The beaver meadow complex revisited – the role of beavers in post‐glacial floodplain development     

Lina E. Polvi  Ellen Wohl 《地球表面变化过程与地形》2012,37(3):332-346

We evaluate the validity of the beaver‐meadow complex hypothesis, used to explain the deposition of extensive fine sediment in broad, low‐gradient valleys. Previous work establishes that beaver damming forms wet meadows with multi‐thread channels and enhanced sediment storage, but the long‐term geomorphic effects of beaver are unclear. We focus on two low‐gradient broad valleys, Beaver Meadows and Moraine Park, in Rocky Mountain National Park (Colorado, USA). Both valleys experienced a dramatic decrease in beaver population in the past century and provide an ideal setting for determining whether contemporary geomorphic conditions and sedimentation are within the historical range of variability of valley bottom processes. We examine the geomorphic significance of beaver‐pond sediment by determining the rates and types of sedimentation since the middle Holocene and the role of beaver in driving floodplain evolution through increased channel complexity and fine sediment deposition. Sediment analyses from cores and cutbanks indicate that 33–50% of the alluvial sediment in Beaver Meadows is ponded and 28–40% was deposited in‐channel; in Moraine Park 32–41% is ponded sediment and 40–52% was deposited in‐channel. Radiocarbon ages spanning 4300 years indicate long‐term aggradation rates of ~0.05 cm yr^‐1. The observed highly variable short‐term rates indicate temporal heterogeneity in aggradation, which in turn reflects spatial heterogeneity in processes at any point in time. Channel complexity increases directly downstream of beaver dams. The increased complexity forms a positive feedback for beaver‐induced sedimentation; the multi‐thread channel increases potential channel length for further damming, which increases the potential area occupied by beaver ponds and the volume of fine sediment trapped. Channel complexity decreased significantly as surveyed beaver population decreased. Beaver Meadows and Moraine Park represent settings where beaver substantially influence post‐glacial floodplain aggradation. These findings underscore the importance of understanding the historical range of variability of valley bottom processes, and implications for environmental restoration. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Advance in Research of Ecology and Landscape Reconstruction of the River Floodplain In China     

QIAO Lifang　QI Anguo　ZHANG Yichuan 《湿地科学》2008,6(1):80-86

The research of ecology and landscape reestablishment of river floodplain is considered favorable to its conservation and development.The similarity and difference among river floodplain,wetland,riverside and shore have been reviewed,as well as the progress in the research of floodplain ecology reestablishment in quantitative evaluation,vegetation restoration,the influence on animal habitat and the application of eco-engineering;and of the landscape reestablishment in resource development and utilization,landscape feature and changes,landscape function,structure and control.The potentially important fields are expected to be the change of landscape pattern in different scales,the reasonable protection and utilization in the floodplain tourism,the simulating and monitoring of landscape dynamics,the planning and designing methods of floodplain landscape and the management of floodplain ecosystems.  相似文献   

The application of caesium‐137 measurements to investigate floodplain deposition in a large semi‐arid catchment in Queensland,Australia: a low‐fallout environment     

Kathryn J. Amos  Jacky C. Croke  Heiko Timmers  Philip N. Owens  Celia Thompson 《地球表面变化过程与地形》2009,34(4):515-529

