Effects of Accelerated Soil Erosion on Soil Nutrient Loss After Deforestation on the Loess Plateau

Soil erosion and nutrient losses on newly-deforested lands in the Ziwuling Region on the Loess Plateau of China were monitored to quantitatively evaluate the effects of accelerated soil erosion, caused by deforestation, on organic matter, nitrogen and phosphorus losses. Eight natural runoff plots were established on the loessial hill slopes representing different erosion patterns of dominant erosion processes including sheet, rill and shallow gully (similar to ephemeral gully). Sediment samples were collected after each erosive rainfall event. Results showed that soil nutrients losses increased with an increase of erosion intensity. Linear relations between the losses of organic matter, total N, NH4-N, and available P and erosion intensity were found. Nutrient content per unit amount of eroded sediment decreased from the sheet to the shallow gully erosion zones, whereas total nutrient loss increased. Compared with topsoil, nutrients in eroded sediment were enriched, especially available P and NH4-N. The intensity of soil nutrient losses was also closely related to soil erosion intensity and pattern with the most severe soil erosion and nutrient loss occurring in the shallow gully channels on loessial hill slopes. These research findings will help to improve the understanding of the relation between accelerated erosion process after deforestation and soil quality degradation and to design better eco-environmental rehabilitation schemes for the Loess Plateau.

Remote-sensing data reveals the response of soil erosion intensity to land use change in Loess Plateau, China

Developing an effective approach to rapidly assess the effects of restoration projects on soil erosion intensity and theirextensive spatial and temporal dynamics is important for regional ecosystem management and the development of soilconservation strategies in the future. This study applied a model that was developed at the pixel scale using water soilerosion indicators （land use, vegetation coverage and slope） to assess the soil erosion intensity in the Loess Plateau,China. Landsat TM/ETM＋ images in 2000, 2005 and 2010 were used to produce land use maps based on the object-oriented classification method. The MODIS product MOD13Q1 was adopted to derive the vegetation coveragemaps. The slope gradient maps were calculated based on data from the digital elevation model. The area of watersoil-eroded land was classified into six grades by integrating slope gradients, land use and vegetation coverage. Resultsshow that the Grain-To-Green Project in the Loess Plateau worked based on the land use changes from 2000 to 2010and enhanced vegetation restoration and ecological conservation. These projects effectively prevented soil erosion.During this period, lands with moderate, severe, more severe and extremely severe soil erosion intensities significantlydecreased and changed into less severe levels, respectively. Lands with slight and light soil erosion intensities increased.However, the total soil-eroded area in the Loess Plateau was reduced. The contributions of the seven provincesto the total soil-eroded area in the Loess Plateau and the composition of the soil erosion intensity level in eachprovince are different. Lands with severe, more severe and extremely severe soil erosion intensities are mainly distributedin Qinghai, Ningxia, Gansu and Inner Mongolia. These areas, although relatively small, must be prioritised andpreferentially treated.

Cropland physical disturbance intensity： plot-scale measurement and its application for soil erosion reduction in mountainous areas

Various kinds of human disturbances on cropland are the main reasons for soil erosion and land degradation.Farming practices in mountainous areas vary greatly among cropland plots because of the heterogeneity of biophysical conditions and differences in farmers'management behavior.The main purpose of this paper is to develop a composite index of cropland physical disturbance intensity(CLDI)to reflect the plot-scale discrepancy of potential soil erosion in mountainous areas.The study was based on both plot survey and household interview data,collected from six typical catchments in mountainous areas of southwestern China.Four kinds of physical disturbance practices and two kinds of conservation practices during one crop rotation period were synthesized to develop the CLDI index.The rough set theory was referenced to avoid subjectivity during weight allocation.The results show that conventional tillage,deep fertilization,and manual weeding are the main causes of cropland soil erosion,whereas manure application in combination with seasonal fallow reduces soil erosion.Different crop types as well as cropland location factors determine the spatial pattern of CLDI.Crop rotation modes with major crops of tobacco and maize resulted in a maximal CLDI,and cropland plots with a distance radius of 150 meters away from households received the most intensive physical disturbance.These results are critical to help better protect rural environments in mountainous areas.Based on the results,methods to reduce cropland soil erosion are suggested.

