (i.e., weeks to months) alter freshwater carbon processing, burial, and greenhouse gas emissions. Against the backdrop of multiple-week shifts between oxic and anoxic conditions in the bottom waters of the experimental reservoir over multiple years, we observed that the dominant scale of variability in dissolved organic matter (DOM) concentrations was predominantly at the daily scale in the summer and monthly scale in the winter. At the monthly time scale, dissolved oxygen concentrations controlled DOM; at the daily time scale, water temperature and photooxidation controlled DOM. Modeling and field results show that intermittent week-long oxic conditions mineralized “legacy” carbon that had accumulated over years of sedimentation and changed the dominant terminal electron acceptor pathways used for mineralization on the daily scale. Building off of this work, future oxygenation experiments will examine the role of alternate electron acceptors in carbon release from sediments on the daily scale, the impact of carbon quality on carbon processing under varying oxygen conditions at the daily to week scale, and the effects of future oxygen scenarios on carbon cycling in lakes and reservoirs around the world on the annual to decadal scale.

How to cite: Carey, C., Hounshell, A., Howard, D., Lewis, A., McClure, R., Hammond, N., Lofton, M., Hanson, P., Little, J., Schreiber, M., and Birgand, F.: Dynamic carbon-oxygen interactions over minute to annual time scales in an experimentally-oxygenated reservoir, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22197, https://doi.org/10.5194/egusphere-egu2020-22197, 2020.

The phenomenon of increasing DOC levels in water systems over the last decades is confirmed by numerous studies (Driscoll et al., 2003; Stoddard et al., 1999; Skjelkvale et al., 2001a; Montein et al., 2007; Evans et al., 2008; Clark et al., 2013).  The increasing of organic matter content in lake waters is being also observed for the totality of lakes in the Kola North, more markedly in forest and water-logged subregions. This conforms to the data reported by Skjelkvale et al. (2001a) which demonstrates the significant increase of DOC. Montein et al. (2007) explain the increased DOC levels by reduction in strong acid flow and return of water chemistry to its natural parameters of specifying organic matter concentrations in water.

Clark et al. (2013) demonstrated that natural humus substances are capable of producing strong organic acids and increase water acidity. It is known that DOC level has a direct relationship with water color. In analyzing long-term study data with regard to the group of 75 lakes (obtained during 1990-2010) DOC is increased year-over-year, but the color decreased.

More evident dependence the increasing the content of DOC on reduced color from year to year (Fig.). The following chemical processes developing in water can explain this phenomenon.

Figure.  The correlation between the change of DOC (ΔDOC) and color (ΔColor) - file  

The water color is predominantly determined by large molecules of humus acids which molecular weight >1000 Da. Macromolecular organic substances of humus type can be dissociated in water with formation of a free proton, as well as enter into reactions of decomposition (hydrolysis) and disproportionation with formation of low-molecular weight fragments. Its fragments also are dissociated of proton (see the diagram below). The above processes may be catalyzed by non-organic strong acids supplied from anthropogenic and natural sources. The diagram of the organic substances destruction of humus origin is given below, where R_i  means non-symmetrical fragments of a natural polymer, Х_iH - functional groups of organic substances of humus origin, and n - number of protons.

When strong acids get into a water environment humus acids are degraded into fractions.  It could be supposed that the organic matter structure undergoes changes in natural waters, as the fraction of high-molecular weight humus acids decrease. As a consequence of interaction between humus substances and protons the humic acids precipitate to form bottom sediments, whereas fulvic acids remain in water. Fulvic acids are characterized by lower molecular weights (from 500 to 2000 Da) and exert an insignificant effect on the water color. This phenomenon is well proved in a study published by Clark et al. (2013). However, to define more exactly this phenomenon, further experimental work is required.

Financing RSF 18-17-00184

How to cite: Moiseenko, T. and Dinu, M.: DOC trend in Arctic lakes as a response to air pollution reduction by Kola North Smelter, Russia (1980-2018): possible mechanisms of transformation of organic substances, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5941, https://doi.org/10.5194/egusphere-egu2020-5941, 2020.

