Reducing Water Erosion Research Articles

Quantifying soil erosion and soil organic carbon conservation services in indian forests: A RUSLE-SDR and GIS-based assessment

Indian forests, having sixteen types of vegetation, provide various ecosystem services. Forests reduce water erosion of soil, reduce floods and conserve low river flow during dry seasons. Present study estimated annual sedimentation, texture, soil organic carbon control service of forests of India using the Revised Universal Soil Loss Equation (RUSLE) and Sediment Delivery Ratio (SDR) approach through GIS technique along with identifying important drivers responsible for erosion in forests. The soil erosion control service was based on five factors viz., rainfall erosivity, soil erodibility, slope, crop management, conservation practice factor and SDR across the various forest dominated river basins. Geo-detector modelling was performed to evaluate environmental drivers responsible for soil erosion. Valuation of soil control service of the India’s forests was estimated based on damage and replacement cost method. Annual soil loss rate was maximum in Tropical Thorn Forest and in Ganga River basin. Maximum sediment control and SOC conservation against the soil erosion control service by India’ forests were due to Tropical Dry Deciduous Forest with a total annual sedimentation control and SOC conservation of 33,056,560 tonnes and 3,31,115.06 tonnes, respectively. The conservative estimate of the economic value of soil conservation service by the forests of India was US$ 535.6 M with an average of 4.40 US$ ha−1 and a maximum share of value for Tropical Dry Deciduous Forest i.e. 294.18 million US$ and average maximum value for Littoral and Swamp Forest (28.91 US$ ha−1). The soil erosion in Tropical and Sub-tropical Forest was influenced by the interactive effects between NDVI and Bulk Density. In contrast, soil erosion in the temperate and alpine area was influenced by anthropogenic activity in combination with climatic factors. Present study accounts the role of India’s forests for the soil conservation service and may provide inputs to implement forest and reservoir management strategies besides providing information for Integrated Watershed management and Catchment Treatment Plans.

Water soil erosion modeling with RUSLE, GIS & remote sensing: A case study of the AL-Sanaoubar River basin (Syria)

Soil erosion forms a serious ecological challenge to future production and sustainability, with implications of the environmental crisis and the food supply. It is one of the more critical geomorphological problems that threaten environmental sustainability and cause soil degradation along the Syrian coast. The object of this research is to evaluate the rate of probable annual water-induced soil erosion in the AL-Sanaoubar River Basin. By Integrating geographic information system (GIS), and remote sensing techniques with the Universal Soil Loss Equation (RUSLE). The results showed that the soil loss values in the AL-Sanaoubar River Basin ranged between 0–138.15 tons/ha/year, an average of 52.4 tons/ha/year. The total soil loss reached 12,606.11 tons/year for the entire studied area.The classification of possible spatial risk included five grades: very low (91.91%), low (7.62%), medium (0.35%), high (0.10%), and very high (0.01%).It has been noticed high soil erosion values in few portions of the study area, indicating that they had reached a risk stage; these sites were concentrated in the center and east of the studied basin, especially in the plateau and mountainous parts, Slope was a major factor that caused a direct impact on soil erosion. Soil erosion gradually increased with increasing slope in all types of land uses.To test the effectiveness of some soil conservation practices against water erosion, an experiment was conducted at the Mazar Qatrya site in Lattakia governorate during two consecutive seasons. Contour cultivation of the pea crop was applied at different distances, the agricultural method showed a high efficiency in reducing water erosion. Land use managers and Planners can benefit from this research to make suitable provisions and activities to conserve the soil.

