Evolution Of Wetlands Research Articles

Impacts of human activities on the evolution of estuarine wetland in the Yangtze Delta from 2000 to 2010

Impacts of human activities on the evolution of estuarine wetland in the Yangtze Delta from 2000 to 2010

Response of two dominant boreal freshwater wetland plants to manipulated warming and altered precipitation.

This study characterized the morphological and photosynthetic responses of two wetland plant species when they were subject to 2–6°C fluctuations in growth temperature and ±50% of precipitation, in order to predict the evolution of natural wetlands in Sanjiang Plain of North-eastern China. We investigated the morphological and photosynthetic responses of two dominant and competitive boreal freshwater wetland plants in Northeastern China to manipulation of warming (ambient, +2.0°C, +4.0°C, +6.0°C) and altered precipitation (−50%, ambient, +50%) simultaneously by incubating the plants from seedling to senescence within climate-controlled environmental chambers. Post-harvest, secondary growth of C. angustifolia was observed to explore intergenerational effects. The results indicated that C. angustifolia demonstrated a greater acclimated capacity than G. spiculosa to respond to climate change due to higher resistance to temperature and precipitation manipulations. The accumulated effect on aboveground biomass of post-harvest secondary growth of C. angustifolia was significant. These results explain the expansion of C. angustifolia during last 40 years and indicate the further expansion in natural boreal wetlands under a warmer and wetter future. Stability of the natural surface water table is critical for the conservation and restoration of G. spiculosa populations reacting to encroachment stress from C. angustifolia expansion.

An approximate solution to the flow field on vegetated intertidal platforms: Applicability and limitations

AbstractTidal wetland evolution is governed by interactions between topography, vegetation, and the flow field. Aiming to provide an appropriate hydrodynamic tool within a long‐term geomorphic model of vegetated wetlands, we describe an approximate procedure to model the depth‐averaged flow field on vegetated intertidal platforms. The procedure is tested by a qualitative comparison with laboratory experiments and quantitatively comparing with a numerical model, focusing on the influence of spatial variations in friction on the flow field. Overall, satisfactory comparisons are obtained. Nevertheless, some limitations of the approach are apparent. These are discussed in the light of the model assumptions. We analyze the impact of the observed limitations on the ability of the approximate solution to describe the morphodynamic evolution of the bed elevation. This is performed by evaluating the changes in the bed elevation after one tidal cycle on the intertidal platform based on flow velocities obtained with a numerical model and those of the simplified procedure. It is found that the bed evolution on the platform is reasonably described with the approximate solution, even though the accumulation of sediment is underestimated near the watershed divide by the approximate model. Taking into account the computationally economic character of the approximate procedure, the analysis indicates that the model provides a suitable tool to investigate the long‐term morphodynamic evolution of tidal wetlands.

Postglacial environmental change in the valley of Malye Chily River (the basin of Lake Teletskoye), northeastern Russian Altai

The evolution and current state of landscapes around Lake Teletskoye have not previously been studied in detail. In the valley of the Malye Chily River, which flows into Lake Teletskoye, the timing of dam failure and draining of two moraine-dammed lakes has been identified. Botanical analysis, ash content determination, and radiocarbon dating of two peat profiles provide insight into postglacial evolution of wetlands related to this landscape. We found clear evidence of the disappearance from the peat of higher vascular species that, today, grows mostly in the plains of Siberia. Correlation of the data obtained with the accepted chronology of the Holocene events in the Russian Altai suggests the following stages of postglacial environmental change in the Malye Chily River valley: (1) the continuation of the Late Würm glaciation degradation (before 7000 cal. yr BP); (2) Holocene Climate Optimum (7000–5000 cal. yr BP); (3) Akkem cooling (5000–4200 cal. yr BP); (4) warm period (4200–3700 cal. yr BP); and (5) Historical cooling (3700–1600 cal. yr BP).

