Terrain units, land use and land cover, and gross primary productivity of the largest fluvial basin in the Brazilian Amazonia/Cerrado ecotone: The Araguaia River basin
Graphical abstract
Introduction
Wetlands play an important role in the regional hydrological cycle and carbon dynamics, providing several benefits for local population (Mitsch et al., 2010). The integrity of most of tropical wetlands from South America, Africa, and Asia has been heavily threatened for being considered freely available resources of land and water (Junk, 2002). The main factors responsible for their degradation are deforestation, food and energy production, burning activities, and industrial pollution (Naranjo, 1995).
Approximately 20% of the Brazilian territory is covered by wetlands (Junk et al., 2014). They are under heavy pressure from agroindustry. The current Forest Code (Federal Law no. 12.561/2012) is unfriendly in terms of wetland protection (Piedade et al., 2012). The Araguaia River Basin, located in the transition region between the Amazon and Cerrado biomes, is composed of a mosaic of grass, shrubs, and trees in different proportions (Aselmann & Crutzen, 1989; Valente, Latrubesse & Ferreira, 2013). The drainage network reveals different dissection degree of the relief as well as the landforms that were developed through geological ages under various endogenic and exogenic processes (both denudation and aggradation processes) (Valente, 2007). The Araguaia River Basin contains the most geodiverse floodplain of the Cerrado and is home to more fish species than any other basin in this biome (Valente, Latrubesse & Ferreira, 2013). Therefore, it's regional landscape characterization and land use and land cover (LULC) monitoring are crucial, but so far underdeveloped, even after the signature of the Ramsar Convention in 1993 by the federal government (Junk et al., 2014). Because of the large extension of this basin, any initiative of landscape characterization and land use monitoring at a regional scale relies on remote sensing data.
Among several types of remotely sensed data available at different spatial, temporal, and spectral resolutions, we can point out (a) the Shuttle Radar Topography Mission (SRTM) data (Farr et al., 2007) that provides digital elevation models (DEM) at a spatial resolution of 30-m or 90-m regular grid; (b) the Landsat satellite (1984-present), with spatial resolution of 30 m and repeat cycle of 16 days (Roy et al., 2014) and (c) the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor onboard Terra and Aqua platforms obtain spectral data from the Earth surface with the 250 m, 500 m, and 1 km spatial resolutions and temporal resolution of around one day (Justice et al., 2002). The National Aeronautics and Space Administration (NASA) provides different ready-to-use products derived from MODIS sensor, including vegetation indices, surface temperature and gross primary productivity (GPP) (Zhao, Heinsch, Nemani, & Running, 2005), among others. The aim of this study is to integrate landscape structural and functional factors with the GPP dynamics over different terrain units in the Araguaia River Basin.
Section snippets
Study area
The Araguaia River Basin is the largest basin in the seasonal tropics in Brazil and is located in the border of the states of Pará, Tocantins, Goiás, and Mato Grosso (Fig. 1). The elevation varies between 55 m and 1060 m. The dominant type of climate is Aw, according to the Köeppen's classification system (Alvares, Stape, Sentelhas, Gonçalves, & Sparovek, 2013), with dry winter (from April to September) and wet summer (from October to March), and with rainfall and temperature increasing from
Land use and land cover
The DLS, DCS, PS, and AS domains occupy 12%, 30%, 28%, and 29% of the total area of the Araguaia River Basin, respectively. The spatial distribution of LULC classes is strongly correlated with the terrain units, as has been shown in other studies in the same region (Latrubesse et al., 2019; Latrubesse & Stevaux, 2002; Valente, Latrubesse & Ferreira, 2013). In the AS domain, the original Cerrado vegetation prevails and is composed of pioneer vegetation, with distribution pattern controlled by
Final remarks
The time series decomposition showed to be a practical method of visualizing the long-term increase or decrease of GPP as well as the short-term variations of GPP, related to the seasonality in the Araguaia River Basin. The use of RGB color composites also showed to be a useful tool for understanding the spatial and temporal patterns of LULC.
Regarding dominant LULC types in the Araguaia River Basin, we found pasturelands in the entire basin, covering 40% of the total area. Croplands were mostly
CRediT authorship contribution statement
Pedro R. Martins: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing - original draft, Writing - review & editing, Visualization, Supervision. Edson E. Sano: Formal analysis, Investigation, Writing - review & editing. Eder S. Martins: Formal analysis, Investigation, Writing - review & editing. Ludgero C.G. Vieira: Formal analysis, Investigation, Writing - review & editing. Luiz F. Salemi: Formal analysis, Investigation,
Acknowledgements
We acknowledge the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for a scholarship received by PRM. EES and LCGV were supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) productivity fellowships. We also acknowledge the two anonymous reviewers that have greatly contributed with highly relevant comments.
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