SSP1.13

EDI
The future of lakes: how can our knowledge about ancient and modern lakes contribute to anticipate the evolution of lacustrine systems over the next decades, up to 2100?

Limnogeologists and paleolimnologists investigate ancient to recent lakes, either from geological archives preserved in sedimentary basins, or from sediment cores collected from the bottom of lakes. We all come from different disciplines (sedimentology, biology, geochemistry, geophysics, geomorphology, paleontology, archeology, …) and analyse a great diversity of archives (exposures, cores, multibeam bathymetric maps, seismic profiles, landforms, …) in order to reconstruct the story of past lacustrine geo-eco-systems, and to reveal the various factors that have driven their evolution over time, often with annual-seasonal resolution.
This session examines how we can transfer our tremendous knowledge about the evolution of lakes in the past, to realistically imagine and anticipate the near future of lakes? The ongoing climate change and the growing demand on natural resources has already started to impact continental hydrosystems (rivers, lakes, and wetlands), and this is likely to increase in the next few decades, leading to significant water-level changes for many lakes around the world. As such, the near future of lakes, firstly terminal lakes but ultimately all lakes, sounds rather uncertain.
We welcome all contributions concerning past and present lakes, and orientated toward a better understanding of future evolution of lakes (water balance, sediment budget, algal blooms, hydrodynamics, shoreline trajectory, coastal erosion, storm surges, water quality, …) and their consequences on social-ecological systems (biodiversity and human activities). All abstracts submitted should include a reflection of the main results towards the future development of lakes.

Convener: Mathieu Schuster | Co-conveners: Alexis Nutz, Joep Storms, Helena van der VegtECSECS
vPICO presentations
| Mon, 26 Apr, 09:00–10:30 (CEST)

Session assets

Session materials Session summary

vPICO presentations: Mon, 26 Apr

Chairpersons: Joep Storms, Helena van der Vegt, Alexis Nutz
09:00–09:05
09:05–09:15
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EGU21-14808
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solicited
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Highlight
Matthias Prange, Sri Nandini-Weiss, Thomas Wilke, and Frank Wesselingh

Continental drying in response to global warming will entail declining lake levels all over the world. Falling lake levels will have many far-reaching consequences that are underappreciated, but affect the livelihoods and economies of millions of people. A massive warning signal is the projected twenty-first century water level drop of up to 18 m in high emissions scenarios for the Caspian Sea, the largest lake in the world, which could hit stakeholders unprepared. Such a catastrophic drop in the Caspian Sea level would lead to a surface area decrease of 34% including the loss of the highly productive northern Caspian shelf and important wetlands such as the Volga Delta and other Ramsar sites. The disappearance of the vast shallow shelves, which are major food suppliers for fish and birds, will devastate native and endemic fish species, the Caspian seal and a richness of molluscs and crustacean species unique to the lake. The falling water level will not only threaten the unique ecosystem, but will also have severe impacts on regional economies and geopolitical stability.

In the first part of this presentation, we discuss the extent of twenty-first century projected continental drying on a global scale and its potential effect on worldwide lake levels. In the second part, we focus on the Caspian Sea and discuss the potential impacts of water level fall on biodiversity and ecosystem services. Finally, we address the question to which extent paleoclimates can be used as analogs for future global warming scenarios with respect to changes in the Caspian Sea level.

How to cite: Prange, M., Nandini-Weiss, S., Wilke, T., and Wesselingh, F.: The future decline in lake levels puts an evolutionary giant at risk, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14808, https://doi.org/10.5194/egusphere-egu21-14808, 2021.

09:15–09:17
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EGU21-15440
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ECS
Jean-Philippe Jenny, Olivia Itier, Victor Frossard, David Etienne, and Jean Guillard

Climate change raises many questions about the future of lakes’ thermal regime and hypolimnetic oxygen conditions. One dimensional models have been widely implemented over that last years 1–3, but most of these models are calibrated against very few years of limnological records, potentially limiting the robustness in long-term reconstructions and preventing inclusion of future scenarios. To analysis the variability and the effects of climate change on thermal regime and oxygen conditions of deep hard-water lakes, we relayed on paleolimnological records and 1D thermal lake model calibrated against time series of limnological data collected by the French Observatoire des LAcs (OLA). Continuous sediment records on four peri-alpine lakes (Lake Geneva, Lake Annecy, Lake Bourget and Lake Aiguebelette) were analysed using micro-XRF Mn-Fe ratio as proxy to infer near-annual trends of oxygen conditions for the past 300 years4. Past hypoxia dynamics were further inferred from varved records preserved in sediment cores5. General Lake Model (GLM), i.e. a 1-D modelling tool, has been constrained by climate data derived from meteorological observations and CMIP6 simulations in order to reconstruct and forcast stratification regims for the next century. Our paleolimnological results show that fluctuations in hypoxic volumes since the 1950s were great and that these fluctuations were essentially driven by climatic factors, legitimating the use of thermal model approaches for future projections of hypolimnetic oxygen conditions. In this line, thermal regime simulations based on GLM forecast an intensification in thermal stratification and an increase in volumes of water warmer than 9°C over the period 1850-2100 with potential consequence for hypolimnetic oxygen conditions and ecological habitats. Coupling model and paleolimnological approaches seem a promising way to examine the evolution of lakes in the past, and to realistically anticipate the future of lakes for the next decades.

How to cite: Jenny, J.-P., Itier, O., Frossard, V., Etienne, D., and Guillard, J.: Projecting thermal stratification and hypolimnetic oxygen conditions by coupling paleolimnological and 1D lake model approaches, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15440, https://doi.org/10.5194/egusphere-egu21-15440, 2021.

