BG4.3

Dissolved organic matter (DOM) is an important component in carbon and nutrient cycles in terrestrial and aquatic ecosystems. For three decades, concentrations of dissolved organic carbon (DOC) have been increasing in European and North American surface water bodies. The increase has been mainly attributed to export of DOC from terrestrial ecosystems. Depending on the hydrological regime in a catchment (stormflow vs. baseflow conditions), the flow pathways through different soil horizons are varying and in result, the drivers determining the amount and chemical composition DOM vary as well. By studying soil water and surface water at the catchment scale, we aim at identifying the main sources and environmental conditions driving the ongoing trend of increasing DOM in aquatic ecosystems.

To understand the spatial and temporal variations of the export of DOM from soils to surface waters the catchment of the drinking water reservoir Sosa in the Ore Mountains (Germany) is instrumented and monitored along the terrestrial−aquatic continuum for 1 ½ years. We installed plate lysimeters and suction cups to collect soil water at three soil depths, including topsoil organic and subsoil mineral horizons at four different sites (peatland, degraded peatland, cambisol and podzol) representing the potential terrestrial DOM sources within the catchment. In addition, two tributaries of the reservoir were equipped with fluorescence-based probes to continuously monitor DOC. Water samples were taken fortnightly and event-based during heavy rain and snowmelt. All soil and stream water samples were analyzed for DOC, dissolved organic nitrogen (DON), as well as inorganic cations and anions. To identify possible DOM sources, the DOM composition of all samples was additionally analyzed by fluorescence spectroscopy (Excitation-Emission-Matrices – EEMs).

We found the different soils contributed differently to the aquatic DOM, depending on seasons and hydrological conditions. The highest DOC concentrations in the organic layer and upper mineral horizon of the podzol did not correspond with high average DOC concentrations in the stream. However, the stream affected by the peatland had much higher DOC concentrations. All organic topsoil horizons had low DOC concentrations in winter and high concentrations in summer, but only streams fed by peat soils followed this pattern. During stormflow events (snowmelt and strong rainfall), both monitored streams showed DOC concentrations 5 to 6 times higher than the average, illustrating the large potential of all soils (i.e. peatlands, cambisols, podzols) for DOM export. The DOC:DON ratios clearly reflect the differences in DOM composition of the different soils, with high proportions of plant-derived DOM in soil water and the corresponding streams. In conclusion, our research indicates that organic soils, such as peatlands, contribute most to stream DOM under baseflow conditions, while under high-flow conditions, as during snowmelt or rainstorms, mineral soils become additional strong DOM sources. Ongoing analyses of the DOM composition will provide further insights into specific DOM sources and the related spatial and temporal variations of DOM export from soils to surface waters.

How to cite: Krüger, S., Kaiser, K., Julich, S., Müller, I., and Kalbitz, K.: Drivers of spatial and temporal variability of dissolved organic matter across the terrestrial−aquatic continuum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7444, https://doi.org/10.5194/egusphere-egu22-7444, 2022.

A major challenge for predicting future landscape carbon (C) balances is to understand how environmental changes affect the transfer of C from soils to surface waters. Here we evaluated 14 years (2006-2019) of data on stream dissolved inorganic carbon (DIC) concentrations and export rates for 14 nested boreal catchments that are subject to climatic changes, and compared long-term patterns in DIC with patterns in dissolved organic carbon (DOC). Few streams displayed significant concentration or export trends at annual time scales. However, a clear majority of streams showed decreasing DIC concentrations during spring flood, and about half showing declines during summer. Although annual runoff has generally not changed during the studied period, intra-annual redistribution in runoff explained much of the seasonal changes in stream DIC concentration. We observed negative DIC-discharge relationships in most streams, suggesting supply limitation of DIC with increasing discharge. This was in contrast to DOC, which mostly showed a chemostatic behaviour. The distinct trend patterns observed for DIC and DOC underpin intra-annual changes in the total C pool (DIC/DOC ratio) in most streams and reflect differences in how these C forms are produced and stored, are mobilized by hydrological events, and are responding to long-term environmental changes. Collectively, our results indicate that future changes in hydro-meteorological conditions will affect the transfer of DIC from soils to water, and that these changes contrast to those of DOC. Such information is critical for future projections on how total C transfer from boreal system will respond on a changing climate.

