When archives are missing, deciphering the effects of public policies and climate variability on the Brazilian semi-arid region using sediment core studies

• Published in: The Science of the total environment 2020-06, Vol.723, p.137989-137989, Article 137989
• Main Authors: Ledru, Marie-Pierre, Jeske-Pieruschka, Vivian, Bremond, Laurent, Develle, Anne-Lise, Sabatier, Pierre, Martins, Eduardo Sávio Passos Rodrigues, de Freitas Filho, Manuel Rodrigues, Fontenele, Diógenes Passos, Arnaud, Fabien, Favier, Charly, Barroso, Francisco Rony Gomes, Araújo, Francisca Soares
• Format: Article
• Language: English
• Subjects: Caatinga; Continental interfaces, environment; Drought; Environment and Society; Environmental Sciences; Global Changes; Human impact; Lake reservoir; Land degradation; Sciences of the Universe; Sediment
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.137989

The northeastern region of Brazil is the most densely populated and biodiverse semi-arid regions of the planet. Effects of the natural climate variability and colonization on the landscape have been described since the beginning of the 16th century but little is known about their effects on natural resources. Climate projections predict temperatures above 40 °C and an increase in the number and duration of droughts at the end of the 21st century with strong societal impacts. Here, we analyze the influence of public policies, human activities and natural climate variability on the environment over the last 60 years. Our study is based on sedimentological and environmental reconstructions from two sediment cores collected in two dam lakes on the river Acaraú in the State of Ceará. Multiproxy analyses of both cores (inorganic geochemistry, pollen, charcoal, remote sensing) at an annual resolution showed that 1) at interannual scale composition and distribution of the dry forest (known as Caatinga) were not affected by the alternance of drought and high moisture episodes; 2) at decadal scale human activities such as agriculture were reflected by changes in vegetation cover and fishery by progressive changes in lake trophic status; 3) public policies were able to promote changes in the landscape e.g., land colonization with the regression of the dry forest and irrigation plan able to amplify the deforestation and change the floristic composition. Thanks to paleo-science approach, our environmental diagnosis should help future decision-making and provide guidelines for preservation of resources and wellbeing of the inhabitants. [Display omitted] •Brazilian semi-arid will face drastic decrease in precipitation in the coming years.•Archives show both human activities and public policies impact on the resources.•Ecosystems proved to be resilient to natural climate variability.•Paleolimnology a good tool to reconstruct the evolution of the landscape•New management forms account for physical, societal, sustainability specificities.