Late Holocene in central Brazil: vegetation changes and humidity variability in a tropical wetland     

SHIRLEY MARIA LIMA SABINO  RAQUEL FRANCO CASSINO  MAKÊNIA OLIVEIRA SOARES GOMES  ENEIDA MARIA ESKINAZI SANT'ANNA  CRISTINA HELENA RIBEIRO ROCHA AUGUSTIN  DIEGO ALVES DE OLIVEIRA 《第四纪科学杂志》2021,36(6):1028-1039

The Pandeiros wetland is a high biodiversity ecosystem located within a semiarid region of the Cerrado biome, a neotropical savanna. This large wetland is of key importance for ecological and hydrological balance in central Brazil and for the conservation of the Cerrado fauna and flora. In this study, we present the first palaeoecological investigation of the Pandeiros wetland based on pollen analysis of a palm swamp sediment core encompassing the Late Holocene. Our results show that the wetland was subject to multicentennial-scale oscillations in water availability during the Late Holocene; in particular, higher local humidity was documented between 4100 and 3100 cal a bp and from 2600 to 1000 cal a bp , and two events of drier local conditions occurred at approximately 2900 and 900 cal a bp. Our results also indicate a general decreasing trend in arboreal density in the Pandeiros River Basin from the beginning of the Late Holocene to the present, with the greatest expansion of dry forest occurring between 3600 and 3100 cal a bp.  相似文献   

Run‐off formation in a humid,temperate headwater catchment using a combined hydrological,hydrochemical and isotopic approach (Jizera Mountains,Czech Republic)          下载免费PDF全文

M. Šanda  T. Vitvar  A. Kulasová  J. Jankovec  M. Císlerová 《水文研究》2014,28(8):3217-3229

The formation of baseflow and stormflow was examined in the 1.18 km² part of the headwater catchment Uhlí?ská, Jizera Mountains, Czech Republic, over the period 2007–2011, by means of run‐off data and environmental tracers ¹⁸O and SiO₂. The baseflow, computed using the digital filter approach BFLOW, contributes 67% to total streamflow and has a mean residence time of 12.3 months. It is formed by groundwater discharge from the valley deluviofluvial granitic sediments, in combination with soil water in weathered layers on hillslopes during rainfall and snowmelt periods. The prevailing source of the groundwater is the infiltration of snowmelt water. Analysis of 20 run‐off events and their hysteretic patterns demonstrated that the stormflow water has a residence time of about 4 months and is generated by preferential flow on hillslopes combined by soil matrix drainage. Because of slower flow in the soil matrix, the enrichment of pore water in SiO₂ is more pronounced. The stormflow and snowmelt water flowing via preferential pathways of upslope minerals soils pushes the pre‐event groundwater through the pathways in wetlands to the stream, and the wetland can be therefore considered as groundwater supplied. This mechanism has been found to be typical for the groundwater‐supplied headwater catchments of the Jizera Mountains and can be also assumed in other mountainous headwaters of the granitic massif in Central Europe. The main methodological contribution of this study are the residence time calculations stratified by baseflow and event flow, identifying run‐off components of different travel times to streams and linking them with geochemical run‐off sources. This achievement was possible because of a comprehensive dataset on hydrology, stable isotopes and silica hydrochemistry in all relevant run‐off generation components. This concept indicates that a possible long‐term change in snowmelt may affect the run‐off regime of headwater catchments to climate or land‐use changes. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

中国海洋科技创新效率发展格局演变与类型划分   总被引：2，自引：0，他引：2  

王晓辰  韩增林  彭飞  蔡先哲 《地理科学》2020,40(6):890-899

科技创新是促进海洋产业发展的新兴驱动力，对提高发展质量至关重要。研究使用SBM超效率模型测度中国沿海11省市（不包括港澳台地区）2006?2014年海洋科技创新效率，结合核密度估计分析其时空分异特征，再从投入规模和创新效率2个维度，划分出海洋科技创新发展类型区。结果表明：① 从效率变化角度来看，2006?2014年间研究区海洋科技创新效率存在小幅增长，但整体效率水平较低，地区之间效率差异先缩小后扩大，最终形成以辽宁、上海、广东三地为主的北、中、南三方向的海洋科技创新发展核心。② 从海洋科技创新投入规模和创新效率双维度综合来看，进一步将沿海地区海洋科技创新发展模式划分成 4种类型：引领区（广东、上海、辽宁）、追赶区（广西）、突破区（天津、山东、福建、江苏、浙江）、落后区（河北、海南）。  相似文献   

典型入海口海岸带生态环境质量遥感评价研究——以宝山区为例          下载免费PDF全文

范小安  王金辉  徐美娜  邓艳芬 《海洋学研究》2020,38(2):66-73

为了研究入海口海岸带生态环境质量状况,基于遥感信息技术,从土地利用的角度,构建入海口海岸带生态环境遥感评价体系,通过层次分析法并结合专家咨询法,以上海市宝山区岸线向陆5 km区域为例进行评价,得到各区域综合评价值。结果表明,宝山区入海口海岸带以工矿仓储用地为主,该区域生态环境质量自西向东逐渐下降,在练祁河和马路河之间区域到达最低点,向东开始回升,总体生态环境质量呈较差状态。  相似文献   

