Jean-Jacques Braun

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Verified

Jean-Jacques verified their affiliation via an institutional email.

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• PhD, HDR
• Senior Researcher at Institute of Research for Development

Sone Essoh, W.; Onguene, R.; Ndongo, B.; Nshagali, G.; Colmet-Daage, A.; Guillaume, M.; Iroume, J.; Stieglitz, T.; Besck, F.; Efole Ewoukem, T.; Tomedi Eyango, M.; Etame, J., and Braun, J.J., 2023. Using GIS and multicriteria analysis to map flood risk areas of the Tongo Bassa River Basin (Douala, Cameroon). Journal of Coastal Research, 39(3), 531–...

A hydrological and hydrochemical database (produced by the M-TROPICS critical zone observatory) in the upper Nyong Basin from 1998 to 2017 was used to evaluate the river’s response to climatic and anthropogenic forcing and examine chemical weathering processes. SiO2 and HCO3 constitute about 85 % of the Total dissolved solids (TDS) load, equivalent...

Studies of landscape dynamics in protected areas often rely exclusively on remotely-sensed data, leading to bias by neglecting how local inhabitants, who often have a long history of interaction with their environment, perceive and structure the landscape over time. Using a socio-ecological system (SES) approach in a forest-swamp-savannah mosaic wi...

This study investigates teleconnections between rainfall in the Ogooué River Basin (ORB) and sea surface temperature (SST) in the tropical ocean basins. The Maximum Covariance Analysis (MCA) is used to determine coupled patterns of SST in the tropical oceans and rainfall in the ORB, depicting regions and modes of SST dynamics that influence rainfal...

The impact of human activity on soil carbon stock and soil fertility is at the forefront of scientific research. In the past, human practices improved soil fertility and increased carbon storage over long periods of time. Studying the resulting anthrosols provides access to their evolution over time scales that are unavailable otherwise. These arch...

Bullet points 21 • The Ogooué River catchment is denuding at a low rate (38 t/km 2 /a, 15 m/Ma) 22 • There is substantial chemical denudation: > 30% of the total denudation 23 • Batéké Px not producing solutes because constituted by already weathered material 24 • The southern part of the catchment is denuding twice as fast as the northern part 25...

Flooding constitutes a major problem for the inhabitants of Douala City in general and those of the Tongo Bassa watershed (TBW) in particular. Faced with this situation, public authorities need to put in place measures to mitigate the vulnerability of populations to these disasters. This article aims to map flooding risk areas in the TBW using the...

Studies of landscape dynamics in protected areas often rely exclusively on remotely-sensed data, leading to bias by neglecting how local inhabitants, who often have a long history of interaction with their environment, perceive and structure the landscape over time. Using a socio-ecological system (SES) approach in a forest-swamp-savannah mosaic wi...

The objective of this study is to understand the impact of rainfall variability and anthropization on the flows of the Mefou watershed over a recent period. For this, the hydropluviometric data of the catchment concerned were analyzed using the Pettitt test. Likewise, the dynamics of the main land-use patterns have been assessed, using supervised c...

The purpose of this article is to get an idea of the evolution of the flows of the So'o basin in the relatively near future (2022-2060), but also in the distant future (2061-2100). In this perspective, the Cellular Automata (CA)-Markov was used to predict the evolution of the future land use of the basin, and the outputs of three regional climate m...

Due to climate and environmental changes, sub-Saharan Africa (SSA) has experienced several drought and flood events in recent decades with serious consequences on the economy of the sub-region. In this context, the region needs to enhance its capacity in water resources management, based on both good knowledge of contemporary variations in river fl...

A major flood event occurred on 21 August 2020 in the densely populated Makèpè Missokè neighborhood in the city of Douala (Cameroon, Africa). Nearly 2210 buildings and 12,376 victims spread over 82 hectares were affected. A 2D HEC-RAS model is applied to simulate and characterize this event. A cross analysis of flood depth and flow velocity is used...

Climate change, variability and anthropogenic forcings such as land use change are the main forcings of river discharge variability. However, an understanding of their simultaneous impacts on river discharge remains limited in some parts of the world. To shed light on this issue, the objective of this article is to investigate the effects of rainfa...

This chapter describes the variability of rainfall and river discharges in the Ogooué River Basin (ORB) in recent decades (since 1940). Due to its location crossing the Equator, the ORB receives abundant precipitation, which maintains one of the world's best‐preserved ecosystems. In contrast to neighboring forest basins that have been severely degr...