Inland water process large amounts of dissolved organic matter (DOM), representing an important component in the global carbon cycle. Locally, DOM has an important ecological and biogeochemical role that may vary according to its quality (e.g. composition). Land use, season and hydrologic regime are some factors that possibly will influence the changes in DOM composition. State-of-the art technique to study the molecular chemical composition of DOM is Fourier transform ion cyclotron resonance mass spectrometry (FT ICR MS). The analysis of changes in DOM quality by FT ICR MS allows conclusions to be drawn about the sources and mobilization processes of the organic material. In this study we investigate the changes in DOM quality over a period of 1.5 year in a small forested catchment composed of two different zones: wetland (zone A) and steep slope areas (zone B). The catchment is located in the National Park Bayerischer Wald in Southern Germany. This offers a natural environment unaffected by direct anthropogenic influence. Therefore, only indirect anthropogenic effects and natural vegetation disturbances and possible interactions between them can affect DOM dynamics. Monthly samples were taken along the rivers (1^st and 2^nd order) from September 2018-November 2018 and from April 2019-November 2019 with a total of 124 samples. The samples were analyzed by FT ICR MS, total organic carbon analyzer and UV/VIS spectrometer. Our results showed that the concentration of dissolved organic carbon between the sampling points is similar, but differs over the year at normal discharge conditions. FT ICR MS analysis indicated that the main molecular composition of DOM was CHO (38-47%), with the majority of the composition consisting of highly unsaturated compounds. Conversely, samples in zone A had more aliphatic compounds and nitrogen formulas than the ones sampled in zone B during the year. UV/VIS data also indicated that DOM is more aromatic in the zone B. The results suggest that DOM coming mainly from ground water is the dominant pool of organic matter in the wetland during the year, while in the steep zone a contribution from fresh-plant derived DOM is expected. We also found predominantly low averaged molecular weight DOM in summer in the catchment, suggesting that biological activity plays an important role during this season in DOM quality. We conclude that understanding the dynamic and mobilization mechanisms of DOM in catchments with low human impact are important for the conceptual understanding of natural DOM regulation mechanisms.

How to cite: da Silva, M. P., Reemtsma, T., Blaurock, K., Beudert, B., and Lechtenfeld, O.: Use of FT ICR MS to characterize seasonal and spatial variability of dissolved organic matter in a small forested catchment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19822, https://doi.org/10.5194/egusphere-egu2020-19822, 2020.

Daily monitoring over a period of one year in Lake Taihu, China, included chlorophyll a (Chl-a) and nutrient measurements, determining the taxonomic composition of the phytoplankton community and various water column physicochemical parameters. Chl-a and nutrient concentrations showed strong circadian variations ‒ Chl-a rised during daylight hours, while ammonium and phosphate rised at night. Chl-a concentrations also showed strong seasonal variations, with one annual peak in spring and another from summer to autumn, dominated by Dolichospermum spp. and Microcystis spp. respectively. Temperature appeared to exert the most important effect in this species succession. A nutrient‒Chl-a balance calculation indicated that both nitrogen and phosphorus in the water column could be limiting factors for phytoplankton growth during bloom periods. Over two thirds of particulate nutrients was attributed to phytoplankton biomass during blooms. Daily (or weekly) monitoring data provided more precise description of water quality, capturing short-term peaks in phytoplankton biomass, and reduced risks of under- or overestimating trophic levels in lakes, which always happened when using monthly monitoring data.

How to cite: Zhu, M., Zhu, G., Paerl, H., Zhang, W., and Xu, H.: Dynamics of annual nutrinets and bloom-forming cyanobacteria, revealed by daily observation in a hyper-eutrophic lake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9515, https://doi.org/10.5194/egusphere-egu2020-9515, 2020.

