Mass balances of major solutes, nutrients and particulate matter as water moves through the floodplains of the Pantanal (Paraguay River, Brazil)

Marcia Divina De Oliveira,Debora Fernandes Calheiros,Stephen Kimber Hamilton

doi:10.1590/2318-0331.231820170169

Marcia Divina De Oliveira, Debora Fernandes Calheiros + Show 1 more

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https://doi.org/10.1590/2318-0331.231820170169

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Abstract

ABSTRACT In the upper Paraguay River basin, which includes the Pantanal, one of the largest wetlands in the world, rivers connection the surrounding upland plateaus with lowland floodplains. Agriculture, erosion, urban effluent, and hydropower in the uplands can alter the transport of materials by rivers to the Pantanal. Information about material transport, particularly nutrients, is still insufficient to evaluate changes. In this study we estimated rates of dissolved and suspended material transport from the upland watersheds into the Pantanal, and through the Paraguay River, and calculated mass balances of these flows to reveal net losses and gains inside the Pantanal. We sampled fifteen tributaries and the Paraguay River for seven years. The annual water balance in the basin was almost complete, with a deficit of only 11%. Predicted:Observed ratios close to one indicated a near balance between inputs and outputs for dissolved solutes and nutrients, however sedimentation losses of suspended solids and particulate carbon were significant. In spite of a high degree of river-floodplain contact, no significant changes on solutes concentrations were observed between inputs and outputs, enough to alter the transport of solutes though the Pantanal, indicating equilibrium in biogeochemical process on floodplain.

Highlights

The upper Paraguay River and its tributaries originate in surrounding plateaus of elevations around 800 m before descending to lower elevations of around 200 m where the rivers pass through vast floodplains lying on alluvial sediments
Recent changes in the course of the river due to sediment deposition on the alluvial fan have been documented by Padovani et al (2005), who estimated that approximately 77% of the sediment load of the Taquari River is deposited on the floodplains
This study considers the 240,000 km2 of the upper Paraguay River basin above Porto Esperança, which includes the majority of the Brazilian Pantanal, a 140,000-km2 area subject to seasonal inundation by riverine overflow as well as slow drainage of local rainfall (Figure 1)

Summary

Introduction

The upper Paraguay River and its tributaries originate in surrounding plateaus of elevations around 800 m before descending to lower elevations of around 200 m where the rivers pass through vast floodplains lying on alluvial sediments. The rivers of the basin transport massive quantities of sediments from the plateaus to the floodplains of the Pantanal, amounting to 29,000 t/day, principally via the Taquari and São Lourenço drainage basins (SEMMELMANN et al, 1996; Barbedo, 2003). The transported sediments tend to accumulate as river water first enters the flooded areas, forming alluvial fans that are readily observed in satellite images of the Pantanal (ASSINE; SOARES, 2004; ZANI et al, 2009). The Taquari River region has the most sediment accumulation, forming one of the world’s largest active alluvial fans. Other tributaries including the São Lourenço, Vermelho, Itiquira, Correntes, Aquidauana and Miranda rivers display sedimentation and geomorphological changes within the Pantanal, they have been less studied

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