Water Erosion Response to Rainfall Type on Typical Land Use Slopes in the Red Soil Region of Southern China

Land use and rainfall are two important factors affecting soil erosion processes. The red soil region of southern China is a representative region with high rainfall amounts and rapidly changing land use patterns where the water erosion process is sensitive to changes in land use and rainfall. To comprehensively understand the water erosion response to land use and rainfall in this region, a 6-year in situ experiment based on eight plots (bare land and seven typical land uses) was conducted from 2015 to 2020. The 320 rainfall events were divided into 4 types, and there were 3 main rainfall types. The runoff of different rainfall types was primarily determined by the rainfall amount, while the soil erosion of different rainfall types was primarily determined by the rainfall intensity. High-intensity rainfall contributed the most to both total runoff and soil erosion. Compared with bare land, the seven typical land uses reduced runoff and soil erosion by more than 75%. Grassland, cropland, and forest with low vegetation coverage experienced high runoff and soil erosion, while shrubland most effectively reduced runoff and soil erosion. The combination of land use and rainfall type significantly affected the annual average runoff depth, soil erosion modulus, and soil loss coefficient. Rainfall types can change the relationship between runoff and soil erosion for different land uses. The runoff and soil erosion of bare land were highly correlated with rainfall characteristics, while vegetation weakened this relationship under short- or moderate-duration rainfall. To effectively reduce water erosion, high-intensity rainfall should receive special attention, and all land uses should ensure that vegetation is well developed, especially understory vegetation.

Synergy between vegetation patterns and sedimentation has a temporal effect on water erosion in a slope‐gully system

AbstractMultiple soil and water conservation measures applied together perform better at reducing runoff and sedimentation than individual measures, which can be attributed to their synergistic effects on water erosion. However, whether these synergistic effects are always effective at reducing water erosion remains unclear. In this study, a series of physical models representing a slope‐gully system were tested to quantify the trend of synergistic effects of multi‐measure over time through simulated rainfall. The tested scenarios included four vegetation patterns on the slope—Pattern A: no grass, Pattern B: grass on the up‐slope, Pattern C: grass on the middle‐slope and Pattern D: grass on the down‐slope—and five levels of runoff path length decrease (RPLD) in the gully caused by sedimentation of a check dam (0, 1, 2, 3 and 4 m). Synergistic effects on runoff and sediment yields were influenced by vegetation patterns and RPLDs. Under the same vegetation patterns, synergistic effects increased with increase of RPLD. Under the same RPLD, the mean value of synergistic effects on runoff was in the following order: Pattern D (0.10%) > Pattern C (0.09%) > Pattern B (0.06%), and synergistic effects on sediment yields had a similar order: Pattern D (0.60%) > Pattern C (0.42%) > Pattern B (0.22%). Under Pattern B, based on the Mann–Kendall trend test, the synergistic effects on the runoff yields decreased over time. Contrastingly, under Patterns C and D, the synergistic effects on the runoff yields increased over time. The results show that the synergistic effect has time effect, and its change trend is related to vegetation patterns. Additionally, the results suggest that the middle‐ and lower‐slopes should be prioritized when restoring vegetation as the synergistic effects on runoff tend to increase when these have good vegetation cover.

Effects of contour farming and tillage practices on soil erosion processes in a hummocky watershed. A model-based case study highlighting the role of tramline tracks

To reduce water erosion, one of the most severe land degradation processes on arable soils, conservation measures such as contour farming or reduced tillage practices can be applied. The general effectiveness of these measures on reducing soil erosion is well understood, however, little is known about the influence on tramline tracks, which have considerable impact on the transport of sediment and runoff. This study assesses the impact of reduced and conventional tillage and slope-related tramline directions on runoff and soil erosion rates at catchment level. For this purpose, a published and freely available dataset was used consisting of soil loss and runoff data modelled for a single soil erosion event considering courses and structural properties of tramlines (cf. Saggau et al., 2022). The orientation of tramlines against the slope direction was defined as contouring efficiency (Cef) and calculated by an approach that relates slope and tramline directions. Finally, results of the statistical analyses are compared with mapped soil erosion data. Results show that i) high-resolution derivation of Cef, based on tramlines, shows reasonable results in capturing variations in slope curvatures within the fields, ii) increased Cefs can significantly reduce runoff and soil erosion in tramlines and, iii) reduced tillage indicates significantly lower runoff and soil erosion rates in tramlines and cultivated areas. The results reveal that tramlines have strong interrelations with surface runoff, water connectivity and soil erosion. The consideration of tramlines in process-based models should be employed in other model approaches as it improves assessments of soil erosion risk and efficiencies of conservation measures, which are necessary in taking appropriate actions in support of soil and water conservation.

