On the interest of using the multiple center approach in ESR dating of optically bleached quartz grains: Some examples from the Early Pleistocene terraces of the Alcanadre River (Ebro basin,Spain)

The present work reports the first numerical ages obtained for the two highest fluvial terraces (Qt1 and Qt2) of the Alcanadre River system (Northeastern Spain) representing the earliest remnants of Quaternary morphosedimentary fluvial activity in the Ebro basin. ESR dating method was applied to optically bleached quartz grains and both the Al and Ti centers were measured, in accordance with the Multiple Center approach. The results are overall in good agreement with the existing preliminary chronostratigraphic framework and our interpretation indicate that terraces Qt1 and Qt2 have an ESR age of 1276 ± 104 ka and 817 ± 68 ka, respectively. These data provide some chronological insights on the beginning of the fluvial sedimentary processes in a scenario of incision maintained over Quaternary in the Ebro Basin. These are among the first numerical ages obtained for such high terraces in the Iberian Peninsula.Our results demonstrate the interest of using the Multiple Center approach in ESR dating of quartz, since the two centers provide complementary information, i.e. an independent dose control. The overall apparent consistency between the ESR age estimates and the existing preliminary chronostratigraphic framework may be considered as an empirical evidence that the Ti–Li center may actually work for Early Pleistocene deposits, whereas the Ti–H center shows some clear limitations instead. Finally, these results demonstrate the interest of using ESR method to date Early Pleistocene fluvial terraces that are usually beyond the time range covered by the OSL dating method.     

Modeling the effects of riparian planting strategies on stream temperature: Increasing suitable habitat for endangered Formosan Landlocked Salmon in Shei‐Pa National Park,Taiwan

Reducing or stabilizing the stream temperature of ChiChiaWan Creek is a crucial work for Formosan Landlocked Salmon because ChiChiaWan Creek is the only one habitat for this endangered species. Planting trees in the riparian zone would be one of the alternatives. The purpose of this study was to evaluate the effects of several planting strategies on daily maximum stream temperature along the river. The results showed the effective vegetative shading angles should be more than 50° along ChiChiaWan Creek to reduce the direct solar radiation heating effectively. Upstream planting with 70° vegetative shading angle could be the most effective way among all the scenarios. However, this planting strategy could not improve the worst situations in summer because of the large solar elevation angles. The upstream planting in ChiChiaWan Creek was strongly recommended because the canopies could be easier to extend to totally cover the narrow width of river producing the most effective shades. Practicing the upstream planting with 90° vegetative shading angle can increase more than 1 km long suitable habitats for the endangered Salmon in summer. Alternatively, the west‐side planting scenario was the second effective way for temperature reduction. Our result provided a useful suggestion for the authorities in charge of saving the Formosan Landlocked Salmon, particularly under the stress of global warming. Copyright © 2011 John Wiley & Sons, Ltd.     

Testing links between river patterns and in-channel characteristics using MRPP and ANOVA

This study tests the assumption that the characteristics of channels within multiple channel rivers are different from those of single channel rivers. Some river restoration approaches propose radical transformation of river patterns, from multiple to single channels, based on the link between river patterns and their in-channel characteristics. Determining the links between river patterns and their in-channel characteristics is complicated by differences in geology, history, climate and discharge among rivers. Furthermore, multiple channel rivers are composed of a mosaic of channel types with a range of in-channel characteristics. This study minimizes these problems by analysing a single river containing neighbouring single and multiple channel patterns with little change in discharge downstream, and by analysing all channel types. The study addressed two objectives: to determine the hydraulic geometry, energy, and sediment mobility characteristics of neighbouring single and multiple channel river patterns, and to test for statistical differences in these characteristics between patterns. The Renous River shows a wandering pattern for 11.5 km, with multiple channels around semipermanent islands and abandoned channels in the flood plain. The river displays a single channel river pattern where channels are confined by their valley walls, upstream and downstream of wandering. The analysis was conducted at three scales. First, the confined single channel and wandering multiple channel patterns were compared (pattern scale). Second, the confined channel pattern was compared to single and multiple channel sections within the wandering pattern (section scale). Third, all channel types were compared (channel type scale). Multi response permutation procedure (MRPP) and analysis of variance (ANOVA) were used to analyze differences between channels. Difference tests found no simple discrimination between the single and multiple channel river patterns of the Renous River. Tests between the single confined and multiple wandering channel patterns found few differences in the in-channel variables. The tests did find differences between multiple channel sections within the wandering pattern and confined single channels; however, a greater number of differences were found between multiple channel and single channel sections within the wandering pattern, highlighting the variability within the wandering pattern. Two groups emerged when all channel types were tested for differences: perennial main-channels containing the thalweg, and ephemeral side-channels. Therefore, side-channels define the in-channel characteristics of wandering rivers because few differences were found among main-channels in either pattern. This analysis suggests that all channel types, not just main-channels, should be investigated to obtain a complete picture of a river pattern prior to any restoration efforts. Engineers must exercise caution when applying the link between river patterns and in-channel characteristics to river restoration efforts.     