The evolution of Mediterranean wetlands in the first millennium AD: The case of Les Arenes floodplain (Tortosa, NE Spain)

Mediterranean wetlands are characterised by two factors: (1) a remarkable seasonal fluctuation in the water table and (2) a long history of anthropisation. Being exceptional archives for palaeoenvironmental and archaeological research, humid areas have been thoroughly studied to assess the interplay between people and the environment during the Holocene. We present here the study of a sedimentary sequence from a Mediterranean wetland: the Les Arenes floodplain (Tortosa, NE Spain). Fully dry to date, Les Arenes is documented as a partially drained floodplain in the 12th century records. With the aim of assessing the climatic and anthropic contribution to its desiccation, we report here the results of bulk sediment analyses, environmental magnetism, soil micromorphology and AMS dating of this sedimentary sequence, plus a review of the available historical records. The outcome is a clearer understanding of the evolution of this Mediterranean floodplain during the 1st millennium AD, which implications may be extrapolated to other floodplain wetlands in the Iberian Peninsula and the Mediterranean. Wet conditions and a low to medium-energy depositional environment are attested in Les Arenes between the 1st and 7th centuries coinciding with the Iberian-Roman Humid Period (IRHP) and the Dark Age Humid Period (DAHP). Drier conditions between the 7th and 10th centuries concur with enhanced fluvial dynamics, the Medieval Climate Anomaly (MCA) and the first arrival of Arabic-Berber populations in the Iberian Peninsula (al-Andalus, starting in AD 711). Results suggest that although the shift from wet to dry conditions in Les Arenes complies with major climatic trends, the construction of the first drainage canals by Arab-Berber groups likely contributed to the enhancement of on-going climate-related environmental processes.

Holistic geoarchaeology in the Penobscot Valley, Maine, USA: context, scale, and interpretation

A holistic landscape approach to cultural resource analysis of a set of archaeological sites in the central Penobscot Valley led to inferences regarding the Holocene physical and biological environmental context. Targeted environmental studies include (1) examination of forest and wetland changes through time and (2) lake-level studies as a key to paleohydrology. These studies were combined with broad-scale geomorphic investigations and detailed stratigraphic analyses, and studies of archaeological sites and their artifact assemblages. Together, these studies provide a picture of dramatic changes to the physical and vegetational landscape. These included reestablishment of a major river following deglaciation, evolution of extensive lakes to uplands and peatlands, and a shifting mosaic of open and closed forest composed of a variety of hardwood and softwood species. Inferences based on buried soils exposed in archaeological excavations supported climatic interpretations based on vegetation and paleohydrology. As a result, this work allowed evaluation of (1) site formation and preservation processes and (2) occupational patterns. Site formation and preservation of Early Holocene sites can be linked to sedimentation by hydraulic damming upstream of rapids at the mouths of tributary streams. Shifting human land use reflected by changes in occupation patterns appears to correspond to changes in forest composition as well as wetland and stream evolution through time.

Seasonal evolution of the zooplankton community in two riverine wetlands of the Ticino River (Lombardy, Northern Italy)

Riverine wetlands are vulnerable ecotonal environments and are often threatened by human activities. A project supported by the Cariplo Foundation, called “Ecological and hydromorphological requalification of wetlands in the Ticino area around Pavia” (South-East Lombardy, Northern Italy), was started in 2010 with the aim of improving the chemical, bio-ecological and hydrological conditions of these wetlands. In line with the aim of this project, we selected two wetlands near the main course of the Ticino River for investigation, one of which is impacted by a combined sewer overflow from the sewerage networks which is always active (San Lanfranco (SL) wetland), whereas the other (Topo (TO) oxbow lake) is less directly impacted by anthropogenic activities. In this paper, we report the ecological situation of these two wetlands before the requalification process by investigating the way the zooplankton assemblages, considered as bio-indicators, respond to anthropogenic pressure. Overall, we collected 19 taxa : 4 cladocerans, 1 copepod and 14 rotifers. In the TO oxbow lake, we found a stable community, dominated by the cladoceran Bosmina longirostris. By comparison, in the SL wetland we found a pioneer community, dominated by the juvenile stage of the copepod Thermocyclops dybowskii . The SL wetland was shown to be most urgently in need of improvement and is therefore first in line for requalification, whereas the TO oxbow lake needs less drastic measures to ensure the long-term ecological functioning of the aquatic environment. After these requalification activities, a systematic zooplankton survey will be carried out to monitor the evolution of the riverine wetlands.

