土地利用方式对土壤团聚体稳定性和有机碳含量的影响

探究不同土地利用方式下土壤团聚体的粒径分布、稳定性及有机碳在各粒径团聚体中的分布规律,以期为重庆地区土壤结构的改善及土壤有机碳库的维持及提高提供依据.以重庆市北碚区6种土地利用方式(针阔叶混交林、竹林、果园、旱地、水田和荒草地)为研究对象,采用湿筛法对土壤进行粒径分组,对比分析了6种土地利用方式处理下土壤团聚体和团聚体有机碳在0～20、20～40、40～60和60～100 cm土壤剖面中的分布规律.结果表明,不同土地利用方式下,土壤的结构和肥力水平存在显著的差异.在0～100 cm土层土壤的各粒径团聚体中,6种土地利用方式的团聚体粒径均以 0. 25 mm为主;其中,竹林 0. 25 mm团聚体含量最高,其次是荒草地,旱地与果园含量最低.不同土地利用方式下0. 25～2 mm的粒径团聚体主要分布在0～20 cm土层(28. 78%～50. 08%),而0. 053～0. 25 mm和0. 053 mm的粒径团聚体主要集中在40～60cm土层.在整个土壤深度内,竹林和荒草地的土壤团聚体MWD和GMD均高于其他土地利用方式,即二者的土壤团聚体稳定性较强.土壤团聚体稳定性与土壤团聚体有机碳呈极显著正相关(r=0. 569,P 0. 01),在0～100 cm土层中,土壤0. 25～2 mm和0. 053 mm粒径的有机碳含量较高,其中0. 25～2 mm的最高,平均含量为56. 54 g·kg~(-1).除旱地土壤各粒径团聚体有机碳含量在20～40 cm土层内最高,其他土地利用方式下土壤各粒径团聚体内有机碳含量均随土壤深度的增加而降低,表现出显著的表层富集现象.总体上,6种土地利用方式下,竹林和荒草地在各土层中的土壤团聚体稳定性较好,且在各土层中,竹林土壤各粒径团聚体有机碳含量最高.     

国家环境保护模范城市现状分析及展望

改革开放以来,在我国经济快速发展的同时,产生了巨大的环境问题,为此,原国家环保总局审时度势,开展了创建国家环境保护模范城市的活动。本文对“创模”考核指标的调整情况进行概括,从总体情况、所属行政区、所属行政区级别、面积4个方面对目前“环保模范”城市状况进行了深入地分析,并对日后的“创模”工作进行了展望。     

四川省农村环境空气污染源分布及其对自动监测点位设置影响的研究

将四川省农村地区分成平原和浅丘区、小起伏山地和高丘区、高山峡谷区三种类型区域。利用GIS软件,将四川省划分网格,分别统计每个网格中的工业废气污染点源数量和主要交通线路长度,得出四川省工业废气污染点源密度分级图和四川省主要公路密度分布图,以及结合农村污染面源的情况分析,总结出农村区域的主要污染密度分布类型。结果表明,在一定区域范围内,农村平原和浅丘区的工业源、交通源、农村面源分布均匀;高丘区、小起伏山区、高山峡谷区的污染源分布均具有明显的地理分布特性,山间平地和山谷台地的污染源分布密度高;根据四川省污染源分布规律给农村空气自动监测布点提供了指导。     

Incorporating low-resolution historic species location data decreases performance of distribution models

Developing robust species distribution models is important as model outputs are increasingly being incorporated into conservation policy and management decisions. A largely overlooked component of model assessment and refinement is whether to include historic species occurrence data in distribution models to increase the data sample size. Data of different temporal provenance often differ in spatial accuracy and precision. We test the effect of inclusion of historic coarse-resolution occurrence data on distribution model outputs for 187 species of birds in Australian tropical savannas. Models using only recent (after 1990), fine-resolution data had significantly higher model performance scores measured with area under the receiver operating characteristic curve (AUC) than models incorporating both fine- and coarse-resolution data. The drop in AUC score is positively correlated with the total area predicted to be suitable for the species (R² = 0.163-0.187, depending on the environmental predictors in the model), as coarser data generally leads to greater predicted areas. The remaining unexplained variation is likely to be due to the covariate errors resulting from resolution mismatch between species records and environmental predictors. We conclude that decisions regarding data use in species distribution models must be conscious of the variation in predictions that mixed-scale datasets might cause.     

