Soil Scientist   9611 South Riverbend Avenue Parlier, California 93648-9757 Phone: (559) 596-2870 Fax:  (559) 596-2851 sgao@fresno.ars.usda.gov     Research Interests Education Work Experience Selected Professional Affiliations and Service Honors and Awards Current Research Grants Publications Peer Reviewed Proceedings
Research Interests:   Source, transport, and fate of pollutants under various agronomic systems Redox chemistry and processes affecting the fate of pollutants Toxic trace element speciation and remediation Agricultural management practices to minimize fumigant emissions Analytical chemistry and instrumental analysis for environmental samples   ^Back to Top^
Education:   1992 - Ph.D. - Soil Science, University of California, Davis, CA 1985 - M.S. - Soil Science, Chinese Academy of Agricultural Sciences, Beijing 1982 - B.S. - Agricultural Chemistry, Hebei Agricultural University, China   ^Back to Top^
Work Experience:   2004 to present - Soil Scientist, USDA-ARS, Parlier, CA 1997 to 2003 - Assistant Research Soil/Water Scientist, University of California, Davis 1992 to 1997 - Postdoctoral Research Associate, University of California, Davis 1987 to 1992 - Research Assistant, University of California, Davis 1985 to 1987 - Research Associate, Chinese Academy of Agricultural Sciences, Beijing   ^Back to Top^
Selected Professional Affiliations and Service:   Associate Editor, Soil Science Society of America Journal (2005–present) Board Member, California Chapter of the American Society of Agronomy (2006–present); Committee Member of Undergraduate Scholarship and Graduate Research Poster Award (2007) Member, American Society of Agronomy/Soil Science Society of America (1989–present) Member, Environmental & Water Resources Institute, ASCE; also a member of Water Quality and Drainage Technical Committee (2005–present)           Member, Woman’s Soil Scientist Association (WSSA) (2001–present); Member, American Geophysical Union (1997–2005) Member, Division of Environmental Chemistry, ACS (1993–1996) Member, Hydrologic Sciences Graduate Group, UCD (1998–2004) Member of Ad Hoc Review Panel for the Graduate Research Award, the Consortium for Women and Research, UC Davis (2003–2004) Reviewer for Journals (J. Environ. Qual., Soil Sci. Soc. Am. J., Chemosphere, Water Air Soil Poll., Environ. Sci. Technol., Geochim. Cosmochim. Acta., Chem. Geol., Appl. Geochem., Irri. Sci.), and proposals (NSF, USDA-CSREES; CALFED; KFSS)   ^Back to Top^
Honors and Awards:   Gamma Sigma Delta Membership, 2003 The Best Research Paper in the Irrigation and Drainage Engineering Journal 2004, EWRI   ^Back to Top^
Current Research Grants:   Tanji, K.K. and S. Gao. Mechanisms of arsenic accumulation and biogeochemistry in evaporation ponds. 7/2004-6/2007, $107,000, UC Salinity/Drainage Program. Ajwa, H., S. Gao, D. Sullivan, R. Segawa, and D. Shatley. Reduce fumigant emissions using impermeable film and water seal in strawberry raised beds 2/2006-1/2008, $434,762, California Strawberry Commission, Gao, S. and T. Trout. Develop management practices using surface water seals and tarps to reduce fumigation emissions. 11/2005-10/2008, $275,396, California Department of Food and Agriculture (CDFA). Gao, S. and T. Trout. Developing methods to reduce emissions from soil fumigation. 