A large fraction of marine primary production is directed towards the synthesis of polysaccharides, most of which are rapidly degraded by heterotrophs, including heterotrophic microbes. However, a novel class of polysaccharides characterized by high N-acetyl aminosugar and 6-deoxysugar content, escapes rapid degradation and accumulates as a constituent of marine dissolved organic matter (DOM). These polysaccharides, which comprise ~25% of total dissolved organic carbon, also represent a large reservoir of the potentially bioavailable organic N and P stored in DOM.   To better understand the accumulation and microbial degradation of DOM polysaccharides we used size-exclusion chromatography and diffusion-ordered NMR spectroscopy to examine the size-distribution and composition of DOM recovered from seawater by ultrafiltration. Our results show that DOM polysaccharides are relatively small, with a molecular weight range of 1.3–7.7 kD and an average molecular weight of ~6 kD in surface waters decreasing to ~3 kD at 900m. Acid hydrolysis of DOM polysaccharides releases a suite of characteristic neutral sugars (glucose, galactose, mannose, rhamnose, fucose and xylose), but most of the polysaccharide (80-90%) resists hydrolysis and undergoes Maillard-like reactions between amino- and reducing sugars. To circumvent this, we modified our hydrolysis conditions to promote sugar-sugar cleavage. With this approach, we were able to generate a suite of oligosaccharides with molecular weights between 0.3-1.8 kD that carry the same spectral characteristics as DOM polysaccharides. We are using transposon insertion sequencing (Tn-seq) of marine bacteria cultured on these oligosaccharides to identify genes and degradation pathways responsible for DOM polysaccharide degradation.

How to cite: Repeta, D. J., Granzow, B. N., Burger, A., and DeLong, E. F.: Characterization and microbial degradation of polysaccharides in high molecular weight dissolved organic matter., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16877, https://doi.org/10.5194/egusphere-egu23-16877, 2023.

Microbial metabolisms are directly responsible for the production, degradation and recycling of dissolved organic matter (DOM) in the ocean. Many compounds within the DOM contain sulfur (dissolved organic sulfur, DOS) and in sum they represent the largest reservoir of organic sulfur in the ocean. Recent studies indicated an abundant and diverse suite of marine bacteria with the genetic capacity for DOS transformation. However, there is currently very little experimental data regarding the marine sediment microbial communities that are actively using DOS substrates as a source of carbon. Here, we use quantitative ¹³C DNA stable isotope probing (qSIP) to provide the first quantitative measurements of DOS (taurine and methionine) utilization by specific operational taxonomic units in seafloor sediments from continental shelf of Puerto Rico (493 meter below sea surface). Immediately after sampling, seafloor sediments were amended with 500 µg / g ¹³C-labeled taurine or methionine as well as natural-abundant (¹²C) substrates as a control and were incubated in gas-tight glass flasks with no headspace in the dark over two different timepoints (30 hours and 10 days) to unravel the active microbial communities. Our preliminary results by gas-chromatography mass spectrometry showed that there was 6 – 10% of ¹³CO₂-remineralization compared to control samples. This indicates that taurine and methionine are important DOS substrates supporting the activity of benthic microbial populations. Notably, the rate of taurine remineralization was five-fold higher than glucose and 50-fold higher than methionine over the first 30-hours of incubation, suggesting that taurine is an underappreciated, yet important DOS substrate for microbial activity at the seafloor. Oxygen was rapidly consumed to anoxic levels over the first 12 hours in all incubations, indicating that the taurine was utilized via anaerobic microbial metabolism. This was reflected by changes in the initial microbial community that was dominated by Thaumarchaeota (29%), Gammaproteobacteria (15%) and Planctomycetes (13%), which changed to being enriched by Firmicutes (8%-43%), Deltaproteobacteria (10%-26%), and Gammaproteobacteria (10%-29%) in the presence of taurine and methionine. Further quantitative DNA isotope probing study (in progress) will reveal the specific anaerobic microbial taxa that are responsible for driving the biogeochemical cycling of these important, yet overlooked DOS substrates at the seafloor.

How to cite: Coskun, Ö. K., Orsi, W. D., D'Hondt, S., and Gomez-Saez, G. V.: Dissolved organic sulfur utilization by marine benthic microbial communities revealed by quantitative DNA stable isotope probing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16424, https://doi.org/10.5194/egusphere-egu23-16424, 2023.

