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• Recurrent fire leads to degraded rainforest (DRf) and herbaceous-shrubby (HS). • Ksat and 6 years of rainfall-soil suction interactions are analyzed. • HS provide shallow soil saturation even during long dry periods. • Fire decreases Ksat in topsoil and it increases soil suction in depth at HS. • Post-fire soil changes tend to favor rapid suction loss in the unsatured zone. The role of fire in vegetation-soil–water interactions and its implications for soil stability and slope failures is poorly documented in humid tropical regions. This paper focuses on the relationships between vegetation change through recurrent fire and its effects on hydraulic conductivity and soil suction. Two monitoring sites were chosen on steep slopes in the mountainous domain of the Atlantic rainforest: the first is representative of degraded secondary rainforest (DRf) 25–30 years after slash and burn agriculture; the other represents herbaceous-shrubby vegetation (HS) resulting from wildfires in short-time intervals (<5 years). Two fires had previously occurred on the HS slope, one in December 2014 and the other in September 2019. Continuous records of rainfall and soil suction at depths of 10, 20, 50, 100, 150, and 220 cm provided a 6-year data collection from January 2015 to December 2020. Hydraulic conductivity (Ksat) field tests were conducted around the two monitoring sites before and after the September 2019 fire. The main results include: a) soil suction in the topsoil of both vegetation covers follow the rainfall inputs with high values of Ksat (DRf = 195 mm/h; HS = 203 mm/h); b) while quick rainfall-suction responses prevail within the DRf soil profile, soil suction at HS maintains a mean suction value around -27 kPa below 100 cm deep; c) field observations attest to the occurrence of hydrophobicity after the 2019 fire; d) Ksat tests just after this fire indicated a decreasing mean value from 203 mm/h to 46 mm/h; and e) by the end of the dry season after fire, there is a delayed increase in soil suction reaching -143 kPa at a depth of 100 cm and in smaller proportions at 220 cm deep. These results indicate that post-fire soil changes tend to favor the sudden loss of soil stability and slope failure during extreme rainfall events. [ABSTRACT FROM AUTHOR]

Abstract Brazilian Atlantic Forest is recognized by the UNESCO as one of the most important biosphere reserves on the planet but is threatened by extinction. The objective of this study was to analyze the main components of the water balance in an Atlantic Forest (Neotropical Forest) catchment in the Mantiqueira Range, Brazil, which is a Tropical Montane Cloud Forest. The main focuses was to analyze baseflow, evapotranspiration, soil moisture, and canopy rainfall interception to understand the hydrologic dynamics in this specially important montane forest. On average from the two studied hydrological years (2009/2010 and 2010/2011), evapotranspiration (ET), streamflow (SF), and water storage in the catchment at the end of hydrological year corresponded, respectively, to 50%, 34.8% and 15.2% of total gross precipitation (P). On average, baseflow corresponded to 73.5% of SF. The estimated potential groundwater recharge during the wet seasons was 403.8 mm (21.7% of P observed in the wet season) and 710.5 mm (28.5% of P observed in the wet season), respectively, for 2009/2010 and 2010/2011 hydrological years, showing that the catchment is able to store groundwater to provide the maintenance of the streamflow during early recessions and drought periods. Therefore, the baseflow is important in mountainous catchments in the tropical regions to provide important ecological functions, mainly as freshwater reserve. Highlights • Mountainous Neotropical Forest has fundamental hydrologic role in tropical regions • Baseflow has been sustained by groundwater recharge in forested mountainous sites • Interaction forest canopy/transpiration and soil moisture define water balance • Catchment was capable of close water year with surplus for sustaining main outputs [ABSTRACT FROM AUTHOR]

