Sediment Reduction Research Articles

Multiple sulfur isotope chemostratigraphy across the Permian–Triassic boundary at Chaotian, China: Implications for a shoaling model of toxic deep‐waters

AbstractPrevious studies on multiple sulfur isotopes (32S, 33S, and 34S) in sedimentary pyrite at the end‐Permian suggested a shoaling of anoxic/sulfidic deep‐water contributing to the extinction. This scenario is based on an assumption that the sedimentary sulfur cycle was largely controlled by benthos activity, though a stratigraphic correlation between the sulfur records and ichnofabrics of the sediments at the end‐Permian has not yet been examined. We report the multiple sulfur isotopic composition of pyrite in the Permian–Triassic boundary interval at Chaotian, South China. Our data can be generally explained by a mixing of sulfur in sulfide from two different sources: one produced via sulfate reduction in an open system with respect to sulfate and the other produced in a closed system. In particular, the former with the substantially low δ34S (<−40 ‰) and high ∆33S (up to +0.100 ‰) values was likely produced via water‐mass sulfate reduction or via sulfate reduction in oxic sediments with common burrows. The frequent occurrence of small pyrite framboids (mostly <5 μm in diameter) in the Lopingian (Late Permian) Dalong Formation of deep‐water facies supports the enhanced water‐mass sulfate reduction in an anoxic deep‐water mass. The negative ∆33S values are observed only in the oxic limestones, and no substantial ∆33S change is observed across the extinction horizon despite of the disappearance of bioturbation. Our results are apparently inconsistent with the previous shoaling model. We expand the model and infer that, when the deep‐water was sulfidic and its shoaling rate was high, a substantial amount of hydrogen sulfide (H2S) was supplied onto the shelf via the shoaling; that resulted in the positive ∆33S value of the bulk sediments. The observed ∆33S variation on a global scale suggests a substantial variation in H2S concentration and/or in upwelling rate of shoaling deep‐waters during the Permian–Triassic transition.

A Soil Water Assessment Tool (SWAT) Modeling Approach to Prioritize Soil Conservation Management in River Basin Critical Areas Coupled With Future Climate Scenario Analysis

About 44% of the Indian landmass experiences the adverse impact of land degradation. This loss of sediments caused by soil erosion reduces the water quality of local water bodies and decreases agricultural land productivity. Therefore, decision-makers must formulate policies and management practices for sustainable management of basins that are cost-effective and environment friendly. Application of the best management practices (BMPs) to properly manage river basins is difficult and time-consuming. Its implication under various climate change scenarios makes it more complicated but necessary to achieve sustainable development. In this study, the soil and water assessment tool (SWAT) model was employed to prioritize the Tons river basin’s critical areas in the central Indian states coupled with future climate scenario analysis (2030–2050) using Representative Concentration Pathway (RCP) 4.5 and RCP 8.5 scenarios. The SWAT model was calibrated and validated for simulation of streamflow and sediment yield for daily and monthly scales using the sequential uncertainty fitting (SUFI-2) technique. The values of coefficient of determination ( R2), Nash–Sutcliffe efficiency (NSE), percent bias (PBIAS), and root mean square error (RMSE)-observations standard deviation ratio (RSR) were .71, .70, −8.3, and .54, respectively during the calibration period, whereas for validation the values were .72, .71, −3.9, and .56, respectively. SWAT model underestimated the discharge during calibration and overestimated the discharge during validation. Model simulations for sediment load exhibited a similar trend as streamflow simulation, where higher values are reported during August and September. The average annual sediment yield of the basin for the baseline period was 6.85 Mg ha−1, which might increase to 8.66 Mg ha−1 and 8.79 Mg ha−1 in the future years 2031–2050 and 2081–2099, respectively. The BMPs such as recharge structure, contour farming, filter strip 3 and 6 m, porous gully plugs, zero tillage, and conservation tillage operations have been considered to evaluate the soil and water conservation measures. Recharge structure appeared to be the most effective measure with a maximum reduction of sediment by 38.98% during the baseline period, and a 37.15% reduction in the future scenario. Sub-watersheds, namely SW-8, SW-10, SW-12, SW-13, SW-14, SW-17, SW-19, SW-21, SW-22, and SW-23, fall under the high category and are thus considered a critical prone area for the implementation and evaluation of BMPs. Compared to the baseline period, the effectiveness of BMPs is slightly decreasing in the 2040s, increasing in the 2070s and decreasing in the 2090s. Recharge structure and filter strip 6 m have been found to nullify the high soil erosion class completely. Overall, SWAT model simulations under the RCP 8.5 scenarios were observed to be reliable and can be adopted to identify critical areas for river basins having similar climatic and geographical conditions.

