ORIGINAL ARTICLE The effects of damming on the materials flux in the Colorado River delta Jose ´ D. Carriquiry • Julio A. Villaescusa • Vı ´ctor Camacho-Ibar • L. Walter Daessle ´ • Pedro G. Castro-Castro Received: 2 June 2009 / Accepted: 13 June 2010 Ó Springer-Verlag 2010 Abstract During the last century, the Colorado River delta (CRD) has been dramatically altered by the diversion of river water for use in human activities. This alteration has eliminated the delivery of fresh water to the Gulf of California radically transforming the former estuary into an inverse-estuary. Under the new conditions, the new mate- rials budget was estimated at the mouth of the Colorado River in terms of salts, total suspended sediments, organic suspended matter and nutrients. The results of this study show that, because of the asymmetry of the tidal wave, the variability of seston concentration follows a sedimentation pattern of three successive stages: re-suspension (erosion at ebb flow) [ dilution (during flood flow) [ sedimentation (at the end of the flood stage). The tidal asymmetry during neap tides was characterized by longer ebb (at least, 30 min longer) than flood and more intense ebb currents (as much as 43% higher), hence characterizing an ebb- dominated system. The CRD is characterized by high nutrients concentrations. Maximal levels are: nitrates (41 lM), phosphates (2.6 lM) and silicates (68 lM), nitrite (15 lM). The mass balance indicates that the system acts as a net exporter of suspended sediment with rates as high as 7 tons per tidal cycle. This behavior indicates that the CRD is in a destructive stage as a result of the lack of freshwater inflow and supply of sediment into the system. Keywords Sedimentation cycles  Delta  Sediment export  Estuarine fluxes  Nutrient balance  Tidal control Introduction The Colorado River basin is one of the most manipulated fluvial systems of the world. Once one of the greatest desert estuaries in the world, the delta of the Colorado River hosted vast riparian, freshwater, brackish and tidal wet- lands (McDougal 1904; Glenn et al. 1996). River diversion and dam construction during the twentieth century have not only severely transformed the hydrology of the fluvial system, but also impacted the ecology and sediment bud- gets of its delta, the upper Gulf of California and the northern Gulf of California. Due to erosion, the delta structure has shrunk approximately five times its historic size, and endemic species and fishery resources have been endangered or even become extinct (Thompson 1968; Glenn et al. 1996, 2001, Rowell et al. 2005, 2008). Before the construction of Hoover (1935) and Glen Canyon (1964) dams, river discharges to the delta region were estimated to reach 6,000 m 3 s -1 and the delta occupied 780,000 ha (Glenn et al. 1996). Using stable oxygen isotopic information from bivalve mollusk shells, it has been esti- mated that the mixing zone of marine and freshwater was located [ 65 km south of the mouth of the river (Rodriguez et al. 2001). However, after dam construction, practically no water flowed into the Gulf of California, and sediment supply to the estuarine basin decreased to \ 0.5% of the original annual sediment discharge calculated at 160 9 10 6 metric tons (van Andel 1964; Milliman and Meade 1983). Practically, no fresh water has reached the Colorado River delta (CRD) since dam construction, causing the J. D. Carriquiry (&)  J. A. Villaescusa  V. Camacho-Ibar  L. Walter Daessle ´  P. G. Castro-Castro Environmental Geosciences Research Group, Instituto de Investigaciones Oceanolo ´gicas, Universidad Auto ´noma de Baja California, Apdo. Postal # 453, Ensenada, Baja California, Mexico e-mail: carriquiry@uabc.edu.mx 123 Environ Earth Sci DOI 10.1007/s12665-010-0626-z