Low Coverage Grassland Research Articles

Characteristics Analysis and Prediction of Land Use Evolution in the Source Region of the Yangtze River and Yellow River Based on Improved FLUS Model

Climate change profoundly alters land use in alpine regions, and delving into the evolutionary characteristics of these changes is crucial for the sustainable development of regional land resources and the gradual enhancement of the ecological environment. Taking the source region of the Yangtze and Yellow River (SRYAYE) as a case study, we integrate permafrost and snowfall data into the Future Land Use Simulation model (FLUS). Analyzing historical land use, we predict and simulate the land use scenarios for 2030, 2035, and 2060 under SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 climates, and conduct a detailed analysis of the scale, composition, and pattern of land use in this area. Scale. The results showed that ① the Kappa coefficient of the improved FLUS model was higher than 0.927, and that the overall accuracy of the simulation was increased by 2.64%; ② the area of forest land and the high-coverage grassland will increase in the future and the center of gravity will migrate to the west, and that the area of moderate and low-coverage grassland will slightly decrease but tend to become green to the west; and ③ the fragmentation degree of the SRYAYE is decreasing, and the influence of human activities on the landscape pattern is weaker than in the past.

Study of the effects of land use change on water yield in the Qilian Mountains in western China

The Qilian Mountains serve as significant ecological security barriers in the western region of China. Their continuous and stable water supply is essential for the sustainability of the human oasis in the Hexi Corridor, as well as for the maintenance of the desert ecosystem in the north. In the past three decades, land use in this area has changed significantly because of human activities, which has had a profound impact on water yield services. Based on the Water Yield module of the InVEST model, we evaluated the area and water yield of land use during 1990–––2020, and discussed the characteristics of water yield response to changes in land use. As a result of the study, it was found that in the Qilian Mountains during the period 1990–––2020: (1) the areas of swamp, unused land, medium coverage grassland, and woodland reduced, while the areas of high coverage grassland, low coverage grassland, cultivated land, construction land, glaciers, and water area increased, and each land use type exhibited a different degree of transformation. (2) In terms of total water yield, this declined by 1.09 × 108 m3, water yield of medium coverage grasslands, unused land, and swamp decreased, while water yield of other land uses increased, however, the responses to the change in water yield as a result of the change in land use were significant. (3) The areas with decreased water yield fall mainly within the high-altitude areas of the Qinghai Lake and Qaidam river watersheds, while the low-altitude areas were characterized by an increase in water yield. This study may provide decision-makers with guidance for protecting the ecosystem of the Qilian Mountains and developing a national park in the Qilian Mountains.

Change characteristics and influencing factors of grassland degradation in adjacent areas of the Qinghai-Tibet Plateau and suggestions for grassland restoration.

Natural grasslands are being progressively degraded around the world due to climate change and socioeconomic factors. Most of the drivers, processes, and consequences of grassland degradation are studied separately, and it is not yet clear whether the change characteristics and influence factors of adjacent areas of grassland are identical. We analyzed changes in grassland area and quality, and the influences of climate changes and socioeconomic factors from 1980-2018 in Maqu County, Xiahe County and Luqu County on the eastern Qinghai-Tibet Plateau (QTP). We found that areas with high and medium coverage grassland in Maqu County and Luqu County decreased continuously with time, while low coverage grassland areas increased in three counties. In Xiahe County, the medium coverage grassland area reduced with time (except for 2010), while the high and low coverage grassland areas increased. The actual net primary productivity of the three counties showed a downward trend. In Maqu County, the total grassland area had an extremely significant positive correlation with number of livestock going to market, commodity rate, gross domestic product (GDP), primary industry, tertiary industry, household density, and levels of junior middle school education and university education in the area. In Luqu County, the total grassland area high coverage grassland area were significantly negatively correlated with total number of livestock, secondary industry, levels of primary school education, and temperature. Ecological education was positively correlated with high coverage grassland, and negatively correlated with low coverage grassland in all three areas. The results of this study suggest that the best ways to restore the area and quality of grasslands in these areas would be to reduce the local cultivated land area and slow down the development of the primary and tertiary industries in Maqu County, and to control industry development and the total number of livestock in Luqu County. This study also suggests that improving education level and strengthening the level of ecological education are conducive to the restoration of grasslands.

