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Authors: Jacobs, E.M.; Advisor: -; Participants: Bertassello, L.E.; Rao, P.S.C. (2020) - o identify differences in temporal hydrologic variability between sites with different soil and vegetation characteristics, we focus on daily data from 10 locations, representative of three major land cover types in the region. We use the concepts of (a) soil water memory to evaluate differences in landscape buffering of rainfall and (b) persistence to evaluate the threshold‐crossing properties of statistically defined “wet” and “dry” soil water conditions. Power spectral analyses of soil water storage reveal that regionally consistent patterns emerge in memory at multiple temporal scales. Threshold‐crossing analyses reveal corresponding similarity in persistence between sites. The analyses show that stochastic rainfall is the key driver of landscape hydrologic dynamics, with rainfa...
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Authors: Denager, T.; Advisor: -; Participants: Looms, M.C.; Sonnenborg, T.O.; Jensen, K.H. (2020) - Evapotranspiration from eddy covariance (ETEC) is cross‐checked with evapotranspiration calculated as the residual of the water balance (ETwb). The water balance closure using ETEC is simultaneously validated. Over a 6‐yr period, all major terms of the water balance are measured including precipitation, recharge from percolation lysimeters, and soil moisture content from a cosmic‐ray neutron sensor, a capacitance sensor network, and time domain reflectometry (TDR), respectively. In addition, we estimate their respective uncertainties. The study demonstrates that both monthly and yearly ETEC and ETwb compare well and that the water balance is closed when ETEC is used. Concurrently, incoming available energy (net radiation minus ground heat flux) on average exceeds the turbulent energ...
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Authors: Rahmati, M.; Advisor: -; Participants: Groh, J.; Graf, A.; Pütz, T.; Vanderborght, J.; Vereecken, H. (2020) - All components of the water balance were determined from 2012 until 2018. Budyko analysis was used to characterize the hydrological status of the studied sites. Wavelet analysis was also applied to study the power spectrum of ETa, vegetation‐height‐adjusted reference evapotranspiration (ETcrop), and water stress index (WSI) defined as ETa/ETcrop, as well as SWC at three different depths and the coherence between SWC and ETa and WSI. The Budyko analysis showed that 2018 resulted in a shift of both locations towards more water‐limited conditions, although Rollesbroich remained an energy‐limited system. Based on the power spectrum analysis, the annual timescale is the dominant scale for the temporal variability of ETa, ETcrop, and SWC. The results also showed that increasing dryness at...
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Authors: Huang, Y.; Advisor: -; Participants: Franssen, H‐J.H.; Herbst, M.; Hirschi, M.; Michel, D. (2020) - These lysimeter time series are affected by data gaps that must be filled to estimate actual ET totals and long‐term trends. In this paper, we explore four different gap‐filling methods: the potential ET‐method, the ratio method, the FAO‐based water balance method, and HYDRUS modeling. These gap‐filling methods were evaluated for three time series of actual ET measured by lysimeters and meteorological data of three European sites. Separate evaluations were made for the five driest and five wettest April–October periods to investigate whether the performance of the gap‐filling methods was affected by hydrological conditions. Series of random gaps were artificially created for the three time series, including gaps of four different lengths. Actual ET was estimated for these gaps with ...
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Authors: Bean, E.Z.; Advisor: -; Participants: Huffaker, R.G.; Migliaccio, K.W. (2018) - We evaluated competing approaches for automated soil water cycles analysis that use widely available R packages based on pattern recognition and machine learning (findpeaks [R‐FP], symbolic aggregate approximation [R‐SAX], and density histogram [R‐DH]), and a MATLAB code based on soil water dynamic principles (SWDP). These approaches were applied to three SMS datasets. Our empirical results showed superiority of R‐SAX for identifying valid soil water cycles, probably due to benefiting from training sets to calibrate to correct cycles. Two other approaches (SWDP and R‐FP) provided similar results without need of training sets or preprocessing data. Three approaches for estimating field capacity were applied to valid cycles, R‐FP, regression of exponential decay (SWDP‐R), and estimate...