The Arctic Ocean receives more terrestrial dissolved organic matter (tDOM) on a per volume basis than any other ocean, resulting in Arctic coastal waters harboring the highest concentration of tDOM among the world’s oceans. Due to climate change induced intensification of the hydrological cycle, permafrost thaw, and coastal erosion, tDOM input into Arctic coastal waters has been steadily increasing. Nguyen et al. (2022) have speculated that the increasing presence of tDOM in the Arctic Ocean is causing a shift in the local microbiological communities. This may significantly affect CO₂ fluxes and food web dynamics in the ocean. Despite recent incubation experiments reporting substantial biodegradation of tDOM in Arctic coastal waters, very few studies have attempted to examine the genetic capacity of Arctic marine microorganisms to process lignocellulose and other recalcitrant aromatic compounds of terrestrial origin. In this study, we perform comparative metagenomics in order to assess the diversity and distribution of microbial genes responsible for tDOM degradation in the Western Arctic. We searched 361 seawater metagenomes from the Bering Shelf, Bering Strait, and Chukchi Shelf for orthologs responsible for ring-opening reactions associated with degradation of tDOM (Grevesse et al., 2022). Like others, we identified Rhodobacterales as important contributors to microbial communities encoding the ring-opening reactions required for degradation of aromatic compounds such as tDOM and petroleum products, including members of the Roseobacteraceae (Sulfitobacter, Roseomonas) and Rhodobacteraceae (Planktomarina, Ascidiaceihabitans, and uncultured taxa). We found the presence of degradation genes to be widely distributed across temperature-, salinity-, depth-, and latitudinal gradients, with no clear patterns in the richness of genes. Future work will investigate the relative abundance of these functional genes among metagenome assembled genomes derived from these samples. Doing so, we hope to elucidate the environmental factors supporting the presence of tDOM degrading microorganisms. This study will contribute to the accumulating knowledge on adaptability of marine microorganisms to inputs of recalcitrant organic compounds.

How to cite: Kazmiruk, Z. and Collins, E.: Comparative metagenomics of terrestrial organic matter degradation in the Western Arctic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9999, https://doi.org/10.5194/egusphere-egu23-9999, 2023.

Marine DOM constitutes one of the most complex chemical mixtures on earth containing hundreds of thousands of different compounds. In nearshore systems like coral reefs metabolites exuded by primary producers comprise a significant fraction of this marine DOM pool. To learn more about the chemical composition we performed untargeted molecular analysis of exudates released by coral reef primary producers (corals and algae) using liquid chromatography–tandem mass spectrometry. Of 10,568 distinct ion features recovered from reef waters, 1,667 were primary producer exudates; the majority (86%) of these exudates were organism specific, reflecting a clear divide between coral and algal exometabolomes. The stoichiometric analyses of the exudates revealed a significantly reduced nominal carbon oxidation state of algal- compared to coral exometabolites, illustrating an ecological mechanism by which algal phase shifts engender fundamental changes in the biogeochemistry of reef biomes. Coral exometabolomes were enriched in diverse sources of nitrogen and phosphorus, including tyrosine derivatives, oleoyltaurines, and acyl carnitines. In contrast DOM released by algae was dominated by nonnitrogenous compounds, including diverse prenol lipids and steroids. Additional experiments indicate that exudates, specifically exudates unique to the respective treatment, were the main substrate used by heterotrophic microbes exposed to the respective exometabolome. This data provides molecular-level insights into biogeochemical cycling on coral reefs and illustrates how changing benthic cover on reefs influences reef water chemistry with implications for microbial metabolism.

How to cite: Haas, A., Nelson, C., Arts, M., Mueller, B., Hopmans, E., and Kelly, L.: Molecular characterization of coral reef exometabolites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1987, https://doi.org/10.5194/egusphere-egu23-1987, 2023.

With the Anthropocene, thermogenic organic carbon, also known as black carbon (BC) is increasingly introduced to ecosystems worldwide. BC is formed by incomplete combustion or pyrolysis of fossil fuels, at wildfires or by the intentional burning of biomass, emitted to the atmosphere and hydrosphere or remaining in the bio-/pedosphere. With its high molecular proportion of elemental carbon, BC is regraded to be protected from fast microbial degradation by its inherent molecular properties. In aquatic systems, BC is partly sedimented or buried when reaching endorheic lakes or the ocean, where it is withdrawn from the carbon cycle. The biogeochemical implications of BC or its degradation products in aquatic systems have therefore not received much attention. Especially in sensitive oligotrophic alpine systems, such as the treeless Tibetan Nam Co catchment, part of the biggest connected alpine pasture system in the world, which is exposed to increasing anthropogenic pressure, any nutrient and carbon surplus can threaten the ecological status.

This was studied by an ultra-high resolution mass spectrometry approach that identifies several thousands of molecular formulae in dissolved organic matter (DOM). Including polycondensed aromatics (pcAro) that are considered to include thermogenic DOM.

