Kesterson Reservoir Research Articles

Use of Site-Specific Data for Modeling Selenium Bioaccumulation by Terrestrial Animals.

We developed a bioaccumulation model from an extensive set of monitoring data to predict selenium (Se) concentrations in biota within a terrestrial system (Kesterson Reservoir, CA). The model uses water-extractable Se and total Se concentrations in soil to estimate the expected mean and ranges of Se concentrations in biota at Kesterson for future scenarios. Biological monitoring data collected at Kesterson from 1989 to 1994 were used to parameterize the initial model. The model was tested and updated with additional sample results from 1995 through 2001 biological monitoring and validated and calibrated using Se concentrations from sampling conducted in 2004 and 2006. Minor adjustments were made to the model based on each additional year's results, and the model was used in 2014 to assess whether there were continuing threats to wildlife at Kesterson. The model predicts Se concentrations in small mammals, bird blood, and bird eggs in common species found at Kesterson. This model was used for the final assessment of Kesterson in 2014 and performed well, but there was variability in results, probably due to differences in individual diets and feeding ranges of animals. The model has been further refined since 2014, as we describe here. The model performs well for predicting central tendency and is conservative as the predicted upper limits of the biotic exposure distributions were mostly similar or higher than the measured. The trophic and tissue transfer factors and regression equations should be applicable to other Se-contaminated sites; adjusting weighting factors based on diet and range allows the model to be adapted and used at other sites.

Policy Innovation and Governance for Irrigation Sustainability in the Arid, Saline San Joaquin River Basin

This paper provides a chronology and overview of events and policy initiatives aimed at addressing irrigation sustainability issues in the San Joaquin River Basin (SJRB) of California. Although the SJRB was selected in this case study, many of the same resource management issues are being played out in arid, agricultural regions around the world. The first part of this paper provides an introduction to some of the early issues impacting the expansion of irrigated agriculture primarily on the west side of the San Joaquin Valley and the policy and capital investments that were used to address salinity impairments to the use of the San Joaquin River (SJR) as an irrigation water supply. Irrigated agriculture requires large quantities of water if it is to be sustained, as well as supply water of adequate quality for the crop being grown. The second part of the paper addresses these supply issues and a period of excessive groundwater pumping that resulted in widespread land subsidence. A joint federal and state policy response that resulted in the facilities to import Delta water provided a remedy that lasted almost 50 years until the Sustainable Groundwater Management Act of 2014 was passed in the legislature to address a recurrence of the same issue. The paper describes the current state of basin-scale simulation modeling that many areas, including California, are using to craft a future sustainable groundwater resource management policy. The third section of the paper deals with unique water quality issues that arose in connection with the selenium crisis at Kesterson Reservoir and the significant threats to irrigation sustainability on the west side of the San Joaquin Valley that followed. The eventual policy response to this crisis was incremental, spanning two decades of University of California-led research programs focused on finding permanent solutions to the salt and selenium contamination problems constraining irrigated agriculture, primarily on the west side. Arid-zone agricultural drainage-induced water quality problems are becoming more ubiquitous worldwide. One policy approach that found traction in California is an innovative variant on the traditional Total Maximum Daily Load (TMDL) approach to salinity regulation, which has features in common with a scheme in Australia’s Hunter River Basin. The paper describes the real-time salinity management (RTSM) concept, which is geared to improving coordination of west side agricultural and wetland exports of salt load with east side tributary reservoir release flows to improve compliance with river salinity objectives. RTSM is a concept that requires access to continuous flow and electrical conductivity data from sensor networks located along the San Joaquin River and its major tributaries and a simulation model-based decision support designed to make salt load assimilative capacity forecasts. Web-based information dissemination and data sharing innovations are described with an emphasis on experience with stakeholder engagement and participation. The last decade has seen wide-scale, global deployment of similar technologies for enhancing irrigation agriculture productivity and protecting environmental resources.

Kesterson Reservoir: 30 Years of Selenium Risk Assessment and Management.

