Nitrate leaching and nitrogen recovery following application of polyolefin-coated urea to potato

High N fertilizer and irrigation amounts applied to potato (Solanum tuberosum L.) on coarse-textured soils often result in nitrate (NO3) leaching and low recovery of applied fertilizer N. This 3-yr study compared the effects of two rates (140 and 280 kg N ha(-1)) of a single polyolefin-coated urea (PCU) application versus split applications of urea on 'Russet Burbank' potato yield and on NO3 leaching and N recovery efficiency (RE) on a loamy sand. Standard irrigation was applied in all years and excessive irrigation was used in another experiment in the third year. At the recommended rate of 280 kg N ha(-1), NO3 leaching during the growing season was 34 to 49% lower with PCU than three applications of urea. Under standard irrigation in the third year, leaching from five applications of urea (280 kg N ha(-1)) was 38% higher than PCU. Under leaching conditions in the first year (> or = 25 mm drainage water in at least one 24-h period) and excessive irrigation in the third year, PCU at 280 kg N ha(-1) improved total and marketable tuber yields by 12 to 19% compared with three applications of urea. Fertilizer N RE estimated by the difference and 15N isotope methods at the 280 kg N ha(-1) rate was, on average, higher with PCU (mean 50%) than urea (mean 43%). Fertilizer N RE values estimated by the isotope method (mean 51%) were greater than those estimated by the difference method (mean 47%). Results from this study indicate that PCU can reduce leaching and improve N recovery and tuber yield during seasons with high leaching.     

Endangered species: Deciding which species to save

Many species face extinction because preservation organizations do not have the resources to mount all of the interventions that are needed. Decision analysis provides techniques that can help managers of these organizations to make judgments about which species they will attempt to rescue. A formal analysis of the choices available to the US Fish and Wildlife Services' endangered species program with regard toIsotria medeoloides illustrates how the difficulties of making preservation decisions can be lessened.I. medeoloides is perhaps the rarest orchid in the United States. Little is known of the species' biology and less about effective management. Yet unless a preservation effort is mounted, the species will continue to be threatened by habitat destruction and botanical collecting. The analysis employs formal probabalistic techniques to weigh the utility of possible intervention strategies, that is, their likelihood of achieving different amounts of increase in the longevity of the species, and to balance these gains against their costs. If similar decision analyses are performed on other endangered species, the technique can be used to choose among them, as well as among strategies for individual species.     

Freshwater Wetland dynamics in South Kingstown,Rhode Island, 1939–1972

The extent and causes of changes in the fresh-water wetlands of South Kingstown, Rhode Island were determined through field work and through the analysis of panchromatic aerial photographs taken in 1939 and 1972. During this period, there was a net loss of 0.9 percent of the total area (2345.2 ha) of wetland present in 1939. Highway construction and residential development accounted for most of this loss. Approximately 17 percent of the wetland present in 1939 had changed sufficiently by 1972 to warrant reclassification. Plant succession alone accounted for 57 percent of the changes in wetland types, while man's activities were influential in 41 percent of the cases. Ninety-two percent of the natural changes in wetland types was progressive, while 58 percent of the changes induced by man and undetermined causes was retrogressive. Man's major role was to alter the water regimes and vegetation of wetlands. There was a decrease in wetland diversity as the most abundant type, wooded swamp, grew in area while the abundance of shallow marshes, meadows, and shrub swamps declined. A knowledge of wetland dynamics is essential in the management of wetlands for a diversity of wildlife and other natural values.     

Critical Review on the Public Health Impact of Norovirus Contamination in Shellfish and the Environment: A UK Perspective

We review the risk of norovirus (NoV) infection to the human population from consumption of contaminated shellfish. From a UK perspective, risk is apportioned for different vectors of NoV infection within the population. NoV spreads mainly by person-to-person contact or via unsanitary food handling. NoV also enters the coastal zone via wastewater discharges resulting in contamination of shellfish waters. Typically, NoV persists in the marine environment for several days, with its presence strongly linked to human population density, wastewater discharge rate, and efficacy of wastewater treatment. Shellfish bioaccumulate NoV and current post-harvest depuration is inefficient in its removal. While NoV can be inactivated by cooking (e.g. mussels), consumption of contaminated raw shellfish (e.g. oysters) represents a risk to human health. Consumption of contaminated food accounts for 3–11% of NoV cases in the UK (~74,000 cases/year), of which 16% are attributable to oyster consumption (11,800 cases/year). However, environmental and human factors influencing NoV infectivity remain poorly understood. Lack of standard methods for accurate quantification of infective and non-infective (damaged) NoV particles represent a major barrier, hampering identification of an appropriate lower NoV contamination limit for shellfish. Future management strategies may include shellfish quality assessment (at point of harvest or at point of supply) or harvesting controls. However, poor understanding of NoV inactivation in shellfish and the environment currently limits accurate apportionment and risk assessment for NoV and hence the identification of appropriate shellfish or environmental quality standards.     

