BG4.3

Aquatic biogeochemical cycles of carbon, nitrogen and phosphorus. From measurements to understanding hydrochemical patterns and processes

Our ability to understand biogeochemical cycles of carbon, nitrogen and phosphorus in aquatic ecosystems has evolved enormously thanks to advancements in in situ and laboratory measurement techniques. We are now able to provide a detailed characterisation of aquatic organic matter with spectroscopic and chromatographic methods and collect data on nitrogen and phosphorus concentrations in relation to highly dynamic hydrological events thanks to automated in situ instruments. Therefore, the aim of this session is to demonstrate how this methodological advancement improves our understanding of coupled hydrological, biogeochemical and ecological processes in aquatic environments controlling the fate of organic matter, nutrients and other chemicals.

Specifically, our ability to characterise different fractions of natural organic matter and organic carbon has increased thanks to a range of analytical methods e.g. fluorescence and absorbance spectroscopy, mass spectrometry and chromatography combined with advanced data mining tools. Matching the water quality measurement interval with the timescales of hydrological responses (from minutes to hours) thanks to automated in situ wet-chemistry analysers, optical sensors and lab-on-a-chip instruments has led to discovery of new hydrochemical and biogeochemical patterns in aquatic environments e.g. concentration-discharge hysteresis and diurnal cycles. We need to understand further how hydrochemical and ecological processes control those patterns, how different biogeochemical cycles are linked in aquatic environments and how human activities disturb those biogeochemical cycles by emitting excess amounts of nutrients to aquatic systems. In particular, there is a growing need to better characterise the origins, delivery pathways, transformations and environmental fate of organic matter and nutrients in aquatic environments along with identification of robust numerical tools for advanced data processing and modelling.

Co-organized by HS13
Convener: Magdalena Bieroza | Co-conveners: Andrea Butturini, Diane McKnight
Presentations
| Mon, 23 May, 08:30–11:50 (CEST)
 
Room 3.16/17

Presentations: Mon, 23 May | Room 3.16/17

Chairpersons: Magdalena Bieroza, Andrea Butturini
Stream biogeochemistry
08:30–08:40
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EGU22-7444
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ECS
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solicited
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On-site presentation
Stephan Krüger, Klaus Kaiser, Stefan Julich, Ingo Müller, and Karsten Kalbitz

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.

08:40–08:46
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EGU22-2148
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Virtual presentation
Marcus Wallin, Lukas Rehn, Hjalmar Laudon, and Ryan Sponseller

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.

08:46–08:52
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EGU22-2051
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ECS
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On-site presentation
Nicolas Valiente, Andrea L. Popp, Peter Dörsch, Laurent Fontaine, Dag O. Hessen, Sigrid Trier Kjær, Anja Sundal, and Alexander Eiler

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.

08:52–08:58
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EGU22-5422
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ECS
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Presentation form not yet defined
Tamara Michaelis, William Orsi, Anja Wunderlich, Thomas Baumann, and Florian Einsiedl

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.

08:58–09:04
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EGU22-5655
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Presentation form not yet defined
Peter Chifflard, Martin Reiss, Lukas Ditzel, Kyle S. Boodoo, and Christina Fasching

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.

09:04–09:10
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EGU22-7419
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ECS
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On-site presentation
Matthias Pucher, Elisabeth Bondar-Kunze, and Thomas Hein

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.

09:10–09:16
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EGU22-9071
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On-site presentation
Michael Rode, Xiangqian Zhou, Seifeddine Jomaa, and Xiaoqiang Yang

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.

09:16–09:22
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EGU22-9256
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ECS
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Virtual presentation
Alberto Zannella, Karin Eklöf, Hjalmar Laudon, Eliza Maher Hasselquist, and Marcus Wallin

Boreal water courses are large emitters of carbon dioxide (CO2) to the atmosphere. In Sweden, a high share of these water courses are man-made ditches, created to improve drainage and increase forest productivity. Previous studies from boreal regions have mainly suggested that terrestrial sources sustain the CO2 in these ditches and with variability in hydrology as the main temporal control. However, few studies have quantified ditch CO2 dynamics in harvested catchments. An altered hydrology, increased nutrient export and light availability upon forest harvest are all factors that potentially can change the main source control. Thus, there is a strong need to better understand how clear-cut forestry affects the ditch CO2 dynamics in boreal regions.