Severe effects of selenium (Se) occurred among birds feeding and nesting at Kesterson Reservoir (San Joaquin Valley, California, USA) in 1983 to 1985. This paper describes the integration of site monitoring, risk assessment, and management actions conducted after the effects of Se were discovered. Selenium contamination of the site occurred over just a few years, but actions to resolve the contamination issues required >20 y. The reservoir, a series of 12 ponds totaling about 1280 acres (518 hectares), served for storage and evaporation of subsurface agricultural drainage. Selenium concentrations in reservoir inflow in 1983 were about 300 µg/L, primarily as selenate; within the ponds it was biogeochemically reduced to other inorganic and organic forms and bioaccumulated by biota or deposited to sediments. An estimated 9000 kg of Se were delivered to Kesterson in 1981-1986. A 1985 order required cleanup and abatement of the reservoir, so the United States Bureau of Reclamation and the US Department of the Interior undertook actions and studies to reduce hazards to birds. In 1988, about 1 million cubic yards (764 500 m3 ) of soil were used to fill portions of the reservoir, transforming it into terrestrial habitat. Intensive monitoring began in 1989 to assess the impact of the reservoir on wildlife, provide a basis for adjusting site management, verify the effectiveness of cleanup actions, and provide a basis for modifying future monitoring. Monitoring continued until 2014, with modifications and management actions based on results of 2 risk assessments (1993 and 2000). Monitoring results in 2013-2014 showed that Se concentrations were relatively stable over time and risks to wildlife were low. From the initial problem discovery to the conclusion of actions taken to remediate the site, combining responsive, reactive, and adaptive monitoring; modeling; risk assessment; and mitigation actions proved effective in solving the problem so that risks to wildlife were reduced to minimal levels. Integr Environ Assess Manag 2020;16:257-268. © 2019 SETAC.

Arthropod communities in a selenium-contaminated habitat with a focus on ant species

The selenium contamination event that occurred at Kesterson Reservoir (Merced Co., CA) during the 1970–80s is a frequently cited example for the negative effects of contamination on wildlife. Despite the importance of arthropods for ecosystem services and functioning, relatively little information is available as to the impacts of pollution on arthropod community dynamics. We conducted surveys of the arthropod community present at Kesterson Reservoir to assess the impacts of selenium contamination on arthropod diversity, with a focus on ant species richness, composition and density. Trophic groups were compared to determine which arthropods were potentially receiving the greatest selenium exposure. Plant samples were analyzed to determine the selenium content by site and by location within plant. Soil concentrations varied across the study sites, but not across habitat types. Topsoil contained higher levels of selenium compared to core samples. Plants contained similar concentrations of selenium in their leaves, stems and flowers, but flowers contained the greatest range of concentrations. Individuals within the detritivores/decomposers and predators accumulated the greatest concentrations of selenium, whereas nectarivores contained the lowest concentrations. Species composition differed across the sites: Dorymyrmex bicolor was located only at the site containing the greatest soil selenium concentration, but Solenopsis xyloni was found at most sites and was predominant at six of the sites. Selenium concentrations in ants varied by species and collection sites. Nest density was also found to differ across sites, but was not related to soil selenium or any of the habitat variables measured in our study. Selenium was not found to impact species richness, but was a significant variable for the occurrence of two out of the eight native species identified.

Science, policy, and management of irrigation-induced selenium contamination in california.

Selenium was recognized as an important aquatic contaminant following the identification of widespread deformities in waterfowl at the agricultural drainage evaporation ponds of the Kesterson Reservoir (California) in 1983. Since then, California has been the focal point for global research and management of Se contamination. We analyzed the history and current developments in science, policy, and management of irrigation-induced Se contamination in California. In terms of management, we evaluated the effects of improvements in the design of local attenuation methods (drainage reuse and evaporation ponds) in conjunction with the development of programs for Se load reductions at the regional scale (namely the Grassland Bypass Project). In terms of policy, the USEPA is currently working on site-specific water quality criteria for the San Francisco Bay Delta that may be a landmark for future legislation on Se in natural water bodies. We provide a critical analysis of this approach and discuss challenges and opportunities in expanding it to other locations such as the Salton Sea. Management lessons learned in California and the novel policy approach may help prevent future events of Se contamination.