Evaluation of soil erosion from chestnut forests: A case study in the Yanshan Mountains, China

Soil erosion from chestnut forests has many types and intensities. However, less attention has been paid to the increasing soil erosion in the chestnut forests of Yanshan Mountains region, North China. The objective of this study was to discuss forest ages(<5, 5~<10, 10~<20, and 20~ yr), slopes(5°~<15°, 15°~<25°, 25°~<35°, and 35°~), slope positions(upslope, midslope, downslope, and whole slope), and slope aspects(sunny, half-sunny, shade, and half-shade) effects on soil erosion types and intensities in chestnut forests. A field survey was applied to investigate in detail the contiguous chestnut forests near Changfu village of Hebei Province, China on October 9-30, 2016. Results showed that chestnut forests are dominated by moderate erosion in this region, and the soil erosionfrom chestnut forests tended to deteriorate gradually. The average land degradation index was 0.31. The erosion intensity from chestnut forests will gradually increase with the year of planting. Most of the slopes are greater than 15°, accounting for 86.7% of the total chestnut forests. Most of the chestnut forests occupy the whole slope, accounting for 47.5% of the total area. Moderate erosion occurs most commonly for different slope aspects. In conclusion, improving the preparation efficiency of chestnut forests and enhancing the construction standards of soil and water conservation measures would be useful measures to avoid soil erosion from chestnut forests reaching a more severe level.

Historical evolution of gully erosion and its response to land use change during 1968–2018 in the Mollisol region of Northeast China

Gully erosion is one of the most severe types of land degradation,hindering food production and sustainable agricultural development.However,the historical evolution process and the impact of land use change on gully erosion remain unclear.To address this issue,we conducted a field investigation on gully erosion in 2018 and interpreted land use and gullies using historical remote sensing images in 1968 and 1978 over an area of 84.48 km^(2).The study found that from 1968 to 1978 to 2018,all gully morphological parameters including gully length density and gully areal density increased significantly.The main origin of gully erosion found was from dry farmland.The annual soil loss rate induced by gully erosion was 1.46 mm during 1968–2018.Gully erosion rates were higher during 1968–1978 than during 1978–2018.Furthermore,the length,areal and volumetric erosion rates in gullies formed by multiple gullies merging was greater than that of newly formed gullies(NFG)and gullies developing continuously from a single pre-existing gully,while the widening rate of NFG was highest.The susceptibility of land use types to gully erosion was in the order of woodland<dry farmland<degraded land.The annual average increase in gully area was 871.09 m^(2) km^(-2) year^(-1) for parcels that were converted from woodland to dry farmland,which was 5.56 times and 1.78 times greater than that of woodland and dry farmland maintenance,respectively.Therefore,urgent implementation of ecological land use plans and gully erosion control practices is suggested for this region.

Aeolian Activities and Protective Effects of Artificial Plants in Re-vegetated Sandy Land of Qinghai Lake,China

Land desertification and aeolian activity are currently the greatest threats to alpine ecological environments and are also the primary challenges of desertification control and ecological restoration projects.Afforestation of sandy lands around the Qinghai Lake in China has effectively controlled the desertification of this watershed.However,certain issues remain which challenge its overall success,including lack of diverse biological species and poor theoretical understanding of aeolian processes,such as controlling wind-sand flow in relation to complex alpine ecological factors.Therefore,to help improving afforestation techniques,this research focused on Hippophae rhamnoides,Salix cheilophila,Pinus sylvestris,Populus simonii and Artemisia desertorum vegetation implanted in the mobile dunes on the eastern shore of Qinghai Lake.Aeolian transport characteristics and annual changes to community ecological factors from 2010–2016 were monitored in comparison with uncontrolled sand dunes.Based on simultaneous observations using gradient anemometers and sand samplers,it was found that the aeolian activities exhibited the following features:1)In re-vegetated lands,the logarithmic growth of wind speed was disrupted by the wind speed amplification in the middle and high layers and wind speed reduction in the low layers,while vegetation had significant wind-breaking(>37%)and sand-fixing(>85%)effects in 2016.2)Wind speeds in re-vegetated lands and mobile dunes showed a linear correlation,especially in lower layers of H.rhamnoides and S.cheilophila,while sand transport in re-vegetated land increased linearly or exponentially with increasing wind speed.3)The four artificial shrubs and forests had greater sand deposition with intensities of 280–860 t/(ha·yr),largely concentrated during winter and spring which accounted for 60%–85%of the annual cycle,while A.desertorum experienced significant root undercutting;and 4)Intensity of aeolian activity in re-vegetated lands,except for A.desertorum,was significantly negative with respect to plant growth structure,community cover,topsoil moisture,and regional precipitation.Overall,these five sand-binding species produced optimistic wind-sand protection effects for the alpine sandy lands,which relied on the plants’physical disturbance of wind-sand flow during the early stages of community development.In comparison,H.rhamnoides and S.cheilophila individually maintained stable wind-sand protection effects,while P.sylvestris and P.simonii were better in mixing with other shrubs and herbs to achieve a comprehensive ecological system for future control of aeolian activity.

