Progress 10/01/03 to 09/30/08
Outputs
OUTPUTS: The main output of this project has been publication of 21 peer-reviewed technical articles in journals read by soil scientists, water scientists, agronomists, environmental chemists, geochemists, limnologists, microbiologists, and biologists. In addition, several technical reports have been submitted to granting agencies and regulatory agencies interested in the management of agricultural wastewater and water quality. This work has been presented at national and international meetings including several invited presentations such as: the keynote speech at The International Salinity Forum (4/25-27/2005), Riverside CA; a California Department of Water Resources sponsored workshop on restoration alternatives for the Salton Sea (8/22/2005) in Sacramento, CA; Salton Sea Authority Technical Advisory Committee Meetings (2/2/2006 and 3/13/2006) in Salton City, CA; and two Community Forums entitled "Exposed: How the Plans for a Restored Sea Could Affect the Air You Breathe," sponsored by the Salton Sea Coalition and the American Lung Association (6/14/2006 in Palm Desert, CA and 6/15/2006 in El Centro, CA). In addition, this work has been presented at technical meetings and invited university presentations including: University of Las Vegas, Biology Department (2/10/2006), Purdue University, Department of Agronomy (9/11/2006); Universitat fur Bodenkultur Wien (University of Natural Resources and Applied Life Sciences), Department of Forest- and Soil Sciences, Vienna, Austria (5/8/ 2007); American Geophysical Union Annual Meeting (12/15/2006), San Francisco, CA; and European Geosciences Union General Assembly (4/19/2007), Vienna, Austria. The most significant output and dissemination activities have been the technical publications, which reach a wide audience of scientists, resource managers, farm advisors, and consultants in industry. In addition, the presentations, both to technical audiences and interested public audiences, were well attended and received. This work was highlighted in several local newspapers including the Orange County Register, Riverside Press Enterprise, and The Desert Sun in the Coachella Valley, CA. PARTICIPANTS: J.B. Geraci and J.R. Alder were undergraduate students in the Department of Environmental Sciences, U.C. Riverside who were co-authors on two of the technical journal publications. The contribution these undergraduate students made to this project was a unique training experience for these students. I.R. Rodriguez, J.P. de Koff, E. Wakefield, D.R. Hirmas, Y.A. Wood, B.K. Reese, J. Berkowitz, L.B. Mason, and B.D. Lee were graduate students in the Soil and Water Sciences graduate program in the Department of Environmental Sciences, U.C. Riverside. These students completed much of the research and were authors on 9 of the 21 technical journal publications. From this group of students, three completed Ph.D. degrees and six completed M.S. degrees. X. Yu was a Ph.D. graduate student in Environmental Engineering, UCR who worked on water treatment technology and was the senior author on three of the papers. M.A. Anderson, R.C. Graham, C. Chang, and W.T. Frankenberger, Jr. are professors in the Dept. of Environmental Sciences, UCR, who assisted with the research and writing of the papers, and served on committees of the graduate students. M.A. Deshusses and M.R. Matsumoto are professors in the Department of Environmental Engineering, UCR, who guided the studies of X. Yu. C.M. Grieve and J.A. Poss are research scientists at the USDA-ARS George E. Brown, Jr. Salinity Laboratory who participated on a project studying the reuse of saline drainage water for irrigation and were co-authors on a paper. C.C. Goodson, Z. Zhang, and L. Whiteaker were research staff in the Dept. of Environ. Sci., UCR. In addition, this projected spawned a collaboration with G. Schwartz, a research engineer at Kent SeaTech, a private company in the Coachella Valley. G. Schwartz was a coauthor on one of the papers and this work helped Kent SeaTech redirect their mission to the development of biodiesel from algae. TARGET AUDIENCES: Government agencies that were directly served by this project were: the U.S. Bureau of Reclamation, US Dept. of the Interior; US Dept. of Agriculture, Agricultural Research Service; the California Department of Water Resources; the Salton Sea Authority; and the U.S. Fish and Wildlife Service. Other organizations, companies, and private individuals that benefited from this work include: the Imperial Valley Farm Bureau, Imperial Irrigation District, Imperial and Coachella Valley farmers and farm advisors, Kent SeaTech, now Kent BioEnergy (a private company), and the citizens of the Imperial and Coachella Valleys. A large group of regulators and environmental scientists, chemists, agriculturalists, and consultants are using the technical research papers and reports for developing policy and management guidelines for wastewater. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
