M-TROPICS Observatory

M-TROPICS Observatory

Scientific context

Tropical ecosystems are impacted by the increase in human population and are associated with rapid changes in land use, leading to the degradation of water and soil resources in these regions. Multiscale TROPIcal CatchmentS (M-TROPICS) observatory aims to quantify the matter balance of a range of river basins of contrasting and complementary vegetation cover and land use in Cameroon, India and Southeast Asia. In Cameroon, the conversion of rainforest ecosystems to slash-and-burn agriculture is studied thanks to 5 nested watersheds, from the experimental Mengong basin (Nsimi, 0.6 km²) to Nyong River basin (Olama, 18,500 km²). In Southern India, the impact of groundwater-irrigated agriculture in a subhumid cimate is adressed by comparing an agricultural experimental basin (Berambadi, 80 km2) with a preserved forest experimental basin (Mule Hole, 4.1 km2), both located in the Kabini river basin. In Southeast Asia, the erosion generated by land use changes in a mountainous area is studied in 3 experimental basins under humid climate: Houay Pano (0.60 km²), North Laos, which is the most instrumented site, Huay Ma Nai (0.93 km²), North Thailand, and Dong Cao (0.47 km²), North Vietnam. The impact of land use on water quality, including bacterial pathogen dissemination, is therefore assessed at multiple scales in Laos (0.6-26,000  km²).


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Starting year: 1993 Cameroon, 2000 Southeast Asia, 2003 India

Locations: Cameroon, Inde, Laos, Vietnam, Thailand

Keywords: tropical climate, tropical agrosystems and forest ecosystems, monsoon, hydrochemistry, erosion, weathering


Web site:

Cameroon : Stéphane AUDRY and Jules NDAM ;
India : Jean RIOTTE, Laurent RUIZ and Sekhar MUDDU ;
Southeast Asia: Laurie BOITHIAS, Olivier RIBOLZI, Alain PIERRET, Arthon BOONSANER, Tien MINH TRAN, Nivong SIPASEUTH

Scientific questions

The scientific question that led to the creation of the M-TROPICS observatory concerns the response of tropical watersheds to global change (land use, climate). More specifically, M-TROPICS aims to:

  • Determine the flux of water and organic and inorganic dissolved matter (major anions and cations, carbon) and matter in suspension (particulate organic carbon),
  • Establish physical weathering and chemical alteration balances.

In all sites, hydrological, biogeochemical (Cameroon and India especially) and erosive (Southeast Asia) questions are addressed.

Sites and measured variables

Meteorological variables (daily rainfall, temperature, wind speed and direction, relative humidity, solar radiation, atmospheric pressure) are measured for all the experimental basins by automatic weather stations. In Cameroon, 6 measuring stations (source and outlet of the Mengong near Nsimi village, Messam bridge on the Awout stream, So’o bridge on the So’o river, Mbalmayo and Olama on the Nyong river) collect data of river flows and water chemistry. At Nsimi, soil pits and piezometers network are installed to monitor groundwater levels.

In India, both Mule Hole and Berambadi sites are instrumented to carry out hydro-geochemical monitoring of river and ground waters.

In Southeast Asia, in each basin, monitoring of several sub-basins is performed at scales ranging from microplots (1 m²) to small watersheds (~1 km²). Data from land use, agricultural practices, flows, suspended matter and bedload are collected. Each site has a weir for monitoring water flows and bedload and an automatic sampler for monitoring suspended matter.

In Laos, additional grab samples of river water are collected every ten days in the Mekong river and in three ot its tributaries to monitor Escherichia coli.

Partners and further information

M-TROPICS is managed by the Géosciences Environnement Toulouse and iEES Paris laboratories, as a collaboration between researchers from IRDCNRS, Université Paul Sabatier, and partner institutions in the South. In India, the local partner is the Indian Institute of Sciences, Bangalore. In Cameroon, it is IRGM-CRH, Yaoundé and Dschang Universities. In Southeast Asia, partners are the Ministry of Agriculture et Forestry of Laos, the Department of National Park, Wildlife and Plant Conservation, in Thaïland and the Soils and Fertilizers Research Institute in Vietnam.