Incubation experiments of water samples indicated that pcAro DOM was transformed by microbes to a comparable degree such as other natural organic matter (NOM) in the samples, removing pcAro DOM by defunctionalization or metabolization. In the environmental samples we found that pcAro DOM discharged to the endorheic Nam Co Lake was transformed by photodegradation along with other aromatic compounds. For DOM of streams and the lake of the high-alpine Nam Co watershed, most pcAro is likely of local origin, i.e. derived from burning of yak faeces by pastoralist households. This pcAro formed from cellulose-rich and lignin-poor Cyperaceae fodder is chemically distinct from low-land natural biomass, usually including the burning of wood.

Thus pcAro DOM appeared to be a more viable part of the carbon cycle than previously assumed. Our data support the hypothesis that the fate of polycondensed aromatic DOM depends on several environmental factors, such as catchment characteristics, water opacity, solar irradiation and actual light penetration into the water column, as well as on the carbon source, driving the molecular composition of thermogenic NOM.

How to cite: Maurischat, P., Seidel, M., Donnerhack, O., and Guggenberger, G.: Assessing the fate of polycondensed aromatic natural organic matter (NOM) in a high-alpine aquatic system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9168, https://doi.org/10.5194/egusphere-egu23-9168, 2023.

Understanding biogeochemical processes in groundwater is paramount for safety management of our water supplies. The AquaDiva project has been investigating a groundwater probing site in central Germany to monitor hydrology, biology and dissolved organic matter (DOM) chemistry in a multiannual project (Küsel et al., 2016). As part of this, we are addressing how deep surface-derived signals can be traced on their passage through the critical zone and into the groundwater.

We acquired a multiannual DOM data set from an untargeted liquid chromatography coupled to mass spectrometry (LC-MS) monitoring and have previously shown that fingerprints from mass-signals associate with water flows (Zerfaß et al., 2022). Using tandem mass spectrometry, we have now identified DEET (N,N-diethyl-m-toluamide) and 7-ODAA (7-oxodehydroabietic acid, putative) in groundwater samples, compounds that are released to aerosols as insect repellent sprays and through conifer wood burning for heating, respectively. We show that these signals are found in groundwater throughout the year, but with elevated intensities in summer (DEET) and winter (7-ODAA), respectively, corresponding to their primary seasons of release.

This demonstrates by the counter-periodic DEET and 7-ODAA patterns how surface-derived (aerosol) organic matter signals arrive in groundwater down to 88 m of sampling depths with intra-annual dynamics.

References

Küsel, K., Totsche, K.U., Trumbore, S.E., Lehmann, R., Steinhäuser, C., Herrmann, M., 2016. How Deep Can Surface Signals Be Traced in the Critical Zone? Merging Biodiversity with Biogeochemistry Research in a Central German Muschelkalk Landscape. Front. Earth Sci. 4. https://doi.org/10.3389/feart.2016.00032

Zerfaß, C., Lehmann, R., Ueberschaar, N., Sanchez-Arcos, C., Totsche, K.U., Pohnert, G., 2022. Groundwater metabolome responds to recharge in fractured sedimentary strata. Water Res. 223, 118998. https://doi.org/10.1016/j.watres.2022.118998

How to cite: Zerfass, C., Ueberschaar, N., and Pohnert, G.: Aerosols to groundwater: DEET (N,N-diethyl-m-toluamide) and 7-ODAA (7-oxodehydroabietic acid) as markers for anthropogenic emissions in the Hanich CZO, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1007, https://doi.org/10.5194/egusphere-egu23-1007, 2023.

  Dissolved organic matter (DOM) in soil consists of a diverse mixture of water-soluble soil organic matter (SOM) molecules that are highly mobile and reactive. These molecules play various roles with different capacities in biogeochemical processes. Theoretically, the persistence of DOM molecules in soils is controlled by interactions between i) DOM leaching and desorption that release DOM from plant residues and SOM and ii) sorption and decomposition that remove DOM. However, there is still no consensus on the dominant factor(s) or dimension(s) driving the yield and molecular signatures of DOM in soil environments.

  Molecular variations of soil DOM from distinct geographical regions are primarily attributed to variations in geographical climate conditions and soil clay content. Soil weathering condition is highly related to geographical climate conditions, such as temperature and precipitation, and could be a reflection of the soil mineral characteristics. However, there is a distinct paucity of information concerning how the molecular signatures of soil DOM vary with different degrees of weathering across wide geographic scales.