北极海冰快速减少期间加拿大海盆上层海洋夏季淡水含量变化

北极海冰近年来快速减少,北冰洋淡水含量也出现了急剧变化。加拿大海盆作为北冰洋淡水的主要存储区域,研究其淡水含量变化对于认识北冰洋淡水收支有重要意义。本文根据2003年、2008年中国北极考察以及2004年至2007年的加拿大考察数据进行计算,发现除2006年以外,夏季加拿大海盆淡水含量在此期间每年增加1m以上厚度。增加主要发生在冬季白令海水以上的上层海水中,而在此之下,淡水含量维持在3m左右,没有显著年际差异。在2006年,加拿大海盆西部上层淡水含量略微减少,但东部和北部海域淡水含量仍略有增加。与2003年相比,2008年加拿大海盆中心海区淡水含量增加量最高可达7m。分析表明,近年来的海冰减退对加拿大海盆上层淡水含量的增加起着重要作用,北极涛动(AO)正负相位变化也是控制其淡水含量变化的一个重要因素。而降水、径流以及白令海峡入流水的变化对加拿大海盆淡水含量变化影响较小。     

Influence of sea ice and sea surface temperature on the abundance of Antarctic krill in Area 48.2

In this paper we examine the relationship between Antarctic krill catch, sea ice concentration, and sea surface tempera- ture （SST）. Data on the Antarctic krill catch from 2003 to 2010 in CCAMLR Area 48.2 were combined with sea ice and SST data. Results showed that krill fishing in Area 48.2 took place from February to August each year but the catch was concentrated from March to July, with production during this period accounting for about 99.3% of the annual catch. Regression analysis showed that the catch per unit effort （CPUE） was clearly related to sea ice concentration and SST intervals. CPUE was negatively correlated with the area of sea ice among years （R2=0.64）, and the correlation was strongest （R2=0.71） when sea ice concentration was greater than 90%. Over the months the CPUE initially increased, then decreased as the area of sea ice increased. The relationship was strongest （R2=0.88） when the concentration of sea ice was 60%--70%. There was no negative correlation among years between CPUE and the ice-free area when S ST was between -2 ℃ and 3 ℃ （R2=0.21）, but there was a significant negative correlation when SST was between 1 ℃ and 2℃ （R2=0.82）. Over the months, CPUE initially increased then decreased with increasing sea ice-free area, and the relationship was strongest （R2=0.94） when SST was between 0℃and 1 ℃. This study shows that sea ice concentra- tion and SST have significant effects on the abundance of krill in Area 48.2, and the findings have practical significance for the use and conservation of Antarctic krill resources.     

新疆塔里木河流域水资源承载力评价研究

结合塔里木河2002年自然、社会和经济以及水资源资料,选取了耕地灌溉率、水资源利用率、供水模数、需水模数、人均供水量、生态用水率6个主要因素作为评价因素,应用模糊综合评判模型对塔里木河流域水资源承载能力进行了评价研究。结果表明,流域水资源开发利用已经达到相当规模,在现有经济技术条件下,该地区的水资源承载潜力已相对较小,水资源供需矛盾突出,应由耗水型经济结构向节水型经济结构转变,加强水资源的综合管理,以便科学、合理地利用流域内有限的水资源。     

河流对0.8 Ma B.P.环境突变事件的地貌响应研究

以兰州盆地0.8 Ma B.P.阶地为例证,运用古地磁测年方法,通过收集相关文献,分析讨论了0.8 Ma B.P.阶地与0.8 Ma B.P.环境突变事件的联系。结果表明：① 0.8 Ma B.P.环境突变事件主要表现在气候转型、构造运动等方面,具有群发性和全球性特点;② 兰州盆地以及其他区域0.8 Ma B.P.阶地存在的证据,表明河流在0.8 Ma B.P. 前后普遍发生过一次下切事件;③ 0.8 Ma B.P.阶地是河流对0.8 Ma B.P.环境突变事件的地貌响应,构造运动为提供了下切驱动力,而气候变化则控制了下切时间。     