09:17–09:19
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EGU21-527
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ECS
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Highlight
Sien Liu, Qinghua Ye, and Jie Zhou

Large shallow lakes globally are threatened by eutrophication, and climate change is believed to aggregate the situation. Wind, as the most important momentum source and the major contributor to consistently change the hydrodynamic patterns inside the large shallow lakes, is highly susceptible to climate change. Taihu Lake, which is the 3rd largest shallow lake in China and pertains crucial social and economic values, is chosen in this study as an example. Due to climate change, the wind condition of Taihu Lake shows a significantly decreasing trend of wind speed and the frequency of extreme wind events. Previous studies have paid little attention to the climate change effects on wind hydrodynamics and its implications on water quality has not yet been thoroughly described. Here in this study, we use a well-calibrated and validated three-dimensional Delft3D model to investigate the spatial and temporal heterogeneity of wind induced hydrodynamics and its water quality implications with climate change. The model results give a prediction of less current speed, lower wave height and bottom shear stress compared to the reference scenario, while the three dimensionality of flow field remains. Further, water age is used to demonstrate the influence of external nutrient sources, i.e. the input from adjacent river networks in the basin. Large water ages are observed and potentially it would enhance the accumulation of nutrients and deterioration of water quality.

How to cite: Liu, S., Ye, Q., and Zhou, J.: Wind effects change in Taihu Lake with climate change background, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-527, https://doi.org/10.5194/egusphere-egu21-527, 2021.

09:19–09:21
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EGU21-3716
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ECS
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Highlight
Chao Liu and Zaixing Jiang

Lacustrine sedimentation, which is considered to be relatively simple, can be dominated by high-energy wind-driven process. Qinghai Lake, located at the northeastern margin of the Qinghai-Tibet Plateau, western China, is a typical “wind-driven lake”, of which the sedimentation and evolution of shorelines are impacted by prevailing wind. In this research, Buha River Delta and Hargai River Delta, located at the northwestern and northeastern of the lake respectively, are studied through field investigation and remote sensing images analysis. The outcrop section of Buha River Delta is characterized by channel lag deposits, planar cross-beds, and trough cross-beds, indicating a dominant effect of river. However, the section of Hargai River Delta displays planar cross-beds, as well as swash cross-beds (beach deposits) and high-angle cross-beds dip to land (washover deposits), revealing a combined effect of river and waves. Remote sensing images in recent 40 years showed that Buha River Delta remained a stable shape except for the migration of mouth bars, which may be caused by lake level fluctuation. Nevertheless, Hargai River Delta has recorded a noteworthy change in its appearance, which was characterized by the formation of a barrier bar outside the estuary. Meteorological Data reveals that the Qinghai Lake is mainly affected by north-west wind and north wind, thus Buha River Delta is located at the leeward side, while Hargai River Delta is situated at the windward side and significantly influenced by high-energy wind-driven lake currents and waves. When the prevailing wind direction is oblique to the lake shoreline, the coastal current parallel to the shoreline formed by the decomposition of wind-driven waves would transport the clastic materials provided by Hargai River and then deposit them along the lake bank, finally forming a barrier bar parallel to the shoreline. This study reveals that wind-driven process could have totally different effects on either side of a “wind-driven lake”, thus can help us anticipate the evolution of shoreline landform of a “wind-driven lake” in the near future.

How to cite: Liu, C. and Jiang, Z.: The effect of prevailing wind on shoreline landform evolution - Illustrated by the case of Buha River Delta and Hargai River Delta in the Qinghai Lake, western China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3716, https://doi.org/10.5194/egusphere-egu21-3716, 2021.

09:21–09:23
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EGU21-1850
Jonathan Puddick, Carrie Page, Donato Romanazzi, Katie Gunning, Jamie Howarth, Adelaine Moody, Jenny Dahl, Xun Li, Sebastian Naeher, Lizette Reyes, Claire Shepherd, Marcus Vandergoes, and Susie Wood

Phytoplankton (including cyanobacteria) are a natural component of lake ecosystems and are the base of many food webs. However, changes in the lake catchment, the lake itself and the wider environment (e.g., climate change) can alter the composition of phytoplankton communities. Of recent concern is the increase in the abundance of cyanobacteria and the formation of blooms in many of New Zealand’s low-land lakes (>30% of those that are monitored). Because regular monitoring data does not stretch back more than 10-30 years and many lakes are not regularly monitored, it is difficult to ascertain whether the intensity of present-day blooms are a new phenomenon or are part of a pre-existing cycle. The pigments produced by cyanobacteria (and other phytoplankton) are deposited in lake sediment and can be extracted from sediment cores and surface sediment samples. Analysis of these pigments by high-performance liquid chromatography has allowed us to reconstruct the historical phytoplankton community from nine New Zealand lakes and to track the emergence of cyanobacteria in impacted lakes. We will present data on the performance of different cyanobacteria pigment indicators and several case studies to demonstrate how fossilised pigment data can be used to understand shifts in lake phytoplankton communities.

How to cite: Puddick, J., Page, C., Romanazzi, D., Gunning, K., Howarth, J., Moody, A., Dahl, J., Li, X., Naeher, S., Reyes, L., Shepherd, C., Vandergoes, M., and Wood, S.: Using fossilised pigments to understand cyanobacterial blooms in New Zealand lakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1850, https://doi.org/10.5194/egusphere-egu21-1850, 2021.

