Nepal is a mountainous country sandwiched between China and India that extends along the Hind Kush Himalayan range. The entire country sits on a geological formation that has witnessed massive transformation in the past several decades. Land degradation is active in Nepal. This study reviews the causes of land degradation in Nepal based on publicly available reports, books, journal articles, and government policy and regulations. The review also uses publicly available global datasets to contextualize local conditions. The review shows that topography; land use and cover change driven by population growth and urbanization; traditional agricultural practice in steep slope; soil erodibility due to unscientific ways of farming; use of chemical fertilizers and, pest and disease control techniques; unsustainable land management by the government; unscientific infrastructure development has been the proximate causes of land degradation in the majority of the cases. While underlying causes include population and poverty; out migration; deforestation; land tenure and property rights, non-farm employment; and technological change. The situation when combined with the Landslide Susceptibility Index and Land Cover data shows that the country needs to make concerted effort to stop and minimize the damage of land degradation in the country.
Habitat structure is a key determinant of variation in biodiversity. The effects of increased vertical and horizontal vegetation structure can result in marked shifts in animal communities. This is particularly true for ants in response to woody thickening, with predicted negative impacts on ant diversity. We used pitfall traps to study the response of epigeic ants in two co-occurring dominant habitats (closed and open) of an African savanna biome experiencing extensive woody thickening. Although species richness was higher in open habitats, evenness was significantly lower. Thickening explained significant amounts of variation in ant composition, but site-specific characteristics and seasonality were more important. These site-specific characteristics were largely linked to Anoplolepis custodiens, a species that were locally abundant in open habitats with clayey soils, where they often accounted for more than 90% of all ant activity. As A. custodiens also responds positively to disturbance, indiscriminate bush clearing could lead to knock on effects associated with the numerical and behavioural dominance of this species.
Farmlands contamination with heavy metals (HMs) can be considered as a global issue especially in developing countries. The current study investigates the various pollution indices, potential ecological risk index (PERI) and human health risk caused by HMs in some selected regions of Punjab Province, Pakistan. Farmlands soil samples were collected, acid extracted and analyzed via ICP-MS (Agilent 7500c) for selected HMs. All the HMs were found within permissible limits set by worldwide regulatory authorities except Cd which exceeded its limit in 68% agricultural soils of the study area. The CF values for Cd showed high (CF≥6) degree of contamination to considerable contamination (3≤CF≤6). The CD values indicated low (CD≤6) contamination to moderate (6dermal>inhalation. Furthermore, the RI values were observed higher than 1.0×10–4 for Cd (Lahore and Faisalabad regions) and Cr (Multan and Faisalabad regions) in children working in farmlands and likely exposed to high cancer risk. So, minimization of pollutants must be the top priority of the state to reduce contaminants inputs and immobilization in soil through environmental protection laws and regulations
Afforestation is among the most effective means of preventing and controlling desertification. Silver poplar (Populus alba) is commonly planted tree species for afforestation of the Horqin Sandy Land of China. However, this species has exhibited some drawbacks such as top shoot dieback, premature senescence and mortality, and soil and ecosystems degradation. In contrast, Siberian elm (Ulmus pumila) rarely experiences these problems in the same regions. Ecological stoichiometry plays a vital role in exploring ecological processes and nutrient cycle relationships in plant–litter–soil systems. We measured C, N, and P concentrations in leaves, branches, roots, litter, and soils and analyzed N and P resorption efficiencies, and stoichiometric homeostasis in elm and poplar plantations in the Horqin Sandy Land. The results showed that soil C and N concentrations, C:P, and N:P were greater in the elm plantation than in the poplar plantation. The plant N concentrations, C:P, and N:P and litter N and P concentrations were greater, whereas N and P resorption efficiencies were lower, in the elm plantation than in the poplar plantation. Generally, elm exhibited greater homeostasis than poplar. These findings indicate that poplar exhibited more developed internal nutrient conservation and allocation strategies but poor nutrient accumulation in soil, which may contribute to degradation of poplar plantation. In contrast, elm tended to return more nutrients to the soil. Therefore, compared with poplar, elm may be a more suitable afforestation tree species for the Horqin Sandy Land, where it may promote the accumulation of soil nutrients and enhance ecosystem stability.