Ce chapitre décrit la variabilité des précipitations et des débits des rivières dans le bassin de l'Ogooué (ORB) au cours des dernières décennies (depuis 1940). En raison de sa situation géographique, traversant l'équateur, l'ORB reçoit des précipitations abondantes qui maintiennent l'un des écosystèmes les mieux préservés au monde. Contrairement a...

Tropical rivers emit large amounts of carbon dioxide (CO2) to the atmosphere, in particular due to large wetland-to-river carbon (C) inputs. Yet, tropical African rivers remain largely understudied, and little is known about the partitioning of C sources between wetland and well-drained ecosystems to rivers. In a first-order sub-catchment (0.6 km2)...

This paper investigates links between rainfall variability in the Ogooué River Basin (ORB) and El Niño Southern Oscillation (ENSO) in the Pacific Ocean. Recent hydroclimatology studies of the ORB and surrounding areas resulting in contrasting conclusions about links between rainfall variability and ENSO. Thus, to make the issue clearer, this study...

In Central Africa, the malaria vector Anopheles coluzzii is predominant in urban and coastal habitats. However, little is known about the environmental factors that may be involved in this process. Here, we performed an analysis of 28 physicochemical characteristics of 59 breeding sites across 5 urban and rural sites in coastal areas of Central Afr...

Despite the importance of tropical ecosystems for climate regulation, biodiversity, water and nutrient cycles, only a few Critical Zone Observatories (CZOs) are located in the tropics. Among these, most are in humid climates, while very few data exist for semi‐arid and sub‐humid climates, due to the difficulty of estimating hydro‐geochemical balanc...

We characterized the spatio-temporal dynamics of carbon (C) in rivers of the tropical Nyong catchment (South Cameroon). In 2016, we measured fortnightly at 6 locations along an upstream-downstream gradient from groundwater to the main stream of order 6, total alkalinity, dissolved inorganic C (DIC) used together with pH to compute pCO2, dissolved a...

Simultaneously acquiring time series of climate, hydrology and hydrochemical data over decades on river systems is pivotal to understand the complex interactions involving rock, soil water, air and biota in the Critical Zone, to build integrated modeling and to propose predictive scenarios. Among the Critical Zone Observatories (CZOs) implemented i...

Stream carbon fluxes are one of the major components in the global C cycle, yet the discrimination of the various sources of stream carbon remains to a large extent unclear and less is known about the biogeochemical transformations that accompany the transfer of C from soils to streams. Here, we used patterns in stream water and groundwater δ13C va...

Despite the absence of tectonic activity, cratonic environments are characterized by strongly variable, and in places significant, rock weathering rates. This is shown here through an exploration of the weathering rates in two inter-tropical river basins from the Atlantic Central Africa: the Ogooué and Mbei River basins, Gabon. We analyzed the elem...

The Nature Conservancy, Libreville, Gabon At the global scale and on geological time scales, mechanical erosion and chemical weathering budgets are linked. Together, these processes contribute to the formation and the degradation of the Earth's critical zone and to the biogeochemical cycles of elements. While the weathering of hot and humid shields...

The bivalve genus Galatea Bruguière, 1797 (Venerida: Donacidae) was thought to contain exclusively brackish-water clams, the ranges of which are confined to estuaries and lower tidal parts of large rivers in West Africa. This genus was therefore included to the global freshwater bivalve checklists (Bogan 2013; Graf 2013) as a largely estuarine grou...

Radar altimetry, initially developed to observe the surface topography of the ocean, is now commonly used for the monitoring of inland water bodies. In this study, an altimetry-based gauging network was built in the Ogooué River Basin (ORB), in Gabon, Central Africa. It is composed of altimetry-based virtual stations (VS) under the altimetry tracks...

Hydrological models are important tools for the simulation of water storage and hydrological fluxes in large basins and complex river systems. The hydrological models can compensate the lack of observed data in ungauged basins. In this study, the hydrological model of large basins MGB (for Model of Large Basins in Portuguese) is used to evaluate th...

Incipient groundwater salinization has been identified in many arid and semi-arid regions where groundwater is increasingly used for irrigation, but the dominant processes at stake in such context are yet uncertain. Groundwater solutes originates from various sources such as atmospheric inputs, rock dissolution and fertilizer residues, and their co...

Inter-tropical regions are nowadays faced to major land-use changes in data-sparse context leading to difficulties to assess hydrological signatures and their evolution. This work is part of the theme Panta Rhei of the IAHS, and aims to develop a combined approach of data acquisition and a new semi-distributed model taking into account land-use cha...