The influence of climate and sea-level change on the Holocene evolution of a Mediterranean coastal lagoon: Evidence from ostracod palaeoecology and geochemistry

Coastal lagoons provide an excellent basis for the study of processes controlling the evolution of a coastal zone. We examine the relative importance of these processes during the middle to late Holocene through a study of an 8.5meter-long sediment record from the Albufera de Valencia (Spain). We combine sedimentological analyses with investigations into the palaeoecology, taphonomy and geochemistry (Mg/Ca, Sr/Ca, δ18O and δ13C) of ostracod valves in order to assess the effects of sea-level changes, storm events and effective moisture on the evolution of a Western Mediterranean coastal wetland. The late Pleistocene sediments represent a subaerial environment, which was followed by a hiatus in deposition. The first Holocene unit (∼8700–7500 calendar yr. BP) is composed of typical lagoon-barrier and backshore sediments, deposited when seawater intruded into the lake and the climate was arid. The upper part of the sequence (between 7500 and 3400 yr.) is characterized by two sedimentary units, which correspond to Holocene progradation phases and humid climate associated with an increased freshwater influx to the lake accompanied by several high-energy events (palaeostorms). Overall, the record shows that an arid climate prevailed in the western Mediterranean area between 8400 and 7600 yr. The main marine transgression and accompanying progradational phases occurred between 7000 and 3400 yr., which is confirmed by other studies of coastal evolution along the Mediterranean coast. The multiproxy reconstructions demonstrate that controls on sedimentation and palaeoecology in this Mediterranean coastal lagoon were complex.

Driving forces analysis of reservoir wetland evolution in Beijing during 1984–2010

The reservoir wetland, which is the largest artificial wetland in Beijing, constitutes one of the important urban ecological infrastructures. Considering two elements of natural environment and socio-economy, this paper established the driving factor indexing system of Beijing reservoir wetland evolution. Natural environment driving factors include precipitation, temperature, entry water and groundwater depth; social economic driving factors include resident population, urbanization rate and per capita GDP. Using multi-temporal Landsat TM images from 1984 to 2010 in Beijing, the spatial extent and the distribution of Beijing reservoir wetlands were extracted, and the change of the wetland area about the three decade years were analyzed. Logistic regression model was used to explore for each of the three periods: from 1984 to 1998, from 1998 to 2004 and from 2004 to 2010. The results showed that the leading driving factors and their influences on reservoir wetland evolution were different for each period. During 1984-1998, two natural environment indices: average annual precipitation and entry water index were the major factors driving the increase in wetland area with the contribution rate of Logistic regression being 5.78 and 3.50, respectively, and caused the wetland growth from total area of 104.93 km2 to 219.96 km2. From 1998 to 2004, as the impact of human activities intensified the main driving factors were the number of residents, groundwater depth and urbanization rate with the contribution rate of Logistic regression 9.41, 9.18, and 7.77, respectively, and caused the wetland shrinkage rapidly from the total area of 219.96 km2 to 95.71 km2. During 2004–2010, reservoir wetland evolution was impacted by both natural and socio-economic factors, and the dominant driving factors were urbanization rate and precipitation with the contribution rate of 6.62 and 4.22, respectively, and caused the wetland total area growth slightly to 109.73 km2.

An efficient method for change detection of soil, vegetation and water in the Northern Gulf of Mexico wetland ecosystem

Mapping and monitoring wetland ecosystems over large geographic areas based on remote sensing is challenging because of the spatial and spectral complexities of the inherent ecosystem dynamics. The main objective of this research was to develop and evaluate a new method for detecting and quantifying wetland changes in the Northern Gulf of Mexico (NGOM) region using multitemporal, multispectral, and multisensor remotely sensed data. The abundance of three land- cover types (water, vegetation, and soil) was quantified for each Landsat 30 m pixel for 1987, 2004, 2005, and 2006 using a regression tree algorithm. The performance of the algorithm was evaluated using an independent reference data set derived from a high-resolution QuickBird image, and several statistics including average error (AE), relative error (RE), and the Pearson correlation coefficient (r). For per-pixel percentage estimation, the AE is under 10% for water prediction, 9.5–11.4% for vegetation, and 9–11.1% for soil. The correlation coefficients between predicted and reference data range from 0.90 to 0.96 for water, from 0.80 to 0.89 for vegetation, and from 0.79 to 0.86 for soil. The high accuracy achieved by this method is attributed to the high quality of training data and the rigorous calibrations applied to multisensor and multitemporal satellite imagery. Based on the multitemporal estimation of the three land-cover components, spatial and temporal changes of the land-cover types from 1987 to 2006 were quantified and analysed. The study demonstrates that the method provided useful information on the abundance and changes of the key land-cover types in the NGOM region where long-term disturbances and episodic events occurred. Such information is valuable for monitoring land and vegetation loss and recovery processes, and for understanding possible drivers of the coastal wetland evolution in the region.

