SSP1.13

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.

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 3^rd 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.