09:23–09:25
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EGU21-3436
John Pearman, Laura Biessy, Georgia Thomson-Laing, Lizette Reyes, Claire Shepherd, Jamie Howarth, Andrew Rees, Xun Li, Marcus Vandergoes, Susie Wood, and Team Lakes380

A continuous record of environmental history is stored in lake sediments providing an avenue to explore current and historical lake communities. Traditionally paleolimnological methods have focussed on macroscopic indicators (e.g. pollen, chronomids, diatoms) to investigate environmental changes but the application of environmental DNA techniques has enabled the investigation of microbial communities and other soft bodied organisms through time. The ‘Our lakes’ health; past, present, future (Lakes380)’ project aims to combined traditional and molecular methods to explore shifts in biological communities over the last 1,000 years (pre-human arrival in New Zealand). Sediments cores have been collected from a wide diversity of lakes across New Zealand and 16S rRNA gene metabarcoding approaches of both DNA and RNA applied to reveal how microbial community changes across time and especially in response to the arrival of humans and associated changes to the landscape and lake environments. We further investigate the changes in inferred metabolic potential of the microbial communities as the taxonomic composition of the lake differs over time. Finally, we combine these novel molecular methods with hyperspectral scanning and pollen data to increase the knowledge of changes in lake communities and identifying the timing of changes in lake health. The combination of methodologies provides a greater understanding of the environmental history of lake systems and will help to inform management decisions relating to the restoration and protection of lake health.

How to cite: Pearman, J., Biessy, L., Thomson-Laing, G., Reyes, L., Shepherd, C., Howarth, J., Rees, A., Li, X., Vandergoes, M., Wood, S., and Lakes380, T.: Clearer than mud? Using environmental DNA to track historical shifts in lake communities., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3436, https://doi.org/10.5194/egusphere-egu21-3436, 2021.

09:25–09:27
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EGU21-3706
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ECS
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Highlight
Maïlys Picard, Xavier Pochon, Andrew Rees, Jamie Howarth, Marc Schallenberg, Chris Moy, Marcus Vandergoes, Ian Hawes, and Susie Wood

Anthropogenic nutrient enrichment, hydrological modifications, and introduced species are contributing to an increase in the frequency and intensity of cyanobacterial blooms. This study aimed to document the evolution of cyanobacterial assemblages over time and explore the drivers of cyanobacterial blooms. Environmental DNA was extracted from sediment cores dating back approximately 1,000-years collected from six New Zealand lakes (Rotoehu, Pounui, Wairarapa, Paringa, Johnson, Hayes). Samples were analysed using cyanobacterial 16S rRNA metabarcoding and droplet digital PCR. Picocyanobacteria had the highest relative abundance. Marked shifts in species composition were observed over time but species varied between lakes. Marked shifts in total abundance (from ddPCR data) were observed through time in all lakes, and the metabarcoding data revealed these abundances to be bloom-forming taxa only in impacted lakes. Historical cyanobacterial communities seemed to be mostly influenced by anthropogenic activities and the geographic location of the lakes. Comparison with other paleolimnological proxies suggests land-use and non-native fish as key drivers in species and abundance shifts. Sedimentary environmental DNA analysis can complement traditional paleo-approaches, and provide novel information on microbial communities, and new insights into causes and consequences of cyanobacterial blooms.

How to cite: Picard, M., Pochon, X., Rees, A., Howarth, J., Schallenberg, M., Moy, C., Vandergoes, M., Hawes, I., and Wood, S.: Bloom Story: reconstructing historical cyanobacterial communities in six contrasting New Zealand lakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3706, https://doi.org/10.5194/egusphere-egu21-3706, 2021.

09:27–09:29
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EGU21-8920
Purificacion Lopez-Garcia, Guillaume Reboul, Gwendoline David, Ludwig Jardillier, Nataliia Annenkova, Paola Bertolino, Ana I. Lopez-Archilla, Konstantin Vershinin, and David Moreira

Understanding how abiotic and biotic factors influence microbial community assembly and function is crucial to understand ecological processes and predict how communities will respond to environmental change. Lake Baikal (Russian Federation) is the oldest, deepest and most voluminous freshwater lake on Earth, resembling in several respects sea environments. It thus offers a unique opportunity to test the effect of horizontal versus vertical gradients in community structure. Since climate change is rapidly affecting Siberia and Lake Baikal, this information can be useful both, as a reference for future monitoring of the lake and to help predictions about how local communities change as a function of environmental parameters. In order to address these questions, in 2017, we carried out a comprehensive sampling of Lake Baikal water columns and sediments along a North–South latitudinal gradient (ca. 600 km) across the three major basins of the lake, from coastal to pelagic areas and from surface to the deepest zones (0.5 to 1450 m deep). We then applied metabarcoding approaches based on 16S and 18S rRNA gene amplicon sequencing to characterize the composition of microbial communities, in particular, both prokaryotes and eukaryotes in sediments and microbial eukaryotes (0.2-30 µm cell size) in plankton (65 samples from 17 water columns). As expected, depth had a strong significant effect on protist community stratification in the water column. The effect of the latitudinal gradient was marginal and no significant difference was observed between coastal and surface open water communities. Co-occurrence network analyses showed that epipelagic protist communities were significantly more interconnected than in the dark water column. Surprisingly, Baikal benthic communities (13 sites) displayed remarkable stability across sites and seemed not determined by depth or latitude. Comparative analyses with other freshwater, brackish and marine sediments confirmed the distinctness of Baikal benthic communities, which show some similarity to marine and hydrothermally-influenced systems likely owing to its high oligotrophy, depth and fault-associated seepage. Metagenomic analyses of sediment samples show a wide metabolic potential of Baikal benthos and highlight the relative importance ammonia-oxidizing archaea in upper sediment layers.

How to cite: Lopez-Garcia, P., Reboul, G., David, G., Jardillier, L., Annenkova, N., Bertolino, P., Lopez-Archilla, A. I., Vershinin, K., and Moreira, D.: Environmental drivers of plankton and sediment microbial communities along latitudinal and vertical gradients in the deepest freshwater lake (Baikal, Southern Siberia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8920, https://doi.org/10.5194/egusphere-egu21-8920, 2021.