Planting trees is one of the most effective activities in recovering soil organic carbon (SOC) stocks of degraded areas, but we still lack information on how different tree species can influence soil respiration, one of the main sources of dioxide carbon (CO2) to the atmosphere. This study aimed to explore the influence of different forest species on the autotrophic and heterotrophic components of the total soil respiration in a bauxite mining area under reclamation. We analysed the soil CO2 efflux under five treatments: i) monoculture of clonal Eucalyptus; ii) monoculture of Anadenanthera peregrina (L.); iii) a mixed plantation of 16 native forest species (Nat); iv) a mined area without vegetation cover; and v) a natural forest cover. This design allowed exploring the soil CO2 dynamics in a gradient of recovery, from a degraded area to natural vegetation. Additionally, we measured soil temperature, moisture and soil characteristics. Soil CO2 efflux increased with increasing forest species cover in the rainy months. There was no significant change in CO2 efflux among the tree species. Heterotrophic soil respiration contributed to 64% of total soil CO2 efflux and was associated with litter decomposition. Amongst the abiotic variables, increases in soil moisture had the most influence on CO2 efflux. Therefore, these results help to understand the factors that underpin the loss of SOC and can orient management practices to improve soil organic matter and restore soil quality in degraded areas.
The restoration of surface mining is a key to meet the global ecosystem restoration target. With increased data accessibility and computing tool capabilities, it becomes possible to expand mine restoration monitoring from single mine sites to multiple mine sites on a large scale. This study constructed a new index, Mine Landscape Restoration Index (MLRI), by coupling Land Surface Temperature (LST) and Enhanced Vegetation Index (EVI) to simultaneously monitor the restoration of regional multiple mine sites. We analyze historical and future trends of restoration using Mann-Kendall test, Sen’ slope, and Hurst exponent for MLRI time series. The restoration effects of 46 surface coal mine sites located in the northwestern ecologically fragile region of China from 2000 to 2019 were assessed, based on 3675 Landsat images on Google Earth Engine. The results showed that MLRI was effective in identifying restoration areas and processes in surface mine sites, which was validated by high-resolution images and field investigation of mine samples. The restoration area overall percentage was significantly higher in mines started mining before 2000 than after 2000. According to the restoration effects, we clustered the 46 sites into high, medium, and low restoration area percentage clusters with 13, 11, and 22 mine sites, respectively. Individual clusters have aggregation characteristics within each mine region, but are distributed irregularly across the different six mine regions. This study provides a new approach to monitoring the restoration of surface coal mine sites and inform government managers in developing mine restoration programs and sustainable mining development plans.
The main objective of this study was to evaluate two restoration techniques, “stone rows” and “stone rows + tree planting” on soil organic carbon (SOC) sequestration and structure in terms of water stable aggregates as well as the time required to restore soil fertility. The Carbon, Aggregate and Structure Turnover (CAST) model was used to model the changes of SOC content and water stable aggregate formation under the two restoration techniques. Field experiments used for calibration of the model were conducted using a randomized block design. Soil samples were class fractionated followed by a micro-aggregate isolation procedure. The two restoration techniques contributed significantly to improving soil total carbon content. By running five year simulation of the “stone rows”, the estimated total carbon input was 27 Mg ha-1 of which 6.1 Mg ha-1 were sequestered in the soil and 20.7 Mg ha-1 were released as CO2. In “stone rows + planting”, the total SOC content after five years was estimated to be 22.96 Mg ha-1, which was broken down to 15.43 Mg ha-1 aggregated carbon and 26.60 Mg ha-1 CO2. Fifty-year simulations showed a SOC increase to 54.8 Mg ha-1 in “stone rows”, and to 86.0 Mg ha-1 in “stone rows + planting”. This means that natural grassland vegetation slowly improves soil carbon content and soil quality, but with trees behind stone rows, the result will be about 50% higher.