It has been estimated that 20% of all irrigation water used in the U.S. becomes agricultural wastewater, and in California, this volume may be as much as 30%. Treating this water before discharge is an often necessary to protect wildlife and downstream users. In addition, treatment can lead to direct reuse, thereby expanding our water supply. State and Federal agencies are currently evaluating options to mitigate damages to the Salton Sea, which is shrinking as California reduces its take of the Colorado River and transfers water to the metropolitan areas away from the farms in the Imperial Valley. The outcomes and impacts of this work are being used to address the issues of restoring the fish and wildlife habitat at the Sea, and beneficially using the agricultural drainage from the Imperial and Coachella valleys. Over the five years of this project, we have identified and tested new methods for treating wastewater to reduce its nutrient and contaminant load. In particular, we have developed a new method for removing phosphorus (P) from the wastewater and modeled the fate of P after it enters the Salton Sea. This has spawned an active area of research and commercial development to produce algae under conditions that optimize for phosphorus removal and production of algae that can be extracted for biodiesel fuel. A new company, Kent BioEnergy (formerly Kent SeaTech) in the Coachella Valley, has started producing algae for energy, biomass, and water treatment applications based on our work from this project. We have developed and tested a new method for removing selenium from agricultural wastewater. Selenium is a potent toxin in the aquatic food web and concentrations above 5 ppb in wastewater limit the reuse of the water for wildlife habitat and constructed wetlands. This new method reduces water soluble selenium to elemental Se using zero-valent iron and redox mediators. The treatment process is highly efficient, fast, and cost effective. Another outcome from this work has been a new understanding of the source of odors from the Salton Sea and how to control them. Hydrogen sulfide is a toxic gas that smells like rotten eggs and is produced in the sediments of the Sea due anaerobic microbial respiration of sulfate. The process is highly accelerated in the Salton Sea due to the abundance of algae and sulfate in the water. The garlic smell that emanates from the Sea is due to dimethylsulfide that is produced by diatoms in the Sea. The production of both of these gases is stimulated by the input of fertilizer nutrients (N and P) to the Salton Sea. We have quantified the flux of hydrogen sulfide to the atmosphere at 335 Mg per year from the surface of the Sea. For comparison, the total annual California statewide industrial emissions of hydrogen sulfide from facilities reporting under the Air Toxics Hot Spots Information and Assessment Act are 2,600 Mg per year, indicating that the Salton Sea is a significant source. This research has provided options for treating and reusing agricultural wastewater, and quantifying downstream effects of contaminants in the water.
Publications
- de Koff, J.P., Anderson, M.A., and C. Amrhein. 2008. Geochemistry of iron in the Salton Sea, California. Hydrobiologia 604:37-44.
- Geraci, J.B., Amrhein, C., and Goodson, C.C. 2008. Barnacle growth rate on artificial substrate in the Salton Sea, California. Hydrobiologia 604:77-84.
- Rodriguez, I.R., Amrhein, C., and Anderson, M.A. 2008. Laboratory studies on the coprecipitation of phosphate with calcium carbonate in the Salton Sea, California. Hydrobiologia 604:45-55.
- Rodriguez, I.R., Amrhein, C., Anderson, M.A. 2008. Reducing dissolved phosphorus loading to the Salton Sea with aluminum sulfate. Hydrobiologia 604:37-44.
- Anderson, M.A., Whiteaker, L., Wakefield, E., and Amrhein, C. 2008. Properties and distribution of sediment in the Salton Sea, California: An assessment of predictive models. Hydrobiologia 604:97-110.
- Graham, R.C., Hirmas, D.R., Wood, Y.A., and Amrhein, C. 2008. Large near-surface nitrate pools in soils capped by desert pavement in the Mojave Desert, California. Geology 36:259-262.
- Reese, B.K., Anderson, M.A., Amrhein, C. 2008. Hydrogen sulfide production and volatilization in a polymictic eutrophic saline lake, Salton Sea, California. Sci. Tot. Envir. 406:205-218.
- Zhang, Y., Amrhein, C., Chang, A., Frankenberger, Jr., W.T. 2008. Effect of zero-valent iron and a redox mediator on removal of selenium in agricultural drainage water. Sci. Tot. Envir. 407:89-96.