  Herein, we resolved the DOM molecular signatures from 22 diverse Chinese reference soils and linked them with soil organic matter and weathering-related mineralogical properties. The mixed-effects models revealed that the yields of DOM were determined by soil organic carbon content, whereas the molecular signature of DOM was primarily constrained by the weathering-related dimension. The soil weathering index showed a positive effect on the lability and a negative effect on the aromaticity of DOM. Specifically, DOM in highly weathered acidic soils featured more amino sugars, carbohydrates, and aliphatics, as well as less O-rich polyphenols and condensed aromatics, thereby conferring a higher DOM biolability and lower DOM aromaticity. This study highlights the dominance of the weathering-related dimension in constraining the molecular signatures and potential functions of DOM in soils across a wide geographic scale.

How to cite: Wang, Y., Zhang, P., He, C., Shi, Q., Dahlgren, R., Spencer, R., and Wang, J.: Molecular signatures of soil-derived dissolved organic matter constrained by mineral weathering, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4329, https://doi.org/10.5194/egusphere-egu23-4329, 2023.

While the complexity of prokaryotic communities in soil is relatively well understood, we are currently ignorant of the role of viruses in influencing their ecology. Viruses infect every living organism and affect rates of biogeochemical processes by killing active cells via cell lysis, or augmenting function through the transfer of auxiliary metabolic genes. The microbially-mediated process of nitrification is central to nitrogen losses and emissions of the greenhouse gas nitrous oxide, contributing to global warming and stratospheric ozone depletion, and viruses may impact this central step of the global N cycle. However, challenges remain in identifying active interactions with specific host or functional groups and virus populations within structurally complex and diverse soil environments. To address this, discrete active interactions between individual hosts and viruses in soil microcosms were examined using the transfer of assimilated carbon from autotrophic prokaryotes to viruses. Microcosms were established with amendments of urea to fuel nitrification and ¹³C carbon dioxide, followed by DNA stable-isotope probing (SIP) combined with metagenomic analyses. Hybrid analysis of GC mol% fractionation and ¹³C-DNA-SIP resulted in the identification of active ammonia oxidizing archaea (AOA) hosts and viruses only. To enable characterization of viruses actively infecting all active ammonia- and nitrite oxidizing bacteria (AOB, NOB), a second approach was used where incubations were performed using filtration of virus-like particles to increase the recovery of virus metagenomes. This included differential inhibition of specific nitrifier groups to alleviate competition and potentially increase the abundance of viruses infecting non-inhibited groups. Applications of DMPP or octyne were added to preferentially inhibit AOB and encourage growth of AOA, or acetylene to inhibit all ammonia oxidizing activity as a negative control. This approach dramatically increased the recovery of high-quality virus contigs, with 225 contigs associated with those infecting AOA, AOB or NOB including 69 complete or near-complete genomes. Viruses of ammonia-oxidizers contained auxiliary metabolic genes involved in central metabolic pathways, and analysis of viral hallmark genes revealed that they were distinct from previously cultivated viruses. Results demonstrate that virus infection of nitrifiers and propagation of viruses is a dynamic process during soil nitrification, providing insights into potential impacts of viruses on a specific functional process in soil.

How to cite: Hazard, C., Lee, S., and Nicol, G. W.: Characterization and potential impacts of active nitrifier host–virus interactions in soil, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16956, https://doi.org/10.5194/egusphere-egu23-16956, 2023.

Rivers are important contributors to the global carbon cycle as they actively transform terrestrial organic matter (OM) during transport to the oceans. The efficient OM processing results from a diverse assemblage of consumers including heterotrophic microbes (i.e., fungi, bacteria and protists) and macroinvertebrates, which interact with an equally diverse pool of OM. Ecologically, OM can be understood as forming a multidimensional resource space for consumers, whose understanding, however, requires an advanced capability to describe relevant dimensions (i.e., traits of OM) at a level that matches the resolution of consumer diversity, where significant advancement is generated by molecular biological means (i.e., DNA sequencing). This implies moving beyond proxy-based indirect descriptors (e.g., indices derived from absorbance or fluorescence spectroscopic analyses), integrative bulk property measures (e.g., C, N, P, lignin, tannins and fibre content) or bulk amounts of operational size fractions (e.g., dissolved, fine and coarse particulate OM). Recent technological advances such as size-exclusion, liquid or ion chromatography coupled to mass spectrometry have allowed to describe dissolved OM (DOM) on a molecular species level, setting a great step forward in the highly resolved description of DOM properties. However, particulate OM (POM) characterization remains behind significantly. Here, a per-particle basis description with regard to physical features and macromolecular composition is needed. We propose a procedure to asses both physical and chemical molecular properties of individual POM particles by combining (i) photometrical techniques, which are based on image processing and particle analysis (e.g., ImageJ) of pictures obtained with microscopes or cameras, and (ii) attenuated total reflectance infrared spectroscopy (ATR-FTIR) to measure particle-specific chemical composition. We apply this method to POM samples collected along large-scale environmental gradients in river networks.