红树林生态系统遥感监测研究进展

PDF HTML阅读 XML下载 导出引用 引用提醒 红树林生态系统遥感监测研究进展 DOI: 10.5846/stxb201205150715 作者: 作者单位: 国家海洋环境监测中心 海洋遥感室,国家海洋环境监测中心 海洋遥感室,奥胡斯大学生命科学系,奥胡斯 C丹麦,国家海洋局南海环境监测中心,国家海洋环境监测中心 海洋遥感室,国家海洋环境监测中心 海洋遥感室; 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目(41201179);海洋公益性行业科研专项(DOME(MEA)-01-03) A review on the application of remote sensing in mangrove ecosystem monitoring Author: Affiliation: National Marine Environmental Monitoring Center,National Marine Environmental Monitoring Center,Department of Bioscience,Plant Biology,Aarhus University Ole Worms Allé , Aarhus C,Denmark,,National Marine Environmental Monitoring Center,National Marine Environmental Monitoring Center;China;Department of Bioscience,Plant Biology,Aarhus University Ole Worms Allé , Aarhus C,Denmark Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:随着现代遥感技术的迅速发展,遥感监测已经成为红树林生态系统变化监测的重要手段和方法。从遥感技术在生态系统变化监测应用领域入手,综述了国内外红树林遥感监测的发展历程,系统总结了遥感技术在红树林湿地动态、种间分类、群落结构(叶面积指数、冠幅、树高等)、生物量、灾害灾情(病虫害、风暴潮等)、景观格局动态、驱动力、红树林湿地保护与管理等领域应用现状,归纳了不同应用领域遥感监测的理论、方法及研究现状。指出我国在红树林遥感监测中存在的不足。提出红树林遥感监测应在分类标准体系规范化、分类精度提升、红树林生态学特征参数(物种多样性、优势度等)、生态系统环境空间演变过程及遥感监测的尺度效应方面加大研究力度。充分发挥区域综合监测模型在红树林生态系统变化遥感监测中的作用。 Abstract:Mangrove trees form a community of woody plants in intertidal areas periodically immersed by sea water, and are located in tropical and sub-tropical zones. Mangrove forests are complicated ecological systems with characteristics of both land and sea, and form coastal ecologically critical areas (ECA). Monitoring ecological parameters of mangrove ecological systems has gained increased attention from governments and scholars. Ground-based investigation can lead to comprehensive understanding of the structure and functions of the mangrove ecosystem. However, because of spatial and temporal limitations, information on ecological changes of mangrove trees over long periods and large regions cannot be obtained in this way. Advancements in modern remote sensing technology, modeling and simulation, and landscape pattern analysis have provided important technological means for discerning spatiotemporal ecological ecosystem changes. In particular, remote sensing has become an important tool for obtaining temporal and spatial dimensions of ecological parameters of the mangrove forest ecological system. Statistics show that by May 2012, a total of 233 academic papers had been published outside China on remote sensing for monitoring mangrove forests, a number which is increasing yearly. This research mainly focuses on dynamic monitoring, inter-species classification, and structural monitoring of those forests. Especially since 2000, structural monitoring of mangrove communities and investigation of their driving forces and other aspects (sea level changes and comprehensive investigations) have become primary research topics. The application of remote sensing to mangrove forest ecosystem monitoring in China began in the 1990s and has been increasing remarkably in recent years, particularly during the period 2008-2011. This paper summarizes the status of such application and current problems. Specifically, the work expounds on the following aspects: 1) Theories and methods of dynamic monitoring of mangrove-covered wetlands. 2) Theories and methods of inter-species classification technology, as well as requirements of image data. In particular, classification of mangrove trees does not rely only on spectral characteristics, but also requires consideration of structural information that helps enhance classification precision. 3) Theories and methods of remote monitoring of structural parameters of mangrove communities (LAI, crown diameter, tree height and others). In addition, investigations of the relationship between the radar backscattering coefficient and crown diameter and vertical structure of mangrove trees, through establishing a model of their quantitative relationships; this facilitates remote monitoring of mangrove forest growth by applying C-band, L-band, P-band, C-VV and C-HH bands of NASA/JPL. 4) Theories and methods of remote monitoring and inversion of primary production of mangrove forests. Comparative analysis shows that the radar backscattering coefficient is more precise than the NDVI model in estimating vegetation biomass. 5) The status of disasters affecting mangrove forests (diseases, insect infestation and storm surges) and of monitoring theories. 6) Remote dynamic monitoring of and comments on the mangrove-covered region and inter-species landscape patterns. 7) Remote sensing of and comments on driving mechanisms of dynamic evolution of mangrove-covered wetlands. 7) Status and methods of application of remote sensing technology in protection and management of mangrove-covered wetlands. This paper points out existing deficiencies and challenges in remote monitoring of elements of the mangrove forest ecosystem, and emphasizes the need for more research into standardization of classification systems and enhancement of classification precision. Also needed is research into parameters of the ecological characteristics of mangrove forests (diversity and species dominance), spatial evolution of the ecological system, and dimensional effects of remote monitoring. Remote monitoring of the mangrove forest ecosystem lags behind in China, so more such studies should be undertaken in the country. 参考文献 相似文献 引证文献

