Toxic cyanobacteria at Nakuru sewage oxidation ponds - A potential threat to wildlife

Phytoplankton composition and biomass, and microcystin content were determined on diverse dates between November 2001 and June 2006 in the final oxidation pond of the Nakuru town sewage treatment plant. The oxidation ponds as well as the rivulet that drains the same are important water sources for some wildlife in the park. The phytoplankton composition of the pond studied mostly comprised coccoid green alga species. However, occasionally cyanobacteria or euglenoids were dominant. Among the cyanobacteria, Microcystis sp. made periodic appearance in the phytoplankton, and was the dominant species on some occasions. Total phytoplankton biomass varied widely from 48 to 135 mg L⁻¹ (wet weight) while cyanobacteria biomass ranged from undetectable levels to 130 mg L⁻¹. Most phytoplankton biomass was due to one or a few species. Detectable cyanotoxin concentrations (sum of microcystins) of up to 551.08 μg mg⁻¹ dry weight (DW) of cyanobacteria biomass or 0.28 μg mg⁻¹ DW of total phytoplankton biomass were recorded in samples collected on different dates. Microcystin content did not appear to correspond to the biomass of cyanobacteria suggesting that toxin production is possibly triggered by environmental changes or changes in the proportion of toxic strains. An occasional presence of microcystins in the pond water suggests that the wildlife species, which regularly use the ponds as drinking water sources are potentially exposed to intoxication. A close monitoring of pond water phytoplankton composition is necessary to accurately quantify the potential impact of cyanotoxins on these wildlife species.     

High accuracy measurements of water storage change in Mining Lake 111, Germany

Several pressure sensors were deployed in a small lake to determine its storage change. It could be shown that a deep enough deployment and an averaging over a time interval of 1 hour and 5 measuring points allowed for a measurement of 1 or 2 kg/m² (i.e. 2 mm of water column) of changes in the storage on the scale of the lake size. This accuracy for the lake storage could not be achieved by other methods, especially if conditions were difficult, e.g. snowfall, or in cases when precipitation was small. Finally, the pressure measurement - originally intended to roughly determine the water level - turned out to be a direct measurement of water mass in the lake, which was the proper magnitude for exchanges between atmosphere and lake. Hence the measurement of lake storage could become an interesting approach even for meteorological measurements, such as precipitation and evaporation on a water surface.     

Local variability of sedimentation rate in Lake Arendsee, Germany

We measured the thickness and the dry weight of recently deposited sediment along several transects across Lake Arendsee in order to quantify the sedimentation rate and its local variability. As a time marker, we used an artificial marl layer that was deposited by a remediation program in the year 1995. A portion of the sediment deposited during the year was transported from the littoral and the top of the submerged hills to the foot of the slope, where we found the greatest deposition. Within the same lake, the deposited sediment layer varied by a factor of 4 between minimal and maximal values over the same time periods. Lake Arendsee is a holomictic and eutrophic lake with depletion of oxygen in summer time.     

青藏高原西缘班公错地区新构造运动特征

青藏高原西缘的班公错地区是青藏高原西构造结的典型区域,更是研究青藏高原中更新世以来构造活动、地貌演化和环境演变的重要区域。依据野外调查结果,借助卫星遥感影像的解译和数字高程模型地形地貌特征的分析,对该地区的新构造运动特征以及其与地形地貌特征的耦合进行了研究。研究结果显示,研究区地貌分区特征以中大起伏山地（地势起伏度500~2 500 m）地貌为主,平原、台地少有发育;班公错地区断层走向分为近EW向、NW向、NE向和NNE向4组,其中近EW向为主体,断陷盆地多具有拉分断陷特征;区内晚新生代地层发育,尤其第四纪冲洪积物和湖积物广泛展布,并受断层的控制具有线性发育特征,湖积阶地和冲洪积阶地发育,班公错北岸乌奖附近拔湖高度62 m、65 m、98 m的沉积阶地钙质堆积物年龄为（23.8±2.3)、（33.9±4.0)、（78.0±8.0)万年;区内地震频发,1970年以来的40年间,4级以上地震达到303次,其中6级以上强震达到7次。众多地质事实指示该地区的中更新世以来为较强烈的、阶段性快速构造抬升和剧烈的剥蚀作用、动荡的构造环境。     

青海湖流域河川径流特征及其对降水的滞后效应

以青海湖流域的布哈河为例,采用变差系数、集中度和集中期等指标,对青海湖流域内径流量、降水量在年代、年际、季节等时间尺度上进行分析,并用集中期来反映河川径流对降水的滞后效应。结果显示,河川径流年内主要集中在6—10月,特别是7月中旬至8月中旬之间;降水主要集中在5—9月,特别是7月;径流量与降水量存在极大的相关性（r=0.746＞0.443=α0.001(47)）,径流对降水具有滞后效应,多年平均滞后时间为20 d左右。     

“水资源域”概念在美国五大湖的应用(英文)

"水资源域"为在某一时段向河口或某一地点,传送水、水中营养物、泥沙或其它物质的空间范围。这一新概念与"流域"概念既相似又不同:1)流域边界以地貌特征来确定,相对稳定。而水资源域的边界以水文事件中的水和物质传播范围来确定,随时空而变化;2)流域强调给定空间范围内水和物质的时间分布,而水资源域强调水和物质随时间和空间二者相互变化的动态分布;3)水资源域综合考虑了不同尺度的时空即时变化对水资源及物质传播的影响。这一新概念应用遥感、空间分析、追踪及模拟技术分析流域空间模式与过程,为水资源探索、分析、模拟及预测提供了一种全新的方法与途径。该文以美国伊利湖茅密河为例,应用分布式大流域模型计算了水资源域的分布。     