During the last years fluorescence spectroscopy was developed to be a fast and inexpensive way for water quality measurement in various water systems to characterize natural and human influenced water bodies regarding organic matter and contamination. Analyzing samples in a timely manner is crucial to gain valid and reproducible excitation emission matrix (EEM) data, but often difficult, specifically in transnational projects. In this project the shift of fluorescence spectra and other parameters over time is evaluated. Ten different ground-, creek- and river water, as well as wastewater treatment plant effluent samples were stored for more than 20 days. EEM data, as well as high pressure liquid chromatography (HPLC) spectra data and chemical standard parameters like pH, ORP (oxidation/reduction potential), TOC, NH₄, NO₃, NO₂ and PO₄ were measured daily and correlated. With this dataset the sample and fluorescence spectra stability were evaluated. Different mathematical and statistical methods, including Parallel Factor Analysis (PARAFAC) as well as novel statistical approaches, were applied for assessment of EEM and HPLC spectra. This further enables the direct comparison of the included analysis methods.

How to cite: Zoboli, O., Peer, S., Saracevic, E., Tauber, J., Vybornova, A., Zessner, M., and Krampe, J.: Stability of fluorescence spectra of various water systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18872, https://doi.org/10.5194/egusphere-egu2020-18872, 2020.

Study of the molecular composition of the dispersed organic matter (OM) in bottom sediments of Lake Baikal was conducted (supported by RSF #19-17-00226). Sediments (11 gravity cores - 28 samples) were collected during research expeditions of the R/V “G.U. Vereschagin” (LIN SB RAS, Irkutsk) in 2016-2018.

Variations in composition and ratios of aliphatic and aromatic components reflect changes of OM sources. Most n-alkane profiles show the distinguishable predominance of terrigenous components C27-C31. The highest biodegradation degree and increased content of isoprenoids is detected near the Gorevoy cliff where the active oil discharge was observed. Biogenic hopanes (ββ-hopanes and hopenes) predominate in most samples and diagenetic type of distribution is identified only in sediments with oil inclusions. Steranes are the minor components with ethylcholestanes as the main peaks attesting to the input of land plants. Increased values of perylene and phenanthrene in polycyclic aromatic HCs composition indicate the mixed biogenic-petrogenic nature of OM of the studied Lake Baikal sediments, while the oily samples contain only trace amounts of perylene.

The branched 2,7-dimethyl alkanes (m/z 127) have been identified in mudstone samples from the Vendian Marna Formation from the Sayan-adjacent Biryusa area and in Permian and Upper Carboniferous coal-bearing rocks from superdeep well SV-27 (Vilui syneclise) [1]. Their precursors most likely are the analogues of branched methylenated acids detected in lipids of modern bacteria (9,10-methylene hexadecane, 9,10-methylene octadecane, and 11,12-methylene octadecane acids). Decarboxylation of the methylenated acids branched at the second and seventh carbon atoms during diagenesis and catagenesis should have resulted in 2,7-dimethyl alkanes that were detected in all immersed sediments of the southern, central and northern parts of Lake Baikal.

Trace amounts of the other poorly studied group of compounds – monoaromatic steroids (MAS) were identified in bottom sediments near the mud volcano Kedr in the southern part of the lake. These structures can be formed during diagenetic transformations of sediments at the contacts of OM with clays (catalyzers) together with the formation of regular steranes and diasteranes (C27-C29). They have been previously detected in apocatagenetic rocks of the East Siberian sedimentary basin (ultradeep hole SV-27 from the Middle Vilyui area of the Vilyui syneclise) [2]. The absence of the main fragmental ion m/z 253 in the analyzed samples points to the migration of methyl alternate from C-17 to C-23 alkyl-chain position and agrees with distribution of the similar structures (m/z 281, 309, 366) in rocks of the hole SV-27. The detected 17-desmethyl-23-methylmonoaromatic steroids appear and exist at high temperatures and pressures and are very thermodynamically stable.

Thus, the input of the OM of catagenetic maturity degree to the bottom sediments of Lake Baikal is likely associated with the deep fluid migration and mud volcanic breccia uplift to the surface.

References

[1] Kashirtsev V.A. et al., 2009. New homologous series of biomarker molecules from Vendian deposits of the Sayan-adjacent Biryusa area. Russian Geology and Geophysics 50, 541–545.

