Osvel Hinojosa-Huerta

Flooding the Colorado River Delta: A Landscape‐Scale Experiment

A large pulse of water is planned to be released into the dry Colorado River channel in Mexico. This engineered experimental spring flood, which will flow from Lake Mead and pass through downstream reservoirs, is the culmination of decades of applied research. The pulse flow is a rare opportunity for research at the landscape scale [Glenn et al., 2013].

Reconciling Environmental and Flood Control Goals on an Arid-Zone River: Case Study of the Limitrophe Region of the Lower Colorado River in the United States and Mexico

Arid zone rivers have highly variable flow rates, and flood control projects are needed to protect adjacent property from flood damage. On the other hand, riparian corridors provide important wildlife habitat, especially for birds, and riparian vegetation is adapted to the natural variability in flows on these rivers. While environmental and flood control goals might appear to be at odds, we show that both goals can be accommodated in the Limitrophe Region (the shared border between the United States and Mexico) on the Lower Colorado River. In 1999, the International Boundary and Water Commission proposed a routine maintenance project to clear vegetation and create a pilot channel within the Limitrophe Region to improve flow capacity and delineate the border. In 2000, however, Minute 306 to the international water treaty was adopted, which calls for consideration of environmental effects of IBWC actions. We conducted vegetation and bird surveys within the Limitrophe and found that this river segment is unusually rich in native cottonwood and willow trees, marsh habitat, and resident and migratory birds compared to flow-regulated segments of river. A flood-frequency analysis showed that the existing levee system can easily contain a 100 year flood even if vegetation is not removed, and the existing braided channel system has greater carrying capacity than the proposed pilot channel.

CONCENTRATION OF CONTAMINANTS IN BREEDING BIRD EGGS FROM THE COLORADO RIVER DELTA, MEXICO

Organic contaminants (organochlorine [OC], organophosphorus [OP] pesticides and polychlorinated biphenyls [PCBs]), and metals (As, Cd, Hg, Pb, and Se) are a concern to avian health in the Colorado River delta, Mexico. We determined concentrations of contaminants in eggs of three breeding species of birds from the delta (mourning doves [Zenaida macroura], burrowing owls [Athene cunicularia], and marsh wrens [Cistothorus palustris]). We collected 27 eggs of mourning doves, eight eggs of burrowing owls, and 18 eggs of marsh wrens for analyses. Polychlorinated biphenyls, OC, and OP pesticides were analyzed by gas chromatography equipped with an electron capture detector, and metals were analyzed by inductively coupled plasma mass spectrometry. The non-ortho PCB congeners (PCB 77 and 126) were found in mourning dove and burrowing owl eggs at concentrations in which hatchability can be affected. Mean selenium concentration found in marsh wren eggs (5.6 microg/g dry wt) exceeded the level of concern. Arsenic and Cd were found at higher than normal concentrations, Hg concentrations did not exceed the level of concern in any of the species, and Pb concentrations were higher in eggs of species subject to hunting. With the exception of lead, marsh wren eggs contained the highest metal concentrations.

Evaluation of call-response surveys for monitoring breeding Yuma Clapper Rails (Rallus longirostris yumanensis)

Abstract During March–June 2000 we evaluated the use of call-response surveys to monitor breeding Yuma Clapper Rails (Rallus longirostris yumanensis) at the Ciénega de Santa Clara, Colorado River Delta, Sonora, Mexico. We assessed the effect that time of day, stage of breeding season, and number of survey periods had on the average number of rails detected at a station. Conducting call-response surveys resulted in a significant increase in the number of detected rails and reduced the coefficient of variation of the average number or rails per station, which increases the statistical power to detect population trends. Using this technique also appears to reduce the variation of rates of responses by rails through the breeding season when compared to passive listening. There was no difference between the number of rails detected during morning and afternoon surveys. The established protocol developed by the U.S. Fish and Wildlife Service for Yuma Clapper Rail surveys is adequate for monitoring, and it should continue to be implemented on a yearly basis at the Ciénega de Santa Clara and other wetlands of the Colorado River Delta in Mexico.