Diogo Costa Buarque

Soil erosion and sediment transport are significant environmental problems in watersheds, with direct impacts on water quality, channel siltation, and the service life of reservoirs. The concept of sediment connectivity has become established as a complementary approach to mathematical modeling for understanding sediment dynamics, although its integration with hydrosedimentological models in large tropical watersheds remains in its infancy. This study evaluated the correlation between the results of the MGB-SED model and the lateral connectivity index developed by Borselli et al. (2008) in the Doce River watershed, Brazil. The MGB-SED model, calibrated for the period 1998–2014, demonstrated good performance for discharge and sediment yield. The estimated average annual sediment production was 1.55 × 10 ⁷ t/yr, with the highest values concentrated in the Piracicaba, Caratinga, Suaçuí Grande, and Santo Antônio river basins, associated with mountainous terrain and the prevalence of degraded pastures. The lateral connectivity index ranged from −11.98 to 1.99, with higher values in the dissected plateaus of the central south and lower values in the Rio Doce Depression and the Espinhaço Mountains. The Spearman correlation between the IC and the MGB-SED variables was low for all metrics evaluated (ρ ≤ 0.165), which is attributed mainly to the distinct nature of the two models: the IC considers exclusively structural aspects, whereas the MGB-SED incorporates functional components. The results indicate the need to develop connectivity indices that incorporate functional components, especially for large basins in humid tropical environments.

Information on sediment generation and transport is essential for identifying areas vulnerable to erosion and for planning conservation interventions in river basins. This study focuses on the Doce River basin, in Southeastern Brazil, a region predominantly covered by pasturelands and historically affected by anthropogenic activities, even before the collapse of the Fundão dam in 2015. The objective of the research was to evaluate different land use and land cover scenarios and their impact on sediment generation and transport, using the MapBiomas dataset and the MGB-SED hydrosedimentological model. Four scenarios were modeled: (1) historical land use changes, (2) and (3) enforcement of Brazilian environmental legislation, and (4) implementation of conservation practices in pasture areas. The results from scenario 1 showed that land use changes over time were insignificant. Scenarios 2 and 3 showed reductions of 11% and 15%, respectively, in sediment generation and transport compared to scenario 1. Scenario 4 achieved the most significant impact, with a 32% reduction, considering less restrictive conservation practices (P MUSLE 0.75). These results highlight the importance of improving pasture management to mitigate sediment generation and transport. Furthermore, the study identified priority sub-basins, Caratinga, Piracicaba, Casca, Santo Antônio, and Carmo, as highly susceptible to erosion and major contributors to sediment production. These areas require restoration and environmental recovery actions, with an emphasis on soil conservation, to enhance environmental resilience and reduce sediment-related impacts throughout the Doce River basin.

River sediment fluxes have been impacted in South America (SA), one of the continents with the highest erosion and sediment transport rates globally. However, the magnitude and spatio‐temporal distribution of the main drivers of changes have been poorly identified and explored. Here, we performed simulations using a hydrological‐hydrodynamic‐sediment model to comprehensively estimate the spatial and temporal sediment changes and trends in SA from 1984 to 2019. We found that 51% of the main SA rivers experienced significant changes in simulated sediment transport (QST) over this period, with 36% due to Amazon deforestation and river damming and 15% due to precipitation changes. We also estimated a 10% reduction in the average sediment delivery to the oceans. Deforestation was responsible for QST changes higher than 80% in some Amazon sites, and hydropower expansion led to a greater reduction of sediment flows (80%–100%) in the Tocantins, Uruguay, Upper Paraná, lower São Francisco, Desaguadero, and Negro rivers. In addition, our results suggest that reservoirs built in the Amazon region in the 2011–2019 period are also affecting sediment transport. Our modeling outputs provide unprecedented information about the status of river sediment dynamics in SA, and a template to develop evidence‐based strategies and transboundary policies related to continental‐wide sediment dynamics and the conservation and restoration of ecosystems.

Sediment flows dynamics (erosion, transport and deposition) have been disrupted in South America (SA), a continent with the highest erosion and sediment transport rates globally. However, the magnitude and spatial distribution of the main drivers of changes have been poorly identified and explored. Here, we performed simulations using a hydrological-hydrodynamic-sediment model to comprehensively estimate the spatial and temporal sediment changes and trends in SA from 1984 to 2019. We found that 51% of the main SA rivers experienced significant changes in simulated sediment transport (QST) over this period, with 36% due to Amazon deforestation and river damming and 15% due to precipitation changes. We also estimated a 10% reduction in the average sediment delivery to the oceans. Deforestation was responsible for QST changes above 80% in some Amazon sites, and hydropower expansion led to a greater reduction of sediment flows (as high as 80-100%) in the Tocantins, Uruguay, Upper Paraná, lower São Francisco, Desaguadero, and Negro rivers. In addition, our results suggest that reservoirs built in the Amazon region in the last decade are also affecting sediment transport. Our modeling outputs provide unprecedented information about the status of sediment dynamics in SA, and a means to develop evidence-based strategies and transboundary policies related to continental-wide sediment dynamics and the conservation and restoration of ecosystems.

