A spatialized assessment of ecosystem service relationships in a multifunctional agroforestry landscape of Senegal.

Agroforestry systems are an integral part of Sub-Saharan agricultural landscapes. Studies conducted at tree or plot scales on the supply of ecosystem services (ES) suggest that agroforestry practices are a promising way to build multifunctional agricultural landscapes. However, the current characterization and understanding of how multiple ES are associated across such heterogeneous agricultural landscapes are still limited. This study provides the first characterization of the multiple ESs supplied by a Sahelian Faidherbia albida agroforestry parkland and their relationships. Relying on field data for 11 ES indicators, recent advances in remote sensing-derived information, and blending different ES mapping approaches, we first assessed the spatial heterogeneity of the supply of each ES. We found that the majority of ES indicators remained below ES potential values over the study area by 25 % to 50 %, revealing that there is a considerable scope for increasing the ES supply in the F. albida parkland. Then, using a scoring approach, we analyzed the supply of multiple ESs. We observed a large number of hotspots and a clear effect of the proximity of F. albida trees fostering the supply of multiple ESs in their vicinity. Finally, we mapped and analyzed the dominant relationships - trade-offs, synergies or losses - between ESs from a cooccurrence spatial approach. We showed that significant trade-offs and losses (58 % of the area) between ESs can exist in the F. albida parkland. Interestingly, we also showed that synergies occurred mainly up to 10 m from the F. albida trees, suggesting that synergies need to be increased beyond this threshold. By adopting an original ES valuation framework, we provided basic insights into ESs and their relationships. The different maps and information generated can support public debates and target new policies fostering the multifunctionality of F. albida parklands as well as in various other parklands of West Africa.

Long-term pollution by chlordecone of tropical volcanic soils in the French West Indies: a simple leaching model accounts for current residue.

Chlordecone was applied between 1972 and 1993 in banana fields of the French West Indies. This resulted in long-term pollution of soils and contamination of waters, aquatic biota, and crops. To assess pollution level and duration according to soil type, WISORCH, a leaching model based on first-order desorption kinetics, was developed and run. Its input parameters are soil organic carbon content (SOC) and SOC/water partitioning coefficient (K(oc)). It accounts for current chlordecone soil contents and drainage water concentrations. The model was valid for andosol, which indicates that neither physico-chemical nor microbial degradation occurred. Dilution by previous deep tillages makes soil scrapping unrealistic. Lixiviation appeared the main way to reduce pollution. Besides the SOC and rainfall increases, K(oc) increased from nitisol to ferralsol and then andosol while lixiviation efficiency decreased. Consequently, pollution is bound to last for several decades for nitisol, centuries for ferralsol, and half a millennium for andosol.