Water Quality in the River Delta Jaqueline García-Hernández, Ph.D. – Centro de Investigación en Alimentación y Desarrollo, Guaymas Unit

he health of the riparian ecosystem therefore expect salinity and selenium of the Delta depends concentrations to be at their maximum. ...riparian areas and T not only on the quantity of water Measurements along the mainstem of wetlands in the delta area available, but also on its quality. For the river in Mexico have shown salinity are supported primarily many years, the lower Colorado River has as high as 4,000 ppm and selenium up by irrigation runoff, and experienced high salinity and elevated to 6.3 ppb (Valdéz-Casillas et al., 2000), concentrations of selenium, a nutrient that supporting this argument. However, the several studies have can be toxic to wildlife. These problems associated riparian areas and wetlands in shown that agricultural are exacerbated as the river flows south, the delta area are supported primarily by practices do not appear and concentrations increase. Where the irrigation runoff, and several studies have to exacerbate salinity Colorado River reaches the Imperial , shown that agricultural practices do not and dissolved selenium about 20 miles north of the United States- appear to exacerbate salinity and dissolved concentrations there. Mexico border, concentrations of salinity selenium concentrations there (Radtke et and selenium are the highest measured al., 1988; García-Hernández et al., 2000; 880 mg/L at set by the U.S. in the United States, with specific García-Hernández et al., 2001). Bureau of Reclamation Colorado River conductance reaching 2,600 microseimens Basin Salinity Control Program. per cubic centimeter (µS/cm3) and Salinity Sources Salinity in the Colorado River primarily selenium at 2.0 micrograms per liter (µg/l, Selenium originates from geologic sources, saline ppb) in water and 7.1 micrograms per Dissolved selenium concentrations in gram (µg/g, ppm) in sediments (Radtke springs, and agricultural sources. Almost half the total salt load is from natural water from the lower Colorado River et al., 1988). In 1984, concentrations of sources, with irrigation return flows appear to have multiple origins. The selenium in sediments were five times adding more than one-third, and municipal natural weathering of seleniferous soils higher than the geochemical baseline and industrial sources responsible for the or rocks in the upper basin is attributed for soils from the western United States, small remaining portion. According to the to selenium concentrations of up to 1,300 which range from less than 0.39 to 1.4 U.S. Department of Interior, more than a ppb in shallow groundwater near upstream µg/g (Shacklette and Boerngen, 1984). million tons of salt per year will have to be reaches of the river (Presser et al., 1994), At the in Mexico, removed from 2003 until 2010 to maintain far exceeding the U.S. Environmental the terminus of the river, we would average salinity below the criterion of Protection Agency’s standard of 5 ppb for

Colorado River at its junction with Montague Island in the upper Gulf of . Photo by C. Valdes.

18 • January/February 2004 • Southwest Hydrology Water Quality in the Colorado River Delta Jaqueline García-Hernández, Ph.D. – Centro de Investigación en Alimentación y Desarrollo, Guaymas Unit

wildlife protection. Additional sources of dissolved selenium in the river may include the combustion of seleniferous coal at electric generating stations and the extraction of seleniferous ore deposits. All of these sources may contribute to the downstream loading and transport of selenium and hence its distribution Concentrations of selenium (Se) in fish and birds from the Colorado River delta wetlands, in ppm and availability for biaccumulation in dry weight (N = number of samples). the ecosystem (Radtke et al., 1988). The construction of , mining, and Other Contaminants and wildlife), cholinesterase inhibition in intensive agriculture activities may also Water quality in the Colorado River Delta birds exposed to pesticides, nest success increase the concentrations of salinity and is affected not only by salinity and natural of different species, and other studies will selenium in the lower Colorado River. elements such as selenium, but also by be necessary to protect the environmental raw sewage from the city of San Luis health of this rich and unique delta. In the Colorado River Delta, selenium and numerous agrochemicals, including Contact Jaqueline García-Hernández at is found in greater concentrations in organophosphorate and carbamate [email protected]. aquatic organisms compared to terrestrial pesticides. Most delta wetland ecosystems wildlife (see table). The selenium cycle are supported, however, by irrigation runoff References is enhanced in aquatic ecosystems due to from the local agricultural valleys. Although García-Hernández, J., E.P. Glenn, J. Artiola, and agricultural practices do not appear to D.J. Baumgartner. 2000. Bioaccumulation of selenium’s solubility and bioaccumulation selenium (Se) in the Cienega de Santa Clara first in sediments, then plants, fish, increase dissolved selenium concentrations Wetland, , Mexico, Ecotoxicology and and birds. Despite elevated selenium in water from the lower Colorado River Environmental Safety 45: 298-304. concentrations found in birds and bird and its delta, agricultural runoff can carry García-Hernández, J., K.A. King, A.L. Velasco, E. Shumilin, M.A. Mora, and E.P. Glenn. 2001. eggs in the delta wetlands, no evidence other contaminants such as pesticides, fecal Selenium, selected inorganic elements, and of deformed embryos has yet been found. coliforms, and other metals. organochlorine pesticides in bottom material and biota from the Colorado River Delta, However, continued monitoring will be Journal of Arid Environments 49(1): 65-89. Concentrations of dichlorodiphenyl- necessary to promptly detect any toxic Mora, M.A., and D.W. Anderson. 1995. Selenium, changes that may occur. dichloroethylene (DDE, a degradation boron, and heavy metals in birds from the product of DDT) in aquatic organisms and Mexicali Valley, , Mexico, Bulletin of Environmental Contamination and birds have been reported in several studies Toxicology 54: 198-206. conducted in the Colorado River Delta, Presser, T. S., M.A. Sylvester and W.H. Low. 1994. but show a marked decrease over time. Bioaccumulation of selenium from natural geologic sources in western states and its However, fish-eating birds like cormorants potential consequences, Environmental still show elevated concentrations of Management 18(3): 423-436. DDE. The presence of organochlorine Radtke, D.B., W.G. Kepner, and R.J. Effertz. 1988. compounds in wildlife is possibly due Reconnaissance investigation of water quality, bottom sediment, and biota associated with to the past intensive use of DDT in irrigation drainage in the lower Colorado River agriculture in the Mexicali Valley. Valley, , California, and , 1986- 87. Tucson, AZ, U.S. Geological Survey. Water- Resources Investigation Report 88-4002. The wetlands of the delta are inhabited Shacklette, H.T., and J.G. Boerngen. 1984. Element by a wide variety of wildlife, including concentrations in soils and other surficial the largest population of the endangered materials of the conterminous United States. U.S. Geological Survey Professional Paper Yuma clapper rail in the Ciénega de Santa 1270. Clara. For the protection of the wetlands Valdés-Casillas, C., O. Hinojosa-Huerta, E.P. Glenn, and its inhabitants, it is important to Y. Carillo-Guerrero, J. García-Hernández, F. Zamora-Arroyo, M. Briggs, and E. Chavarria- maintain an inventory of the chemicals Correa. 2000. Demonstration sites for present in delta wetlands, their behavior in wetland management in the Colorado River the system, and their effects on wildlife. delta. Reporte final para el Consejo para la Conservación de Humedales de Norteamérica Studies on concentrations of chemicals in Guaymas, Sonora, México. different matrices (water, sediment, soil, January/February 2004 • Southwest Hydrology • 19