Riparian vegetation dynamics and evapotranspiration in the riparian corridor in the delta of the Colorado River, Mexico

Like other great desert rivers, the Colorado River in the United States and Mexico is highly regulated to provide water for human use. No water is officially allotted to support the natural ecosystems in the delta of the river in Mexico. However, precipitation is inherently variable in this watershed, and from 1981-2004, 15% of the mean annual flow of the Lower Colorado River has entered the riparian corridor below the last diversion point for water in Mexico. These flows include flood releases from US dams and much smaller administrative spills released back to the river from irrigators in the US and Mexico. These flows have germinated new cohorts of native cottonwood and willow trees and have established an active aquatic ecosystem in the riparian corridor in Mexico. We used ground and remote-sensing methods to determine the composition and fractional cover of the vegetation in the riparian corridor, its annual water consumption, and the sources of water that support the ecosystem. The study covered the period 2000-2004, a flood year followed by 4 dry years. The riparian corridor occupies 30,000ha between flood control levees in Mexico. Annual evapotranspiration (ET), estimated by Moderate Resolution Imaging Spectrometer (MODIS) satellite imagery calibrated against moisture flux tower data, was about 1.1myr(-1) and was fairly constant throughout the study period despite a paucity of surface flows 2001-2004. Total ET averaged 3.4x10(8)m(3)yr(-1), about 15% of Colorado River water entering Mexico from the US Surface flows could have played only a small part in supporting these high ET losses. We conclude that the riparian ET is supported mainly by the shallow regional aquifer, derived from agricultural return flows, that approaches the surface in the riparian zone. Nevertheless, surface flows are important in germinating cohorts of native trees, in washing salts from the soil and aquifer, and in providing aquatic habitat, thereby enriching the habitat value of the riparian corridor for birds and other wildlife. Conservation and water management strategies to enhance the delta habitats are discussed in light of the findings.     

Road de-icing salt as a potential constraint on urban growth in the Greater Toronto Area, Canada

North America's fifth most populated municipality--the Greater Toronto Area (GTA)--is undergoing rapid urban development with serious questions being raised regarding the long-term impacts of urban growth on the quality and quantity of ground and surface water. Degradation of groundwater quality by NaCl de-icing salt is the primary concern since there are no cost effective alternatives to NaCl de-icing salt and there is little evidence that salt loadings to the subsurface can be significantly reduced. In 2001, the issue acquired a new sense of urgency when de-icing chemicals containing inorganic chloride salts (with or without ferrocyanide de-caking agents) were designated as toxic under the Canadian Environmental Protection Act. To heighten concerns, future growth in the GTA will inevitably take place in areas where groundwater is regularly used for potable supply. Studies using groundwater flow and transport models show that significant deterioration of groundwater quality can be expected in shallow aquifers as a result of urban development with chloride concentrations approaching the drinking water quality standard of 250 mg/l. Results demonstrate that urban planning needs a fresh approach that explicitly includes groundwater protection and aquifer management in the decision-making process, clearly defines acceptable environmental performance standards and makes greater use of groundwater models to evaluate alternative urban designs.     

Methyl bromide as a building disinfectant: interaction with indoor materials and resulting byproduct formation