Here, high-frequency (30 min) CO2 concentration dynamics together with other hydro-chemical variables were studied in a forest ditch draining a fully harvested catchment in the Trollberget Experimental Area, northern Sweden. Data were collected during the snow-free season from May to October. Ditch CO2 concentrations displayed a clear seasonal pattern with higher CO2 during summer than in spring and autumn. Concentrations were ranging from 0.41 to 3.99 mg C L-1 (median: 1.69 mg C L-1, corresponding to partial pressures (pCO2) of 2553 μatm, IQR = 1.08 mg C L-1). Strong diel cycles in CO2 were developed during early summer, with daily amplitudes in the CO2 reaching up to 2.1 mg C L-1. These daily cycles in CO2 were likely driven by aquatic primary production consuming CO2 during daytime. In addition, individual high-flow events in response to rainfall had a major influence on the ditch CO2 dynamics with generally a diluting effect, but the strength in the CO2-discharge relationship varied among seasons and between events. It was evident from the study that growing season CO2 dynamics in forest ditches affected by clear-cut forestry are high and controlled by a combination of hydrological and biological factors. These high dynamics and the associated controls need to be considered when scaling ditch CO2 emissions across boreal landscapes affected by clear-cut forestry.

How to cite: Zannella, A., Eklöf, K., Laudon, H., Maher Hasselquist, E., and Wallin, M.: Carbon dioxide dynamics in a boreal forest ditch affected by clear-cut forestry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9256, https://doi.org/10.5194/egusphere-egu22-9256, 2022.

09:22–09:28
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EGU22-9273
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ECS
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On-site presentation
Xiaolin Zhang, Xiaoqiang Yang, Bobby Hensley, Andreas Lorke, and Michael Rode

Stream and river systems are an important compartment of nitrogen (N) transport and retention from terrestrial landscape to marine ecosystems. In-stream nitrate uptake in rivers involves complex assimilatory and dissimilatory pathways, which often exhibit spatiotemporal variability due to stream hydraulic, biotic (e.g., phytoplankton and periphyton) and abiotic (e.g., temperature and light availability) variations. Two-station based multi-parameter high-frequency monitoring allows quantitative disentangling of multi-path nitrate uptake dynamics at the reach scale. However, such monitoring and analysis are still limited to few small river types (e.g., headwaters and spring-fed rivers) and have not been well explored in higher order streams with varying hydro-morphological and biogeochemical conditions. Here, we conducted the two-station high-frequency monitoring in five high-order stream reaches in central Germany (i.e., two in the 4th order Weiße Elster River and three in the 6th order Bode River). Two-station 15-min time series of nitrate-N and dissolved oxygen were used to calculate the N mass balance and whole-stream metabolism, respectively. The mass-balance based net nitrate uptake rates (UNET) differed between reaches with contrasting morphology (e.g., 13.8±3.85 mg N h-1 in the more natural Weiße Elster compared to 2.05±0.83 mg N h-1 in the modified reach of Bode), as well as between different periods in the same reach (e.g., higher in post-wet period than in dry period). The measured GPP and the related autotrophic nitrate assimilation (UA) were determined by seasonal-varying radiation and riparian-canopy shading conditions. Heterotrophic N uptake (UD), including denitrification and heterotrophic assimilation, was further disentangled as the difference between UNET and UA. This rarely reported uptake pathway showed relatively higher values than UA, especially during late spring periods; moreover, it exhibited obvious diel signals that are significantly negatively correlated with DO. We further summarized difficulties and cautious considerations in conducting such two-station monitoring campaign at larger reach scales. In conclusion, benefiting from the less labor-consuming and high-frequency sensor monitoring, the two-station methods for N mass balance and stream metabolism can be applied at larger reach scales, and can well disentangle the multiple N uptake pathways that often exhibit high spatiotemporal heterogeneity.