Spatial–Temporal Changes and Prediction of Carbon Storage in the Tibetan Plateau Based on PLUS-InVEST Model

The changes in the recent and future spatial–temporal patterns of carbon storage of the Tibetan Plateau and its dominant factors in different periods were unclear, and were conducive to optimizing the spatial layout of land. Exploring the spatial and temporal changes in terrestrial ecosystem carbon storage and their influencing factors during a long study period had important theoretical and practical significance for achieving the goal of carbon neutrality. In this study, the Integrated Valuation of Ecosystem Services and Trade-offs model (InVEST) was used to analyze the changes in carbon storage based on vegetation-type data during 2000–2020. The Path-generating Land-Use Simulation model (PLUS) was then used to predict the spatial distribution of carbon storage in the Tibetan Plateau in 2030 and 2060 under inertial development, farmland protection and ecology priority scenarios. The results showed that: (1) The degradation of vegetation types reduced the carbon storage during the study period. During 2000–2020, the desert shrub and non-vegetation area expanded by 63.21% and 13.35%, respectively, while the deciduous scrub, mixed forest and low coverage grassland decreased accordingly. The carbon storage of the Tibetan Plateau showed a decreasing trend by 0.37 × 106 t. (2) The spatial distribution patterns of carbon storage were consistent with that of the vegetation types. (3) In 2030 and 2060, under the constraint of the ecological priority development, the reduction in carbon storage was the smallest, at 0.01 × 106 t and 0.16 × 106 t, respectively. Under the constraint of the inertial development, carbon storage had the largest reduction, at 0.12 × 106 t and 0.43 × 106 t, respectively. (4) During 2000–2020, the dominant single factor that had the greatest impacts on the changes in carbon storage was FVC (vegetation coverage), with q values of 0.616, 0.619 and 0.567, respectively. The interactive dominant effects were mainly nonlinear enhancement and double-factor enhancement. The interactive dominant factors that had the greatest impact were FVC and the DEM (Digital Elevation Model), with q values of 0.94, 0.92 and 0.90, respectively. Therefore, ecological land with a high FVC should be protected and the expansion of non-vegetation areas should be restricted in future planning to improve the carbon storage level of the Tibetan Plateau and achieve the goal of carbon neutrality.

Spatiotemporal pattern and influencing mechanism of the flood-regulating ecosystem service capacity and demand in China’s Yellow River basin, 2000–2020

Study regionThe Yellow River basin (YRB), China. Study focusTo alleviate flood risks and safeguard human well-being, understanding the spatiotemporal pattern of and factors influencing flood-regulating ecosystem service capacity and demand relationship is crucial. This study quantifies the capacity-demand ratio and identifies the regions where capacity did not meet demand from 2000 to 2020. The spatial Durbin models (SDM) were employed to detect the spillovers and assess the direct and indirect effects of factors influencing the capacity-demand relationship in the YRB and across different reaches. New hydrological insights for the regionThe results show that regions with unmet demand has increased since 2000 due to a dramatic increase in demand and a reduction in capacity in the YRB. The SDM results reveal that wetlands and forests had positive direct effects, and cropland and built-up land had adverse effects on the capacity-demand ratios. Heterogeneity tests show that wetland, forest and low-coverage grassland were the biggest contributors to the capacity-demand ratios across upper-, mid- and downstream areas, respectively. Forest in the upper reach had positive direct effects and spillovers on the capacity-demand ratio. Cropland and low-coverage grassland negatively affected the capacity-demand ratio in the middle reach. The capacity-demand relationship in the lower reach needs to be improved by restoring ecologically functional land and enhancing the capacity of artificial hydro facilities.