7//2004-6/2007, $74,200, Almond Board of California. Gao, S., S. Schneider, A. Shrestha, and B. Hanson. Management practices to improve efficacy and reduce emissions of soil fumigants. $41,191 for 2006-2008, Fruit Tree, Nut Tree, and Grapevine (IAB). Hanson, B., S. Gao and others. Efficacy and 1,3-D emissions with approved nursery stock certification treatments applied with two shank designs. Pacific Area-Wide Pest Management Program for Integrated Methyl Bromide Alternatives – Fruit Tree, Nut Tree, Grapevine, and Rose Nursery Sector. 10/2006-09/2009. $70,944 (first year). Wang, D., S. Gao, and others. Methyl bromide alternatives for vineyard replant – assessment of control efficacy, fumigant movement, and crop response. Pacific Area-Wide Pest Management Program for Integrated Methyl Bromide Alternatives – Fruit Tree, Nut Tree, Grapevine, and Rose Nursery Sector. 10/2006-09/2009. $65,544 (first year).   ^Back to Top^
Publications: (For a list of Dr. Gao’s ARS Publications, click here.)   Peer-reviewed journal articles and book chapters   Gao, S. and K.K. Tanji. 1994. Modeling volatilization of selenium from Agricultural evaporation pond in San Joaquin Valley, California. J. Environ. Qual. 24:191–197. Herbel, M.J., K.K. Tanji, R.A. Dahlgren, and S. Gao. 1996. Acidification of agricultural evaporation ponds: effects on trace element chemistry in sediment-water core microcosms. J. Environ. Qual. 25:732–742. Herbel, M.J., R.A. Dahlgren, K.K. Tanji, and S. Gao. 1997. Acidification effects on trace element chemistry in agricultural evaporation pond sediments. J. Environ. Qual. 26:815–829 Gao, S., W.J. Walker, R.A. Dahlgren, and J. Bold. 1997. Simultaneous sorption of Cd, Cu, Ni, Zn, Pb, and Cr on soils treated with sewage sludge supernatant. Water Air Soil Poll. 93:331–345. Gao, S. and R.G. Burau. 1997. Environmental factors affecting rates of arsine evolution from and mineralization of arsenicals in soil. J. Environ. Qual. 26:753–763. Gao, S., K.K. Tanji, and S. Goldberg. 1998. Reactivity and transformation of arsenic. p. 17–38 In L.M. Dudley and J.C. Guitjens (eds.) Agroecosystems and the environment-sources, control, and remediation of potentially toxic, trace element oxyanions. Pacific Division of the American Association for the Advancement of Science, San Francisco, California. Gao. S., K.K. Tanji, D.W. Peters., and M.J. Herbel. 2000. Water selenium speciation and sediment Se fractionation in TLDD Flow-through wetland system. J. Environ. Qual. 29:1275–1283. Herbel, M.J., T.M. Johnson, K.K. Tanji, S. Gao, and T.D. Bullen. 2002. Selenium stable isotope ratios in California Agricultural Drainage water management systems. J. Environ. Quality. 31:1146–1156. Gao, S., K. K. Tanji, S.C. Scardaci, and A.T. Chow. 2002. Comparison of redox indicators in a paddy soil during rice-growing season. Soil Sci. Soc. Am. J. 66:805–817. Ryu, J., S. Gao, R.A. Dahlgren and R.Z. Zierenberg. 2002. Arsenic distribution, speciation and solubility in the shallow ground water of Owens Dry Lake, California. Geochim. Cosmochim. Acta. 66:2981–2994. Tanji, K.K., S. Gao, S.C. Scardaci, and A.T. Chow. 2003. Characterizing redox status of paddy soils with incorporated rice straw. Geoderma. 114:333–353. Gao, S., K.K. Tanji, D.W. Peters, Z. Lin and N. Terry. 