Soil salinization and sodification are types of degradation due to salt accumulation in the soil. They develop in all climatic zones but are prevalent in arid and semi-arid areas. Assessment of their true occurrence is challenging owing to inadequate consideration of their evolution, lack of harmonization steps, and omission of diagnostic soil properties in the assessment. This paper developed a new assessment protocol using combined application of time-series diagnostic soil indicators, remote sensing, and environmental variables related to the occurrence of soil salts. The protocol focuses on standardization of the soil indicators, digital soil mapping, and application of classification schemes to identify levels of salt accumulation in the soil. It was tested in Lesotho, Afghanistan, and Sudan using measured soil electrical conductivity, pH, and exchangeable sodium percent, and covariates such as relief, remote sensing indicators of soil salinity, climate, hydrogeology, and land cover between 2001 and 2018. It was able to identify different types of salt-affected soils and levels of salt accumulation with over 80% accuracy on holdout samples. It identified emerging subsoil (30-100 cm) salt problems in agricultural areas in Lesotho, advancing topsoil (0-30 cm) salinization and subsoil sodification in agricultural areas in Sudan, and salinization of saline topsoils in Afghanistan. It also established important environmental covariates which can be used in periodic monitoring of salt accumulation in the soil. We recommend its wide application in different temporal and spatial scales to improve its performance in identifying salt accumulation in agricultural areas
Passive restoration (without any intervention) has been proposed as an effective strategy for degraded cropland restoration. However, whether the vegetation in abandoned cropland can change towards the desired state and the time needed to reach a stable state are still uncertain. We investigated three abandoned croplands with different recovery times (5, 15 and 20 years) and one natural grassland in each of two different types of grassland (desert steppe and typical steppe) in the agro-pastoral ecotone of northern China to assess the restoration potential of abandoned cultivated grassland. Above- and below-ground productivity as well as species biodiversity increased gradually with increasing recovery time. After 20 years of restoration there was no significant difference between abandoned cropland and natural grassland in the typical grassland site, but above- and below-ground productivity and species biodiversity were still lower in abandoned cropland in the desert steppe site. At the beginning of restoration, the communities were dominated mainly by annual species, especially in the desert steppe. As recovery time increased, the biomass and richness of perennial grasses and forbs increased significantly and replaced annual species as the dominant species. In both desert steppe and typical grassland, species similarity between restored and natural grassland increased over time, suggesting that previously cultivated grassland recovered towards the desired state. Our results indicate that 20 years was long enough for the restoration of previously cultivated grassland in the typical steppe, but more time may be needed in the desert steppe.
This study aimed to research the effects of forest (Pinus elliottii, slash pine) and shrub (Vitex trifolia) plantation on the soil microbial community in sandification land by using the Illumina Miseq sequencing of 16S rRNA and ITS rRNA genes and combined with the soil properties analysis to explore the driving factors. Finally, the results showed that the dominant bacterial phylum was Chloroflexi, Actinobacteria, Proteobacteria, and Acidobacteria, the shrub and forest plantation significantly increasing the proportion of Acidobacteria, while decreasing the proportion of Proteobacteria. For the fungal community, forest plantation was significantly changing the community structure at the phylum level that shifted from Ascomycota to Basidiomycota, and the ectomycorrhizal fungi take the most abundant with genus Rhizopogon predominant. The soil bacterial Chao1 and Shannon indices were significantly increased after revegetation, while the soil fungal Shannon diversity in the forest land that significantly correlated with soil total organic carbon and C/N was lower than that in the sandy and shrub land (p<0.05). Besides, the bacterial and fungal communities were significantly affected by soil water content among all analyzed soil properties. Our results suggest that the revegetation significantly increasing the soil bacterial diversity that correlated with soil water content, total organic carbon, and available phosphorus, but there was no significant change in community structure. In contrast, slash pine plantation changes the fungal community structure and diversity dramatically, and such changes should be attention because the shift of fungi community structure and diversity may lead to the decline of Pinaceae plantation.
Hurricanes are extreme phenomena that affect the coasts of Mexico every year. The economic and biodiversity losses caused by these extreme events are extensive. However, little is known about the effects that these severe weather incidents have on Mexico’s forest conservation and protected areas. A hydrological characterization and regionalization of the storms caused by the rain fields generated by all the hurricanes that touched the Mexican coast from 1966 to 2017 were carried out. Adimensional Huff Curves are proposed to get precipitation hyetograms from which the erosion factor of a storm is obtained; using the Universal Soil Loss Method (USLE). The results made it possible to get the typical precipitation hyetograms in the forests and protected areas, before, during, and after the impact of a hurricane. The proposed hydrological regionalization made it possible to estimate the rainfall intensity in 30 minutes to characterize the start of rain erosion. The method proposed in this research was applied in the 177 Natural Protected Areas (25628239 ha), as well as in the 370 voluntarily designated areas for Conservation (399643 ha), in Mexico. It is concluded that, with the regionalization and the proposed equations, it is possible to get typical hurricane precipitation hyetograms, which would allow us to detail the forest management plans in forests, ecological reserves, and protected areas of Mexico.