Evaluation method of ecological water demand threshold of natural vegetation in arid-region inland river basin based on satellite data

The ecological water demand (EWD) of natural vegetation is a key issue in regional water resource allocation and ecosystem management. Although the evaluation of the EWD of vegetation has been emphasized in numerous studies, research on the threshold EWD of vegetation, including the minimum and optimum EWD, as well as an effective quantitative analysis framework, are still lacking. Therefore, in this study, the evapotranspiration of natural vegetation in the plain area of the Tarim River Basin over the last22 years was estimated based on remote sensing image data. Additionally, the multi-year dynamics of the EWD of natural vegetation were analyzed. In this study, the concept of “latitude” was adopted from studies of ecosystem resilience, to propose a novel analytical framework to measure the minimum and optimal EWD of natural vegetation in inland arid areas. The results show that the average minimum and optimum EWD of natural vegetation is105.45 and 135.53 mm, respectively. The average minimum EWD of woodland and high- and low-coverage grassland is 129.13, 284.38, and 111.40 mm, respectively, and the mean value of the optimum EWD is 152.96, 382.05, and 141.16 mm, respectively. The novel approach of this study is simple and easy to use, and provides an effective method for quantitative evaluation of the EWD threshold of natural vegetation.

Spatial and Temporal Evolution of Vegetation Water Consumption in Arid and Semi-Arid Areas against the Background of Returning Farmland to Forestland

Sustainable development in arid and semi-arid areas is largely constrained by water resources. Expanding ecological space is considered an effective way to conserve water resources. The innovation of this study is the analysis of water consumption in different land-use types from a complete watershed scale, which can evaluate space management against the background of returning farmland to forestland during the past 20 years, and provide suggestions for future space management in semi-arid areas. Based on meteorological data and GIS technology, the current study quantitatively analyzes the spatial and temporal variation characteristics of the water consumption of different vegetation growth stages in the Yanhe River Basin by using the improved Penman formula. The results show that the water consumption of vegetation in the Yanhe River Basin increased from 0.44 km³ in 2000 to 0.68 km³ in 2020. The water consumption of vegetation showed obvious spatial heterogeneity, with the highest value in the central Baota area (1.094 km³) followed by the western Ansai region (0.727 km³), whereas the consumption in the eastern Yanchang area is relatively low (0.483 km³). In addition, the annual average water consumption is (0.381 km³). The cultivated land consumes the most water (0.21 km3), while the woodland consumes the least (0.072 km³). The water consumption per unit area of forested land is the highest, reaching 190 m, and the water consumption of low-coverage grassland is the lowest, only reaching 50 m. Vegetation distribution change could be the main influencing factor of vegetation water consumption change in the Yanhe River Basin. Through the establishment of the sustainable development path of ecological space with water as the core, the high-quality development of ecological environments in arid and semi-arid areas will be achieved.

Temporal and Spatial Variation Characteristics of Carbon Storage in the Source Region of the Yellow River Based on InVEST and GeoSoS-FLUS Models and Its Response to Different Future Scenarios

Regional land use change is the main cause of carbon storage changes in ecosystems. Predicting the impact of future land use changes on carbon storage is of great significance for the sustainable development of carbon storage functions. In recent years, under the combined action of natural and human factors, the land use in the source region of the Yellow River has changed significantly, and its carbon storage function has also changed accordingly. This study combined InVEST and GeoSoS-FLUS models to evaluate land use change and its impact on carbon storage in the source region of the Yellow River from 2000 to 2020 and from 2020 to 2040 under different scenarios. The results showed that:① from 2000 to 2020, the carbon storage in the source region of the Yellow River showed an overall upward trend, with a total increase of 11.59×106 t. ② Over the past 20 years, the land use changes in the source region of the Yellow River included mainly the increase in the area of low-coverage grassland, construction land, and wetland and the decrease in the area of high-coverage grassland, medium-coverage grassland, and unused land, as well as the large-scale reduction of unused land and the reduction of grassland. The increase in the area of wetlands was the main reason for the increase in carbon storage. ③ Under the natural change scenario in 2040, the ecosystem carbon storage in the source region of the Yellow River was 871.34×106 t, an increase of 3.92×106 t compared with that in 2020. Under the ecological protection scenario, carbon storage increased significantly, with an increase of 13.53×106 t compared with that in 2020. The results of this study can provide a scientific reference for the decision-making of land use management and the sustainable development of carbon storage function in the source region of the Yellow River.