Secondary minerals in soils can record climatic changes affecting continental surfaces over geological times. Their dating should refine our present knowledge about their potential periods of formation as well as their relations with the ongoing change of climate and erosion/weathering regimes. In the present study, twenty kaolinite samples from tw...

Core Ideas OZCAR is a network of sites studying the critical zone. OZCAR covers various disciplines. OZCAR will help disciplines to work together for a better representation and modeling of the critical zone. The French critical zone initiative, called OZCAR (Observatoires de la Zone Critique–Application et Recherche or Critical Zone Observatories...

The chemical weathering budget of land surfaces and the associated CO2 consumption are linked to physical erosion processes at the global scale. The weathering rates of tropical, warm and humid cratonic areas are known to be low due to the shielding effect of deep depleted mature regolith covers (laterites). The silicated cratons which dominate the...

Hydrological and hydrodynamic models are core tools for the simulation of large basins and complex river systems to overcome recent decades of depletion of river basins monitoring around the world. In this study, a large scale hydrological-hydrodynamic model (MGB) is used to assess hydrological processes of the ungauged Ogooué river basin in centra...

Long-term environmental research networks are one approach to advancing local, regional, and global environmental science and education. A remarkable number and wide variety of environmental research networks operate around the world today. These are diverse in funding, infrastructure, motivating questions, scientific strengths, and the sciences th...

Urban agriculture is crucial to local populations, but the risk of it contaminating water has rarely been documented. The aim of this study was to assess pesticide contamination of surface waters from the Méfou watershed (Yaoundé, Cameroon) by 32 selected herbicides, fungicides, and insecticides (mainly polar) according to their local application,...

The sources of REY-Th-U and long-term mass balance were assessed in the gneissic tropical forested Critical Zone Observatory of Mule Hole, India. The study relies on the characterization of the solid compartments (bedrock, soils, streambed and suspended sediments), on batch leaching experiments of the parent gneiss and on extractions of cation-exch...

Assessing the dynamics of the silica cycle in the critical zone remains challenging, particularly within the soil, where multiple processes are involved. To improve our understanding of this cycle in the Tropics, and more specifically the role played by vegetation, we combined elemental Si mass balance with the δ³⁰Si signatures of the compartments...

Radar altimetry is now commonly used for the monitoring of water levels in large river basins. In this study, an altimetry-based network of virtual stations was defined in the quasi ungauged Ogooué river basin, located in Gabon, Central Africa, using data from seven altimetry missions (Jason-2 and 3, ERS-2, ENVISAT, Cryosat-2, SARAL, Sentinel-3A) f...

We present new Gabonese locality records, ecological and morphological data or unpublished museum material for Mecistops cataphractus (Crocodylidae), Chamaeleo cristatus and C. owenii (Chamaeleonidae), Hemidactylus fasciatus and H. muriceus (Gekkonidae), Feylinia currori, Trachylepis albilabris (Scincidae), Calabaria reinhardtii (Boidae), Grayia or...

The source and proportion of REY, Th and U exported by groundwater and by the ephemeral stream along with the elemental proportions passing through vegetation have been assessed in the sub-humid tropical forested CZO of Mule Hole, Southern India. The study relies on a pluri-annual hydro-geochemical monitoring combined with a hydrological model. The...

Laterites are commonly considered as old tropical soils and can be used as a record of paleoclimate changes. The Indian lateritic landscape from the Western Ghâts escarpment, for instance, experienced different paleoclimates since the late Jurassic, due to the subcontinent drift. The first dating of local laterite profiles, using the weathering mas...

Yaoundé’s freshwater supply is crucial to the local population and to the production of crops in its humid lowlands. However, contribution of agricultural activities on water pollution is likely to occur but has never been documented in Yaoundé. Thus, in situ physico-chemical measurements, passive (POCIS) and grab sampling was deployed to monitor...

Agriculture has been increasingly relying on groundwater irrigation for the last decades, leading to severe groundwater depletion and/or nitrate contamination. Understanding the links between nitrate concentration and groundwater resource is a prerequisite for assessing the sustainability of irrigated systems. The Berambadi catchment (ORE-BVET/Kabi...

Laterites are common tropical soils covering about one third of the Earth’s continental surface. It is often admitted that they can be very old [1], with ages ranging from Mesozoic to Quaternary. It is important to date laterites to understand the influence of paleoclimates on their formation and to propose time-constrained models of their evolutio...