This study verified the impacts of climate change on river flow in the Doce River basin, using the MGB and RCM Eta projections. Despite the differences between the trends, the basin will certainly be affected by the reduction of precipitation and the increase in temperature between 2025 and 2099. Results show considerable reductions in the trends of the average flow of the basin. In 2025 - 2049, these reduction trends are greater than 64% in 50% of river reaches, according to Eta-HadGEM2-ES RCP 8.5. In 2050 - 2074, the flows simulated with Eta-CanESM2 and Eta-HadGEM2-ES RCP 8.5 achieve reductions greater than 84% and 77%, respectively, in 50% of the simulated reaches. In 2075 - 2099 the reduction trends of Eta-CanESM2 and Eta-HadGEM2-ES RCP 8.5 are greater than 91% and 79%, respectively, in 50% of the drainage reaches.

R E S U M O Esse trabalho é parte complementar de uma pesquisa de pós-graduação que tem como objetivo avaliar a perda de solo na bacia do rio Santa Maria do Doce (Espírito Santos), vez que a região vem sofrendo pressão antrópica quanto ao uso do solo. Nesse sentido, devido ao desencadeamento de problemáticas ambientais diversos, modelos matemáticos foram desenvolvidos a fim de realizar o levantamento dos processos erosivos, com vistas a projetos e pesquisas de conservação. O advento dos sistemas de informações geográficas-SIG’s veio auxiliar essas análises, com a possibilidade de realizar mensurações espaciais a níveis regionais e globais. A partir disso, os parâmetros da Equação Universal Revisada de Perda de Solo-RUSLE foram espacializados pela área da bacia de interesse, resultando em um valor médio de perda de solo de 26,60 t.ha-1.ano-1. A região sudeste da bacia teve destaque por apresentar áreas de valor muito superior à média, possivelmente pelo uso agrícola em consonância a um relevo acidentado, alta taxa pluviométrica e solo do tipo Cambissolo. Em relação a produção de sedimentos enviado ao curso principal do rio Doce, o valor estimado de contribuição é de 5,33 t.ha-1.ano-1. Palavras-Chaves: RUSLE, Perda de solo, Produção de sedimentos. Survey of soil loss and sediment production in the Santa Maria do Doce (Brazil) river basin by mathematical modeling. A B S T R A C T This work is a complementary part of the postgraduate research that aims to evaluate the soil loss in the Santa Maria do Doce river basin, in the state of Espírito Santo, since the region has been suffering anthropogenic pressure in terms of land use. In this sense, due to the triggering of various environmental problems, mathematical models were developed in order to carry out a survey of erosive processes, in the face of projects and research aimed at their conservation. The advent of geographic information systems-GIS's came to help these analyses, with the possibility of performing spatial measurements at regional and global levels. From this, the parameters of the Revised Universal Soil Loss Equation-RUSLE were spatialized by the catchment area of interest, resulting in an average soil loss value of 26.60 t.ha-1.year-1. The southeastern region of the basin stood out for presenting areas with a value much higher than the average, possibly due to agricultural use in consonance with a rugged relief, high rainfall and Cambisol-type soil.. Regarding the production of sediments sent to the main course of the Doce River, the estimated contribution value is 5.33 t.ha-1.year-1. Keywords: RUSLE, Soil loss, Sediment production.

Suspended sediments (SSs) contribute to the maintenance of several ecosystems. However, intense soil erosion can lead to environmental, social, and economic impacts. South America (SA) has very high erosion and sediment transport rates. Here, we present a detailed description of the spatio‐temporal dynamics of natural SS flows in SA using the continental sediment model MGB‐SED AS. We evaluate the model with daily in situ data from 595 stations, information from regional studies and a global model. The model performance analysis showed that, in general, there was a better agreement between simulated and observed data than with the information found in regional studies and of the global model. The use of the hydrodynamic propagation method has allowed a better representation of sediment flows in rivers and floodplains. Based in the calibrated model results, SA delivers 1.00 × 10⁹ t/year of SS to the oceans, in which the Amazon (4.36 × 10⁸ t/year), Orinoco (1.37 × 10⁸ t/year), La Plata (1.11 × 10⁸ t/year), and Magdalena (3.26 × 10⁷) rivers are the main suppliers. The floodplains play an essential role, retaining about 12% (2.40 × 10⁷ t/year) of the SS loads reaching the rivers. In this study, data sets related to SS flows in SA were generated and can be used to support other large‐scale researches or policymakers and stakeholders for adequate management of continental land use.

Suspended sediments (SS) contribute to the maintenance of several ecosystems. However, intense soil erosion can lead to environmental, social, and economic impacts. South America (SA) has very high erosion and sediment transport rates. Here we present a detailed description of the spatio-temporal dynamics of natural SS flows in SA using the continental sediment model MGB-SED AS. We evaluate the model with daily in-situ data from 595 stations, information from regional studies and a global model. The model performance analysis showed that, in general, there was a better agreement between simulated and observed data than with the information found in regional studies and of the global model. The use of the hydrodynamic propagation method has allowed a better representation of sediment flows in rivers and floodplains. Based in the calibrated model results, SA delivers 1.00×109 t/year of SS to the oceans, in which the Amazon (4.36×108 t/year), Orinoco (1.37×108 t/year), La Plata (1.11×108 t/year) and Magdalena (3.26×107) rivers are the main suppliers. The floodplains play an essential role, retaining about 12% (2.40×108 t/year) of the SS loads reaching the rivers. In this study, datasets related to SS flows in SA were generated and can be used to support other large-scale researches or policymakers and stakeholders for adequate management of continental land use.