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.

Dong Cao, Roots and Humans

A documentary film (Dong Cao, des racines & des Hommes, 9’04) featuring Jean-Luc MAEGHT (IRD) and PHAM Dinh Rinh (SFRI) has been shot within the Dong Cao catchment in Vietnam (M-TROPICS/MSEC) to highlight the long term monitoring of the CZO (climate, land use, hydrology, and soil erosion, root density, macrofauna,… Continue Reading

Vietnamese IRD partners visiting the Dong Cao CZO

Scientists from the USTH and from the Thuyloi University visited the monitored catchment of Dong Cao, northern Vietnam (M-TROPICS/MSEC). The visit was led by Rinh Pham Dinh (SFRI) and by Jean-Luc Maeght (IRD, iEES-Paris). Visiting scientists discovered the history of the research carried out on this peri-urban watershed (49.7 ha).

Soils in the critical zone

Christian Valentin (IRD) coordinated a series of 6 books at ISTE Editions about the role of soils within the critical zone, including in the tropics. Renewed interest for soils is due to the social challenges they are associated to: agricultural productions, climate and biogeochemical cycles regulation, urbanization… By locating soils… Continue Reading

Sediment delivery from tropical rivers

Lancelot Pinta defended a master degree (M2) thesis entitled “Impact of rainfall erosivity and land cover change on total organic carbon accumulation in sediments of a water reservoir in Thailand” on Thursday June 28th at Sorbonne Université (Paris). The objectives of this study were to determine, the amount of catchment-derived… Continue Reading

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