Search

Evapotranspiration (ET) is predominant variable for water management in various types of ecosystems, and it has been intensively studied through in situ measuring and modeling methods. However, it is challenging to measure actual ET and upscale it to regional level for karst landscapes, where aquifers typically show remarkable and rapid responses to precipitation events. There is an urgent need to quantify water fluxes to provide reliable evidence for the protection and sustainable management of karst water resources. Therefore, in this study, five plots were built to observe actual ET based on Thermal Dissipation Probes, redesigned ventilated chamber and in‐site microlysimeters in a karst watershed in southwest China. Then, three models (Penman‐Monteith‐Leurning, PML; Remote Sensing‐Priestley and Taylor; and Hargreaves) were constructed to upscale ET estimation to the regional level based on Landsat‐8 images and MODIS data. The results showed that: (a) The PML model performed better than other models (p < 0.01) with higher R2 values (0.72 for MODIS images and 0.87 for Landsat‐8 images); (b) Daily ET exhibited significant seasonal variability and different spatial distribution, and yearly ET exhibited well related with soil thickness (R2 = 0.58); (c) Daily ET had a slightly positive correlation with DEM, however, had a negative correlation with ground temperature. This study is helpful to improve accuracy of measured and estimated ET by combining remote sensing data, and it has important implications for upscaling it to regional level. It suggests that ET is strongly regulated by constant supply of water, vegetation coverage, and available energy in karst catchments. Plain Language Summary: Evapotranspiration (ET) process bonds water, energy cycle, and carbon cycles. Aiming to characterize ET processes and impact controls at regional level for karst landscapes, five plots were built to observe actual ET, and three models were selected to upscale ET estimation to the regional level using Landsant‐8 and MODIS data in this study. The results showed that the Penman‐Monteith‐Leurning model performed the best and additional validation data observed in experimental spots were identified and corresponded with satellite data. Vegetation coverage and the density of conducting tissue (e.g., LAI) both contributed to ET seasonality and the spatial distribution differences. Soil thickness is a key prediction for the ratio distribution of yearly evapotranspiration to precipitation in karst watershed in southwest China. Key Points: Multiple models based on different data sources exhibited different accuracy on evapotranspiration simulation in karst basinYearly evapotranspiration distribution is well related with soil thicknessGround temperature exhibited negative correlation with daily evapotranspiration [ABSTRACT FROM AUTHOR]

Central Asia exports large amounts of virtual water through agricultural trade, a key factor for overexploitation of water resources in the region. Most studies analyze Central Asia's virtual water outflows to the outside world, while ignore the agricultural trade within the region and the varying impacts of virtual water flows on the individual countries. In this study, the changes in virtual water flows embedded in trade with outside regions (external) and Central Asia countries (internal) were analyzed for the period 2000–2018 for wheat, cotton, and livestock. The results show that while Central Asia exported, respectively, 194.3 and 101.8 km3 of virtual water to the outside world through cotton and wheat trade, it imported 53.7 km3 of virtual water via livestock trade. Also, while cotton‐based virtual water outflows decreased, wheat‐based virtual water outflows increased. Total virtual water flows in internal trade reached 71.2 km3, with flow originating mainly from Kazakhstan and heading to other four countries through wheat trade.Kazakhstan was the largest net exporter of virtual water through wheat trade, Uzbekistan was the second‐largest net exporter through cotton trade. Green water (precipitation water used by crops) was dominant in virtual water flow related to wheat and blue water (surface water or groundwater used by crops) was dominant in virtual water flow related to cotton. Uzbekistan and Turkmenistan were most directly influenced by the virtual water trade. [ABSTRACT FROM AUTHOR]