How to cite: Zhang, X., Yang, X., Hensley, B., Lorke, A., and Rode, M.: Disentangling in-stream nitrate uptake pathways based on two-station high-frequency monitoring in high-order streams, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9273, https://doi.org/10.5194/egusphere-egu22-9273, 2022.

09:28–09:34
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EGU22-11857
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On-site presentation
Gianluca Botter, Anna Carozzani, Paolo Peruzzo, and Nicola Durighetto

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.

09:34–09:40
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EGU22-12853
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ECS
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Presentation form not yet defined
Jacob Diamond

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.

09:40–09:46
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EGU22-495
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ECS
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On-site presentation
Katherine Pérez Rivera, Stephen Plont, Morgan Wood, Felicity DeToll, Barbara Niederlehner, Kristen Bretz, Carla López Lloreda, and Erin Hotchkiss

Streams are dynamic ecosystems susceptible to frequent and long-term physical and chemical changes. Characterizing how solute concentrations change with hydrology is key to understanding solute sources, fate, and transport. Here we tested how solute concentrations respond to changes in flow in a stream draining a mixed land use catchment in Blacksburg, Virginia, USA. To do this, we measured how various solutes (i.e., DOC, DIN, Cl-, Na+, Mg+2, Ca+2, SO4-2, K+) changed within and across one baseflow period of 24 hours and three high flow events during summer 2021. Solutes concentration relationship with flow dynamics can result in different responses: (1) enrichment (increase in concentration), (2) dilution (decrease in concentration), or (3) chemostasis (no change in concentration). We found that, overall, solutes responded to changes in flow and the patterns observed for each flow event were variable, resulting in both dilution and enrichment. Discharge (Q) ranged from 0.04 - 3.37 m3/s during our 8-week sampling period. Dissolved organic carbon (DOC) and dissolved inorganic nitrogen (DIN) concentrations ranged from 2 - 5.7 and 0.23 - 0.94 mg/L, respectively. While DOC exhibited enrichment with increasing Q, DIN, Cl-, Na+, Mg+2, Ca+2, SO4-2, and K+ were mainly diluted during higher flows. However, during baseflow conditions the relationship between Q and solute concentrations was more pronounced (R2 >0.30), particularly for DIN and SO4-2 (dilution), and Cl- and Na+ (enrichment). During higher flows, we did not see a general dilution or enrichment pattern for all solutes but there were solute-specific behaviors which were similar among sampling periods. The differences in Q-solute dynamics among the 4 sampling events supports the enhancement of hydrological connectivity and landscape influence during changes in flow and how it can contribute to changes in solute concentration. Additionally, Q-solute patterns observed highlight the importance of time and sampling frequency to develop a well characterization of solute dynamics during changes in flow. Ongoing work is focused on understanding the directionality and timing of responses to further inform changes in solute concentrations during different flow events. Analyses of solute-specific behavior, timing of peak concentrations, and directionality will broaden our understanding of solute chemical dynamics and the different factors that contribute to the variable responses that have been found.

How to cite: Pérez Rivera, K., Plont, S., Wood, M., DeToll, F., Niederlehner, B., Bretz, K., López Lloreda, C., and Hotchkiss, E.: Stream solutes respond differently within and across flow conditions: a comparison of baseflow and higher flow events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-495, https://doi.org/10.5194/egusphere-egu22-495, 2022.

09:46–09:54
Lake biogeochemistry
09:54–10:00
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EGU22-1085
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On-site presentation
Andrea Butturini, Peter Herzsprung, Oliver Lechtenfeld, Paloma Alcorno, Robert Benaiges-Fernandez, Merce Berlanga, Judit Boadella, Zeus Freixinos Campillo, Rosa Gomez, Maria del Mar Sanchez-Montoya, Jordi Urmeneta, and Anna Romaní

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.