基于雷达监测河川径流的测量及算法

祁连山大野口流域由于水流急、河面宽,修筑量水堰有一定的难度,准确监测河川径流成了流域水量平衡和涵养水源功能机理研究的障碍。通过大野口流域雷达测流处水面比降、河川横断面面积、水力半径、流速仪实测流量、糙率和谢才系数等一系列测量和计算,可得出雷达监测水位与相应的河川径流量的函数关系式,并绘制出水位流量图。结果表明:雷达测流处水面平均比降为0.028;河川最大洪水断面宽13.4 m,高1.32 m;河川横断面糙率的平均值为0.059;雷达监测水位与相应的河川径流量的函数关系式为Q=0.0018H2-0.0206H(R2=0.9994),该关系式可有效解决修筑量水堰较难而利用雷达监测河川径流的难题。通过研究,可为中等流域尺度上进一步揭示水源涵养功能机理及其流域产流机制提供参考和科学依据,是实现未来水资源可持续开发利用的基础工作,其对认知特定区域水文过程的演变规律,保障内陆河流域水资源合理开发,维持河西地区农业可持续发展具有重要意义。     

The postglacial environmental development of Raffles Sø, East Greenland: inferences from a 10,000 year diatom record

A 341 cm long sediment sequence was recovered from the unofficially named Raffles Sø on Raffles Ø, outer Scoresby Sund region, East Greenland. The sediment sequence consists in the upper part (0–230 cm) of a stratified gyttja enriched in organic carbon and biogenic silica whereas the lower core part (235–341 cm) is composed of terrigenous, consolidated glacio-limnic sediments. ¹⁴C-AMS measurements indicate that the sediment sequence represents the entire Holocene lake history from 10,030 calibrated radiocarbon years.The geochemical parameters (opal, total organic carbon (TOC), total nitrogen (TN)) and the total diatom concentration show similar developments during the Holocene, and reflect changes in biological production and nutrient input into the lake. These records clearly reveal a broad Holocene TOC-opal-maximum interval between 5200 and 1800 cal. yrs BP.The diatom flora consisted of 66 taxa representing 20 genera but only seven taxa were abundant and, sometimes, these were monospecifically dominant during the Holocene. In the sediment core from Raffles Sø four successive stratigraphical zones can be distinguished. Accumulation of diatom valves began at 9900 cal. yrs BP with a Stephanodiscus minutulus (Kütz.) Cleve and Möller dominated assemblage (stratigraphic zone 1) followed by a diatom flora dominated by Cyclotella pseudostelligera Hustedt and, less frequently, by Diatoma tenuis Agardh (9400 until 5900 cal. yrs BP, zone 2). Cyclotella sp. A, a taxon which belongs to the Cyclotella rossii-comensis-tripartita-complex, was the dominant floral element between 5200 and 1800 cal. yrs BP (zone 3). From 1800 cal. yrs BP, the periphytic taxa Fragilaria capucina var. gracilis (Østr.) Hustedt and F. capucina var. rumpens (Kütz.) Lange-Bertalot attained highest relative abundances, also almost monospecifically (zone 4).The distribution and composition of the diatom assemblages in the sediment record from Raffles Sø probably reflect past variations in the extent of the lake-ice cover during the growing season. More or less ice-free conditions during summer may have prevailed during the early Holocene until ca. 1800 cal. yrs BP, which allowed growth of planktonic diatoms (Cyclotella taxa) in the pelagic lake region. From 1800 cal. yrs BP, colder conditions lead to a perennial lake-ice cover with a small ice-free moat in summer which favored the growth of periphytic, littoral species (Fragilaria capucina varieties).     

桂江流域土壤侵蚀估算及其时空特征分析

桂江流域的水土流失现状研究对珠江三角洲的水生态安全有重要的现实意义。采用修正的通用土壤流失方程（RUSLE）估算了桂江流域的土壤侵蚀模数与年侵蚀总量,分析流域内土壤侵蚀的时空分布特征,探讨了影响该区域土壤侵蚀强度的自然与人文因素。结果表明,桂江流域51.8%的地表都在发生不同程度的土壤侵蚀。从全流域平均土壤侵蚀强度来看,属于中度侵蚀。从土壤侵蚀面积来看,约85%的地表处于微度、轻度与中度侵蚀。4-6月的全流域平均土壤侵蚀强度最大,侵蚀总量也是最大的。流域的土壤侵蚀主要发生在高程在30~600m的低山丘陵-高地地貌区内的林地与耕地中。流域内岩溶区的土壤侵蚀强度随着石漠化程度从无到中度逐渐增加,轻、中度石漠化区的土壤侵蚀强度达到强度侵蚀等级。