洪水对湿地系统的作用

洪水是水流运动的一种自然现象,是河流对河滨洪泛湿地系统的一种正常的干扰。不定期的洪水干扰维持了河流与其洪泛湿地不同程度的水文连通性,成为维持河流洪泛湿地景观异质性和生态系统平衡的重要营力。作为河流极端的水文情势,排除较大规模的洪水所造成的一定的生态环境破坏和社会经济损失以外,洪水干扰对生态环境产生多方面的正效应。从洪水的生态意义角度出发,论述洪水干扰对湿地生态系统及其环境所产生的正面效应,包括洪水干扰对洪泛区湿地沉积过程的影响,促进湿地系统水循环以及对土壤发育产生影响,导致洪泛区及其湿地生态系统和景观的演替。     

Late Holocene history of the floodplain lakes of the Cauca River, Colombia

We conducted a paleolimnological investigation of late Holocene deposits on a distal, constrained floodplain of the Cauca River, northern Colombia, i.e. the La Caimana sedimentary succession. The record starts sometime between 4,500 and 4,000 cal yr BP, when the first high-energy fluvial events inundated an ancient soil surface. From that time until about 3,260 cal yr BP, a stable and probably seasonal flooding regime was established on the floodplain. From ~3,260 to ~2,800 cal yr BP, ephemeral and shallow swamps developed on the floodplain. Their formation and duration depended on their connection with the Cauca River. From ~2,800 to ~2,400 cal yr BP, fluvial influence became more dominant, establishing a semi-permanent connection between the river and the floodplain. From ~2,400 to 1,400 cal yr BP, episodic formation of ephemeral swamps occurred. During this stage, floodplain lakes displayed high salinity and nutrient concentrations, and possibly alkaline conditions as a consequence of reduced water volume when the connection with the river was reduced or lost completely. A change in the hydrological regime occurred from ~1,400 to ~850 cal yr BP, when high-energy fluvial events were punctuated by periods of reduced flooding that enabled soil formation. Generally, connection with the Cauca River resulted in lake waters with low salinity and nutrient concentration, whereas loss of connection with the river led to lakes with greater salinity and nutrient content. Paleocurrent analyses indicate that flows came predominantly from the Cauca River, suggesting the lakes were formed by the impoundment of La Caimana Creek. The sedimentary succession of La Caimana offers a unique, high-resolution record of the evolution and dynamics of an ancient floodplain of the Cauca River and its aquatic ecosystems.     

黄河三角洲刁口河流路湿地恢复遥感监测与评价

利用卫星遥感技术对生态调水及湿地恢复进行实时动态监测, 不仅可以及时掌握宏观地表的快速变化, 还可以为长期的区域生态效应评价提供支持。基于国产自主环境一号小卫星遥感数据, 对2010 年黄河三角洲生态调水暨刁口河流路恢复过水试验进行动态监测和初步评价。研究表明, 刁口河流路恢复过水后, 原废弃河道过流条件得到提高, 部分被开发利用的河滩地得到恢复, 水文条件好转, 河流水面面积总体上增加了526 hm², 有利于河道生态条件的改善。通过对湿地引水修复, 自然保护区试验区块共有437 hm²的退化湿地得到了较大程度的改善。同时, 湿地景观多样性提高, 对维持区域景观多样性、改善鸟类栖息地质量具有重要意义。研究结果表明, 国产环境一号卫星遥感数据能提供丰富的地面信息, 其数据具有较高的时间分辨率, 可以作为中国湿地调查和监测的重要数据源。考虑到大尺度调水和湿地恢复对区域生态环境的影响是一个长期的过程, 今后应进一步挖掘环境一号卫星现有波段的光谱信息, 对湿地恢复进行长期跟踪监测, 为湿地恢复生态效应综合评估提供技术支撑。     