Accounting for land use in an analysis of the spatial and temporal characteristics of ecosystem services supply and demand in a desert steppe of Inner Mongolia, China

Assessing the relationships between ecosystem services supply and demand is crucial to support sustainable planning and human well-being. In the present study, we analyzed the ecosystem services supply and demand, synergies and trade-offs among services, as well as the spatial relationships between supply and demand, for four services in a desert steppe of Inner Mongolia. In terms of the balance between supply and demand, the grass production and carbon stock supply exceeded the demand, whereas the demand of water yield and windbreak and sand fixation services surpassed the supply. The degree of demand in windbreak and sand fixation service was met increased from 14.7% in 2000 to 20.6% in 2017, versus a decrease from 18.0% to 8.2% in water yield. The spatial distributions of the water yield and carbon stock demand were similar, and there was a significant synergy between them. The grass production supply and demand were not spatially matched, with higher supply in the eastern part of the study area and higher demand in the western part. Areas with high demand for the windbreak and sand fixation service also had a high supply. The water supply and demand in the low-coverage grassland were relatively balanced, and the deficiency of carbon stock supply was mainly found in construction land. In summary, for the sustainable development of animal husbandry and to reduce wind erosion, each county should establish an appropriate livestock density standard based on local constraints. Furthermore, it is also crucial for policymakers to develop water-saving industries to improve water utilization efficiency, and to set targets for CO2 emissions to reduce the impact on climate change.

Grassland greening impacts on global land surface temperature.

Grassland vegetation greenness has been increasing globally during the past decades. Although the vegetation coverage change could have significant effects on climate by affecting albedo and evapotranspiration (ET), the effects of global grassland greening on climate remain unclear due to the lack of long-term field observation data. Here, we used satellite measurements of land surface temperature (LST) from high coverage grassland and adjacent low coverage grassland (divided according to the leaf area index) to quantify, for the first time, the biogeophysical effects of global grassland greening on surface temperatures. Results showed that grassland greening decreased the annual mean LST and daytime LST (LSTD), but did not significantly change nighttime LST (LSTN) globally from 2003 to 2017. Spatially, grassland greening had significant cooling effects on the annual mean LST and LSTD for latitudes south of 50°N due to the cooling effect of increased ET, whereas warming affects on the annual mean LST and LSTD in the high northern latitudes (> 50°N) because of the warming effects of decreased albedo. This study revealed that the effects of grassland greening on surface temperatures changed with latitude. During June, July, and August (JJA), the increasing grassland vegetation coverage decreased the LST between 25°S and 50°N, but increased the mean LST in high northern latitudes. By contrast, grassland greening has no significant effect on the mean LST in the temperate southern hemisphere (> 25°S) during JJA due to cooling and warming effects on LSTD and LSTN, respectively. During December, January, and February, grassland greening decreased the mean LST and LSTD for latitudes south of 25°N, but increased the mean LST and LSTN for latitudes north of 25°N. This study highlights the importance of including grassland vegetation coverage in models of regional surface temperature dynamics and future climate forecast.

