Effects of Water Management on the Wetlands of the Colorado River Delta, Mexico

The lower delta of the Colorado River has been severely affected by the upstream diversion of water for human use. No river water is officially appropriated to support delta wetlands, yet large marsh areas of conservation interest still exist below the agricultural fields in Mexico. These are supported by flood water, agricultural drainage water, municipal sewage effluent, and seawater in the intertidal zone. From 1973 to 1993 the area of freshwater and brackish marsh varied widely, from 5800 to 63,000 ha. A new opportunity exists to restore wetlands in the delta now that the upstream water impoundments on the Colorado River are filled and flood flows are once again being directed to the delta. But flood control structures now channel most of the flood water directly to the sea, and most of the effluent waters are deposited in evaporation basins rather than used to support wetlands. If the Yuma Desalting Plant in the United States becomes operational and if the Rio Hardy wetlands continue to be drained, the area of brackish wetlands could decrease to less than 2000 ha in the near future. Preserving the remaining wetlands will require a binational water management plan. The plan should maximize the benefits to wetlands of flood and irrigation return flows that enter the delta, and it should minimize flood risks.     

Separability, partial demand systems, and consumer's surplus measures

In practice, complete demand systems are not estimated. Rather, either an incomplete demand system is estimated, or separability is invoked and a partial demand system is estimated. This paper considers the relationship between the conventional compensating variation (equivalent variation) and the corresponding welfare measure that can be derived from a partial demand system and the current budget allocation to the separable group. Even assuming the separability assumption invoked is appropriate, these partial measures provide, in general, only a limited amount of information about the compensating variation and no information about the equivalent variation. Great care is therefore needed when using partial welfare measures to evaluate policy.     

Phenotype interactions in group behavior of honey bee workers (Apis mellifera L.)

Summary The alarm reaction of groups of honey bee workers was quantified using a metabolic bioassay. The genetic structure of these groups was varied in order to estimate the effects of worker interactions. Though the group phenotype was mainly determined by additive interactions, nonlinear effects were also found. Mixed worker groups, combined from colonies with similar reactivity in the bioassay, showed a stronger response than pure groups. This phenomenon, analogous to the overdominance model for individuals in classical genetics, has implications for mechanisms of natural and artificial selection in social populations and for the evolution of polyandry in social Hymenoptera.     

Queen number and the production of sexuals in the fire ant,Solenopsis invicta (Hymenoptera: Formicidae)

Summary To investigate the possibility of queen control over the production of sexuals in polygyne colonies of the fire ant, Solenopsis invicta, large colonies were divided into polygyne (P) and monogyne (M) or queenless (Q-) halves. Sexual larvae were evident in the M and Q- halves 3 to 4 days after colony division, whereas sexual forms failed to develop in all but one of the 32 P halves examined. Both male and female sexuals were produced in abundance in all M (n=25) and Q- (n=7) halves. Evidently, individuals capable of sexualization are present in colonies with many functional queens but are normally prevented from developing. Electrophoretic and morphometric analyses indicated that both haploid and diploid males were produced in the Q- halves, although diploids far outnumbered haploids. It thus appears that queens exert control over all potential and genetically determined sexuals regardless of sex or ploidy. The timing of the appearance of sexual forms following colony division suggests that queen control may be pheromonally mediated and inhibits the growth of sexuals late in larval development. An experiment in which the queens from M and P halves of colonies were exchanged demonstrated the reversible nature of this inhibition within colonies, but also suggested that once individual larvae develop beyond a critical point they are no longer subject to queen control. Despite seasonal variation in the production of sexuals in the field, no substantial differences between colonies collected in the summer and fall were found in their response to colony manipulations. The interaction of colony weight and number of queens present prior to colony division was associated with the number of males produced in the Q- halves, but no factors examined were associated with the number of females produced in these halves, or with the number of males or females produced in the M halves.     