Coffee break
Chairpersons: Magdalena Bieroza, Matthias Pucher
10:20–10:30
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EGU22-7365
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solicited
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Virtual presentation
Petr Porcal and Tanja Shabarova

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.

10:30–10:36
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EGU22-2334
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Presentation form not yet defined
Peter Herzsprung, Wolf von Tümpling, Norbert Kamjunke, and Oliver J. Lechtenfeld

Dissolved organic matter (DOM) is ubiquitous in aquatic systems. Discharge of DOM to reservoirs via shallow ground and surface waters from the catchment poses major problems for drinking water production. Knowledge had been generated about mobilization and discharge of DOM in catchments based on the bulk parameter dissolved organic carbon (DOC) (1-3) or on bulk optical parameters describing its quality (4). The decomposition of DOC in catchments and reservoir waters was reported using DOC, bulk optical and carbon isotope analysis (5, 6).

For drinking water treatment, removal of humic substances by coagulation / flocculation and the formation of disinfection byproducts are the most pressing challenges. The treatment success depends strongly on the chemical quality of DOM, which probably consists of thousands or even millions of different molecules. The identification of the isomeric structure of each molecule is still far from any instrumental analytical realization. From the analytical point of view the highest resolution of DOM can be achieved by Fourier Transform-Ion Cyclotron Resonance Mass Spectroscopy (FTICR-MS). This analytical tool generates elemental compositions of thousands of DOM components which are water extractable (solid phase extractable DOM, SPE-DOM) and which are ionizable (electrospray ionization, ESI).

Using FTICR-MS, knowledge has been generated about the formation potential of disinfection byproducts and its composition (7) and about the flocculation behavior as function of the raw water DOM quality (8).

Only few knowledge exists about DOM quality variations in the reservoirs and their catchments based on sum formulas from FTICR-MS analysis (8 - 11). Also little is known about transformations of drinking water treatment relevant sub fractions within the complex DOM in catchments and reservoir waters.

As a first result of FTICR-MS measurements we observed that few components (sum formulas) showed high abundance differences as function of depth during reservoir stratification. Some poly-phenol-like components (relevant for flocculation) declined in the epilimnion of a drinking water reservoir potentially due to photo degradation. Some of the (more aliphatic) photo products, which were enriched in the epilimnion, are suspected to be disinfection byproduct precursors. This knowledge can be used to investigate the adaptation of the raw water subtraction depth in the reservoir.

 

1) Blaurock K et al., Hydrol. Earth Sys. Sci. Disc. (2021), https://doi.org/10.5194/hess

2) Werner BJ et al., Biogeosci. (2019), 16, 4497-4516

3) Musolff A et al., J. Hydrol. (2018), 566, 205-215

4) Da Silva MP et al., Biogeosci. (2020), 17, 5355-5364

5) Kamjunke N et al., Sci. Tot. Environ. (2016), 548-549, 51-59

6) Morling K et al., Sci. Tot. Environ. (2017), 577, 329-339

7) Phungsai P et al., Environ. Sci. Technol. (2018), 52, 3392-3401

8) Raeke J et al., Wat. Res. (2017), 113, 149-159

9) Da Silva MP et al., J. Geophys. Res. Biogeosci. (2021), 126, e2021JG006425

10) Herzsprung P et al., Environ. Sci. Technol. (2020), 54, 13556-13565

11) Wilske C et al., Water MDPI (2021), 13, 1703

How to cite: Herzsprung, P., von Tümpling, W., Kamjunke, N., and Lechtenfeld, O. J.: Dissolved organic matter quality variations in drinking water reservoirs and their catchment waters – Scientific knowledge and research gaps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2334, https://doi.org/10.5194/egusphere-egu22-2334, 2022.