2003. Selenium removal from irrigation drainage water flowing through constructed wetland cells with special attention to accumulation in sediments. Water Air Soil Poll. 144:263–268. Gao, S., K.K. Tanji, and S.C. Scardaci. 2003. Incorporating rice straw may enhance sulfide toxicity?  Calif. Agr. 57(2):55–59. Gao, S., K.K. Tanji, Z. Lin, N. Terry, and D. Peters. 2003. Selenium removal and mass balance in a constructed flow-through wetland system. J. Environ. Quality. 32:1557–1570. Chow, A.T., K.K. Tanji, and S. Gao. 2003. Production of dissolved organic carbon (DOC) and trihalomethane (THM) precursor from peat soil. Water Res. 37:4475–4485. Gao, S., R. Fujii, A.T. Chalmers, and K.K. Tanji. 2004. Evaluation of adsorbed arsenic and potential contribution to shallow groundwater in Tulare Lake bed area, Tulare Basin, California. Soil Sci. Soc. Am. J. 68:89–95. Chow, A.T., K.K. Tanji and S. Gao. 2004. Modeling drainwater selenium removal in wetlands. J. Irrig. Drain. Eng. 130(1):60–69. Gao, S., K.K. Tanji and S.C. Scardaci. 2004. Impact of rice straw incorporation on soil redox status and sulfide toxicity to plants. Agron. J. 96:70–76. Ryu, J., R.A. Dahlgren, S. Gao, and K.K. Tanji. 2004. Characterization of redox processes in shallow groundwater of Owens Dry Lake, California. Environ. Sci. Technol. 38:5950–5957. Chow, A.T., Guo, F., Gao, S., and Breuer, R. 2005. Pore size filter selection for characterizing dissolved organic carbon and trihalomethane precursors from soils.  Water Research 39:1255–1264. Gao., S, and K.K. Tanji. 2005. Eh. p. 464–469 In Water Encyclopedia. Volume 2. Water Quality and Resource Development. John Wiley and Sons, Inc. Chow, A.T., F. Guo, S. Gao, and R. Breuer. 2005. Trihalomethane formation potential of filter isolates of electrolyte-extractable soil organic carbon. J. Environ. Qual. 34:1992–1997. Chow, A.T., S. Gao., and R.A. Dahlgren. 2005 Physical and chemical fractionation of dissolved organic matter and trihalomethane precursors: A review. J. Water Supply: Research and Technol - AQUA. 54:475–507. Chow, A.T., F. Guo, S. Gao, and R. Breuer. 2006. Trihalomethane reactivity of water- and sodium hydroxide–extractable organic carbon fractions from Peat Soils. J. Environ. Qual. 35:114–121. Gao, S., S. Goldberg, M.J. Herbel, A.T. Chalmers, R. Fujii, and K.K. Tanji. 2006. Sorption processes affecting arsenic solubility in oxidized surface sediments from Tulare Lake Bed, California. Chem. Geol. 228:33-43. Chow, A.T., K.K. Tanji, S. Gao, and R.A. Dahlgren. 2006.  Temperature, water content and wet-dry cycle on DOC production and carbon mineralization in agricultural peat soils. Soil Biol. Biochem. 38:477–488. Chow, A.T., F. Guo, S. Gao, and R. Breuer. 2006. Size and XAD fractionations of trihalomethane precursors from soils. Chemosphere 62:1636-1646. Ryu , J., R.A. Zierenberg, R.A. Dahlgren, and S. Gao. 2006. Sulfur biogeochemistry and isotopic fractionation in shallow groundwater and sediments of Owens Dry Lake, California. Chem. Geol. 229:257-272. Gao, S. and T.J. Trout. 2006. Using surface water application to reduce 1,3-dichloropropene mission from soil fumigation. J. Environ. Qual. 35:1040-1048. Gao, S. and T.J. Trout. 2007. Surface seals to reduce 1,3-dichloropropen and chloropicrin emissions in field tests. J. Environ. Qual. 36:110−119. Gao, S, K.K. Tanji, and G.S. Bañuelos. 