How to cite: Wallin, M., Rehn, L., Laudon, H., and Sponseller, R.: Long-term changes in dissolved inorganic carbon (DIC) across boreal streams caused by altered hydrology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2148, https://doi.org/10.5194/egusphere-egu22-2148, 2022.

Climate change is causing temperatures in the Arctic to rise faster than in any other region of the world. This rapid warming leads, among other effects, to the massive loss of ice masses, development of thermokarst features when permafrost thaws, intensification of the hydrological cycle, and increasing loads of nutrients and organic carbon to surface waters. Freshwaters are highly sensitive to these changes, which affect microbial community composition and diversity. Therefore, these ecosystems are good sentinels to study processes in primary ecological succession related to ecosystem processes such as productivity and greenhouse gas (GHG) emissions. With this study, we aim to contribute to a deeper understanding of the linkages between biogeochemistry and hydrology in High Arctic freshwaters. To this end, we sampled various water sources (e.g., lakes and streams) in two High Arctic catchments (Bayelva and Lovénbreen, in Svalbard in July 2021) for the analysis of GHGs (CH₄, CO₂, N₂O), noble gases (radon-222, argon-40), major ions, stable water isotopes (δD and δ¹⁸O) and nutrients (organic C, organic -P and organic -N). We used Ar-corrected gas saturation of each GHG as a proxy of net metabolic changes, while tracers such as stable water isotopes help to disentangle water source contributions. Our first results show that lakes and streams were oversaturated in CO₂ as well as N₂O but slightly undersaturated in O₂, suggesting higher respiration activity than primary production. Our data also indicate a  strong oversaturation in CH₄ in lakes, but not in streams. Moreover, we used microbial mineralization of organic matter as a proxy for GHG production. We found similar concentrations of total organic C and N in both lakes and streams and significantly higher concentrations of total P in streams than in lakes. This work furthers our knowledge of the current state of High Arctic freshwaters and helps to predict future effects of climate change impacts on GHG evasion.

How to cite: Valiente, N., Popp, A. L., Dörsch, P., Fontaine, L., Hessen, D. O., Kjær, S. T., Sundal, A., and Eiler, A.: High Arctic freshwaters as emitters of greenhouse gases, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2051, https://doi.org/10.5194/egusphere-egu22-2051, 2022.

Rivers and streams are often supersaturated in methane (CH₄) and emit significant amounts of this potent greenhouse gas to the atmosphere. Methane is produced by methanogenic archaea in anaerobic sediments where energetically more favorable redox processes are substrate-limited. Diffusing up towards the sediment surface, methane can be oxidized in the hyporheic zone (HZ) aerobically with oxygen or anaerobically with nitrate, nitrite, sulfate or iron and manganese oxides as electron acceptors. Yet, knowledge about net carbon emissions from streams is restricted, because high spatial heterogeneities in production and consumption zones make bottom-up global estimations particularly challenging.

In this study we want to increase process understanding of riverine methane cycling, in particular production and oxidation in hyporheic stream sediments. Several studies have investigated predictors for potential methane production and oxidation in river sediments using incubation experiments. We chose a different approach by measuring high-resolution depth-dependent geochemical profiles at five different locations across a stream bed. An in-situ equilibrium dialysis sampler (peeper) was used to obtain pore-water samples with a 1 cm depth-resolution for the measurement of dissolved oxygen, relevant anion and cation concentrations as well as methane concentrations and stable carbon isotopes (δ¹³C) of methane. In the methanogenic zone stable carbon isotopes may provide information about the most relevant methane production pathway, while an isotopic enrichment in δ¹³C-CH₄ towards the sediment surface linked with decreasing methane concentrations may indicate microbial degradation. Production and oxidation rates were estimated using inverse numerical modeling of measured concentration gradients. Additionally, the concentration of 16S rRNA genes (a measure of bacteria biomass) was quantified from one of the locations using quantitative PCR, which revealed an increase in microbial biomass at the nitrate-methane transition zone.  Sequencing of the 16S rRNA genes shows clear shifts in microorganisms driving the streambed methane cycle at and below the nitrate-methane transition zone.

