Use of landslide-dammed lake deposits and pollen tracing techniques to investigate the erosional response of a small drainage basin in the Loess Plateau,China, to land use change during the late 16th century

A major landslide that occurred in 1569 in the Huangtuwa gully catchment within the Rolling Loess Plateau region of China, resulted in the creation of a landslide-dammed lake at the outlet of the small 0.1 km² tributary valley of the Houxiaotan Gully. All the sediment transported to the outlet of this catchment was deposited in the lake. After about 30 years the dam failed and the lake deposits were dissected as the stream cut down to its former base level. Substantial remnants of the sediment deposits that accumulated over the ca. 30 year period are, however, preserved as terraces near the outlet of the catchment and a vertical section through these sediment deposits was investigated using stratigraphic and pollen tracing techniques. Individual flood couplets could be clearly distinguished and these permitted the establishment of a chronology for the sediment deposits and the estimation of the sediment yields associated with individual events and individual years. Pollen analysis undertaken on samples collected from the individual flood couplets also provided information on the variation of the pollen content of the sediment and the proportion of Artemisia pollen during the period represented by the deposits. Interpretation of the information assembled from the sediment section has made it possible to reconstruct the erosional history of the Houxiaotan catchment during the 31 year period following the landslide. The average sediment yield of the catchment in the late 16th century was very similar to its present-day sediment yield. The sediment yield from the catchment and the relative contribution of the inter-gully areas, as compared to the gully system, declined immediately after the landslide as a result of abandonment of the cultivated land within the catchment. The restoration of cultivation in the catchment after about 17 years resulted in an increase in sediment yield from ca. 9000 t km^− 2 yr^− 1 to ca. 30,000 t km^− 2 yr^− 1 and a substantial increase in the proportion of sediment contributed by the cultivated inter-gully areas. Scope exists to apply a similar approach to the sediment deposits that accumulated in other former landslide-dammed lakes within the Rolling Loess Plateau region of China, in order to develop an improved understanding of the erosion history of the region.     

Landslide occurrence as a response to land use change: a review of evidence from New Zealand

Vegetation cover is an important factor influencing the occurrence and movement of rainfall-triggered landslides, and changes to vegetation cover often result in modified landslide behaviour. However, it is difficult to relate the occurrence of landslides directly to variations in land use, especially in some European countries. In contrast, New Zealand provides a good opportunity to investigate geomorphic responses to anthropogenic land cover changes. Before European settlers first arrived in the 1840s, hilly regions were only marginally influenced by human activity. The Maoris, New Zealand's first settlers, lived largely on coastal plains or near lakes and rivers. They influenced general vegetation cover only through localized burning practices. In contrast, European settlers moved into the back country and converted extensive hill areas from native forest and bush to pasture. This reduced the strength of the regolith and rendered the slopes more susceptible to landslides. Pulses of natural sedimentation in the pre-European period have been related to volcanic activity, climatic variability, including changes in frequency of cyclonic storms and wind erosion and fluvial erosion following forest fires initiated either by volcanic eruptions or lightning strikes. Since European deforestation began, sediment production has largely been determined by landslide events. On unstable slopes, thousands of landslides were triggered by high-magnitude/low-frequency climatic events during storms with estimated return periods in excess of 50 years. In contrast, low-magnitude/high-frequency rainfall events have caused gully and channel erosion. Examples from different parts of New Zealand indicate changes in sediment-generating processes following land use modifications. After deforestation, landslides have contributed significantly to sediment sequences in depositional basins such as lakes, swamps, estuaries, coastal wetlands and the nearshore and offshore zones of continental platforms.     

Impact of land use and land cover change on environmental degradation in lake Qinghai watershed,northeast Qinghai‐Tibet Plateau

Lake Qinghai, the largest saline lake in China, covers 4234 km² (2007) with a catchment area of 29 660 km² on the northeastern margin of the Qinghai‐Tibet Plateau. The ecosystem of the lake is extremely vulnerable and sensitive to global climate change and human interference. However, little information is available on land use/cover change (LUCC) in Lake Qinghai watershed. Using a geographical information system (GIS) and remote sensing (RS), this study analysed land use and land cover change pattern in Lake Qinghai watershed between 1977 and 2004 and discussed major environmental issues in this area. LUCC analysis indicated that grassland (63 per cent) and water body (18 per cent) dominated in the watershed and the magnitude of the land use and land cover change was generally low; the percentage of the change of various land types relative to the total area was less than 1 per cent. From 1977 to 2004, cropland, sandy land, bare rock, salinized land, swampland and built‐up areas increased by 0·43, 0·35, 0·24, 0·06, 0·03 and 0·03 per cent of the total area, respectively; in contrast, water body, grassland and woodland decreased by 0·99, 0·22 and 0·05 per cent, respectively. Moreover, the area of LUCC tended to expand from places around the lake to the upper reaches of the watershed during the last three decades. The LUCC transition pattern was: woodland converted to grassland, grassland converted to cropland and water body converted to sandy land. Lake level decline and grassland degradation are major ecological and environmental problems in Lake Qinghai watershed. The level and area of the lake decreased at the rate of 6·7 cm a⁻¹ and 6·4 km² a⁻¹, respectively, between 1959 and 2007, resulting in sandy land expansion and water quality deterioration. Lake level decline and area shrinkage was mainly attributed to climate change, but grassland degradation was mainly resulted from anthropogenic activities (increasing population, overgrazing and policy). Copyright © 2008 John Wiley & Sons, Ltd.     

