From the sky to the ground: fishers knowledge, landscape analysis and hydrological data indicate long-term environmental changes in Amazonian clear water rivers

Abstract

Fishers possess detailed local ecological knowledge (LEK) which can be a valuable resource for tracking longterm environmental changes in less studied tropical rivers. Our goal was to investigate such changes in three clear water rivers in the Brazilian Amazon, focusing on hydrology, water quality and land cover. Additionally, we aimed to compare these changes among three rivers (Trombetas, Tapajos ´ and Tocantins) representing a potential gradient of environmental changes. We interviewed 129 fishers (67 in Tapajos, ´ 33 in Tocantins and 29 in Trombetas), and analyzed temporal series on land cover and hydrology respectively through maps produced by the project MapBiomas, and data from the Brazilian National Water Agency across the last 34 years (from 1985 to 2019). The complementary analyses of these three databases (mapping, hydrological data and fishers' knowledge) revealed environmental changes in the studied rivers. The maps showed a gradient of anthropic changes on land cover, from the less altered Trombetas river, the moderately altered Tapajos ´ and the more intensely changed landscape in the Tocantins River. Fishers from the Tocantins River reported a greater variety of negative changes * Corresponding author. E-mail address: carolbatistanunes@gmail.com (C.B. Nunes). Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv https://doi.org/10.1016/j.scitotenv.2023.166763 Received 29 June 2023; Received in revised form 22 August 2023; Accepted 31 August 2023 Science of the Total Environment 904 (2023) 166763 2 in water quality related to anthropic actions, such as dams, deforestation, and pollution. Additionally, most fishers indicated hydrological changes making the Tocantins River drier in more recent years, which would cause negative effects on fish populations. In the Tapajos ´ River, fishers mentioned more varied hydrological patterns and negative effects on water quality linked to mining activities, whereas in Trombetas fishers perceived increased floods. The changes mentioned by the interviewed fishers matched observed trends from hydrological data indicating a trend of increasing droughts in the more impacted Tocantins River. Fishers' knowledge provided exclusive ‘on the ground’ data to track long-term changes on local hydrology and water quality, as well as inform the effects of these changes on fish and fisheries