Floodplains comprise geomorphologically important sources and sinks for sediments and associated pollutants, yet the sedimentology of large dryland floodplains is not well understood. Processes occurring on such floodplains are often difficult to observe, and techniques used to investigate smaller perennial floodplains are often not practical in these environments. This study assesses the utility of ¹³⁷Cs inventory and depth‐profile techniques for determining relative amounts of floodplain sedimentation in the Fitzroy River, northeastern Australia; a 143 000 km² semi‐arid river system. Caesium‐137 inventories were calculated for floodplain and reference location bulk soil cores collected from four sites. Depth profiles of ¹³⁷Cs concentration from each floodplain site and a reference location were recorded. The areal density of ¹³⁷Cs at reference locations ranged from 13 to 978 Bq m^–2 (0–1367 Bq m^–2 at the 95% confidence interval), and the mean value ± 2 (standard error of the mean) was 436 ± 264 Bq m^–2, similar to published data from other Southern Hemisphere locations. Floodplain inventories ranged from 68 to 1142 Bq m^–2 (0–1692 Bq m^–2 at the 95% confidence interval), essentially falling within the range of reference inventory values, thus preventing calculation of erosion or deposition. Depth‐profiles of ¹³⁷Cs concentration indicate erosion at one site and over 66 cm of deposition at another since 1954. Analysis of ^239+240Pu concentrations in a depositional core substantiated the interpretation made from ¹³⁷Cs data, and depict a more tightly constrained peak in concentration. Average annual deposition rates range from 0 to 15 mm. The similarity between floodplain and reference bulk inventories does not necessarily indicate a lack of erosion or deposition, due to low ¹³⁷Cs fallout in the region and associated high measurement uncertainties, and a likely influence of gully and bank eroded sediments with no or limited adsorbed ¹³⁷Cs. In this low‐fallout environment, detailed depth‐profile data are necessary for investigating sedimentation using ¹³⁷Cs. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

河南沿黄湿地景观格局及其动态   总被引：3，自引：2，他引：1  

梁国付  丁圣彦 《地理学报(英文版)》2004,14(3):339-348

By using GIS and remote sensing techniques, the paper discusses how human activities have changed along the Yellow River in Henan province, China and how these altered activities have influenced the wetland landscape pattern change from 1987 to 2002. Results show that the total area of the wetland reduces dramatically compared to 1987, the total area of wetland reduces by 19.18%, the number of the patches in 2002 increases by 21.17%, the density increases by 50%, and the total perimeter increases by 1,290,491 m. Disturbed by human activities, landscape diversity index decreases from 1.1740 in 1987 to 0.9803 in 2002. During the last 20 years, the total area of the rice wetland increases, while the others decrease. Among those, the area of the bulrush wetland decreases most. In 1987, it takes 0.5% of the total area, but in 2002, it only takes 0.11%. The interpenetration of human influences on the wetland natural system has been long and close. The impacts of human activities on the spatial pattern of the wetland landscape along the Yellow River in Henan from 1987 to 2002 are great.  相似文献   

鄱阳湖苔草洲滩湿地土壤胞外酶活性和化学计量比的高程变化特征     

黄幸运  温秀婷  张研  戎俊  聂明  郑博福  沈瑞昌 《湖泊科学》2022,34(3):894-905

土壤胞外酶参与土壤的生物化学过程,其活性和化学计量比能够反映土壤微生物的功能动态.然而,目前湿地生态系统中催化不同生物地球化学关键过程的土壤胞外酶的活性和化学计量比随高程的变化特征还不清楚.以鄱阳湖苔草洲滩湿地6个不同高程样带的表层土壤(0～10 cm)为研究对象,通过测定与土壤碳、氮、磷循环相关的7种水解酶的活性,分...  相似文献   

苏北黄泛平原典型城市天然“海绵体”潜力评价体系     

黄倩  李朗 《江苏地质》2023,47(2):203-207

苏北黄泛平原地势平坦，浅部地层结构松散,可储水“海绵体”特征明显。为评价该区域“海绵体”雨水渗储潜力，以南部的江苏宿迁市区为例，在系统分析天然“海绵体”渗储能力主要影响因素的基础上，构建了天然“海绵体”雨水渗储潜力两级评价指标体系，借助层次分析法计算各指标权重，运用MapGIS进行综合评价。结果表明，废黄河漫滩区天然“海绵体”雨水渗储潜力较好，漫滩区以外区域渗储潜力一般或较差。  相似文献   