Dust arising mechanism and dust reduction technology of open-pit coal mine using water and sediment reduction effect

Dust arising mechanism and dust reduction technology of open-pit coal mine using water and sediment reduction effect

Streamflow and Sediment Yield Estimation, and Area Prioritization for Better Conservation Planning in the Dawe River Watershed of the Wabi Shebelle River Basin, Ethiopia

Estimating sediment yield and streamflow, as well as identifying soil erosion processes, are necessary for properly designing superior management techniques, monitoring and evaluating various management scenarios, and prioritizing better conservation planning. Therefore, this study estimates Streamflow and sediment yield and prioritizes the catchment sub-watersheds for conservation planning in the Dawe River watershed. In the incessant-time step, sediment load data is generated by developing a sediment rating curve. Statistical measures were used to weigh the SWAT's performance in estimating streamflow and sediment output over the calibration (2000-2008) and validation (2009-2013) periods. The model's performance in estimating the monthly streamflow was 0.73, 0.55, and 0.79 for NSE, R-factor, and R2, respectively, according to the calibration results. For sediment yield, the Nash Sutcliffe efficiency (NSE), R-factor, and R2 were 0.77, 0.47, and 0.82, respectively. Estimated sediment output rates were higher in agricultural lands with eutric and rendzic leptosols soil types and gradients in the study watershed. For the indicated sub-watersheds in the catchment, the three best sediment management scenarios (BMPs) were considered: S1 (filter strip), S2 (terrace/bund), and S3 (reforestation). With the implementation of S1, S2, and S3, the sediment yield was reduced by 15.7 percent, 21.3 percent, and 24.9 percent, respectively, based on the chosen BMPs. As a result, adopting S3 for the Dawe River watershed for productive sediment reductions should be encouraged. As a result, our findings point to the best strategy for negotiating a stronger conservation plan.

Modeling and Prioritizing Interventions Using Pollution Hotspots for Reducing Nutrients, Atrazine and E. coli Concentrations in a Watershed

Excess nutrients and herbicides remain two major causes of waterbody impairment globally. In an attempt to better understand pollutant sources in the Big Sandy Creek Watershed (BSCW) and the prospects for successful remediation, a program was initiated to assist agricultural producers with the implementation of best management practices (BMPs). The objectives were to (1) simulate BMPs within hotspots to determine reductions in pollutant loads and (2) to determine if water-quality standards are met at the watershed outlet. Regression-based load estimator (LOADEST) was used for determining sediment, nutrient and atrazine loads, while artificial neural networks (ANN) were used for determining E. coli concentrations. With respect to reducing sediment, total nitrogen and total phosphorus loads at hotspots with individual BMPs, implementing grassed waterways resulted in average reductions of 97%, 53% and 65% respectively if implemented all over the hotspots. Although reducing atrazine application rate by 50% in all hotspots was the most effective BMP for reducing atrazine concentrations (21%) at the gauging station 06883940, this reduction was still six times higher than the target concentration. Similarly, with grassed waterways established in all hotspots, the 64% reduction in E. coli concentration was not enough to meet the target at the gauging station. With scaled-down acreage based on the proposed implementation plan, filter strip led to more pollutant reductions at the targeted hotspots. Overall, a combination of filter strip, grassed waterway and atrazine rate reduction will most likely yield measureable improvement both in the hotspots (>20% reduction in sediment, total nitrogen and total phosphorus pollution) and at the gauging station. Despite the model’s uncertainties, the results showed a possibility of using Soil and Water Assessment Tool (SWAT) to assess the effectiveness of various BMPs in agricultural watersheds.