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Progress 01/01/07 to 12/31/07
Outputs
OUTPUTS: The overall objective of the project is to quantify the chemical, physical, and biological processes controlling the fate of contaminants in agricultural wastewater, irrigation water, and receiving waters. One of the specific objectives was to develop new methods to treat or reuse contaminated water. Laboratory, bench-scale, and field experiments were conducted to evaluate the effectiveness of treating drainage water and irrigation water using bacteria supported on zero-valent iron and redox mediators that accelerate selenium reduction by microorganisms. Important factors we considered were the amendment and contaminant concentrations, residence time, microbial densities, and type of redox mediators for the removal of redox-sensitive contaminants. A large field study on the Salton Sea was conducted to quantify the factors affecting hydrogen sulfide production and other organic sulfur compounds within the Sea and the fluxes from the sediments to the overlying water and to the
atmosphere. Flux calculations were used to quantify the amount of calcium carbonate that is forming in the Sea, which is an important sink for phosphate. Results of this original research were presented at the European Geosciences Union General Assembly in Vienna, Austria, April 2007, and at an invited talk at the University of Natural Resources and Applied Life Sciences, Vienna, Austria, May 2007.
PARTICIPANTS: C. Amrhein (PI). Lead on the project. Directly involved in planning, sampling, data collection, and reporting of results. M.A. Anderson (collaborator). Assisted with design, sampling, and report writing. B.K. Reese (M.S. student) Student trained on the project. X. Yu (Ph.D. student) Student trained on this project. W. Smith (Staff Research Associate). Assisted with data collection. M.A. Deshusses and M.R. Matsumoto (collaborators) Professor of Environmental Engineering at U.C. Riverside, assisted with manuscript editing. W.T. Frankenberger and A. Chang (collaborators). Professors of Soil Science at U.C. Riverside. Assisted with manuscript preparation. The Salton Sea Authority (partner organization).
TARGET AUDIENCES: The U.S. Bureau of Reclamation, Salton Sea Authority, Imperial Irrigation District, Coachella Valley Water District, Fish and Wildlife Service, Department of Fish and Game, California Regional Water Quality Control Boards, California Department of Water Resources, environmental scientists, geochemists, soil and water scientists, farm advisers, and residents of the Imperial and Coachella Valleys.
Impacts
In this reporting period there are two papers on the treatment and management of contaminated water. The first paper is the latest in a series on the use of zero-valent iron (ZVI) to remediate perchlorate-, selenium-, and arsenic-contaminated waters. This paper reports that perchlorate can be effectively removed from drinking water, groundwater, and agricultural wastewater using bacteria that obtain energy from ZVI and carbon from bicarbonate. The big advantage of this method is no organic matter is added to the water and excessive bacterial growth does not occur. The end product of perchlorate reduction is the harmless chloride ion. The results of this project have lead to a pilot-scale project to treat perchlorate-contaminated groundwater in southern California. The second paper investigates a new method to accelerate the reduction of selenium to elemental Se, which is insoluble and can be filtered from the wastewater. Redox mediators act as electron shuttles and are
not consumed in the reaction, thereby making them highly efficient and cost effective. Discharge of agricultural wastewater in the San Joaquin Valley and the Imperial Valley will likely require treatment to remove selenium and this research is finding ways to improve treatment technologies. Earlier work on the Salton Sea focused on methods of reducing nutrient loading. In this latest work, we investigated the biologically-produced hydrogen sulfide (H2S) and dimethylsulfide that form in the Sea as a result of excess nutrient loading. We quantified the fluxes of H2S from the sediments to the overlying water, and then to the atmosphere. We estimated that 58,000 Mg per year of H2S is transferred from the lake sediments to the overlying water. The volatilization of H2S was calculated to be 335 Mg per year. For comparison, the total annual California statewide industrial emissions of H2S from facilities reporting under the Air Toxics Hot Spots Information and Assessment Act is 2,600 Mg per
year. Thus, the Salton Sea is a significant source of H2S. Only 1 percent of the total H2S produced in the lake is volatilized and the remaining 99 percent is reoxidized within the water column. Extensive fish kills have been attributed to H2S and the associated low oxygen conditions. Concentrations of dimethylsulfide exceeded 6 uM in the surface water of the lake, which are the highest ever reported. State and Federal agencies are currently evaluating options to mitigate damages to the Salton Sea, which will greatly reduce in size due as California reduces its take of the Colorado River and transfers water to the metropolitan cities away from the farms in the Imperial Valley. Evaluating proposals to restore the fishery and wildlife habitat at the Sea requires and understanding of the chemical and biological processes that affect water and air quality in the area. This research is providing options for treating and reusing agricultural wastewater, and quantifying downstream effects of
contaminants in the water. Work on this project continues as mitigation projects at the Salton Sea are being developed and pilot projects have begun.
