Effects of precipitation on summer epilimnion thickness in tropical lakes     

《Limnologica》2019

This study aimed to evaluate the importance of physical, chemical and biological factors (e.g., chlorophyll-a, and carbon) in the regulation of the summer epilimnion thickness (Zmix) of the tropical lakes focusing on trends of the current environmental variability. We sampled a set of tropical lakes from the middle Rio Doce lacustrine system (Minas Gerais, Brazil) for two consecutive summers. Besides Zmix, we analyzed the visible light attenuation (Kd_PAR), dissolved organic carbon (DOC), chlorophyll-a (Chl-a), total suspended solids (TSS), and fetch. We also analyze the quality of the dissolved organic matter (DOM) through colored dissolved organic matter (CDOM), spectral slope (S), DOC-specific absorbance (SUVA) and the ratio between the absorbance at 250 nm and 365 nm (E_250:365). Our results showed quite different results during the two years studied. In the summer of 2012, when there was higher rainfall, variations in Zmix were correlated to the optical factors associated with DOM quality, while in the drier summer of 2013 Chl-a, TSS and fetch were the variables that more explained Zmix. It suggests that DOM regulates the Zmix in the rainy periods in the studied tropical lakes and that control is determined by the balance between the DOM input (runoff) and output (such as photodegradation) of the aquatic systems. In reduced rain conditions (summer 2013), the factors responsible by chemistry photodegradation of DOM were predominant, and the organic matter was no longer controlling Zmix, which was driven by internal mixing, productivity, and the wind (Chl-a, TSS and fetch). In this study we showed how changes in precipitation might cause shifts in the factors that regulate the epilimnion thickness in tropical lakes.  相似文献   

云南星云湖水质变化及其人文因素驱动力分析   总被引：1，自引：0，他引：1  

郑田甜  赵祖军  赵筱青  顾泽贤  普军伟  卢飞飞 《湖泊科学》2018,30(1):79-90

星云湖目前存在水污染加重、富营养化进程加快、水体功能受损等问题.以星云湖为研究对象,根据星云湖2005-2015年的水质数据、社会经济统计数据和遥感影像图,运用目视解译、叠加分析、污染足迹模型及主成分分析法,分析了星云湖流域近10年以来水质变化趋势、入湖河流污染物污染足迹及其人文因素驱动力.结果表明:(1)水质数据趋势表明,从月变化看,3月份水质最好,9月份水质最差;从年变化看,2005-2015年间,2008年水质状况最好,2014年的水质状况最差,从2008-2014年水质持续变差,到2015年好转.(2)2015年有机物、氮和磷的污染足迹分别为583.26、705.88和494.11 km~2.污染足迹前4位的入湖河流依次为:大街河东西大河东河渔村河东西大河西河,占星云湖流域总污染足迹的66.21%.污染程度大的大街河、东西大河和渔村河周边土地利用类型为水田、旱地和村庄.(3)星云湖水质影响因素第1主成分(总人口、播种面积、农村人口、化肥使用量、农膜使用量、大牲畜存栏量)与农村生活和农业面源污染有关;第2主成分(人均GDP、第一产业产值、第二产业产值、第三产业产值)与社会经济发展有关.因此,星云湖流域水质变化的人文因素驱动力为农村生活和农业面源污染类和社会经济发展类,其中第1主成分的贡献率是84.389%,农村生活和农业面源污染是水质变化的主要驱动力.  相似文献   

