Effects of initial irrigation,seeding date and directlyhauled topsoil on mined land community composition

This study was implemented to determine the effects of one, two, or three months of establishment irrigation, after spring or summer seeding on the long-term composition of mined land plant associations. While the treatment plots were seeded with the same diverse mixture of native species, floristic differences among treatment combinations were apparent after five growing seasons. Summer seeding enhanced the development of seeded warm-season grasses by retarding the initial development of seeded cool-season grasses and by limiting competitive effects of nonseeded species through seedbed tillage. Supplemental irrigation was substantially more important to the development of warm- than cool-season grasses. Seeded perennial forbs performed poorly on all treatments, presumably due to low seed viability, low germination, and/or competition from more water-responsive species. Despite drought conditions during plant establishment, supplemental irrigation was not critical to the ultimate development of nonseeded plant species when seedbed tillage occurred shortly after topsoil was applied. However, irrigation became more important to the long-term development of these species when tillage was delayed. Most forbs encountered were perennial natives that had volunteered from the direct-haul topsoil.Atriplex canescens was the only successful seeded shrub and performed particularly well on the summer seeded plot that received one month of initial irrigation.Authors are research plant ccologist and director of research. This contribution submitted as Montana Agricultural Experiment Station Journal Series No. J-1560. This study was funded entirely by the Western Energy Company, Butte, Montana. The authors express their appreciation to Bill Schwarzkoph and Joe Cocnenberg of Western Energy Company, and former Reclamation Research Unit members Ed DePuit, Chet Skilbred, and Steve Young for their participation in the early stages of this study.     

Feeding behavior in sexual and clonal strains of Poeciliopsis

Summary Sexual and clonal fish of the genus Poeciliopsis occur together in desert streams of Sonora, Mexico. Their coexistence has been explained in terms of niche partitioning for food and space. We examined predatory behavior that might influence niche relationships, and found significant differences among two coexisting sperm-dependent clonal strains and their two sexual progenitors. Handling time and prey manipulation of free-swimming (Artemia) and benthic (chironomid larvae) prey differed significantly among sexual and clonal strains. Analyses of gut contents from field-collected fish revealed that the laboratory estimates of predatory efficiency were related to their feeding behavior in nature. Behavior differences, such as those described herein, contribute to our understanding of the mechanisms of unisexual/bisexual coexistence in Poeciliopsis. Offprint requests to: R.C. Vrijenhoek     

“Applicability of the t-Test for Detecting Trends in Water Quality Variables,” by Robert H. Montgomery and Jim C. Loftis2

Montgomery and Loftis (1987) have listed several situations for which the t-test does not accurately reproduce Type I errors, and should therefore be avoided. Characteristics common to water quality data (skewness or other non-normality, presence of outliers and less-thans) also reduce the power of the t-test, in relation to nonparametric alternatives. Thus if one is interested in reaching correct decisions when trends or differences exist, and not just when they do not, the t-test should not be considered “robust” (in the sense of being generally applicable) when its assumptions are violated. Further, t-tests assume that differences in means are relevant (the mean is a good measure of central tendency), and that data groups differ by some additive amount. When all of these assumptions are recognized, and in light of the availability of truly robust and comparatively powerful non-parametric alternatives, we believe there is little applicability of the t-test for detecting trends or differences in water quality variables.     

Towards a national reference center for environmental information in The Netherlands: A review

For improvement of the accessibility and use of environmental information a prototype national reference center (CIMI) was constructed in the Netherlands in 1986. Target groups were identified on the basis of an analysis of the demand side. They were questioned about their needs in the field of environmental information. On the basis of these experiences an automated integrated system has been built that is composed of subsystems for reference to expertise in organizations (specialisms), literature, research, and databases of site-specific data. This system is also equipped with a thesaurus. The system has been tested and examined in several ways. The outcome of these independent tests and investigations confirm the usefulness of this center for information transfer. The reference center can be helpful in providing overviews on and structuring of environmental information in the Netherlands. The results of the activities have been presented in several ways and were described extensively in a number of reports.     

Soil- and surfactant-enhanced reductive dechlorination of carbon tetrachloride in the presence of Shewanella putrefaciens 200

Sorption of organic contaminants to soils has been shown to limit bioavailability and biodegradation in some systems. Use of surfactants has been proposed to reverse this effect. In this study, the effects of a high organic carbon content soil and a nonionic surfactant (Triton X-100) on the reductive dechlorination of carbon tetrachloride (CCl₄) were examined in anaerobic systems containing Shewanella putrefaciens. Although more than 70% of the added CCl₄ was sorbed to the soil phase in these systems, the reductive dechlorination of CCl₄ was not diminished. Rather, rates of CCl₄ dechlorination in systems containing soil were enhanced relative to systems containing non-sorptive sand slurries. This enhancement was also observed in sterile soil slurries to which a chemical reductant, dithiothreitol was added. It appears that the organic soil used in these experiments contains some catalytic factor capable of transforming CCl₄ in the presence of an appropriate chemical or microbial reductant. The addition of Triton X-100 to sand and soil slurries containing S. putrefaciens resulted in increased CCl₄ degradation in both systems. The effect of Triton could not be explained by: (i) surfactant induced changes in the distribution of CCl₄, (i.e. decreased sorption) or the rate of CCl₄ desorption; (ii) a direct reaction between Triton and CCl₄; or (iii) increased cell numbers resulting from use of the surfactant as a substrate. Rather, it appears that Triton X-100 addition resulted in lysis of bacterial cells, a release of biochemical reductant, and enhanced reductive transformation of CCl₄. These results provide insights to guide the development of more effective direct or indirect bioremediation strategies.