Mingbin Huang

Actual evapotranspiration estimation for different land use and land cover in urban regions using Landsat 5 data

Evapotranspiration (ET) is deemed critical for water resources management. Even in the same climatic and meteorological conditions, actual ET (ET a) may exhibit remarkable spatial variability across different vegetation covers, agricultural land use practices, and differing types of urban land development. The main objectives of this study are (1) to evaluate the possible closure of the heat balance equation using Oklahomas unique environmental monitoring network; and (2) to estimate ET a and determine the variation with regards to varying types of land use and land cover in urban settings. In this study, a Surface-Energy-Balance ET algorithm was implemented to estimate ET a at a higher spatial resolution using Landsat 5 satellite images while the Oklahoma Mesonet observations can be used as our ground truth data. Accuracy of the estimated ET a was assessed using latent heat flux measurements provided by AmeriFlux towers. The associated bias ratios of daily mean ET a with respect to both burn and control sites are -0.92%, and -8.86% with a correlation of 0.83 and 0.81, respectively. Additionally, estimated ET a from a water balance budget analysis and the remotely sensed ET a are cross-validated with a low bias ratio of 5.2%, and a correlation coefficient of 0.7 at the catchment scale. The lowest ET a was observed for developed urban areas and highest for open water bodies. The ET a difference is also demonstrated from two contrasting counties. The results show Garfield County (agricultural) has higher ET a values than Oklahoma County (urban) for all land cover types except open water bodies.

An evaluation of EPIC soil water and yield components in the gully region of Loess Plateau, China

The Erosion and Productivity Impact Calculator (EPIC) has been used to determine the effect of different cropping systems and management practices on soil productivity in the Loess Plateau of China. However, its crop growth and soil water balance submodels have not been verified in this region. The objective of the present study was to evaluate the ability of EPIC to estimate soil water content (θ in m 3 /m 3 ), seasonal evapotranspiration (ET in mm/season) and crop yield ( Y in t/ha) for winter wheat and maize. A 20-year field experiment was conducted at the Changwu Agro-ecological Experimental Station of the Loess Plateau, and divided into a calibration period and a validation period. Data from calibration (1984–94) were used to optimize the four most sensitive parameters of the EPIC crop yield submodel, whereas data from 1994 to 2004 were used for validation. For both crops, there were no significant differences between measured and estimated long-term means of the three variables ( P =0·05) for either the calibration or validation periods. EPIC estimated all three variables with a small relative root mean square error (RRMSE), i.e. the ratio of root mean square error to the mean value. For wheat and maize, the calibration period resulted in respective RRMSE values of 0·112 and 0·100 for θ, 0·121 and 0·116 for ET, and 0·135 and 0·147 for Y. During the validation period, the RRMSE values obtained were 0·090 and 0·085 for θ, 0·129 and 0·135 for ET, and 0·169 and 0·149 for Y, for wheat and maize, respectively. The performance of EPIC in estimating annual values of θ, ET and Y was variable. For validation, EPIC explained 65, 79 and 64% of the measured variations of θ, ET and Y, respectively, for wheat, and 60, 70 and 67% for maize. The EPIC-estimated long-term average values of the three variables were not significantly different from measured values for winter wheat and maize during the calibration and validation periods. It can therefore be used in the gully region of the Loess Plateau to define alternative cropping systems and management practices.

Black Locust Transpiration Responses to Soil Water Availability as Affected by Meteorological Factors and Soil Texture

ABSTRACT On the Loess Plateau of China, a dry soil layer may form due to excess transpiration, leading to degradation of black locust (Robinia pseudoacacia) stands. In order to better manage projects involving black locust, this study was intended to investigate the response of black locust transpiration rate to soil water availability as affected by meteorological factors using two representative soils (loamy clay and sandy loam) on the Loess Plateau. Four soil water contents were maintained for black locust seedlings grown in pots initially outdoors and then in a climate-controlled chamber, by either drying or irrigating the pots. In both environments, daily transpiration rates were related by a power function to air temperature and by a logistic function to reference evapotranspiration (ET0). Transpiration rates were more susceptible to changes in the meteorological conditions in the sandy loam than in the loamy clay soil. The transpiration rate in the well-watered treatment was greater for black locust grown in the sandy loam than in the loamy clay soil. Normalized transpiration rates were unaffected by ET0 until a critical value of soil water content (θc) was attained; the θc value decreased significantly for the loamy clay soil but increased significantly for the sandy loam soil when ET0 increased. These suggested that the effect of the meteorological condition on the transpiration characteristics of black locust was dependent on soil texture.