• An approach is proposed to assess extreme rainfall-triggered landslides. • 3D unsaturated flow is coupled with the infinite slope method. • Extreme precipitation events are investigated using soil depth models. • 1-year spin up for moisture conditions has little impact on the safety factor. • Simple soil depth models are viable options for landslide susceptibility studies. The susceptibility to shallow landslides is affected by several factors. Rainfall intensity, soil thickness distribution, and antecedent moisture conditions are components that influence the spatio-temporal prediction of landslides at the watershed scale. Yet, the combined impact of these factors on the susceptibility to landslides has been overlooked. The purpose of this paper is to investigate landslides triggered by extreme precipitation in the Tijuca Massif, Rio de Janeiro, southeastern Brazil. Our approach couples a 3D variably saturated flow solver with the infinite slope stability method to calculate the statistical distributions of the safety factor and the pore pressure at the soil–bedrock interface. Numerical simulations were performed for 6 scenarios considering 1-year spin-up time for soil moisture and different spatially distributed soil depths. The results show that during extreme precipitation events, soil depth and initial moisture conditions may not have much influence on the safety factor, as the intensity and duration of rainfall will be the triggering agents. Comparison of simulated unstable zones and field data from mapped landslide scars further supported this conclusion. We conclude that simple soil depth models are feasible options for regional studies of landslide susceptibility. Our findings are relevant to understanding shallow landslides induced by extreme rainfall in Rio de Janeiro and other regions with similar geological and climate settings. [ABSTRACT FROM AUTHOR]

In natural ecosystems, soil respiration is one of the important components of carbon emission into the atmosphere – CO 2 efflux. Soil CO 2 efflux has both temporal (due to temperature and moisture changes) and spatial variability, which can be explained by different types of soil, soil use and management, as well as the influence of vegetation on CO 2 efflux. The aim of this study was to measure the spatial variability of soil CO 2 efflux, soil temperature and soil moisture in areas of archaeological dark earth cultivated with the guandu bean (GB) and pasture (PT), compared to soil use in natural forests (NF) in Amazonas state, Brazil. To that end, regular meshes were marked out in areas of forest (6 × 6 m spacing), guandu bean (4 × 5 m spacing) and pasture (8 × 8 m spacing) measuring 2500 m 2 , 1700 m 2 and 4800 m 2 , respectively, with 88 sample points georeferenced in each area. Soil CO 2 efflux (FCO 2 ) and soil temperature (ST) were measured at the intersection points of the meshes, and soil samples were collected at a depth of 0.00–0.10 m to determine soil moisture (SM) in the laboratory. FCO 2 measurements were taken using LI-6400 systems. Soil temperature (ST) was measured at 0.00–0.10 m, using a portable thermistor thermometer, and soil moisture (SM) using soil samples collected at 0.00–0.10 m. FCO 2 and ST were lower in the forest area, with higher SM content, no difference between FCO 2 and ST in GB and PT, but with lower SM content in PT. The models of the experimental semivariogram were predominantly spherical, except for FCO 2 in the NF and GB areas, and SM in the PT area, which were fit to the exponential model. The maps of spatial distribution patterns indicate a trend in concentration, with a positive correlation between FCO 2 and SM and negative correlation between FCO 2 and ST in natural forest. Positive correlations were observed between FCO 2 and ST and SM in GB, but in PT, FCO 2 correlations were restricted to SM. [ABSTRACT FROM AUTHOR]

The current paper presents the evaluation of the ability of the SWAT hydrological model (Soil and Water Assessment Tool) to reproduce continuous daily streamflows of the upper Itapemirim River basin (Brazil). The model parameters were calibrated and validated with data collected from 1993 to 2000. The model was found to be highly sensitive to baseflow, its primary calibration variable. Validation analyses resulted in values of statistical indexes (NS = 0.67; NSlog = 0.68; PBIAS = 22% and RSR = 0.57) that show that SWAT performance was satisfactory in this application. [ABSTRACT FROM AUTHOR]