Modeling Long‐Term Trends of Chlorinated Ethene Contamination at a Public Supply Well

A mass‐balance solute‐transport modeling approach was used to investigate the effects of dense nonaqueous phase liquid (DNAPL) volume, composition, and generation of daughter products on simulated and measured long‐term trends of chlorinated ethene (CE) concentrations at a public supply well. The model was built by telescoping a calibrated regional three‐dimensional MODFLOW model to the capture zone of a public supply well that has a history of CE contamination. The local model was then used to simulate the interactions between naturally occurring organic carbon that acts as an electron donor, and dissolved oxygen (DO), CEs, ferric iron, and sulfate that act as electron acceptors using the Sequential Electron Acceptor Model in three dimensions (SEAM3D) code. The modeling results indicate that asymmetry between rapidly rising and more gradual falling concentration trends over time suggests a DNAPL rather than a dissolved source of CEs. Peak concentrations of CEs are proportional to the volume and composition of the DNAPL source. The persistence of contamination, which can vary from a few years to centuries, is proportional to DNAPL volume, but is unaffected by DNAPL composition. These results show that monitoring CE concentrations in raw water produced by impacted public supply wells over time can provide useful information concerning the nature of contaminant sources and the likely future persistence of contamination.     

手性农药丁氟螨酯对斑马鱼胚胎的选择性发育毒性

近年来丁氟螨酯（CYF）对非靶标生物的发育毒性已成为一个值得关注的问题,但其对水生生物的对映选择性效应尚不清晰.为评估丁氟螨酯对斑马鱼胚胎的对映选择性毒性,通过96 h的暴露试验,研究了梯度浓度的丁氟螨酯消旋体及对映体对斑马鱼胚胎的急性毒性.此外,试验还研究了丁氟螨酯对斑马鱼胚胎孵化率、卵黄囊水肿、心包囊水肿和身体弯曲的影响.根据急性毒性结果可知,毒性大小为S-CYF > Rac-CYF > R-CYF,其中S-CYF的毒性是R-CYF的2.3倍.72 hpf,500 mg·L^-1的S-CYF可显著诱导胚胎产生卵黄囊水肿（YSE）、体轴弯曲（CB）等畸形效应（p<0.05）,而Rac-CYF降低了斑马鱼胚胎的孵化成功率.在本研究中发育毒性效应结果与急性毒性结果一致,均为S-CYF > Rac-CYF > R-CYF,表明丁氟螨酯对斑马鱼胚胎存在显著的对映选择性发育毒性,研究结果为丁氟螨酯的环境风险评估提供了理论依据.     

Kin conflict over caste determination in social Hymenoptera

We argue that caste determination, the process whereby females in the social Hymenoptera develop into either queens or workers, is subject to kin-selected conflict. Potential conflict arises because developing females are more closely related to their would-be offspring than to those of other females. Therefore, they may favour becoming queens contrary to the interests of other developing females and of existing queens and workers. We suggest two contexts leading to potential caste conflict. The first occurs when queens are reared in a reproductive phase following an ergonomic phase of worker production, while the second occurs when queens and workers are reared simultaneously. The first context assumes that workers' per capita contribution to colony survival and productivity falls with rising colony size. A critical feature influencing whether potential conflict is realized is the extent to which developing females can determine their own caste (“self-determination”). Self-determination is facilitated when female larvae control their own food intake and when queen-worker size dimorphism is low. We know of no strong evidence for actual conflict over caste fate arising in the first context. However, stingless bees and polygynous ants with excess queen-potential larvae that are either forced to develop as workers or are culled as adults demonstrate actual caste conflict in the second context. Caste conflict does not preclude caste regulation for “the good of the colony”, but such regulation is contingent on either the absence of potential conflict or on developing females losing control of their caste fate. Received: 22 March 1999 / Received in revised form: 15 June 1999 / Accepted: 19 June 1999