A high-resolution record of carbon accumulation rates during boreal peatland initiation

Abstract. Boreal peatlands are a major global C sink, thus having important feedbacks to climate. A decreased concentration in atmospheric CO2 7000–10 000 yr ago has been linked to variations in peatland C accumulation rates attributed to a warm climate and increased productivity. Yet, this period also corresponds to early stages of peatland development (as peatland was expanding) following retreat of ice sheets and increases in C storage could be associated with wetland evolution via lake filling or following marine shoreline emergence. Unravelling past links amongst peatland dynamics, C storage, and climate will help us assess potential feedbacks from future changes in these systems, but most studies are hampered by low temporal resolution. Here we provide a decadal scale C accumulation record for a fen that has begun transformation from salt marsh within the last 70 yr on the isostatically rebounding coast of James Bay, Québec. We determined time frames for wetland stages using palynological analyses to reconstruct ecological change and 210Pb and 137Cs to date the deposit. The average short-term C accumulation rates during the low and high tidal marsh and incipient fen stage (42, 87 and 182 g C m−2 yr−1, respectively) were as much as six times higher than the global long-term (millennial) average for northern peatlands. We suggest that the atmospheric CO2 flux during the early Holocene could be attributed, in part, to wetland evolution associated with isostatic rebound, which makes land for new wetland formation. Future climate warming will increase eustatic sea level, decrease rates of land emergence and formation of new coastal wetlands, ultimately decreasing rates of C storage of wetlands on rebounding coastlines.

Hydrological Evolution of Wetland in Naoli River Basin and its Driving Mechanism

Naoli river basin(NRB), with an area of 24,863 km2, is the largest basin and also the largest marsh distribution area in Sanjiang Plain, Heilongjiang, China. The hydrological evolution process of wetland in NRB has made a marked ecological responses for anthropic activities, also reflects the drying trend of the Sanjiang Plain, Northeast China. Global climate warming also contributes to the hydrological evolution process. The following key research results are obtained: (1) The monthly average water level of Naoli river at Caizuizi hydrological station in different ages showed a marked decline tendency, the annual mean water level dropped from 96.63 m during 1960–1969 to 95.59 m during 2000–2005, the water level drawdown is 1.04 m; (2) The annual runoff flowing into wetlands in NRB decreased. Duration of Naoli river and its tributaries being thoroughly frozen from riverbed to river-water-surface showed an prolonged trend, and the water level drawdown in frozen seasons increased. The water storage capacities of wetlands in NRB declined. (3) The interactions between ground water and surface water in wetland areas are close. The ground water level variation span is bigger than that of surface water level in wetland areas of NRB. The drawdown of ground water level promotes the surface water level to decline, correspondingly. In recent 20 years, the cultivated area extension of rice field in upstream NRB has made an adverse influence on the hydrological processes of wetlands. (4) The wetland area decrease and farmland area increase significantly contribute to the runoff depth decrease of wetlands in NRB. The runoff depth variability has been mostly posed by anthropic activities. (5) Reservoirs, ditches and dykes in NRB have greatly changed the runoff generation processes. Thickness of the seasonal frozen soil layer becoming thinner and the evaporation potential becoming bigger also contribute to the runoff depth reduction and the water level drawdown of rivers. The present study results will provide a scientific basic for developing an integrated watershed management program for NRB, especially, restoring the wetland hydrological processes, maintaining or improving the wetland structure and enhancing the wetland service functions.

