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71.
浑浊度对总氮测定影响的探讨 总被引:4,自引:0,他引:4
依据国家标准方法:碱性过硫酸钾-紫外分光光度法(GB1189—89)检测地表水中的总氮,通过实验分析发现,水样的浑浊度对波长在275nm处的吸光度值有严重影响,消解降低水样的浑浊度后,会使275nm处的吸光度值下降。 相似文献
72.
Wang L Brenden T Seelbach P Cooper A Allan D Clark R Wiley M 《Environmental monitoring and assessment》2008,141(1-3):1-17
Identification of reference streams and human disturbance gradients are crucial steps in assessing the effects of human disturbances
on stream health. We describe a process for identifying reference stream reaches and assessing disturbance gradients using
readily available, geo-referenced stream and human disturbance databases. We demonstrate the utility of this process by applying
it to wadeable streams in Michigan, USA, and use it to identify which human disturbances have the greatest impact on streams.
Approximately 38% of cold-water and 16% of warm-water streams in Michigan were identified as being in least-disturbed condition.
Conversely, approximately 3% of cold-water and 4% of warm-water streams were moderately to severely disturbed by landscape
human disturbances. Anthropogenic disturbances that had the greatest impact on moderately to severely disturbed streams were
nutrient loading and percent urban land use within network watersheds. Our process for assessing stream health represents
a significant advantage over other routinely used methods. It uses inter-confluence stream reaches as an assessment unit,
permits the evaluation of stream health across large regions, and yields an overall disturbance index that is a weighted sum
of multiple disturbance factors. The robustness of our approach is linked to the scale of disturbances that affect a stream;
it will be less robust for identifying less degraded or reference streams with localized human disturbances. With improved
availability of high-resolution disturbance datasets, this approach will provide a more complete picture of reference stream
reaches and factors contributing to degradation of stream health. 相似文献
73.
Rocky intertidal habitats frequently are used by humans for recreational, educational, and subsistence-harvesting purposes,
with intertidal populations damaged by visitation activities such as extraction, trampling, and handling. California Marine
Managed Areas, particularly regulatory marine reserves (MRs), were established to provide legal protection and enhancement
of coastal resources and include prohibitions on harvesting intertidal populations. However, the effectiveness of MRs is unclear
as enforcement of no-take laws is weak and no regulations protect intertidal species from other detrimental visitor impacts
such as trampling. The goal of this study was two-fold: (1) to determine impacts from human visitation on California mussel
populations (Mytilus californianus) and mussel bed community diversity; and (2) to investigate the effectiveness of regulatory MRs in reducing visitor impacts
on these populations. Surveys of mussel populations and bed-associated diversity were compared: (1) at sites subjected to
either high or low levels of human use, and (2) at sites either unprotected or with regulatory protection banning collecting.
At sites subjected to higher levels of human visitation, mussel populations were significantly lower than low-use sites. Comparisons
of mussel populations inside and outside of regulatory MRs revealed no consistent pattern suggesting that California no-take
regulatory reserves may have limited effectiveness in protecting mussel communities. In areas where many people visit intertidal
habitats for purposes other than collecting, many organisms will be affected by trampling, turning of rocks, and handling.
In these cases, effective protection of rocky intertidal communities requires an approach that goes beyond the singular focus
on collecting to reduce the full suite of impacts. 相似文献
74.
Abstract: The successful invasion of exotic plants is often attributed to the absence of coevolved enemies in the introduced range (i.e., the enemy release hypothesis). Nevertheless, several components of this hypothesis, including the role of generalist herbivores, remain relatively unexplored. We used repeated censuses of exclosures and paired controls to investigate the role of a generalist herbivore, white‐tailed deer (Odocoileus virginianus), in the invasion of 3 exotic plant species (Microstegium vimineum, Alliaria petiolata, and Berberis thunbergii) in eastern hemlock (Tsuga canadensis) forests in New Jersey and Pennsylvania (U.S.A.). This work was conducted in 10 eastern hemlock (T. canadensis) forests that spanned gradients in deer density and in the severity of canopy disturbance caused by an introduced insect pest, the hemlock woolly adelgid (Adelges tsugae). We used maximum likelihood estimation and information theoretics to quantify the strength of evidence for alternative models of the influence of deer density and its interaction with the severity of canopy disturbance on exotic plant abundance. Our results were consistent with the enemy release hypothesis in that exotic plants gained a competitive advantage in the presence of generalist herbivores in the introduced range. The abundance of all 3 exotic plants increased significantly more in the control plots than in the paired exclosures. For all species, the inclusion of canopy disturbance parameters resulted in models with substantially greater support than the deer density only models. Our results suggest that white‐tailed deer herbivory can accelerate the invasion of exotic plants and that canopy disturbance can interact with herbivory to magnify the impact. In addition, our results provide compelling evidence of nonlinear relationships between deer density and the impact of herbivory on exotic species abundance. These findings highlight the important role of herbivore density in determining impacts on plant abundance and provide evidence of the operation of multiple mechanisms in exotic plant invasion. 相似文献
75.