鄱阳湖拟建水利枢纽工程对洪泛区地下水动力的影响及其生态意义          下载免费PDF全文

曹思佳  李云良  姚静  李宁宁  赵贵章  李志萍 《湖泊科学》2023,35(4):1457-1469

洪泛湿地是位于水生系统和陆生系统之间的过渡带，在河流和陆地之间的水文生态方面起着纽带作用，受气候变化和人类活动的叠加影响，其水文过程改变很大程度上影响了湿地生态系统循环、结构和功能的稳定。本文以鄱阳湖洪泛区湿地为研究区，应用湖泊水动力和洪泛区地下水数值模型，评估鄱阳湖拟建水利枢纽工程对洪泛区地下水系统的影响。模拟结果表明，拟建水利枢纽工程将会遵循调度方案使得湖泊水位明显提高，但同时导致洪泛区地下水位的整体抬升，且东部主湖区附近的地下水位受到的影响（约1～3 m）要明显强于洪泛区其它区域（约小于1 m）。地下水位的变化同时导致不同典型时期洪泛区地下水流速的减小及地下水流向的改变，表现为枢纽建设后地下水流向的逆转和流速基本小于0.1 m/d。鄱阳湖涨水-丰水期总体为湖水补给洪泛区地下水模式，枯水-退水期主要为地下水补给湖水模式，但水利枢纽可能导致洪泛区地下水系统水均衡状态发生转变，影响了地下水系统的补给和排泄状态，最终形成了长期稳定的湖泊补给地下水的作用模式。从地下水-生态系统响应变化的角度分析，拟建水利枢纽建设引起的地下水位上升，可能会给湿地生物地球化学元素的迁移转化、植被群落的演变与退...  相似文献   

鄱阳湖典型洪泛区地下水数值模拟研究          下载免费PDF全文

曹思佳  李云良  李宁宁  陈静  宋炎炎  赵贵章  李志萍 《湖泊科学》2023,35(1):298-312

受地表河湖系统水情变化干扰，高度动态和异质性的洪泛区地下水文对河湖水资源、水污染以及生态环境功能等方面具有重要影响和贡献。鄱阳湖洪泛区湿地在长江中下游具有重要区位优势和研究特色，但变化环境下其水动力特征和水量交换情况等仍存在许多不确定性。本文以鄱阳湖典型洪泛区为研究区，采用地下水流二维数值模型，开展了洪泛区地表地下水转化作用与水量变化的模拟研究。结果表明，鄱阳湖季节性水位变化很大程度上决定了主湖区与周边地下水之间的动态补排模式，即洪泛区地下水补给湖泊主要发生在枯水和退水时期，而湖泊补给地下水主要发生在涨水和高洪水位时期。一般情况下，整个洪泛区地下水位与湖水位的年内变化态势基本一致，主湖区附近的地下水位年内变幅较大，而大部分洪泛区的地下水位变幅相对较小。北部地下水流速明显大于南部，主湖区附近地下水流速明显大于洪泛区，地下水流速基本小于1～2 m/d。水均衡分析发现，洪泛区地下水系统以接受降雨输入（52%）和主湖区补给（39%）为主，以地下水蒸发输出（72%）和向湖排泄（24%）为主，但补给主要发生在春、夏季，而排泄则发生在秋、冬季。地形地貌对洪泛区地下水位分布以及流速场演化具有主控作用，...  相似文献   

鄱阳湖湿地中低滩典型植物群落的生物多样性及影响因子          下载免费PDF全文

郭宇菲  万荣荣  龚磊强  秦风约  王经波  王晓龙 《湖泊科学》2023,35(4):1370-1379

周期性水文节律是影响洪泛湖泊洲滩湿地植物群落物种组成与生物多样性的重要驱动力。本研究以鄱阳湖中低滩典型植物群落为研究对象，通过实地样方调查与统计方法分析植物群落的生物多样性格局及其关键环境因子。结果表明：鄱阳湖中低滩代表性群落分别是灰化薹草群落和虉草群落；植物群落的Shannon-Wiener多样性指数均值为1.5,Pielou均匀度指数均值为0.55，生物多样性与物种均匀度偏低。虉草群落的均匀度、多样性指数高于灰化薹草群落，但二者物种丰富度差异不明显。土壤铵态氮、总磷及土壤含水量和高程是影响植物群落结构与生物多样性的关键因子，其中灰化薹草的物种多样性与土壤铵态氮高度相关，而虉草的均匀度则与土壤总磷关系更密切。此外，鄱阳湖中低滩环境下，灰化薹草群落的均匀度随土壤总磷含量的升高呈现U型响应曲线，虉草则是倒U型，这表明，鄱阳湖中低滩环境下，灰化薹草群落和虉草群落生物多样性对单个、同一的环境因子存在不同的适应机制。  相似文献