2007. Chapter 15. Processes and conditions affecting elevated arsenic concentrations in groundwaters of Tulare Basin, California, USA. p. 383−410. In P. Bhattacharya, A.B. Mukherjee, J, Bundschuh, R. Zevenhoven, and R.H. Loeppert (eds.) Trace metals and other contaminants in the Environment. Vol. 9 Elsevier Book Series, Elsevier. Herbel, M.J., D. Suarez, S. Goldberg, and S. Gao. 2007. Evaluation of chemical amendments for pH and redox stabilization in aqueous suspensions of three California soils. Soil Sci. Soc. Am. J. 71:927-939. Gao, S, J. Ryu, K.K. Tanji, and M.J. Herbel. 2007 Arsenic accumulation and speciation in evaporating waters of agricultural evaporation basins. Chemosphere. 67:862−871. Gao, S., K.K. Tanji, R.A. Dahlgren, J. Ryu, M.J. Herbel, and R. Higashi. (in press). Chemical status of selenium in evaporation basins for disposal of agricultural drainage. Chemosphere. Available online on 24 April 2007: http://www.sciencedirect.com/science/journal/00456535 Gao, S., T.J. Trout, S. Schneider. (in press). Evaluation of fumigation and surface seal methods on 1,3-dichloropropene and chloropicrin emissions in an orchard field trial. J. Environ. Qual.   ^Back to Top^   Proceedings   Chow, A.T., K.K. Tanji, and S. Gao. 2003. Modeling drain water selenium removal in vegetated wetlands. p.357-366 In A.J. Clemmens and S.S. Anderson (ed.) Proceedings of 2nd International Conference on Irrigation and Drainage. Water for a Sustainable World – Limited Supplies and Expanding Demand. Phoenix Arizona. May 12-15, 2003. U.S. Committee on Irrigation and Drainage, Denver, CO 80202. Chow, A.T., R.A. Dahlgren, S. Gao, F. Guo, and R. Breuer. 2004. Relationships between specific UV absorbance and trihalomethane precursors from water sources of the Sacramento-San Joaquin Delta, California. Proceedings. Annual Water Quality Technology Conference, American Water Works Association, November 14-18, 2004, San Antonio, TX. 13 p. Chow, A.T., F. Guo, S. Gao, and R. Breuer. 2004.  Filter pore size selection for characterizing trihalomethane precursors from California Delta soils.  Proceedings. Annual Water Quality Technology Conference, American Water Works Association, November 14-18, 2004, San Antonio, TX. 15 p. Gao, S., T. Trout, S. Schneider, H. Ajwa, and G. Browne. 2004. Distribution and dissipation of 1,3-D and chloropicrin after shank and drip applications in a clay loam soil. 2004 Proc. Annual Intern’l Res Conf on MeBr Alt. & Emiss. Red. p.801-804. Orlando, FL., Oct. 31-Nov. 3, 2004.  Available at http://www.mbao.org/2004/Proceedings04/mbrpro04.html. Trout, T. and S. Gao. 2004. Minimizing emissions from chloropicrin soil fumigation. p. 221-222 In 2004 Proc. 32nd Almond Industry Conf. Modesto, CA, Dec. 11-12, 2005. Gao, S., K.K. Tanji, and J. Ryu. Chemical Behavior of Selenium and Arsenic in a Saline Agricultural Drainage Disposal Pond Facility. International Salinity Forum, Riverside, CA, April 25-27, 2005. p. 185-188 In Oral Presentation Abstract.. Herbel, M.J., S. Gao, and T. Johnson. Selenium Transformations in Salinity-Affected Agricultural Drainage Water Management Areas of California as Determined by Selenium Stable Isotope Ratios. International Salinity Forum, Riverside, CA, April 25-27, 2005. p. 231-234. In Oral Presentation Abstract.    Gao, S., and T. Trout. 