License extensions for clean-record drivers: A 4-year follow-up

Over 4,000,000 of California's 17,000,000 licensed drivers used to come to the California Department of Motor Vehicles (DMV) annually to take written and vision tests in order to renew their driver licenses. In an effort to increase public convenience and reduce costs, extension of the license by mail was implemented for selected groups of drivers with clean records over the life of their previous licenses. Continued implementation of the program was subject to evaluation of its effect on traffic safety. Since clean-record drivers make up about 50% of the renewal population, this program made it possible for some 2,000,000 drivers annually to avoid coming to the DMV for license renewal. Two studies of program safety effects were conducted, one evaluating a 2-year extension (760,000 subjects), and the other a 4-year extension (407,000 subjects). Random assignment to a group offered extension by mail or to a control group undergoing standard renewal testing and procedures was followed by careful tracking of accident and conviction activity. During the 48-month period following mailing of renewal notices or extension offers, the extension group had a slightly higher accident rate than did the in-person renewal group — an increase of 1%, or 13 accidents for every 10,000 extension offers. Although this small increase in accident rate would translate into about 2,500 additional accident involvements per year if applied to the current volume of clean-record drivers eligible for extension, statistical tests of significance indicated that the increase could easily be due to sampling error (p>.10). A supplemental Bayesian analysis resulted in a .24 probability that there was no true increase. The administrative cost savings attributable to the extension program were conservatively estimated to be $3,000,000 per year.     

Nutrient and sediment removal by a restored wetland receiving agricultural runoff

Few studies have measured removal of pollutants by restored wetlands that receive highly variable inflows. We used automated flow-proportional sampling to monitor the removal of nutrients and suspended solids by a 1.3-ha restored wetland receiving unregulated inflows from a 14-ha agricultural watershed in Maryland, USA. Water entered the wetland mainly in brief pulses of runoff, which sometimes exceeded the 2500-m3 water holding capacity of the wetland. Half of the total water inflow occurred in only 24 days scattered throughout the two-year study. Measured annual water gains were within 5% of balancing water losses. Annual removal of nutrients differed greatly between the two years of the study. The most removal occurred in the first year, which included a three-month period of decreasing water level in the wetland. In that year, the wetland removed 59% of the total P, 38% of the total N, and 41% of the total organic C it received. However, in the second year, which lacked a drying period, there was no significant (p > 0.05) net removal of total N or P, although 30% of the total organic C input was removed. For the entire two-year period, the wetland removed 25% of the ammonium, 52% of the nitrate, and 34% of the organic C it received, but there was no significant net removal of total suspended solids (TSS) or other forms of N and P. Although the variability of inflow may have decreased the capacity of the wetland to remove materials, the wetland still reduced nonpoint-source pollution.     

Laboratory evaluation of zero-valent iron to treat water impacted by acid mine drainage

This study examines the applicability and limitations of granular zero-valent iron for the treatment of water impacted by mine wastes. Rates of acid-neutralization and of metal (Cu, Cd, Ni, Zn, Hg, Al, and Mn) and metalloid (As) uptake were determined in batch systems using simulated mine drainage (initial pH 2.3-4.5; total dissolved solids 14000-16000 mgl(-1)). Metal removal from solution and acid-neutralization occurred simultaneously and were most rapid during the initial 24 h of reaction. Reaction half-lives ranged from 1.50+/-0.09 h for Al to 8.15+/-0.36 h for Zn. Geochemical model results indicate that metal removal is most effective in solutions that are highly undersaturated with respect to pure-metal hydroxides suggesting that adsorption is the initial and most rapid metal uptake mechanism. Continued adsorption onto or co-precipitation with iron corrosion products are secondary metal uptake processes. Sulfate green rust was identified as the primary iron corrosion product, which is shown to be the result of elevated [SO(4)(2-)]/[HCO(3)(-)] ratios in solution. Reversibility studies indicate that zero-valent iron will retain metals after shifts in redox states are imposed, but that remobilization of metals may occur after the acid-neutralization capacity of the material is exhausted.     

Evaluation of soil-washing process for “unwashable” clays and silts from the palmerton zinc site

The Palmerton Zinc Site is a Superfund site in Palmerton, Pennsylvania. Its former mineral processing operations have contaminated nearby wells and soils with zinc and cadmium. Preliminary analysis of soil and dust sampling conducted in May 1991 has revealed that the dust poses a potential threat to human health. Based on the results of a previous study, which showed a high percentage of silt and clay in soils from Palmerton residential properties, it was concluded that soil washing is not likely to be a viable method to treat the soil and dust contamination in Palmerton. However, since the completion of this study, a soil-washing process for “unwashable” clays and silts has been developed. A residential soil sample from Palmerton, which had low concentrations of arsenic, cadmium, and lead, and a somewhat high concentration of zinc, was washed in a bench-scale version of this process. The results showed that the new soil-washing process for “unwashable” clays and silts may be a viable method to treat the soil and dust contamination in Palmerton, depending on the soil quality criteria concentrations selected for site cleanup.     

Genetic evidence for multiple parentage in eastern kingbirds (Tyrannus tyrannus)

Summary Electrophoretic analysis was performed on 28 families of eastern kingbirds (Tyrannus tyrannus) from northern Michigan to estimate the occurrence of multiple parentage. Out of 19 families used in the final analysis, at least one putative parent was excluded in 9 families, or 18 out of 60 offspring (30% of offspring). Distribution of exclusion types conforms most closely to a model of quasi-parasitism, rather than extra-pair fertilizations, with secondary females laying their eggs in the primary female's nest, but random brood parasitism cannot be ruled out as an additional or alternative source of stray genes. Based on the model of random parasitism, an estimated 39% of all offspring in this population may be unrelated to one or both of the putative parents, or 53% based on a model of quasi-parasitism. Heretofore, eastern kingbirds have been considered to be exclusively monogamous; no behavioral evidence for alternative reproductive strategies has ever been reported for this species.     

Genetic Diversity in a Threatened Wetland Species, Helonias bullata (Liliaceae)

Genetic variation was examined in Helonias bullata , a threatened perennial plant species that occurs in isolated wetland habitats. Fifteen populations representing the species' geographic range were sampled. Genetic diversity was low for the species ( H _es = 0.053) as well as within populations ( H _ep = 0.029). Of the 33 allozyme loci examined, 11 (33%) were polymorphic, while on average only 12.8% (4) of the loci were polymorphic within populations. The number of alleles per polymorphic locus was 2.36 for the species and averaged 2.09 across populations. For every genetic parameter calculated, variation in H. bullata was lower than that typically found for narrowly distributed plant species. The lowest levels of genetic diversity were found in northern areas that were colonized following the last glacial epoch. The number of genotypes detected per population ranged from three to 21, with a mean of 13 for this clonally reproducing species. We found a relatively high proportion of total genetic diversity (30.6%) among populations and a significant correlation (p < 0.002) between genetic distance and geographic distance. Genetic drift phenomena appear to play a major role in the population genetics of this species. Anomalously, several populations that appeared most limited in size and vigor were genetically most variable, perhaps because they represent older, relictual populations. Life-history characteristics of H. bullata coupled with low levels of genetic diversity and the degradation and disappearance of wetlands threaten the existence of this species.