Hydrological and mechanical properties of loess landslides under different vegetation restoration types

Loess landslide is a common geological disaster in northern Shaanxi, which seriously affects people's life and property safety and social and economic development. The research on vegetation restoration types and hydrological and mechanical properties of loess landslides can provide basic data support for landslide stability prediction, and further provide reference for landslide prevention and treatment. In the present study, the loess landslide point of Zhang Zi Gou in Gan Quan County, Yan’an City was taken as the research object. On the basis of the existing natural condition data, the basic physical and mechanical properties and hydrological characteristics were obtained by collecting field landslide soil samples for indoor experimental analysis. The indoor analysis shows that the landslide is mainly distributed in dry land, medium coverage and low coverage grassland, indicating that the surface vegetation coverage can affect the stability of landslide. The worse the vegetation coverage, the more landslides occur. The void ratio and porosity of landslide soil decrease with the increase of dry density. The cohesion of natural soil is obviously higher than that of saturated soil, and the internal friction angle of natural soil is slightly lower than that of saturated soil. In general, due to the influence of water content, the shear strength of natural soil samples is higher than that of saturated soil samples. Therefore, in order to improve the accuracy of prediction and early warning system, it is necessary to consider the response of hydrological and mechanical properties of loess to vegetation restoration. The results provide basic data support for the establishment of loess landslide stability prediction system and provide reference for geological disaster management. Bangladesh J. Bot. 50(3): 795-801, 2021 (September) Special

Modelling the Impact of Vegetation Change on Hydrological Processes in Bayin River Basin, Northwest China

Vegetation change in arid areas may lead to the redistribution of regional water resources, which can intensify the competition between ecosystems and humans for water resources. This study aimed to accurately model the impact of vegetation change on hydrological processes in an arid endorheic river watershed undergoing revegetation, namely, the middle and lower reaches of the Bayin River basin, China. A LU-SWAT-MODFLOW model was developed by integrating dynamic hydrological response units with a coupled SWAT-MODFLOW model, which can reflect actual land cover changes in the basin. The LU-SWAT-MODFLOW model outperformed the original SWAT-MODFLOW model in simulating the impact of human activity as well as the leaf area index, evapotranspiration, and groundwater table depth. After regional revegetation, evapotranspiration and groundwater recharge in different sub-basins increased significantly. In addition, the direction and amount of surface-water–groundwater exchange changed considerably in areas where revegetation involved converting low-coverage grassland and bare land to forestland.

Analysis of Changes in Landslide Susceptibility according to Land Use over 38 Years in Lixian County, China

Landslides occur frequently in Lixian County, China, and land use has changed significantly in recent decades. We obtained land use data for the years 1980, 2000, and 2018, as well as three landslide susceptibility maps from a Random Forest model. Agricultural land, low coverage grassland, water area, and urban, rural and other construction land were prone to landslides. Landslide susceptibility was low in areas of woodland, moderate and high coverage grassland, bare rock land, desert and tundra. Areas with high landslide susceptibility were mainly located in the catchment of the study region, and a 2.61% decrease in high landslide susceptibility areas over the 38-year period was primarily driven by changes in agricultural and rural land. By contrast, a 1.42% increase in low landslide susceptibility areas over the 38-year period was driven by changes in moderate and high coverage woodland and moderate coverage grassland. There is a need for effective management measures to be implemented because areas with high landslide susceptibility are still present. We also found that human aggregations, or the absence of these, vary in their effects on the areas of Lixian County most susceptible to landslides.

The Spatiotemporal Changes and the Impacts of Climate Factors on Grassland in the Northern Songnen Plain (China)