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Authors: Smith, E.A.; Advisor: -; Participants: Capel, P.D. (2018) - A specific conductance end‐member mixing analysis (SC‐EMMA) was used to determine the volume of water that infiltrated through preferential flow pathways. The SC‐EMMA was used for 20 of the 25 paired rainfall–SC events; of the 20 classified events, the maximum preferential flow ranged from 11 to 75% of the total subsurface drain flow, with a mean maximum preferential flow of 31%. Overall, SC‐EMMA illustrated that a significant portion of the subsurface drain discharge can be attributed to preferential flow, mainly through macropores or other largely open preferential flow pathways. The other primary mechanism, antecedent moisture conditions shifts, could only be shown for four of the 25 classified events. Specific conductance as a tracer of preferential flow was shown to be an effec...
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Authors: Singh, G.; Advisor: -; Participants: Kaur, G.; Williard, K.; Schoonover, J.; Kang, J. (2018) - A number of contaminants including agrochemicals (fertilizers, pesticides), heavy metals, trace elements, and pathogenic microbes along with pharmaceuticals and hormones used in animal production move through the soil and are responsible for degradation of groundwater quality. Therefore, it is essential to sample soil solution for better understanding of movement and environmental fate of various contaminants in soils. We review different soil solution extraction samplers. The soil solution samplers discussed here are: drainage lysimeter or soil column, pan lysimeter, resin bags or membranes, wick lysimeters, suction cup, and suction plate. We have reviewed 304 journal articles representing a wide array of scientific disciplines. A brief history of soil solution monitoring and termi...
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Authors: Graham, S.L.; Advisor: -; Participants: Srinivasan, M.S.; Faulkner, N.; Carrick, S. (2018) - This study investigated, for a heterogeneous stony soil, four methods of soil hydraulic parameterization: (i) use of a pedotransfer function with a four‐layer soil profile based on detailed soil physical and textural description; (ii) use of a pedotransfer function with a single‐layer soil description; (iii) inverse estimation from soil moisture data; and (iv) inverse estimation from lysimeter drainage. Soil drainage, volumetric water content, and evapotranspiration were each modeled using HYDRUS‐1D for an irrigated pasture in New Zealand during the time period 1 July 2011 to 15 Mar. 2014. The first 15 mo were used for model spin‐up and inverse parameter estimation, while the remainder of the study period was used as a validation period, during which model results were compared agai...
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Authors: Torrentó, C.; Advisor: -; Participants: Prasuhn, V.; Spiess, E.; Ponsin, V.; Melsbach, A. (2018) - Conditions for preferential flow were promoted by applying heavy simulated rainfall shortly after pesticide application. In some of the experiments, preferential flow was also artificially simulated by injecting the solutes through a narrow tube below the root zone. With depth injection, preferential leaching of atrazine occurred shortly after application in both soil types, whereas with surface application, it occurred only in the moraine soil. Thereafter, atrazine transport was mainly through the porous soil matrix, although contributions of preferential flow were also observed. For all the application approaches and soil types, after 900 d, <3% of the applied amount of atrazine was recovered in the drainage water. Only uranine realistically illustrated the early atrazine breakthr...
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Authors: Nocco, M.A.; Advisor: -; Participants: Kraft, G.J.; Loheide II, S.P.; Kucharik, C.J. (2018) - We found that interannual climate variability, subtle differences in soil texture, and cropping system type drove potential recharge to varying degrees during the summer and fall seasons. Relatively finer soil texture was positively correlated to point estimates of potential recharge. This correlation was the strongest following large precipitation events. June to November cumulative potential recharge for 2013 to 2016 averaged 71 ± 235 mm across all lysimeters. Our findings suggest that aquifer depletion will be an episodic process that leaves surface waters most vulnerable to pumping and recharge impacts during and following drier years in the WCS. Differences among cropping systems were most pronounced under average precipitation conditions, which facilitated potential groundwate...
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