195 research outputs found
Modeling nitrogen loading in a small watershed in southwest China using a DNDC model with hydrological enhancements
The degradation of water quality has been observed worldwide, and inputs of nitrogen (N), along with other nutrients, play a key role in the process of contamination. The quantification of N loading from non-point sources at a watershed scale has long been a challenge. Process-based models have been developed to address this problem. Because N loading from non-point sources result from interactions between biogeochemical and hydrological processes, a model framework must include both types of processes if it is to be useful. This paper reports the results of a study in which we integrated two fundamental hydrologic features, the SCS (Soil Conservation Service) curve function and the MUSLE (Modified Universal Soil Loss), into a biogeochemical model, the DNDC. The SCS curve equation and the MUSLE are widely used in hydrological models for calculating surface runoff and soil erosion. Equipped with the new added hydrologic features, DNDC was substantially enhanced with the new capacity of simulating both vertical and horizontal movements of water and N at a watershed scale. A long-term experimental watershed in Southwest China was selected to test the new version of the DNDC. The target watershed\u27s 35.1 ha of territory encompass 19.3 ha of croplands, 11.0 ha of forest lands, 1.1 ha of grassplots, and 3.7 ha of residential areas. An input database containing topographic data, meteorological conditions, soil properties, vegetation information, and management applications was established and linked to the enhanced DNDC. Driven by the input database, the DNDC simulated the surface runoff flow, the subsurface leaching flow, the soil erosion, and the N loadings from the target watershed. The modeled water flow, sediment yield, and N loading from the entire watershed were compared with observations from the watershed and yielded encouraging results. The sources of N loading were identified by using the results of the model. In 2008, the modeled runoff-induced loss of total N from the watershed was 904 kg N yr−1, of which approximately 67 % came from the croplands. The enhanced DNDC model also estimated the watershed-scale N losses (1391 kg N yr−1) from the emissions of the N-containing gases (ammonia, nitrous oxide, nitric oxide, and dinitrogen). Ammonia volatilization (1299 kg N yr−1) dominated the gaseous N losses. The study indicated that process-based biogeochemical models such as the DNDC could contribute more effectively to watershed N loading studies if the hydrological components of the models were appropriately enhanced
Forages for the Red Soils Area of China - Proceedings of an International Workshop, Jianyang, Fujian Province, P. R. China, 6–9 October 1997
Crop Production/Industries,
Subdividing large mountainous watersheds into smaller hydrological units to predict soil loss and sediment yield using the geowepp model
Our research was funded by Artvin Coruh University, Coordinatorship of Scientific Research Projects (project No: 2011.F10.02.13).The number of studies using prediction models on measuring soil loss and/or sediment yield has been continuously increasing since these models are considered timely and cost-effective. Similarly, in this study, we used the GeoWEPP model to determine how much soil is being lost and the amount of sediment being yielded from Godrahav Creek Watershed (GCW) located in northeastern Turkey. Because the watershed is large (5,298.21 ha) and has mountainous and steep terrain, it was subdivided into smaller hydrological units (SHUs) so that the model can run easily and give detailed findings. The results revealed that out of 18,596.8 t of soil loss generated from both hillslopes and channels within the whole GCW, approximately 9,854.8 t y(-1) reached Borcka Dam reservoir as sediment. The model also predicted annual average soil loss and sediment yield as 1.73 t ha(-1)y(-1) and 1,86 t ha(-1)y(-1), respectively. In addition, with a sediment delivery ratio (SDR) of 0.530, the results indicated that almost half of the detached soil particles were carried away as sediment. Despite the dominant vegetation coverage, relatively high SDR and soil loss - particularly in certain SHUs - can be associated with steep terrain and conversion of natural lands in the watershed
The Effect of Rainfall and Post-revolutionary Land-use Changes on Sediment Yield in Weixi Basin, Yunnan, China : New insights from multi-temporal land-use classification and radionuclide analyses
This paper looks at the dynamic interphase connecting post-revolutionary politics, modern land use practices, precipitation patterns, basin slope, and sediment yield records in Weixi basin, a small mountainous watershed in Southwestern China with a total upstream area of 198 m2. The goal is to identify what processes, climatic or not, account for the changes in local sediment yield and erosion budget. Weixi basin has an average annual sediment yield of 175 ton/km2 with two anomalously large peaks in 1979 and 1984. Precipitation is moderately correlated with sediment yield at interannual scale. It also affects seasonal fluctuations in sediment yield as major sediment loading events correspond to spring snowmelt and monsoon rainfall. However, there is no long-term trend in precipitation that could explain the peak in sediment yield. Land use/land cover classification shows an average of 22.8% bare land in Weixi basin, but no definitive conclusion about temporal changes could be drawn yet due to the discrepancy in imagery resolution. Short-lived radionuclide analyses show there is no correlation between upstream land use and depth of erosion, whereas slope is a moderate control for erosion depth
The Effect of Rainfall and Post-revolutionary Land-use Changes on Sediment Yield in Weixi Basin, Yunnan, China : New insights from multi-temporal land-use classification and radionuclide analyses
