查看更多>>摘要：Efforts made to restore the degraded landscape of the Tigray region,Northern Ethiopia,over the last three decades have been relatively successful.However,an armed conflict that broke out in the region in November 2020 has significantly destroyed the restored vegetation,either directly associated with conflict(environment,pollution,fire)or indirectly(agricultural abandonment).This study aimed at assessing spatio-temporal changes in vegetation cover in a 50 km radius zone centered on Mekelle city,Tigray.Vegetation cover dynamics was evaluated using Landsat Enhanced Thematic Mapper Plus(ETM+)and Operational Land Imager(OLI)datasets for the years 2000,2020,and 2022 and analysed using ENVI 5.3 and ArcGIS 10.8.1 software.These data were analysed using the Modified Normalized Difference Vegetation Index(MNDVI),Optimized Soil Adjusted Vegetation Index(OSAVI),and Moisture Adjusted Vegetation Index(MAVI).Based on the MNDVI,results show that vegetation cover increased in the period 2000-2020 by 179 km2 or 2％of the area,whereas in the period 2020-2022,there was a decrease in vegetation cover by 403 km2 or 5％of the area.This was accompanied by a decrease in vegetation density.These vegetation changes in 2020-2022 are attributed to the impact of armed conflict on the land surface which can include farmlands and village abandonment,spread of weeds and scrub vege-tation,or failure to harvest crops.Monitoring vegetation change using Landsat data can help understand the environmental impacts of armed conflict in rural agricultural landscapes,including potential food security risks.
Javier M.GonzalezWarren A.DickKhandakar R.IslamDexter B.Watts...
650-662页
查看更多>>摘要：Conservation practices are encouraged to improve soil health and sustain agronomic crop production.Mehlich-3 is often used as a multi-nutrient extractant to determine soil fertility status.A study inves-tigated the impacts of the conservation practices of gypsum,cover crops,and crop rotation on 28 Mehlich-3 extractable elements,of which 11 were considered plant nutrients,from soil at three mid-western US locations.Soil was collected from 0 to 15 and 15-30 cm depths 5 years after implementing the conservation practices.Treatments consisted of(1)with and without cereal rye(Secale cereale L.)winter cover,(2)continuous soybean[Glycine max(L.)Merr.]vs.soybean-corn(Zea mays L.)rotation,and(3)annual gypsum application(0,1.1,and 2.2 Mg ha-1).Differences were observed by site,depth,and conservation practice depending on the element evaluated.Minimal interactive effects were observed among treatments.The most consistent effect was observed for crop rotation across sites.Gypsum only affected the site with the greatest clay content,where more Ca and S were retained,and Mg and Mn displaced.Cover crop only affected elements at this high clay site,where different elements were positively or negatively affected.Results suggest that not one practice fits all,and optimum conservation practices must be tailored for the site.
Kifle WoldearegayBerhane GrumRudi HesselFrank van Steenbergen...
663-683页
查看更多>>摘要：Rainfall variability coupled with poor land and water management is contributing to food insecurity in many sub-Saharan African countries such as Ethiopia.To address such challenges,various efforts have been implemented in Ethiopia.The objective of this study was to evaluate the long-term impacts of different soil and water conservation and water harvesting interventions on groundwater and drought resilience of the Gule watershed,northern Ethiopia.The study involved:(i)documentation of the ap-proaches followed and the technologies implemented in Gule since the 1990s,(ii)monitoring the hy-drological effects of the interventions for ten years,and(iii)evaluation of the effects of the interventions on groundwater(level and quality),spring discharge and suspended sediment concentration(SSC)in runoff.Results showed that interventions were implemented at different stages and scales.As a result of the interventions,the watershed was transformed into a landscape resilient to rainfall variability:(a)dry shallow groundwater wells have become productive and the level of water in wells has raised,(b)the groundwater quality has improved,(c)SSC in high floods has reduced by up to 65％,(d)discharge of existing springs has increased by up to 73％and new springs have started to emerge.Due to improved water availability,irrigated land has increased from less than 3.5 ha before 2002 to 166 ha in 2019.Communities have remained water-secure during an extreme drought in 2015/2016.Implementation of watershed management practices has transformed the landscape to be resilient to rainfall variability in a semi-arid environment:a lesson for adaptation to climate variability and change in similar environments.
查看更多>>摘要：Soil aggregate stability is an important index that reflects soil quality and anti-erosion ability and strongly affects soil processes and functions.Bedrock strata dips(dip and anti-dip slopes)and land use types primarily influence soil aggregate stability,whereas the detailed mechanisms are unclear in karst trough valley.Therefore,to explore the effects of bedrock strata dip and land use type on soil aggregate stability in karst trough valleys,soils were collected from five major land use types(abandoned land,grassland,pepper fields,corn fields and forest)on dip and anti-dip slopes.The soil was fractionated into macroaggregates and microaggrates using dry and wet sieving analysis.The soil particle size distribu-tions in the macroaggregates and microaggregates were measured in conventional laboratories.The results showed significant differences in soil aggregate stability among different bedrock strata dips,slope positions,and land use types(P＜0.05).The variation ranges of macroaggregates and micro-aggregates in the pepper fields of the dip slope were higher than those on the anti-dip slope.Comparing all land use types,the forest of the anti-dip slope had＞0.25 mm water-stable aggregates(85.31％)and mean weight diameter(2.67 mm)on the upper slope compared to that in the other slope positions of the dip slope.In addition,the dip slope had a higher percentage of aggregate destruction(35.57％)than the anti-dip slope(29.81％),and the soil erodibility factor value of the natural forest of the dip/anti-dip slope was significantly lower than that of the other land use types(P＜0.05).When the content of large macroaggregates was larger,the soil macroaggregate weight was greater.When the failure rate of the soil aggregates was lower,the stability of the soil structure was better.Overall,these results suggest that natural forests can significantly improve the stability of soil aggregates,thereby improving soil erosion resistance.Therefore,natural recovery measures should be implemented on dip/anti-dip slopes of karst trough valleys.
