Convergence of trophic state and the lower food web in Lakes Huron,Michigan and Superior

Signs of increasing oligotrophication have been apparent in the open waters of both Lake Huron and Lake Michigan in recent years. Spring total phosphorus (TP) and the relative percentage of particulate phosphorus have declined in both lakes; spring TP concentrations in Lake Huron are now slightly lower than those in Lake Superior, while those in Lake Michigan are higher by only about 1 μg P/L. Furthermore, spring soluble silica concentrations have increased significantly in both lakes, consistent with decreases in productivity. Transparencies in Lakes Huron and Michigan have increased, and in most regions are currently roughly equivalent to those seen in Lake Superior. Seasonality of chlorophyll, as estimated by SeaWiFS satellite imagery, has been dramatically reduced in Lake Huron and Lake Michigan, with the spring bloom largely absent from both lakes and instead a seasonal maximum occurring in autumn, as is the case in Lake Superior. As of 2006, the loss of cladocerans and the increased importance of calanoids, in particular Limnocalanus, have resulted in crustacean zooplankton communities in Lake Huron and Lake Michigan closely resembling that in Lake Superior in size and structure. Decreases in Diporeia in offshore waters have resulted in abundances of non-dreissenid benthos communities in these lakes that approach those of Lake Superior. These changes have resulted in a distinct convergence of the trophic state and lower food web in the three lakes, with Lake Huron more oligotrophic than Lake Superior by some measures.     

近100多年来香港和澳门气温时序变化特征及其与ENSO的关联性

基于近 100 多年来的均一化气温数据,从趋势变化、季节差异、突变特征、周期振荡方面诊断香港和澳门的气温变化特征。结果表明: ( 1) 港澳年平均气温和不同季节气温在近 100 多年来均呈显著增加趋势,其中春冬季节增加速率较大,夏秋季节增加速率较小。除秋冬季节外,其它时间上的香港气温增加趋势均大于澳门。港澳夏冬季节气温差异均呈减少趋势。( 2) 香港和澳门年平均气温分别于 1963 年和 1991 年发生突变。在季节上,港澳地区的气温突变均在秋季发生年份最晚,冬季次之,夏季再次之,春季最早。( 3) 香港年平均气温分别存在 3 a、7 a、15 a 和 30 a、60 a 和 120 a 的周期振荡特征。澳门年平均气温存在 3 a、6 a、12 a、24 a 和 48 a 左右的周期振荡特征。( 4) ENSO 与香港年平均气温在 4 a 以下尺度以同位相或提前 1 a 位相变化关系为主,在 4 a 以上尺度以同位相变化关系为主。ENSO 与澳门年平均气温在不同时频域均以同位相变化关系为主。     

新疆奎屯河流域地下水砷超标原因分析

新疆奎屯河流域是我国大陆第一个地方性砷中毒的区域,然而在人类活动与自然条件下,对该区地下水砷超标的原因未得到清楚的解释.通过2017年在研究区采集地表水、地下水样品51组,分析了主、微量元素组分;2019年在典型的高砷区钻井2个孔,采集沉积物样品44组,分析了粒径、化学成分.结果表明,研究区地下水砷浓度范围为10～88...     

The World's Great Lakes

Most of the large lakes lie in glacial scour basins in the northern hemisphere. These lakes are closely similar in physicochemical characteristics and in their biota. Most of the other large lakes are tectonic in origin and they differ greatly among themselves and from other lakes since they occur in a diversity of terrestrial environments under a broad range of climatic conditions. Large lakes have a great diversity of habitats resulting in great species diversity and endemism in ancient lakes. The pronounced horizontal gradients in physicochemical conditions in large lakes contribute to the diversity of habitats. Conditions found in Lakes Michigan and Skadar are examples.     

东亚冬、夏季风的年代际振荡及其对夏季西太平洋副高和贵州降水的影响

主要研究了东亚冬、夏季风不同长度的年代际振荡特点及其对夏季百太平洋副高和贵州降水的影响。分析表明：冬季风与赤道东太平洋海温存在着大体一致的约３０年左右年代际振荡，７０年代末发生突变；夏季风与青藏高原位势高度存在着大体一致的约２０年左右的年代际振荡，６０年代末和８０年代末发生突变。由于冬、夏季风不同长度的年代际振荡，它们同位相增阶段夏季西太平洋副高位置容易偏北，贵州降水偏少；它们同位相减弱阶段夏季西太平洋副高易偏南，贵州降水偏多；但它们反位相组合时夏季西太平洋副高位置偏北、偏南的机会及贵州降水偏少、偏多几乎均等。     