09:29–09:31
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EGU21-4533
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ECS
Miguel Iniesto, Karim Benzerara, David Moreira, Nina Zeyen, Rosaluz Tavera, Damien Daval, and Purificación López-García

Modern microbialites are frequently studied as analogues of ancient microbialites, the oldest of which date back to ~3.5 Ga. These organo-sedimentary structures are generated by complex microbial communities developing under specific physicochemical conditions, such that fossil microbialites attest for past microbial ecosystems. Lacustrine microbialites, in contrast with marine ones, show a large range of morphologies and mineralogical compositions, including various carbonate and non-carbonate (e.g. Mg-silicates) phases. Major dominant prokaryotic groups (e.g. Cyanobacteria, Planctomycetes or Alphaproteobacteria) and taxa‐associated functions (e.g. oxygenic and anoxygenic photosynthesis) appear conserved across microbialite ecosystems. However, the evolution of the microbial community and/or the chemical and mineralogical composition of lacustrine microbialites with the hydrogeochemistry of lakes remains undescribed. In the present work, we analysed the mineralogical and chemical composition, including major and trace element composition of microbialites as well as their microbial community using samples from ten crater lakes of the Trans‐Mexican volcanic belt along an alkalinity-salinity gradient. We also characterized lake hydrochemistry and planktonic communities to compare them with those of microbialites. We found a large diversity of microbialites in terms of mineralogical composition which was primarily controlled by orthosilicic acid (H4SiO4) concentrations and Mg/Ca ratios of the solutions. In addition, microbialite size correlated positively with salinity, (Mg/Ca)aq ratio and alkalinity. Our observations suggest that alkalinity values above 1.23 mM and salinity above 0.08 g.L-1 constitute potential chemical threshold above which lacustrine microbialites can occur. The composition of both prokaryotic and the eukaryotic microbialite-associated communities varied significantly across lakes, correlating with the alkalinity and salinity gradient. Moreover, microbialite-associated communities were clearly distinguishable from their surrounding planktonic communities, being more similar to those of microbialites from distant and chemically different lakes than to planktonic communities present in the same lake. In fact, we identified a microbial core of 247 operational taxonomic units shared by all lake microbialites. This core, mainly dominated by Cyanobacteria, Bacteroidetes, Planctomycetes, Chloroflexi, Alphaproteobacteria and Gammaproteobacteria, represented up to 40% of the relative abundance of the community in lakes displaying the highest alkalinity and most conspicuous microbialites (Alchichica and Atexcac). This suggests a prominent ecological role for those organisms in microbialite formation. We could also show that, in Lake Alchichica, microbialites formed very rapidly on inert surfaces (e.g. plastic) with rates of ~0.6 (and up to 1) mm/year and that nascent hydromagnesite and aragonite-rich microbialites harboured communities   similar to the mature ones in native microbialites. Our study establishes a connection between the chemical, mineralogical and microbial composition of microbialites and the hydrogeochemical evolution of lakes. Alkalinity and salinity gradients reflect lake hydrological balance and status along an evaporation progress trend and/or weathering intensity of the surrounding bedrocks. In this context, microbial communities associated with modern lacustrine microbialites may possibly be used as indicators for management/prediction of limnologic states along alkalinity-salinity gradients.

 

How to cite: Iniesto, M., Benzerara, K., Moreira, D., Zeyen, N., Tavera, R., Daval, D., and López-García, P.: Microbialites as bioindicators of lake hydric dynamics: the evolution of microbial populations and mineralogy of Mexican lacustrine microbialites along an alkaline-saline gradient, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4533, https://doi.org/10.5194/egusphere-egu21-4533, 2021.

09:31–09:33
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EGU21-5331
Ludwig Jardillier, Gwendoline David, Philippe Deschamps, Paola Bertolino, David Moreira, Benjamin Alric, Gwendal Restoux, Emma Rochelle-Newall, Elisa Thébault, Marianne Simon, and Purificación López-García

Small freshwater ecosystems are highly diverse, widely distributed, may be identified as major actors in greenhouse gas fluxes and are potential stocks of freshwater for human usages. In principle, they are more sensitive to environmental disturbance than large aquatic ecosystems because their small volumes provide low buffering capacity. However, little is yet known about their microbial biodiversity and function and how it is structured over time. Yet, understanding the structuring of microbial primary producers, predators, parasites and degraders in these ecosystems is essential to appreciate and model their functioning in the next decades. We investigated the spatial distribution and temporal dynamics of microorganisms of the three domains of life (bacteria, archaea, microbial eukaryotes) at the intra- (seasonal) and inter-annual (pluri-annual) scale in five small freshwater ecosystems. We focused on four ponds and a brook located in northwestern France under temperate climate that we studied for eight years (2011-2019) at seasonal frequency. Microbial diversity was assessed through Illumina MiSeq sequencing of 16S and 18S rDNA amplicons. Several abiotic parameters (physical and chemical) were measured in situ and in the laboratory to characterise the environmental conditions. Multivariate statistical analyses were conducted to identify temporal patterns and link them to environment changes. Microbial communities differed among the ecosystems despite their spatial proximity, likely due to differences in local environmental conditions. Microbial eukaryotic and prokaryotic communities exhibited seasonal temporal patterns and a shift in composition over the years. Microbial communities experienced a strong turnover at the seasonal scale leading to a low fraction (< 2%) of recurrent taxa. In each ecosystem, the measured physico-chemical parameters slightly influenced the microbial community variance over time. These results suggest that biotic interactions but also dormancy, immigration and genetic evolution superimpose to environmental selection through time. Understanding their interplay will be essential to explain microbial community composition change in these ecosystems. 

How to cite: Jardillier, L., David, G., Deschamps, P., Bertolino, P., Moreira, D., Alric, B., Restoux, G., Rochelle-Newall, E., Thébault, E., Simon, M., and López-García, P.: Microbial community composition seasonality and drift over years in small freshwater ecosystems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5331, https://doi.org/10.5194/egusphere-egu21-5331, 2021.