查看更多>>摘要：The changes in the mechanical properties of collapsing walls under the influence of natural factors in the hilly area of southern China need to be determined.We systematically studied the influence of the interaction of dry density ρ(1.0,1.1,1.2,1.3,1.4 g/cm3)and moisture content w(0.05,0.1,0.15,0.2,0.25 g/g)on the stability of four soil layers in a collapsing wall.The soil cohesion decreased with increasing soil depth.The cohesion force initially increased and then decreased with increasing ω and increased with increasing ρ;the internal friction angle was mainly affected by ω and decreased with increasing ω.The cohesion could be used to effectively characterize the stability of the collapsing wall.The shear strength index was modeled based on interaction between the dry density and moisture content(R2＞0.95).The optimal combination of moisture content and dry density was obtained,and the collapsing wall was in the most stable state at a moisture content of 0.12-0.19 g/g and a dry density of 1.40 g/cm3.Based on the analysis of the critical height and safety factor(FS),the FS values of the sandy layer(C)was 0.53 and 0.57 for ω values of 0.25 g/g and 0.05 g/g,respectively.In the alternating process of soil wetting and drying,the basic properties of the soil changed;caused traceback erosion,and thereby affected the stability of the collapsing wall.Our study provides a theoretical basis for the investigation of the factors influencing the stability of collapsing walls.
查看更多>>摘要：Saltwater intrusion along rivers is a complex process controlled by multiple factors and thus fluctuates with a highly nonlinear nature and time-varying characteristics.It is challenging to monitor saltwater intrusion.The objective of this study was to clarify the spatial-temporal variation of saltwater intrusion and its potential impact on agriculture in the Po River Delta(Italy).2006 was the most severe year of saltwater intrusion in the period we considered.2022 was even worse,but the data are still under processing.In this study,the Hilbert-Huang transform(HHT)and rescaled range(R/S)were used to identify the multi-time scales and change trends of the salinity and discharge in 2006.After that,the time-dependent intrinsic correlation(TDIC)was used to depict intrinsic relationships between salinity and discharge at different time scales.The results showed that discharge and salinity exhibited behav-iours of positive long-range correlation during different periods.The temporal series of salinity and discharge was decomposed into six intrinsic mode functions(IMF)and residuals based on the ensemble empirical mode decomposition(EEMD).The sum of variance contribution rates of IMF1(4 days),IMF2(10 days),and IMF3(12.1 days)of salinity was more than 75％.All measured TDICs have highlighted strong correlations between salinity and discharge.Furthermore,we used spatial interpolation tech-niques to map salinity data along rivers.This allowed the investigation of dynamic changes in saltwater intrusion patterns during periods of severe drought.Outcomes show a significant negative correlation between salinity and normalized difference vegetation index(NDVI),indicating that the study area's agricultural greening was affected by saltwater intrusion.
查看更多>>摘要：Soil salinization and water scarcity are main restrictive factors for irrigated agriculture development in arid regions.Knowing dynamics of soil water and salt content is an important antecedent in remediating salinized soils and optimizing irrigation management.Previous studies mostly used remote sensing technologies to individually monitor water or salt content dynamics in agricultural areas.Their ability to asses different levels of crop water and salt management has been less explored.Therefore,how to extract effective diagnostic features from remote sensing images derived spectral information is crucial for accurately estimating soil water and salt content.In this study,Linear spectral unmixing method(LSU)was used to obtain the contribution of soil water and salt to each band spectrum(abundance),and endmember spectra from Sentinel-2 images.Calculating spectral indices and selecting optimal spectal combination were individually based on soil water and salt endmember spectra.The estimation models were constructed using six machine learning algorithms:BP Neural Network(BPNN),Support Vector Regression(SVR),Partial Least Squares Regression(PLSR),Random Forest Regression(RFR),Gradient Boost Regression Tree(GBRT),and eXtreme Gradient Boosting tree(XGBoost).The results showed that the spectral indices calculated from endmember spectra were able to effectively characterize the response of crop spectral properties to soil water and salt,which circumvent spectral ambiguity induced by water-salt mixing.NDRE spectral index was a reliable indicator for estimating water and salt content,with determination coefficients(R2)being 0.55 and 0.57,respectively.Compared to other models,LSU-XGBoost model achieved the best performance.This model properly reflected the process of soil water-salt dynamics in farmland during crop growth period.This study provided new methods and ideas for soil water-salt estimation in dry irrigated agricultural areas,and provided decision support for gover-nance of salinized land and optimal management of irrigation.
Sana KhanRebecca BartleyAnne Kinsey-HendersonAaron Hawdon...
741-745页
查看更多>>摘要：Daley et al.(2023a)argue that at least 10-15 years apart Digital Elevation Model(DEM)derived DEMs of Difference(DoD)surveys are needed to detect reliable geomorphic change within the gullied landscapes of the Great Barrier Reef,Australia.We acknowledge that the reliability of observed geomorphic change increases as more subtle geomorphic processes are detected with longer monitoring periods.As further good quality long-term legacy datasets become available,we encourage utilising these to improve confidence in targeting erosion rehabilitation.However,our approach to consistently apply 2-3 year DoDs to contrasting gully morphologies enabled capture of more intense geomorphic processes acting over shorter timeframes and provided valuable and timely information on(i)contrasting erosional mechanisms and erosion rates between variable gully morphologies,and(ii)rehabilitation efforts un-dertaken.In this paper,we take the opportunity to concisely address all the concerns raised by Daley et al.(2023a).
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