In the last decades, globally several small experimental watersheds were set up to study the climate and agricultural influences on water and biogeochemical cycles. Recently, the concept and importance of Critical Zone Observatory (CZO) was made and this resulted in developing such observatories in several countries including a global network of CZ...

Les latérites sont des sols anciens couvrant à l’heure actuelle un tiers des surfaces continentales terrestres. Elles ont ainsi été témoins des variations climatiques depuis la fin du Mésozoïque [1]. Si leurs grands processus de formation sont connus, il n’y a encore que peu d’informations sur leurs âges, lesquels constituent pourtant des données e...

South Cameroon is located in a tropical and tectonically quiescent region, with landscapes characterized by thick highly weathered regolith, indicative of the long-term predominance of chemical weathering over erosion. Currently this region undergoes huge changes due to accelerated mutations related to a growing population and economical developmen...

poster presented at the AGU fall meeting

River water composition (major ion and 87Sr/86Sr ratio) was monitored on a monthly basis over a period of three years from a mountainous river (Nethravati River) of southwestern India. The total dissolved solid (TDS) concentration is relatively low (46 mg L-1) with silica being the dominant contributor. The basin is characterized by lower dissolved...

Systematic monitoring of subsurface hydrogeochemistry has been carried out for a period of one year in a humid tropical region along the Nethravati–Gurupur River. The major ion and stable isotope (d18O and d2H) compositions are used to understand the hydrogeochemistry of groundwater and its interaction with surface water. In the study, it is observ...

The small experimental watershed of Mule Hole has been monitored for hydrology and chemistry since the last decade at hourly frequency for stream and monthly frequency for groundwater. It is covered by a dry tropical forest which generates intense evapotranspiration, limiting both runoff and groundwater recharge. Stream and groundwater fluxes are t...

The proportion of chemical elements passing through vegetation prior to being exported in a stream was quantified for a forested tropical watershed (Mule Hole, South India) using an extensive hydrological and geochemical monitoring at several scales. First, a solute annual mass balance was established at the scale of the soil-plant profile for asse...

The potential of Citrobacter freundii, a Gram negative bacteria for the remediation of hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) from aqueous solutions was investigated. Bioremediation of Cr(VI) involved both biosorption and bioreduction processes, as compared to only biosorption process observed with respect to Cr(III) bioremed...

Total suspended sediment (TSS) data from 1960-1970 and from recent investigations (1990-2000) are used to evaluate the variability in sediment yield of the Sanaga catchment (Cameroon) and the equivalent rates of erosion. At the annual and seasonal timescale, total suspended sediment concentrations for the Mbam sub-catchment are three to four times...

Amorphous silica (ASi) pool and fluxes have become parameters of a growing interest in the understanding of the biogeochemical cycle of Si and the modeling of anthropogenic impacts. Extraction by 1% Na2CO3 followed by a correction for crystalline Si (DeMaster, 1981) has recently become widely used and is proposed as the standard technique for quant...

The flotation of sphalerite and galena in the presence of intra- and extra-cellular components isolated from Bacillus circulans before and after adaptation to the chosen minerals has been studied. Based on various biochemical treatments, the key biomolecule primarily responsible for the flotation of sphalerite has been identified as DNA, which func...

The study presents a 3-year time series data on dissolved trace elements and rare earth elements (REEs) in a monsoon-dominated river basin, the Nethravati River in tropical Southwestern India. The river basin lies on the metamorphic transition boundary which separates the Peninsular Gneiss and Southern Granulitic province belonging to Archean and T...

The thermal history of the Ardèche paleo-margin (south-eastern France) has been reconstructed using various analytical data from minerals and organic matter and conventional interpretation. These methods comprise Tmax and vitrinite reflectance measurements on organic matter, determination of the smectite content in mixed-layer illite/smectite, flui...

Hydrogeological and climatic effect on chemical behavior of groundwater along a climatic gradient is studied along a river basin. ‘Semi-arid’ (500–800 mm of mean annual rainfall), ‘sub-humid’ (800–1,200 mm/year) and ‘humid’ (1,200–1,500 mm/year) are the climatic zones chosen along the granito-gneissic plains of Kabini basin in South India for the p...

Forested areas play a dominant role in the global hydrological cycle. Evapotranspiration is a dominant component most of the time catching up with the rainfall. Though there are sophisticated methods which are available for its estimation, a simple reliable tool is needed so that a good budgeting could be made. Studies have established that evapotr...

The comparison between contemporary and long-term weathering has been carried out in the Small Experimental Watershed (SEW) of Nsimi, South Cameroon in order to quantify the export fluxes of major and trace elements and the residence time of the lateritic weathering cover. We focus on the hillside system composed of a thick lateritic weathering cov...

