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One of the challenges of modern agriculture is to adapting to climatic effects, including the capacity of rainy events in causing erosion. The understanding of these phenomena relies on monitoring rain variables that express the magnitude and pattern of erosive agents. Kinetic energy (E) is a fundamental variable to represent the erosivity and to enable the estimation of erosion and sediment yield in mathematical models. In Brazil, there are no direct and continuous measurements of E, and empirical equations to estimate rainfall intensity (I) are used instead. As a result, empirical equations to estimate E from I are used. To assess local behavior between these variables, rain variables (energy, volume and intensity) and associated processes (water flow (Q) and suspended sediment concentration (SSC)) were measured in a small rural catchment. The work was developed in a small rural catchment (1.23 km 2 ) located in southern Brazil where intensive land use with tobacco cultivation has caused high rates of erosion and sediment yield. This study proposes an alternative equation E = f(I) for the study region and provides a comparison with previous equations already proposed by Foster et al. (1981); van Dijk et al. (2002); Wilkinson (1975); Brown and Foster (1987) and USDA-ARS (2013). Furthermore, this work explores the seasonal variations and the differences in the magnitude of the events of these relationships. The measured E values were similar to those estimated by the equations of Foster et al. (1981); USDA-ARS (2013) and van Dijk et al. (2002), whereas Brown and Foster (1987) underestimate the estimation of E. Finally, it was evaluated the predictive ability of the total kinetic energy, 30 min maximum intensity (I 30 ) and total volume of the rainfall (P total ) in explaining the response variables which reflect the hydrology and sediment yield processes considering the Q and SSC. The main results of the work were: i) a new equation to estimate E based on the I measured, its seasonal variation and similarity with the previously known equations and ii) the relationship between E and the hydrological variables at catchment scale. [ABSTRACT FROM AUTHOR]

• Geochemical tracers were not conservative in a catchment with highly weathered soils. • Magnetic and UV tracers had low discriminating potential between land uses. • The low discrimination between sources results in great uncertainties in the results. • Quantifying sediment contributions from more than three sources remains challenging. • Despite limited discrimination, results of all tracers combinations remained consistent. An important step in the sediment source fingerprinting approach is the selection of the appropriate tracing parameters to maximize source discrimination. The use of multiple tracing properties may reduce uncertainties and increase discrimination between sources. Accordingly, this study investigates the discrimination and quantifies the contribution of sediment sources delivering sediment to a river draining a homogeneous subtropical agricultural catchment based on the combination of ultraviolet–visible spectra derived parameters (UV), magnetic (M), and geochemical tracers (GEO). The investigated catchment (Conceição River − 804 km2), located in Southern Brazil, has predominantly deep and strongly weathered Ferralsols. The main land-uses found in the area are cropland (89%), pasture (5%) and forest (5%). A total of 187 samples were collected to characterise the five main sediment sources, including cropland, pastures, unpaved roads, gullies and stream banks. A total of 53 tracers, including 21 geochemical tracers, two magnetic properties and 30 parameters derived from UV spectra, were analysed. Tracers were selected following a three step procedure, including: (i) an interquartile range test, (ii) a Kruskal–Wallis H test, and (iii) a linear discriminant function analysis (LDA). The LDA was performed using six different sets of variables: (i) GEO only; (ii) UV only; (iii) M + UV (MUV); (iv) GEO + UV (GUV); (v) GEO + M (GM) and (vi) GEO + M + UV (GMUV). The selected tracers were introduced into a mass balance mixing model to estimate the source contributions to in-stream sediment by minimizing the sum of square residuals. Most geochemical tracers were considered not conservative by using the interquartile range test in this catchment with highly weathered soils. The GM approach resulted in the highest percentage of samples correctly classified (SCC), with 74%, followed by the approaches with GMUV and GUV, with 73%. Alternative tracers, UV individually or combined with M tracers, correctly classified only 59 and 60% of the samples, respectively. Moreover, they did not provide significant additional discrimination power even when combined with the GEO tracers. The apportionment model resulted in similar source contribution results for all approaches, with the absence of significant difference when comparing the mean source contributions obtained for the entire set of sediment samples (Cropland: 17–23%; Pastures: 24–34%; Unpaved Roads: 3–12%; Stream Banks: 26–31%; Gullies: 14–19%). Due to the strong homogeneity of soil types found in the Conceição catchment, these differences in source contributions remained very low and the results of the mixing model were impacted by the high number of potential sources and the relatively limited quality of the sediment source discrimination. According to the model results, the low discrimination between the potential sediment sources illustrates the difficulties for discriminating land-used based sediment sources, with more than three potential sources, in homogeneous catchments with highly weathered soils (e.g. Ferralsols, Nitisols) under tropical conditions. [ABSTRACT FROM AUTHOR]

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 km2), 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 (Fe2+, Zn2+, Cu2+, Mn2+, Si4+) 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 (Mg2+, K+, Ca2+, 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. Unlabelled Image • The study described the transport of chemical elements during rainfall events. • Particulate matter and PO 4 −3 were linked to sediment dynamics. • Fe2+, Zn2+, Cu2+, Mn2+, Si4+ concentrations decreased with increasing flow. • Na+, Cl− and DOC showed a dilution pattern at the beginning of the rainfall events. • Mg2+, K+, Ca2+, NO 3 −, SO 4 2− showed a chemostatic pattern. [ABSTRACT FROM AUTHOR]

The intensification of agricultural activities increases the transfer of phosphorus (P) to surface water bodies causing a wide range of environmental, social and economic problems, such as eutrophication. This paper describes the dynamics of P loss during rainfall events (intra-event) and between events (inter-event) in a rural catchment with intensive soil use in southern Brazil, emphasizing the relationships of the solutes with the hydrosedimentological variables. The information on the magnitude and the pattern of P transport was obtained during eighth significant rainfall events, in addition to the sampling performed during the baseflow period (between events). During the events, we evaluated the transfer dynamics of the total P (TP), dissolved P (DP), particulate P (PP) and suspended sediment concentration (SSC). Phosphorus (dissolved and particulate) is predominantly lost during events. The concentrations of DP and PP were low in samples collected in the period between events, when groundwater flow predominates. There is predominance of subsurface flow for the total volume of DP drained into the catchment. The hysteresis of TP forms a loop in the counterclockwise direction at the moment the soil is exposed by plowing, due to P transfer from the cropland to the water course. The transfer of P occurred predominantly in the particulate form (88%) due to the high affinity of P with mineral colloids. There was predominance of clockwise hysteresis for TP and SSC during the fallow period and at the beginning of soil mobilization, indicating the presence of P and sediment sources closer to the catchment outlet. However, during the development period of the crop, when the soil was more exposed due to plowing, counterclockwise hysteresis was observed for TP, which indicates a predominance of sources farther from the outlet, such as the cropland. Thus, we believe that efforts towards adopting practices that reduce erosion can contribute to a reduction of P transfer to water sources. Consequently controlling the process of eutrophication. [ABSTRACT FROM AUTHOR]