2007 Annual Report 1a.Objectives (from AD-416) Objective 1. Develop improved understanding and quantitative descriptions of the effects of degraded irrigation waters on root water uptake and soil hydraulic properties. Objective 2. Develop improved knowledge and predictive capabilities of unsaturated flow and transport processes affecting retention, transformation, and transport of pesticides, pathogens, pharmaceuticals and other contaminants. 1b.Approach (from AD-416) Measurements of compensatory uptake are needed to formulate improved models of root water uptake. We will conduct greenhouse studies aimed at observing compensatory uptake in cotton for different stress conditions. Cotton is deep rooted, has high salt tolerance, and is an agronomically important crop in San Joaquin Valley, CA. In the past cotton has been observed to exhibit some compensatory behaviors, e.g. utilizing shallow groundwater to varying degrees depending upon root zone conditions. Current guidelines for degraded water use are based on the effects of sodium and salinity on the soil saturated conductivity, and do not consider the impact on unsaturated hydraulic properties. Experimental data for the unsaturated properties is sparse and contradictory. To aid in the formulation of improved guidelines for irrigating with degraded waters, we propose experiments aimed at elucidating the effects of saline-sodic irrigation water on unsaturated soil hydraulic properties. The HYDRUS software will be expanded to include features that enhance its suitability as an advanced simulation model and decision support tool for testing and implementing site-specific soil, water and crop management practices. Among the features to be added are modules to account for the transport of pesticides, pathogenic microorganisms, colloids, pharmaceuticals, and related constituents in unsaturated soils. Planned modifications include improved representations of straining processes, colloid aggregation, colloid transport in unsaturated soil, size exclusion in structured soils, colloid-facilitated transport, and chemical reaction, sorption, and degradation processes. Formerly 5310-61000-009-00D (5/07). 4.Accomplishments New model for assessing of root zone contaminants Land application of biosolids can introduce into the subsurface persistent, slow moving trace metals and other contaminants that may impact environmental quality and human health for decades to come; safe use of biosolids in agriculture requires accurate risk assessment of contaminant fate and transport. Researchers at the U.S. Salinity Laboratory, in collaboration with scientists in Sweden and Brazil, developed a new contaminant transport model suitable for assessing the transport of slow moving contaminants in the root zone. The new model has relatively modest data requirements yet was found to provide more realistic assessments than other root-zone models currently used or proposed for use in biosolid risk assessment. The research addresses NP201 (Watershed Management, Water Availability and Ecosystem Restoration) and it will assist researchers and regulators assessing the impacts of persistent contaminants in the root zone. 5.Significant Activities that Support Special Target Populations None 6.Technology Transfer Number of web sites managed 2 Number of non-peer reviewed presentations and proceedings 20 Review Publications Skaggs, T.H., Van Genuchten, M.T., Shouse, P.J., Poss, J.A. 2006. Macroscopic approaches to root water uptake as a function of water and salinity stress. Agricultural Water Management. 86:140-149 Wood, Y.A., Fenn, M., Meixner, T., Shouse, P.J., Breiner, J., Allen, E., Wu, L. 2007. Smog Nitrogen and the Rapid Acidification of Forest Soil, San Bernardino Mountains, Southern California. The Scientific World. Vol 7:175-180 Simunek, J., Van Genuchten, M.T. 2007. Contaminant Transport in the Unsaturated Zone; Theory and Modeling. In: J.W. Delluer(ed.), The Handbook of Groundwater Engineering, 2nd ed. CRC Press, Boca Raton, FL. 22.1-22.46 Raats, P.A., Van Genuchten, M.T. 2006. Milestones in soil physics. Soil Science. Vol 171,Supp1:S21-S28. Nemes, A., Rawls, W.J., Pachepsky, Ya. A., van Genuchten, M. Th. 2006. Sensitivity analysis of the nonparametric nearest neighbor technique to estimate soil water retention. Vadose Zone Journal. 5:1222-1235. Liu, G., Li, B., Hu, K., Van Genuchten, M.T. 2006. Simulating the Gas Diffusion Coefficient in Macropore Network Images: Influences of Soil Pore Morphology. Soil Science Society of America Journal. Vol 70:1252-1261 Gargenas, A.I., Simunek, J., Jarvis, N., Van Genuchten, M.T. 2006. Two-dimensional modeling of preferential water flow and pesticide transport from a tile-drained field. Journal of Hydrology. Vol 329: 647-660 Ramos, T.B., Goncalves, M.C., Martins, J.C., Van Genuchten, M.T., Pires, F.P. 2006. Estimation of Soil Hydraulic Properties from Numerical Inversion of Tension Disk Infiltrometer Data. Vadose Zone Journal. Vol 5:684-696 Jacques, D., Simunek, J., Mallants, D., Van Genuchten, M.T. 2006. Operator-splitting errors in coupled reactive transport codes for flow and transport under atmospheric boundary conditions or layered soil profiles. Journal of Contaminant Hydrology. Vol 88:197-218 Lin, H., Bouma, J., Pachepsky, Y.A., Western, A., Thompson, J., Van Genuchten, M.T., Vogel Hans-Jorg, Lilly, A. 2006. Hydropedology: Synergistic integration of pedology and hydrology. Water Resources Research. [WO5301.doc:10.1029/2005WR004085.2006] (42):1-13. Illangasekare, T., Tyler, S.W., Clement, T.P., Villholth, K.G., Perera, A.P., Obeysekera, J., Gunatilaka, A., Hyndman, D.W., Cunningham, K.J., Kaluarachchi, J.J., Yeh, W.W., Van Genuchten, M.T., Jensen, K. 2006. Impacts of the 2004 tsunami on groundwater resources in Sri Lanka. Water Resources Research. Vol 42, W05201, doi:10.1029/2006WR004876. Castiglione, P., Shouse, P.J., Wraith, J.M. 2006. Multiplexer-induced interference on tdr measurements of electrical conductivity. Soil Science Society of America Journal. Vol. 70:1453-1458 Wang, H., Shan, X., Liu, T., Xie, Y., Wen, B., Zhang, S., Han, F., Van Genuchten, M.T. 2006. Organic acids enhance the uptake of lead by wheat roots. Planta. Vol.225:1483-1494 Williamson, T.N., Gessler, P.E., Shouse, P.J., Graham, R.C. 2006. Pedogenesis-Terrain Links in Zero-Order Watersheds after Chaparral to Grass Vegetation Conversion. Soil Science Society of America Journal. Vol 70:2065-2074