SWAT model application and prediction uncertainty analysis in the Lake Tana Basin,Ethiopia

Lake Tana Basin is of significant importance to Ethiopia concerning water resources aspects and the ecological balance of the area. Many years of mismanagement, wetland losses due to urban encroachment and population growth, and droughts are causing its rapid deterioration. The main objective of this study was to assess the performance and applicability of the soil water assessment tool (SWAT) model for prediction of streamflow in the Lake Tana Basin, so that the influence of topography, land use, soil and climatic condition on the hydrology of Lake Tana Basin can be well examined. The physically based SWAT model was calibrated and validated for four tributaries of Lake Tana. Sequential uncertainty fitting (SUFI‐2), parameter solution (ParaSol) and generalized likelihood uncertainty estimation (GLUE) calibration and uncertainty analysis methods were compared and used for the set‐up of the SWAT model. The model evaluation statistics for streamflows prediction shows that there is a good agreement between the measured and simulated flows that was verified by coefficients of determination and Nash Sutcliffe efficiency greater than 0·5. The hydrological water balance analysis of the basin indicated that baseflow is an important component of the total discharge within the study area that contributes more than the surface runoff. More than 60% of losses in the watershed are through evapotranspiration. Copyright © 2009 John Wiley & Sons, Ltd.     

A modified landform development model for the topography of drained thermokarst lake basins in fine‐grained sediments

Permafrost degradation associated with the expansion of thermokarst lakes is commonly interrupted by catastrophic drainage. Subsequently, in tundra areas, permafrost aggradation in drained basins leads to uneven topography characterized by raised centres and wet, depressed margins. The genesis of such topography has been investigated in Old Crow Flats (OCF), a glaciolacustrine plain in the continuous permafrost of northern Yukon. The thermokarst lakes of OCF have a mean depth of only 1.5 m because excess ice is dominantly found only in the uppermost 10 m of the ground. Surface conditions were measured in three drained thermokarst lake basins, including relief, snow conditions, ground temperatures, near‐surface ground ice, and sediment stratigraphy. Four nearby lakes provided information on wave base, shore recession patterns, and bathymetry before drainage: the bottoms of these lakes were not raised in the centre. An elevation difference of up to 2 m was recorded between drained basin margins and centres but was not associated with variations in ice‐wedge density or segregated ice content. Hence basin topography was not controlled by differences in volumetric ground‐ice content between margins and centres. We propose that transport of fine sediment away from eroding lake margins during lake development is the primary mechanism for the genesis of depressed margins and raised centres in drained basins of OCF. Over time, the transport results in the deposition of more and finer sediment in the central parts of lakes, where the lake bottom has subsided below wave base, than at the shallow margins, where resuspension by wave action occurs frequently. This difference in sediment volume is revealed in the topography after drainage, when permafrost aggrades in the lake‐bottom sediment and underlying talik. Copyright © 2016 John Wiley & Sons, Ltd.     

青藏高原可可西里卓乃湖溃堤成因及其影响分析

受青藏高原暖湿化趋势的影响,近年来高原湖泊水位普遍上涨,湖泊溃堤时有发生.利用青藏高原可可西里卓乃湖、库赛湖、海丁诺尔湖和盐湖所在区域的TM（ETM+）等历史文献数据和环境减灾卫星（HJ1A/B） CCD数据,结合五道梁气象站气温、降水资料,分析了卓乃湖周边湖泊面积变化情况.结果表明：1961-2014年近54 a来,可可西里地区持续增加的降水是卓乃湖溃堤的基础,2011年8月22日之前的两次强降水过程和之后的持续降水是导致卓乃湖湖水大量外泄,并最终溃堤的主要原因;溃堤前的两次地震可能对卓乃湖的湖盆结构产生了一定的影响,从而加速了溃堤过程.溃堤导致湖岸线退缩,并产生大片的沙化土地,恶化了藏羚羊的产仔环境,对周边草地生态环境和重大工程设施产生了不利影响.     

艾比湖区域地表水水化学特征干湿季变化及其控制因素

对2014年艾比湖区域的地表水进行观测和取样,综合运用多元统计、Piper阴阳离子三角图、Gibbs图等方法,对艾比湖区域干湿季地表水化学特征及控制因素进行了分析.结果表明：在湿季5月,Na⁺和Cl^-是占绝对优势的离子,分别占阳离子和阴离子总量的70.34%和52.97%,其次是Mg²⁺和SO₄^2-;在干季10月,Na⁺和Cl^-是占绝对优势的离子,分别占阳离子和阴离子总量的70.57%和66.48%,其次是Mg²⁺和SO₄^2-.进而判断出在湿季,艾比湖区域地表水水化学类型为以碳酸盐岩石和蒸发岩来源为主的HCO₃^--Ca²⁺-Na⁺型;而在干季,艾比湖区域地表水水化学类型为以碳酸盐岩石和蒸发岩来源为主的HCO₃^--Ca²⁺型.此外,探讨了离子控制的因素.就自然因素而言,在干湿季,艾比湖区域地表水化学离子组成受岩石风化作用和蒸发结晶作用的共同影响,大气降水的输入作用十分微弱.就人为因素而言,根据相关研究,干湿季人为活动中的主要因素是人口和地区生产总值,说明该区域受到人为活动的影响.本研究为我国干旱地区对于河水水化学变化、水质特征、水质保护都具有重要的意义.