The measured δ¹³C-CH₄ values between -75 ‰ and -70 ‰ indicate that hydrogenotrophic methanogenesis is the dominant production pathway. However, we found that methane fluxes into the surface water were low. Mainly responsible for a strong decrease in methane concentrations towards the sediment surface were most likely diffusive processes. Decreasing methane concentrations linked with a significant enrichment in δ¹³C towards heavier isotopes was only observed at one of the sampling locations. The isotopic shift together with modeling results and microbiological analyses may reveal microbially driven aerobic and anaerobic methane oxidation in the HZ, but in most locations methane is only oxidized at low rates where the environment is already methane depleted by diffusion. Limiting for both aerobic and anaerobic methane oxidation was supposedly the low methane concentration in zones with available electron acceptors.

How to cite: Michaelis, T., Orsi, W., Wunderlich, A., Baumann, T., and Einsiedl, F.: Spatial variance in river bed methane cycling – measurement and interpretation of geochemical profiles linked with quantitative PCR and 16S rRNA sequencing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5422, https://doi.org/10.5194/egusphere-egu22-5422, 2022.

Glaciers are unique ecosystems with the potential to affect the aquatic carbon cycle, accumulating and releasing organic carbon (OC). OC stored in glaciers may be released as dissolved and particulate OC (DOC and POC), primarily via meltwater at the glacier’s surface into glacier-fed streams. Current global projections indicate an export of 78 Tg POC by 2050, representing more than double the DOC export (32.4 Tg DOC) predicted for the same period. However, POC data for glacier runoff is very limited and existing predictions are primarily based on an integrated approach, using single ice sampling points and mass balances to calculate an average annual export of glacier derived DOC. But this mass balance approach does not account for potential seasonal changes in OC, and may therefore not accurately reflect glacial OC export rates. Additionally, Icelandic glaciers are not included in global predictions of OC export, which is surprising as the largest nonpolar ice cap of Europe (Vatnajökull) is located in Iceland.

Therefore, we analyzed the concentration of DOC and POC, as well as its optical properties (absorbance and fluorescence) in glaciers and glacier-fed streams of Iceland. Sampling points covered ice samples from several glaciers of the Icelandic ice caps Vatnajökull, Langjökull, Hofsjökull, Myrdalsjökull, and Snaefellsjökull (110 ice samples) and water samples of the corresponding glacier-fed rivers (300 water samples) at the glacier termini. The majority of these sampling points were sampled seasonally (winter, spring, summer, autumn) and two times per day to cover temporal changes.

First results show, that DOC and POC concentrations in glacier-fed streams were found to range from 0.03 mg l-1 to 20.1 mg l-1, and from 0.1 mg l-1 to 33.0 mg l-1, respectively, whereas DOC and POC concentrations in glacier ice were found to range from 0.09 mg l-1 to 2.24 mg l-1, and from 0.3 mg l-1 to 39.4 mg l-1, respectively. Based on optical properties, we found that DOM is more proteinaceous and of recent origin (fresher) in summer and autumn. In contrast, DOM is more refractory with a higher contribution of a humic-like component in winter and spring. Based on the concentrations in glacier-fed streams we estimate an annual release of 0.032 Tg C yr-1 (DOC) and 0.128 Tg C yr-1 (POC) from Icelandic glaciers, assuming a mean glacier runoff of 1,500 m³ s-1 from the glaciers, and using the mean concentration of DOC and POC from our seasonal sampling points directly at the glacier terminus. If the annual release of DOC is weighted by the glaciated area of Iceland (11,060 km²), the calculated value is 0.0029 Gg C yr-1 km^-², clearly exceeding the area-weighted estimations of the Greenland Ice Sheet and the European Alps (0.0002 Gg C yr-1 km-² each).