09:33–09:35
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EGU21-16142
Olga Otero

In paleontological context, fish remains are frequently collected and constitute a large part of the lake macro-fossil assemblages. In the presentation, examples from continental Africa chosen in lakes of different dimension, shape and history (mainly Malawi, Chad and Turkana) will illustrate how fish fossil study potentially provides a wide range of information on the paleoenvironment (water salinity, temperature, oxygenation, seasonality, etc.) and the paleogeography (watershed connections) of the lake and its basin. It is based on the knowledge of the ecology and phylogeny of the species and through dedicated biogeochemical and sclerochronological studies of their bones and teeth that also constitute paleo-bio-archives that recorded certain environmental information. Alongside the results extracted from each dedicated study, their combination provide new information and show the gain of extracting different and independent informations from the same object or from objects from the same assemblage, and notably in the case of lake-fish assemblages. For example, the combination of the knowledge on a fish paleo-ecology in a lake with results of a biogeochemical study of their remains can evidence change in the hydrographical regime between successive lake deposits. Finally, fish study also allow an interpolation of change in paleoenvironments at different time scales and their integrative study as paleoenvironmental proxy should be more widely included in the evolution of lakes in the past. The multi-time scale and proxy study enabled on fossil fish is sensible for transfer to predict modern lake evolution.

How to cite: Otero, O.: Fossil fish species and assemblage are relevant integrative paleo-biogeo-archives in ancient lakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16142, https://doi.org/10.5194/egusphere-egu21-16142, 2021.

09:35–09:37
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EGU21-12114
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ECS
Juan Andrade, Mathieu Schuster, Alexis Nutz, and Bert Van Bocxlaer

The northern Turkana Depression of the East African Rift System in Northern Kenya and Southwestern Ethiopia has one of the most complete and well-documented late Cenozoic continental fossil records worldwide, including remarkable finds of early hominins and associated African Cenozoic vertebrates. Most previous paleoenvironmental reconstructions of the depression were developed using terrestrial vertebrate faunas and paleolandscapes, leaving freshwater ecosystems and associated hydrosystems (lakes, tributaries, river deltas, and wetlands) largely unaddressed. African Cenozoic freshwater mollusks were long considered to be good biostratigraphic indicators, given that their communities are able to represent long phases of morphological stability and at other times rapid morphological changes. However, to what extent changes in freshwater mollusk assemblages match with changes in sedimentary landscapes and lake level fluctuations remains unclear. Here, we address this question through integrative studies on Plio-Pleistocene fossil freshwater mollusks assemblages. Specifically, we are developing a taxonomic framework on fossil freshwater bivalves belonging to the families Unionidae, Iridinidae, Etheriidae and Corbiculidae to create a standardized overview of stratigraphically well-characterized fossil assemblages. Subsequently, we integrate this paleontological dataset with sedimentological characterizations of the depositional environments in which shell beds accumulated at high resolution around faunal turnover events. A detailed reconstruction of environmental changes and how these changes affected freshwater ecosystems in the northern Turkana Depression may allow us to recognize key environmental drivers that triggered faunal turnover events. Such an understanding of drivers from the past perhaps provides our best hope to anticipate how future environmental changes will alter freshwater ecosystems in tropical Africa, and, ultimately, the availability of various freshwater resources on which humanity depends.

How to cite: Andrade, J., Schuster, M., Nutz, A., and Van Bocxlaer, B.: A perspective on Plio-Pleistocene hydrosystems of the northern Turkana Depression (East African Rift System) reconstructed from the study of freshwater mollusk communities, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12114, https://doi.org/10.5194/egusphere-egu21-12114, 2021.

09:37–09:39
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EGU21-4634
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ECS
Carlo Mologni, Laurent Bruxelles, Fabien Arnaud, Pierre Sabatier, Anne-Lise Develle, Emmanuel Malet, Eric Chaumillon, Mathieu Schuster, Gourguen Davtian, Jessie Cauliez, Marie Revel, and Lamya Khalidi

Throughout the last 14 ka, tropical Africa experienced significant hydrological changes that were mainly driven by the orbital precession cycle, which controls the intensity of the African monsoon. Recent studies conducted in lake and deltaic sedimentary records suggest that long-term monsoon humid oscillations (African Humid Period / AHP ~14 – ~6 ka) were punctuated by centennial-scale episodes of hyperaridity. However, the abrupt or gradual aridification modalities since the end of the AHP and the modalities of the centennial-scale episodes, as well as their impacts on past and current environments are still debated.

The Lake Abhe basin in the Central Afar region (Ethiopia & Djibouti) is the endorheic receptacle of freshwater originating in the Ethiopian Highlands, and represents a hydro-sedimentary system sensitive to hydro-climatic changes in East Africa. Today it is characterized by residual lakes (Gamari and Afambo lakes) and a hyper-arid climate, while during the AHP, the Abhe basin was occupied by a Mega-lake and by humid environmental conditions. Holocene climatic disruptions drastically changed the landscapes and ways of life along this basin.  

The aim of this study is to describe, interpret and estimate the impact of hydro-climatic oscillations on the evolution of Lake Abhe’s littoral lacustrine environments and palaeolandscapes since the AHP from different viewpoints.

Indeed, this research combines paleoclimatological and geomorphological studies based on a new set of 14C ages on two lacustrine cores and on several morpho-sedimentary outcrops spanning the Early to Late Holocene. Our results allow us to: a) refine the temporal occurrence and the hydrological modalities of the AHP including short-term arid episodes linked to Younger Dryas and 8.2 ka North Atlantic events; b) recognise some paleo-shoreline geomorphic features linked to lake level fluctuations, as well as the development littoral pedological horizons and the activation/shutdown of the perilacustrine fluvial network during humid and arid events; c) track these changes until the present day, and discuss their evolution scenario in the near future.

Comparing with other regional climatic records, we show how Lake Abhe basin was highly reactive to East African monsoonal regimes, and how current hydrological changes could impact its environments.      