10:36–10:42
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EGU22-4564
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Presentation form not yet defined
Alkalinity supports gross primary production in a deep hardwater lake
(withdrawn)
Pascal Perolo, Nicolas Escoffier, Hannah Elisa Chmiel, Gaël Many, Damien Bouffard, and Marie-Elodie Perga
10:42–10:48
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EGU22-5476
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ECS
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On-site presentation
Xingcheng Yan, Vincent Thieu, and Josette Garnier

The impact of reservoirs on downstream water quality has received widespread attention, but most current studies are based on short-term data only, and less attention has been paid to the impact of reservoirs on downstream carbon dioxide (CO2) concentrations. In the present study, we assessed the nutrient budgets (DIN: dissolved inorganic nitrogen, PO43-: orthophosphate, DSi: dissolved silica) of the reservoirs (Marne, Aube, Seine, and Pannecière reservoirs) in the Seine Basin using long-term dataset (1998-2018), and we also evaluated the reservoir effect on downstream partial pressure of carbon dioxide (pCO2) based on field measurements during 2019-2020. The mean annual retention rates accounted for 16%-53%, 26%-48%, and 22%-40%of the inputs of DIN, PO43-, and DSi in the four reservoirs during the period 1998 to 2018, respectively, showing that the four reservoirs play important roles in nutrient retentions. We further identified that three reservoirs (Marne, Aube, and Seine reservoirs) significantly changed downstream water quality during the emptying period, increasing the concentrations of dissolved organic carbon (DOC) and biodegradable DOC, while lowering the concentrations of DIN, DSi, PO43-, and total alkalinity. Interestingly, we found that the three reservoirs notably decreased downstream pCO2(24%-37%) and enhanced the gas transfer coefficient of CO2 (21%) in downstream rivers compared to the upstream ones, during the emptying period, which highlights the necessity to consider the potential impact of reservoirs on downstream riverine not only for water quality variables, but also for CO2 emissions. Finally, the findings of this study highlight the importance of the combination of biogeochemical and hydrological characteristics to understand the biogeochemical functioning of reservoirs to downstream rivers.

How to cite: Yan, X., Thieu, V., and Garnier, J.: The impact of reservoir on downstream water quality and pCO2: a case study in Seine Basin, France, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5476, https://doi.org/10.5194/egusphere-egu22-5476, 2022.

10:48–10:54
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EGU22-7981
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ECS
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On-site presentation
Elisa Merz, Gregory J. Dick, Dirk de Beer, Gaute Lavik, Hannah K. Marchant, and Judith M. Klatt

Diatoms are among the few eukaryotes known to store nitrate (NO3) and to use it for dissimilatory nitrate/nitrite reduction to ammonium (DNRA) to generate enegry in the absence of light and O2. We used stable isotope incubations and in situ microsensor measurements over complete light cycles to study the diel activity transitions of the NO3-storing benthic diatom Craticula cuspidata in the submerged Middle Island Sinkhole, Lake Huron (USA). We found that this diatom links NO3 respiration to diel migration into deep (~4 cm) sulfidic sediments below the microbial mat. This pattern was accompanied by pronounced diel changes in the depth of sulphide consumption. During the day sulphide was consumed by anoxygenic photosynthesis and aerobic sulphide oxidation in the uppermost few mm. Surprisingly, the consumption zone moved downward in the evening and was deepest in the sediment at night. Thus, the sulphide consumption zone strikingly overlapped with the depth of DNRA-performing diatom residence. Using an enrichment of Craticula cuspidata, we found that the nitrate respiration via DNRA was ~10-fold higher in the presence of sulphide. Overall, our data therefore indicate that C. cuspidata and/or their microbiome link NO3 reduction to sulphide oxidation.

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.

10:54–11:00
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EGU22-13525
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Virtual presentation
Almog Gafni, Orit Sivan, Maxim Rubin Blum, and Werner Eckert

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.