Here for the first time, we analyzed the concentration of DOC and POC as well as its optical properties in proglacial streams of Iceland, location of Europe’s largest nonpolar ice cap, and thus established a comprehensive basis for improved prediction of global export of OC from glaciers.

How to cite: Chifflard, P., Reiss, M., Ditzel, L., Boodoo, K. S., and Fasching, C.: Spatial and temporal changes of dissolved and particular organic carbon in Iceland glaciers and glacier-fed streams, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5655, https://doi.org/10.5194/egusphere-egu22-5655, 2022.

Floodplains can contribute enormously to nutrient reduction in streams. The phosphorus cycle at the aquatic–terrestrial interface is driven by hydrology and vegetation. Our aim was to assess conditions relevant to the phosphorus cycle prior to a floodplain restoration. The phosphorus cycle was studied by means of measuring several phosphorus fractions and adsorption/desorption experiments using floodplain soil and river sediment. The study area was located at the Mulde River near Dessau, Germany, and covered different inundation patterns, vegetation and reaches with or without embankment. A shoreline ecotone was identified by means of high vegetation biodiversity with a distinct plant community. In the ecotone, the P cycle was influenced by accumulation of relatively high bioavailable P in the soil (equilibrium phosphate concentration, EPC0) and reduction of the soluble reactive phosphorus (SRP) concentration in the pore water. Both suggested a high productivity of the vegetation. The ecotone also acted as a delineation between the stream sediments with low organic matter and inorganic P and the floodplain soil with high organic matter and inorganic P. Additionally, the study demonstrated a lower SRP concentration and EPC0 in the parts of the floodplain without bank fortification.

Since floodplains were considered ecotones before, we identified another ecotone at another scale, i.e. between floodplain and river. The ecotone does not only show the area with a favourable ratio of disturbance and resource availability but also acts as a location for biogeochemical exchange processes between rivers and floodplains. The identified shoreline ecotone offered a habitat for a specifically diverse vegetation, which itself influenced the P cycle by high biological turnover. As a highly biogeochemically active part of the floodplain, the shoreline ecotone could help in mitigating high nutrient loads in anthropogenically impacted water sheds and provide a habitat for diverse vegetation.

How to cite: Pucher, M., Bondar-Kunze, E., and Hein, T.: Sediment phosphorus stock shows a shift at the river – floodplain interface, accompanied by high vegetation biodiversity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7419, https://doi.org/10.5194/egusphere-egu22-7419, 2022.

European Water Framework Directive (WFD) reported that river morphological alteration and diffuse pollution are two dominant pressures of European water bodies at the catchment scale. To achieve good status targeted by WFD, river restoration has received increasing attention. However, less is known about the spatial and temporal effects of stream morphologic characteristics (i.e., meandering, stream order) on instream nitrate retention at the river network scale. The objective of this study is to explore the relationship between in-stream nitrate retention and stream geomorphologic characteristics (sinuosity, width and order) and to assess the effect of natural river conditions on in-stream nitrate retention. Therefore, we implemented a grid-based nitrate catchment model (mHM-Nitrate, Yang et al. 2018) in the Bode catchment (3200 km²) in central Germany, which offers comprehensive long-term and high-frequency data at several water quality gauge stations for model calibration and validation. We evaluated two alternative empirical approaches to quantify in-stream denitrification (based on denitrification velocity and denitrification rate constant, respectively) and conducted scenario analysis on more natural morphological stream conditions by increasing the river sinuosity according to its relationship with stream power.  Results showed that the model well captured the dynamics of daily discharge and nitrate concentration, with Nash-Sutcliffe Efficiency ≥ 0.87 for discharge and Kling-Gupta Efficiency ≥ 0.59 for nitrate concentration from 2015-2018. In-stream retention (including assimilatory uptake and denitrification) by the whole river network accounted for 3.5% and 35.9% of total nitrate loadings in winter and summer, respectively. The summer in-stream denitrification rate was two times higher in the lowland arable area than in the mountain forest area (225.1 and 68.8 mg N m^-2 d^-1, respectively). Similarly, summer in-stream assimilatory uptake was five times higher in the lowland arable area than the mountain forest area (167.9 and 27.2 mg N m^-2 d^-1, respectively). The model scenario representing more natural river network conditions by restoring the river sinuosity can lead to an additional nitrate loading reduction of 20% in 6th order stream network in summer. Our results show that the renaturation of streams can increase nitrate retention in flowing water, with efficiency increasing significantly with decreasing runoff. However, a significant reduction in the nitrate concentration remains limited to the growing season, especially in summer.