One year wetland survey investigations from quad-pol RADARSAT-2 time-series SAR images

Remotely sensed data are widely used to identify, delineate, and characterize wetlands. Optical data provide interesting information to inventory vegetation and agricultural practices in wetlands but are limited to cloud-free periods. For this reason it is not possible to precisely delineate the extent of saturated areas as well as water cycles and water levels in these areas with passive remote sensing techniques. The objective of this article is to evaluate fully polarimetric RADARSAT-2 time-series datasets to identify and locate the seasonal dynamics of saturated areas in wetlands. To that end, the development and validation of a supervised PolSAR segmentation including multitemporal analysis of wetland evolution and polarimetric decomposition method is presented. The proposed methodology is based on the segmentation of a polarimetric descriptor, the Shannon Entropy, which has been shown to be a very sensitive parameter to the temporal variability of flooded areas. The results were validated using ground truth measurements in the field and a LiDAR image. They showed that it is possible to produce detailed water feature maps useful for delineating and monitoring the seasonal dynamics of saturated areas extent in wetlands. These products provide useful information to identify and delineate wetlands to support conservation and management in these ecosystems across large areas.

基于MODIS的洞庭湖湿地面积对水文的响应

The Dongting Lake is the largest lake in the Middle and Lower Yangtze River and ranks the second largest freshwater lake in China.Seasonal fluctuation of water-level in the Dongting Lake forms stable wetland resources.A large area of shallow marshes and mudflats,which are exposed over water surface during the non-flood season in the winter,provide habitats for several migratory birds.In recent years,the effects of the hydrological processes on wetland ecological system have aroused worldwide attention.The complex nonlinear relationship between the Yangtze River and the Dongting Lake has led significant changes in hydrological processes in the Dongting Lake after the running of the Three Gorges Project. Data sets of surface area in the Dongting Lake were extracted using MODIS imagery from 2000 to 2010.During interpretation process,NDVI index and NIR band threshold were set to 1000,meaning that NDVI and NIR band values less than 1000 were water wetlands and values higher than 1000 were beach wetlands,including mudflat wetlands,grass wetlands and reed wetlands.Since the water-level of the Chenglingji was proportional to the surface area in the Dongting Lake,the observed water-level data sets were used to validate the rationality of the extracted surface area data sets.The results revealed that correlation coefficient of the extracted surface area and water-level was 0.8058.Mann-Kendall(MK) nonparametric test showed that the Zs statistics were-2.4986,-3.0867 and-2.5421 in the 0.05 level of significance for the whole year,from June to September(flood season) and from October to May in the next year(non-flood season) during 2000 to 2010,respectively.The trends indicated that runoff in the Dongting Lake was reduced dramatically during the last decade.The average surface water area decreased 15.21% and 32.05% during flood season and non-flood season in 2010 compared with that in 2000. In the paper,wetlands in the Dongting Lake were divided into water wetlands and beach wetlands.More attention was paid to the changes of beach wetlands area during non-flood season because of its importance for migratory bird.The data sets of area of water wetlands and beach wetlands indicated that the area of water wetlands decreased dramatically while beach wetlands increased correspondingly from 2000 to 2010.Compared with the data in February,October,and December in 2000,29.98%,26.76%,and 9.02% water wetlands were changed into beach wetlands in the corresponding month in 2010,respectively.According to the statistics of observed water-level of the Chenglingji that firstly and lastly reached 24m,25m,26m,27m and 28m,water-level fluctuation was investigated.The results showed that water-level fluctuation from 24 m to 26 m led to earlier exposure of beach wetlands and later flood of beach wetlands,which prolonged the exposure time of beach wetlands.The change of water wetlands and beach wetlands promoted the evolution of mudflat wetland to grass wetland in the East Dongting Lake at water-level of 24m to 26m.In conclusion,it is multi-factors,including reduction of runoff from Sankou(Songzi,Ouhe,Taiping) and Sishui(River Xiang,River Zi,River Yuan and River Li) and reduction of rainfall etc.,that contributed to the responses of wetlands area to hydrological process of the Dongting Lake.The impoundment of the Three Gorges Project in September to October would further aggravate the trend of water wetlands changing into beach wetlands.