This study is to establish a new approach to estimate river salinity of semi‐arid agricultural watershed and identify drivers by using hydrologic modeling and machine learning. We augmented the limitations of the Soil and Water Assessment Tool (SWAT) to model salinity by coupling with eXtreme Gradient Boosting (XGBoost), a decision‐tree‐based ensemble machine learning algorithm. Streamflow, precipitation, elevation, main reach length, and dominant soil texture of the top two layers were used along with NO3, NO2, and total phosphorus (TP) output from a calibrated SWAT model are used as predictors to Total Dissolved Solids (TDS) in the XGBoost algorithm. Then, the SWAT model simulations of streamflow, NO3+NO2, and TP from 2000 to 2015 are used as inputs of the XGBoost model to predict monthly water TDS distribution along the river. The predicted river water TDS showed a higher concentration as going downstream from El Paso (inlet) through the Hudspeth canal to Fort Quitman (outlet). Finally, this study carried out cause analysis focusing on soil physical characteristics. The soil salinity level is directly affected by the soil permeability and irrigation water. As a result, the highest TDS is shown in sites with silt loam, whereas the lowest TDS was shown in sites with very cobbly soil. Silt soils can hold more water and are slower to drain than soils of a sand type. These analyses can be used to better understand the mitigation of water salinity. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2004.11.023 Byline: Charles R. Hart (a), Larry D. White (c), Alyson McDonald (a), Zhuping Sheng (b) Abstract: A large scale ecosystem restoration program was initiated in 1997 on the Pecos River in Western Texas. Saltcedar (Tamarix spp.), a non-native invasive tree, had created a near monoculture along the banks of the river by replacing most native vegetation. Local irrigation districts, private landowners, federal and state agencies, and private industry worked together to formulate and implement a restoration plan, with a goal of reducing the effects of saltcedar and restoring the native ecosystem of the river. An initial management phase utilizing state-of-the-art aerial application of herbicide began in 1999 and continued through 2003. Initial mortality of saltcedar averaged about 85-90%. Monitoring efforts were initiated at the onset of the project to include evaluating the effects of saltcedar control on salinity of the river water, efficiency of water delivery down the river as an irrigation water source, and estimates of water salvage. To date, no effect on salinity can be measured and irrigation delivery was suspended in 2002-2003 due to drought conditions. Water salvage estimates show a significant reduction in system water loss after saltcedar treatment. However, a flow increase in the river is not yet evident. Monitoring efforts will continue in subsequent years. Author Affiliation: (a) The Agriculture Program, Texas A&M University, Texas Cooperative Extension, Fort Stockton, TX 79735, USA (b) The Agriculture Program, Texas A&M University, Texas Agricultural Experiment Station, El Paso, TX 79927, USA (c) The Agricultural Program, Texas A&M University, Texas Cooperative Extension, College Station, TX 77843, USA Article History: Received 1 August 2004; Revised 1 October 2004; Accepted 1 November 2004

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2004.10.007 Byline: Zhuping Sheng Abstract: The traditional concept of Aquifer Storage and Recovery (ASR) has been emphasized and extensively applied for water resources conservation in arid and semi-arid regions using groundwater systems as introduced in Pyne's book titled Groundwater Recharge and Wells. This paper extends the ASR concept to an integrated level in which either treated or untreated surface water or reclaimed wastewater is stored in a suitable aquifer through a system of spreading basins, infiltration galleries and recharge wells; and part or all of the stored water is recovered through production wells, dual function recharge wells, or by streams receiving increased discharge from the surrounding recharged aquifer as needed. In this paper, the author uses the El Paso Water Utilities (EPWU) ASR system for injection of reclaimed wastewater into the Hueco Bolson aquifer as an example to address challenges and resolutions faced during the design and operation of an ASR system under a new ASR system definition. This new ASR system concept consists of four subsystems: source water, storage space-aquifer, recharge facilities and recovery facilities. Even though facing challenges, this system has successfully recharged approximately 74.7 million cubic meters (19.7 billion gallons) of reclaimed wastewater into the Hueco Bolson aquifer through 10 recharge wells in the last 18 years. This ASR system has served dual purposes: reuse of reclaimed wastewater to preserve native groundwater, and restoration of groundwater by artificial recharge of reclaimed wastewater into the Hueco Bolson aquifer. Author Affiliation: Agricultural Research and Extension Center, Texas A&M University, Texas Agricultural Experiment Station, 1380 A&M Circle, El Paso, TX 79927, USA