Spatial variability in water quality and surface sediment diatom assemblages in a complex lake basin,lake of the woods,ontario,canada

Lake of the Woods (LOW) is an international waterbody spanning the Canadian provinces of Ontario and Manitoba, and the U.S. state of Minnesota. In recent years, there has been a perception that water quality has deteriorated in northern regions of the lake, with all increase in the frequency and intensity of toxin-producing cyanobacterial blooms. However, given the lack of long-term data these trends are difficult to verify. As a first step, we examine spatial and seasonal patterns in water quality in this highly complex lake on the Canadian Shield. Further, we examine surface sediment diatom assemblages across multiple sites to determine if they track within-take differences in environmental conditions. Our results show that there are significant spatial patterns in water quality in LOW. Principal Component Analysis divides the lake into three geographic zones based primarily on algal nutrients (i.e., total phosphorus, TP), with the highest concentrations at sites proximal to Rainy River. This variation is closely tracked by sedimentary diatom assemblages, with [TP] explaining 43% of the variation in diatom assemblages across sites. The close correlation between water quality and the surface sediment diatom record indicate that paleoecological models could be used to provide data on the relative importance of natural and anthropogenic sources of nutrients to the lake.

用XPS振起伴峰表征聚苯醚酮的辐射凝胶化剂量

X-射线光电子能谱(XPS)振起(Shake-Up)伴峰主要是伴随主光电子的电离所导致的最高占有轨道到最低未占有轨道电子跃迁的结果.Carlson及Clark的工作声明这种振起伴峰是某些共轭π电子体系的表征,振起伴峰的相对强度与π电子共轭情况有关。 含酚酞侧基聚芳醚酮(PEK-C)是一种新型耐高温工程塑料,其主侧链均带苯环:

氢化物发生-多接收杯电感耦合等离子体质谱同位素稀释法测定硒同位素

使用改进的巯基棉分离流程和^74硒-^77硒双稀释剂，在氢化物（HG）-多接收器电感耦合等离子体质谱仪（MC—ICP—MS）实现了高精度硒同位素组成的测定。巯基棉用于分离样品基质中的硒，随后使用HNO3＋H2O2消除干扰的有机质，^74硒-^77硒双稀释剂校正样品分离和质谱测定过程中的硒同位素质量分馏。硒标准溶液NIST SRM5149和MH495几个月的测定表明，该方法的外精度为0．1‰（2σ），样品的外精度为0．15‰～0．2‰（2σ）。以TCF分离硒的平均回收率85％计算，最小硒需要量为20ng。实验结果以相对于NIST SRM3149的δ^82／76Se表达，δ^82/76MH98/SRM3149=-3．44±0．1‰（2σ），优于已发表的数据δ^82/79MH495/SRM3149=-3．04±0．5‰。测定样品的δ82/76 SRM3149为-13．53‰～11．37‰，为硒同位素在环境、农业、生命和地球科学中的拓展应用与发展奠定了基础.