How to cite: Estévez, E., Mützel, S., del Campo, R., Stalder, R., and Singer, G.: A procedure to characterize physical and chemical molecular properties of individual organic matter particles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9304, https://doi.org/10.5194/egusphere-egu23-9304, 2023.

Ultrahigh-resolution mass spectrometry like FT-ICR MS has greatly expanded our view of the complexity and reactivity of complex dissolved organic matter (DOM) in the environment. However, both the structural characterization and (semi)-quantification DOM are methodologically not fully resolved, despite recent advances with coupling liquid chromatography (LC) to FT-ICR-MS that allows isomeric separation. Likewise, matrix effects and the existence of multiple isomers with largely varying – but unknown – ionization efficiencies that are simultaneously ionized and detected in direct infusion (DI)-FT-ICR MS prevents (semi)-quantification of DOM compounds and has limited the comparability of samples. Finally, common normalization strategies applied for non-targeted DOM analysis with DI cannot be easily transferred to LC-type DOM data. Here we present a new method that combines a post-column infusion of internal standard (PCI-IS) with LC-FT-ICR MS in order to reduce and compensate matrix effects as well as to provide a robust and reliable way to normalize MS peak intensities and compare samples measured with LC-FT-ICR MS. To this end, DOM samples were analyzed and the peak intensity data normalized by the internal standard and other frequently used normalization methods (e.g. sum of intensity, base peak), and absolute intensity indicating that PCI-IS normalization provides superior precision and accuracy. The potential of this method to provide semi-quantitative information on polarity fractions of DOM is assessed by testing the precision, accuracy, and linearity of PCI-IS normalization of model compounds spiked into DOM samples. Our results indicate that the use of LC separation reduced matrix effects (as compared to DI) and, in combination with the internal standard, improved to potential to obtain reliable peak intensity information.

How to cite: Rodrigues Matos, R., Jennings, E., Koch, B., and Lechtenfeld, O.: Towards semi-quantification of DOM: isomer separation with LC-FT-ICR-MS combined with a post-column infusion of standard., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16616, https://doi.org/10.5194/egusphere-egu23-16616, 2023.

Dissolved organic matter (DOM) is a complex mixture of thousands of natural molecules that undergo constant transformation in the environment, such as sunlight induced, photochemical reactions. Despite molecular level resolution obtained by ultra-high resolution mass spectrometry, the mechanistic understanding of DOM transformations is still hampered due to a multitude of simultaneous reactions. Temporal trends of mass peak intensities are currently the only way to follow photochemical induced molecular changes in DOM, but are often limited by low temporal resolution or the necessity to apply monotonic regression models. Here, we present a novel computational approach using a temporal graph (a temporal molecular network) to model the transformation of DOM molecules in a photolysis experiment by employing a predefined set of basic molecular transformation units (like oxidation, decarboxylation, etc.). The new algorithm focuses on the temporal changes of mass peak intensities of molecular formulas by simultaneously considering educt removal and product formation for molecules linked by a transformation unit (e.g. -CO2). The transformations and molecules are further weighted by the extent of intensity change and grouped by unsupervised machine learning algorithms to find clusters of similar reactivity. The temporal graph thus allows to simultaneously identify relevant molecules subject to similar reactions and to study their time course. The graph can be constructed for low and high temporal resolution data without presumptions on reaction kinetics and with different sets of transformation units according to the experimental design. Our approach overcomes previous data evaluation limitations for mechanistic studies of DOM transformation and leverages the potential of temporal graphs to study the reactivity of complex DOM by means of ultra-high resolution mass spectrometry.

How to cite: Lechtenfeld, O., Plamper, P., Herzsprung, P., and Groß, A.: A temporal graph to predict chemical transformations in complex dissolved organic matter, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2837, https://doi.org/10.5194/egusphere-egu23-2837, 2023.