Synergistic effects of vegetation restoration and check dams on water erosion in a slope‐gully system

AbstractRestoring vegetation and constructing check dams are important measures for controlling water erosion in slope‐gully systems. However, percolation through the dam body could lead to shortened runoff paths in the gully. Moreover, the synergistic effects of vegetation patterns and siltation‐induced runoff path length decrease (RPLD) in slope‐gully systems on reducing water erosion remain unclear. In this study, 20 physical models of slope‐gully systems were constructed to quantitatively evaluate the synergistic effect of these measures under simulated rainfall. The models included four slope vegetation patterns (no vegetation, up‐slope, middle‐slope, and down‐slope) and five levels of RPLD in the gully (0, 1, 2, 3, and 4 m). Owing to synergistic effects, combined measures led to a more considerable reduction in soil and water loss than a single measure. Furthermore, the synergistic effect was related to vegetation patterns and shorter siltation‐induced runoff paths. The mean synergistic effect produced the following runoff yield order: down‐slope (2.84%) > middle‐slope (2.81%) > up‐slope (1.78%); and 4 m (3.18%) > 3 m (2.66%) > 2 m (2.29%) > 1 m (1.78%). The sediment yields were in the following order: down‐slope (18.15%) > middle‐slope (12.63%) > up‐slope (6.67%), and 4 m (14.56%) > 3 m (12.82%) > 2 m (11.73%) > 1 m (10.82%). These results suggest that revegetation of the lower parts of the slope, along with check dams, will be more effective for controlling soil erosion. Such synergistic effects should be considered in future soil erosion modeling.

The legacy of forest logging on organic matter inputs and storage in tropical streams

AbstractRiparian forests play an important role in stream ecosystems, as they support biodiversity, reduce water erosion, and provide litter that fuels aquatic biota. However, they are affected by great array of anthropogenic threats (e.g., fire, logging, and organic pollution), which alter species composition and their physical structure. Although forest recovery after disturbance such as logging can take decades, the legacy of forest clear‐cut logging on key processes in tropical riparian ecosystems is mostly unknown. Here, we investigated how litter inputs (leaves, twigs, and reproductive parts) and storage, key processes for carbon and nutrient recycling and for forest and stream biota, are influenced by riparian vegetation undergoing succession (after 28 years from logging) through the comparison of reference and logged forest sites in the Cerrado biome. Litterfall was overall similar between forest types, but litterfall of twigs was twofold higher at logged than reference sites. Similarly, litter inputs from the bank to the stream (i.e., lateral inputs) and streambed storage were 50–60% higher at logged than reference sites. The higher litterfall observed in logged forests could be related to higher proportion of tree species that are characteristic of primary and secondary successional stages, including fast‐growing and liana species, which often are more productive and common in anthropogenic areas. Our results showed that the legacy impact of clear‐cut logging, even if residual woody vegetation is maintained in riparian buffers, can shift the type, quantity, and seasonality of litter subsidies to tropical streams. This knowledge should be considered within the context of management and conservation of communities and ecosystem processes in the forest‐stream interfaces.Abstract in Portuguese is available with online material.

Fragmentation of soil-root complexes in sloping landscapes during tillage and soil translocation