Snowmelt variability in Polar Bear Pass,Nunavut, Canada,from QuikSCAT: 2000–2009     

Stephen E. L. Howell  Jane Assini  Kathy L. Young  Anna Abnizova  Chris Derksen 《水文研究》2012,26(23):3477-3488

Snowmelt onset and end date estimates are made from QuikSCAT scatterometer measurements in the Canadian High Arctic wetland of Polar Bear Pass (PBP) and the surrounding region of Bathurst Island, Nunavut. In situ data within PBP is used to validate QuikSCAT snowmelt onset/end date estimates. Results indicate that within PBP from 2000 to 2009, the mean snowmelt onset date was Year Day (YD) 162, the mean snowmelt end date was YD179, and the mean snowmelt duration was 17 days. More interannual variability was apparent in snowmelt end date and duration compared with onset, and only snowmelt end date was significantly correlated with mean June air temperature at ?0.78. Cooler air temperatures in 2004 contributed to a long snowmelt duration of 24 days, and the very short snowmelt duration in 2007 of just 11 days was caused by rapid and sustained increases in air temperature. For snowmelt end date and duration the mean spatial pattern revealed two centres of later snowmelt end date/longer snowmelt duration over Bathurst Island. They were separated by early snowmelt end date/short snowmelt duration in PBP. These patterns are in agreement with the spatial distribution of mean May to July air temperature over Bathurst Island and are likely influenced by the local‐scale topography of Bathurst Island. Given the correlation between air temperature and snowmelt end date, we might expect quicker snowmelt under increased warming. The latter process may have implications for the sustainability of the PBP wetland under a warmer climate. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

The Fill–Spill Hydrology of Prairie Wetland Complexes during Drought and Deluge     

Dean A. Shaw  Garth Vanderkamp  F. Malcolm Conly  Al Pietroniro  Lawrence Martz 《水文研究》2012,26(20):3147-3156

The fill–spill of surface depressions (wetlands) results in intermittent surface water connectivity between wetlands in the prairie wetland region of North America. Dynamic connectivity between wetlands results in dynamic contributing areas for runoff. However, the effect of fill–spill and the resultant variable or dynamic basin contributing area has largely been disregarded in the hydrological community. Long‐term field observations recorded at the St. Denis National Wildlife Area, Saskatchewan, allow fill–spill in the basin to be identified and quantified. Along with historical water‐level observations dating back to 1968, recent data collected for the basin include snow surveys, surface water survey and production of a light detection and ranging–derived digital elevation model. Data collection for the basin includes both wet and dry antecedent basin conditions during spring runoff events. A surface water survey at St. Denis in 2006 reveals a disconnected channel network during the spring freshet runoff event. Rather than 100% of the basin contributing runoff to the outlet, which most hydrological models assume, only approximately 39% of the basin contributes to the outlet. Anthropogenic features, such as culverts and roads, were found to influence the extent and spatial distribution of contributing areas in the basin. Historical pond depth records illustrate the effect of antecedent basin conditions on fill–spill and basin contributing area. A large pond at the outlet of the St. Denis basin, which only receives local runoff during dry years when upstream surface storage has not been satisfied, has pond runoff volumes that increase by a factor of 20 or more during wet years when upstream antecedent basin surface storage is satisfied and basin‐wide runoff contributes to the pond. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

The hydrodynamics and salinity regime of a coastal lagoon – The Coorong,Australia – Seasonal to multi-decadal timescales     

Ian T. Webster 《Estuarine, Coastal and Shelf Science》2010

The Coorong is a choked coastal lagoon in South Australia that forms part of the terminal lake system at the end of the River Murray, Australia’s major river. It is an inverse estuary with a constricted channel connection to the sea at one end and extends parallel to the coast for more than 100 km away from this inlet. The present paper considers the physical dynamics of the Coorong, particularly its ecologically important salinity and water level regimes, and how these respond to connectedness with the ocean, barrage flows and meteorological conditions. The approach combines hydrodynamic modelling with measurements and considers temporal variation in the system ranging from seasonal to multi-decadal timescales.  相似文献   

山东半岛冷流暴雪过程的个例分析     

朱营礼  吴增茂  林曲凤  周淑玲 《中国海洋大学学报(自然科学版)》2010,(Z1)