基于TM影像的银川平原湖泊湿地景观空间格局动态演化研究

区域生态安全是区域可持续发展的基础，银川平原湖泊湿地对于宁夏沿黄经济区、中国西部生态安全的维护具有十分重要的意义。本研究应用3S技术以及景观空间格局指数方法，利用1987、1997、2004和2012年四个年份的遥感影像，对1987~2012年25年间银川平原湖泊湿地进行了动态演化研究。分析得出：1) 近25年来，银川平原湖泊湿地景观斑块数量N、总面积A总、斑块最大面积Amax、斑块最小面积Amin、斑块平均面积A、平均周长L等特征整体呈增加的趋势；2) 银川平原湖泊湿地景观内部结构中,虽然部分指标特征有所改 善，但整体仍呈脆弱化、不稳定化的变化趋势，如2012年FD、D、FN、D等指数特征虽都明显好于1997年，但是与1987年状态相比仍有差距；3) 银川平原湖泊湿地景观动态演化的驱动力因子有气候和水文的自然因子以及工业发展和农业开发活动等人为因子，其中人为因子为主要的驱动力因子。根据结论进一步提出对策及建议，以期为银川平原生态建设和生态安全维护提供参考。 The regional ecological security is the basis of sustainable development, and the lake wetland in Yinchuan Plain (Ningxia, China) is of great importance for maintaining regional ecological security in the Yellow River Economic Zone in Ningxia and Western China. This study uses 3S technologies, i.e., remote sensing, geographic information sys-tem and global positioning system, to outline the dynamic evolution of lake wetlands in the Yinchuan Plain based on remote sensing images obtained from 1987 to 2012. The results are as follows: 1) The characteristic values, such as the landscape patch number, the total areas, average and maximum areas of the lake wetlands in Yinchuan Plain, i.e., are in a gradual increasing trend since recent 25 years; 2) The internal hierarchical structure of the lake wetlands in Yinchuan Plain is improved in some aspects, but the overall hierarchical structure is still fragile and unstable, for example, some characteristic indexes, such as the FD, FN and D, were obviously better in 2012 than that in 1997, but there were still some gaps compared with that in 1987; 3) The driving forces resulting in the dynamic evolution of the lake wetland landscapes in Yinchuan Plain include both the natural and artificial factors, such as the climate change, hydrological process, agricultural and industrial development activities, i.e., in which the artificial factors are dominant. According to the conclusions, some measures and suggestions are put forward, which can be referred in the ecological construction and the maintenance of ecological security in Yinchuan Plain.

Relating accretion and erosion at an exposed tidal wetland to the bottom shear stress of combined current–wave action

Sediment dynamics have an important influence on the morphological evolution of tidal wetlands, which consist of mudflats and salt marshes. To understand the nature of sediment behavior under combined current–wave action at an exposed tidal wetland, we measured the waves, currents, water depths, bed-level changes, and sediment properties at a mudflat–salt marsh transition on the Yangtze Delta, China, during five consecutive tides under onshore winds of ~ 8 m/s, and calculated the bed shear stresses due to currents ( τ c ), waves ( τ w ), combined current–wave action ( τ cw ), and the critical shear stress for erosion of the bottom sediment ( τ ce ). The bed shear stresses under combined current–wave action ( τ cw ) were approximately five times higher on the mudflat (up to 1.11 N/m 2; average 0.27 N/m 2) than on the salt marsh (up to 0.14 N/m 2; average, 0.06 N/m 2). On the mudflat, τ cw was larger than the critical erosion shear stress ( τ ce = 0.103 N/m 2) for 70% of the period of submergence, whereas τ cw was always lower than τ ce at the salt marsh site ( τ ce = 0.116 N/m 2). This result indicates that the sediment dynamics on the mudflat were dominated by erosion, whereas at the salt marsh they were governed by deposition, which is in agreement with the observed bed-level change during the study period (− 3.3 mm/tide on the mudflat and 3.0 mm/tide on the salt marsh). A comparison of τ cw values calculated using the van Rijn (1993) and Soulsby (1995) models for bed shear stresses under combined current–wave action indicates that both models are applicable to the present case and effectively predict the bottom shear stress under combined current–wave action. Overall, we conclude that τ cw in combination with τ ce is useful in assessing the hydrodynamic mechanisms that underlie the morphological evolution of exposed tidal wetlands.