The fall and rise of the wetlands of California's Great Central Valley

List of Illustrations Acknowledgments Introduction Part One. Wetlands and Waterfowl 1. The Nature of the Great Central Valley and the Pacific Flyway Part Two. The Fall 2. From Native American Lands of Plenty to Waste Lands 3. The San Joaquin Valley: A Tale of Two Basins 4. Reclamation and Conservation in the Sacramento Valley 5. The Sacramento--San Joaquin Delta and the Central Valley Project's Origins Part Three. The Rise 6. Turning the Tide: Federal and State Responses to the Waterfowl Crisis 7. Battles for the Grasslands and the San Joaquin River 8. Conflicting Agendas: New Refuges and Water Projects for the San Joaquin Valley 9. Tragedy at Kesterson Reservoir 10. Wetlands Resurgent: The Central Valley in the Twenty-First Century Epilogue: Global Climate Change and the Wetlands of the Great Central Valley Appendix. Animals and Plants of the Central Valley Discussed in the Text Notes Bibliography Index

Nest Box and Site Use by, and Selenium Concentrations in, American Kestrels at Kesterson Reservoir, Central California

Abstract During 1997 and 1998, we studied American Kestrels (Falco sparverius) using nest boxes at Kesterson Reservoir (Merced County, central California), a site with elevated soil selenium concentrations. We radiotagged male kestrels to determine their foraging ranges. Nest-box use was lower than expected; eleven nest boxes at Kesterson were used during the two years (16% and 20% occupancy) and five offsite nest boxes were used (60 and 40% occupancy). Kestrel pairs in 60% and 67% of onsite nest boxes that were used successfully fledged chicks in 1997 and 1998, respectively; pairs in offsite nest boxes had 100% (1997) and 50% (1998) success. Concentrations of Se in blood and eggs of kestrels at Kesterson were similar to concentrations in offsite kestrels. We analyzed 31 pellets and we used previously measured selenium concentrations in prey items from Kesterson to estimate dietary Se exposure of 8.1 µg Se/g for kestrels at Kesterson. We estimated that radiotagged male kestrels foraged onsite 58% of the t...

Small Mammals Collected from a Site with Elevated Selenium Concentrations and Three Reference Sites

Small mammals were trapped in July, August, and September 1999 at Kesterson Reservoir (Merced County, CA), a site with elevated concentrations of selenium (Se), and at three nearby reference sites. Deer mice (Peromyscus maniculatus) were the most frequently trapped species at all of the sites, and western harvest mice (Reithrodontomys megalotis) and house mice (Mus musculus) were also trapped frequently. About half the animals collected from the reference sites were in reproductive condition, compared to less than a quarter of the animals from Kesterson. A lower proportion of the deer mice trapped at Kesterson was male, compared to about half at the reference sites. Deer mice from Kesterson also tended to have a lower condition index (body weight/body length) than those from the reference sites. Mice from Kesterson had enlarged livers, based on a higher liver-to-body-weight ratio (% liver). Male mice from Kesterson tended to have a smaller anogenital distance than male mice from reference sites, suggesting some feminization of Kesterson mice. Mice from Kesterson had higher liver Se concentrations than mice from reference sites, and some mice from reference sites had surprisingly low liver Se concentrations. It is possible that the effects observed were caused by physical stressors at Kesterson such as lower water and food availability but it also suggests that long-term exposure to elevated levels of Se may be, in part, the cause of some of the differences observed in small mammals from Kesterson.

Selenium Accumulation in European Starlings Nesting in a Selenium-Contaminated Environment

Abstract I compared selenium (Se) levels in blood, liver, egg, and diet samples from European Starlings (Sturnus vulgaris) nesting at Kesterson Reservoir, Merced County, California and the surrounding area. Concentrations were highest in adult and nestling blood (8.3 and 5.5 µg g−1, respectively), nestling liver (7.5 µg g−1), and eggs (4.6 µg g−1) from nest boxes in interior parts of Kesterson compared to those from the perimeter (adult and nestling blood = 4.0 and 1.4 µg g−1, respectively, nestling liver = 4.7 µg g−1, eggs = 2.8 µg g−1) and off-site (nestling blood = 3.8 µg g−1, liver = 4.3 µg g−1, egg = 2.7 µg g−1). No hatching failure or embryo effects were observed. Although I found strong positive relationships in Se levels among tissues and eggs, variability of dietary exposure and differences in depuration rates across tissues confounds prediction of Se concentration. Nevertheless, I found blood Se to be a good indicator of dietary exposure that can be sampled nondestructively.