Yang, X., Jomaa, S., Zink, M., Fleckenstein, J. H., Borchardt, D., Rode, M. (2018): A New Fully Distributed Model of Nitrate Transport and Removal at Catchment Scale. Water Resources Research, 54 (8) 5856.

How to cite: Rode, M., Zhou, X., Jomaa, S., and Yang, X.: The influence of river morphology on nitrogen retention at river network scale in the agricultural Bode River, Germany, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9071, https://doi.org/10.5194/egusphere-egu22-9071, 2022.

Headwater streams represent a key component of the global carbon cycle, as they are hotspots for the evasion of carbon dioxide from surface waters. Gas emissions from rivers and streams are modulated by the gas transfer velocity at the water-air interface, k, which is physically related to the energy dissipated by the flow field, ε. Here we study how local relations between gas transfer rate and energy dissipation can be spatially averaged in presence of heterogeneous flow fields, e.g. as induced by changes in the local slope. Furthermore, we develop mathematical tools for the quantification of the fraction of gas emission that is related to localized energy losses (e.g. sudden drops and step-pool formations). The study complements numerical simulations and direct measures of stream CO2 outgassing in an Italian headwater catchment. Our theoretical results indicate that reach-scale relations between k and ε in general differ from the corresponding local scaling laws. In particular, we show that high energy heterogeneous streams are characterized by a gas transfer velocity significantly higher than that of an equivalent homogeneous stream. The empirical data suggest that the outgassing is highly heterogeneous along a river network, with the outgassing generated by localized gas emissions in correspondence of hydraulic discontinuities that might be a dominant contribution to the total gas evasion in many settings. These results offer a clue for the interpretation of empirical data about stream outgassing in heterogeneous reaches and complex river networks.

How to cite: Botter, G., Carozzani, A., Peruzzo, P., and Durighetto, N.: The role of stream heterogeneity in gas emissions from headwater streams., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11857, https://doi.org/10.5194/egusphere-egu22-11857, 2022.

Synchrony of dissolved oxygen (DO) signals among river network elements reflects the dynamic balance between shared regional drivers, signal propagation, and local hydraulic, energetic, and metabolic heterogeneity. We used high frequency DO measurements at 42 sites across five watersheds catchments to evaluate DO signal synchrony among reaches in response to dynamic variation in light availability and discharge. We hypothesized that homogeneity of light availability and longitudinal hydrologic connectivity between sites would enhance synchrony in DO signals. We observed strong support that increasing spatial homogeneity of light inputs, both in magnitude and diel variation, greatly increase diel DO signal synchrony both within and across stream networks during early spring and fall. We further observed the central role of longitudinal connectivity in controlling within network synchrony. Specifically, shared regional drivers (light, temperature) increase the synchrony in DO signals when flow connectivity was high, whereas fine-scale patch behavior and low synchrony, especially in smaller streams, occurred when connectivity declines. A model including light synchrony and longitudinal connectivity explained 65% of variation in dynamic DO synchrony. We provide a framework for evaluating DO signal synchrony at confluences with implications for broadly understanding solute where network flow elements mix. DO synchrony and network and confluence scales provides an empirical demonstration of the dynamic balance between regional drivers and local patch dynamics modulated by the flow-varying length scales of signal integration.