湿地生态系统碳循环研究进展

碳在不同类型湿地中储藏量约占地球陆地碳总量的15%。由于全球湿地面积迅速减少,湿地生态系统正常的水循环和碳循环过程产生一定的变化,湿地生态系统的演变也可能是全球大气CO₂含量升高的一个不可忽视的重要因素。气候条件是湿地碳循环生物地球化学过程的重要驱动因素,湿地特殊的生态水文过程和土壤环境条件,使得湿地碳循环具有区别于其它生态系统碳循环的特征。影响湿地中碳积累与分解过程的重要控制因子是温度、水文条件和植物群落,特别是水文条件对湿地碳循环过程影响较大。湿地土壤呼吸通量与根层土壤温度呈正相关关系,并受地表积水深度和地下潜水水位的影响,另外,洪泛作用会增加湿地CO₂的排放率,湿地水文过程决定溶解有机碳的输入与输出过程。     

Using palaeoecological records to disentangle the effects of multiple stressors on floodplain wetlands

Ecosystems worldwide are subject to the deleterious effects of multiple anthropogenic stressors. Understanding and mitigating the effects of these stressors is difficult both because stressors are confounded in space and have the potential to act both synergistically and antagonistically. Palaeoecological approaches applied to systems where stressors may be confounded in space but not in time offer a way to explore the effects of multiple stressors. This multi-proxy study of sediment records from four floodplain lakes (billabongs) on a dryland river floodplain subject to grazing, commencing in the late 1800s, and irrigated cropping, commencing in the late 1900s, tests this approach. The results suggest that the effects of both grazing and irrigation on floodplain ecosystems can be detected in the pollen and diatoms preserved in sedimentary records of billabongs. For the pollen, these changes are inconsistent, but appear to reflect local shifts in dominance among major tree taxa and among key understorey plant families. For the diatoms, the changes were also not consistent across sites, but can be generalised as reductions in epiphytic diatoms and increases in planktonic and facultative planktonic taxa that likely reflect increased fluxes of sediments and nutrients and reduced flood frequency. Overall, the effects of grazing appear to have been greater than irrigated cropping. The results also show that the relative effects of grazing and irrigated cropping on floodplain and riparian vegetation and on diatom communities vary between billabongs, with some evidence that at least some of this variation relates to the level of hydrological connection to the mainstream. Finally, the study suggests that for the most part, grazing and irrigated cropping act antagonistically in the way they impact these floodplain ecosystems, a pattern that likely reflects a release from grazing pressure associated with the increase in irrigated cropping. Future applications of the approach should increase spatial and temporal replication and develop more sophisticated frameworks that account for temporal variation in driver intensity and proxy indicators of the specific stressors that influence ecosystem structure and function.     

河流静水滩区潜流带水交换空间分布模式研究（英文）

Hyporheic zone(HZ) influences hydraulic and biogeochemical processes in and alongside streams, therefore, investigating the controlling geographic factors is beneficial for understanding the hydrological processes in HZ. Slack water pool (SWP) is an essential micro-topographic structure that has an impact on surface water and groundwater interactions in the HZ during and after high flows. However, only a few studies investigate HZ surface water and groundwater exchange in the SWP. This study used the thermal method to estimate the HZ water exchange in the SWP in a segment of the Weihe River in China during the winter season. The findings show that on the flow-direction parallel to the stream, river recharge dominates the HZ water exchange, while on the opposing flow-direction bank groundwater discharge dominates the water exchange. The water exchange in the opposing flow-direction bank is about 1.6 times of that in the flow-direction bank. The HZ water exchange is not only controlled by flow velocity but also the location and shape of the SWP. Great water exchange amount corresponds to the shape with more deformation. The maximum water exchange within the SWP is close to the river bank where the edge is relatively high. This study provides some guidelines for water resources management during flooding events.     

Total N, total P and organic matters content in floodplain soils of Xianghai Nature Reserve

Soil sediment samples of 10 layers with a spacing of 10 cm each were collected in different floodplain zones adjacent to Huolin River in the Xianghai Nature Reserve, and contents of total N, total P and organic matters were analyzed. The results showed that contents of total N, total P and organic matters were generally decreasing with the increase of distance from sample locations to the river channel, and contents of the three items were generally higher in the upper soil layer than that in the lower soil layer. The content variations displayed how flooding functions influenced nutrient matter content variations in floodplain soils since the flood inundation frequencies of the sample locations varied. The correlation analysis displayed that there were remarkable relativities between total N, total P and organic matters within definite spatial distance from the Huolin River channel.     