We investigated the soil physicochemical property and arbuscular mycorrhizal fungi (AMF) resilience to degradation and deforestation of the Chilimo dry evergreen Afromontane forest. Topsoil (1-10cm) physicochemical property was determined across four land uses, viz. natural forest (NF), shrubland (ShL), cropland (CrL), and grazing land (GrL). AMF spore abundance (SA) and AMF infectivity of these land uses were also determined. One-way ANOVA results indicated that most soil physicochemical variables were significantly affected by land-use change. According to the nonmetric multidiamentiaonal scaling ordination result, soil physicochemical property was found to be resilient to degradation (NF-ShL conversation) but not deforestation (NF-CrL or NF-GrL conversions) of Chilimo forest. Whereas SA was found to be resilient to both the degradation and deforestation, infectivity was resilient only to NF-CrL conversion. Although our results did not show a similar pattern in soil property, SA and AMF infectivity resilience due to Chilimo forest degradation and deforestation, both the soil physicochemical property and AMF infectivity were found to be not resilient to NF conversion to GrL. Hence, based on our results, it can be concluded that AMF inoculation could be more beneficial to NF restoration if the planting sites are in GrL. However, in the future, the AMF community composition of these four land uses should be determined morphologically and molecularly from field soil and trap culture so that AMF resilience to DAF deforestation and degradation is better understood.
Soil salinisation is vital factor limited crop yield in dryland oasis cropland. A film-mulched drip irrigation and subsurface pipe drainage (MDI-SPD) system has been proved its high efficiency all over the world. However, soil salt balance and simulation in time and spatial dimension are unclear in this system. Based on four-year observation data, we use HYDRUS-2D model to simulate the soil salt balance in a MDI-SPD system in western China. We conducted a set of MDI-SPD experiments three times in a ﬁeld in Manas River Basin, western China: The laying depth of the subsurface pipe was 1 m, and drain spacing was 15 m. Three treatments were set at 0, 5, and 7.5 m horizontal from the subsurface pipe. Results after four years indicated that the total salt output in the irrigated area was 260.16 t, with 103.4 t salt drained by the subsurface pipe (39.74% of the total salt output in the irrigation area). Soil salt balance indicated desalination state. Soil EC response ranged from 8.33 to 11.21 dS m-1. The mineralization of subsurface pipe drainage was positively correlated with drainage flow and salt discharge, and negatively correlated with drainage discharges and time (P<0.05). If salinity leaching stops, 0−200 cm depth soil salt balance will achieve critical value in 8 years. Thus, we recommend salinity leaching once every three years. An increase in shaft drainage would also reduce the deep seepage of salt.
Fertilizer application in excess of plant nitrogen requirements, leading to nitrogen use inefficiency has become main culprit of nitrogen surplus, posing nonpoint pollution threats. Chao Lake has been recipient of nitrogen loadings, mainly coming from the agroecosystem surrounding it. This study was conducted in Chao Lake watershed to assess nitrogen use efficiency, crop yield and nitrogen loading, using reduced and conventional fertilizer rates, based on ten years field monitoring and experiment. Paddy rice - wheat rotational tillage arranged in a completely randomized design using 30m2 treatment plots was employed to study hypothesis. Three indicators namely agronomic efficiency (kgkg-1), recovery efficiency (%) and partial factor productivity (kgkg-1) were considered for nitrogen use efficiency. For nitrogen loading, nitrogen loading (kg ha-1yr-1), nitrogen runoff loss ratio (%) and net nitrogen runoff loss ratio (%) were taken. Results revealed, empirical formula of an exponential model explains the relationship. Reduced fertilizer levels produced high nitrogen use efficiency, high economic yield and less nitrogen loading. Nitrogen use efficiency was in order of: reduced > high > conventional fertilization treatments, while it decreased in ten years (2008 -2018) across all treatments. Nitrogen loading increased in ten years, both for rice and wheat growing seasons. Runoff volume influenced nitrogen loading more than other environmental factors considered. Such strategies that further reduce fertilizer levels by accounting for excessive supplies are critically important to consolidate effective nitrogen management measures.