近30 a云贵高原湖泊表面水体面积变化遥感监测与时空分析   总被引：3，自引：0，他引：3  

肖茜  杨昆  洪亮 《湖泊科学》2018,30(4):1083-1096

以云贵高原湖泊近30 a来的TM、ETM~+和OLI遥感影像为数据源,采用归一化水体指数(NDWI)、改进归一化水体指数(MNDWI)、新型水体指数(NWI)、增强型水体指数(EWI)和自动水体提取指数5种水体指数提取了1985—2015年云贵高原10个湖泊表面水体面积,并对各种算法进行精度对比分析.针对湖泊各自特点采用不同的水体指数提取其表面水体面积,并进行水体面积变化时空分析.结果表明:云贵高原湖泊表面水体面积总体呈现先增加后缩减趋势,1985—1995年湖泊表面水体面积增加了30.86 km~2,1995—2015年湖泊水体表面面积减少了48.12 km~2,其中,面积变化最大的是杞麓湖与异龙湖.对云贵高原湖泊表面水体面积变化与该区域的年降水量、蒸发量、平均气温、流域植被覆盖面积和人类活动时空进行相关分析,结果表明:1)高原湖泊对区域气候变化的响应具有明显的空间差异性,云贵高原湖泊的表面水体面积与气候相关性较显著,气温升高引起蒸发加速,降水量下降,湖面不断缩小,与逐年上升的气温呈负相关,与逐年波动上升的蒸发量呈负相关,与逐年减少的降水量呈正相关;2)云贵高原湖泊各流域的植被覆盖面积与湖泊面积变化相关性较弱;3)人类活动是影响湖泊面积变化的重要因素,大肆围湖造田、围湖养殖以及旅游开发等人类活动直接导致云贵高原湖泊面积的锐减,并对湖泊生态环境产生重要影响.  相似文献   

How well can we simulate complex hydro‐geomorphic process chains? The 2012 multi‐lake outburst flood in the Santa Cruz Valley (Cordillera Blanca,Perú)          下载免费PDF全文

Martin Mergili  Adam Emmer  Anna Juřicová  Alejo Cochachin  Jan‐Thomas Fischer  Christian Huggel  Shiva P. Pudasaini 《地球表面变化过程与地形》2018,43(7):1373-1389

Changing high‐mountain environments are characterized by destabilizing ice, rock or debris slopes connected to evolving glacial lakes. Such configurations may lead to potentially devastating sequences of mass movements (process chains or cascades). Computer simulations are supposed to assist in anticipating the possible consequences of such phenomena in order to reduce the losses. The present study explores the potential of the novel computational tool r.avaflow for simulating complex process chains. r.avaflow employs an enhanced version of the Pudasaini ( 2012 ) general two‐phase mass flow model, allowing consideration of the interactions between solid and fluid components of the flow. We back‐calculate an event that occurred in 2012 when a landslide from a moraine slope triggered a multi‐lake outburst flood in the Artizón and Santa Cruz valleys, Cordillera Blanca, Peru, involving four lakes and a substantial amount of entrained debris along the path. The documented and reconstructed flow patterns are reproduced in a largely satisfactory way in the sense of empirical adequacy. However, small variations in the uncertain parameters can fundamentally influence the behaviour of the process chain through threshold effects and positive feedbacks. Forward simulations of possible future cascading events will rely on more comprehensive case and parameter studies, but particularly on the development of appropriate strategies for decision‐making based on uncertain simulation results. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Motile phytoplankton species such as Gonyostomum semen can significantly reduce CO2 emissions from boreal lakes     

《Limnologica》2020

Boreal lakes typically have high levels of allochthonous dissolved organic matter (DOM), causing light limitation of photosynthetic CO₂ consumption while stimulating CO₂ production. They are therefore considered as important sources of atmospheric CO₂. However, boreal lakes are also experiencing a marked expansion of bloom-forming motile phytoplankton organisms that can circumvent the shading effect of DOM by performing phototaxis and that thus might have an impact on the lakes’ CO₂ balance. We tested this idea in a DOM-rich lake using the widespread raphidophyte flagellate Gonyostomum semen as model organism. Employing continuous field measurements, we found that G. semen can reduce the partial pressure of CO₂ even at low algal densities. Periods with high algal densities were associated with CO₂ undersaturation and invasion of atmospheric CO₂. The mean daily net losses of CO₂ to the atmosphere during and after a G. semen bloom were estimated at 12.9 and 70.4 mmol C m^–2 day^–1, respectively. G. semen caused steep pCO₂ gradients in space and time, which make it difficult to unveil the species’ impact without employing continuous pCO₂ vertical profiling. This suggests that the effect of G. semen on the CO₂ balance of boreal lakes might have been overlooked in the past. Taken together, our data suggest that G. semen can significantly reduce the CO₂ emissions from boreal lakes despite high concentrations of allochthonous DOM. G. semen and other motile phytoplankton species should therefore be considered when estimating CO₂ emissions from boreal lakes, especially if these organisms continue their expansion.  相似文献   

