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Abstract: Sediments produced from eroding cultivated land can cause on‐site and off‐site effects that cause considerable economic and social impacts. Despite the importance of soil conservation practices (SCP) for the control of soil erosion and improvements in soil hydrological functions, limited information is available regarding the effects of SCP on sediment yield (SY) at the catchment scale. This study aimed to investigate the long‐term relationships between SY and land use, soil management, and rainfall in a small catchment. To determine the effects of anthropogenic and climatic factors on SY, rainfall, streamflow, and suspended sediment concentration were monitored at 10‐min intervals for 14 years (2002–2016), and the land use and soil management changes were surveyed annually. Using a statistical procedure to separate the SY effects of climate, land use, and soil management, we observed pronounced temporal effects of land use and soil management changes on SY. During the first 2 years (2002–2004), the land was predominantly cultivated with tobacco under a traditional tillage system (no cover crops and ploughed soil) using animal traction. In that period, the SY reached approximately 400 t·km−2·year−1. From 2005 to 2009, a soil conservation programme introduced conservation tillage and winter cover crops in the catchment area, which lowered the SY to 50 t·km−2·year−1. In the final period (2010–2016), the SCP were partially abandoned by farmers, and reforested areas increased, resulting in an SY of 150 t·km−2·year−1. This study also discusses the factors associated with the failure to continue using SCP, including structural support and farmer attitudes. [ABSTRACT FROM AUTHOR]

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The article presents the study which explores the relationship between suspended sediment concentration (SSC) and turbidity for a small rural catchment in Brazil. It evaluates two calibration methods by comparing the SSC estimates obtained from the calibrated turbidity readings with direct measurements using the soil taxonomy system of the U.S. Department of Agriculture. The first method is derived by relating the turbidity reading to simultaneous measurements of concentration obtained from SSC samples collected from the vicinity of the turbidity probe during flood events, while the second is based on the readings obtained from the turbidity meter when the probe immersed in samples using soils collected from the catchment. The study shows the efficiency of the first method over the second.

The hydrological dynamics of a small rural river catchment in southern Brazil have been used to understand the impact of agricultural activity on soil and water resource degradation. The monitoring and modeling strategies employed to better understand the integrated phenomena focus on surface flow dynamics and the associated processes, such as erosion, sediment yield (SY), and chemical element transfer. In this context, monitoring and modeling techniques are combined in order to include the main hydrological processes involved in soil and water resource degradation. The project began in 2002 and over 500 rainfall-runoff-sediment events and suspended sediment concentration make up the hydrological database under different land use and soil management conditions. The 1.2 km2 catchment of the study is characterized by the presence of shallow soils, high slope, intense agricultural activity, and high SY (~150 t.km-2.y-1). Techniques that enable the identification of the origin and redistribution of sediments (e.g fingerprinting approach and Cs137) and hydrograph analysis are being used to further understand the dynamics of SY in the catchment. The comprehension of the factors involved in the SY dynamics has allowed the improvement and application of different mathematical models (e.g., LISEM and WATERSHED) to simulate surface flow and SY. These models are used to represent the influence of soil and water conservation practices while considering the interaction between the different landscape components (crops, roads, drainage network, etc.). From this set of data and tools, the capacity of the agricultural production system, drainage network, wetlands and riparian forests in accelerating or retarding water flow, sediment, and chemical elements in the landscape are evaluated. All of these studies have been used to improve soil and water conservation practices at catchment scale, meeting the expectations of farmers in erosion control and water storage as well as of the society interested in maintaining the hydrological functions of soils in catchment scale. [ABSTRACT FROM AUTHOR]

Atmospheric nuclear tests (1945-1980) have led to radioactive fallout across the globe. French tests in Polynesia (1966-1974) may influence the signature of fallout in South America in addition to those conducted by USA and former USSR until 1963 in the Northern hemisphere. Here, we compiled the 240 Pu/ 239 Pu atom ratios reported for soils of South America and conducted additional measurements to examine their latitudinal distributions across this continent. Significantly lower ratio values were found in the 20-45° latitudinal band (0.04 to 0.13) compared to the rest of the continent (up to 0.20) and attributed to the contribution of the French atmospheric tests to the ultra-trace plutonium levels found in these soils. Based on sediment cores collected in lakes of Chile and Uruguay, we show the added value of measuring 240 Pu/ 239 Pu atom ratios to refine the age models of environmental archives in this region of the world., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Solute and particulate elemental concentrations (C) exhibit different responses to changes in discharge (Q), and those relationships are not well understood in subtropical agricultural environments. The objective is to describe the transport processes of different chemical elements during a set of contrasted rainfall events (2011-2015) that occurred in a small rural catchment under subtropical climate. The study was carried out in the Lajeado Ferreira Creek catchment (1.23 km 2 ), southern Brazil. To this end, the concentrations in dissolved organic carbon (DOC), Cl - , NO 3 - , SO 4 - , ten chemical elements (in either dissolved or particulate forms) and suspended sediment concentrations (SSC) were determined. Metric indices were then calculated to characterize their transport patterns: (i) the best fit slope between log-C and log-Q (β), (ii) the coefficient of variation of C and Q, (iii) shape of the hysteresis loop and hysteresis index, and (iv) the flushing index. All particulate elements along with the dissolved inorganic phosphorus (PO 4 -3 ) were shown to be controlled by the sediment dynamics. Geogenic elements (Fe 2+ , Zn 2+ , Cu 2+ , Mn 2+ , Si 4+ ) showed a dilution effect with increasing Q values, likely because they were mainly transported with subsurface and base flow. Dissolved elements that are mainly supplied with fertilizers (Na + and Cl - ) as well as DOC showed a dilution effect, although they were mainly transported by surface runoff. Finally, a chemostatic behavior was found for those chemical elements (Mg 2+ , K + , Ca 2+ , NO 3 - and SO 4 2- ) that are supplied by more than one flow pathways. The results demonstrate that under subtropical climate conditions, the transport of essential nutrients including PO 4 -3 and metals (in particulate form), are mainly transported with surface runoff. Accordingly, runoff control on cultivated hillslopes should be improved to reduce the potential contaminant supply to the river and to reduce the potentially deleterious impacts that they may cause in downstream regions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)