2005. Potential of using surface water applications to reduce fumigation emissions. p. 109 (1−4). In Proc. Annual Intern’l Res Conf on MeBr Alt. & Emiss. Red. San Diego, CA, Oct. 31-Nov. 3, 2005. Available at http://www.mbao.org/2005/05Proceedings/mbrpro05.html. Gao, S. and T. Trout. 2005. Surface water applications to reduce fumigant emissions. p. 235-241 In Proc. 33rd Almond Industry Conf., Modesto, CA, Dec. 7-8, 2005.. Shrestha, A., S. Gao, and T. Trout. Surface water applications for reducing emissions from Telone C35: Their effect on weed populations. p. 116(1–4) In Proc. Ann. Int. Res. Conf. on MeBr Alternatives and Emission Reductions. Orlando, FL, Nov. 6–9, 2006. Available at http://www.mbao.org/2006/06Proceedings/mbrpro06.html. Gao, S. and T. Pflaum. 2006. Trapping efficiency of cis-1,3-dichloropropene by XAD-4 sorbent tubes for emission studies. p. 121(1–4) In Proc. Ann. Int. Res. Conf. on MeBr Alternatives and Emission Reductions. Orlando, FL, Nov. 6–9, 2006. Available at http://www.mbao.org/2006/06Proceedings/mbrpro06.html. Gao, S. and T.J. Trout. 2006. Evaluation of water seals on Emission Reductions of 1,3-dichloropropene and chloropicrin. p. 9 (1– 4). In Proc. Ann. Int. Res. Conf. on MeBr Alternatives and Emission Reductions. Orlando, FL, Nov. 6–9, 2006. Available at http://www.mbao.org/2006/06Proceedings/mbrpro06.html. Gao, S., T. J. Trout, and S. Schneider. 2006. Soil fumigation and surface seal methods on 1,3-dichloropropene and chloropicrin emissions in an orchard replant field trial. p. 120(1–4) In Proc. Ann. Int. Res. Conf. on MeBr Alternatives and Emission Reductions. Orlando, FL, Nov. 6–9, 2006. Available at http://www.mbao.org/2006/06Proceedings/mbrpro06.html. McDonald, J., R. Qin, S. Gao, and T.J. Trout. 2006. Reduction of fumigant emissions using chemical and organic amendments. p. 125(1–4) In Proc. Ann. Int. Res. Conf. on MeBr Alternatives and Emission Reductions. Orlando, FL, Nov. 6–9, 2006. Available at http://www.mbao.org/2006/06Proceedings/mbrpro06.html. Qin, R., J. McDonald, S. Gao, B. Hanson, H. Ajwa, and T. Trout. 2006. The effect of ammonium thiosulfate on reducing fumigant concentration under tarp. p. 124(1–4). In Proc. Ann. Int. Res. Conf. on MeBr Alternatives and Emission Reductions. Orlando, FL, Nov. 6–9, 2006. Available at http://www.mbao.org/2006/06Proceedings/mbrpro06.html. Gao, S. and T. Trout. 2006. Surface water applications to reduce fumigant emissions. p. 262-270. In Proc. 34rd Almond Industry Conf., Modesto, CA, Dec. 6–7, 2006. Gao, S. and T. Trout. 2007. Minimizing emissions from soil fumigation by surface seal methods. p. 1-24. In Proc. International Conference on the Future of Agriculture: Science, Stewardship and Sustainability, August 7–9, 2006, Sacramento, CA. 2007 CD Track 1 – Pest and Nutrient Management. The Center of Hazardous Substance Research, Kansas State University, Manhattan, KS. Ajwa, H., S. Gao, D. Sullivan, R. Segawa, and D. Shatley. 2007. Method to Reduce Fumigant Volatilization Losses from Agricultural Fields. p. 93–96. In Proceeding 2007 CA-ASA Plant and Soil Conference, Feb. 6–7, Sacramento, CA. Available at http://calasa.ucdavis.edu. Gao, S. Irrigation management to minimize soil fumigant (Telone Product) emissions. Handout for 2007 DPR Symposium “VOC Reduction from Pesticides”, May 22–23, 2007, Sacramento, CA. 9 p. Presentation available at http://www.cdpr.ca.gov/docs/pur/vocproj/voc_symposium.htm.   ^Back to Top^