Land Degradation Evaluation in North Hebei Province Based on Remote Sensing and GIS

Land degradation is one of the serious environmental problems that can lead to poverty, and is especially prominent in eco-fragile areas in developing countries and increases the risk of environmental safety. North Hebei Province belongs to an ecologically fragile region in North China, which has great impact on the eco-safety of Beijing and Tianjin. Using Landsat TM data and GIS, this paper evaluates land degradation in North Hebei province of China from the the 1960′s to 1987 and 2000. Land use/cover change pattern from 1987 to 2000, its regional difference and forest change characteristics will also be analyzed; soil erosion intensity and arable land suitability were also evaluated. Results revealed that land use/cover pattern in this study area did not change greatly from 1987 to 2000. The structure and function of regional land ecosystem was at a level of local improvement and integral deterioration. Land above medium soil erosion intensity reached 21 percent, which was also the area with a serious soil erosion and land degradation problem. Soil erosion and land degradation intensity of grassland was the biggest. For the present arable land, the proportion of high suitability was 13 percent.

Indication of paleoecological evidence on the evolution of alpine vegetation productivity and soil erosion in central China since the mid-Holocene

Although alpine ecosystems have been commonly recognized as sensitive to recent climate change,few studies have examined its impact on the long-term productivity of vegetation and soil erosion.Using paleoecological records,these two aspects were examined in the alpine zone of the Taibai Mountains(elevation,3767 m)in monsoon-dominated East Asia since the middle Holocene.Proxies for the productivity of vegetation and severity of soil erosion from high-resolution alpine lacustrine records show that the productivity and soil erosion were closely related to mean annual temperature and summer precipitation from the East Asian Summer Monsoon(EASM),respectively.Specifically,when the mean annual temperature was low and precipitation was abundant,during 5800–4000 calendar years before the present(cal.yr BP),the alpine ecosystem was characterized by low vegetation productivity and severe soil erosion.However,the productivity increased and soil erosion decreased from 4000 cal.yr BP onwards.These results highlight the role of paleoecological evidence in studying ecosystem services on longer time scales,which is significant in making policies for sustainable development under climate change in regions for which such long-term monitoring data are not available.

Prediction of recent bank retreat processes at typical sections in the Jingjiang Reach

The Jingjiang Reach is experiencing continuous channel degradation owing to operation of the Three Gorges Project （TGP） in 2003. Significant retreat processes at composite riverbanks have occurred at local sites of this reach, which may influence the stability of the fiver regime and the effect of existing river training works. Therefore, bank retreat plays a key role in fluvial processes of the Jingjiang Reach, and it is necessary to predict the long-term processes of bank retreat at typical sections in the reach. In this study, various factors influencing bank retreat in the Jingjiang Reach are investigated, based on bank erosion processes at four sections and the corresponding flow and sediment conditions. It is discovered that fluvial erosion intensity is a dominant factor in controlling the processes of bank retreat in the reach, although other factors, such as bank soil properties, can also influence bank retreat. The bankfull width at a section with severe bank erosion since 2002 is defined as being equal to the sum of the bankfull width in 2002 and the accumulated bank retreat distance after 2002. The magnitude of the bankfull width can be expressed as an exponential function of the previous 5-year average fluvial erosion intensity during flood seasons. The accumulated distances of bank retreat at four sections over the period 2002-2012 are predicted using the proposed empirical relationships, with the calculated bank retreat processes agreeing well with observed data.

Model Study of Basin Soil Loss (BSL) in the Loess Plateau of China (Ⅰ)

According to the influence of underlayer factor upon the basin erosion and in the support of Geographic Information System (GIS) of Loess Plateau(LPIS), the Gushanchuan Basin is divided into several regions with different erosion intensity. Correlating them to the BSL quantity, the complete soil loss model is established. By using this model, the soil loss quantity of the whole basin as well as each erosion intensity region can be estimated.