[Display omitted] • We used artificial neural networks to predict surface and subsurface soil moisture. • The effects of topography, climate, soil, land use, and rainfall were evaluated. • Artificial neural networks efficiently modelled soil moisture. • Climate-related variables are most important for the performance of the surface model. • Soil-related variables are most important for the performance of the subsurface model. Soil moisture, which impacts various hydrological processes, can be estimated from point measurements in a watershed or via remote sensing. As both methods are expensive and complex, efforts have been made to develop empirical models based on data that affect the occurrence of soil moisture. However, these models have been based only on surface-layer data. We present an original approach for investigating regional empirical models of soil moisture, both for the surface (0–10 cm) and subsurface (10–20 cm) layers, and evaluate the main factors which affect the model results. Based on data about the climate, soil properties, topographic features and rainfall, we applied artificial neural network soil-moisture models for a small watershed, in southern Brazil. The models for each layer, with all selected variables, showed Nash-Suitcliffe coefficients of 0.870 and 0.893, respectively, for the surface and subsurface models. We then tested the effects of removing each variable or categories of variables. The most important variables for the surface model were the season, followed by exponential weighted moving average (EWMA) of rainfall. For the subsurface model, the most important variables were the season (although less so than for the surface model), followed by microporosity. All of the variable categories were important in the surface model. In the subsurface model, the soil-related variables were the most important, whereas the rainfall and topography variables were of little importance. It was possible to estimate soil moisture for both layers with good performance. The subsurface model, which used only the soil- and climate-related variables, explained more of the variance in soil moisture than the other models. The subsurface layer is easier to model, because the variation in moisture that is induced by recent climate and precipitation effects is attenuated by the physical features of the soil which control water infiltration. [ABSTRACT FROM AUTHOR]

• The long-term (26 years) irrigation suppressed the soil salinity and sodicity. • Weathering and pedogenetic evolution were induced by irrigation. • Mineralogical pathway driven by irrigation improved agricultural soil properties. • Progressive mineral change is due transformations of the illitic phases. • Mixed-layered minerals indicate changes in monosialitization and bisialitization. Long-term irrigation in semi-arid regions leads to shifts in the soil moisture regime, affecting soil attributes and pedogenesis. Drylands are expected to increase worldwide, possibly because of climate change. Few studies have investigated changes in the pedogenic processes due to extensive irrigation in the Brazilian semi-arid region. This study assesses the effects of land use changes (irrigation and cultivation) on the morphological, physical, chemical, and mineralogical properties of soils. We evaluated two soil profiles in the semi-arid region in northeastern Brazil. We investigated an irrigated profile (IP) with long-term irrigation (26 years) and cultivation, and another profile under natural conditions (rain-fed hyperxerophilic Caatinga), that is, a non-irrigated profile (N-IP). The results indicate that land use affected chemical and mineralogical attributes of soils as well as the pedogenetic processes. Both soil profiles showed different behaviors in relation to salts: (1) reduction in soil exchangeable Na content (solodization) in IP, and (2) accumulation of soluble salts (salinization) and increased soil exchangeable Na content (solonization) in N-IP. Land use, possibly irrigation, induced mineralogical alteration pathways, such as the progressive mineral transformations via R0 MLM (mixed-layered minerals), suggesting differences in weathering and mineral evolution. The K-I (kaolinite-illite) and I-V (illite-vermiculite) phases predominated in the clay fraction in both soils and exhibited a greater trend for progressive kaolinization in IP. The other two MLMs (kaolinite-vermiculite, K-V and illite-smectite, I-S) were detected in N-IP and could be a proxy for the lowest weathering degree. This is consistent with the trend for a slight reduction in the SiO 2 /Al 2 O 3 molecular ratio in IP. Illite was possibly the precursor mineral for other phyllosilicates, such as kaolinite, in IP. Fe-enriched MLM was detected in the decreasing sequence: illite, smectite, and kaolinite layers. The pedogenic trends observed, such as mineral weathering, may be attributed to system response to climate change. [ABSTRACT FROM AUTHOR]

