WSP12518 - Laserfiche WebLink

Home Browse Search

66 J. GARciA-HERNANDEZ ET AL. California 1,_ Colorado River 2" Geothermal lagoons 3.- Hardy River 4.- EI Mayor 5.- Cucapa complex 6.- Ayala drain 7,- Campo Rafael 8.- Zacatecas drain 9,- Laguna dellndio 10.- Canal Sonora 11.- Cienega de Santa Clara 12.- HI Doctor 13,- Bocana 14,- Upper Gulf t'V Streams Railroad tracks m WeIland area ~ 10 0 10 Figure 1. Colorado River delta ecosystems. Sampling locations are indicated with numbers. Hardy River-Cucapa wetlands complex (Fig. 1). Occasional flood releases into the delta (as much as 16 x I 09 m~ yr-I) have re-established an active floodplain from Morelos Dam on the border to the intertidal zone in the Gulf of California, and have res~ored a 14000-ha riparian corridor on the north (Zamora-Arroyo et al., 2001). Drainage wate~ from the Wellton-Mohawk Irrigation District in Yuma, Arizona, that began entering the eastern portion of the delta in 1977 created the Cienega de Santa ,Clara which is a cattail- (Typha domingensis) dominated marsh (Glenn et aI., 1996) (FIg. 1). These ecosystems cover an area of approximately 60,000 ?a an~ support a great number (up to 213 species) of birds (Glenn et aI., 1996; Valdes-CasIllas et aI., 1998). The Cienega de Santa Clara contains the largest populations of the endangered Yuma clapper rail (Rallus longirostris yumanensis) (Hinojosa-Huerta et aI., 2001) and desert pupfish (Cyprinodon macularius maculariuS) (Varela-~omer~ et aI., 1998). The riparian corridor is an important st~pover are~ ~or n,eotroplcal ";1lgrants. such as the endangered willow flycatcher (Emptdonax trazlln exumus) (Garcia-Hernandez et aI., 2001), and the intertidal mudflats, on the southern portion of the delta, are important ~or migratory and wintering waterfowl (Me\1ink et .aI., 1997). Two endangered man~e species, the totoaba fish (Totoaba macdonaldz) (Clsneros-Ma~ et al:, 1995) and vaquJta porpoise (Phocoena sinus) Oaramillo-Legorreta et aI., 1999) inhabIt the upper Gulf of California. ' . Contaminants derived from natural origin (e.g. selenium) and anthrop.ogemc activ- ities (e.g. pesticides, metals), are commonly found in the lower Colorado Rive~ an~ d~lta region and represent a potential threat to the. health of w~t1ands ~n~ theIr wlldbfe. Cretaceous marine sedimentary rocks or volcamc rocks are dlrect.or indIrect sou~ces of selenium in the western United States (Presser et aI., 199~). Selemum concentrations of 1300 ~g 1- I in water have been detected in shallow wells In the upstream reaches of the Colorado and Uncompahgre River Valleys in the States of Utah and Colorado (presser I I ~ l I i ~. f , € . i i SELENruM, SELECTED INORGANIC ELEMENTS FROM COLORADO RNER DELTA 67 et aI., 1994). Concentrations of selenium in the Colorado River are enhanced due to low rainfall and high evaporation, and topographically restricted basins. It is calculated that an average of 70 kg per day of selenium enters and leaves Lake Powell, fonned by Glen Canyon Dam, the northernmost dam on the mainstem of the Colorado River (Engberg 1992). ' Elevated concentrations of selenium in diet or in water have been associated with acute t?xicity, impaired reproduction.(including developmental abnormalities, embryo mortality, and reduced growth or SUrvival of young), pathological changes in tissues and chronic pOisoni?g of wil?life (Le~ly? 1986; Ohlendorf et aI., 1986, 1989; ~mlY, 1?93a!. According to vanous studIes In the Lower Colorado River selenium levels in bIrd tlSSU~S and prey species are within the toxic range where adverse effects on reproductlo~ could be expected (Rusk, 1991; King et aI., 1993, 1994, 1997, 2000; Lusk, 1993; Martinez, 1994; Welsh & Maughan, 1994; Mora & Anderson 1995' King & Baker, 1995; Garcia-Hernandez et aI., 2000). ' , According to the regional ecological authority in Mexico (Direcci6n General de Ecologia), the agricultural drainage system originating in the Mexicali Valley has a mean salinity o~ 3000.mg 1-,1" and carries a yearly mean of 70 x 106 kg of fertilizers and 400,000 bters of insectiCIdes (Valdes-Casillas et aI., 1998). The use of DDT was banned in Mexico for agricultural use in 1978 due to its persistence in the environment and to the rejection by other countries of DDT contaminated products (Canseco-Gonzalez et aI., 1997). Nevertheless, 230,000kg of DDT were used in 1971 in the Mexicali Valley, which ~eft resid.ual concentrations ofDDE in wildlife. However, breeding success of some species studIed (Cattle egret, Bubulcus ibis); was not seriously affected by this or other organochlorines (Mora, 1991; Mora et aI., 2001). The main objectives of the present study were to determine the distribution of selenium in bonom material and biota among different ecosystems in the delta relate these res~ts ~o the physico-chemical characteristics of each site, to find pattern~ that can be applied In the proper management of these areas, in order to restore or create wetlands that have less possibilities to accumulate selenium at concentrations above toxic th~esholds for wildlife. The final objective was to analyse biota for other potential contaminants such as metals and organochlorine pesticides. ~ F'" -.." c:.) W ['.) \" .,;.~ Materials and me~ods Study area Following is a description of the most important ecosystems found in the Colorado River delta (Fig. 1). Riparian corridor This area is a 100-kIn river stretch from Morelos Dam to the junction of the Colorado River with the Hardy River This 14,000-ha stretch contains a mixture of regenerated native trees and scrub vegetation. The most common species found in the area are: arrowweed, seepwillow (Baccharis salicifolia), willow (Salix gooddingiO and cottonwood trees (Populus jrernontiz), common reed (Phragmizes australis) and salt cedar (Tamarix ramosissima) (Zamora-Arroyo et aI., 2001). Hardy river I This is a reservoir of agricultural runoff from the Mexicali Valley (Fig. 1). Mean dissolved-solids content is 7000 mg I-I (Garcia-Hernandez, unpublished data) and vegetation is dominated by salt cedar.