Dominions and site-fixed aggressive behavior in breeding male Leucorrhinia intacta (Odonata: Libellulidae)

Summary We report aggressive spacing behavior in male dragonflies, Leucorrhinia intacta, that is characterized by variations in the probability of chasing conspecific male intruders within a defined area around a male's perch. The chase probability depends on the total intruder pressure and the behavior and distance of the intruder from the perched male (Fig. 2). This nonexclusive, site-fixed area has been called a dominion.We also examined the distribution of intruders among the various behavior-distance categories. Chase rates (per 15 min) were correlated mostly with number of intruders that hovered (rather than flew) close to the territorial male. Finally, we examined the impact of the changing chase probabilities on the variation in aggressive interactions as a function of intruder pressure. We conclude that, to some extent, territorial males stabilized defense costs across a variety of intruder pressures by maintaining dominions.     

Potential topsoiling strategies for enhancement of vegetation diversity on mined lands

Topsoiling methods may exert a strong influence on diversity of vegetation on mined lands. Actual. potential, and/or hypothetical effects of various topsoil application and management practices on diversity both within and among plant communities are discussed. Specific partices/principles addressed include direct place topsoiling, supplemental top-dressing, multiple lift topsoiling, topsoil management, topsoil depth, and selective soil handling.     

Trace Metal Distribution and Enrichment in Benthic, Estuarine Sediments: Southport Broadwater, Australia

The distribution and enrichment of selected trace metals (Cd, Cr, Cu, Ni, Pb, Sn, Zn) in benthic sediments of the Southport Broadwater, a semi-enclosed coastal body of water adjacent to the Gold Coast city, south-eastern Queensland, Australia, was studied with the objective of assessing the extent and degree of sediment contamination. Sediment samples from the 0–10 cm and 10–20 cm depth intervals of 32 sites within the Southport Broadwater and surrounding residential canals were analysed for particle size distribution, pH, organic C and ‘near-total’ major (Al, Ca, Fe, Mn) and trace (Cd, Cr, Cu, Ni, Pb, Sn, Zn) metal contents. Sediment contamination for each trace metal was assessed by (1) comparison with Australian sediment quality guidelines, (2) calculation of the index of geoaccumulation based on regional background values, and (3) geochemical normalisation against Al (i.e. the abundance of alumino-silicate clay minerals). Based on this approach, the results indicate that submerged sediments in the study area are not presently enriched with Cd, Cr or Ni, with the spatial distribution of these metals being very well explained by the abundance of alumino-silicate clay minerals. However, several sites were strongly enriched with Cu, Pb, Sn and Zn, arising from sources related to either urban runoff or vessel maintenance activities. The study indicates that several varying approaches are needed for a satisfactory assessment of contaminant enrichment in estuarine sediments.     

What Is Ecosystem Management?

The evolving concept of ecosystem management is the focus of much current debate. To clarify discussion and provide a framework for implementation, I trace the historical development of ecosystem management, provide a working definition, and summarize dominant themes taken from an extensive literature review. The general goal of maintaining ecological integrity is discussed along with five specific goals: maintaining viable populations, ecosystem representation, maintaining ecological process (ie., natural disturbance regimes), protecting evolutionary potential of species and ecosystems, and accommodating human use in light of the above. Short-term policy implications of ecosystem management for several groups of key actors (scientists, policymakers, managers, citizens) are discussed. Long-term (> 100 years) policy implications are also reviewed including reframing environmental values, fostering cooperation, and evaluating success. Ecosystem management is not just about science nor is it simply an extension of traditional resource management; it offers a fundamental reframing of bow humans may work with nature.     

Development of a continuously stirred flow cell for investigating sorption mass transfer

This paper introduces a new reversible-flow design for a continuously stirred reactor used to study sorption mass transfer in soil and solvent systems. The stirred reactor has potential advantages over conventional packed column or batch reactors because it isolates intraparticle sorption rate limitations from advective-dispersive transport, yet allows changes to flux through the reactor for analysis of sorption kinetics under dynamic conditions. Previously, stirred reactors have often failed due to clogging of sediment on the effluent frit. The reverse-flow backwashing design allows longer life and higher confidence in maintaining mixed conditions than previous designs. Mass transfer 'rate coefficients estimated from stirred and column experiments are compared; both techniques produced results consistent with a published correlation. The data also show that fitted sorption mass transfer coefficients can be strongly dependent on the choice of equilibrium partition coefficient (i.e. batch or first-moment derived values), and that the conventional two-site sorption kinetics model fails to accurately predict sorption mass transfer in the presence of changing solvent velocity through the reactor.