Cascades of sub-decadal,channel-floodplain changes in low-gradient,non-vegetated reaches near a dryland river terminus: Salar de Uyuni,Bolivia     

Jiaguang Li  Stephen Tooth  Guangqing Yao 《地球表面变化过程与地形》2019,44(2):490-506

The terminus of the ephemeral Río Colorado is located at the margins of Salar de Uyuni, Bolivia, the world's largest salt lake. The low-gradient (<0.0006 m m^-1), non-vegetated reaches approaching the terminus provide an excellent natural laboratory for investigating cascades of channel-floodplain changes that occur in response to quasi-regular flows (at least once annually) and fine-grained sediment supply (dominantly silt and clay). High-resolution satellite imagery (<0.65 m, various dates from 2004 onwards) and field data reveal widespread, pronounced and rapid morphodynamics on sub-decadal timescales, including channel erosion and chute cutoff formation, and development of crevasse channels and splays, floodouts (unchannelled surfaces at channel termini), and erosion cells (floodplain scour-transport-fill features). In particular, following high annual precipitation (>400 mm) in 2004–2005 and two subsequent high magnitude daily precipitation events (~40 mm), all of which led to widespread flooding, numerous crevasse splays formed between 2004 and 2016, avulsions occurred at nearby floodouts, and erosion cells downstream of the splays and floodouts underwent striking morphological changes. High-precision GPS data reveal two preferential localities for erosion cell development: partially or fully abandoned channels with crevasse splay remnants, and topographic lows between channels. In this overall low-gradient setting, comparatively high gradients (up to ~0.0006 m m^-1) at the edge of splay deposits and topography created by crevasses and abandoned channels may initiate knickpoint retreat and thereafter erosion cell development. Abandoned channels with splays tend to give rise to narrow, deep erosion cells, while topographic lows promote relatively shallow, wide erosion cells. In both situations, erosion cells may extend upslope and downslope, and eventually connect to form straight channels. The channel-floodplain morphodynamics near the Río Colorado terminus extend previous analyses of low-gradient, dryland river systems, particularly because the lack of vegetation and quasi-regular floods drive cascades of rapid changes on sub-decadal timescales. © 2018 John Wiley & Sons, Ltd.  相似文献   

Observations of canopy storage capacity and wet canopy evaporation in a humid boreal forest     

Bram Hadiwijaya  Pierre-Erik Isabelle  Daniel F. Nadeau  Steeve Pepin 《水文研究》2021,35(2):e14021

Evaporation of intercepted rain by a canopy is an important component of evapotranspiration, particularly in the humid boreal forest, which is subject to frequent precipitation and where conifers have a large surface water storage capacity. Unfortunately, our knowledge of interception processes for this type of environment is limited by the many challenges associated with experimental monitoring of the canopy water balance. The objective of this study is to observe and estimate canopy storage capacity and wet canopy evaporation at the sub-daily and seasonal time scales in a humid boreal forest. This study relies on field-based estimates of rainfall interception and evapotranspiration partitioning at the Montmorency Forest, Québec, Canada (mean annual precipitation: 1600 mm, mean annual evapotranspiration: 550 mm), in two balsam fir-white birch forest stands. Evapotranspiration was monitored using eddy covariance sensors and sap flow systems, whereas rainfall interception was measured using 12 sets of throughfall and six stemflow collectors randomly placed inside six 400-m² plots. Changes in the amount of water stored on the canopy were also directly monitored using the stem compression method. The amount of water intercepted by the forest canopy was 11 ± 5% of the total rainfall during the snow-free (5 July–18 October) measurement periods of 2017 and 2018. The maximum canopy storage estimated from rainfall interception measurements was on average 1.6 ± 0.7 mm, though a higher value was found using the stem compression method (2.2 ± 1.6 mm). Taking the average of the two forest stands studied, evaporation of intercepted water represented 21 ± 8% of evapotranspiration, while the contribution of transpiration and understory evapotranspiration was 36 ± 9% and 18 ± 8%. The observations of each of the evapotranspiration terms underestimated the total evapotranspiration observed, so that 26 ± 12% of it was not attributed. These results highlight the importance to account for the evaporation of rain intercepted by humid boreal forests in hydrological models.  相似文献   

Size of anal papillae in chironomids: Does it indicate their salinity stress?     

Ben J. Kefford  Kasturi Reddy-LopataColin Clay  Tarah HagenOrsolya Parkanyi  Dayanthi Nugegoda 《Limnologica》2011,41(2):96-106