Sedimentation and its response to management strategies of the Three Gorges Reservoir, Yangtze River, China

The Three Gorges Dam (TGD), on the upper valley of the Yangtze River, China, is the largest water conservancy and power generation project in the world. Problematic sedimentation in the Three Gorges Reservoir (TGR) is related to the reservoir lifetime, hydropower generation, riverbed erosion, and sustainable development of ecosystems. In this study, measures to holistically and systematically address sedimentation in the TGR are -discussed and demonstrated, including upstream sediment trapping, regulatory optimisation with respect to sediment peaks and reservoir tail sedimentation reduction, and sediment dredging. Owing to upstream reservoir sediment trapping, the incoming sediment load of the TGR has decreased markedly. Results showed that the annual incoming sediment was only 164 million tons, nearly 70% lesser than the preliminary design value. By intercepting the sediment in the upstream reservoirs and conducting sediment peak regulation, the volume and rates of sedimentation in the TGR decreased significantly. Meanwhile, through sediment peak regulation during the flood season, increased volumes of sediment could be discharged downstream, thereby relieving sediment starvation downstream of the TGD. Overall, through adoption of the related sedimentation management strategies, sediment deposition decreased considerably, to approximately 33% of the preliminary design value, thereby successfully addressing the sediment problems in the TGR. Useful sedimentation management strategies learned from the TGR experience can be applied elsewhere to ensure the sustainable use and management of reservoirs.

Microbial antimonate reduction and removal potentials in river sediments

Antimony (Sb), a toxic metalloid, exists mainly as Sb(V) and Sb(III) in the aquatic environment. Sb(V) displays greater solubility and can be reduced to insoluble Sb(III) compounds by microbial activities under anaerobic conditions, thus affecting the environmental fate of Sb. This study was conducted to evaluate the potential of Sb(V) reduction and removal from the aqueous phase by microbial communities existing in river sediments with and without the impact of Sb mining activities. Among the 14 tested sediment samples, which were collected from an urban river without Sb impact and a river flowing through mining area, microbial communities in two samples could reduce and remove Sb(V) in the presence of high concentrations of sulfate, whereas those in other six samples could reduce Sb(V) even under low sulfate concentrations, indicating the relatively wide distribution of microbial Sb(V) reduction potential in the environment, irrespective of the anthropogenic impact. The Sb(V) reduction and removal abilities under different sulfate levels also suggested the presence of multiple types of Sb(V) reduction and removal pathways, including the direct Sb(V) reduction by anaerobic respiration, indirect (chemical) Sb(V) reduction by sulfide produced by microbial sulfate reduction, and their combination. Furthermore, analysis of microbial communities in two enrichment cultures, which were constructed from sediment samples with Sb(V) reduction ability under the minimum sulfate condition and maintained Sb(V) removal ability during 28-d enrichment process, revealed possible contribution of several microbial taxa such as Azospira, Chlostridium, Dechloromonas, Dendrosporobacter, and Halodesulfovibrio to Sb(V) reduction in sediment microbial communities.

An Assessment of xsBa Flux as a Paleoproductivity Indicator and Its Water‐Depth Dependence in the Easternmost Equatorial Pacific Ocean

AbstractWe present the first regional‐scale records of biogenic Barium (xsBa) fluxes in the Panama basin of the eastern‐equatorial margin of the Pacific Ocean in order to assess xsBa as a paleoproductivity proxy. Measurements of xsBa from 13 cores that range in water depths from about 700 to 3,000 m show an increase in 230Th‐normalized xsBa mass accumulation rates (MARs) with increasing water depth during both marine oxygen isotope stages (MIS) 1 and 2. The correlation of xsBa MARs with depth are strong despite differences in bulk sediment MARs and differing degrees of sediment redistribution. We interpret the increasing xsBa with water depth as likely due to the continued decomposition and remineralization of falling and/or resuspended biogenic particles. xsBa does not seem to be affected by diagenetic sulfate reduction in most of the cores. Calculated estimates of xsBa preservation in the sediment pile are high and fluctuate between 45% and 52% throughout the last 25 kyr. Although xsBa fluxes can be a robust indicator of paleoproductivity, caution is needed if (a) there is evidence of sulfate reduction in sediments being analyzed, and (b) one is trying to quantify differences in paleoproductivity among sites that are located at different depths in the water column.