Grasslands on the northeastern Tibetan Plateau are particularly sensitive to changes in climate and herbivory. As two main compositions, Poaceae and Cyperaceae supply forage and support herbivory survival. However, to taxonomic resolution restriction of traditional plant proxies, the plant composition and richness change of vegetation in particular of Poaceae and Cyperaceae are still largely unknown. Here, we reconstruct the vegetation using Lake Donggi Cona sediment ancient DNA metabarcoding, targeting chloroplast trnL P6 loop (g h primer). To increase Poaceae and Cyperaceae taxonomic resolution we currently also investigate ITS1 of nuclear ribosomal DNA in Poaceae and Cyperaceae. A total of 257 terrestrial higher plant taxa, 14 Pteridophyta taxa and 9 aquatic taxa were detected. Before ca. 12.6 cal ka BP, Asteraceae dominate terrestrial plant communities, which are commonly associated with cold and arid conditions during the late glacial; after 12.6 cal ka BP, Asteraceae abundance decline, Poaceae, Rosaceae, and Salicaceae abundance increase likely related to an increase in precipitation and temperature. At 6.5 cal ka BP, the Asteraceae abundance increase, Poaceae and Salicaceae abundance decrease, which is possibly related to cold and dry environments. The plant richness increase sharply since 6.5 cal ka BP and continually maintain relatively high richness values, which may be related to herbivory. Our analyses combine different plant sedaDNA markers will help to elucidate vegetation shifts in the past with deeper taxonomic resolution and provide reference on grassland protection under future climate change scenarios.

How to cite: Liu, Y., Stoof-Leichsenring, K., Diekmann, B., and Herzschuh, U.: Plant sedaDNA reveals grassland change on the Northeastern Tibetan Plateau during the past 17 ka, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8793, https://doi.org/10.5194/egusphere-egu23-8793, 2023.

Since many lakes in Yakutia, eastern Siberia, are of thermokarst origin, it can be challenging to reach ages of paleorecords beyond the Holocene, hence limiting the understanding of long-term key interactions between climate change, vegetation dynamics, biodiversity shifts, and lake development. However, with a new paleoenvironmental multiproxy project at an intermontane basin we aim to reconstruct lake-vegetation feedbacks since the Late Glacial Maximum (LGM). For that purpose, a 10.8 m long sediment core has been extracted from the deepest part (22.3 m) of the Lake Khamra (59.99095° N, 112.98345° E) and dated back to 18.4 cal ka BP. Lake Khamra is situated in South-Western Yakutia, the transitional zone of discontinuous to continuous permafrost, it is also in the zone of mixed evergreen-deciduous forest. We applied sedimentological and XRF-derived geochemical parameters in addition to palynological analyses of plant fossils and metabarcoding analyses of diatoms and plants sedimentary ancient DNA (sedaDNA). Our genetic analyses of diatoms revealed 45 unique sequence types. A high distribution of several small fragilarioid types indicates the initial formation of the lake, started in the LGM (15.4 cal ka BP), and high abundance of planktonic taxa since 8 cal ka BP indicates lake deepening in the Mid-Holocene. SedaDNA composition of 38 unique sequence types of aquatic and 155 unique sequence types of terrestrial plants revealed the agreement with pollen and non-pollen palynomorph derived vegetation composition. LGM vegetation was represented as wet tundra and both analyses revealed refugia of Larix. Tundra vegetation only appeared in LGM. The Holocene warming led to the forest establishment and therefore lake vegetation feedback intensification, seen from the turnover of diatoms. Diatoms assemblages of LGM which were represented by only few epiphytic taxa significantly increased the richness, as well as increasing of planktonic and benthic diatom assemblages. The lake expansion resulted in a diversification of emergent aquatic plants. And again, because the lake is not of thermokarst origin it shows more stable insight to environmental variability. This study provides a better understanding of the climate, lake system dynamics, and vegetation in Siberia, and simultaneously fills in the very scarce paleolimnological data in eastern Siberia.

How to cite: Baisheva, I., Biskaborn, B. K., Stoof-Leichsenring, K. R., Andreev, A. A., Meucci, S., Ushnitskaya, L., Pestryakova, L. A., Dietze, E., and Herzschuh, U.: Lake ecology and catchment vegetation changes reconstructed for the last 18,400 years in South-Western Yakutia, Siberia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13403, https://doi.org/10.5194/egusphere-egu23-13403, 2023.

The sediment fill at Summit Lake shows strong potential for reconstructing past changes (Holocene to present) in the paleoecology and regional paleoclimate for the subalpine region of the Black Rock Range, northwestern Nevada, USA. Summit Lake is a high desert terminal lake with a surface elevation of 1780m.a.s.l. and is a eutrophic, alkaline (~8.4), dimictic lake with a maximum depth of ~10 m and a small surface area (2.8 km²). There is abundant growth of macrophytes, including Polygonium (smartweed), Myriophyllum (milfoil), and Ceratophyllum (coon tail), and growth progresses throughout the summer months. The lake falls within the domain of the Summit Lake Paiute Tribe, who has an inextricable cultural connection to the lake via the native Lahontan cutthroat fishery. The tribe’s original name, Agai Panina Ticutta, translates as the Summit Lake Fish Eaters.