How to cite: Diamond, J.: Metabolic synchrony in stream networks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12853, https://doi.org/10.5194/egusphere-egu22-12853, 2022.

Hyper-Saline Endorheic Aquatic Systems (H-SEAS) are shallow lakes in arid and semiarid climatic zones that undergo to extreme oscillation in salinities and large drought episodes. Although their geochemical uniqueness and microbiome are deeply studied, very little is known about availability, transformation and fate of dissolved organic matter (DOM) in water column, interstitial waters and in salts that precipitate under driest conditions. To advance in this direction, a small hypersaline shallow lake from Monegros desert (Zaragoza, NE, Spain) has been studied during a complete hydrological wet-drough-rewetting transition. DOM analysis includes: i) a dissolved organic carbon (DOC) mass balance;  ii) optical spectroscopy (absorbance and fluorescence) characterization and; iii) molecular description by negative electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS).

The studied system stored large amount of DOC and the mass balance revealed that under highest salinity conditions, salt-saturated waters (i.e. brines, salinity >30%) accumulated a disproportionate quantity of DOC indicating a significant net in-situ DOM production. Simultaneously, during the hydrological transition from wet to drought, the DOM pool changed drastically its qualitative properties: thus, aromatic and humified moieties were rapidly replaced by fresher, relatively small size and microbial derived moieties with large C/N ratio. Further FT-ICR-MS highlight the accumulation of small-size, saturated and, highly oxidized molecules (O/C molar ratio >0.5) with a remarkable increase of relative contribution of sugar-like molecules and decrease of aliphatic and carboxyl-rich alicyclic like molecules. Overall, there results highlight that H-SEAS are extremely active in accumulating and processing DOM and, the observed patterns pointed to a notable release of organic solutes from decaying microplankton probably triggered by the osmotic stress under extremely high salinities.

How to cite: Butturini, A., Herzsprung, P., Lechtenfeld, O., Alcorno, P., Benaiges-Fernandez, R., Berlanga, M., Boadella, J., Freixinos Campillo, Z., Gomez, R., Sanchez-Montoya, M. M., Urmeneta, J., and Romaní, A.: Origin, accumulation and fate of dissolved organic matter in an extreme hypersaline shallow lake., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1085, https://doi.org/10.5194/egusphere-egu22-1085, 2022.

The transformation of organic matter in lentic and lotic conditions are dominated by different processes. The special attention deserves the transition from riverine to lacustrine conditions. In our experiment we incubated the stream and pond water inside of mesocosms in the small forest ponds for 28 days. That time was previously observed as sufficient for the reestablishing of chemical and biological processes after severe rain events in the same pond. We aimed to evaluate the dynamics in organic matter, nitrogen, and phosphorus concentrations, fractioning between particulate and dissolved forms, as well as the development of microbial community. Additionally, we tested the influence of presence and absence of solar radiation in one experiment and the effect of different transparency of surrounding environment. The observed changes in C, N, and P fluxes were simulated by the first order kinetics model. The slowest processes were observed in dark mesocosms with the highest initial color and organic carbon content, while the light exposed and less colorful mesocosms revealed fastest rates.

How to cite: Porcal, P. and Shabarova, T.: Transformations of C, N, P in lotic-lentic transition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7365, https://doi.org/10.5194/egusphere-egu22-7365, 2022.

How to cite: Merz, E., Dick, G. J., de Beer, D., Lavik, G., Marchant, H. K., and Klatt, J. M.: Sulphide stimulates nitrate reduction in benthic diatoms from a microbial mat, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7981, https://doi.org/10.5194/egusphere-egu22-7981, 2022.