Several buildings were contaminated with Bacillus anthracis in the fall of 2001. These events required consideration of how to disinfect large indoor spaces for continued worker occupation. The interactions of gaseous disinfectants with indoor materials may inhibit the disinfection process, cause persistence of the disinfectant, and lead to possible byproduct formation and persistence. Methyl bromide (CH3Br) is a candidate for disinfection/deactivation of biological agents in buildings. In this study, 24 indoor materials were exposed to CH3Br for 16 hr at concentrations ranging from 100 to 2500 ppm in 48-L electropolished stainless steel chambers. CH3Br concentrations were measured during and after disinfection. Its interactions with materials were observed to be small, with nearly complete and rapid desorption. Between 3% and 8% of CH3Br adsorbed to four materials (office partition, ceiling tile, particle-board, and gypsum wallboard with satin paint), and the degree of adsorption decreased with increasing relative humidity. The percentage of adsorption to all other materials was <2%. This result suggests that when designing disinfection events with CH3Br, loss to indoor materials can be neglected in terms of disinfectant dose calculations. Possible reaction products were identified and/or quantified before and after exposure to CH3Br. Several monomethylated and dimethylated aliphatic compounds were observed in chamber air at low concentrations after the exposures of six materials to CH3Br. Concentration increases also occurred for chemicals that were observed to naturally off-gas from materials before exposure to CH3Br, suggesting that CH3Br may play a role in enhancing the natural off-gassing of chemicals, for example, by competitive displacement of compounds that already existed in the materials. The results described in this paper should facilitate the design of building disinfection systems involving CH3Br.     

Adaptation of a Canadian culpability scoring tool to Alberta police traffic collision report data

Objective: The objective of this study was to adapt a previously validated Canadian Culpability Scoring Tool (CCST) to Alberta police report data.

Methods: Police traffic collision reports from motor vehicle (MV) collisions in Calgary and Edmonton (Alberta, Canada) from 2010 to 2014 were used. Adaptation of the CCST was completed with input from personnel within Alberta Transportation, contributing to face and content validity. Two research assistants, given only the information necessary for scoring, evaluated 175 randomly selected MV–MV collisions. Interrater agreement was estimated using kappa (k) and reported with 95% confidence intervals (CIs). Discussion of disagreements between the research assistants and consultation from Alberta Transportation informed the algorithm used in the Alberta Motor Vehicle Collision Culpability Tool (AMVCCT). The AMVCCT was automated and applied to all motorists involved in collisions. Binary logistic regression was used to examine characteristics of the culpable and nonculpable drivers and their effects were reported using odds ratios (ORs) with 95% CIs.

Results: Interrater agreement for the random sample was excellent (k = 0.95; 95% CI, 0.92–0.99). Of those drivers hospitalized, 1,130 (37.54%) were rated not culpable and 1,880 (62.46%) were rated culpable. The odds of being culpable were higher for males than for females (OR = 1.43; 95% CI, 1.23–1.66). The odds of being culpable were higher in those impaired by alcohol than those considered “apparently normal” (OR = 61.10; 95% CI, 22.66–164.75). The odds of being deemed culpable, when compared with drivers >54 years old, were higher for those <25 years old (OR = 1.72; 95% CI, 1.35–2.20) and lower for those in the 40- to 54-year-old age group (OR = 0.78; 95% CI, 0.63–0.96). Driving between 12 a.m. and 6 a.m. resulted in higher odds of being culpable compare with all other 6-h time blocks. Direction and statistical significance remained consistent when applying the tool to all MV collisions. Sensitivity analysis including the removal of single vehicle collisions did not affect the direction or statistical significance of the main results.

Conclusions: The AMVCCT identified a culpable group that exhibited characteristics expected in drivers who are at fault in collisions. The age groups 25–39 and 40–54 demonstrated different results than the CCST. However, this is the only difference that exists in the findings of the AMVCCT compared to the CCST and could exist due to differences between the driving populations in Alberta and British Columbia. It is possible to adapt the CCST to provinces outside British Columbia and, in doing so, we can identify risk factors for collision contribution and not-at-fault drivers who represent the driving population.     

The interplay between incremental,transitional, and transformational adaptation: a case study of Canadian agriculture

Regional Environmental Change - We develop and apply a synthetic framework for understanding potential adaptations to climate change in the Canadian agriculture sector through a case study of...     

