The Observatory of water and erosion in the Antilles (OBServatoire de l’Eau et de l’éRosion aux Antilles – ObsERA) is located on Basse-Terre Island, a volcanic island of the Guadeloupe archipelago. The island is mainly composed of andesitic rocks which are particularly reactive and vulnerable to chemical weathering and erosion. The climate is humid tropical and and the cyclonic season is marked. ObsERA monitors the evolution of two catchments, Capesterre and Bras-David. Both of them are located inside the national park of Guadeloupe, but they differ in terms of age, geological formation, rainfall and relief. The Capesterre catchment (16.4 km2), south of the island, is located on relatively recent terrain (600,000 to 400,000 years), with poorly developed soils and steep slopes (average altitude of 1,140 m). The average annual rainfall rate is 5,200 mm/year. The Bras-David river drains a 11.9 km2 catchment over an older terrain (1 million years), with gentler relief and very thick ferralitic soils. The annual rainfall rate is 3,300 mm/year. When normalized to their area, the flux of dissolved and solid matter exported out of these two catchments is amongst the highest in the world. In this respect, Basse-Terre can be regarded as a hot spot of weathering and erosion.
Starting year: 2005
Keywords: weathering, tropical forest, tropical climate, volcanic lands, geochemical cycles
The objectives of ObsERA are
- To investigate chemical and physical erosion, their feed backsand their influence on the carbon and water cycles and the environment in the peculiar context of a tropical volcanic island,
- To promote the development of new instruments and methods for monitoring sediment transport by rivers and slope processes and characterizing the ecosystem dynamics,
- To investigate how extreme events (floods induced by heavy rains and tropical storms, earthquakes, …) influence geochemical cycles (e.g. carbon cycle), denudation rates and landscape morphology.
ObsERA collects long-term data to understand the development of soils and the morphology of watersheds in a tropical climate, the residence time of materials in rivers and watersheds, the
coupling between chemical and physical erosion processes (strongly active in the Antilles), and finally the role of the primary tropical forest in sedimentary carbon sequestration.
Sites and measured variables
Both Capesterre and Bras-David catchments are instrumented with gauging and automatic sampling stations. The Quiock ravine, a sub-basin of Bras-David (0.78 km2), is also equipped with a series of boreholes that monitor groundwater. These instruments are used to measure the discharge, the turbidity, the conductivity and the temperature of rivers, the air temperature, the atmospheric pressure, the rainfall rate, the water table elevation, the chemical composition of rivers (pH, conductivity, main elements in solution, particulate and dissolved organic carbon), the chemical composition of soil solutions in the saprolite, as well as that of the atmospheric deposits, and the morpho-sedimentary evolution of river beds (drone imagery and terrestrial LIDAR).
Partners and further information
ObsERA is a Service National d’Observation (SNO) from INSU- CNRS, operated by the Institut de Physique du Globe de Paris (IPGP) in collaboration with Observatoire des Sciences de l’Univers de Lyon and Université de Bretagne Occidentale. It has established local partnerships with the Guadeloupe National Park, the Direction de l’Environnement, de l’Aménagement et du Logement (DEAL) and l’Université des Antilles. It has active collaborations with the observatory of the Critical Zone of Puerto Rico (Luquillo Forest Experimental Catchment).