不同水温时底泥扰动对不同形态磷分布的影响 总被引:3,自引:0,他引:3
研究了江南地区典型水温条件下,底泥扰动对上覆水中不同形态磷迁移的影响.结果表明,不同水温条件下,底泥扰动均有利于上覆水中溶解态磷(即溶解性总磷酸盐(DTP),包括溶解性正磷酸盐(DIP)和溶解性有机磷(DOP))向底泥迁移.与对照试验相比,不同水温时的扰动均导致DIP/TP和DTP/TP明显降低.与初始状态(第0天时)相比,扰动导致DIP/TP分别降低了39.61百分点(冬季水温)和17.38百分点(夏季水温),而DTP/TP则分别降低了39.16百分点(冬季水温)和19.06百分点(夏季水温).相反,对照试验中,DTP/TP分别上升了24.90百分点(冬季水温)和23.37百分点(夏季水温).这说明底泥扰动促进了溶解态磷向颗粒态磷(PP)的转化. 相似文献
76.
为了阐明反复扰动下,不同初始浓度藻对沉积物中各形态磷释放的影响.以太湖梅梁湾沉积物和上覆水作为研究材料,探讨了扰动和藻类共同作用下沉积物中各形态磷的变化规律.结果表明,无扰动状态下,NH4Cl-P和Res-P均有所降低,而Fe/Al-P和Ca-P则有所增加.其中,Ca-P随藻类初始浓度增加而增加,分别增加48%、66%、74%.但是,扰动状态下,NH4Cl-P和Res-P也明显降低.Fe/Al-P明显增加,其占总磷的百分比为66.2%(3组试验的平均值)高于不扰动状态(53.4%,3组试验的平均值);此外,Ca-P占总磷的百分比为24.1%(3组扰动试验的平均值)明显低于不扰动状态(33.0%,3组试验的平均值).这暗示了扰动和藻类共同作用下促进了Fe/Al-P的形成,而无扰动下藻类却促进了Ca-P的形成. 相似文献
77.
Valeria Spagnuolo Flavia De Nicol Stefano Terracciano Roberto Bargagli Daniela Baldantoni Fabrizio Monaci Anna Alfani Simonetta Giordano 《环境科学学报(英文版)》2014,26(12):2493-2499
We determined genetic variation and metal and polycyclic aromatic hydrocarbon concentrations in Leptodon smithii moss collected in holm oak stands at cities, outskirts and remote areas of Campania and Tuscany(Italy) to investigate if anthropogenic pressure(pollutant emissions and land use change) affects moss genetic richness. In both regions, metal and polycyclic aromatic hydrocarbon concentrations reflected the trend urban 〉 outskirts 〉 remote areas, excepting Tuscany remote site. In both regions,the moss gene diversity increased from urban to remote areas. The findings suggest the extent and the fragmentation of urban green areas, as drivers of moss genetic richness. 相似文献
78.
79.
不同扰动强度下城市重污染河道底泥对磷吸收和固定的影响 总被引:3,自引:2,他引:1
以重污染河道底泥和上覆水为材料,研究了周期性加入外源磷条件下,不同扰动强度下底泥吸附和固定磷的作用机制.结果表明,扰动可以增加底泥对外源磷的吸附,而且扰动强度越大,底泥对外源磷吸附效率越高.另外,尽管加入的磷以溶解性磷酸盐(DIP)形态存在,但扰动强化了DIP向颗粒态磷(PP)的转化,从而降低了水体中生物可利用磷含量.内源磷形态分析表明,弱吸附态磷(NH4Cl-P)呈降低趋势,而铁铝结合态磷(Fe/Al-P)、钙结合态磷(HCl-P)和残渣磷(Res-P)均呈增加趋势,但以Fe/Al-P增加幅度最大(占总磷的百分比超过80%,以3种扰动强度下平均值计).结合到非闭蓄态Fe/Al-P中的外源磷逐渐增加占Fe/Al-P净增加量的百分比分别为37.49%(100 r·min-1)、42.32%(200 r·min-1)、54.24%(300r·min-1),导致闭蓄态铁铝结合态磷净增加量占总磷净增加量的百分比随扰动强度增加有所降低,同样,钙结合态磷的变化趋势也基本一致.说明在较短的时间尺度上和较大的扰动强度下,连续加入的外源磷主要以易释放态磷形式存在,即底泥对外源磷的吸附以暂时性的持留为主. 相似文献
80.