Evapotranspiration Estimation for an Oasis Area in the Heihe River Basin Using Landsat-8 Images and the METRIC Model

The Heihe River Basin is the second largest inland river basin in arid northwestern China. Accurate estimation of regional evapotranspiration (ET) and its spatial distribution in the oasis area plays an important role for water resource management in the whole basin. The objective of this study was to estimate the temporal and spatial variations of ET for different land cover types in the oasis. To estimate ET values in the growing season of 2013, 14 Landsat-8 images of the study area were processed using the Mapping Evapotranspiration at High Resolution with Internalized Calibration (METRIC) model. A new approach selected hot extreme pixels separately for the desert and oasis sub-areas due to large differences in soil thermal characteristics. Results indicated large temporal-spatial variations in ET in the oasis. The largest ET values occurred over water bodies, followed by arable land, low-lying land and forest. The desert-oasis transition zones (shrubland, sparse forest, medium- and low-coverage grassland) had lower ET values, while the lowest ET values occurred in unused lands (salt meadows, sandy and Gobi deserts). Monthly ET values of all land cover types increased from April, peaked in July, before decreasing until October. Overall, METRIC can provide reasonable ET estimates in a heterogeneous land use types under advective environmental conditions with the selection of appropriate extreme pixels.

Fate and transport of dissolved methane and ethane in cretaceous shales of the Williston Basin, Canada

Baseline characteristics of dissolved methane (CH4) and ethane (C2H6) and their stable isotopes in thick, low hydraulic conductivity, Cretaceous shales were determined using high-resolution core profiling at four sites in the Williston Basin (WB), Canada. Positive correlations with the conservative natural tracer Cl- reflected a lack of measureable production or consumption of gases in the shale to the depth investigated (150 m below ground, BG) and suggest CH4 and C2H6 concentrations near the interface with overlying Quaternary sediments are controlled by lateral migration and dilution in permeable zones. Curvilinear increasing concentrations with depth in the shale at all sites coupled with 1-D solute transport modelling suggest long-term (over millions of years) upward diffusion of CH4 and C2H6 from deeper WB sources, likely the Second White Speckled Shale Formation (SWSS; ∼790 m BG). δ13C-CH4 profiles in the shale are consistent with upward diffusional fractionation of isotopes from the SWSS. Distinct CH4 and C2H6 isotope values of gases in the shales vs. 13C-enriched thermogenic isotopic signatures of CH4 and C2H6 in deeper oil-producing WB intervals could be used to identify fugitive gases originating deeper in the Basin. This article is protected by copyright. All rights reserved.

Impact of Textural Layering on Water Retention Within Drained Sand Profiles

Abstract The impact of textural layering on water retention in sand profiles was evaluated through a series of laboratory column tests and numerical modeling. Alternating horizontal layers of coarse and medium sand were placed in 100-cm-long soil columns with three different layer thicknesses (5, 10, and 25 cm). A fourth column was constructed with a homogeneous mixture composed of equal amounts of coarse and medium sand. The soil columns were completely saturated and then allowed to drain to a water table boundary at the base of the columns. The changes of water storage with time were measured by weighing the columns during drainage and by measuring the soil water content profile after 120 h of drainage. The hydraulic properties of the coarse, medium, and the mixed sand were measured in the laboratory and also optimized using numerical simulations of the column tests. These properties were then used to simulate the longer-term drainage of deeper profiles, more typical of field conditions. The long-term simulations considered a 320-cm deep soil profile in which the upper 100 cm was composed of layers of the two sands or was a homogeneous profile of each sand or a mixture of the two. The lower 220 cm of the column was always coarse sand. A 320-cm homogeneous medium sand profile was also simulated. The laboratory tests suggested that, after 96 h of drainage, the 5- and 10-cm layered columns exhibited similar water retention that was higher than the 25-cm layered column or the mixture. The numerical modeling presented the same trends as the experimental results. Field capacity (FC) was assumed to have been attained in the simulations when the drainage rate reached 0.3 mm/d (10% of the mean daily potential evapotranspiration) at a depth of 100 cm. The water stored at FC was found to be 143, 145, 138, and 111 mm for the 5-, 10-, 25-, and 50-cm layered columns, respectively, much higher than that observed for the homogeneous medium (47 mm) and coarse (46 mm) sand columns. The time to reach FC after a large rainfall pulse (50 mm) was 100, 99, 72, and 45 days for the 5-, 10-, 25-, and 50-cm layered columns, respectively; again, a much longer time than that required for the homogeneous medium (24 days) and coarse (28 days) sand columns. These results highlight the role of textural layering in not only increasing FC but extending the time frame during which this water is available for plant growth.

Fate and Transport of Shale-derived, Biogenic Methane

Natural gas extraction from unconventional shale gas reservoirs is the subject of considerable public debate, with a key concern being the impact of leaking fugitive natural gases on shallow potable groundwater resources. Baseline data regarding the distribution, fate, and transport of these gases and their isotopes through natural formations prior to development are lacking. Here, we define the migration and fate of CH4 and δ13C-CH4 from an early-generation bacterial gas play in the Cretaceous of the Williston Basin, Canada to the water table. Our results show the CH4 is generated at depth and diffuses as a conservative species through the overlying shale. We also show that the diffusive fractionation of δ13C-CH4 (following glaciation) can complicate fugitive gas interpretations. The sensitivity of the δ13C-CH4 profile to glacial timing suggests it may be a valuable tracer for characterizing the timing of geologic changes that control transport of CH4 (and other solutes) and distinguishing between CH4 that rapidly migrates upward through a well annulus or other conduit and CH4 that diffuses upwards naturally. Results of this study were used to provide recommendations for designing baseline investigations.