SELENIUM ACCUMULATION IN EUROPEAN STARLINGS NESTING IN A SELENIUM-CONTAMINATED ENVIRONMENT

Abstract I compared selenium (Se) levels in blood, liver, egg, and diet samples from European Starlings (Sturnus vulgaris) nesting at Kesterson Reservoir, Merced County, California and the surrounding area. Concentrations were highest in adult and nestling blood (8.3 and 5.5 µg g−1, respectively), nestling liver (7.5 µg g−1), and eggs (4.6 µg g−1) from nest boxes in interior parts of Kesterson compared to those from the perimeter (adult and nestling blood = 4.0 and 1.4 µg g−1, respectively, nestling liver = 4.7 µg g−1, eggs = 2.8 µg g−1) and off-site (nestling blood = 3.8 µg g−1, liver = 4.3 µg g−1, egg = 2.7 µg g−1). No hatching failure or embryo effects were observed. Although I found strong positive relationships in Se levels among tissues and eggs, variability of dietary exposure and differences in depuration rates across tissues confounds prediction of Se concentration. Nevertheless, I found blood Se to be a good indicator of dietary exposure that can be sampled nondestructively.

Reuse of agricultural drainage water in central California: phytosustainability in soil with high levels of salinity and toxic trace elements

Abstract Agricultural drainage waters in the western San Joaquin Valley of Central California contained high levels of salts, boron (B) and selenium (Se). Discharge of the drainage directly into the Kesterson Reservoir was hazardous to plants and wildlife. To investigate the plausibility of using plants as recipients for disposing of poor-quality drainage-waters, multi-year field studies were conducted to reuse drainage water on plants that are salt and B tolerant, and accumulate or stabilize soluble Se from the drainage. Installation of a subsurface tile drainage system in cropping fields allowed drainage waters to be collected and subsequently reused on tolerant plants. The tested plant species included Lactuca sativa, Lycopersicon esculentum, Gossypium hirsutum L., Medicago sativa L., Brassica napus var. Hyola, Helianthus annuus, Distichlis spicata L., and Salicornia bigelovii Torr. The quality of drainage water decreased along the water reuse path, with a sulphate-dominated salinity change from 4.5 to 15.2 dS m -1 ; soluble B from 3.4 to 14.5 mg L -1 ; and soluble Se from 0.08 to 1.18 mg L -1 . Soil salinity and concentrations of B and Se increased with decreasing quality of reused drainage waters. This study demonstrated the importance of monitoring changes in soil quality for sustaining such a plant-based system.

Selenium and nitrate removal from agricultural drainage using the AIWPS® technology

Monthly Maximum Discharge Limits (MMDL) have been established for selenium in irrigation drainage by the State of California and the U.S. Environmental Protection Agency following observations of avian teratogenesis at the Kesterson Reservoir in the San Joaquin Valley of California. As a result of these and other adverse effects, farmers and drainage districts on the western side of the San Joaquin Valley must reduce selenium concentrations in irrigation drainage discharged to the San Joaquin River. Drainage treatment will be required in the near future to meet existing MMDL and future Total Maximum Discharge Limits (TMDL) for the San Joaquin River. A 0.4-hectare Algal Bacterial Selenium Removal (ABSR) Facility was designed and constructed at the Panoche Drainage District in 1995 and 1996 using the Advanced Integrated Wastewater Pond Systems or AIWPS Technology. Each of two physically identical systems combined a Reduction Pond (RP) with a shallow, peripheral algal High Rate Pond (HRP). A Dissolved Air Flotation (DAF) unit and a slow sand filter were used to remove particulate selenium from the effluent of each system. The two systems were operated under different modes of operation and the bacterial substrate varied in each system. The rates of nitrate and selenium removal were compared. Microalgae were harvested using DAF and used as a carbon-rich substrate for nitrate- and selenate-reducing bacteria. Mass removals of total soluble selenium of 77% or greater were achieved over a three-year period. Nitrate and selenate were removed by assimiliatory and dissimiliatory bacterial reduction, and nitrate was also removed by algal assimilation. The final removal of particulate selenium is the focus of ongoing investigations. The removal of particulate selenium is expected to increase the overall removal of selenium to greater than 90% and would allow farmers and drainage districts to discharge irrigation drainage in compliance with regulatory discharge limits.

New evidence for the combined influence of vapor condensation and thermal convection on groundwater monitoring wells

Data from hydrogeochemical logging in two observation wells at the Kesterson Reservoir (Central Valley, California) are considered. The wells are equipped with polyvinyl chloride risers, the internal diameter of the wells is 10.16 cm. The logging used a multi-channel hydrogeochemical probe. Measurements were performed under undisturbed conditions and after purging the wells. Comparison of the logging data obtained before and after purging revealed that under undisturbed conditions water in the both wells was less mineralized and more oxidized than formation water. This can be explained by periodic condensation of air moisture on the internal surface of the well casing above the water level due to daily temperature variations at the site. Theoretical estimation shows that the depth–temperature distribution causes free thermal convection in the both wells that leads to a movement of less mineralized water from the top of the wells down to the well screens. This conclusion is confirmed by the characteristics of water salinity at the screen depths measured before and after purging.