It is well known that roots play a significant role in reducing water erosion in soil, yet few studies have reported the influence of crop roots on soil translocation induced by tillage in sloping fields. To examine the relationship between soil-root complexes (i.e., complexes of wheat roots and soil) and soil redistribution caused by tillage, a series of tillage experiments were carried out on bare soil and areas of wheat sown by drilling ( DS ) and nesting ( NS) using nine slopes with gradients varying from 0.19 to 0.32 m m −1 . The magnetic tracing technique was used to determine soil translocation rates under hoeing tillage in sloping landscapes in response to soil-root complexes and bare soil. The results indicated that mean displacement distance for DS and NS in the downslope direction was 0.15 m and 0.16 m, respectively. This was much shorter than that of bare soil which was 0.26 m. Mean tillage erosion rates ranged from 14.58 to 19.15 Mg ha −1 per tillage pass for DS and 13.90 –21.10 Mg ha −1 per tillage pass for NS , while reached 31.23–36.31 Mg ha −1 per tillage pass for bare soil. Tillage transport coefficients ( k 3 and k 4 ) were 6.31 and 106.46 kg m −1 per tillage pass for DS , 6.58 and 118.68 kg m −1 per tillage pass for NS , and 28.12 and 151.07 kg m −1 per tillage pass for bare soil, respectively. A significant difference in cohesive force ( C ) was found between DS ( NS ) and bare soil ( P < 0.05), thereby resulting in an increase in the soil shear strength of soil-root complexes. Compared with those of bare soil, the soil fractal dimension of soil-root complexes decreased significantly due to an increase in the percentage of coarse clods (>100 and 100–80 mm) and a decrease in the percentage of fine clods (50–20 and < 20 mm). Mean soil displacement distance caused by tillage displayed a negative relationship with C and wheat root traits (the root density, the root length density, and the root area ratio) within the hilly landscape of soil-root complexes ( P < 0.05), implying that wheat roots played a crucial part in soil translocation and soil fragmentation during hoeing tillage. Our study revealed that soil-root complexes markedly reduce the soil downslope transfer process during tillage and prevent the break-up of large clods by tillage implements on sloping farmland. • Wheat root attenuated the mechanical breakage of clods during tillage operation. • Root systems increase soil shear strength and reduce fragmentation of soil clods. • Displacement distance for soil-root complexes was smaller than that for bare soil. • Tillage erosion decreased with increasing structure stability and cohesive force.

Modeling of soil loss by water erosion in the Tietê River Hydrographic Basin, São Paulo, Brazil

Since the mid-16th century, the Tietê River has been an important route for the territorial occupation and exploitation of natural resources in the interior of São Paulo and Brazil. Currently, the Tietê River is well known for environmental problems related to water pollution and contamination. However, little attention has been focused on water erosion, which is a serious issue that affects the soils and waters of the hydrographic basin. Thus, this work aimed to estimate soil loss caused by water erosion in this basin, which has an area of approximately 72,000 km², using the Revised Universal Soil Loss Equation (RUSLE). The RUSLE parameter survey and soil loss calculation were performed using geoprocessing techniques. The RUSLE estimated an average soil loss of 8.9 Mg ha-1 yr-1 and revealed that 18% of the basin's territory presents high erosion rates. These are priority zones for conservation practices to reduce water erosion and ensure long-term soil sustainability. The estimated sediment transport was 1.3 Mg ha-1 yr-1, whereas the observed sedimentation, which was calculated based on data from the fluviometric station, was 0.8 Mg ha-1 yr-1. Thus, the results were equivalent considering the large size of the study area and can be used to assist in managing the basin. Estimating soil losses can help in the planning of sustainable management of the Tietê River Hydrographic Basin and highlights the importance of minimizing water erosion, thus helping to prevent additional pollution and contamination with sediments, agrochemicals, and fertilizers.

Impactos do reflorestamento nas perdas de solo e de carbono orgânico do solo

ABSTRACT Water erosion is a serious environmental problem that causes soil degradation, compromises its fertility and causes soil organic carbon (SOC) losses. Reforestation, encouraged by Brazilian environmental legislation, is a way to reduce water erosion. However, in tropical and subtropical regions, there is little information on the impact of reforestation on soil loss rates and SOC. Therefore, this study aimed to apply the Erosion Potential Method, combined with multitemporal data from soil samples collected in situ, to estimate and spatialize soil and SOC losses in a predominantly agricultural Brazilian watershed that showed high rates of reforestation in the period studied from 2011 to 2019. The determination of the EPM parameters was carried out with the aid of a Geographic Information System and the soil loss estimate was validated with information from a hydrosedimentological collection station. The results showed that between 2011 and 2019 water erosion was reduced by 27.5%, while carbon losses were reduced by 32.7%. Among the evaluated crops, corn showed the highest soil and SOC losses, while coffee and forest areas exhibited the lowest rates. Reforestation of the basin is the main factor responsible for the reduction of soil losses. This process was initiated seeking to meet the requirements of the Brazilian Forest Code, which highlights the positive role that public policies can play in environmental conservation when respected and well applied.