Grassland is an important ecosystem; the spatiotemporal evolution trend of grassland and its impacts on climatic factors play an irreplaceable role in maintaining regional sustainable development and ecological balance. In this paper, based on the remote sensing images of 1990, 2000, 2010, 2020, and 3S technology, we use the methods of dynamic rate and transfer matrix to analyze the spatiotemporal evolution trend of the northern Songnen Plain (China). The method of grey correlation is used to analyze the impact of climate factors on it. The results showed that the grassland changed dramatically and unevenly across the three periods of 1990–2000, 2000–2010, and 2010–2020, with the biggest change in the last period. The internal conversion of grassland mainly occurred between H-grassland (high coverage grassland) and M-grassland (medium coverage grassland), while the transformation rarely occurred in L-grassland (low coverage grassland) due to its small area. There has been a transfer-in from cultivated land, woodland, and unused land to H-grassland and M-grassland. The grassland transfer-out was mainly from H-grassland and M-grassland to cultivated land and unused land. What’s more, the transformation mainly occurred in Daqing City, Suihua City, Qiqihar city, as well as occurring in the west of Harbin and the southwest of Heihe city. Climate change has exacerbated the reduction of grassland areas. In summary, the spatiotemporal change rates of grassland area in the north of Songnen Plain initially showed a mild decrease and were then followed by a rapid decrease. Climate factors were of great significance to the spatiotemporal changes of grassland, and precipitation had a greater impact on the reduction of grassland. The results can provide meaningful information for grassland change, grassland protection, and management in the northern Songnen Plain.

Spatial-Temporal Changes and Driving Force Analysis of Green Space in Coastal Cities of Southeast China over the Past 20 Years

The purpose of this study is to reveal the spatial-temporal change and driving factors of green space in coastal cities of southeast China over the past 20 years. A supervised classification method combining support vector machines (SVMs) and visual interpretation was used to extract the green space from Landsat TM/OLI imageries from 2000–2020. The landscape pattern index was used to calculate geospatial information of green space and analyze their spatial-temporal changes. The hierarchical partitioning analysis was then used to determine the influences of anthropogenic and geographic environmental factors on the spatial-temporal changes in green space. The results indicated that the total area of green space remained constant over the past 20 years in coastal cities of southeast China (1% reduction). The spatial change of green space mainly occurred in the area near the ocean and the southern region. 41.37% of forest land was transferred from cultivated land, while 44.56%, 41.83%, 43.20%, 46.31%, 41.98% and 40.20% of shrub land, sparse woodland, other woodland, high-coverage grassland, moderate-coverage grassland and low-coverage grassland were transferred from forest land. The number of patches, patch density, edge density, landscape shape index and Shannon’s diversity index increased from 2000–2015, and then decreased to the minimum in 2020, while largest patch index continued to decline from 2000–2020. The contribution of anthropogenic factors (0.53–0.61) on the spatial-temporal changes of green space continually increased over the past 20 years, which was also higher than geographical environment factors (0.39–0.41). Our study provides a new perspective to distinguish the impact of anthropogenic activities and geographical environmental factors on the change of green space area, thereby providing a theoretical support for the construction and ecological management of green space.

Climate Dynamics of the Spatiotemporal Changes of Vegetation NDVI in Northern China from 1982 to 2015

As an important part of a terrestrial ecosystem, vegetation plays an important role in the global carbon-water cycle and energy flow. Based on the Global Inventory Monitoring and Modeling System (GIMMS) third generation of Normalized Difference Vegetation Index (NDVI3g), meteorological station data, climate reanalysis data, and land cover data, this study analyzed the climate dynamics of the spatiotemporal variations of vegetation NDVI in northern China from 1982 to 2015. The results showed that growth season NDVI (NDVIgs) increased significantly at 0.006/10a (p < 0.01) in 1982–2015 on the regional scale. The period from 1982 to 2015 was divided into three periods: the NDVIgs increased by 0.026/10a (p < 0.01) in 1982–1990, decreased by −0.002/10a (p > 0.1) in 1990–2006, and then increased by 0.021/10a (p < 0.01) during 2006–2015. On the pixel scale, the increases in NDVIgs during 1982–2015, 1982–1990, 1990–2006, and 2006–2015 accounted for 74.64%, 85.34%, 48.14%, and 68.78% of the total area, respectively. In general, the dominant climate drivers of vegetation growth had gradually switched from solar radiation, temperature, and precipitation (1982–1990) to precipitation and temperature (1990–2015). For woodland, high coverage grassland, medium coverage grassland, low coverage grassland, the dominant climate drivers had changed from temperature and solar radiation, solar radiation and precipitation, precipitation and solar radiation, solar radiation to precipitation and solar radiation, precipitation, precipitation and temperature, temperature and precipitation. The areas controlled by precipitation increased significantly, mainly distributed in arid, sub-arid, and sub-humid areas. The dominant climate drivers for vegetation growth in the plateau climate zone or high-altitude area changed from solar radiation to temperature and precipitation, and then to temperature, while in cold temperate zone, changed from temperature to solar radiation. These results are helpful to understand the climate dynamics of vegetation growth, and have important guiding significance for vegetation protection and restoration in the context of global climate change.