Salinity of inland waters is affected by a range of human activities and is regarded as a major environmental contaminant in many parts of the world. Changes in salinity are well known to be associated with changes in macroinvertebrate communities of flowing waters. However, as many environmental factors co-vary with salinity, it is not known whether, and if so how, salinity causes communities to change. Being able to measure the osmoregulatory stress that individual stream macroinvertebrates are experiencing would be useful to understand if and how salinity affects their populations and thus communities. Additionally, inferring salinity stress in individual invertebrates could provide a valuable biomonitoring tool to detect the initial effects of salinity before major ecological changes have occurred. Osmoregulation in larval Chironomidae (Diptera) takes place in the anal papillae and their size is believed to be associated with osmoregulatory stress. In two laboratory experiments and a field survey in southern Victoria, Australia, we determine if the size of the anal papillae of larva chironomids is a useful biomarker of salinity stress. Experiments with Chironomus oppositus showed that the surface area of the anal papillae was similar in larva hatched across 5 egg masses collected from 3 sites but were affected by salinity treatments. Furthermore, the (transformed) ratio of this surface area to the body length of the larva was independent of the size of C. oppositus. However, for Chironomus cloacalis, this surface area differed between larva hatched from egg masses collected from the same site. The expected trend in surface area of the anal papillae relative to the size of larva (Chironomu alternans, C. cloacalis, Dicrotendipes sp., Criptochironomus sp. and Tanypodinae) was not duplicated in the field survey. It would appear that unknown factors, other than salinity, are affecting the size of the anal papillae of chironomids in southern Victoria.  相似文献   

不同水深条件下菹草(Potamogeton crispus)的适应对策   总被引：1，自引：0，他引：1  

陈正勇  王国祥  吴晓东  王立志  徐伟伟  俞振飞 《湖泊科学》2011,23(6):942-948

用盆栽试验方法,将菹草石芽种植在水下0.5、1.0、1.5、2.0、2.5、3.0、3.5、4.0m的花盆内,研究了水深梯度对菹草生长、繁殖和生物量分配的影响,得出在不同水深条件下,菹草的能量分配适应对策.结果表明:不同水深未影响菹草石芽的萌发,水深0.5 -4 m各实验组,菹草石芽的萌发率均达到70％以上,各实验组之...  相似文献   

Biosorption of Dyes by Natural and Activated Vine Stem. Interaction between Biosorbent and Dye     

Ebru Mavioglu Ayan  Asli Toptas  Gulsah Kibrislioglu  Esra Evrim Saka Yalcinkaya  Jale Yanik 《洁净——土壤、空气、水》2011,39(4):406-412

In the present study, the vine stem and modified vine stem were used as low cost adsorbents for the removal of acidic and basic dyes from aqueous solutions. A comparative study was also carried out with activated carbon obtained from vine stem and then the adsorption capacities of all adsorbents were evaluated by batch adsorption process. The effects of various adsorption parameters (initial pH, particle size, and contact time) were investigated. The modification of the vine stem with nitric acid increased its adsorption capacity for the basic dye. Both, vine stem and modified vine stem exhibited higher adsorption capacities than activated carbon. The adsorption capacities were found to be 322.58, 250, and 200 mg g^?1 for modified, natural vine stem, and activated carbon, respectively. In the case of acidic dye, the pH strongly affected the adsorption capacity and the maximum dye uptake was observed at pH 2 for all adsorbents. The acidic dye adsorption was lower compared to basic dye on both biosorbents and activated carbon tested. The maximum acidic dye adsorption values (58.82 and 59.88 mg g^?1) were obtained with the vine stem and activated carbon, respectively. In the case of lignocellulosic adsorbents, both surface charge and surface groups had main effect on the adsorption of basic dye, while adsorption mechanism in activated carbon was mainly through the physical adsorption. The results of comparative adsorption capacity of adsorbents indicated that vine stem or modified vine stem can be used as a low cost alternative to activated carbon in aqueous solution for basic dye removal.  相似文献   

低分子量氨基糖及其衍生物对角膜细胞生长影响的研究     

赵国燕  刘万顺  韩宝芹  梁晔 《中国海洋大学学报(自然科学版)》2011,41(3):52-56

体外培养兔角膜上皮细胞和基质细胞,采用显微观察和MTT相结合的方法分析低分子量氨基糖(包括壳寡糖(chitosan)、羧甲基壳寡糖(Carboxymethyl chitosan oligosaccharide)、羧甲基甲壳寡糖(Carboxymethyl chitin oligosaccharide)、N-乙酰氨基葡萄糖(N-acetyl-glucosamine))对细胞生长的影响。结果在0~1000μg/mL浓度范围内4种氨基糖对角膜上皮细胞和基质细胞均没有细胞毒性,且均能促进角膜上皮细胞的生长,以壳寡糖和羧甲基甲壳寡糖效果最佳,二者与对照组相比均具有显著性差异(P<0.05)。壳寡糖、羧甲基甲壳寡糖和N-乙酰氨基葡萄糖能明显促进角膜基质细胞的生长,与对照组相比具有显著性差异(P<0.05),其中壳寡糖的促进作用最明显。提示低分子量氨基糖可适用于角膜细胞促生长的培养,为壳聚糖衍生物材料用于眼科研究提供一定的实验依据。  相似文献   

Dieback affects forest structure in a dry Afromontane forest in northern Ethiopia     