Can cover crops improve soil ecosystem services in water‐limited environments? A review

AbstractCover crops (CCs) are considered to deliver multiple soil ecosystem services, but such potential could vary by climatic region. This leads to the question: can CCs improve soil ecosystem services in low precipitation regions? To answer this, we reviewed published data up to 27 July 2021 regarding CC impacts on CC biomass production, soil organic C (SOC) accumulation, water and wind erosion, soil water, nitrate leaching potential, soil microbial biomass, weed management, crop yields, and livestock production (i.e., CCs as forage) across regions with &lt;500 mm precipitation. Literature indicates that CCs produce 2.37 ± 2.30 Mg ha−1 of aboveground biomass, but belowground biomass data are unavailable. Cover crops increased soil wet aggregate stability (63% of CC vs. no CC comparisons), suggesting reduced water erosion potential with CCs. Also, CCs reduced nitrate leaching potential (74% of comparisons) and soil water (50%), increased soil microbial biomass (73%), and did not affect dry aggregate stability (67%) and crop yields (56%). Cover crops accumulated SOC in 59% of comparisons. Averaged across all comparisons, CCs accumulated 0.43 Mg SOC ha−1 yr−1 in the upper 30‐cm depth. This SOC accumulation rate is within the range of SOC accumulation across all regions in previous reviews. Cover crops can reduce weed biomass by 89%. Also, when hayed or grazed, CCs could provide net economic returns without negating soil benefits. Overall, CCs improve most soil ecosystem services without many detrimental effects on crop yields in water‐limited environments, although more long‐term (&gt;10 yr) data are needed for definitive conclusions.

Effectiveness of conservation agriculture (tillage vs. vegetal soil cover) to reduce water erosion in maize cultivation (Zea mays L.): An experimental study in the sub-humid uplands of Guatemala

Cultivated uplands in tropical latitudes are severely affected by soil water erosion. Conservation agriculture (CA) is specifically intended to control erosion. The aim of the present study is to analyse the effectiveness of CA measures to reduce the erosion in maize cultivation (Zea mays L.) on andosols in the mountains of southern Guatemala. Resolving this question is crucial to the development of sustainable soil policies appropriate to the conditions prevailing in this region. The study was conducted over a three-year period, from 2017 to 2019, on three experimental plots managed under conventional tillage (CT), reduced tillage (RT) and no-tillage (NT). The general-to-specific (GETS) method, based on reduction theory, was used to generate explanatory models of the erosion-affected surface. The study was carried out at two scales, first, with the complete database, and second, the database was segmented according to the agricultural management systems. The results showed different rates of eroded soil surface between the three management systems: 73.2% under CT, 41.3% under RT and 20.4% under NT. Analysis of the complete database (n = 36) showed that the litter cover (ryl.p = –0.86, p < 0.001) and the soil disturbance (ryp.l = 0.57, p < 0.001) were, in that order, the factors with the greatest explanatory power of the eroded surface. The segmented analysis (n = 12) showed that the management system adopted had a decisive influence on the ground cover (litter and weed cover) and, therefore, on the soil erosion. Under CT, the eroded surface was only correlated with the weed cover (ryw.l = –0.68, p < 0.05), under NT only with the litter cover (ryl.w = –0.89, p < 0.001) and under RT the erosion did not correlate with either of the vegetal layers. Three conclusions are derived from this study. First, litter layer was the key explanatory factor of erosion. Second, this factor is highly influenced by the agricultural management system. The proportion and distribution of the litter layer in each management situation were key to explaine the different soil erosion rates between the three management systems. And finally, it is proposed for the area of this study the soil management under NT with a dense and well distributed litter cover.

