Impact of land use on weathering rates in Guadeloupe, Caribbean islands
Résumé
Guadeloupe is located in Lesser Antilles with a tropical climate with very high precipitation, temperature, very dense vegetation (forest on the steepest slopes, agricultural on the lowlands) and sharp relief. Rivers present torrential hydrological regime with extreme erosion conditions. The tropical context contributes to important development of saprolitic profile, with extreme chemical weathering rates (e.g. 100 to 600 t/km2/yr). As for many volcanic islands erodible lithology such as pyroclastic flows with ashes or even massif lava flows involve important material transported during the erosion processes. The lithyology is also very porous with high infiltration rates, which induces that most of the elements fluxes are produced on subsurface as the chemical erosion rates are 2 to 5 time higher than the rates from surface water (Rad et al., 2007). Moreover kinetic of chemical weathering rates depends on the age of the lava flows (with a NS gradient of age) and subsurface circulation with local hydrothermal springs, which highly increases chemical weathering rates. It appears that first stage of erosion are characterized by high chemical denudation rates and high physical denudation rates, the erosion products chemical compositions are then close to the bedrock one. It is then followed in a second stage by constant chemical weathering rates and lower mechanical denudation rates. Moreover Guadeloupe islands is highly impacted by agriculture (banana and sugar cane plantations), which significantly influence the hydrological cycle. It is therefore interesting to asses the impact of such influence on the weathering rates on this island. Chemical and physical weathering rates will be correlated to the different land use to quantify the impact of human activities and explain its role in the evolution of the Critical Zone