Despite the crucial role of lake sediments in global biogeochemical cycling as a source of the greenhouse gas methane, our understanding the intrinsic microbial communities and their role in geochemical cycles in this environment is limited. Here, we used metagenomics and geochemical analyses to assess the microbial methane, iron, sulfur, and nitrogen cycling in depth profiles of sedimental samples from lake Kinneret, a warm monomictic subtropical lake. In these sediments microbes catalyze anaerobic methane oxidation and iron reduction beneath the sulfate reduction and the main methanogenic zones. High quality metagenome-assembled genomes revealed a broad potential for respiratory sulfur and nitrogen metabolism. Wood-Ljungdahl pathway used by acetogens and methanogens was found to be highly common given the widespread occurrence of the genes encoding the key enzyme carbon-monoxide dehydrogenase. Acetate, alcohol, and hydrogen are the prominent substrates for the fermentative metabolism. Methane metabolism was found in Methanotrichales Methanomicrobiales, Methanomethyliales, ANME-1 and Methanomassiliicoccales, and the bacterial Methylomirabilales. Iron reduction genes such as porins, MtrABC and outer membrane cytochromes were observed in Thermodesulfovibrionales, Geobacterales, Burkholderiales and Myxococcales. Our results indicated flexible metabolic capabilities of core microbial community, which could adapt to changing redox conditions.

How to cite: Gafni, A., Sivan, O., Blum, M. R., and Eckert, W.: Metabolic potential of the microbial community along a depth gradient in Lake Kinneret sediments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13525, https://doi.org/10.5194/egusphere-egu22-13525, 2022.

Here we report on the porewater dissolved organic matter dynamics and underlying benthic biogeochemical processes in a historically brackish, diked, peatland located along the Baltic Sea in northeastern Germany.  The regeneration process of the “Heiligensee and Hütelmoor” includes a return of freshwater inputs as well as increased connection to the sea.  For porewater observations, two stationary multiport (about 0.5 m intervals) lances are located in the coastal sediments coastward of the sand-dune dyke, reaching down to ~5 meters through permeable sediments and peat layers.  Frequent sampling of these porewater lances indicates substantial influences by fresh submarine ground water discharge in the middle depths.  Therefore, we studied the impact by mixing of these groundwater (as, for example, a source of Fe, DOM, DIC, P, Ca) with saltwater (a source of SO₄ to fuel sulfate reduction) and the role of organic matter in the drowned peat layers.  We were particularly interested in the sulfurization of DOM, as biogenic sulfide can react both with Fe and DOM/POM.  Samples for a suite of analyses were taken in November 2020.  Characterizations included dissolved organic matter (21T FT-ICR-MS, National High Magnetic Field Laboratory), major and trace elements (ICP-OES), nutrient and sulfide concentration, as well as stable isotopes of sulfate, DIC, and water. Results are compared to nearby groundwater wells (a coastal sandy aquifer, a coastal peat layer, and an inland well), the brackish Baltic Sea and  the Hütelmoor surface waters, as well as the river Warnow.  Thus, we characterize the endmembers as well as the mixing zones in order to understand their influence on the chemical alterations of dissolved organic matter in this dynamic region.

How to cite: Zeller, M., von Ahn, C., Jenner, A.-K., Racasa, E., McKenna, A., Janssen, M., and Böttcher, M.: Linking the carbon and sulfur cycles in a historically brackish diked peatland: Stable Isotopes and FT-ICR-MS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9904, https://doi.org/10.5194/egusphere-egu22-9904, 2022.

Lignin, a macromolecule found in all vascular plants, can be used as a biomarker for terrestrial dissolved organic matter in the ocean. Measuring lignin in the ocean can help us quantify the supply to and fate of terrestrial carbon in the ocean. Lignin analyses in aquatic samples quantify phenolic products after cupric oxidation using gas or liquid chromatography, with detection either by mass spectrometry or UV-Vis spectroscopy. Mass spectrometry yields low detection limits and high specificity, but requires specialized and expensive instrumentation. In contrast, liquid chromatography coupled with UV-Vis spectroscopy is more readily available and cheaper to operate, but traditionally suffers from lower specificity due to overlapping signals of the bulk organic matter background.