How to cite: Mologni, C., Bruxelles, L., Arnaud, F., Sabatier, P., Develle, A.-L., Malet, E., Chaumillon, E., Schuster, M., Davtian, G., Cauliez, J., Revel, M., and Khalidi, L.: Hydro-climatic fluctuations and their impact on Lake Abhe environments (Ethiopia & Djibouti): a lesson from the past 10,000 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4634, https://doi.org/10.5194/egusphere-egu21-4634, 2021.

09:39–09:41
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EGU21-1624
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ECS
Xue Xinyu, Jiang Zaixing, and Wang Li

Existing fan-delta depositional models for lacustrine basins do not adequately address significant wave- and storm-related processes. However, in many lakes, such high-energy processes can be effectively driven by winds. As such, the prevailing wind direction determines the progradation direction of wind-induced waves. Observations from modern cases show that wave-dominated deposits commonly exist on one side of the lake, and their sedimentary processes are completely distinct from those on the opposite side, such as in Qinghai Lake in China. However, equivalent deposits have seldom been identified from subsurface data. We present an ancient example from the Upper Tongbomiao Formation in the Tanan Depression (Tamtsag Basin, Mongolia), which was previously interpreted as a fan-delta depositional system. Based on extensive core investigations, eighteen lithofacies, six lithofacies associations and two genetic deposition systems are identified, and a new sedimentological interpretation is proposed for the Upper Tongbomiao Formation containing a wave-dominated clastic shoreline system in the western half-graben dip slope (W-DS) and a fluvial-dominated fan-delta system in the eastern half-graben (E-HG). Sediments within the E-HG unit are grouped into the three lithofacies associations of braidplain, fan-delta front and prodelta, while those within the W-DS unit comprise dominantly alluvial fan, wave-reworked beach, storm-affected shoreface and offshore sediments. Several factors contribute to the preservation of these two distinct sedimentary systems that developed on opposite shores of the lake: (i) the southeast to northeast prevailing wind direction during the deposition period; (ii) a gentle paleotopographic slope in the W-DS unit, while a steep one in the E-HG unit; (iii) a climate shift toward more humid climatic condition from Lower to Upper Tongbomiao Formation intensified hydrodynamic conditions that were able to rework the sediments distributed in the W-DS unit. Finally, we discuss their implications for the future development of shoreline morphology of continental lakes affected by a monodirectional prevailing wind.

How to cite: Xinyu, X., Zaixing, J., and Li, W.:  Wind-induced waves and storms in fan-delta lacustrine successions: New observations from Tanan Depression, Tamtsag Basin, Mongolia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1624, https://doi.org/10.5194/egusphere-egu21-1624, 2021.

09:41–09:43
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EGU21-6447
Patrick Lajeunesse, Annie-Pier Trottier, Antoine Gagnon-Poiré, Alexandre Normandeau, Etienne Brouard, Antoine Morissette, and Geneviève Philibert

Hydroacoustic surveys were conducted in eight fjord-lakes of Québec-Labrador in order to analyse their Late-Quaternary geomorphological and stratigraphic record of glaciation, paleoseismicity and postglacial environmental changes. This large morphostratigraphic dataset provided a unique opportunity to establish a conceptual model of the evolution for fjord-lakes in relation to deglaciation, glacio-isostatic rebound, sediment fluxes and paleoseismicity. The analysis of the morphology and distribution of many morainic deposits into the fjord-lakes (hummocky moraines, morainic sills and morainic complexes) allows relating their formation to the glacial erosion potential, as well as to climatic and topographic controls. During past glaciations, a topographic sill was left uneroded at the opening of valleys due to the decrease in the glacial erosion potential associated with the lateral extension of the glacier down-ice; this bedrock sill created in turn an anchoring point to the ice during deglaciation. Hummocky moraines were documented at the outlet of five fjord-lakes that are located within the deepest and narrowest valleys of the studied systems. Based on our analysis of these sublacustrine landform-sediment assemblages, fjord-lakes constitute distinct sedimentary systems that should be differentiated from typical fjord system (i.e., in marine waters). The large-scale landforms contained in the fjord-lakes of Québec-Labrador (i.e., esker, moraines, gullies, lateral banks, turbidity channels and circular cavities) are inherited from their past subglacial, glaciomarine and paraglacial conditions, while only small deltaic bedforms (i.e., sediment waves and crescent-shaped bedforms) were formed in postglacial times. The present-day hydrological regime of fjord-lakes of Québec-Labrador is considered river-driven, except for the lakes located near active seismic zones where widespread postglacial mass-movements are documented.

How to cite: Lajeunesse, P., Trottier, A.-P., Gagnon-Poiré, A., Normandeau, A., Brouard, E., Morissette, A., and Philibert, G.: The Late-Quaternary morphostratigraphic record of glaciation, paleoseismicity and postglacial environmental changes in fjord-lakes of Québec-Labrador , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6447, https://doi.org/10.5194/egusphere-egu21-6447, 2021.

09:43–09:45
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EGU21-15787
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ECS
Nikolina Ilijanić, Slobodan Miko, Ozren Hasan, Dea Brunović, Martina Šparica Miko, Željka Sladović, Ivona Ivkić Filipović, Natalia Šenolt, and Gordana Goreta

Lake Visovac is a tufa barrier lake on the Krka River between Roški slap (60 m asl) and Skradinski buk (46 m absl) waterfalls, included in the Krka national park as primarily unaltered area of exceptional natural value. Paleolimnological research was conceived to address a lake evolution and depositional environments through the geophysical survey and collection of the lake sediment cores. A high-resolution bathymetric map was obtained using a multibeam sonar. The average lake depth varies between 20 and 25 m. Sediment cores were investigated to extract physical properties, sedimentological, mineralogical, geochemical and paleoecological records constrained by the radiocarbon chronology, to understand what was happening to both the landscapes and lakescapes of Lake Visovac during the last 2.000 cal yr.