In 2021 and 2022 C.E., we collected a series of surface and long sediment cores from multiple sites in the lake. This study focuses on sediments collected from the lake’s central depocenter. Preliminary age control of Summit Lake sediments is determined by ²¹⁰Pb-dating (corroborated by the stratigraphic profiles of the man-made radionuclides ¹³⁷Cs, ²⁴¹Am) for the upper ~40 cm, and the Mount Mazama tephra (~7.6 ka) at 410cm depth. The age model suggests high and increasing sedimentation rates between early 1900 C.E. and 2021 C.E. (from 0.05 to 1.87 cm/yr). In comparison, the mean sedimentation rate between the Mazama tephra and ~1900 C.E. is low (0.05 cm/yr). We present preliminary sedaDNA and diatom data for the last ca. 140 years. Plant sedaDNA shows good preservation, with a stable alpha diversity of ~40 ASVs. The plant record is dominated by the aquatic plants Myriophyllum and Potamogeton (pondweed) in the upper 40cm, and terrestrial plants are also represented, including sagebrush, willow, aspen, and a variety of herbaceous plants, including aster, rose, primrose, buckwheat, borage, lupin, and saxifrage. The diatom flora of the upper 40cm is dominated by the benthic epiphyte Cocconeis placentula, which is consistent with a large macrophyte community seen in the modern system and indicated by the plant sedaDNA. Modern sampling shows the epiphytic relationship between C. placentula and milfoil. Future work will include pairing and harmonizing the diatom record derived from traditional morphotaxonomy and eDNA, contextualizing the plant eDNA with the modern plant community, and refining the age model to better discern Holocene climate events that may be driving the changes in sediment flux and the floral community. These data will be extended down-core to reconstruct the past climate and lake levels, informing the Tribe’s management efforts for a resilient watershed and fishery in the future.

How to cite: Noble, P., Crump, S., Muscott, A., Larsen, D., Ruiz Fernandez, A. C., Chandra, S., Simmons, J., Fifo, A., and Csank, A.: Floral analysis of a ~140 yr sediment record using sedaDNA and diatoms, Summit Lake Nevada, USA, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10354, https://doi.org/10.5194/egusphere-egu23-10354, 2023.

Across the globe, freshwater ecosystems have experienced a decline in biodiversity resulting from increasing anthropogenic pressure. Over the past decennia the scientific community has developed new and efficient biomonitoring techniques to register these shifts in biodiversity. A promising technique is the capture and analysis of eDNA and eRNA (environmental DNA and RNA; i.e. eNA). eNA constitutes the genetic material released by a host species into the environment in different forms, such as mucous, skin tissue, scales and saliva. However, in lotic ecosystems, such as streams and rivers, detected eNA concentrations can currently not be translated into the spatial and temporal distribution of the associated species. This is due to the lack of knowledge about the processes (e.g. transport and degradation) that influence eNA presence between the moment of release by its host, and the capture of the eNA by the practitioner.

The authors have conducted a set of laboratory experiments to shed light on these processes (i.e. transport and degradation). The objective was to test the influence of flow velocity on concentrations of both eDNA and eRNA. In an annular flume (depth = 19.7 cm; Ø = 3.7 m), which features counter-rotating bottom and top components, we performed eDNA and eRNA degradation experiments under four different flow rates, each with a duration of seven days. The source of eNA originated from water previously inhabited by wildtype zebrafish (Danio rerio). The tested angular velocities of the top lid (ν_{t top lid}) are 0.00, 0.35, 1.05 and 1.80 m/s with corresponding velocities of the bottom component in a constant ratio (ν_{t top lid}/ν_{t bottom}) as to reduce secondary circulations in the cross section of the flume. Flow velocity measurements were taken using an acoustic Doppler velocimeter (ADV) across the depth of the flume. During the experiment, abiotic measurements (of pH, temperature and conductivity) as well as water samples were taken. eDNA and eRNA concentrations (in copy numbers per volume) were gathered from these water samples by means of ddPCR, targeting a species-specific 73 base pair fragment in the Cytochrome c Oxidase subunit 1 gene. The abiotic measurements are consistent over the duration of the experiment (average conductivity of 520.1 µS, average temperature of 20.3 °C, average pH of 8.3). Concerning the eNA results, a decrease in both eDNA and eRNA concentrations can be noted over the span of the experiment regardless of the rotation speed. Additionally, eRNA concentrations generally decreased in concentration at a higher rate than eDNA concentrations. These experiments advance the understanding of eNA degradation in lotic ecosystems, and bring forth new directions of research to improve inference in eNA-based biomonitoring.