Vegetation greening partly offsets the water erosion risk in China from 1999 to 2018

Soil erosion by water is a major threat to land degradation. The United Nations Decade on Ecosystem Restoration 2021–2030 calls for massive ecosystem restoration to address land degradation impacts. Due to the implementation of large-scale soil and water conservation programs in China (i.e., the Grain for Green Program), the area covered by vegetation has increased. Climate change may exacerbate soil erosion risk, while vegetation greening may alleviate this risk. This work aims to assess China's water erosion risk over the past two decades since the implementation of the Grain for Green Program (1999–2018) and explore the relative importance of precipitation and vegetation on erosion risk dynamics. An integrated method was developed using the Revised Universal Soil Loss Equation and the Pressure-State-Response model. An indicator contribution index was applied to detect the impacts of soil cover and management (C) and rainfall erosivity (R) on risk changes. The results showed that China's water erosion risk had a decreasing trend (23% between 1999 and 2018), especially in areas with middle and high state indicator values. R contributed more than C in northern China, whereas the opposite occurred in southern China. The contribution of R decreased while that of C increased. Vegetation greening partly offset the pressure from climate change. Overall, this work highlights the importance of vegetation recovery in reducing water erosion.

Soil quality assessment using erosion-sensitive indices and fuzzy membership under different cropping systems on a Ferralsol in Brazil

The objective of this study was to evaluate soil quality under different cropping systems through two erosion-sensitive indexing methodologies applying fuzzy membership functions to a minimum data set (MDS) of soil properties. The experiment was conducted in a Ferralsol, in annual growing cycles from 2007 to 2014. The evaluated cropping systems included individual and intercropped treatments using: sunn hemp (Crotalaria juncea L.), pearl millet (Pennisetum glaucum L.), jack bean (Canavalia ensiformis L.), pigeon pea (Cajanus cajan L. Huth), and maize (Zea mays L.). Sampling in an adjacent area under native forest was also performed as a reference ecosystem. Soil properties such as bulk density, micro-, macro- and total porosity, aggregates stability, laboratorial soil fertility properties, and soil organic matter content were selected as MDS of physical and chemical properties, being used to compute two soil quality indices: 1) Integrated Quality Index (IQI), and 2) Nemoro Quality Index (NQI). Soil quality results showed the lowest values of soil and water losses corresponded to the largest soil quality indices evidencing that the usage of water-erosion-sensitive indices can be useful for the prediction of soil quality status. The selected MDS of soil properties were adequate indicators of soil quality as reduced water erosion was associated with large soil quality indices, e.g. negative correlation between soil macroporosity and soil erosion processes. The fuzzy methodology was effective in predicting soil quality using a MDS of soil property indicators, which can benefit various stakeholders in their decision-making process to ensure continuing and sustainable crop production.

Effect of land set up systems on soil losses

Agricultural land set up systems comprise those agronomic structures able to preserve the soil fertility from water erosion, such as: ditching, contouring, earth-riser and stonewall terracing, draining, and channelization, etc.. However, in the past 60 years, agricultural mechanization has led to an expansion of the field size and reduction in land set up system intensity to make machine operation more feasible and cheaper. As a consequence, these transformations have made sloping fields less resilient to the storms and accelerated the soil erosion processes. Based on an 8- year field study in ‘Chianti Classico’ area (Tuscany, Central Italy), this research aimed to evaluate the effectiveness of the land set up systems such as diversion ditch, earth-riser and stonewall terracing on reducing water erosion from field crops, olive orchards, and vineyards. The results showed that diversion ditches were effective on herbaceous crop fields with slope steepness lower than 9%. While, for higher slopes, diversion ditches were not sufficient to contain the soil loss within OECD 2008 tolerable limits in none of the considered land uses. On the opposite, in steep slopes, earth-riser terraces and stonewall terraces have shown their value as land set up system capable of reducing the erosive process. Their greatest drawback is the reduction of the cultivable surface deriving from the presence of the riser and the walls. However, their added value as a precious element characterizing the local landscape was of considerable importance for the local economy linked to tourism. Highlights - Diversion ditches reduce soil erosion on herbaceous crop fields with slope lower than 9%. - Diversion ditches did not contain the soil loss within acceptable limits on steep slopes. - Earth-riser terraces and stonewall terraces reduced soil losses within acceptable limits. - Terraces reduced soil loss by 4.7-12.3 times with respect to diversion ditches. - The analysis was performed on measured average annual soil loss data from 695 fields.