Significant findings of the project are geomorphological features on the lake bottom: submerged sinkholes of various sizes (up to 40 m deep); submerged tufa barriers in the area of Kalički kuk (southern part of Lake Visovac) at the depths of 15 and 17 m, followed by a series of buried cascade tufa barriers at the depth of 25 m covered with up to 10 m of Holocene lake sediments; submerged vertical tufa barrier up to 32 m-high near the mouth of Čikola River; submerged landslides, small (river) fan structures characterized by sediment waves. Ground-penetrating-radar (GPR) data have been acquired due to the presence of gas-saturated sediments over a large area of the lake, that limited the use of high-resolution acoustic profiling. A total thickness of sediments is up to 40 m. High resolution paleoenvironmental record through the Late Holocene gives evidence of high sedimentation rates in Lake Visovac, variable soil erosion impact on lake sediment composition and carbonate authigenic sedimentation. Higher organic carbon is observed in the last 50 years due to changes in land cover and reforestation. Pleistocene lake sediment outcrops occur up to 20 m above the present lake levels indicating higher lake levels as a consequence of higher elevation of tuffa barriers. Kalički kuk, which lies up to 20 m above present lake level, is a remnant of these barriers which have been dated to MIS5. Results allow us to interpret the environmental and evolutionary dynamics of Lake Visovac in the following way: lake level more than 20 m higher than today in mid-Pleistocene with significantly larger lake volume in Lake Visovac, with active Kalički kuk and Skradinski buk waterfalls; lower lake-level at the beginning of the Holocene when several small lakes existed in isolated basins in the area of Lake Visovac. The tufa barrier at Skradinski buk started to grow faster than the Kalički kuk barriers and waterfalls resulting in their flooding and submergence during the Holocene. The tufa barrier at Skradinski buk has grown 15 m since then. This study demonstrates the role of geomorphological lakebed characteristics in reshaping our understanding of the environmental changes and the future of Lake Visovac.

The research was conducted as part of the project funded by the Krka National Park and CSF funded QMAD project (IP-04-2019-8505).

How to cite: Ilijanić, N., Miko, S., Hasan, O., Brunović, D., Šparica Miko, M., Sladović, Ž., Ivkić Filipović, I., Šenolt, N., and Goreta, G.: Geomorphology of the lakebed and sediment deposition during the Holocene in Lake Visovac, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15787, https://doi.org/10.5194/egusphere-egu21-15787, 2021.

09:45–09:47
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EGU21-14576
Sebastien Joannin and the Sevan-upians

To understand the long-term patterns of atmospheric circulation in Eurasia, current paleoclimatic reconstruction syntheses lack accurate data for the Near East. In this semi-arid zone, precipitation is the key factor to be studied that strongly controls ecosystems and human societies. Few data are available from Lake Sevan (1900.52 m above sea level, 1,279 km², 38.2 km3 as of January 1, 2021), the largest fresh-water lake in the Near East, whose past level variations may document seasonal to millennial precipitation changes.

We present here the preliminary results of the interdisciplinary Sevan-up Project. Its ambition is to develop a high resolution lake level reconstruction (which is expected to be preserved from the influences of long ecological processes and from human activities) and other climatic proxies (from pollen and molecular biomarker) in view to quantify precipitation changes during the Holocene.

The Early Holocene climate characteristics (strong seasonality) and environment (prevalence of steppe ecosystems) may raise an analogous model of future conditions in the Near East which will be affected by enhanced continentalism. The study of littoral and deep sedimentary deposits will potentially reveal the consequences of past variations in lake levels on its hydrodynamic functioning and trophic status. These results will give crucial information on how to improve the lake's water management with the goal to reach a sustainable use and a better ecological state. Indeed, seasonal stratification onsets and trophic status dramatically changed since the man-made water-level fall during the Soviet times (40% of its volume).

How to cite: Joannin, S. and the Sevan-upians: Past variations of Lake Sevan (Armenia, lesser Caucasus): documenting climate triggers for the Near East and delivering insights for a sustainable management, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14576, https://doi.org/10.5194/egusphere-egu21-14576, 2021.

09:47–09:49
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EGU21-8467
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Highlight
Daniel Ariztegui, Clément Pollier, and Andrés Bilmes

Lake levels in hydrologically closed-basins are very sensitive to climatically and/or anthropogenically triggered environmental changes. Their record through time can provide valuable information to forecast changes that can have substantial economical and societal impact.

Increasing precipitation in eastern Patagonia (Argentina) have been documented following years with strong El Niño (cold) events using historical and meteorological data. Quantifying changes in modern lake levels allow determining the impact of rainfall variations while contributing to anticipate the evolution of lacustrine systems over the next decades with expected fluctuations in ENSO frequencies. Laguna Carrilaufquen Grande is located in the intermontane Maquinchao Basin, Argentina. Its dimension fluctuates greatly, from 20 to 55 km2 water surface area and an average water depth of 3 m. Several well-preserved gravelly beach ridges witness rainfall variations that can be compared to meteorological data and satellite images covering the last ~50 years. Our results show that in 2016 lake level was the lowest of the past 44 years whereas the maximum lake level was recorded in 1985 (+11.8 m above the current lake level) in a position 1.6 km to the east of the present shoreline. A five-years moving average rainfall record of the area was calculated smoothing the extreme annual events and correlated to the determined lake level fluctuations. The annual variation of lake levels was up to 1.2 m (e.g. 2014) whereas decadal variations related to humid-arid periods for the interval 2002 to 2016 were up to 9.4 m. These data are consistent with those from other monitored lakes and, thus, our approach opens up new perspectives to understand the historical water level fluctuations of lakes with non-available monitoring data.