How to cite: Dercksen, J. A., Stancanelli, L. M., and Blom, A.: The effect of flow velocity on eDNA and eRNA concentration, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17137, https://doi.org/10.5194/egusphere-egu23-17137, 2023.

Lacustrine sediment sequences represent highly valuable, continuous records of continental climate and ecosystem change. As such, they provide vital information on both the timing and magnitude of long-term climate trends as well as abrupt climate change events and associated biotic responses. Assessing this information, however, is often not straight forward as many conventional lipid-based temperature proxies are affected not only by temperature but also other environmental parameters. Here, we show that the distribution of heterocyte glycolipids (HGs), which are synthesized by N₂-fixing heterocytous cyanobacteria and abundantly present in modern freshwater environments, are strongly correlated to lake surface water temperatures. We used these components, in form of the novel organic temperature proxy HDI₂₆, to reconstruct climate variations in tropical East Africa and simultaneously study the impact of climate change on the frequency and intensity of cyanobacterial blooms using a sediment record from Lake Tanganyika (Tanzania). HDI₂₆-reconstructed surface water temperatures varied from ~22 °C to 26 °C in Lake Tanganyika over the last 40,000 years. Lowest temperatures were observed during the Last Glacial Maximum, which is followed by a 3 to 4 °C deglacial warming to yield highest temperatures in the Late Holocene. This general warming trend is interrupted by up to 1 °C cooling during abrupt climate change events (e.g. Younger Dryas). Lipid-based reconstructions of past cyanobacterial activity indicate that although continuously present in Lake Tanganyika, cyanobacteria only became bloom-forming in the late Holocene and in particular during the last 200 years. Our data thus provides new insights and quantitative estimates on Pleistocene to Holocene climate changes in tropical East Africa and associated ecological responses. Given that heterocyte glycolipids are present ubiquitously in polar to tropical lakes and that they have been identified in lacustrine sediments of Early Cenozoic age, the HDI₂₆ and other HG-based indices provide valuable novel tools to extract the highly sensitive climate and ecosystem information that is stored in sediments of lakes worldwide.

How to cite: Bauersachs, T., Russell, J. M., and Schwark, L.: Heterocyte glycolipids: novel tools to obtain high-resolution climate and ecosystem data from lacustrine archives, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17512, https://doi.org/10.5194/egusphere-egu23-17512, 2023.

How to cite: Pilade, F., Vasiliev, I., Birgel, D., Natalicchio, M., Dela Pierre, F., Mancini, A., Lozar, F., and Gennari, R.: Alkenones, as tool for reconstructing surface water temperature and salinity changesduring the Miocene-Pliocene transition in the northern Mediterranean basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14571, https://doi.org/10.5194/egusphere-egu23-14571, 2023.

The organic-rich mudstones and dolostones of the Permian Fengcheng Formation (Fm.) are typically alkaline lacustrine source rocks, which are typified by impressively abundant β-carotane. Abundant β-carotane has been well acknowledged as an effective indicator of biological sources or depositional environments. However, the coupling control of biological precursors and environmental factors on the enrichment of β-carotane in the Fengcheng Fm. remains obscure. Based on a comprehensive investigation of the bulk and molecular geochemistry of sedimentary rocks and the biochemistry of phytoplankton in modern alkaline lakes, we proposed a new understanding of the biological precursors of β-carotane and elucidated the coupling control of biological precursors and environmental factors on the enrichment of β-carotane in the Fengcheng Fm. The results show that the biological precursors crucially control the enrichment of β-carotane in the Fengcheng Fm. The haloalkaliphilic cyanobacteria are the primary biological sources of β-carotane, which is suggested by a good positive correlation between 7-+8- methyl heptadecanes/Cmax and β-carotane/Cmax in sedimentry rcoks and the predominance of cyanobacteria with abundant β-carotene in modern alkaline lakes. Land plants and algae do not significantly contribute to the enrichment of β-carotane, which is indicated by negative or weak correlations between terrigenous/aquatic ratio, C₁₉ tricyclic terpene/C₂₃ tricyclic terpene ratio, the concentration of C₂₇ sterane, and β-carotane/Cmax. The environmental facors such as paleoclimate, paleoredox, paleosalinity, and thermal maturity are the indirect factors that control the enrichment of β-carotane by affecting the precursor supply from cyanobacteria and the preservation conditions in the Fengcheng Fm.

How to cite: Hou, M., Zha, M., and Liu, H.: The coupling control of biological precursors and environmental factors on β-carotane enrichment in alkaline lacustrine source rocks: a case study from the Fengcheng Formation in the western Junggar Basin, NW China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4100, https://doi.org/10.5194/egusphere-egu23-4100, 2023.