The Silicate Weathering Rate (SWR) and associated Carbon dioxide Consumption Rate (CCR) in tropical silicate terrain is assessed through a study of the major ion chemistry in a small west flowing river of Peninsular India, the Nethravati River. The specific features of the river basin are high mean annual rainfall and temperature, high runoff and a...

River Nethravati is a small west flowing river originating in the Western Ghatsand falling into the Arabian Sea after traversing for 147km. The river flows through a densely vegetated forest with steep gradient in the youthful stages of the river which rapidly decreases in the plains. The catchment of the river is spread out in an area of 3657km2 w...

Water–rock reactions are driven by the influx of water, which are out of equilibrium with the mineral assemblage in the rock. Here a mass balance approach is adopted to quantify these reactions. Based on field experiments carried out in a granito-gneissic small experimental watershed (SEW), Mule Hole SEW (~ 4.5 km2), quartz, oligoclase, sericite, e...

The hydrological role of a headwater swamp in a tropical rainforest is studied using chloride mass balance (CMB) and end-member mixing analysis. There are three main contributions to streamflow: (1) the hillside bedrock aquifer, (2) overland flow from the swamp during storm events and (3) groundwater flow from the swamp aquifer. Before rainfall eve...

This study examined the water and chemical cycles of a small forested head catchment. Application of Cl− mass balance lead to the identification of a groundwater baseflow located into the active zone of the crystalline aquifer, below the weir. These findings indicate that groundwater contributes to a large part of chemical outputs at the catchment...

The global Si cycle is strongly controlled by riverine input. Over the last decade two parameters have been shown to play a significant role in the control of dissolved Si (DSi): biology, through the effects of diatom blooms and vegetation growth, and human activity, through the effects of eutrophication, urbanisation, agriculture, deforestation an...

Geophysical methods are becoming more popular nowadays in the field of hydrology due to their time and space efficiency. So an attempt has been made here to relate electrical resistivity with soil moisture content in the field. The experiments were carried out in an experimental watershed 'Mulehole' in southern India, which is a forested watershed...

The influence of the pedogenic and climatic contexts on the formation and preservation of pedogenic carbonates in a climosequence in the Western Ghats (Karnataka Plateau, South West India) has been studied. Along the climosequence, the current mean annual rainfall (MAR) varies within a 80 km transect from 6000 mm at the edge of the Plateau to 500 m...

We investigate the chemical weathering processes and fluxes in a small experimental watershed (SEW) through a modelling approach. The study site is the Mule Hole SEW developed on a gneissic basement located in the climatic gradient of the Western Ghats, South India. The model couples a lumped hydrological model simulating the water budget at the wa...

The efficiency of red mud as an adsorbent for the removal of metal ions and sulphate from synthetic acid mine water was assessed. Almost complete removal of Fe?z (98%), Fe3+ (99%) and Cu2+ (97%) and a significant removal of Zn2+ (84%) was achieved from acid mine water at pH 2?3. However, only about 27% of sulphate reduction could be attained. A not...

In sub-humid South India, recent studies have shown that black soil areas (Vertisols and vertic Intergrades), located on flat valley bottoms, have been rejuvenated through the incision of streambeds, inducing changes in the pedoclimate and soil transformation. Joint pedological, geochemical and geophysical investigations were performed in order to...

Accurate estimations of water balance are needed in semi-arid and sub-humid tropical regions, where water resources are scarce compared to water demand. Evapotranspiration plays a major role in this context, and the difficulty to quantify it precisely leads to major uncertainties in the groundwater recharge assessment, especially in forested catchm...

Accurate estimations of water balance are needed in semi-arid and sub-humid tropical regions, where water resources are scarce compared to water demand. Evapotranspiration plays a major role in this context, and the difficulty to quantify it precisely leads to major uncertainties in the groundwater recharge assessment, especially in forested catchm...

Water – rock reactions are driven by the reactions of water with the mineral assemblage in the rock. These reactions evolve towards equilibrium with the primary minerals while a series of secondary minerals precipitate. Mass balance approach is adopted to quantify the rate at which the water – rock interactions occur in order to reach the equilibri...

One of the major concerns for the mining industry especially after the mine closure is the generation of acid mine drainage (AMD), and its discharge into the environment surrounding the abandoned mines, leading to serious environmental pollution. AMD is usually characterized by high concentration of dissolved metal ions, sulfate and low pH. The eff...