Ecological restoration is not sufficient for reconciling the trade-off between soil retention and water yield: A contrasting study from catchment governance perspective

Ecological restoration program (ERP) is widely recognized as an effective measure to combat land degradation and improve environmental quality. However, inappropriate ERPs lead to trade-offs between soil retention and water yield as well as conflicts of soil and water resources between the midstream and the downstream of catchment. This study aims to assess the efficiency of ERPs in soil erosion control and identify the trade-offs between soil retention and water yield through the lens of runoff and sediment regimes in contrasting catchments of the Loess Plateau (LP) and the Karst Plateau (KP). Although favorable climate and rapid vegetation restoration substantially reduced water erosion in both these areas, the hydrological responses were not the same because of climate differences. In the arid LP, water and energy variables correlated closely with vegetation cover. Excessive afforestation programs in drylands increased vegetation transpiration and soil evaporation, further exhausting soil water resources, and eventually causing water yield reduction. However, soil and water conservation programs (SWCPs) in the humid KP reduced sediment yield substantially, and the runoff remained stable. Significant runoff reduction in the midstream of the Yellow River aggravated water scarcity and threatened the downstream water demand. Meanwhile, sediment load decline in the LP and the KP impacted sediment deposition in the downstream and estuary formation. From the perspective of integrated catchment governance, human interventions including ERP and SWCP should be more sustainable and consider not only the target process at the local scale (intracoupling effect), but also unprecedented non-target process at the regional scale (telecoupling effect). In addition, it should allow for the supply-demand balance of competing soil and water resources to achieve the coordinated development of resources, environment, and production.

Quantifying the effects of contour tillage in controlling water erosion in China: A meta-analysis

Contour tillage is a widely practiced conservation tillage in China. The beneficial effects of contour tillage in controlling water erosion have been recognized, further researches are needed to quantify the effectiveness of contour tillage in reducing water erosion and identify the influencing factors in China. We conducted a nationwide meta-analysis based on 229 runoff and 290 sediment paired observations from 47 published papers from national and international literatures. The results showed that compared to traditional tillage, the benefits of contour tillage in China with respect to runoff and sediment reduction were 35.86% and 49.02%, respectively. Sediment yield reduction by contour tillage was greater under simulated rainfall than under natural rainfall. Runoff reduction by contour tillage decreased with the increasing mean annual precipitation and temperature, while sediment yield reduction was not affected by climate factors. Contour tillage in loamy soils and soils with organic carbon content > 1% showed the greatest benefits in reducing sediment yield (64.26% and 52.52%, respectively). The greatest runoff and sediment yield reduction (61.04% and 67.24%, respectively) occurred at slope length > 20 m. The greatest runoff reduction by contour tillage was found for tillage duration > 10 years (44.08%), while the greatest sediment yield reduction occurred at tillage duration ≤ 5 years (52.89%). The effectiveness of contour tillage under cereals was better for runoff and sediment yield reduction compared to legumes and rotation as consequence of the high biomass quantity and lower mineralization rate of cereal straw. Our results conclude that contour tillage is an effective measure for controlling water erosion, and its benefits in reducing runoff and sediment yield are different according to the climate, soil properties, topography and management practices.

