Accumulation of As, Pb, and Cu Associated with the Recent Sedimentary Processes in the Colorado Delta, South of the United States-Mexico Boundary

Abstract

Sediment cores from the Colorado River (CR) remnant delta were used to assess the changing sedimentation and pollutant deposition processes in response to extensive human manipulation of the river. The cores are formed of alternating layers of clays and silts, with isolated sandy horizons. The clayey units are interpreted as periods of flood flows into this low gradient and meandering estuary after dam construction in the United States. The geochemistry of these sediments is particular because of the association of MnO with CaO rather than with the Fe(2)O(3)-rich clays. Past pollution of the CR delta by As, and probably also Pb and Cu, is recorded in some cores. Enrichment factors (EFs) >1 for these elements and their statistical association suggest anthropogenic inputs. The most likely sources for these element enrichments (especially As) are the arsenate-based pesticides used intensively in the area during the first half of the 20th century. The transport of these elements from the nearby agricultural lands into the present river reaches appears to have been driven in part by flooding events of the CR. Flushing by river and tide flows appear to be responsible of a lower pollutant deposition in the CR compared to the adjacent Hardy River (HR). Arsenic in the buried clay units of the HR has concentrations above the probable toxic effect level (PEL) for dwelling organisms, with maximum concentrations of 30 microg g(-1). Excess (210)Pb activities ((210)Pb(xs)) indicate that fluxes of this unsupported atmospheric isotope were not constant in this estuarine environment. However, the presence of (210)Pb(xs) does indicate that these sediments accumulated during the last ~100 years. Aproximate sediment ages were estimated from the correlation of historic flooding events with the interpretation of the stratigraphic record. They are in fair agreement with the reported onset of DDT metabolites at the bottom of one core.

The effects of damming on the materials flux in the Colorado River delta

“…This water, however, is polluted due to agricultural and municipal water returns, as seen in the high concentration of Se and organochlorine pesticides in the biota from the estuary exceeding the toxic threshold in 23 and 30%, respectively (García-Hernández et al 2001). Also, a slight increase in As concentrations (up to 30 lg g -1 ) in sediment cores from the estuarine section have been associated with the main flooding events of the twentieth century (Daesslé et al 2009). Part of the estuarine basin of the Colorado River is regarded now as the agricultural ''sewer'' of the Wellton-Mohawk irrigational system of the Imperial Valley (González-Casillas 1991).…”

“…These clays are characterized by their relatively high metal contents and a characteristic partitioning of Mn within the more labile sediment phases (Daesslé et al 2002(Daesslé et al , 2004). It appears, however, that sediments from the upper Gulf of California (UGC) remain relatively unaffected by anthropogenic metal-input (Shumilin et al 2002), with only minor enrichments of As in buried (\1 m) sediments (Daesslé et al 2009). …”

Turnover and release of P-, N-, Si-nutrients in the Mexicali Valley (Mexico): Interactions between the lower Colorado River and adjacent ground- and surface water systems

“…In addition, toxic substances from land and subsurface runoff into the Colorado River basin have increased with the use of fertilizers (García-Hernández et al, 2013). Specifically, agricultural drains have increased organic and inorganic compounds including mercury, copper, arsenic and insecticides (DDT, DDE and DDD) in surface and groundwaters, wetlands and riverbeds (García-Hernández et al, 2013;Lugo-Ibarra et al, 2011;Rozemeijer et al, 2010;Daesslé et al, 2009).…”

Trace elements as tracers of environmental pollution in the canal sediments (alluvial formation of the Danube River, Serbia)

“…Trace element may be introduced into the aquatic systems by both natural processes (e.g., weathering and erosion) and as a result of human activities, for which reason they can be useful tracers of environmental pollution (Manta et al 2002). In recent years, investigations of these potentially toxic inorganic pollutants have increased (van Ryssen et al 1999;Li and Thornton 2001;Relić et al 2005;Silveira et al 2006;Farkas et al 2007;Daesslé et al 2009;Ahmad et al 2009;Morillo et al 2008;Egiarte et al 2009;Mil-Homens et al 2009;Nguyen et al 2009;Widmeyer and Bendell-Young 2008).…”