中国积雪时空演变特征及其与海气环流因子的时序关联性

积雪时空变化作为表征增暖背景下冰冻圈的重要指标之一,在全球气候变化科学研究中具有重要作用。采用1961—2016年中国545个气象观测站的积雪日数、积雪深度日值数据和3个海气环流因子,通过多种统计方法,诊断中国积雪的时空演变特征及积雪与海气环流因子的时频相关性。结果表明:(1)1961—2016年中国积雪日数和深度在波动中呈缓慢增加趋势,且具有明显的年代分段变化特征。中国积雪日数和深度均具有30a和50a的周期振荡特征,其中积雪深度在1969年发生突变。(2)1961—2016年中国气候态积雪日数和深度具有明显的南低北高的空间分异特征,尤其是东北、内蒙古东部和新疆北部的积雪较多分布。中国积雪多寡具有明显的年代和区域分异特征。(3)在变化趋势上,1961—2016年中国积雪日数在东北和内蒙古东部趋于增多;而积雪深度除上述区域外,在华北、西北和江淮东部也趋于增多。在波动特征上,中国积雪日数和深度在华南南部、云南和四川东部波动较大,其它地区波动相对较小。(4)与海气因子时频关联性上,中国积雪与不同海气因子关联性不同,且与同一因子在不同时段的关联性也有一定差异。     

三峡库区消落带土壤金属污染特征的研究进展

三峡库区蓄水后的生态环境问题受到人们和政府的高度重视,库区消落带是水库生态环境的重要组成部分。近年来,针对库区消落带土壤金属环境问题,国内外相关学者开展了大量的研究工作。基于近十年相关研究成果,本文对三峡库区消落带土壤金属含量、时空分布特征及生态环境风险进行了梳理、归纳和分析。结果表明,三峡库区消落带土壤金属含量总体呈现库区上游及下游较高,库区中游较低的空间格局,不同水位高程不同土壤层中各金属元素的分布特征存在一定差异。与蓄水前期相比,库区消落带土壤金属含量随干湿交替周期的增加呈现动态变化,且存在向江水中迁移的环境风险。由土壤环境质量评价结果可知,研究区域土壤总体上为二类土,处于轻度污染等级,存在轻微生态风险,主要风险元素为Cd,其次为As和Hg,但目前其含量并未影响人体生命健康。针对库区消落带的研究现状,本文提出今后相关研究的着眼方向,以期为三峡库区消落带土壤重金属污染防控及库区水生态环境保护提供参考。     

Evidence for bottom-up control of recent shifts in the pelagic food web of Lake Huron

The magnitude of the spring bloom in the open waters of Lake Huron has declined dramatically in recent years, beginning in 2003. May chlorophyll values, as estimated by SeaWiFS imagery, for 2003-2006 have been 50-60% of 1998-2002 values. April phytoplankton biovolumes have also declined; average biovolume in 2003-2004 was approximately 25% of 2001-2002. Most of this decline was due to reduction in biovolume of colonial diatoms. Reductions in the spring bloom have been closely associated with abrupt declines in cladoceran populations, as well as with declines in cyclopoid copepod populations. In addition, Daphnia population egg ratios in August exhibited a pronounced decrease between 2002 and 2003 and have remained depressed through 2005. Taken together, these data suggest a role for reduced food supply in the dramatic shifts seen in the Lake Huron crustacean zooplankton community since 2003. Additionally, summer chlorophyll values have shown signs of decline in 2005 and 2006 in spite of the historically low populations of cladocerans, suggesting that control of summer phytoplankton populations in Lake Huron is determined by nutrient supply rather than grazing pressure.     

中国碾压混凝土坝技术的进展与运行经验

中国碾压混凝土坝建设始于８０年代中期，１９８６年从第１座坑口碾压土坝完成后，１０多年来已竣工２８座，在建的有１５座，合计４３座，居世界之首，还有２１座正在设计中，在设计、科研、施工实践中，碾压混凝土筑坝技术有所发展，有所进步。通过运行证实，这些成熟的经验将对下一世纪继续发展碾压混凝土坝有指导和推动作用。即将开工兴建的友滩水电站一期工程大坝高１９２ｍ，将是世界上最高的碾压混凝土重力坝。     

A comparative study of the nutrient status of two reservoirs in southeast Ghana

The nutrient status of Weija and Kpong reservoirs, southeast Ghana, was assessed by determining seasonal indices and interannual changes. The nutrient levels were found to be higher in Weija Reservoir. However, ammonia did not follow that pattern. Seasonal distribution of nutrients also showed higher levels in Weija than in Kpong. Seasonal variation showed higher levels of nitrates in the rainy season at Weija than at Kpong; however, data from Kpong Reservoir involved considerable experimental error. The monthly trend of nitrates showed a unique pattern in the months of March and May, the main ploughing periods for farming in the Weija catchment area when most fertilizer is applied. In general, over a 5-year period, there were no trends in nutrient levels. However, for sulfates there was a gradual decrease in spatial distribution from 1993 to 1997. The seasonal distribution for sulfate increased slightly. Seasonal trends as well as a seasonal index were determined and in all cases Weija showed higher levels than Kpong derived from land-based fertilizers on the reservoir. On average, there was a higher seasonal index in the rainy season than in the dry season. However, the phosphate index in January at both Weija and Kpong was high. The seasonal index for both Weija and Kpong was high in the rainy season and low in the dry season. However, the phosphate index in January at both Weija and Kpong was high. The high nitrate index in March was due to rain in the latter part of that month. Ammonia–nitrogen in November also showed high levels; November was just after the rainy season so some influence from rain persisted.