Characteristics of refused materials are prerequisite information required to determine the strategic reclamation of extreme land degradation in post-tin mining areas. The objective of the study was to evaluate mineralogical, chemical, and physical properties and heavy metals of spoil and tailing as the basis for reclamation measures. Seven representative soil profiles were made and sampled to a depth of 130 cm for various soil analyses. Results showed that tin mining has drastically altered the soil texture from sandy clay loam under native conditions to loamy sand and sand under post-tin mining. Mineralogical constituents of refused materials were mainly mineral resistant to chemical weathering, consisting of predominant quartz with small amounts of tourmaline, opaque, zircon and garnet. Total X-ray fluoresce elemental analysis showed extreme high SiO2 content (92-96%) associated mainly with quartz mineral, and extremely low oxides of Ca, Mg, P, K and S (< 0.2% altogether). This suggests all nutrients are severe problems for crops. Type of total heavy metals showed the Cr2O3 was high in sandy tailing (204 - 286 mg kg-1), while the SnO was low (0 -153 mg kg-1) and they were preserved in the structure of host minerals, thereby the health risk is negligible. Based on many serious constraints of soils, the strategic reclamation to recover soil productivity and ecological function was the building up soil organic matter, establishing “pot planting point” technique, complete fertilizer application, and selection of crops with an ability to fix N nutrient from the atmosphere, and adaptive to low soil nutrients.
Natural fallow practice has been identified as an effective way to overcome obstacles of continuous cropping. However, how the resulting soil microbial changes impact plant fitness, and how the context-specific differences diverge from those caused by continuous cropping remain largely unknown. This study used the third-year continuous tobacco cropping soil (CCS) and natural fallow soil (FS) to cultivate Nicotiana tabacum. The influences of soil microorganisms on the fitness of N. tabacum were assessed by reassembling soil microbial communities. Then, the bacterial and fungal community assembly of the bulk soil and the rhizosphere were characterized using amplicon sequencing and statistical analysis. The results indicated that soil microorganisms play more important roles for plant fitness for N. tabacum grown in FS compared with CCS. Moreover, the abiotic context of FS exerts stronger effects compared with those of CCS for the reassembly of soil microbiomes. Comparative analysis identified the context-specific microbial clades and the differential strength of rhizosphere effects. In conclusion, this paper provides context-specific microbial evidence, which may unravel the potential mechanism underlying the different response of N. tabacum to changes of soil microbiomes induced by natural fallow and continuous cropping practices.
Anthropogenic impacts from the construction and operation of high-voltage transmission lines on a land in a right-of-way (ROW) result in soil cover disturbances varying in scale, age and origin. This affects soil diversity. We found that the distribution of disturbed soil areas follows a power distribution. The following main types of anthropogenic soils were identified within the ROW: filled soil, slightly disturbed resectozem, moderately disturbed resectozem 2 and abrazem. The areas of disturbed soils are superimposed on the natural heterogeneity of the remaining forest soils. We found that soil diversity within a ROW consists of 2.2% filled soils, 3.9% resectozem 1, 11% resectozem 2 and 10.4% abrazems. The total area of anthropogenically changed soils is 27.5% of the entire study area. Soil degradation causes resectozem 2 and abrazem. An increase in a surface slope angle till 2°–4о results in the growth of moderately degraded areas, whereas, an increase of more than 10о leads to highly degraded areas. The degree of soil cover degradation in the ROW is 3 out of 5. Comparison of disturbed areas based on the types of anthropogenic soils revealing significant differences between resectozems 2 and abrazems. The form factor of disturbances occurring during construction has a modal value of 0.8–0.9, whereas, that during operation is 0.7–0.8. Currently, the soil cover contains accumulated traces of degradation. Thus, the cumulative potential for soil degradation accumulated over the past 60 years of intensive economic development must be considered.
Blending FGD gypsum with surface sodic soil is a universally recognized method for the rapid amelioration of sodic soils; however, there are few reports on whether other application methods (band application) will reclaim sodic soil. Three FGD gypsum application methods, single-band application, dual-band application and blending, were carried out using sodic soil in soil bins to investigate the effects of application method on the wetting front, major cation concentrations and ESP during the process of water infiltration and in the soil profile after infiltration. The results showed that the wetting fronts in the band treatments were denser in the horizontal direction than in the vertical direction, but the blend treatment only had vertical migration. There was an exponential relationship between time and depth of penetration. The orders of desalting capacity were blend treatment, dual-band treatment and single-band treatment for the same volume of outlet water. Na+ was the primary ion in the leachate. The main channel in the band treatments was concentrated below the application site of FGD gypsum. The dual-band treatment significantly decreased the soil ESP of the whole soil bin, while the single-band treatment only effectively reclaimed half of the soil. In the blend treatment, the ESP was 21.32% and 34.66% at depths of 30–35 cm and 35–40 cm and was close to zero at a depth of 0–30 cm. Compared with blend treatment, band treatments have the advantage of long-term amelioration of local sodic soil, and the performance is mainly affected by the Ca2+ pathway.