[2] Kashirtsev V.A. et al., 2016. New monoaromatic steroids in organic matter of the apocatagenesis zone. Doklady Earth Sciences 469, 815–818.

How to cite: Morgunova, I., Krylov, A., Semenov, P., Zemskaya, T., Khlystov, O., Petrova, V., Batova, G., Kursheva, A., and Litvinenko, I.: Specific hydrocarbon molecular markers in bottom sediments of Lake Baikal discharge zones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7427, https://doi.org/10.5194/egusphere-egu2020-7427, 2020.

Estuaries are key ecosystems from economical and ecological points of view. This is especially true for the Seine Estuary, its watershed representing 12% of the France area (78 600 km²) in which 30% of the French population, 40% of the industry and 25% of the agriculture are concentrated. Estuaries transfer material from the continent to the oceans, including organic matter (OM), for which they are highly reactive zones. Elucidating the estuarine OM dynamics remains challenging, due to (i) the high variability of environmental parameters, such as salinity, light penetration and tidal range, (ii) the intrinsic heterogeneity and molecular diversity of OM and (iii) the permanently changing nature of this material. Estuarine OM can originate from various sources (transported from rivers or coastal ocean or be produced within the estuary itself) with a different composition, and thus a different behaviour in the ecosystem.

The aim of this work was to better constrain the sources of OM in the Seine Estuary. In order to take into account the spatiotemporal variability of OM characteristics, water and sediment samples (10 cm-long cores) were collected all along the estuary, i.e. in the upstream, maximum turbidity and downstream zones, during 5 campaigns with different tidal intensities and river flows. Elemental (C, N) and isotopic composition (δ¹³C and δ¹⁵N) as well as lipid biomarkers were analyzed in both particulate (POM) and sediment OM. This allows comparing the bulk and molecular composition as well as sources of OM in the particulate and sediment pools.

Several lipid biomarkers (n-alkanes, fatty acids, n-alcohols, sterols/stanols, GDGTs) were investigated in this study, as they provide complementary information of the sources and degradation degree of OM. Lipids from terrigenous sources were predominant in all samples, even though the concentrations of these compounds as well as those of anthropogenic origin were shown to decrease towards the mouth of the Seine Estuary. In addition, significant differences in bulk and molecular composition were observed between the particulate and sediment pool, especially with a higher abundance of aquatic (i.e. algal/bacterial) vs. terrigenous lipids in POM than sediment OM. Last, bulk and molecular analyses both showed the strong seasonal and spatial variability (along the estuary and with depth) of OM composition in the water column and sediment, which has to be taken into account when investigating estuarine OM dynamics.

How to cite: Huguet, A., Thibault, A., Anquetil, C., and Derenne, S.: Tracing the sources of organic matter in the Seine Estuary (NW France) using bulk and molecular analyses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9939, https://doi.org/10.5194/egusphere-egu2020-9939, 2020.

Dissolved organic matter (DOM) in fresh groundwater is generally low in concentration compared to other fresh waters. However, the overall amount of groundwater DOM is huge, as there is 100 times more fresh groundwater than fresh surface water. To date, research on groundwater DOM has merely focused on specific threats to humans such as e.g. DOM and heavy metal complexations and DOM from hydrocarbon contamination. Only few studies targeted to understand DOM as energy source of groundwater food webs and the role of groundwater DOM in the global carbon cycle. While research on these two subjects in surface waters flourish, a comprehensive, large-scale study of groundwater is still missing. Since a major fraction of Earth’s microbial biomass is found in the subsurface, mainly in aquifers, this represents a major knowledge gap. Moreover, researchers found that groundwater DOM concentrations worldwide increase alarmingly. Here, for the first time, we examine DOM properties and heterogeneity in a large-scale approach with regards to aquifer characteristics and physical-chemical as well as microbial features. We hypothesize that groundwater DOM quality shows high diversity and plays an important, yet complex role in these ecosystems, where bioavailability is influenced by intrinsic molecular properties, as well as environmental conditions.

