Evapotranspiration (ET) is a vital component of a field water balance. Canopy chambers are a promising method for determining crop ET because they are portable and applicable at a relatively small plot (m2) scale. Although a variety of canopy chamber designs have been proposed, field tests are still necessary to evaluate chamber performance for measuring crop ET. The objectives of this study are (1) to construct and use an improved canopy chamber to measure ET of three crops [corn (Zea mays, L.), soybean (Glycine max), and reconstructed mixed prairie] and (2) to compare the canopy chamber measurements with flux tower results and field water balance measurements (i.e., rainfall, soil water storage, ET and drainage). Three cropping systems including corn/soybean in a corn-soybean rotation, and reconstructed mixed prairie were studied in central Iowa. Canopy chamber daytime measurements were performed on 18 days in 2013 (a relatively dry growing season) and on 15 days in 2014 (a relatively wet growing season). Based on the results, the differences in daily ET and seasonal cumulative ET between canopy chambers and an eddy covariance flux tower over the measurement periods were within 5%, providing evidence that the portable canopy chamber can accurately measured ET. The chamber ET values and field water balance ET values had similar patterns over the 2013 and 2014 measurement periods, and the differences of cumulative results were less than 10%. In conclusion, the canopy chamber was proven to be an effective method for measuring small plot ET. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. b s t r a c tEvapotranspiration (ET) is a vital component of a field water balance. Canopy chambers are a promising method for determining crop ET because they are portable and applicable at a relatively small plot (m 2 ) scale. Although a variety of canopy chamber designs have been proposed, field tests are still necessary to evaluate chamber performance for measuring crop ET. The objectives of this study are (1) to construct and use an improved canopy chamber to measure ET of three crops [corn (Zea mays, L.), soybean (Glycine max), and reconstructed mixed prairie] and (2) to compare the canopy chamber measurements with flux tower results and field water balance measurements (i.e., rainfall, soil water storage, ET and drainage). Three cropping systems including corn/soybean in a corn-soybean rotation, and reconstructed mixed prairie were studied in central Iowa. Canopy chamber daytime measurements were performed on 18 days in 2013 (a relatively dry growing season) and on 15 days in 2014 (a relatively wet growing season). Based on the results, the differences in daily ET and seasonal cumulative ET between canopy chambers and an eddy covariance flux tower over the measurement periods were within 5%, providing evidence that the portable canopy chamber can accurately measured ET. The chamber ET val...

Tangent line (TL) methods and the second-order bounded mean oscillation (BMO) method have been proposed for determining the reflection positions of time domain reflectometry (TDR) waveforms, especially for short-probe TDR sensors. However, the accuracy of TL methods is limited by the multi-reflection effects of the short-probe TDR sensor, and an automatic implementation of the second-order BMO is challenging because of the superimposition of the TDR waveforms. In this study, we combined a TL method with second-order BMO to develop a tangent line/second-order bounded mean oscillation (TL-BMO) method. Laboratory and field data were used to evaluate the TL-BMO method. Separate tests were performed on laboratory data to compare the TL-BMO method with the TL method and the second-order BMO method. For selected waveforms, the TL-BMO was more accurate than the TL method (the RMSE of TL-BMO was 0.0197 m 3 m −3 and the RMSE of the TL method was 0.1071 m 3 m −3 ). The TL-BMO was able to avoid calculation errors associated with automatic analysis by the second-order BMO (RMSE of TL-BMO automatic analysis was 0.0199 m 3 m −3 and the RMSE of second-order BMO automatic analysis was 0.1414 m 3 m −3 ). For analyzing field measurements, the TL-BMO method was able to determine soil water contents accurately during a 3-wk-long measurement period. Conclusively, the new TL-BMO method was more accurate than the TL method, and it demonstrated the stability necessary for automatic analysis of short-probe TDR sensors.Abbreviations: BMO, bounded mean oscillation; TDR, time domain reflectometry; TL, tangent line; TL-BMO, tangent line/second-order bounded mean oscillation; T-TDR, thermotime domain reflectometry.

Groundwater contamination with chlorinated hydrocarbons has become a widespread problem that threatens water quality and human health. Permeable reactive barriers (PRBs), which employ zerovalent iron, are effective for remediation; however, a need exists to reduce the economic and environmental costs associated with constructing PRBs. We present a method to produce zerovalent iron supported on macroporous carbon using only lignin and magnetite. Biochar-ZVI (BC-ZVI) produced by this method exhibits a broad pore size distribution with micrometer sized ZVI phases dispersed throughout a carbon matrix. X-ray diffraction revealed that pyrolysis at 900 °C of a 50/50 lignin–magnetite mixture resulted in almost complete reduction of magnetite to ZVI and that compression molding promotes iron reduction in pyrolysis due to mixing of starting materials. High temperature pyrolysis of lignin yields some graphite in BC-ZVI due to reduction of carbonaceous gases on iron oxides. TCE was removed from water as it passed through a column packed with BC-ZVI at flow rates representative of average and high groundwater flow. One-dimensional convection–dispersion modeling revealed that adsorption by biochar influences TCE transport and that BC-ZVI facilitated removal of TCE from contaminated water by both adsorption and degradation.

No abstract

Tangent line methods and adaptive waveform interpretation with Gaussian filtering (AWIGF) have been proposed for determining reflection positions of time domain reflectometry (TDR) waveforms. However, the accuracy of those methods is limited for short probe TDR sensors. Second order bounded mean oscillation (BMO) may be an alternative method to determine reflection positions of short probe TDR waveforms. For this study, an algorithm of second order BMO is developed. Example waveforms are analyzed with tangent line methods, AWIGF method and second order BMO, to illustrate the difference among the three methods. For some waveforms, second order BMO appears be able to give more plausible results. Automatic implementation was challenging for the second order BMO. With second order BMO, it is difficult to set a default threshold suitably for all TDR waveforms. Thus, manual adjustment may be required to select suitable threshold for second order BMO analysis.