Publications
- Yu, X., Amrhein, C., Deshusses, M.A. and Matsumoto, M.R. (2007). Perchlorate reduction by autotrophic bacteria attached to zero-valent iron in a flow-through reactor. Environ. Sci. Tech. 41:990-997.
- Zhang, Y.Q., Zahir, Z.A., Amrhein, C., Chang, A., and Frankenberger, Jr., W.T., (2007). Application of redox mediator to accelerate selenate reduction to elemental selenium by Enterobacter taylorae. J. Agric. Food Chem. 55: 5714-5717.
- Amrhein C., Reese, B.K., and Anderson, M.A. (2007). Biogeochemistry of the Salton Sea, California. Geochim. Cosmochim. Acta 71: A21. Supplement.
- Reese, B.K., Anderson, M.A., and Amrhein, C. (2007). Inorganic carbon precipitation and anaerobic reactions in agricultural wastewater. Final Report to the Kearney Foundation of Soil Science. (15 pages).
- Reese, B.K., Anderson, M.A., and Amrhein, C. (2007). Hydrogen sulfide production and volatilization in the Salton Sea. Final Report to U.S. Bureau of Reclamation and TetraTech, Inc., Lafayette, CA. (45 pages).
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Progress 01/01/06 to 12/31/06
Outputs
Agricultural wastewater consists of subsurface drainage water and excess irrigation water that runs off the end of the field, called tailwater. In some areas, the subsurface drainage water percolates to groundwater, contaminating this resource. In other cases, subsurface drainage water and tailwater are combined and discharged to streams or rivers. In either case, the agricultural wastewater contains elevated concentrations of salt, fertilizer nutrients, naturally-occurring toxic trace elements, anthropogenic contaminants, and suspended solids (mud). Streams, rivers, and lakes receiving wastewater can be adversely impacted, and require mitigation and changes in farm management. In this reporting period there are four papers on the treatment and management of wastewater and irrigation water. Two of the papers are on the use of zero-valent iron (ZVI) to remediate perchlorate and arsenic contaminants in water. These papers continue last-year's work on the treatment of
selenium, molybdenum, and perchlorate with ZVI. ZVI is an excellent, low-cost reductant that can used to remove Se, Mo, As, and perchlorate (ClO4) from contaminated wastewater. The work has focused on understanding the mechanisms of removal, which differ for each of the contaminants. In particular, perchlorate reduction requires the presence of iron-oxidizing microbes which supply reactive hydrogen for the reduction reaction. The end products of perchlorate reduction are water and the harmless chloride ion. Significant work was accomplished on methods for controlling phosphorus and suspended solids in agricultural wastewater and phosphorus-impacted lakes. Both alum (aluminum sulfate) and PAM (polyacrylamide) are practical for the removal of phosphorus and suspended solids in agricultural wastewater and lake water. The removal of these contaminates reduces algae bloom in receiving waters and improves water quality for aquatic life and recreation. The last paper published this year
reports on the salt tolerance of a new cut-flower crop that could be grown commercially with saline wastewater.
Impacts
Irrigators are coming under increasing pressure to reduce the volumes and improve the quality of wastewater discharged from fields. It has been estimated that 20% of all irrigation water used in the U.S. becomes agricultural wastewater, and in California this volume may be as much as 30%. The implementation of total maximum daily loads (TMDL) for "impaired" water bodies throughout the U.S. is forcing farmers to identify methods of reducing contaminant discharges and reuse saline water to supplement fresh water supplies. California produces 60% of the domestically grown, commercially sold cut flowers in the U.S. Identifying new flower varieties that can be grown with saline water can provide grows with economical and environmentally sound water reuse options. This research is providing options for treating, reusing, and reducing agricultural wastewater.
Publications
- Yu, X., C. Amrhein, M.A. Deshusses, and M.R. Matsumoto. 2006. Perchlorate reduction by autotrophic bacteria in the presence of zero-valent iron. Environ. Sci. Tech. 40: 1328-1334.
- Berkowitz, J., M.A. Anderson, and C. Amrhein. 2006. Influence of aging on phosphorus sorption to alum floc in lake water. Water Research. 40: 911-916.