We analyzed 1000 water samples from 100 groundwater bodies all over Austria with regards to their DOM quantity, quality and bacterial abundance (BA). From fluorescence excitation-emission-matrices (EEMs) we derived indices and components to describe DOM quality. Next, we explored this data with principal component analysis, where we used convex-hull areas to estimate the heterogeneity of DOM composition within the groundwater bodies. In parallel, the similarity of DOM quality was evaluated with self-organizing maps on EEMs to test if we captured the heterogeneity of the data set sufficiently with the previous analysis. DOM quantity and quality was then related to BA and physical-chemical parameters.

Our results show that water from fractured and karstic aquifers exhibit significantly higher terrestrial DOM origin and less degraded DOM than porous aquifers. This result can be explained by abiotic factors such as adsorption of large, aromatic compounds, as well as biological factors, specifically, larger surface areas for biofilm development in porous aquifers. The latter is supported by our observation that porous aquifers showed higher BA values. Remarkably, we found that BA was related to different DOM quality in each aquifer type: In porous aquifers BA was related to large, aromatic DOM molecules indicating that these are important for bacterial growth, while in fractured and karstic aquifers BA was related to fulvics and highly degraded humic compounds. Bacterial growth and degradation of complex DOM might be limited by low retention times in some of these aquifers.  Also, we found that groundwater bodies located in river valleys display high heterogeneity in DOM quality spanning across the whole DOM compositional diversity found in this study. This finding could either be explained by surface water infiltration in some parts and younger groundwater or the fact that river valleys are main settlement areas.

How to cite: Harjung, A., Schweichhart, J., Rasch, G., and Griebler, C.: Large-scale study on groundwater dissolved organic matter reveals strong heterogeneity and a complex microbial footprint, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16308, https://doi.org/10.5194/egusphere-egu2020-16308, 2020.

The temporal dynamics of nutrient cycles and the remineralization of micropollutants in given stream or river sections are driven by a complex interplay of hydraulic, climatic and ecological processes which are difficult to quantify and to predict. Typically, we use either e.g. water levels or velocity, radiation input, oxygen availability, water and air temperatures, hyporheic exchange or the activity of auto- and heterotroph organisms alone or in combination to explain observed rates of substance cycling. To improve the predictability of occurring nutrient cycles and biomass growth we selected seven river reaches (1.5 -3.3 km) throughout the Mosel-region in western Germany which are located down stream of sewage water treatment plant effluents. Over a time span of four months we carried out about 10 longitudinal snapshot sampling campaigns at each of the river sections. We sampled for nutrients (C, N, P) and selected pharmaceutical products as well as the hydraulic and climatic and boundary conditions. Additionally, at one of the river sites we observed along the river reach weekly microbial biofilm growth rates, microbial biodiversity (DNA), macrozoobenthos biodiversity in the dominating streambed substrates as well as weekly samples of C, N, P in the sediment.

The results show clearly how the interplay between hydraulic and climatic boundary conditions controls ongoing nutrient cycles and process rates; e. g. the spatial (downstream) extent of measurable surplus C, N, and P varies clearly over time as well as between the substances (P > C > N). Restricted by hydraulic boundary conditions, biomass production and a reduced (function specific) biodiversity of microbial biofilms coincide either with high nutrient surplus or with exposition to solar radiation. Favorable ambient conditions (lower water levels and higher energy availabilty) are dominant drivers for observable removal of pharmaceutical products rather than nutrient availability. Overall, our results demonstrate the importance of the local settings (cross section, shading) in combination with season and hydraulic loadings at given river sections for occurring process rates in nutrient cycles and biomass growth.

How to cite: Schuetz, T., Kurm, A., Gößges, T., Groß, M., Schmitz, S., and Krehenwinkel, H.: Dynamic boundary conditions control the spatial and temporal variations of nutrient turnover in human impacted surface waters , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16704, https://doi.org/10.5194/egusphere-egu2020-16704, 2020.