M-TROPICS Critical Zone Observatories

The Earth Critical Zone (CZ) is defined as the thin layer between the top of the canopy and the bottom of groundwater aquifer in which complex interactions involving rock, soil water, air and living organisms regulate the natural habitat and determine availability of life sustaining resources. This concept allows bringing together scientific disciplines in the aim to tackle crucial environmental issues regarding how the various components of the CZ interact with global change, including land use and climatic changes? More specifically, what are the impacts of the conversion of annual to perennial crops upon biodiversity, soils, hydrological, sedimentary and biogeochemical fluxes within the catchments, and with which off-site effects? What are the consequences of climate variability and climate change upon these CZ components and these fluxes?

The strategies adopted to answer these questions are often integrated approaches on experimental catchments, where hydrological, sedimentary, biogeochemical and ecological studies can be coupled. Acquiring simultaneously time series of climate, hydrology and geochemical and ecological data over decades on river systems (both small experimental watersheds and larger basins) representative of the diversity of ecosystems is pivotal for the understanding of these processes, building integrated modeling and for proposing predictive scenarios.

Among the Critical Zone Observatories (CZOs) that have been implemented by the Earth Science community in the past 25 years, very few were set up in the Tropics despite the huge importance of these regions in terms of population density, fast-changing land use, biodiversity hotspots, biomass stock on continents (humid forests), size of river systems. In addition, rainfall in the Tropics is mostly governed by monsoon systems, which are particularly sensitive to climate change.

The CZO Multiscale TROPIcal CatchmentS (M-TROPICS) consists in the merging of two previously-existing CZOs: BVET (India and Cameroon) and MSEC (Laos, Vietnam, Thailand). The CZO M-TROPICS is included in OZCAR, the French contribution to the international CZO initiative.

The CZO M-TROPICS provides the international scientific community with unique decennial time series of climatic, hydrological and geochemical variables in tropical environments. More specifically, the CZO M-TROPICS aims at (1) determining the fluxes of water, of inorganic and organic matter present in solution (major anions and cations, carbon) and in suspension (particulate organic carbon); (2) proposing budgets of chemical weathering and physical erosion; and (3) evaluating the impact of global change (land-use, climate) upon the above parameters. Its strengths are (1) multiscale approaches, both in space (from micro-plot to catchment and larger river basins) and in time (from hourly to multi-decennial time-series); and (2) multidisciplinary approach, currently involving hydrology, biogeochemistry, soil science, agronomy, remote sensing, ecology, experimentation and modelling.

Fecal bacteria occurrence in tropical rivers

Floriann Langlet, a master student from the Université de Toulouse III Paul Sabatier, just finished his internship at GET laboratory. He analyzed the occurrence of bacterial pathogens along the Mekong river basin (M-TROPICS/MSEC) and found that soil type, discharge, and turbidity were among the key variables associated to E. coli… Continue Reading

Field experiment of the ANR ATCHA project

Jean Riotte (IRD-GET) and Laurent Ruiz (INRA/IRD-GET), together with M. Tripti (Post doc IISc) and Nils Dubois (M2 ISTOM), performed a field experiment within the frame of the ANR ATCHA project, aiming at assessing the fate of nitrates from irrigation by groundwater. The experiment was performed in the Berambadi catchment (M-TROPICS/BVET)… Continue Reading

Critical zone analysis with GRASS and QGIS

A book authored by Yves AUDA has been published, handling the analysis of the critical zone with open-source softwares GRASS and QGIS: field sampling, hydrological models, landscape analysis, remote sensing mapping, digital elevation models, etc. Theory and exercises are based on data from the M-TROPICS/MSEC CZO in Northern Laos, gathered… Continue Reading

The roots of the drought: Hydrology and water uptake strategies mediate forest-wide demographic response to precipitation

An inter-disciplinary team at Bengaluru’s Indian Institute of Science (IISc) studied how different tree species partition underground water resources up to 30m depth and co-existing tree species diverge in water uptake depths (M-TROPICS/BVET). Deep rooted trees turn to be more vulnerable to severe droughts than shallow rooted species : climate… Continue Reading

Processes controlling silicon isotopic fractionation in a forested tropical watershed: Mule Hole Critical Zone Observatory (Southern India)

The analyses of silicon isotopes in soil, water and plant compartments of the Mule Hole forested watershed (M-TROPICS/BVET) reveal that vegetation takes up twice more silica than first estimates using elemental mass balance. This flux is 30 times higher than the solute silica flux exported by the stream, itself resulting… Continue Reading