- Goodson, C.C., G. Schwartz, and C. Amrhein. 2006. Controlling tailwater sediment and phosphorus concentrations with PAM in the Imperial Valley, CA. J. Environ. Qual. 35, 1072-1077.
- Yu, X., C. Amrhein, Y. Zhang, M.R. Matsumoto. 2006. Factors influencing arsenite removal by zero-valent iron. J. Environ. Engin. 132: 1459-1469.
- Grieve, C.M., J.A. Poss, C. Amrhein. 2006. Response of Matthiola incana to irrigation with saline wastewaters. Hort. Sci. Vol. 41: 119-123.
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Progress 01/01/05 to 12/31/05
Outputs
NON-TECHNICAL SUMMARY: Fertilizer nutrients, toxic trace elements, and suspended solids are often discharged to lakes, rivers, and the ocean in agricultural wastewater. This work is directed at finding methods for treating wastewater and irrigation water that are effective, economical, and can be adapted on a large scale. OBJECTIVES: The specific objectives of the project are: 1. Identify ways to remove phosphate, selenium, arsenic, and suspended solids from the New, Alamo, and Whitewater Rivers, which flow into the Salton Sea. 2. Determine the chemical and biological reactions that control the solubility and biological availability of phosphate, selenium, arsenic, and other contaminants in the sediments of the New, Alamo, and Whitewater Rivers, and the Salton Sea. 3. Develop new methods to treat irrigation water contaminated with perchlorate. APPROACH: Laboratory, bench-scale, and field experiments were conducted to evaluate the effectiveness of treating drainage
water and irrigation water using adsorbents, flocculants, zero-valent iron, and polymers to remove suspended solids, phosphate, selenium, perchlorate, and arsenic. KEYWORDS: water quality; selenium; arsenic; perchlorate; phosphate; suspended solids; drainage; waste water; water management; waste management; water treatment; waste treatment; water chemistry; water pollution; pollution control; water resources; water; contaminants; water contamination; trace elements; toxic substances PROGRESS: 2005/01 TO 2005/12 Agricultural wastewater consists of subsurface drainage water and excess irrigation water that runs off the end of the field, called tailwater. Agricultural wastewater contains elevated concentrations of salt, fertilizer nutrients, naturally-occurring toxic trace elements, anthropogenic contaminants, and suspended solids (mud). Streams, rivers, and lakes receiving wastewater can be adversely impacted, and require mitigation and changes in farm management. In this reporting
period there are four papers on the treatment and management of wastewater and irrigation water. Three of the papers are on the use of zero-valent iron (ZVI) to remediate selenium, molybdenum, and perchlorate contaminants in water. In the first two papers we found that ZVI is an excellent reductant and can be use to precipitate Se and Mo from the wastewater. The third paper reports that ZVI alone does not capable of removing perchlorate from irrigation water. However, if the ZVI is colonized by iron-oxidizing bacteria, perchlorate can be converted to non-toxic chloride. Significant work was accomplished on methods for controlling phosphorus and suspended solids in agricultural wastewater. This work, reported in the fourth paper, focused on treating drainage water entering the Salton Sea, CA. In this study, aluminum sulfate and water-soluble polyacryamide were used to precipitate, flocculate, and settle phosphate and suspended solids from the drainage water. Removal of soluble P and
particulate-bound P will reduce the algal blooms in the Salton Sea, which contribute to the fish kills and bad smells at the Sea.
Impacts
IMPACT: 2005/01 TO 2005/12 Irrigators are coming under increasing pressure to reduce the volumes and improve the quality of wastewater discharged from fields. It has been estimated that 20% of all irrigation water used in the U.S. becomes agricultural wastewater, and in California this volume may be as much as 30%. The implementation of total maximum daily loads (TMDL) for "impaired" water bodies throughout the U.S. is forcing farmers to identify methods of reducing contaminant discharges. This research is providing options for treating, reusing, and reducing agricultural wastewater.
Publications
- Zhang, Y.Q., J.F. Wang, C. Amrhein, W.T. Frankenberger. 2005. Removal of selenate from water by zero-valent iron. J. Environ. Qual. 34: 487-495.
- Yu, X.Y., M.R. Matsumoto, C. Amrhein, and M. Deschusse. 2005. Perchlorate reduction by bacteria supported on zero-valent iron. Abstracts of papers of the American Chemical Society 229: U831-U831 034-ENVR Part 1.