The success of Gonyostomum semen (Raphidophyceae) in a boreal lake is due to environmental changes rather than a recent invasion     

《Limnologica》2020

The freshwater microalgal species, Gonyostomum semen, has increased in abundance and distribution in boreal lakes during the past few decades, concerning ecologists and water managers. Due to its rapid spread, G. semen has often been referred to as an invasive species, although it was first described in the 1800s. We hypothesized that G. semen is not an invasive species in Norwegian lakes, and that the increasing success is due to beneficial changes in environmental conditions for this species during the past century. We tested these hypotheses by performing a paleolimnological study of a Norwegian Lake, Skjeklesjøen, with known mass occurrence of G. semen. A specific G. semen pigment biomarker, heteroxanthin, was used to detect this species in layers of a sediment core with known age determinations. Environmental factors in both lake and catchment were further investigated and the relationships with the amounts of G. semen was tested. Our results suggested that G. semen was in fact not an invasive species in this lake the past decades. Several factors were identified as plausible drivers for G. semen in this boreal lake. Between 1874–2016, the increasing levels of G. semen in Lake Skjeklesjøen was most closely correlated with Carbon (C), lake color (measured as absorbance of sediment extracts), Nitrogen (N) and spring temperature. Our results suggest that the rapid increase in G. semen population in this boreal lake over the past 70 years was probably due to a combination of climate change and local anthropogenic activities in the catchment, causing increased browning and increased inputs of organic matter and nutrients.  相似文献   

循环应力比和振动频率对盐渍土微观结构影响分析   总被引：1，自引：1，他引：0  

赵福堂  常立君  张吾渝 《冰川冻土》2020,42(3):854-864

以青海省察尔汗地区盐渍土为研究对象， 借助扫描电子显微镜（SEM）设备和颗粒孔隙及裂隙图像识别与分析系统（PCAS）， 应用图像分割原理和分形理论， 对交通循环荷载作用下的盐渍土微观结构进行研究， 探讨不同循环应力比和不同振动频率下孔隙分布特征及其微观机制。结果表明： 循环应力比R由0.375增加到0.75， 临界破坏动应变由2.32%增高到3.17%， 动载循环次数相应减少； 振动频率f由0.5 Hz增加到2.0 Hz， 临界破坏动应变由2.82%减小到2.48%， 动载循环次数相应增多； 盐渍土孔隙参数随循环应力比的增大， 孔隙尺度分维值D_v 增长了0.12， 概率熵H_m 减小了0.017， 孔隙的形态分形维数D减小了0.27， 平均形状系数F增加了0.14， 变化规律较明显； 随振动频率的增大， D_v 增长了0.014， H_m 减小了0.002， D变化了0.06， F变化了0.003， 变化规律不明显； 在动荷载作用下， 试样的孔隙空间排列与宏观上的褶皱鼓状变形具有一致性。通过未加载试样与加载后试样的微观结构参数变化对比， 从循环应力比和振动频率对盐渍土微观孔隙特征的影响到宏观变形的相互作用机制进行了系统分析。  相似文献   

基于HICO波段的滨海土壤盐分遥感反演研究   总被引：1，自引：0，他引：1  

安德玉  邢前国  赵庚星 《海洋学报》2018,40(6):51-59

本研究以黄河三角洲滨海盐渍土为例，尝试使用HICO （Hyperspectral Imager for the Coastal Ocean）高光谱影像结合现场实测高光谱数据进行表层土壤全盐含量的反演。采用波段组合的方法建立光谱参量，通过相关分析筛选出敏感光谱参量，以决定系数R2选出最佳模型；利用HICO影像反射率与实测高光谱反射率之间的关系，对模型进行修正，并应用于影像。研究发现，比值（RI）、差值（DI）波段组合方法建立的光谱参量与表层土壤全盐含量的相关性明显提高。DI_{（845，473）}、DI_{（839，490）}、DI_{（845，496）}及DI_{（839，501）}的幂函数模型效果最好，且验证决定系数R2均大于0.86，相对分析误差RPD>3，RMSE较小。此外，HICO遥感影像的模型反演结果较为一致，能够反映表层土壤全盐含量的分布。研究显示，利用高光谱数据进行表层土壤全盐含量的反演建模具有可行性，可为区域表层土壤全盐含量的定量反演提供参考。  相似文献   