 

Laguna de los Cisnes in the Chilean section of the island of Tierra del Fuego, is a closed-lake presently divided into two sections of 2.2 and 11.9 km2, respectively. These two water bodies were united in the past forming a single larger lake. The lake level was  ca. 4 m higher than today as shown by clear shorelines and the outcropping of large Ca-rich microbialites. Historical data, aerial photographs and satellite images indicate that the most recent changes in lake level are the result of a massive decrease of water input during the last half of the 20th century triggered by an indiscriminate use of the incoming water for agricultural purposes. The spectacular outcropping of living and fossil microbialites is not only interesting from a scientific point of view but has also initiated the development of the site as a local touristic attraction. However, if the use of the incoming water for agriculture in the catchment remains unregulated the lake water level might drop dangerously and eventually the lake might fully desiccate.

These two examples illustrate how recent changes in lake level can be used to anticipate the near future of lakes. They show that ongoing climate changes along with the growing demand of natural resources have already started to impact lacustrine systems and this is likely to increase in the decades to come.

How to cite: Ariztegui, D., Pollier, C., and Bilmes, A.: Quantifying recent lake level changes in Patagonia (Argentina and Chile): Back to the future?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8467, https://doi.org/10.5194/egusphere-egu21-8467, 2021.

09:49–09:51
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EGU21-9168
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ECS
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Highlight
Kristin Haas, Kim J. Krahn, Sara Saeidi Ghavi Andam, Rik Tjallingii, Matthias Hinderer, Elena Marinova, Manfred Rösch, and Antje Schwalb

Seasonally laminated lacustrine sediments of Lake Stadtsee, located in the city of Bad Waldsee (Southern Germany), offer a continuous archive that allows a unique and yearly correlation of sedimentary signals and historic documents since medieval times. Comparison of the economic and environmental history of an urban centre will provide detailed insight into how the history of a city and its periphery region affected lake development and water quality, and how fast water quality and aquatic ecosystem recovered from human impact and activities. An interdisciplinary research team consisting of geologists, biologists, and historians from various universities and institutions has been established and started its work recently. The common goal of the different working groups and disciplines is to investigate temporally highly resolved sediment records of diatom and pollen spectra, geochemical proxies, and sediment facies of profundal sediment cores from Lake Stadtsee and to compare and calibrate these results with historic documents, stock books, archive records, dendrochronology records, and maps. So far, continuous geochemical sediment records of Lake Stadtsee were acquired non-destructively using X-ray fluorescence (XRF) core scanning. These element intensity records of the major elements (e.g. Al, Si, K, Ca, Ti, Fe) were measured every 2 mm. Sampling and subsequent analyses (e.g. pollen, PAH, isotopes) are ongoing.

Overall, the environmental impact of socio-economic development for the preindustrial development phase of a city from AD 1200 to 1800 will be assessed for the first time. The research will focus on the effects of population growth or decrease, farming intensity, economic production, trade activity in relation to environmental, and climate change, including catastrophic events such as fires and floods. The results will provide important insights about the response of urban surface waters to changing emissions of the city and the long-term behaviour of persistent pollutants on lakes. The project will thereby contribute to the knowledge of historic human impact on the environment in Germany, pre-medieval reference conditions, and the limits of resilience of aquatic systems. Thus, it will target the past environmental footprint of anthropogenic induced events on urbanized lake ecosystems and help to understand the mechanism behind such processes in the future.

How to cite: Haas, K., Krahn, K. J., Saeidi Ghavi Andam, S., Tjallingii, R., Hinderer, M., Marinova, E., Rösch, M., and Schwalb, A.: Impact of urban development on waterbodies during medieval and early modern ages in Bad Waldsee (Germany), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9168, https://doi.org/10.5194/egusphere-egu21-9168, 2021.

09:51–09:53
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EGU21-14459
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Highlight
Raimond Christine, Yalikun Tashi, Créteaux Jean-François, Berge-Nguyen Muriel, Schuster Mathieu, and Sylvestre Florence

The Sahel, located at the southern edge of the Sahara is defined as the transitional boundary of the Sahara, whose aridification since the late Holocene has profoundly affected landscapes, human occupation and ecosystems. Current climate change, characterized by an increase in temperature, raised the idea of aridification and the disappearance of surface water in the Sahelian zone. However, in central Sahel, the trend towards increasing open water surfaces seems to be confirmed over the last decade, particularly during extreme rainfall episodes. Here, we show the current changes of Lake Fitri, a remnant of the mega-lake Chad during the Holocene 6,000 years ago, whose seasonal flooding has reached unequaled levels in the last 50 years. This terminal and shallow lake and spreading out over a vast flat sedimentary plain irrigates a variable surface area. During exceptional rainy years such as the current one (2020-2021), the waters from the Batha river basin (main tributary of Lake Fitri), in the Sahelian zone, can reach the Chari catchment area (main tributary of Lake Chad) by passing through a succession of basins.

The diachronic analysis of Landsat images combined with ground-based observations recorded during the year 2020-2021 will be compared with the previous available time-series, in particular the monthly series already analysed for the year 2015 (Yalikun and al., 2019). The results confirm the trend towards the extension of the lake and the "outflow" of its waters to the west. These observations raise many questions related to the definition of a lake and its precise shoreline in this context. We will also specify the consequences in terms of the recomposition of the social-ecological system (changes in land use, recomposition of activity systems and access to natural resources, governance issues). Finally, we will discuss the timing of the changes observed in the short (annual, decade), medium (25 years), long and very long term (Holocene), on the comparability of these changes and on the elements to be considered in order to envisage the future evolution of such sahelian social-ecological system.

How to cite: Christine, R., Tashi, Y., Jean-François, C., Muriel, B.-N., Mathieu, S., and Florence, S.: Anticipating the evolution of the Fitri lake system: temporalities of an overflowing flood and its socio-ecological consequences, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14459, https://doi.org/10.5194/egusphere-egu21-14459, 2021.

09:53–10:30