分子表面积的解析计算和它与正辛醇/水分配系数的相关性

详细列出了分子表面积计算中所用的公式，并详尽地说明了所涉及各量的计算方法和应用注意的问题。在此基础上编写的ＳＡＳＡ程序成功地应用于酚取代衍生物，所得表面积对于氯化酚能很好地预言其正辛醇／水分配系数，但对于带７种不同取代基的酚取代衍生物，除了分子表面积，还必须引入代基当量作描述变量，才能较好地预言其正辛醇／水分配系数，而且个别化合物应 被看作ｏｕｔｌｉｅｒ，不能正确地被预言。     

Use of nucleic acids as indicators of growth in juvenile white shrimp,Penaeus vannamei

The use of nucleic acids to estimate crustacean growth is not well documented, and may be complicated by biochemical changes associated with their molt cycle. The objectives of this study were to assess the effects of molt stage on nucleic acid concentrations in abdominal muscle tissue of juvenile white shrimp,Penaeus vannamei, and to examine the relationship between nucleic acid concentrations and growth rates of shrimp exposed to different feeding regimes throughout a 12 d feeding experiment. RNA and DNA concentrations and RNA:DNA ratios were not significantly different among the five major molt stages early postmolt, late postmolt, intermolt, early premolt, and late premolt. In the feeding experiment, RNA concentrations and RNA:DNA ratios accounted for >70% of the variation in shrimp growth on three different sampling days. In addition, RNA concentrations and RNA:DNA ratios were used successfully to discriminate between unfed, moderately-fed, and well-fed shrimp. These variables exhibited significant treatment differences in <24 h after the initiation of the different feeding regimes, whereas significant changes in whole-body weight took longer to detect. Rapid detection of significant treatment effects can be useful in ecological studes, especially those concerned with food-web interactions.     

Absorption of decabromodiphenyl ether and other organohalogen chemicals by grey seals (Halichoerus grypus)

An input-output balance study was performed for polybrominated diphenyl ethers, polychlorinated biphenyls and some organochlorine pesticides on three captive, juvenile grey seals (Halichoerus grypus). The animals were fed a diet of herring for six months, during the last three months of which this study was performed. A supplement of decabromodiphenyl ether was included in the diet during the second month of the study. Consistently high absorption (>89%) was observed for all of the chemicals studied, whereas work on other animals has generally shown high (>80%) net absorption at log K(OW) < approximately 6, dropping towards higher log K(OW), and very low absorption of decabromodiphenyl ether. The half-life of decabromodiphenyl ether in blood was estimated to be between 8.5 and 13 days. Measurable concentrations of decabromodiphenyl ether were detected in seal blubber at the end of the study, indicating that this chemical can be stored in adipose and may bioaccumulate. Current understanding of the mechanism of absorption of organohalogen chemicals and the potential for accumulation of decabromodiphenyl ether will need reassessing in the light of these results.     

Analysis and structure prediction of chlorinated polycyclic aromatic hydrocarbons released from combustion of polyvinylchloride

Chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) released from combustion of polyvinylchloride (PVC) at different furnace temperatures were investigated. A laboratory-scale tube-type furnace with electric heating was utilized to control combustion conditions. Glass fabric filters and adsorbents were used to collect the combustion emissions. Following Soxhlet extraction, concentration and column chromatography purification, isomers separation, selective detection and identification of Cl-PAHs were performed on GC/MS system on the basis of retention data and mass spectra. Their quantification was accomplished by using external standard calibration technique. About 18 Cl-PAHs were determined, most of which were monochlorinated derivatives of naphthalene, biphenyl, fluorene, phenanthrene, anthracene, fluoranthene and pyrene. Only two dichlorophenanthrenes or anthracenes were identified. The possible positions of chlorine atoms attached to the aromatic rings are predicted by quantitative structure-property relationship. The levels of these compounds were in the range of 0.30-29.08 microg/g PVC. The relationship between the formation of Cl-PAHs and PAHs was discussed.     

基于遗传算法的PLS分析在QSAR研究中的应用

将遗传算法和偏最小二乘法结合应用于定量结构活性关系研究中 ,进行变量选择和建立最终模型 .以较少的变量个数包含较多的变量信息 ,且变量间没有线性相关问题 ,因而得到较好的 QSAR模型 .将这种方法应用于氯代酚和单取代苯 2种系列化合物 ,可以得到几种常规多元回归分析方法不能得到的质量较高的 QSAR模型 .     

Applications of Explicitly Incorporated/Post‐Processing Measurement Uncertainty in Watershed Modeling

In the field of watershed modeling, the impact of measurement uncertainty (MU) on calibration results indicates the potential issue of inaccurate model predictions. It is important to note that MU refers to the uncertainty in measured data such as flow and nutrient values that are used to evaluate model outputs. The calculation of error statistics assuming measured data are deterministic may not be appropriate as has been frequently stated in literature. Although MU can affect model calibration results, it is rarely incorporated in modeling practice. MU can be incorporated in two schemes: explicitly incorporated (MU‐EI) during model calibration and post‐processed (MU‐PP) after calibration is completed. In this study, both schemes are implemented in a case study of the Arroyo Colorado Watershed, Texas. Unexpectedly, no substantial differences were observed between each scheme for flow predictions. Although MU did not cause dramatic differences in most sediment and NH₄‐N predictions, error statistics were affected in cases with MU greater than 50%, especially for sediment and NH₄‐N. Therefore, it is concluded that MU may not exert a significant impact on model predictions until certain threshold is reached. This study demonstrates that high levels of uncertainty in measured calibration/validation data significantly affect parameter estimation, especially in the auto‐calibration process.     