富营养化初期湖泊放养鲢(Hypophthalmichthys molitrix)、鳙(Aristichthys nobilis)控藻生态效果的初步评估     

杨姣姣  过龙根  尹成杰  陈晓希  倪乐意 《湖泊科学》2019,31(2):386-396

放养鲢（Hypophthalmichthys molitrix）、鳙（Aristichthys mobilis）控制富营养化湖泊蓝藻水华暴发是当前最有效的手段之一.为评估富营养化初期湖泊鲢、鳙控藻的生态效果，2016年在洱海红山湾开展原位围栏鲢、鳙控藻实验，对围栏内外的浮游生物群落结构及水环境因子的变化进行对比分析，同时测定了围栏内鲢、鳙的生长及摄食节律.结果表明：围栏内鲢、鳙呈现匀速生长，围栏生存环境适宜.根据Egger''s模型估算鲢、鳙的日摄食量分别为24.96%和18.18%，鲢的日粮高于鳙；滤食率结果表明，鲢对浮游植物的摄食率高于鳙（分别为3.01和2.19 L/（g·h），而鳙对浮游动物的滤食率高于鲢（分别为18.61和13.54 L/（g·h））.研究期间，围栏内外水体理化因子无显著差异；但围栏内外微囊藻生物量差异明显，并且在7月达到生物量峰值（围栏内为1.7 mg/L，围栏外为2.4 mg/L）.鲢、鳙对浮游植物的优势种类——微囊藻和隐藻有明显的削减效果，6-8月逐渐上升并在8月达到最高（64%）；当浮游植物优势种由微囊藻替换为硅藻门和绿藻门的种类时，鲢、鳙的削减效率不明显（10-11月为负值）.此外，鲢、鳙放养显著降低了浮游甲壳动物的总生物量和枝角类生物量.因此，结合实验结果得出，鲢具有更高的控藻能力，尤其对微囊藻水华，但同时具备了较高对浮游甲壳动物的削减能力，需要进一步分析富营养化初期湖泊——洱海中实施非经典生物操纵的适宜性.  相似文献   

Estimating daily inflows of large lakes using a water‐balance‐based runoff coefficient scaling approach     

Zhaoliang Peng  Weiping Hu  Gang Liu  Rui Gao  Wei Wei 《水文研究》2019,33(19):2535-2550

Daily river inflow time series are highly valuable for water resources and water environment management of large lakes. However, the availability of continuous inflow data for large lakes is still relatively limited, especially for large lakes situated within humid plain regions with tens or even hundreds of tributaries. In this study, we choose the fifth largest freshwater Lake Chaohu in China as our study area to introduce a new approach to reconstruct historical daily inflows at ungauged subcatchments of large lakes. This approach makes use of water level, lake surface rainfall, evaporation from the lake, and catchment rainfall observations. Rainfall–runoff relationship at a reference catchment was analysed to select rainfall input and estimate run‐off coefficient firstly, and the run‐off coefficient was then transferred to ungauged subcatchments to initially estimate daily inflows. Run‐off coefficient was scaled to adjust daily inflows at ungauged subcatchments according to water balance of the lake. This approach was evaluated using sparsely measured inflows at eight subcatchments of Lake Chaohu and compared with the commonly used drainage area ratio method. Results suggest that the inflow time series reconstructed from this approach consistent well to corresponding observations, with mean R² and Nash–Sutcliffe efficiency values of 0.69 and 0.6, respectively. This approach outperforms drainage area ratio method in terms of mean R² and Nash–Sutcliffe efficiency values. Accuracy of this approach holds well when the number of water‐level station being used decreased from four to one.  相似文献