• Each stage of cultivation indicated different rates of water and soil loss. • Conventional onion crops in southern Brazil induce land degradation. • Agricultural activities during the different phases indicated variation in the soil surface. • Agricultural activities during cultivation are determining factors in soil erosion. • Soil compaction increases water and soil loss. Onion is one of the most important vegetables grown in southern Brazil. However, despite its profitability, little is known about its response to soil erosion throughout its productive cycle divided into 5 stages: S1 (germination), S2 (formation of leaves and roots), S3 (bulbification), S4 (snap) and S5 (harvesting). With the aim of providing knowledge in this matter we have analyzed the intra-cycle dynamics of some parameters such as bulk density (BD), porosity, soil penetration resistance (SPR), and soil and water losses. To do that we have assessed these parameters in 40 random points and at different depths in a representative farm of 3 ha located in the municipality of Irati (Paraná, Brazil). BD was quantified by using the core method, porosity after particle density quantification by the volumetric balloon method, and SPR by impact penetrometer. Soil and water losses were estimated after carrying out 30 rainfall simulations (6 per crop stage). The results showed that bulk density increased progressively and continuously from 1.06 to 1.36 g cm−3. This greater compaction was also observed in the values of SPR that increased from 2.0 to above 3.0 MPa at the end of the cycle. Regarding soil erosion the highest rates were recorded at S4 when onions are snapped (431.0 g m−2). We conclude the occurrence of runoff and soil erosion is a consequence of the increase in soil compaction throughout the cycle provoked by the repeated pass of heavy machinery and workers to apply herbicides and fertilizers. Since soil erosion rates found are relatively high (1437.1 g m−2 y−1) we suggest the progressive implementation of conservationist practices to guarantee its sustainability. [ABSTRACT FROM AUTHOR]

• Capacitive probes calibration showed good results under different land uses. • Changes in land use influence the spatial and temporal variability of θv. • The deforestation of the caatinga reduces the θv in 47%. • Converting the Caatinga for forage cactus decreases the reduction of θv for 26%. • It is recommended to establish forage cactus in already deforested areas. The semiarid region of Brazil undergoes constant changes in land use due to the process of deforestation and high water seasonality, represented among other variables by a decline in the soil moisture content. In this study, the influence of land use on the soil moisture dynamics is analysed. For this purpose, three experimental sites were evaluated, characterised by different types of land use: an agroecosystem of forage cactus, a deforested environment and an area of Caatinga vegetation, located in the semiarid central hinterlands of Brazil. Calibration of the Diviner2000® capacitive probes was carried out using the relationship between the soil volumetric moisture content (θv), obtained by the gravimetric method, and the relative frequency readings of the probes. Weekly measurements of the moisture content were taken at 22 points at depths of 0.00–0.60 m from November 2014 to October 2017, providing 157 sampled days. The mean values and standard deviations of the θv variable for the three surfaces were analysed over twelve periods, and grouped according to the local water regime into rainy, dry and transitional. To analyse the temporal stability of θv, the relative difference and the Spearman correlation matrix were calculated. Finally, multivariate principal component analysis (PCA) was used to identify associations between the mean values of θv and physical properties in the different soil layers. Based on the results, the local calibration curves presented significant coefficients of determination, showing that the equations can be used for reliable estimates of θv. The θv was higher in the Caatinga (0.086 m3 m−3), intermediate in the forage cactus (0.064 m3 m−3) and lower in the deforested area (0.045 m3 m−3). Changes in land use influence the spatial variability of θv in the soil layers, which responded to the local rainfall regime, especially in the upper layers (0.05–0.25 m). Significant differences in θv between soil surface coverage occurred during the dry sub-periods and the transition periods, when the Caatinga was superior to the other areas. The temporal stability analysis identified the forage cactus area as the most representative location for θv estimates, while the Spearman correlation matrix detected the more-unstable areas of moisture, with persistent moisture patterns between the dry sub-periods and transition periods only. Associations between moisture and different soil properties were affected by soil surface coverage and soil layer depth. All the proprieties explained moisture distribution along the profile. It can be concluded that converting the Caatinga vegetation into other soil surface coverages changes soil-moisture distribution patterns, resulting in a reduction in θv of 26% and 47% for forage cactus and deforested areas, respectively. Therefore, the establishment of forage cactus in current deforested areas of the Brazilian semiarid may attenuate the temporal variability and reduction of soil moisture compared to bare soil surfaces. [ABSTRACT FROM AUTHOR]