Sediment source and volume of soil erosion in a gully system using UAV photogrammetry

Gully erosion is a severe way of land degradation. Gullies threaten the sustainability of agro-ecosystems, causing quantitative and qualitative reduction of groundwater, farmland productivity, and waterways sedimentation. Since the gully development on the surface begins with water flow and sheet erosion, accurate monitoring of the erosive processes in a gully system and its quantification is key for the development of effective strategies to control soil erosion in gullies. Here, we demonstrate the first use of unmanned aerial vehicle (UAV) [...]

Sediment budget and morphological change in the Red River Delta under increasing human interferences

The Red River sediment dispersal system has been increasingly altered by human activities, but the resultant morphodynamic change and sediment budget in the Red River Delta (RRD) has been little studied in a holistic perspective. In this study, time-series analysis of river water and sediment discharges from 1960 to 2010 was carried out to trace human interferences on sediment routing processes, and historical charts from 1930 to 2008 were digitized to reconstruct the Digital Elevation Models for investigating spatiotemporal variations in the RRD morphology and calculating their depositional and erosional fluxes. The results show that sediment reduction by 61.3% in the Red River is mainly induced by constructing the Hoa Binh Dam at the lower reach of the Da river, and deforestation and other land-use change have recently increased significantly the sediment loads in the Thao and Lo rivers. Intertidal and subtidal morphological changes in the RRD are highly site-specific in response to natural and anthropogenic drivers. Rapid intertidal accretion majorly occurs near the distributary mouths because of abundant sediment supply and artificially promoted siltation by land reclamation projects, but severe coastal erosion may occur secularly after the distributary outlet shifting or temporarily by storm events. The subaqueous RRD is generally featured by the contour-parallel zonation of erosion and accretion determined by strong longshore currents associated with monsoon winds. Net accretion was observed in the tide-dominated northern subaqueous RRD and has recently changed into a slight erosion due to reduced sediment input in the last two decades, while net erosion was monitored in the southern subaqueous RRD predominated by wave and longshore currents and has recently entered into a slight accretion phase in response to the distributary outlet shifting and secular morphodynamic adjustment. The study RRD region received on average 41.1 Mt./yr (Mt = 106 t) of suspended sediments, and 14.2 Mt./yr and 28.6 Mt./yr were estimated to accumulate on the intertidal flats and in the northern subaqueous RRD, respectively. However, erosion in the southern subaqueous RRD could contribute 42.9 Mt./yr of sediment to the system. Therefore, 41.2 Mt./yr of suspended sediment was indicated to escape from the study RRD region and transport further southward by longshore current to form the distal muddy clinoform along the inner Vietnam shelf. This sediment budget estimation should bear a significant uncertainty, but provides important information for multi-decadal sediment dispersal in a mega-delta system and coastal management.

A secondary assessment of sediment trapping effectiveness by vegetated buffers

Vegetated buffers and filter strips are a widely used Best Management Practice (BMP) for enhancing streamside ecosystem quality and water quality improvement through nonpoint source pollutant removal. Most existing studies are either site-specific, rely on limited data points, or evaluate buffer width and slope as the only design variables for predicting sediment reduction, not considering other parameters such as soil texture, vegetation types, and runoff loads that can significantly influence the buffer efficiency. In this paper, we carry out a meta-analysis of published studies and fit regression models to explore the sediment removal capacity of riparian buffers. We compiled 905 data points from over 90 studies (including data from an online BMP database) documenting sediment trapping by vegetated buffers and recorded data regarding buffer characteristics such as buffer width, slope, area, vegetation type, sediment loading, water flow rates, and sediment removal efficiency. We found that an exponential regression model describing the relationship between sediment removal efficiency by the buffer and water inflow/outflow volume ratio explained 44% of the variance. Adding the square root of roughness increased the R2 to 0.50. The model performance was compared with other sediment reduction regression models reported in the literature. The results point towards the importance of considering flow parameters in vegetative buffer design. The improved empirical relationships derived here can be used at local scales to understand sediment trapping potential by vegetated buffers for water quality mitigation purposes and can be built into extant hydrologic models for improved watershed-scale assessments.