Examining Flood Frequency Distributions in the Midwest U.S.1

Villarini, Gabriele, James A. Smith, Mary Lynn Baeck, and Witold F. Krajewski, 2011. Examining Flood Frequency Distributions in the Midwest U.S. Journal of the American Water Resources Association (JAWRA) 47(3):447‐463. DOI: 10.1111/j.1752‐1688.2011.00540.x Abstract: Annual maximum peak discharge time series from 196 stream gage stations with a record of at least 75 years from the Midwest United States is examined to study flood peak distributions from a regional point of view. The focus of this study is to evaluate: (1) “mixtures” of flood peak distributions, (2) upper tail and scaling properties of the flood peak distributions, and (3) presence of temporal nonstationarities in the flood peak records. Warm season convective systems are responsible for some of the largest floods in the area, in particular in Nebraska, Kansas, and Iowa. Spring events associated with snowmelt and rain‐on‐snow are common in the northern part of the study domain. Nonparametric tests are used to investigate the presence of abrupt and slowly varying changes. Change‐points rather than monotonic trends are responsible for most violations of the stationarity assumption. The abrupt changes in flood peaks can be associated with anthropogenic changes, such as changes in land use/land cover, agricultural practice, and construction of dams. The trend analyses do not suggest an increase in the flood peak distribution due to anthropogenic climate change. Examination of the upper tail and scaling properties of the flood peak distributions are examined by means of the location, scale, and shape parameters of the Generalized Extreme Value distribution.     

辽河口湿地土壤多环芳烃的分布与生态风险评价

2008年10月,2009年5月和8月分别对辽河口湿地土壤进行分层取样,利用GC-FID技术定量分析PAH含量.结果表明,不同站位表层土壤中PAHs总量变化范围为268.7-2853.8 ng·g<'-1>,平均值为1241.9ng·g<'-1>.2008年10月份土壤PAHs以高环为主,2009年5月和8月均是以低环...     

铅在搬迁企业原址场地土壤中的空间分布及生态风险

对重庆市某实施搬迁的烧结厂原址场地土壤中的铅进行了测定.采用富集系数法,研究了该企业原址场地土壤中铅的空间分布;采用Hakanson潜在生态危害指数法,评价了土壤铅的生态风险.研究表明,土壤总铅含量在23.4-8.90×10<'3>mg·kg<'-1>之间,其最大含量严重超过国家相应标准(HJ350-2007).土壤铅...     

镉胁迫下两种不同小白菜的生长、镉吸收及其亚细胞分布特征

通过室内溶液培养试验,研究了镉（0.5 m·gL-1、5.0 m·gL-1）胁迫对两个不同镉耐性小白菜品种上海青（Cd敏感型）和杭油冬（Cd耐性）的生长、Cd吸收及亚细胞分布的影响.结果表明,高Cd胁迫10 d后两个小白菜生长受到严重抑制,植物地上部和地下部Cd含量随着Cd处理浓度的增加而增加,且Cd主要积累在植物的根...     

Movement distances enhance validity of predictive models

Including the distance species are able to move in predictive models improves conservation practice. Bird inventory projects carried out from 1993 to 2004 in Taiwan provide an opportunity to investigate the relationships among species distribution, movement distance, and the environment. We compared projected distributions of 17 Taiwanese endemic bird species using what we called the Standard Method (i.e. movement distance is zero) and what we called the Buffer Method (i.e. movement distance is longer than zero) in three presence-only models (GARP, MAXENT and LIVES). The Standard Method used species original occurrence records directly while the Buffer Method expanded the occurrence of species to areas 1 km² around each recorded location. We first tested the efficacy of the Buffer Method using ten common species of the 17, and then applied the method to two rare species of the 17. For both the common and rare species, the distributions predicted by the two methods showed slight but important differences. The Buffer Method for all species had a higher average predictive probability, while the Standard Method had a higher maximum predictive probability. Most of the values for the area under the curve (AUC) were over 0.8 with the exceptions of Taiwan Barbet (Megalaima nuchalis) and Taiwan Hwamei (Garrulax taewanus), which have recently separated from Indochinese Barbet (Megalaima annamensis) and Chinese Hwamei (Garrulax canorus), and since 2008 and 2006 have been regarded as species endemic to the study area. Kappa values showed good performance for all species using both methods. The Buffer Method, however, resulted in significantly higher sensitivity and accuracy values for all models of species (p < 0.05). We conclude that when modeling species distribution including the area where the species was censused along with areas within the minimum movement areas better defines the surrounding areas that might supplement core habitat requirements. Therefore, using the Buffer Method, species surrounding distribution can be obtained which provides a better understanding of the species distributions. Given that distribution size is a key to the conservation of species, we suggest the Buffer Method can be used in conservation planning.