Policy-driven wetland degradation by artificial drainages in Brazil

Le résumé fourni par la source

Abstract Wetlands provide essential hydrological and ecological functions, yet policy definitions often overlook these processes. In the Brazilian state of Mato Grosso, one of the world’s largest agricultural hubs, the recently approved Complementary Bill 43/2025 authorizes artificial wetland drainage based solely on restrictive soil criteria, disregarding hydrological functioning. In this study, we evaluated long-term (1985–2023) streamflow changes in the Araguaia and Guaporé basins, quantified pre-policy land-use transitions in areas with and without artificial drainage, and estimated the extent of remaining wetlands newly exposed to degradation under the criteria established by CB 43/2025. We analyzed streamflow data using dynamic quantile regressions and evaluated long-term land cover trends, subsequently applying the new pedological criteria to identify the wetland area newly eligible for legal drainage. As historical diagnostics, dry-season flows declined in 95%–100% of gauging stations, while wet-season flows increased, indicating reduced water retention across the basins. Furthermore, observed wetland conversion to pasture and agriculture was widespread and up to ten times faster near artificial drains. Regarding future policy implications, spatial projections indicate that the new legal framework exposes 2.3 million hectares of these wetlands to potential drainage, as over 80% of floodplain soils no longer meet the narrowed protection criteria. Consequently, this legislation may intensify ongoing ecological degradation and hydrological instability in two major South American floodplains. By undermining water security and the long-term productive capacity of a global agricultural region, CB 43/2025 may generate substantial environmental and economic risks. Robust scientific standards and hydrological criteria should be incorporated into wetland policy.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.