Degradation of Aromatic Compounds Coupled to Selenate Reduction

The degradation of a range of aromatic compounds under selenate-reducing conditions was examined. Enrichment cultures were initiated with a 10% sediment slurry from the Arthur Kill, an intertidal strait in the New York/New Jersey harbor, and from the Kesterson Reservoir, California, with selenate as the sole electron acceptor. After repeated feeding, activity was maintained with either benzoate, 3-hydroxybenzoate, or 4-hydroxybenzoate as the sole carbon substrate. Degradation of the benzoic acid derivatives did not occur without the addition of selenate, or in sterile controls, indicating that substrate utilization was dependent on selenate reduction. Degradation of each of these aromatic compounds was coupled stoichiometrically to the reduction of selenate to selenite. Two selenate-reducing bacterial strains that utilized 4-hydroxybenzoate as a carbon source were isolated from the Arthur Kill and the Kesterson Reservoir, respectively. Based on analysis of their 16S rRNA gene sequences these isolates were 98.3% similar to one another, but distinct from other known Se(VI)-reducing bacteria. Phylogenetic analysis indicated that they were affiliated with the gamma subgroup of the Proteobacteria , with uncultured sulfur-oxidizing symbionts as their closest neighbors.

The birds of Kesterson Reservoir: a historical perspective

Beginning in the late 1970s, Kesterson Reservoir was used for disposal of subsurface drainage from agricultural fields in California's San Joaquin Valley. During 1983–1985, studies were conducted to evaluate the effects of chemicals in this agricultural drainwater on aquatic birds using Kesterson Reservoir. These studies included analyses of food-chain biota (such as plants, aquatic invertebrates, and fish) and bird tissues or eggs, as well as measuring adverse effects on health and reproduction of the birds. Results of the integrated set of field and experimental studies showed that selenium was the only chemical found at concentrations high enough to cause the adverse effects on bird health or reproduction that were observed. This article provides a summary of the field studies conducted at Kesterson Reservoir (and some of the related field and experimental studies conducted elsewhere) to evaluate the effects of irrigation drainage water contaminants on aquatic birds.

Selenium in Blood of Predatory Birds from Kesterson Reservoir and Other Areas in California

Kesterson Reservoir (Merced County, California) is a selenium-contaminated grassland (previously a wetland) that supports a variety of upland birds and other wildlife. Although aquatic birds that occupied a wet Kesterson Reservoir in the early to mid-1980s suffered high mortality and reproductive failure due to selenium exposure, similar effects have not been identified in terrestrial birds. To better characterize selenium exposure and potential effects in terrestrial species, we analyzed blood for selenium concentrations (blood-Se) from predatory bird species at Kesterson and reference areas in California from 1994 to 1998. Except for loggerhead shrikes (Lanius ludovicianus), blood-Se was significantly higher in birds from Kesterson than in birds from other areas. Among species at Kesterson, blood-Se was higher in loggerhead shrikes and northern harriers (Circus cyaneus) than in other species sampled, possibly due to shrikes spending a relatively large proportion of time foraging at Kesterson. In general, data corroborated earlier modeled predictions of selenium accumulation in Kesterson raptors. Calculated (based on blood-Se) but not observed selenium concentrations in eggs of predatory birds from Kesterson exceed a previously established avian toxicity threshold of 10 ppm.

Selenium Was a Time Bomb

At high dietary levels, selenium causes adverse effects in animals. Aquatic birds are among the more sensitive wildlife species, because their reproduction can be impaired when dietary selenium levels exceed about 4 µg/g (dry weight basis). Fish can also be adversely affected at similar dietary exposures. Conversely, low dietary levels of selenium (below about 0.1 to 0.5 µg/g) cause nutritional deficiencies in domestic animals, fish, and wildlife. Selenium became recognized as a significant environmental contaminant for wildlife in 1983, with the discovery of developmental abnormalities and excessive embryonic mortality in aquatic birds at Kesterson Reservoir, California. There are a number of environmental settings in which selenium warrants concern and must be considered carefully in relation to potential effects to fish and wildlife, and there may still be surprises in which it unexpectedly becomes a significant ecological issue. However, if selenium is included among the chemicals of potential ecological concern when ecological risk assessments are planned and conducted, there is enough information to thoroughly evaluate its environmental significance in much the same way as other contaminants. The main difference is that it is essential to have a good understanding of selenium's occurrence, complex biogeochemistry, and ecotoxicology to avoid serious errors.