E. Aynekulu  M. DenichD. Tsegaye  R. AertsB. Neuwirth  H.J. Boehmer 《Journal of Arid Environments》2011,75(5):499-503

Forests are highly susceptible to dieback under ongoing climate warming. In degraded forests, dead standing trees, or snags, have become such prominent features that they should be taken into account when setting management interventions. This study investigated (1) the extent and spatial pattern of standing dead stems of Juniperus procera and Olea europaea subsp. cuspidata along an elevational gradient, and (2) the effect of dieback on forest stand structure. We quantified abundance, size, and spatial pattern of tree dieback in 57 plots (50 m × 50 m) established at 100 m intervals along five transects. The snag density and basal area (mean ± SE) of the two species combined were 147 ± 23 stems ha⁻¹ and 5.35 ± 0.81 m² ha⁻¹, respectively. The percentages of snags were extremely high for both J. procera (57 ± 7%) and O. europaea subsp. cuspidata (60 ± 5%), but showed a decreasing trend with increasing elevation suggesting that restoration is even more urgent at the lower elevations. Snags of the two species accounted for 31 and 45% of total stand density and basal area, respectively. Living stems exhibited truncated inverse-J-shaped diameter and height class distributions, indicating serious regeneration problems of these foundation species in the study area. In addition to direct interventions to assist recruitment of climax tree species, sites with high dieback would probably benefit from snag reduction to prevent fire incidents in the remaining dry Afromontane forests in northern Ethiopia.  相似文献   

Rickettsial-like cells in the Cretaceous tick,Cornupalpatum burmanicum (Ixodida: Ixodidae)     

《Cretaceous Research》2015

Rickettsial-like cells are reported from the body cavity of the Myanmar amber larval tick, Cornupalpatum burmanicum (Ixodida: Ixodidae). These cells are characterized and described in a new collective fossil genus erected for putative rickettsia in fossil ticks. The size and shape of the fossil cells resemble those of present day members of the Rickettsiaceae, many of which occur in the body cavity of present day ticks.  相似文献   

圆紫菜人工色素突变体的诱导与分离   总被引：1，自引：0，他引：1  

赵爽  丁洪昌  刘长军  严兴洪 《海洋学报》2019,41(2):114-122

为获得圆紫菜人工色素突变体，本文使用一定剂量的紫外线辐照其叶状体，培养数天后，在叶状体上出现了少量颜色变异细胞，它们呈斑点状无规则地分布在野生型细胞中间。再培养2~3周，这些色素变异细胞分裂形成了不同颜色的细胞块，其颜色呈浅绿黄、橄榄色、草绿、绿褐、黄褐、浅褐、深紫红和浅紫红色等。在辐照强度0~80 μW/cm2范围内，叶状体上色素变异细胞块出现的频率随辐照强度的增加而增加，但增加至80 μW/cm2以上时，随着辐照强度的增加，色素变异细胞块出现的频率反而下降，这表明80 μW/cm2为有效的辐照强度。将色素变异细胞块切下，置入充气瓶内充气培养，待其释放出单孢子，随后从单孢子萌发体中挑选出了黄褐、橄榄色、红色、褐红等纯色的突变体，并利用叶状体单性生殖分别获得它们的遗传纯合丝状体（品系）。各突变品系的F₁叶状体与各自母体的颜色一样，说明其颜色是可稳定遗传的。与野生型品系相比，各色素突变品系的F₁叶状体的生长速度、活体吸收光谱、3种主要光合色素和色素蛋白的含量及它们相互间的比值均发生了明显改变。  相似文献   

ENSO期间海洋性大陆典型地区闪电活动特征分析   总被引：2，自引：1，他引：1  

林锦冰  马明  傅云飞 《气象学报》2013,71(1):109-120

利用星载闪电探测器(光学瞬变探测器(OTD)和闪电成像传感器(LIS))的观测资料,配合其他气象资料,对厄尔尼诺期间(1998年春季)和拉尼娜期间(1999年春季)海洋性大陆典型地区(11.25°S—3.75°N,96.25°—128.75°E)的闪电活动变化特征进行研究,分析了雷暴单体数目以及雷暴单体闪电率对闪电活动变化的影响,并通过对比厄尔尼诺年春季和拉尼娜年春季的大气环流形势、相对湿度、最大对流有效位能、对流风暴高度等气象要素,讨论闪电活动变化的原因。结果表明:(1)从ENSO期间雷暴单体密度和闪电密度的空间分布变化特征来看,厄尔尼诺年春季的闪电活动及雷暴活动均比拉尼娜年春季的多,并且,从闪电数目和雷暴单体数目的纬向平均、经向平均的年际变化可以发现在厄尔尼诺年春季闪电活动、雷暴活动有东伸南移的趋势。(2)在海洋性大陆典型地区,雷暴单体数目的变化是闪电数目变化的主要因子,而雷暴单体闪电率的变化是闪电数目变化的次要因子。(3)与1999年春季相比,1998年春季的副热带高压范围大、强度大;地面相对湿度大,高空相对湿度小,上下层湿度差异大,有利于对流发展;对流风暴高度较高,冰相粒子层厚度也较深厚,对流发展旺盛;最大对流有效位能大于300 J/kg的天数的空间分布极大值区域正好与闪电密度、雷暴单体密度的大值区域对应,雷电活动与对流有效位能值密切相关。  相似文献