The driver-pattern-effect connection of vegetation dynamics in the transition area between semi-arid and semi-humid northern China

Vegetation is at the nexus of water, soil, and the atmosphere, making it a significant indicator of climatic variability and shifts in human activity. The spatial attribution analysis of vegetation changes may help us to identify and estimate the relationship between variation in vegetation and different erosion types, and their correspondence may be in the antecedents and consequences of vegetation dynamics. Here, based on time series datasets for the Bashang Plateau and northern North China’s mountainous region from 1998 to 2015, we used trend analysis, partial correlation analysis, and univariate linear regression to investigate the sustainability of vegetation variations and to determine the driving mechanisms of climatic and anthropogenic factors in vegetation dynamics at the regional scale. Further, we applied correlation analysis and models (i.e., USLE and RWEQ) to detect the spatial heterogeneity of soil erosion dynamics and the effects of vegetation coverage variation on the dynamics of water erosion, wind erosion, and wind-water erosion. Our results revealed a significant increasing trend in Normalized Difference Vegetation Index (NDVI) and the improved area accounted for more than 80% of the study area. The response of vegetation variation to climatic factors displayed a high correlation with precipitation for a 1-month lag in the semi-humid area, especially in forestland, and with temperature for a 0-month lag in the semi-arid area, particularly in farmland. These results suggest human activity has had a greater effect on vegetation variations than climatic factors during 2011–2015, and that human activity was the dominant factor controlling vegetation changes in terms of the spatial distribution of major drivers; notably, the implementation of the vegetation restoration projects affected the spatiotemporal patterns of vegetation cover. During 1998–2015, the increased vegetation coverage played a dominant role in reducing water erosion of the forestland, and it had a vital impact on lessening wind erosion in open land and sparsely vegetated areas, while the increased fractional vegetation coverage (FVC) may have been a contributing factor to aggravated soil erosion in the wind-water erosion zone of grassland and forestland. Hence, the importance of the implementation of revegetation projects on soil erosion reduction should not be underestimated.

Tracing the origin of reservoir sediments using magnetic properties in Southeastern Brazil

Determining the origin of eroded soil is essential to design effective soil erosion control strategies which preserve the soil resource, enhance agricultural productivity, and reduce the negative impacts of soil erosion, in-field and off-field. Magnetic properties have been widely used in temperate environments to identify sediment sources, pathways and links, but there have been very few applications in tropical and subtropical environments. Therefore, in this paper we investigated reservoir sediment sources in the Upper Grande River Basin, Southeastern Brazil, using sediment tracing techniques based on magnetic parameters (low and high frequency magnetic susceptibility, frequency dependent susceptibility). The different parent materials and subtropical weathering conditions resulted in soils having different Fe oxide minerals and Fe oxide contents, promoting magnetic variability that allowed comparison and identification of possible sources of reservoir sediments in order to reduce water erosion impacts. The results indicate the suitability of magnetic properties as a tracer for soil erosion studies in tropical environments.

Assessing rainfall erosivity and erosivity density over a western Himalayan catchment, India

The present study aims to assess rainfall erosivity and erosivty density both in space and time over the Suketi River catchment of western Himalayan region in India during 1971–2015. The data used comprises of daily rainfall measurements at three rain gauge stations, which are sparsely distributed over the catchment. Rainfall erosivity was assessed by employing Wischmeier and Smith algorithms, whereas erosivity density was estimated by applying Kinnell’s algorithm. The spatial distribution of both algorithms was analyzed through Kriging method based on geographical information system. The obtained results indicate remarkable year-to-year, seasonal and monthly variations in average annual rainfall erosivity and erosivity density. Apart from this, individual cases of high and very high rainfall erosivity and erosivity density were noticed. The long-term average annual rainfall erosivity and erosivity density revealed a general decreasing trend. This decreasing trend in rainfall erosivity was found to be statistically significant at 0.05 significance level, whereas it was found to be non-significant for erosivity density. The highest values of both indices were observed in the month of July followed by August and June particularly in northern parts. These results indicate that July month followed by August and June are the most susceptible months for soil erosion over the Suketi River catchment with lower reaches (northern) being the most vulnerable one. Finally, results of this study will be valuable for farmers, agronomists and regional planners in chalking out best management practices for reducing water erosion in vulnerable areas of the catchment.