Total N,total P and organic matters content in floodplain soils of Xianghai Nature Reserve

Soil sediment samples of 10 layers with a spacing of 10 cm each were collected in different floodplain zones adjacent to Huolin River in the Xianghai Nature Reserve, and contents of total N, total P and organic matters were analyzed. The results showed that contents of total N, total P and organic matters were generally decreasing with the increase of distance from sample locations to the river channel, and contents of the three items were generally higher in the upper soil layer than that in the lower soil layer. The content variations displayed how flooding functions influenced nutrient matter content variations in floodplain soils since the flood inundation frequencies of the sample locations varied. The correlation analysis displayed that there were remarkable relativities between total N, total P and organic matters within definite spatial distance from the Huolin River channel.     

Holocene floodplain metamorphosis in the Midlands, United Kingdom

Many lowland rivers in the United Kingdom, including the Nene, Soar and Severn, have layered floodplains with a basal gravel of Pleistocene or Late glacial age and a structureless silty clay superficial unit burying the entire former floodplain. This burial is illustrated by the existence of variable, mixed and pedologically disturbed sediments and palaeo landsurfaces between the basal gravels and superficial silty clay. This paper presents a comparison of the pre- and post-late Holocene palaeo landsurfaces and palaeochannels using data from the Nene, Soar and Severn valleys. From this comparison it is argued that during the mid to late Holocene (ca 4500 yr BP to 2500 yr BP) floodplains and river channels underwent a metamorphosis. This is indicated by accelerated vertical accretion, a reduction in floodplain relative relief, changed floodplain soil conditions, a reduction in channel W/D ratios and a resultant increase in the silty clay proportion of channel perimeter sediments. There are indications that hydrological change preceded this metamorphosis but the primary cause was an increase in fine sediment supply during the later Holocene and a disequilibrium between channel bed and floodplain aggradation rates resulting in relative incision. This metamorphosis, which is explained in this paper by the proposed stable-bed aggrading-banks model (SBAB), is the key factor in the Holocene evolution of low-energy floodplain systems in the United Kingdom, upon which more subtle short-term fluctuations are superimposed.     

In-channel geomorphic complexity: The key to the dynamics of organic matter in large dryland rivers?

Large rivers are often considered to retain less organic material than smaller streams primarily because of a decrease in retentive structures. From our observations on the Barwon–Darling River, a semi-arid river in southeastern Australia, we suggest that geomorphic complexity plays a fundamental role in the retention of organic matter. The Barwon–Darling River has a ‘complex’ river channel cross-section with large inset benches being a prominent morphological feature within the channel. The importance of geomorphic complexity for retaining organic material is likely to be significant in dryland rivers. These rivers spend extended periods at low flow with infrequent large floods that inundate the floodplain. They do, however, experience more frequent within channel floods that inundate in-channel ‘bench’ features. In-channel geomorphic complexity and its ability to retain organic material, therefore, means that although the dominant lateral movements of organic material will still occur during large overbank flows, smaller ‘pulse’ inputs will occur with each in-channel rise and fall in water level. In dryland rivers, where large overbank flows may only occur every seven or more years, these small ‘pulse’ inputs of organic material may well be vital for the integrity of the system.This paper describes the contemporary complexity of a channel in a regulated and an unregulated reach of the Barwon–Darling and compares this with cross-sections surveyed in 1886. We show that flow regulation has greatly reduced channel complexity. We estimate the potential organic matter input to each bench level within the channel (using data collected under near natural riparian conditions) and measure the contemporary organic loads within the channel of the regulated and unregulated reach. This modelling suggests that the development of water resources has reduced the complexity of the channel in the regulated reach, resulting in a potential decrease in the retention of organic matter in this region of the river. The importance of this organic matter to the aquatic food web of the Barwon–Darling River is also demonstrated.     