Environmental change in the Great Whale River region, Hudson Bay: Five decades of multidisciplinary research by Centre d'études nordiques (CEN)

The Great Whale River region on the eastern shore of Hudson Bay, Canada, encompasses the villages of Whapmagoostui (Cree First Nation) and Kuujjuarapik (Inuit) and surrounding areas. The principal field station of Centre d'études nordiques (CEN: Centre for Northern Studies) has operated at Whapmagoostui-Kuujjuarapik (W-K; 55° 15′ N, 77° 45′ W) since the 1970s, with diverse research projects on past and present environments. The climate at W-K is strongly influenced by the proximity of Hudson Bay, and the recent pronounced loss of sea ice in this sector of northern Canada has been accompanied by large increases in air temperature. Discontinuous or scattered permafrost occurs throughout the region and is degrading rapidly. The W-K region continues to experience particularly rapid isostatic uplift in response to the retreat of the Laurentide Ice Sheet. Parabolic dunes occur along the coast and are strongly influenced by the plant cover. Paleoecological studies have documented the Holocene evolution of landscapes, including lakes, wetlands, and forests. The vegetation type is coastal forest tundra, with some 400 recorded species. Studies on certain insect groups provide a baseline for assessing future ecological change. The first signs of human occupation in the W-K region have been dated at 3800 BP. The arrival of the Hudson's Bay Company in the 18th century marked the onset of continuous occupation. Rapid social, economic, and environmental change initiated in the mid-20th century continues to this day.

Limnology wetland change trends and perspectives in arid Yinchuan plain, China

In this paper, the distribution area of limnology wetland in Yinchuan plain at different times was obtained through literature analysis and remote sensing techniques. This study analyzed the evolution process of limnology wetland in Yinchuan plain under environmental change and human socio-economic activities interference. In its long geological period, limnology wetland in Yinchuan plain has experienced the process of area reduction from lake to lake. In the history of mankind and as a result of poor irrigation and drainage water with formation of low-lying land, limnology wetland area has increased in a period of time. In the last 60 years, limnology wetland shrunk rapidly because of excessive exploration of agriculture and extraction of groundwater for industrial development. The results show that the temperature and precipitation changes in environmental factors play a decisive impact on the evolution of limnology wetland in Yinchuan plain. Human activities have accelerated the trend of limnology wetland area reduction. Currently, wetland ecosystems and wetland landscape pattern still develop in a deteriorate way, but the pace of deterioration is obviously slowing down. Key words: Yinchuan plain, limnology wetland, change trends, impact analysis, arid environment.

SALINE WETLANDS' FATE IN INLAND DESERTS: AN EXAMPLE OF 80 YEARS' DECLINE IN MONEGROS, SPAIN

ABSTRACTWetlands inventory is one of the goals of conservation plans on a national scale and a global scale. Inventories are needed for long‐term monitoring or for identifying lost wetlands and those where restoration is feasible. In this article, we present an updated inventory of the saline wetlands of Southern Monegros, Spain. We depicted the evolution of these saline wetlands, locally named saladas with a unique long‐term retrospective study based on aerial photographs from 1927. Their inventory has been accomplished through a map analysis based on a geographical information system using aerial photographs and orthophotographs, topographic maps, unpublished local studies and field surveys. Remaining vegetation, changes in soil moisture and colour, and geomorphology have been the key features in identifying the saladas. Their changes in number, size and shape have been driven by human pressure, the main modifier of landscape in the last 80 years. The information gathered will contribute to the awareness of stakeholders and decision makers for their conservation as natural resources. Moreover, our large retrospective approach is a consistent base from which to propose the inclusion of the saladas of Monegros in the Ramsar list of Wetlands of International Importance. Copyright © 2011 John Wiley & Sons, Ltd.