Good Seeds Bear Good Fruit: Using Benefit-to-Cost Ratios in Multiobjective Spatial Optimization under Epistasis

Many biophysical models exhibit epistasis (interdependence), where a conservation action impacts the effectiveness of another elsewhere. At the same time, ranking conservation actions according to the independent benefit-to-cost ratios is cost-efficient when epistasis is absent. We use benefit-to-cost rankings as starting points for an evolutionary algorithm employing an epistatic biophysical model. We model a variety of conservation actions to assess trade-offs for sediment reduction and wildlife conservation in the study watershed. We find that despite the presence of epistasis, the weighted benefit-to-cost ratio-derived solutions perform remarkably well in the decision space, but effects in objective space need the model evaluation.

Evaluation of runoff and soil erosion under conventional tillage and no-till management: A case study in northeast Italy

Conservation agriculture, and in particular no-till systems, generally yield improvements in both soil characteristics (e.g. structure, and water holding capacity) and soil processes (such as runoff and hence erosion). Nevertheless, during the first years of no-till, the soil is prone to compaction due to the poor structure, missing ploughing activities, and passage of tractors and machinery, thus favouring surface runoff and soil erosion. Little information exists about the effect of no-till when applied during the transition period from conventional to conservation agriculture. This study aimed at analysing runoff and soil erosion in a non-tilled field in comparison with a tilled field during the transition period. The study was conducted at the Padova University Experimental Farm, in northeast Italy. Six sub-plots (2.5 m × 5 m) were established, three in a tilled field (CT plot) and three in a non-tilled field (NT plot). Each sub-plot was equipped with a runoff water collection system. Runoff was monitored during two sampling seasons: from May to October 2017 and May to September 2018. Runoff water volume was measured at each rainfall event, and the amount of sediment was quantified by drying the runoff samples. This technique is simple and inexpensive and suitable to be applied also in rural areas with inadequate infrastructures and economic resources. Two indices, runoff reduction benefits (RRB) and sediment reduction benefits (SRB), were computed. During the monitoring period, 24 runoff events occurred. NT practices coincided with reductions of over 50% in runoff volumes and 50% to 95% in sediment losses. Only the runoff event just after the CT soil harrowing produced a significantly lower runoff and sediment loss in CT than in NT field, due to the effect of soil tillage on surface roughness and rainfall infiltration. The average sediment concentration in NT was only 47% of CT. The RRB and SRB values confirmed a reduction in runoff and sediment loss in the NT compared with the CT plot, but SRB was greater than the RRB, indicating that the no-till regime showed a better control of sediment loss than it did the runoff amount. The reduced runoff and sediment yield in the NT plot could have important on-site benefits in terms of both sustainable soil management and surface water quality.

Causes of Variations in Sediment Yield in the Jinghe River Basin, China

The Jinghe River remains the major sediment source of the Yellow River in China; however, sediment discharge in the Jinghe River has reduced significantly since the 1950s. The objective of this study is to identify the causes of sediment yield variations in the Jinghe River Basin based on soil and water conservation methods and rainfall analyses. The results revealed that soil and water conservation projects were responsible for half of the total sediment reduction; sediment retention due to reservoirs and water diversion projects was responsible for 1.3% of the total reduction. Moreover, the Jinghe River Basin has negligible opportunity to improve its vegetation cover (currently 55% of the basin is covered with lawns and trees), and silt-arrester dams play a smaller role in reducing sediment significantly before they are entirely full. Therefore, new large-scale sediment trapping projects must be implemented across the Jinghe River Basin, where heavy rainfall events are likely to substantially increase in the future, leading to higher sediment discharge.

Solidification effect of river bottom sediments after flocculation via different composite flocculants.

