skip to main content


Search for: All records

Award ID contains: 1654957

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Soil water is vital for sustaining semiarid ecosystems. However, data on soil moisture have unlikely been continuously collected for a long time (e.g., >50 years), let alone under various combinations of climates and livestock grazing intensities. The objective of this study was to formulate and parameterize an ecohydrological model for predicting long-termvariability of soil moisture, taking a typical Eurasian grassland located in northeast China as the testbed. The parameters were determined by extensive literature review, field reconnaissance, laboratory analyses of soil and grass samples, and model calibration using daily soil temperatures and soil moistures measured at four depths from 2014 to 2017. The model, driven by the daily climate data from 1955 to 2017, performed well in reproducing the measurements. Across the assessment years of 1960 to 2017, the daily soil moistures were predicted to vary from 0.02 to 0.38. Overall, the soil moistures at a shallower depth were smaller but had a wider range than those at a deeper depth, with a largest mean and a widest range around the 30 cm depth. Regardless of the depths, the soil moistures pulsed in beginning March and plateaued from May to September. Livestock grazing was precited to reduce top 1.5-cm soil moistures but increase moistures of the beneath soils. The optimal grazing intensity was determined to be around 3.0 cattle ha−1, above which wind erosion would become a concern. The grazing impacts on soil moisture were found to monophonically decrease with increase of evapotranspiration or annual precipitation of larger than 220mm. For the years with an annual precipitation of less than 220mm, such grazing impacts either increased or decreased with increase of precipitation, depending on the relative magnitude of evapotranspiration. Climate change will diminish soil moisture pulses in early spring, likely intensifying soil erosion by wind. 
    more » « less
  2. Understanding historical trends in temperature, precipitation, and runoff is important but incomplete for developing adaptive measures to climate change to sustain fragile ecosystems in cold and arid regions, including the Balagaer River watershed on the Mongolian Plateau of northeast China. The objective of this study was to detect such trends in this watershed from 1959 to 2017. The detection was accomplished using a Mann-Kendall sudden change approach at annual and seasonal time scales. The results indicated that the abrupt changes in temperature preceded that in either runoff or precipitation; these abrupt changes occurred between 1970 and 2004. Significant (α = 0.05) warming trends were found at the minimum temperatures in spring (0.041 °C a−1), summer (0.037 °C a−1), fall (0.027 °C a−1), and winter (0.031 °C a−1). In contrast, significant decreasing trends were found in the precipitation (−1.27 mm a−1) and runoff (−0.069 mm a−1) in the summer. Marginally increasing trends were found in the precipitation in spring (0.18 mm a−1) and fall (0.032 mm a−1), whereas an insignificant decreasing trend was found in the runoffs in these two seasons. Both precipitation and runoff in the wet season exhibited a significant decreasing trend, whereas in the dry season, they exhibited a marginally increasing trend. Sudden changes in spring runoff and sudden rises in temperature are the main causes of sudden changes in basin rainfall. 
    more » « less
  3. Soil erosion by wind has been found to be negatively related to soil water content, as evidenced by that for a given area, such a soil erosion can be much less in a wet than a dry year. However, few studies have examined the functional relationship between wind erosion and soil moisture, primarily due to lack of field measured data. The objectives of this study were to: 1) measure wind erosion in field using a portable wind tunnel devised and made by the authors; and 2) use the measured data to calibrate/validate a wind erosion model previously developed by the authors. The study was conducted in the steppe grassland within the Balaguer watershed located in north China. As part of a larger project funded by National Science Foundation, this study focused on soil conditions with a minimal vegetation coverage to understand the functional relationship between wind erosion, soil moisture, and climate. These conditions are similar with those when the grassland degrades and ultimately becomes deserted. Field samples were analyzed in laboratory to determine the soil characteristics (e.g., moisture content, texture, hydraulic conductivity, and organic content). In this conference, we will present our portable wind tunnel, measured data, and the wind erosion model and its predictions. 
    more » « less
  4. Most of the Eurasian steppe grasslands, including the Balagaer River watershed located in north China, have an arid/semiarid climatic, and thus a vulnerable ecohydrologic, condition. The grass growth in such a region is critical to combat negative eco-environmental issues such as land desertification and the subsequent degradation of pasture productivity. How to predict responses of grass growth to climatic variations and human activities (e.g., grazing) is important for the utilization and protection of steppe grasslands. However, the information of such predictions is yet incomplete in existing literature. Taking the Balagaer River watershed as a test bed, this study parameterized a WOFOST (WOrld FOod STudies) simulation model to predict the potential plant growth as influenced by climate and human. The model is calibrated by manually adjusting various eco-physiological parameters, whose initial values were estimated using existing literature, field experiments, and remote sensing techniques. The soil-water parameters (e.g., porosity and saturated hydraulic conductivity) were determined by analyzing least-disturbed soil samples, while the physiological parameters (e.g., assimilation rate) of the dominant vegetation species of Stipa Grandis and Leymus Chinensis were determined by laboratory analyses of grass samples as well as from literature. The grazing frequency and intensity by sheep, horses, and cows were modeled as possible management scenarios. The model was driven by historical climate data recorded in a past half century at a weather station within the watershed. This study firstly expanded the WOFOST’s application to tracing dynamics of steppe grasses, while its results would likely be used to understand the threshold conditions for possibly irreversible degradation of steppe grasslands. In this presentation, we will highlight our successes, challenges, and solutions in parameterizing such a WOFOST model, and show the simulation results. 
    more » « less
  5. The accelerating degradation of native grasslands is becoming a threat to the world’s biome supply and has raised serious environmental concerns such as desertification and dust storm. Given that the steppe grasslands, such as those located in the Inner Mongolia Plateau of north China, have a dry climatic condition, the grass growth closely relies on available soil water, which in turn depends on precipitation prior to the growing season (in particular from May to July). However, our understanding of steppe hydrology and water consumption by grasses is incomplete. In this study, the agro-hydrologic Soil Water Plant Atmosphere (SWAP) model was used to mimic the long-term variations in soil water and vegetation growth in a typical steppe grassland of north China to further understand how alterations of hydrologic processes are related to grassland degradation. A field experiment was conducted to collect the data needed to set up the model. The SWAP model was calibrated using continuous observations of soil moisture and soil temperature at various depths for a simulation period of 2014 to 2017. The results indicated that the SWAP model can be used to simulate the responses of soil moisture and vegetation growth to climates. Moreover, this study examines the water balance and chronological variations of precipitation, evapotranspiration, soil water, and runoff. This study will add new knowledge of steppe hydrologic processes into existing literature. 
    more » « less
  6. Understanding dynamics of soil water content (SWC) and pore air relative humidity (RHpa), as influenced by wetting-drying cycles, is crucial for sustaining fragile ecosystems of desert lands across the world. However, to date, such an understanding is still incomplete. The objective of this study was to examine such dynamics at a typical desert site within the Horqin Sandy Land, located in Mongolian Plateau of north China. The results indicated that vaporization primarily occurred at a depth of around 10 cm below the ground surface. The diurnal variations of the SWC and RHpa in the top 10 cm soils were much larger than those in the soils at a deeper depth. For a non-rainy day, the SWC and RHpa were mainly determined by the relative magnitude of atmospheric temperature over soil temperature, whereas, for a rainy day, the SWC and RHpa were primarily controlled by the rainfall pattern and amount. The retardation role of the top dry soil layer, which is about 10 cm thick and exists most time at the study site, can effectively prevent the beneath moist soils from being further dried up, and thus is beneficial for sustaining the desert ecosystem. 
    more » « less