Selenium

The 4 natural oxidation states of selenium are elemental selenium (0), selenide (-2), selenite (+4), and selenate (+6). Inorganic selenate and selenite predominate in water whereas organic selenium compounds (selenomethionine, selenocysteine) are the major selenium species in cereal and in vegetables. The principal applications of selenium include the manufacture of ceramics, glass, photoelectric cells, pigments, rectifiers, semiconductors, and steel as well as use in photography, pharmaceutical production, and rubber vulcanizing. High concentrations of selenium in surface and in ground water usually occur in farm areas where irrigation water drains from soils with high selenium content (Kesterson Reservoir, California) or in lakes receiving condenser cooling water from coal-fired electric power plants (Belews Lake, North Carolina). For the general population, the primary pathway of exposure to selenium is food, followed by water and air. Both selenite and selenate possess substantial bioavailability. However, plants preferentially absorb selenates and convert them to organic compounds. Aquatic organisms (e.g., bivalves) can accumulate and magnify selenium in the food chain. Selenium is an essential component of glutathione peroxidase, which is an important enzyme for processes that protect lipids in polyunsaturated membranes from oxidative degradation. Inadequate concentrations of selenium in the Chinese diet account, at least in part, for the illness called Keshan disease. Selenium deficiency occurs in the geographic areas where Balkan nephropathy appears, but there is no direct evidence that selenium deficiency contributes to the development of this chronic, progressive kidney disease. Several lines of scientific inquiry suggest that an increased risk of cancer occurs as a result of low concentrations of selenium in the diet; however, insufficient evidence exists at the present time to recommend the use of selenium supplements for the prevention of cancer. The toxicity of most forms of selenium is low and the toxicity depends on the chemical form of selenium. The acute ingestion of selenious acid is almost invariably fatal, preceded by stupor, hypotension, and respiratory depression. Chronic selenium poisoning has been reported in China where changes in the hair and nails resulted from excessive environmental exposures to selenium. Garlic odor on the breath is an indication of excessive selenium exposure as a result of the expiration of dimethyl selenide. The US National Toxicology Program lists selenium sulfide as an animal carcinogen, but there is no evidence that other selenium compounds are carcinogens.

CONTINUOUS MEASUREMENT OF DRAINAGE DISCHARGE

The west side of the San Joaquin Valley of California has had drainage disposal problems since irrigation wasintroduced in the early 1900s. Selenium toxicity problems associated with the Kesterson Reservoir caused closure of theexisting agricultural drainage system in 16 194 Ha (40,000 acres) in 1986. The continuing need for drainage of irrigatedagricultural lands has prompted several water management studies by the Water Management Research Laboratory of theUSDA. One of the essential data requirements in these studies is the quantification of drain flows. A measurement stationwas constructed for this purpose employing a manhole with a 90 V-notch weir and datalogging electronics to providehourly water flow data. Power was supplied by solar and conventional sources. Construction details, costs (for a solar-poweredstation), and resulting data are shown. As configured, the measurement station has provided seasonal datastreams for analysis during three years of operation.

Selenium accumulation in captive american kestrels (Falco sparverius) fed selenomethionine and naturally incorporated selenium

AbstractMale–female pairs of kestrels were maintained for 11 weeks on diets containing 5 or 9 ppm selenium (Se) (dry weight) as seleno‐L‐methionine, or naturally incorporated Se in the form of mammals collected at Kesterson Reservoir, CA, USA. Selenium concentrations in blood and excreta of male and female kestrels within groups were similar. Near‐maximal mean Se concentrations in blood were observed after the 5th week of treatment in the seleno‐L‐methionine‐treated kestrels, and an approximately 1:1 ratio was observed between maximal blood concentrations and dietary concentrations. All treatment groups exhibited reduction of Se concentration in excreta, but not in blood, to baseline values 4 weeks after treatment ended. No birds were observed to exhibit signs of general illness or Se toxicity during the study.