11:00–11:06
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EGU22-11986
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ECS
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Virtual presentation
Annika Feld, Christina Fasching, Martin Reiss, and Peter Chifflard

Springs link the terrestrial and the aquatic ecosystem and connect groundwater and surface water. They are distinguished primarily by their type and discharge, whereby the latter can influence the biogeochemistry. Perennial springs, characterized by continuous spring discharge, show stable conditions and relatively low organic carbon contents. Although previous studies have investigated the sources of dissolved organic carbon (DOC) in streams considering mainly the riparian zone, the hyporheic zone and the hillslopes, our current understanding of springs as sources of organic carbon (OC) is still limited. Thus, our study focuses on intermittent springs, which are particularly vulnerable to climate change induced decreased groundwater levels. Additionally, changing groundwater levels may further increase the frequency of springs with an interrupted discharge during dry periods. Intermittent springs with a temporarily loss of the connectivity to the groundwater, impacting the quantity and quality of received OC and consequently the in-stream respiration, may lead to changed OC quantity and quality transported to downstream ecosystems.

The aim of this investigation is to quantify the export fluxes of OC and to analyze their origin and composition in intermittent springs. For this purpose, 40 springs at four study sites in different low mountain range regions in Germany (Sauerland, Ore Mountains, Hesse Mountains and Black Forest) with different geology and vegetation types will be instrumented with hydrological on-site-measurements for discharge and electrical conductivity. Continuous quarterly biogeochemical sampling campaigns will be carried out and event-based sampling with an autosampler during 4 rainfall events at one spring per site is intended. Additionally, analyses of groundwater, soil water and precipitation samples as well as fDOM and CO2 measurements are implemented. Stable water isotopes (δ2H, δ18O) and nutrient concentrations (PO4, NO3, NH4) will also be determined to enable flux modelling. In this project the combination of continuous measurements and frequent sampling campaigns will be used to gather long-term data with high temporal resolution. Thus, the seasonal dynamics and spatio-temporal variability of OC export fluxes as well as event-based changes in OC and nutrient status and further the influence of spring OC on the following headwater streams will be studied in the next three years. First results show that there are great spatial variabilities in DOC concentration between the 40 intermittent springs in the four study catchments. This underscores that intermittent springs differ substantially from perennial springs in their export behavior.

How to cite: Feld, A., Fasching, C., Reiss, M., and Chifflard, P.: Organic carbon fluxes in intermittent springs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11986, https://doi.org/10.5194/egusphere-egu22-11986, 2022.

11:06–11:12
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EGU22-9904
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ECS
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Virtual presentation
Mary Zeller, Cátia von Ahn, Anna-Kathrina Jenner, Erwin Racasa, Amy McKenna, Manon Janssen, and Michael Böttcher

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.

Estuary biogeochemistry
11:12–11:18
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EGU22-7985
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ECS
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Presentation form not yet defined
Anders Dalhoff Bruhn, Urban Wünsch, Christopher Lee Osburn, and Colin Andrew Stedmon

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.

11:18–11:24
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EGU22-5896
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ECS
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On-site presentation
Yeganeh Mirzaei and Yves Gelinas

Preserving the health of estuarine ecosystems has been an increasing challenge in the recent past with the spreading of areas affected by deep-water hypoxic conditions. Hence, it is of critical importance to identify the causes of such perturbation, triggered by changing ocean circulation and increasing inputs of organic matter (OM), which results in serious threats to living species. Estuaries are large deposition centers for organic matter (OM) where stable carbon isotope ratios of either bulk OM or specific organic compounds provide detailed information about carbon cycling and the tracing of OM sources and transformations along the terrestrial-marine continuum. In particular, the ∂13C values of biomarkers that are specific to heterotrophic bacteria (branched iso- and anteiso-C15:0 fatty acids) can be used to assess the type of OM that they preferentially degrade as the ∂13C values of marine organic carbon (OC) are more enriched in 13C than those of terrestrial OC. However, very little is known on the dynamics between the seasonally varying relative inputs of terrestrial vs. marine OM and the ∂13C values of these bacteria-specific fatty acids. In this study, we will use a kinetic batch incubation approach in which natural sediments from the St. Lawrence Estuary and Gulf, amended with fresh terrestrial or marine OM characterized by a very different 13C/12C ratio (difference of between 10 and 14 ‰ depending on the sampling station), will be incubated for varying amounts of time. Quenching of the incubations followed by the extraction, quantification and isotopic characterization of the bacterial fatty acids will allow determining the rate and temporal extent of change of their compound-specific ∂13C values. Bulk elemental (OC and total nitrogen) and isotopic (∂13C and ∂15N) mass balances will be precisely monitored throughout the experiment. Acquisition of this knowledge, combined with results from other studies carried out in our lab, will provide a better understanding of the relative importance of terrestrial and marine OM processing in the onset of hypoxia and will be exploited as a guide for remedial efforts aiming to improve the health of such an important ecosystem.