Multilevel Water Governance and Problems of Scale: Setting the Stage for a Broader Debate

Environmental governance and management are facing a multiplicity of challenges related to spatial scales and multiple levels of governance. Water management is a field particularly sensitive to issues of scale because the hydrological system with its different scalar levels from small catchments to large river basins plays such a prominent role. It thus exemplifies fundamental issues and dilemmas of scale in modern environmental management and governance. In this introductory article to an Environmental Management special feature on “Multilevel Water Governance: Coping with Problems of Scale,” we delineate our understanding of problems of scale and the dimensions of scalar politics that are central to water resource management. We provide an overview of the contributions to this special feature, concluding with a discussion of how scalar research can usefully challenge conventional wisdom on water resource management. We hope that this discussion of water governance stimulates a broader debate and inquiry relating to the scalar dimensions of environmental governance and management in general.     

Soil microbial communities and enzyme activities under various poultry litter application rates

The potential excessive nutrient and/or microbial loading from mismanaged land application of organic fertilizers is forcing changes in animal waste management. Currently, it is not clear to what extent different rates of poultry litter impact soil microbial communities, which control nutrient availability, organic matter quality and quantity, and soil degradation potential. From 2002 to 2004, we investigated the microbial community and several enzyme activities in a Vertisol soil (fine, smectitic, thermic, Udic Haplustert) at 0 to 15 cm as affected by different rates of poultry litter application to pasture (0, 6.7, and 13.4 Mg ha(-1)) and cultivated sites (0, 4.5, 6.7, 9.0, 11.2, and 13.4 Mg ha(-1)) in Texas, USA. No differences in soil pH (average: 7.9), total N (pasture: 2.01-3.53, cultivated: 1.09-1.98 g kg(-1) soil) or organic C (pasture average: 25-26.7, cultivated average: 13.9-16.1 g kg(-1) soil) were observed following the first four years of litter application. Microbial biomass carbon (MBC) and nitrogen (MBN) increased at litter rates greater than 6.7 Mg ha(-1) (pasture: MBC = >863, MBN = >88 mg kg(-1) soil) compared to sites with no applied litter (MBC = 722, MBN = 69 mg kg(-1) soil). Enzyme activities of C (beta-glucosidase, alpha-galactosidase, beta-glucosaminidase) or N cycling (beta-glucosaminidase) were increased at litter rates greater than 6.7 Mg ha(-1). Enzyme activities of P (alkaline phosphatase) and S (arylsulfatase) mineralization showed the same response in pasture, but they were only increased at the highest (9.0, 11.2, and 13.4 Mg ha(-1)) litter application rates in cultivated sites. According to fatty acid methyl ester (FAME) analysis, the pasture soils experienced shifts to higher bacterial populations at litter rates of 6.7 Mg ha(-1), and shifts to higher fungal populations at the highest litter application rates in cultivated sites. While rates greater than 6.7 Mg ha(-1) provided rapid enhancement of the soil microbial populations and enzymatic activities, they result in P application in excess of crop needs. Thus, studies will continue to investigate whether litter application at rates below 6.7 Mg ha(-1), previously recommended to maintain water quality, will result in similar improved soil microbial and biochemical functioning with continued annual litter application.     

Long‐Term Water Quality and Biological Responses to Multiple Best Management Practices in Rock Creek,Idaho1

Abstract: Water quality and macroinvertebrate assemblage data from 1981 to 2005 were assessed to evaluate the water quality and biological responses of a western trout stream to the implementation of multiple best management practices (BMPs) on irrigated cropland. Data from Rock Creek near Twin Falls, Idaho, a long‐term monitoring site, were assembled from state and federal sources to provide the evaluation. Seasonal loads of the nonpoint source pollutants suspended sediment (SS), total phosphorus (TP), and nitrate‐nitrite (NN) were estimated using a regression model with time‐series streamflow data and constituent concentrations. Trends in the macroinvertebrate assemblages were evaluated using a number of biological metrics and nonmetric multidimensional scaling ordination. Regression analysis found significant annual decreases in TP and SS flow‐adjusted concentrations during the BMP implementation period from 1983 to 1990 of about 7 and 10%, respectively. These results are coincident with the implementation of multiple BMPs on about 75% of the irrigated cropland in the watershed. Macroinvertebrate assemblages during this time also responded with a change in taxa composition resulting in improved biotic index scores. Taxon specific TP and SS optima, empirically derived from a large national dataset, predicted a decrease in SS concentrations of about 37% (52 to 33 mg/l) and a decrease in TP concentrations of about 50% (0.20 to 0.10 mg/l) from 1981 to 1987. Decreasing trends in TP, SS, and NN pollutant loads were primarily the result of naturally low streamflow conditions during the BMP post‐implementation period from 1993 to 2005. Trends in macroinvertebrate responses during 1993 to 2005 were confounded by the introduction of the New Zealand mudsnail (Potamopyrgus  antipodarum), which approached densities of 100,000 per m² in riffle habitat. The occurrence of this invasive species appears to have caused a major shift in composition and function of the macroinvertebrate assemblages.     

Agent-based integrated assessment modelling: the example of climate change

Current approaches to deal with the socio-economic implications of climate change rely heavily on economic models that compare costs and benefits of different measures. We show that the theoretical foundations underpinning current approaches to economic modelling of climate change are inappropriate for the type of questions that are being asked. We argue therefore that another tradition of modelling, social simulation, is more appropriate in dealing with the complex environmental problems we face today.