Spatial patterns of hydrology, geomorphology, and vegetation on the floodplain of the Amazon river in Brazil from a remote sensing perspective

The spatial heterogeneity of hydrology and vegetation during high-water periods in geomorphically distinct reaches of the Amazon River in Brazil was determined based on semivariance statistics. The spatial statistics were derived from three classified Landsat Thematic Mapper images representing upstream to downstream geomorphic characteristics. In the upstream river reach, scroll-bar topography on the floodplain tends to channelize floodwater into floodplain drainage channels, thus reducing the diversity of water types by reducing opportunities for mixing of flooding river water with locally derived floodplain water. The highest diversity of vegetation types is along floodplain drainage channels, while the rest of the floodplain has a more homogeneous cover. In the middle reach of the river the diversity of wetland classes as measured by semivariance is higher than both upstream and downstream, perhaps because of exposure to more water types and landforms. The diversity of water types is high, because flooding river water flows onto the floodplain as diffuse, non-channelized overbank flow, as well as through drainage channels. The non-channelized overbank flow readily mixes with locally derived floodplain water. Floodplain landforms available for colonization by vegetation include scroll bars, swales, lake shores, lake deltas, and floodplain drainage channels. In the downstream reach where the floodplain is wide, relatively flat, and covered with huge lakes, the floodplain supports a moderately heterogeneous mix of vegetation communities. Where landforms are similar, the spatial distribution of the vegetation is similar to that of the middle reach of the river. In the downstream reach flooded forest comprised only 37% of the wetland vegetation. In contrast, in both the upstream and middle reaches, over 70% of the wetland vegetation was flooded forest. Agricultural clearing of the floodplain is more. common in downstream reaches and may account for the smaller percent of floodplain forest cover.     

环青海湖地下水溶解性碳的时空变化特征

区域地下水溶解性碳的时空变化特征研究对于认识区域物质循环和能量传递及推动区域生态可持续发展具有重要意义。本研究在青海湖流域冻结期和融化期分别收集了地下水、河水和湖水样品,研究了环青海湖地下水在冻结期和融化期的溶解性碳特征,并探究了不同类型地下水的溶解性碳特征及其对不同冻融时期的响应,最后揭示了环湖区域不同水体的溶解性碳的差异特征及影响因素。结果表明：冻结期地下水、河水和湖水的溶解性无机碳（DIC）均相对高于融化期,溶解性有机碳（DOC）均相对低于融化期。地下水、河水和湖水的溶解性碳均主要以DIC为主,DIC在溶解性碳的占比高达92%。地下水的DIC平均含量在基岩裂隙水、水量中等和浅埋藏的水文地质条件下相对较高,DOC平均含量在基岩裂隙水、水量丰富和浅埋藏的水文地质条件下相对较高。地下水的DIC在湖滨平原砂砾石层、淤泥质砂层潜水和水量中等的水文地质条件下受冻融期影响较大,DOC在基岩裂隙水和水量贫乏的水文地质条件下受冻融期影响较大。湖水的DIC和DOC均远高于河水和地下水。河水的DIC在融化期和冻结期均低于地下水,DOC在融化期高于地下水,在冻结期低于地下水。     

黄河健康生命的指标体系

河流健康是人们对河流生命存在状态的描述,是人类对河流向其提供服务的认可程度。通过分析人类和河流生态系统的生存需求,认为连续的河川径流、通畅安全的水沙通道、良好的水质、良性运行的河流生态系统和一定的供水能力是健康黄河的标志,提出用低限流量、河道最大排洪能力、平滩流量、滩地横比降、水质类别、湿地规模、水生生物、供水能力等8项定量指标作为健康黄河的标志,并根据相关的历史水文资料和1956~2004年的实测数据分析,确定了相应的健康指标量值。     