How to cite: Mirzaei, Y. and Gelinas, Y.: Exploring the Bacterial Preference for Terrestrial or Marine Organic Matter in Estuarine Sediments Using Compound Specific Stable Carbon Isotope Ratios: A Degradation Kinetics Study , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5896, https://doi.org/10.5194/egusphere-egu22-5896, 2022.

11:24–11:30
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EGU22-6033
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ECS
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On-site presentation
Maria-Elena Radu and Yves Gelinas

As the largest semi-enclosed estuarine system in the world, the St. Lawrence Estuary and Gulf is an ecosystem rich in natural resources and very important in terms of biodiversity, as well as economic, transportation and recreational activities. Since the beginning of the industrialization of the St. Lawrence Valley, this aquatic system has been threatened by human activities resulting in increased industrial and agricultural pollution, eutrophication (nutrient enrichment), biodiversity loss, and landscape deterioration, culminating in the depletion of dissolved oxygen in its bottom waters (hypoxia). Deep water hypoxia conditions have been steadily worsening in the past 80 years, reaching dissolved O2concentrations has low as 35 µM in the fall of 2021. Hypoxia in this system is fueled by changes in oceanic circulation in the North Atlantic as well as by an increase in the water column flux of organic matter (OM) either discharged by the St. Lawrence River and other tributaries (terrestrial OM), or produced in the surface waters from discharged and upwelled nutrients (marine OM). The consumption of the more labile OM components of this sedimenting OM by aerobic heterotrophic bacteria results in sustained pressure on dissolved O2 concentrations and the accumulation of the more recalcitrant fraction of this OM. As cold temperate estuarine systems such as the St. Lawrence are characterized by large seasonal variations in riverine discharge rates and in situ primary production, mineralization of the more recalcitrant sedimentary OM components should be strongly modulated by the priming effect resulting from sudden influxes of fresh and more labile OM. In this study, we will attempt to quantify the priming effect in this system using elemental (organic carbon and total nitrogen) and isotopic (∂13C and ∂15N) mass balances, as well as compound specific stable carbon isotope analysis of the bacterial fatty acids iso- and anteiso-C15:0. We will use a batch incubation approach in which natural sediments from the St. Lawrence Estuary and Gulf will be amended with fresh terrestrial or marine OM characterized by a very different 13C/12C ratio (difference of between 10 and 14 depending on the sampling station). Quenching of the incubations followed by the extraction, quantification and isotopic characterization of the bacterial fatty acids will allow determining the effect of labile OM on the mineralization of recalcitrant OM in this system. Acquisition of this knowledge, combined with results from other studies carried out in our lab, will provide a better understanding of the relative importance of terrestrial and marine OM processing in the onset of hypoxia and will be exploited as a guide for remedial efforts aiming to improve the health of such an important ecosystem.

How to cite: Radu, M.-E. and Gelinas, Y.:  The Priming Effect in Sediments of a Cold Temperate Estuarine System: An Assessment Using Compound Specific Stable Carbon Isotope Ratios Measurements on Bacterial Fatty Acids , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6033, https://doi.org/10.5194/egusphere-egu22-6033, 2022.

11:30–11:36
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EGU22-9455
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ECS
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Virtual presentation
Karuna rao, Tim jennerjahn, Ramanathan al, and Raju nj

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.

11:36–11:42
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EGU22-9757
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ECS
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Virtual presentation
Xianyu Kong, Thomas Jendrossek, Kai-Uwe Ludwichowski, Ute Marx, and Boris Koch

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 (DOCload [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.

11:42–11:50