Study on Ecological Water Requirement of Vegetation in Wuhai Based on GIS

Wuhai City is located in Inner Mongolia, belongs to the arid and semi-arid area of Northwest China, where precipitation is scarce, vegetation coverage is low and evaporation is large. With the exploitation of coal resources, the cultivated land area is gradually reduced and the surface is seriously damaged. After mining, a large number of mines and coal gangue piles are left behind, causing serious ecological problems. In order to ensure the normal growth of vegetation in Wuhai City, it is of great significance to study the ecological water demand of vegetation in Wuhai City for the realization of reasonable allocation of water resources, ecological restoration of mines and sustainable development of the city. Based on remote sensing satellite image data, combined with land use type map and ground meteorological data, this paper analyzes the spatial and temporal variation characteristics of normalized difference vegetation index (NDVI) in Wuhai City, calculates the evapotranspiration of vegetation in reference year, and obtains the ecological water demand of vegetation in Wuhai City by using area quota method according to different water demand spatial areas. The results showed that: in the total ecological water demand of vegetation in Wuhai City, the water demand of medium coverage grassland was the largest, reaching 407.59 mm, while that of forest land was the smallest, reaching 309.01 mm. The other water requirements from large to small are: low coverage grassland, high coverage grassland, sparse forest land, shrub land. Grassland accounts for 98% of ecological water demand, while woodland only accounts for 2%. The total ecological water demand is 326 million m3.

Particulate nutrient loss from drylands to grasslands/forestlands in a large-scale highly erodible watershed

Abstract Land use structure is an important factor affecting soil nutrient loss but the influencing mechanism of land use change on particulate nutrient loss is still unclear in large-scale ecological restoration regions. In this study, an integrated, physically-based modeling framework was put forward to identify the dynamic effects of land use change on particulate nitrogen (N) and phosphorus (P) loss in Jinghe River Watershed (JRW), China. Results indicate that: (i) The proposed modeling framework is a robust tool for quantifying the dynamic effects of land use change on particulate nutrient loss and evaluating agricultural planting stategies at multiple spatial and temporal scales; (ii) The increase of dry land and low-coverage grassland, and the decrease of forestland and high- and middle-coverage grassland from 1985 to 1995 led to a sharp increase of particulate N and P loss load, which increased by 39.06% and 42.69% respectively. (iii) The significant decrease in both dry land and low-coverage grassland from 1995 to 2005 caused the decrease of particulate N and P loss load by 28.22% and 31.99% respectively. This is because the forestland increased but dryland decreased, and the low-coverage grassland was transformed into middle- and high-coverage grassland during this period; and (iv) There was no decrease but increase by 13.65% and 13.50% for particulate N and P loss from 2005 to 2010 because the erosive rainstorm and runoff volume in 2010 were both larger than that in 2005. Results provide effective data support for scientific decision-makers and land management practices in the loess hilly and gully region.