This paper looks at the dynamic interphase connecting post-revolutionary politics, modern land use practices, precipitation patterns, basin slope, and sediment yield records in Weixi basin, a small mountainous watershed in Southwestern China with a total upstream area of 198 m2. The goal is to identify what processes, climatic or not, account for the changes in local sediment yield and erosion budget. Weixi basin has an average annual sediment yield of 175 ton/km2 with two anomalously large peaks in 1979 and 1984. Precipitation is moderately correlated with sediment yield at interannual scale. It also affects seasonal fluctuations in sediment yield as major sediment loading events correspond to spring snowmelt and monsoon rainfall. However, there is no long-term trend in precipitation that could explain the peak in sediment yield. Land use/land cover classification shows an average of 22.8% bare land in Weixi basin, but no definitive conclusion about temporal changes could be drawn yet due to the discrepancy in imagery resolution. Short-lived radionuclide analyses show there is no correlation between upstream land use and depth of erosion, whereas slope is a moderate control for erosion depth
Tropical and Subtropical Maize in Asia: Production Systems, Constraints, and Research Priorities
This book examines future technological and policy prospects for the sustainable intensification of rainfed upland maize production in Asia, and derives R&D priorities for specific maize production environments and markets. Village-level and farmer-group surveys were conducted to characterize upland maize production environments and systems in China, India, Indonesia, Nepal, the Philippines, Thailand, and Vietnam. Survey findings, particularly farmer-identified constraints to maize production, complemented with other relevant data, were used in country-level, R&D priority-setting workshops. High on the list of farmer constraints was drought, estimated to affect three production environments that are home to about 48 million rural poor and produce an estimated 16 million tons of maize, and others such as downy mildew, stem borers, soil erosion/landslides, waterlogging, poor agricultural extension/ technology transfer services, and poor access to low-interest credit and markets. Farmers felt that socioeconomic and policy-related constraints impact maize productivity more than technical constraints do. It is important to recognize that technology is not the only key to increasing productivity and bettering the conditions of marginal maize farmers in Asia. There is a growing trend towards commercializing and intensifying maize production that is different from the staple food self-sufficiency paradigm that has been the cornerstone of agricultural policy in most developing countries. Appropriate government policies could help alleviate the adverse consequences of commercialization and promote sustainable intensification of maize production, especially in marginal environments inhabited by resource-poor subsistence farmersMaize, Agricultural development, Farming systems, Production policies, Environmental factors, Cropping systems, Research projects, Project management, Asia, Crop Production/Industries, E10,
Soil-Water Conservation, Erosion, and Landslide
The predicted climate change is likely to cause extreme storm events and, subsequently, catastrophic disasters, including soil erosion, debris and landslide formation, loss of life, etc. In the decade from 1976, natural disasters affected less than a billion lives. These numbers have surged in the last decade alone. It is said that natural disasters have affected over 3 billion lives, killed on average 750,000 people, and cost more than 600 billion US dollars. Of these numbers, a greater proportion are due to sediment-related disasters, and these numbers are an indication of the amount of work still to be done in the field of soil erosion, conservation, and landslides. Scientists, engineers, and planners are all under immense pressure to develop and improve existing scientific tools to model erosion and landslides and, in the process, better conserve the soil. Therefore, the purpose of this Special Issue is to improve our knowledge on the processes and mechanics of soil erosion and landslides. In turn, these will be crucial in developing the right tools and models for soil and water conservation, disaster mitigation, and early warning systems
Soil erosion and sediment yield in the upper Yangtze, China
Soil erosion and sedimentation are key environmental problems in the Upper Yangtze because of the ongoing Three Gorges Project (TGP), the largest hydro-power project in the world. There is growing concern about the rapid increase of soil erosion over the last few decades and its consequence for potential sedimentation in the reservoir. The study aims to examine controls on the spatial and temporal distributions of sediment transfer within the Upper Yangtze and the hydrological consequences of land use changes, using varied approaches at different catchment scales. First, soil erosion and sedimentation are examined using the radionuclide Cs-137 as a tracer within a small reservoir catchment in the Three Gorges Area. The results indicates that soil erosion on sloping arable land and the rates of reservoir sedimentation have been severe during the past 40 years, mainly due to cultivation on steep slopes. Changes in reservoir sedimentation rates are mainly attributed to land use changes. The suitability of the Cs-137 techniques for investigating soil erosion and sedimentation in intensely cultivated subtropical environments is also considered. The use of the technique for erosion investigation may have limitations due to the abundance of coarse soil textures, uncertainty about fallout deposition rates and the high incidence of human disturbance, but the technique shows promising perspectives for sedimentation investigation since a few dating horizons might be identified. Second, sediment and runoff measurement data for around 30 years from over 250 hydrological stations within the Upper Yangtze have been examined within a GIS framework. The dataset has been integrated with catchment characteristics derived from a variety of environmental datasets and manipulated with Arc/Info GIS. The analysis of the sediment load data has permitted identification of the most important locations of sediment sources, the shifting pattern of source areas in relation to land use change and sub-catchments exhibiting trending sediment yields corrected for hydrological variability. The study demonstrates the importance of scale dependency of sediment yield in both the identification of temporal change and the modelling of relationships between sediment yield and environmental variables, suggesting that the treatment of the scale problem is crucial for temporal-spatial studies of sediment yield
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