长江湖口—彭泽段江岸的变化及其对防洪安全影响

根据历史记载、遥感资料解释和野外现场调查,对长江湖口—彭泽县段江岸冲淤变化,及江中主要江心洲的变迁进行研究,该江段历史变化较复杂,但是总体是河流主流的“S”摆动,主流不断南迁总体南岸以侵蚀为主,北岸以淤积为主,在棉船洲地区由于该洲向北生长,则以北岸侵蚀为主。最后分析江岸变化对防洪安全的影响,江岸变化是重要的致灾因子。

ESTUARINE AND COASTAL CHALLENGES IN CHINA

Estuaries and coasts are conjunctions of four spheres (atmosphere, lithosphere, hydrosphere and biosphere) and important matter and energy convergence/divergence zones, where developed economy, dense population and highly intensive exploitation induce adverse environmental changes and serious destruction of resources, which have great impacts on coastal sustainable development, especially as the highly intensive development in river basins has direct and pronounced effects on estuaries and their adjacent coasts. In the new century, China’s estuaries and coast are faced with four main challenges: sharp decrease of sediment discharge into the sea, rapid increase of pollution matter into the sea, loss of coastal wetland, and the impacts of global sea level rise on the coastal lowlands of China. Therefore, it is undoubtedly very important and urgent to carry out studies on estuarine and coastal environmental changes, in order to resolve the issue of national sustainable development, especially that of rational use of coastal zone resources.

Spatial Variation of Dissolved Organic Carbon in Soils of Riparian Wetlands and Responses to Hydro-geomorphologic Changes in Sanjiang Plain, China

Spatial variation of dissolved organic carbon(DOC) in soils of riparian wetlands and responses to hydro-geomorphologic changes in the Sanjiang Plain were analyzed through in situ collecting soil samples in the Naoli River and the Bielahong River. The results showed that the average contents of DOC for soil layer of 0–100 cm were 730.6 mg/kg, 250.9 mg/kg, 423.0 mg/kg and 333.1 mg/kg respectively from riverbed to river terrace along the transverse directions of the Naoli watershed. The content of the soil DOC was the highest in the riverbed, lower in the high floodplain and much lower in the river terrace, and it was the lowest in the low floodplain. The difference in the content and vertical distribution of DOC between the riverbed and the three riparian wetlands was significant, while it was not significant among the low floodplain, the high floodplain and the river terrace. The variability of soil DOC was related to the hydrological connectivity between different landscape position of the riparian wetlands and the adjacent stream. Extremely significant correlations were observed between DOC and total organic carbon(TOC), total iron(TFe), ferrous iron(Fe(II)) whose correlation coefficients were 0.819, –0.544 and –0.709 in riparian wetlands of the Naoli River. With the increase of wetland destruction, soil p H increased and soil DOC content changed. The correlation coefficients between soil DOC and TOC, TFe, Fe(II) also changed into 0.759, –0.686 and –0.575 respectively in the Bielahong River. Under the impact of drainage ditches, the correlations between soil DOC and TFe, Fe(II) were not obvious, while the soil p H was weakly alkaline and was negatively correlated with soil DOC in the previous high floodplain. It indicates that riparian hydro-geomorphology is the main factor that could well explain this spatial variability of soil DOC, and the agricultural environmental hydraulic works like ditching also must be considered.

Variation of Soil and Water Volumes in Riparian Jungle Soils of Brazil

The objective of this work is to study the relation between humidity, density, porosity and shrinkage of the floodplain soil and riparian vegetation and their ability to store water. For this purpose, two locations for every type of soils were evaluated. Both were placed at the Agronomy University （Faculdade de Cidncias Agron6micas） in SAo Manuel, State of SAo Paulo, Brazil. The floodplain soil was vegetated with Southern Cattail （Typha domingensis）. In both places, soil samples were collected from several depths： 0, 30, 60 and 100 cm. Results show that lower soil density values （0.15 g/cm3） with organic texture and high porosities values （up to 86.2%） were found in samples with the highest organic material content in the floodplain soil. For this field experiment, flood plains soils （characterised as basin gley soils） presented high volumetric instability with a retratibility of 67.49% and higher water storage capacities compared to riparian stands soils （characterised as fluvic neosoils）.

Change Detection of Land Use and Riverbank in Mekong Delta, Vietnam Using Time Series Remotely Sensed Data

By taking the advantages of remote sensing technology, changes of land cover in Ca Mau Peninsular （the Southern part of the Mekong delta） and erosion of riverbank of the Mekong River have been defined. Change detection using time-series optical and radar satellite images （Landsat, SPOT and Radarsat） is the main approach in this study. Typical land cover in Ca Mau Peninsular is mangrove; its changes are observable by analysing imageries from 1973 to 2008. The results showed that more than half of the mangrove area was converted into shrimp farms. This made forest cover severely declined. Riverbank of the Mekong River also was detected to be eroded and accreted in a complicated form. Locations along the left and right banks of Tien and Hau river are defined as hot spots that are seriously suffered erosions. Topographic maps in 1966-1968 were taken into account as base line data, which was analyzed along with satellite images from 1989 to 2009. In addition, the Digital Shoreline Analysis System （DSAS） package was taken to analyze trend of changes in terms of changing prediction.

Riparian plant species differ in sensitivity to both the mean and variance in groundwater stores

Aims Determining the ecological consequences of interactions between slow changes in long-term climate means and amplified variability in climate is an important research frontier in plant ecology.We combined the recent approach of climate sensitivity functions with a revised hydrological‘bucket model’to improve predictions on how plant species will respond to changes in the mean and variance of groundwater resources.Methods We leveraged spatiotemporal variation in long-term datasets of riparian vegetation cover and groundwater levels to build the first groundwater sensitivity functions for common plant species of dryland riparian corridors.Our results demonstrate the value of this approach to identifying which plant species will thrive(or fail)in an increasingly variable climate layered with declining groundwater stores.Important Findings Riparian plant species differed in sensitivity to both the mean and variance in groundwater levels.Rio Grande cottonwood(Populus deltoides ssp.wislizenii)cover was predicted to decline with greater inter-annual groundwater variance,while coyote willow(Salix exigua)and other native wetland species were predicted to benefit from greater year-to-year variance.No non-native species were sensitive to groundwater variance,but patterns for Russian olive(Elaeagnus angustifolia)predict declines under deeper mean groundwater tables.Warm air temperatures modulated groundwater sensitivity for cottonwood,which was more sensitive to variability in groundwater in years/sites with warmer maximum temperatures than in cool sites/periods.Cottonwood cover declined most with greater intra-annual coefficients of variation(CV)in groundwater,but was not significantly correlated with inter-annual CV,perhaps due to the short time series(16 years)relative to cottonwood lifespan.In contrast,non-native tamarisk(Tamarix chinensis)cover increased with both intra-and inter-annual CV in groundwater.Altogether,our results predict that changes in groundwater variability and mean will affect riparian plant communities through the differential sensitivities of individual plant species to mean versus variance in groundwater stores.