The main problem in the reduction of river bottom sediments is to solve the dewatering of the rive sediments. The reduction of river bottom sediments is usually dehydrated by natural air drying and requires more time and economic costs. Different proportions of composite flocculants and curing agents have been developed to the reduction of river bottom sediments according to the requirements of the project. Two or more flocculants were mixed with the rive sediments. Therefore, anionic polyacrylamide (PAM), polyaluminum chloride (PAC), polysilicate aluminum ferric (PSAF), and iron perchloride (IC) were selected for flocculation of river sediments. Through the sedimentation column test, the relationship between sedimentation amount and time was plotted, the turbidity value and pH value of the supernatant filtration supernatant were detected, and the flocculation effect of different flocculants was evaluated to obtain suitable groups of composite flocculants. The optimum ratio of two types of polyacrylamide with a molecular weight of 18 million and 23 million was 3:7. The turbidity of the supernatant of water could well be reduced by adding polysilicate aluminum ferric. Finally, the 6 groups of composite flocculants were determined according to the sedimentation and the turbidity value of the supernatant. The relative water content was maintained at about 60% before and after flocculation. At the same curing age, the compressive strength increased as the amount of curing agent increased after flocculation. At the same curing agent dosage, the overall solidification effect was reduced with increase of curing time after flocculation.

Using two‐dimensional modeling to evaluate strategies of sediment reduction and evacuation for Nanshi river under Guishan dam operations

AbstractThis paper presents a unique case study of Nanshi River in Taiwan which may be able to serve as the basis for decision making and river maintenance operations or as a reference for other cases. This study area is composed of regions from upstream alluvial channel to delta‐front and the Guishan Dam reservoir, with a surplus of material supply to transport capacity in the whole region. Dredging is a standard method by which to deal with the accumulation of sediment within a watercourse; however, our understanding of hydrodynamics and sedimentation is limited by the complexity of the sedimentation process. In addition, most of the similar geomorphological studies did not pay attention to the upstream effects of reservoirs on alluvial channels. Similar examples are more often observed in estuaries and coastal zones. Our objective was to evaluate the morphological impact of river dredging implemented in conjunction with downstream gate operations by employing a 2D hydraulic sediment model, SRH‐2D. With the assistance of the model simulations, we revealed that the deposition in the study area is under the interaction among three main mechanisms: headward deposition of the dam, channel width contraction in midstream, and progressive deposition of sediment from the confluence. Accordingly, this study suggested that dredging focuses on the creation of deep trenches in the midstream and upstream sections. It is also important to coordinate gate operations at Guishan Dam with peak flows in order to facilitate the transport of sediment to the reservoir for subsequent discharge via empty flushing. Regarding the effect of Guishan Dam removal, it would have a more pronounced effect on head cutting which leading to erosion in the reservoir and the downstream transport of substantial quantities of sediment, but its effect would be limited to a certain distance. However, dam removal is not considered a viable option considering the need for local water storage and the benefits of the dam in terms of tourism.

The role of vegetation on earth bunds in mitigating soil erosion in Mollisols region of Northeast China

Vegetated earth bund has been widely established to prevent soil erosion of farmland with the slope of 3–5° in Mollisols region of Northeast China. However, a well-adapted vegetation with greater erosion-control and higher economic benefit has not been determined. Here, an artificially simulated rainfall experiment with rainfall intensity of 25 mm h−1 was conducted on plots with eight kinds of earth bund (six vegetated earth bunds, one naturally grass-covered bund and one artificially bare bund) to investigate the runoff and soil loss process. The economic income of six vegetated earth bunds was also evaluated. The results showed that vegetation growing on earth bund reduced surface runoff and soil loss by 15.3–62.5% and 79.4–93.8%, compared to the bare bund, respectively, of which Medicago sativa, Rheum rhaponticum, Corylus heterophylla and Acanthopanax senticosus showed higher runoff and sediment reduction benefits than natural grass. Surface runoff and soil loss were significantly affected by the diverse community (P < 0.001), especially negatively controlled by plant coverage (P < 0.01). The biomass of legume herb exhibited a higher negative-correlation with surface runoff (P < 0.01) than the whole vegetation (P < 0.05), however, plant diversity and roots had no significant effects on surface runoff and soil loss (P > 0.05). Furthermore, compared to the average farmland economic benefits, Corylus heterophylla, Ribes nigrum, Acanthopanax senticosus and Physalis peruviana improved economic benefits by 1.1–9.9 times, while Rheum rhaponticum and Medicago sativa decreased economic benefits by 22.5% and 32.5%, respectively. Corylus heterophylla and Acanthopanax senticosus with Medicago sativa are highly recommended for controlling soil erosion of earth bund and increasing economic income. Our results provide a scientific reference and technical support for optimizing vegetation measures of slope farmland in Mollisols region of Northeast China.