- Mason, L.B., C. Amrhein, C.C. Goodson, M.R. Matsumoto, and M.A. Anderson. 2005. Reducing sediment and phosphorus in tributary waters with alum and polyacrylamide. J. Environ. Qual. 34:1998-2004.
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Progress 01/01/04 to 12/31/04
Outputs
Agricultural wastewater consists of subsurface drainage water and excess irrigation water that runs off the end of the field, called tailwater. These flows are frequently combined and discharged to streams or rivers. This agricultural wastewater contains elevated concentrations of salt, fertilizer nutrients, pest-control chemicals, naturally-occurring toxic trace elements, and suspended solids (mud). Streams, rivers, and lakes receiving wastewater can be adversely impacted, and require mitigation and changes in farm management. In this reporting period there are three papers on the treatment and management of wastewater. In the first paper, we studied the factors affecting the permeability of wastewater infiltration basins. We hypothesized that organic matter accumulation in the surface layers of these ponds was causing plugging and chemical oxidation of the surface layers might increase the performance of the ponds. We found that in-situ chemical oxidation actually
decreased the permeability due to the dispersion of clays and organic matter, which moved into conducting pores. Chemical oxidation was found beneficial in sand-washing operations currently being used to clean the ponds. In the second paper we report on the use of zero-valent iron for removing selenium, a toxic trace element, from agricultural wastewater. In this paper we found that elemental iron is an excellent reductant and can be use to precipitate Se from the wastewater. The third paper is a review of the chemical, microbial, and physical methods for treating selenium-contaminated drainage water. We evaluated the cost and effectiveness of ion-exchange, reverse osmosis, solar ponds, chemical reduction with zero-valent iron, micro-algal treatment, volatilization, biological precipitation, and flow-through wetlands to remove Se in wastewater. Advantages and disadvantage of each technology were discussed. Work continues on the use of borate salts (boric acid and sodium borates) in
sugar baits to control Argentine ants. This work has lead to the commercialization of borate-based ant baits that can be used in organic orchards and vineyards to control ants. Additional work was done on the mineralogical transformations that occur in upland versus wetland soils on an ultramafic parent material. This work adds to our understanding of soil forming processes. Significant work has begun on methods for controlling phosphorus and suspended solids in agricultural wastewater. This ongoing work is focused on treating drainage water entering the Salton Sea, CA. This drainage water has "impaired" the beneficial uses of the New, Alamo, and Whitewater Rivers which flow into the Salton Sea. We are doing lab and field studies on the use of aluminum sulfate and water-soluble polyacryamide for precipitating, flocculating, and settling phosphorus (P) and suspended solids (SS) from the drainage water. Removal of soluble P and SS-bound P will reduce the algal blooms in the Salton Sea,
which contribute to the fish kills and bad smells at the Sea. We expect publications from this work in the next reporting period.
Impacts
It has been estimated that 20% of all irrigation water used in the U.S. becomes agricultural wastewater. The establishment of total maximum daily loads (TMDL) for "impaired" water bodies throughout the U.S. is orcing farmers to identify methods of reducing contaminant discharges. This research will provide options for treating, reusing, and reducing agricultural wastewater.
Publications
- Zhang, Y., J. Wang, C. Amrhein, W.T. Frankenberger. 2004. Removal of selenate from water by zero-valent iron. J. Environ. Qual. (in press). 25 manuscript pages.
- Amrhein, C., J.R. Alder, R.C. Graham, V.K. Housel. 2004. Can chemical oxidation improve the permeability of infiltration basins? Water Environ. Res. 76:268-271.
- Lee, B.D., R.C. Graham, T.E. Laurent, C. Amrhein. 2004. Pedogenesis in a wetland meadow and surrounding serpentinitic landslide terrain, northern California, USA. Geoderma 118: 303-320.
- Klotz, J., M. Rust, C. Amrhein, R. Krieger. 2004. In search of the 'sweet spot:' A research review. Pest Control. September issue. p. 49-51.
- Frankenberger, W.T., C. Amrhein, T.W.M. Fan, D. Flaschi, J. Glater, E. Kartinen, Jr., K. Kovac, E. Lee, H.M. Ohlendorf, L. Owens, N. Terry, and A. Toto. 2004. Advanced treatment technologies in the remediation of seleniferous drainage waters and sediments. Irrigation and Drainage Systems 18: 19-41.
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