The basin concept: From hydrology to nature management

The main development stages of the basin concept: from landscape hydrology to nature management are considered. It is shown that the river, lake and sea drainage basins are the most widespread natural complexes on and surface, with a high degree of integrity and with clear-cut watershed divides having a powerful integrating factor, the water flow. The substantiation is provided for the concepts of the basis as a geosystem, the runoff-producing complexes and the hydrological functions of landscape as well as for the principles of hydrological, water-resources and water-protection regionalization and zoning. On this basis, a classification of hazardous hydrological processes is developed. The structural patterns of the river network within the framework of structural geography are used for indication of the mean long-term discharge and its mapping, and for a classification of river systems according to their size. It is demonstrated that the integrating properties of the water flow permit the basin to be regarded as an integral system entity not only from the perspective of hydrology but also in terms of geomorphology, biogeocenology, landscape geochemistry as well as in complex physical geography as functionally integral natural complexes thereby creating the natural basis for nature management. On the other hand, many basins are socioeconomic and ethnodemographic entities. Ten principles are formulated for the theoretical justification of the basin concept of nature management where the basin is treated as an integral natural and economic system. It is suggested that such an approach should be used in governance of nature management, especially in international basins, as well as in reforming the system of administrative-territorial division of Russia.     

Geomorphology and dynamics of the Mfolozi River floodplain, KwaZulu-Natal, South Africa

The geomorphology and dynamics of the Mfolozi River floodplain and estuary, located in the subtropical region of northern KwaZulu-Natal, South Africa, were considered with respect to existing models of avulsion and alluvial stratigraphy. The Mfolozi River floodplain may be divided into regions based on longitudinal slope and dominant geomorphic processes. Confinement of the Mfolozi River above the floodplain has led to the development of an alluvial fan at the floodplain head, characterized by a relatively high sedimentation rate and avulsion frequency, at a gradient of 0.10%. The lower floodplain is controlled by sea level, with an average gradient of 0.05%. Between the two lies an extremely flat region with an average gradient of 0.02%, which may be controlled by faulting of the underlying bedrock.Avulsion occurrences on the Mfolozi floodplain are linked to the two main zones of aggradation, the alluvial fan at the floodplain head, and toward the river mouth in the lower floodplain. On the alluvial fan, normal flow conditions result in scour from local steepening. During infrequent, large flood events, the channel becomes overwhelmed with sediment and stream flow, and avulses. The resulting avulsion is regional, and affects the location of the channel from the floodplain head to the river mouth. Deposits resulting from such avulsions contribute significantly to the total volume of sediment stored in the floodplain, and tend to persist for long periods after the avulsion. Contrastingly, on the lower floodplain, reaching of the avulsion threshold is not necessarily linked to large flood events, but rather to long-term aggradation on the channel that decreases the existing channels gradient while increasing its elevation above the surrounding floodplain. Resultant avulsions tend to be local and do not contribute significantly to the overall volume of floodplain alluvium.     

渭河下游河道调整过程中的复杂响应现象

应用系统复杂响应的原理研究三门峡水库上游渭河河道调整过程,表明上游河道河床形态对基面上升所作出的响应是复杂的,弯曲系数的变化为先减小而后增大,宽深比的变化是先增大后减小,比降由先减小而后增大,最后均趋于稳定.     

Regional and local controls on the spatial distribution of bedrock reaches in the Upper Guadalupe River, Texas

While studies on gravel mantled and mixed alluvial bedrock rivers have increased in recent decades, few field studies have focused on spatial distributions of bedrock and alluvial reaches and differences between reach types. The objective of this work is to identify the spatial distribution of alluvial and bedrock reaches in the Upper Guadalupe River. We compare reach length, channel and floodplain width, sinuosity, bar length and spacing, bar surface grain size, and slope in alluvial and bedrock reaches to identify whether major differences exist between channel reach types. We find that local disturbances, interaction of the channel and valley sides, variation in lithology, and regional structural control contribute to the distribution of bedrock reaches in the largely alluvial channel. Alluvial and bedrock channel reaches in the Upper Guadalupe River are similar, particularly with respect to the distribution of gravel bars, surface grain size distributions of bars, and channel slope and width. Our observations suggest that the fluvial system has adjusted to changes in base level associated with the Balcones Escarpment Fault Zone by phased incision into alluvial sediment and the underlying bedrock, essentially shifting from a fully alluvial river to a mixed alluvial bedrock river.