Landscape patches influencing hillslope erosion processes and flow hydrodynamics

Exploring overland flow resistance and sediment delivery capacity under different landscape vegetation conditions is critical for better understanding hydrodynamic mechanisms of soil erosion processes and hydrological connectivity on hillslopes. To evaluate flow resistance relations and sediment transport for landscape vegetation coverage and combinate effect of vegetation patches, field simulated rainfall experiments were conducted using a series of overland runoff and sediment transport rates in 3 m (L) × 2 m (W) experimental plots with coverages of 0%, 20%, 40%, 60% and 90% in a uniformly distributed condition and composited flow paths of different patches (horizonal path, vertical path, random patches and S-shaped path) in the same coverage (40% and 60%). The runoff rates for the grassland with coverages of 20–90% were decreased by 19.3–61.4% (P < 0.05), and the sediment concentrations were reduced by 81.7–97.8% (P < 0.05) compared to the bare land. The Darcy-Weisbach resistance coefficient doubled and the stream power declined by 60.0% when grassland coverage increases to 90%. The runoff rates varied little among the conditions of horizontal, vertical, random and S-shaped flow paths at the coverage of 60%, while the rate apparently reduced by 34.1% (P < 0.05) when the vertical flow path became horizontal under the same coverage of 40%. The sediments for poorly connected flow paths could reduce sediment >90% either on high-coverage or low-coverage grassland. Our field experiments confirmed that the increase of vegetation coverage and the combination of landscape patches could significantly reduce runoff rates, sediment yields and flow velocities, increase surface roughness, promote flow resistance and diminish hydraulic shear stress and the stream power. The poorly-connected paths (horizontal and random) exhibited a stronger flow resistance and weaker sediment transport capacity than the well-connected paths (vertical and S-shaped).

Spatiotemporal characteristics of the expansion of an urban agglomeration and its effect on the eco-environment: Case study on the northern slope of the Tianshan Mountains

Urban agglomerations, which are highly integrated urban groups, form during the advanced stages of industrialization and urban development. The urban agglomeration on the northern slope of the Tianshan Mountains is one of the 19 urban agglomerations promoted by China’s 13th Five-Year Plan and a key area of urbanization in Xinjiang. Based on remote sensing data, we analyzed the expansion of construction land in the urban agglomeration on the northern slope of the Tianshan Mountains and its effect on ecological value in 1980–2015. The results show that the expansion of construction land significantly affected ecological value in the study area over the past 35 years. Among land use types, grassland was the dominant contributor to changes in ecological value; its contribution rate reached 66.27% with an interannual variation of only 5%. The contribution rate of urban and rural residential land along with industrial and mining lands was very low (0.82%), while the interannual variation was large (86%). The area of construction land in the urban agglomeration expanded from 1,067 to 2,586 km2, and the conversions of different land use types had different effects on ecological value. Among land use types, the conversions of low-coverage grassland and dry land made the largest contributions to changes in ecological value. During the study period, a total of 1,685 km2 of ecological land, 69.91% of which belonged to cultivated land and grassland, was converted into construction land. A total area of 1,082 km2 of dry land and low-coverage grassland was converted into construction land, accounting for 64.21% of the total ecological land that was converted into construction land. In 2000–2015, the area of urban construction land increased significantly along with the proportion of unused land, including gobi (172 km2), bare land (65 km2), and salt-affected land (65 km2), being converted into construction land. In contrast, the area of construction land that was converted into ecological land was less than 166 km2. The areas with the largest expansions of construction land were concentrated in Urumqi, Karamay, and Changji, where the areas of construction land increased by 399, 186, and 126 km2, respectively. The areas with the most rapid expansions in construction land were concentrated in Kuytun, Toksun, and Usu. The environmental effects of construction land expansion and land use change were more positive in the late stage of urban agglomeration (2000–2015) compared to in the early stage (1980–2000). Kuytun City, Shihezi City, and Wujiaqu City showed large changes in ecological value caused by the expansion of construction land, whereas the changes in ecological value in the 14 other cities were relatively small, and the expansion of construction land slowed in 2000–2015 compared to in 1980–2000. In the future, further development of the urban agglomeration on the northern slope of the Tianshan Mountains should fully consider the sensitivity and carrying capacity of the vulnerable ecological environment in this area. Population growth and industrial development in the urban agglomeration should be controlled based on the available water resources and ecological capacity to reduce the pressure on the environment and ensure sustainable development.