Facultative sex-ratio adjustment in Norway rats: litters born asynchronously are female biased

Summary Previously we reported that inter-litter competition reduces the survival of pups born to pairs of female rats living and breeding in the same nesting environment. Inter-litter competition occurred when females gave birth asynchronously; specifically, when a female gave birth in the presence of 15 to 28-day-old pups, her newborn pups were likely to die as a result of nest intrusion by the older pups. In contrast, inter-litter competition occurred rarely when the two females gave birth synchronously. Because theories of facultative sex ratio adjustment predict that mothers giving birth in unfavorable circumstances should bias their offspring towards the more viable or less expensive sex, we predicted that litters born asynchronously would be female biased. Conversely, we also predicted that females giving birth under favorable conditions, i.e., synchronously, would bias their litters toward males. We found a female bias in asynchronous litters, but did not find a male bias in synchronous litters. Moreover, in contrast to other reports in the literature, the female bias in asynchronous litters was achieved without a reduction in litter size. Based on correlational data, we suggest several mechanisms that could produce this female bias: conditions at fertilization and implantation, time since the male last mated and number of pups suckling concurrently during gestation. Correspondence to: M.K. McClintock     

Lead in New Orleans soils: New images of an urban environment

This paper describes a survey of lead in soil and computer generated maps that have been derived for New Orleans, Louisiana. The soil survey included streetside, houseside and open space samples. Because the survey covered every census tract in the metropolitan area it was possible to construct a computer-generated map of the distribution of lead dust in the soils of the urban environment. The data base consists of coordinates, site characteristics and lead analytical results of 3,704 soil samples. The resulting graphics show peaks of lead ranging from 600–1,200 g per g in the streetside soil of the inner-city and a steeply declining slope to the suburban areas of the city where the lead content of streetside soils is less than 75 g/g. In the inner-city, the amount of lead in soils found near building foundations is 10 to 20 times higher than the soils adjacent to streets where the median lead content of soils is over 300 g g^–1. In areas surrounding the city core (mid-city), the amount of lead next to the foundation and adjacent to the street are equivalent with medians of 110 g g^–1. In suburban locations, the median lead content of soil along streetsides is 86 g g^–1. Soils adjacent to surburban foundations has a median Pb content of 50 g g^–1. The lowest median lead content in soil is found in open spaces, ranging from 212 to 40 to 28 g g^–1, respectively, for the inner-city, mid-city, and suburbs. These observations are consistent with the production and consumer use of lead-based paint and leaded-fuels within the modern city.     

The prenatal diagnosis of the 48,xxyy syndrome

A 48,XXYY fetus was diagnosed prenatally in a 34-year old female who was seen at 18-5 weeks of pregnancy for genetic counselling and amniocentesis for advanced maternal age. The pregnancy was terminated, and skin and peripheral blood samples were obtained at the time of delivery. These samples also exhibited the 48,XXYY chromosomal complement.     

Effect of water content on transient nonequilibrium NAPL-gas mass transfer during soil vapor extraction

The effect of water content on the volatilization of nonaqueous phase liquid (NAPL) in unsaturated soils was characterized by one-dimensional venting experiments conducted to evaluate the lumped mass transfer coefficient. An empirical correlation based upon the modified Sherwood number, Peclet number, and normalized mean grain size was used to estimate initial lumped mass transfer coefficients over a range of water content. The effects of water content on the soil vapor extraction SVE process have been investigated through experimentation and mathematical modeling. The experimental results indicated that a rate-limited NAPL-gas mass transfer occurred in water-wet soils. A severe mass transfer limitation was observed at 61.0% water saturation where the normalized effluent gas concentrations fell below 1.0 almost immediately, declined exponentially from the initiation of venting, and showed long tailing. This result was attributed to the reduction of interfacial area between the NAPL and mobile gas phases due to the increased water content. A transient mathematical model describing the change of the lumped mass transfer coefficient was used. Simulations showed that the nonequilibrium mass transfer process could be characterized by the exponent beta, a parameter which described the reduction of the specific area available for NAPL volatilization. The nonequilibrium mass transfer limitations were controlled by the soil mean grain size and pore gas velocity, were well described by beta values below 1.0 at low water saturation, and were well predicted with beta values greater than 1.0 at high water saturation.