BVET Outline


The Critical Zone Observatory « Experimental Tropical Watersheds » (CZO BVET) is INSU- and IRD-labeled. It is a monitoring tool that aims to increase our knowledge regarding the continental water and biogeochemical cycles and the dynamics of weathering processes in tropical environments. It is also dedicated to the study of anthropogenic impacts on the natural environment. These goals are achieve by the combined use of hydrological, geophysical, mineralogical, geochemical methods and modeling.

Project leaders :

Stéphane AUDRY
Physicien-Adjoint CNAP, PhD
UMR 5563 – GET
14, avenue Edouard Belin – 31400 Toulouse
Phone: +33 5 61 33 26 05
Fax : +33 5 61 33 25 60

Chargé de Recherche IRD, PhD
UMR 5563 – GET
14, avenue Edouard Belin – 31400 Toulouse
Phone: +33 5 61 33 26 05
Fax : +33 5 61 33 25 60

Program CZO-BVET “Observatory for Research in Environment-Experimental Tropical Watersheds”

The CZO-BVET program is founded by the following French institutions and organizations: the Ministère de l’Enseignement Supérieur, de la recherche et de l’innovation, the National Institute of Universe Sciences (INSU), the Institute of Research for Development (IRD), the Midi-Pyrénées Observatory (OMP, Toulouse). Within the frame of this program, several tropical ecosystems of Cameroon and India are studied in an integrated way at two spatial complementary scales. (a) The local scale concerns small experimental catchments, with a surface area of some square kilometers; these watersheds provide data which are necessary to understand, to quantify and to model the functioning of ecosystems and their short or long-term dynamics. (b) The regional scale concerns basins of about 104 km2 of surface area; the periodic measurements and analyzes on these watersheds permit a better grasp of the water biogeochemical variations and the matter transfers as a function of scale change.

The Cameroonian and Indian sites were chosen after similar characteristics: morpho-tectonic environment of passive margin, archean granito-gneissic craton, tropical temperatures. The first site was opened in 1993 on the humid tropical forested ecosystem constituted by the Nyong River basin in Southern Cameroon, with the experimental catchment of Mengong near Nsimi village. A lot of articles and reports have yet been published on the Nyong watershed. In 2002, we began working on the seasonally contrasted tropical basin of the Kabini River, and on the experimental catchments of Mule Hole and Maddur in Southern India. The data which can be found on this website are those acquired in the frame of the Cameroon CZO-BVET program.
Integrated approaches of experimental catchments, where hydrological and biohydrogeochemical studies are coupled, appear very federative for numerous pluridisciplinary teams in the world. For example, the international LTER Network (Long Term Ecological Research) gathers on this thematic the American watersheds of Hubbarb Brook, Panola, Loch Vale, Rio Icacos and Coweeta. These studies often deal with chemical weathering of silicated rocks, this process being a dominant factor in the long-term control of atmospheric CO2 content. One of the purposes of our program is to monitor some parameters affecting the global climate. The number of monolithologic experimental catchments on granitic or granito-gneissic substratum, where the input/output fluxes are estimated, is rather important (about 60) in the temperate zone. On the other hand, this number is very low in the tropical area; to our knowledge, only the Nsimi catchment and the Rio Icacos catchment in Puerto Rico (pertaining to the environmental observatory of Luquillo Experimental Forest, program WEBB (Water, Energy and Biogeochemical Budgets) have been monitored since more than ten years.

This very low density of sites dedicated to the tropical zones – representing quite one third of the total continental area – is proved to be very insufficient for improvement of our understanding of the weathering processes in these environments. The scientific community needs more data on small experimental catchments and larger basins representative of the diversity of Earth’s ecosystems. The CZO-BVET is registered in the following international projects: IGCP n° 459 “Carbon Cycle and Hydrology” (UNESCO – IUGS), ILTER Networks (International Long-Term Ecological Research), and EUROLAT (European Network on Lateritic Weathering and Global Environment).
The observatory activity aims (a) to measure the fluxes of water, of mineral and organic matters present in solution and in suspension; and (b) to estimate the budget of chemical weathering and physical erosion; this has to be done at a local scale, on small experimental catchments, and at a regional scale, on larger watersheds. The purpose is to provide the international scientific community with climatic, hydrological and biohydrogeochemical pluri-annual or even decadal chronicles on tropical environment.

The observatory actions aim to determine the hydrological fluxes and dissolved and particulate organic and mineral matter fluxes in order to address the chemical and physical weathering balance at the local scale on the experimental watersheds and at the regional on the river watersheds. These actions are based on climatic, hydrological and hydrogeochemical monitoring over multiannual or even decadal periods of time.

  • The climatic parameters are: rainfall, global radiation, air temperature, relative humidity, wind velocity and direction which are continuously measured at meteorological stations and pluviographs; from these data, the Penmann PET can be calculated.
  • The hydrological parameters are : for the drainage waters, the discharges at the outlet of the experimental Nsimi catchment, and at the other stations of the Nyong network; these are continuously measured using automatic limnigraphs. In the saturated zone, the water levels are continuously monitored using piezometers; in the vadose zone, the daily hydric budget at some specific sites can be estimated using a tensio-neutronic probe.
  • The hydrochemical parameters are: the concentrations of dissolved inorganic species (major cations and anions, alkalinity, silica) and dissolved organic carbon (DOC), as well as the concentrations of total suspended sediment (TSS), particulate organic carbon (POC), and some other parameters, like water temperature, electric conductivity and pH. For rivers and watertables, measurement and sampling are bimonthly; for rainfalls, each shower is collected. Note that the atmospheric chemistry monitoring of the Nsimi catchment is managed by the Laboratoire d’Aérologie of Toulouse in the frame of the  IDAF network .

The CZO BVET is the result of a fruitful collaboration between the following partners:

French researchers of IRD, CNRS and UPS Toulouse, based in Géosciences Environnement Toulouse (GET, UMR 5563), Toulouse, or in the Indo-French Cell for Water Sciences, Bangalore;

Cameroonian researchers of IRGM/CRH, and of the Universities of Yaoundé I and of Dschang;

Indian researchers of the Indian Institute of Science in Bangalore.