This study demonstrates a new approach of UV-Vis spectroscopic detection coupled to high-performance liquid chromatography (HPLC) that circumvents common issues and improves the detection limit by a factor of 10. This improvement is accomplished by using the second derivative of the chromatogram and applying a modified parallel factor analysis (PARAFAC2). PARAFAC2 tolerates subtle remaining chromatogram shifts in retention time between samples and successfully separates spectra of co-eluting signals. The isolation of spectra based on this machine learning approach improves both lignin phenol identification and the accuracy of their quantification. The approach developed automates the analysis of chromatograms and considerably reduces the water volumes required, improving the applicability of HPLC-UV-Vis for lignin characterization, which may increase the feasibility for widespread use.

How to cite: Bruhn, A. D., Wünsch, U., Osburn, C. L., and Stedmon, C. A.: Improving lignin quantification and characterization in seawater using spectral liquid chromatography and PARAFAC2, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7985, https://doi.org/10.5194/egusphere-egu22-7985, 2022.

The mangrove ecosystem is an important natural sink of carbon owing to its potential to accumulate and store large amounts of organic carbon, in particular in its anaerobic sediments. To better understand the role of and quantify this carbon sink, the present study measured organic carbon stocks, carbon accumulation rates, and organic matter sources in the sediments of the Gautami-Godavari (Coringa) mangrove ecosystem, Andhra Pradesh, India. The carbon and nitrogen stable isotopic composition and elemental ratios of total organic carbon (TOC) to total nitrogen (TN) have been used to detect the sedimentary organic matter sources in the Coringa mangrove complex. ²¹⁰Pb isotopes have been used to determine the sedimentation rates and carbon accumulation rates. The value of ∂¹³C ranges from -17.8‰ and -26.1‰ with an average value of -23.3‰ and TOC/TN ranges from 9-27 with an average value of 15. The spatial variation of all sedimentary parameters i.e., TOC, TN, ∂¹³C, and ∂¹⁵N is found to be significant at various sites. Both Sedimentary Carbon Stock and Carbon Accumulation Rates also have significant spatial variation among different sites and their values are maximum in an area where mangroves are directly affected by aquaculture effluents. The lowest carbon stock has been observed in an area where mangroves are degraded. The scatter plot between δ¹³C and TOC/TN ratio reveals that most of the sedimentary organic matter originated from non-mangrove sources like algae, phytobenthos, and suspended particulate matter.

How to cite: rao, K., jennerjahn, T., al, R., and nj, R.: Coastal Blue Carbon Storage, Sources and Accumulation in Gautami-Godavari (Coringa) Mangrove sediments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9455, https://doi.org/10.5194/egusphere-egu22-9455, 2022.

Dissolved organic matter (DOM) is an important component in marine and freshwater environments and plays a fundamental role in global biogeochemical cycles. In the past, optical and molecular-level analytical techniques evolved and improved our mechanistic understanding about DOM fluxes. For most molecular chemical techniques, sample desalting and enrichment is a prerequisite. Solid-phase extraction (SPE) has been widely applied for concentrating and desalting DOM. The major aim of this study was to constrain the influence of sorbent loading on the composition of DOM extracts. Here we show that increased loading resulted in reduced extraction efficiencies of dissolved organic carbon (DOC), fluorescence and absorbance, and polar organic substances. Loading-dependent optical and chemical fractionation induced by altered adsorption characteristics of the sorbent surface (PPL) and increased multilayer adsorption (DOM self-assembly) can fundamentally affect biogeochemical interpretations, such as the source of organic matter. Online fluorescence monitoring of the permeate flow allowed to empirically model the extraction process, and to assess the degree of variability introduced by changing the sorbent loading in the extraction procedure. Our study emphasizes that it is crucial for sample comparison to keep the relative DOC loading (DOC_load [wt%]) on the sorbent always similar to avoid chemical fractionation.

How to cite: Kong, X., Jendrossek, T., Ludwichowski, K.-U., Marx, U., and Koch, B.: Solid-phase extraction of aquatic organic matter: loading-dependent chemical fractionation and self-assembly, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9757, https://doi.org/10.5194/egusphere-egu22-9757, 2022.