黄土高原沟壑区典型小流域土地利用变化对产水量的影响——以陕西省长武王东沟流域为例

对黄土高原沟壑区长武王东沟流域土地利用变化对产水量的研究结果表明，王东沟流域土地利用变化主要特点是农田、草地面积所占比重减少，而林果面积迅速增加。同样降雨类型1996年和2010年流域下垫面的产水量分别比1986年少产水5747m^3及5914m^3。产水量的减少使该流域汇入河流的水量减少，土壤蓄水量增加，有利于流域生态环境的持续发展。     

Temporal change in land use and its relationship to slope degree and soil type in a small catchment on the Loess Plateau of China

We sought to detect the temporal change (1958–1999) in land use patterns and its relationship to physical landscape parameters in a small catchment in the semi-arid hilly area of the Chinese Loess Plateau. Degree of slope and soil type were selected as stable discriminating parameters that might constrain land use. With the help of GIS and canonical correspondence analysis, the relationship between rural land use distribution or transformation and the selected physical parameters was examined. The land use had undergone a general shift from farmland to woodland or grassland. Canonical correspondence analyses (CCA) indicated that a relationship between land use and the selected physical parameters was evident, farmland coincided with favorable conditions of fertile soil and gentle slope, while grassland and woodland were associated with conditions of poorer soil and steep slope. In the more favorable conditions the main land use change process was the intensification of farming, while in the less favourable conditions it was the abandonment of farmland. A thorough understanding of the relationship between land use temporal or spatial patterns and landscape physical parameters in the Loess Plateau of China, like degree of slope and soil type, will enhance our capability to predict landscape dynamics and lead to more sound and effective land use management strategies.     

Soil organic carbon distribution in relation to land use and its storage in a small watershed of the Loess Plateau, China

Soil organic carbon (SOC) is an important component in agricultural soil, and its stock is a major part of global carbon stocks. Estimating the SOC distribution and storage is important for improving soil quality and SOC sequestration. This study evaluated the SOC distribution different land uses and estimated the SOC storage by classifying the study area by land use in a small watershed on the Loess Plateau. The results showed that the SOC content and density were affected by land use. The SOC content for shrubland and natural grassland was significantly higher than for other land uses, and cropland had the lowest SOC content. The effect of land use on the SOC content was more significant in the 0-10 cm soil layer than in other soil layers. For every type of land use, the SOC content decreased with soil depth. The highest SOC density (0-60 cm) in the study area was found in shrublandII (Hippophae rhamnoides), and the other land uses decreased in the SOC density as follows: natural grassland > shrublandI (Caragana korshinskii) > abandoned cropland > orchard > level ground cropland > terrace cropland > artificial grassland. Shrubland and natural grassland were the most efficient types for SOC sequestration, followed by abandoned cropland. The SOC stock (0-60 cm) in this study was 23,584.77 t with a mean SOC density of 4.64 (0-60 cm).     

鄂尔多斯高原泊江海子流域土地利用动态变化及驱动因素分析

土地作为陆地生态系统的载体,其利用方式的变化直接影响着陆地生态系统服务功能的种类和强度。泊江海子流域位于鄂尔多斯高原干旱半干旱区,生态系统脆弱,流域生态系统服务功能在近十几年严重退化。本文基于Landsat影像数据提取了研究区1990—2015年间的6期土地利用数据,分析研究区土地利用时空变化特征及其驱动因素。结果显示:研究期内主要的土地利用类型为草地、耕地和未利用地,土地利用总体变化显著。空间变化上呈东西部及中北部耕地增加、南部未利用地减少的主要趋势。各土地利用类型面积变化及转换特征不一。草地整体处于动态转换平衡状态,约占流域总面积的70%。耕地和未利用地分别呈增加和减少的趋势,变化面积分别占流域总面积的6.05%和7.62%,其各自的主要来源或去向均为草地。水域面积减少了总面积的1.45%,主要转出去向为滩地。1995—2000年是土地利用转换最为频繁的时段,2005—2010年间土地利用变化呈动态不平衡状态的表现最为突出。研究期内流域土地利用变化受降雨减少、气温升高等气候变化和生态恢复工程建设、水利工程建设等人类活动的综合驱动影响。合理规划土地利用,限制种植高耗水树种及作物,减少河流上游汇水区耕地等,是保障研究区生态系统可持续健康发展的重要措施。