Grass barriers for mitigating diffuse pollution within a source water area - A case study of Northeast China

Agricultural diffuse pollution caused by runoff and soil loss from cropland has been a serious environmental problem in the black soil area of Northeast China. While water and soil conservation measures have led to a sharp decrease in overland flow within source water sub-watersheds, they have, on the other end, affected the water security of agricultural and domestic use as the water storage capacity of downstream reservoirs decreases year by year. For this study, grass barriers, which are generally considered to have high sediment reduction efficiency, were evaluated for their efficiency as a mitigation measure of diffuse pollution within source water areas. Standard field plots were used to monitor two groups of grass barriers, alfalfa (Medicago sativaL.) and native grass (dominated by Setaria viridis(L.)Beauv.), and slope gradients (3° and 5°) under natural rainfall events over the 2012–2015 period. The results indicated that, during the maize (Zea maysL.) growing season, runoff and sediment reduction efficiencies for the alfalfa barrier were 37.91 % and 62.30 %, respectively. And more than 50 % of the nutrient loads (e.g., total nitrogen (TN), total phosphorus (TP), and nitrate (NO3--N)) could be removed by the alfalfa barrier. The environmental loads mitigation efficiency of grass barrier in spring was relatively low and unstable. Both slope and barrier width had a significant impact on the water and soil conservation function of grass barriers, while rainfall intensity and grass type were mainly related to runoff reduction. Overall, these finding could provide some specific recommendations for future grass barrier design and large-scale application in a source water area of Northeast China.

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.

Estimation of sediment yield and effectiveness of level stone bunds to reduce sediment loss in the Gumara-Maksegnit watershed, Nile Basin, Ethiopia

Soil erosion is one of the most significant environmental problems in the Ethiopian highlands. The study was conducted in the main Gumara-Maksegnit watershed and at the sub-catchment scale with and without soil and water conservation (SWC) measures to estimate event-based sediment yield and evaluate the effectiveness of level stone bunds on sediment reduction. The runoff volume and peak discharge were recorded manually with the help of a time series of pictures using the DOERR digital camera. The sediment concentration was determined from manual runoff samples and grid-based soil samples were collected at 162 points. The slope map and satellite image were obtained from the USGS Earth Explorer database with 30-m and 15-m spatial resolutions, respectively. Finally, all six-model factors were combined using the raster calculator in map algebra through the MUSLE framework. The paired t test parametric procedures were applied to test whether the means of event-based predicted and observed sediment yield values are different. The average event-based observed and estimated sediment yields were 0.5581 and 0.4031 Mg ha−1 for the Gumara-Maksegnit watershed, 0.5125 and 0.4194 Mg ha−1 for the treated (with SWC) sub-catchment, and 1.0694 and 1.0150 Mg ha−1 for the untreated (without SWC) sub-catchment, respectively. The observed and estimated sediment losses within the main watershed and sub-catchments were not significantly different. However, comparing the treated and untreated sub-catchments, the sediment losses were highly significantly different and the stone bunds have a capacity for reducing sediment loss by 58.8%. In general, the MUSLE model performed well to estimate sediment yield in the study area with R2 values of 0.62, 0.72, and 0.7 and NSE values of 0.53, 0.71, and 0.34 for treated, untreated, and the main Gumara-Maksegnit watershed, respectively. The results showed that stone bunds have a capacity for reducing sediment loss by 58.8% as compared with untreated sub-catchment. Therefore, successful implementation of stone bunds in the study area, as well as similar agro-ecologies, has a great benefit to enhance land productivity. Meanwhile, the MUSLE model was well suited for reliable applications of sediment yield estimation in the study area.