2008年12月4~5日,山东半岛出现了1次冷流暴雪过程,渤海上的辐合带对这次暴雪过程起到了重要的作用。本文利用观测资料和数值模式对这次过程进行了研究,探讨渤海辐合带的发展演变机制及对山东半岛冷流暴雪的影响,并分析了太行山脉对渤海辐合带的影响。结果表明,渤海上空生成的西北东南向的中尺度辐合带造成了以烟台-牟平-文登为中心的西北东南向的降雪带。太行山脉的阻挡作用使绕太行山的西北气流在太行山背风侧形成辐合,同时在低层大气存在1个暖脊,所以在渤海形成了1个西北东南向的辐合带。在西北风的水平平流和非地转风的作用下,渤海辐合带向东北移动,当渤海西北岸出现北风后,渤海辐合带西北部在北风的水平平流作用下向南移动,而渤海辐合带东南部在西北风水平平流和非地转风的作用下,继续向东北移动并与山东半岛北部的海岸锋辐合带合并增强,渤海辐合带西北和东南两部分移动方向的不同造成了辐合带的波动。渤海辐合带增强后登陆山东半岛,造成山东半岛西北东南向降雪带。对这次冷流暴雪个例的分析发现,太行山脉通过形成背风低压中尺度系统直接影响渤海上的中尺度辐合带的发展,而渤海辐合带与山东半岛北岸附近海岸锋的耦合使辐合加强,增强了降雪强度。  相似文献   

In two waters: contemporary evolution of lagoonal and marine white seabream (Diplodus sargus) populations     

Mercedes González-Wangüemert  Ángel Pérez-Ruzafa 《Marine Ecology》2012,33(3):337-349

Brackish water ecosystems are often exposed to wide variations in environmental variables, including temperature and salinity, which may cause strong selective pressures on organisms modifying the genetic patterns of species. The aim of this work was to test whether there is a ‘divergence-with-gene flow’ in coastal lagoon populations of white seabream (Diplodus sargus) (Ria Formosa, S Portugal and Mar Menor, SE Spain) respect to four marine populations, by using partial sequences of cyt b mitochondrial gene and information from nine microsatellite loci. Genetic diversity was highest in both coastal lagoons (Mar Menor and Ria Formosa) considering mitochondrial and nuclear markers. Although some of F_ST population pairwise comparisons were not significant, analyses of molecular variance (AMOVAs) detected differences between groups (coastal lagoon and marine) close to significance. Also, only two haplotypes (Cytb-17 and Cytb-18) were detected in both coastal lagoon sampling sites and these localities (Mar Menor and Ria Formosa) showed the highest number of singletons, some of them with a high number of mutations, as has been already described for other Mar Menor populations (Pomatochistus marmoratus and Holothuria polii). Also, several tests detected significant positive and balancing selection considering mtDNA and microsatellite data. These data support the hypothesis of selection as one of the drivers of the genetic differences found between coastal lagoon and marine populations. The life strategy adopted by Diplodus sargus in coastal lagoons allows it to decrease its mortality rate and improve the heritability of its genes. Also, the increase time spent in coastal lagoons with different temperatures and salinities favours the fitness selection and the maintenance of exclusive haplotypes and genotypes in coastal lagoon inhabitants favouring the ‘divergence-with-gene-flow’.  相似文献   

长江河口百米以浅土体含盐特征及其沉积环境演化     

苟富刚  龚绪龙  杨露梅  张岩  刘明遥 《现代地质》2022,36(2):462-473

土体含盐特征是研究环境演化、工程地基基础设计和农业开发的重要参考指标。通过采集长江河口地区土样907件并对土体盐分进行测试,得到土体易溶盐8大离子含量和pH值。根据测试结果对研究区100 m以浅土层含盐特征进行系统分析。研究结果表明:各土层含盐量介于0.028%~1.226%之间。全新世土体随着深度的增加,土体含盐量呈增加趋势。含盐量最大值出现在如东组下段4-1层(埋深约26 m)淤泥质粉质黏土,盐分主要为NaCl。含盐量最小值出现在滆湖组下段的7~2砂层(埋深约81 m),其中HC0₃^-离子含量最高,其次为Cl^-与Na⁺。深部土层(滆湖组)含盐量有所降低,黏性土含盐量一般大于砂土。各土层ESR(交换性钠)值均大于当地地表淡水SAR(钠吸附比)值,ESR最大值为当地地表淡水SAR值的47.7倍,最低值也为当地地表淡水SAR值的2.7倍,说明土体中可交换Na含量高。100 m以浅地层含盐特征受晚更新世晚期海侵和全新世海侵控制,土体盐分主要为NaCl,其主要来源为海水浸渍或浸染。更新世土层为陆相沉积,但受晚更新世晚期海侵与全新世海侵浸染,土体含盐量较高。如东组下段和中段地层为三角洲相沉积,受长江和海侵共同作用,盐渍土广泛分布;如东组上段土层为陆相沉积,土体已普遍脱盐,HC0₃^-离子含量最高。土体中Cl^-含量对混凝土结构中的钢筋腐蚀性较大,特别是4-1淤泥质粉质黏土层,具有弱腐蚀性等级以上的土体占比高达99%,要做好基础防腐蚀工作。如东组上段的2-1和2-2土层(浅表土层)碱性较大,对农业和工程建设影响最大,需添加改良剂进行土体改良。  相似文献