Wan Rongrong

Influence of land use/cover change on storm runoff - A case study of Xitiaoxi River Basin in upstream of Taihu lake watershed

Land use/cover change (LUCC) is one of the main boundary conditions which influence many hydrologic processes. In view of the importance of Taihu Lake Watershed in China and the urgency of discovering the impacts of LUCC on storm runoff, two flood events under five land cover scenarios in the Xitiaoxi River Basin of the upstream of Taihu Lake watershed were simulated by distributed hydrologic modeling system HEC-HMS. The influences of each land cover on storm runoff were discussed. It was concluded that under the same rainstorm the ascending order of runoff coefficient and peak flow produced by the 5 different land covers were woodland, shrub, grassland, arable land, and built-up land; the descending order of swelling time were woodland, shrub, grassland, arable land, and built-up land. Scenario of built-up land was the first to reach peak flow, then arable land, grassland, shrub, and woodland. There were close relationships between the runoff coefficients produced by the 5 different land covers. The degrees of impacts on runoff coefficient of land cover change modes were sorted by descending: woodland to built-up land, shrub to built-up land, grassland to built-up land, arable land to built-up land, woodland to arable land, shrub to arable land, arable land to grassland, shrub to grassland, grassland to arable land, and woodland to shrub. Urbanization will contribute to flood disaster, while forestation will mitigate flood disaster.

Soil Characteristics in Relation to Vegetation Communities in the Wetlands of Poyang Lake, China

Poyang Lake is an important wetland with global ecological functions. Impact of plant species composition on soil physicochemical characteristics is potentially critical but is as yet poorly understood in this great, shallow and water passing lake wetland. Five dominant plant communities, Phragmites communis community (Phragmites), Polygonum hydropiper community (P. hydropiper), Artemisia selengensis community (A. selengensis), Carex cinerascens community (C. cinerascens) and Phalaris ayuyldinacea community (Phalaris) were surveyed to identify the influences of plant species composition on soil properties. Results show great heterogeneity in soil characters among studied vegetation communities. The lowest average values of pH and soil bulk density are presented in soil with Phragmites, while the highest ones are determined in C. cinerascens and A. selengensis, respectively. Moreover, C. cinerascens is determined with the highest average contents of total organic carbon (TOC) and total nitrogen (TN), whereas Phalaris community presents the lowest soil carbon and nutrient accumulation in surface soil. Plots of C. cinerascens, Phragmites and Phalaris are identified with obvious convergence patterns, while dispersive patterns are identified in A. selengensis and P. hydropiper, suggesting great heterogeneity in soil properties among typical communities in Poyang Lake.

Progress of research on the relationship between the Yangtze River and its connected lakes in the middle reaches

The complicated changing water-sediment exchange relationship between the Yangtze River and its naturally connected lakes,Lake Dongting and Lake Poyang,have affected regional flood disaster control,water resources and water environmental protection and maintenance of water ecological security,which has become the core of water problems in the middle reaches of the Yangtze River.The progress of research on river-lake relationship between the Yangtze River and its connected large lakes was systematically reviewed from the point of view of the concept and connotation of river-lake interaction,the evolution process,the influencing factors and effects of changing river-lake relationship.Based on the problems in current research,the following research issues were proposed:how to define a comprehensive index for the river-lake relationship is the premise to correctly understand the relationship between rivers and lakes;how to quantify the effects of human activities and climate change contributions is the emphasis and difficulty of research on the river-lake relationship;it is a long-term task to track the impact of the Three Gorges Project on the river-lake relationship;and it is the ultimate goal to maintain healthy river-lake system pattern in the middle reaches of the Yangtze River which benefits both the Yangtze River and its connected lakes based on the optimization and controlling principles on joint operation of hydraulic engineering group for large river-lake water systems.

Impact of water level change on wetland vegetation of rivers and lakes

Water level is one of the key factors of the eco-hydrological process in wetlands. The change of water level often results in variations in wetland vegetation coverage and species composition,and leads to community succession. This article summarized the impact of water level on wetland vegetation in three different aspects: water level gradient,water level fluctuations and artificial lake / river control projects. The results showed that: 1) Wetland species exhibited grade distribution along water level gradient mainly due to their distinct responses to water level and their different competitiveness. Meanwhile,morphological plasticity influenced the distribution range of individual species; 2) The rate and duration of water level fluctuations,rather than depth,had important influence on vegetation succession; periodic water level fluctuations maintained the species diversity and ecological stability,however,a periodic water level fluctuations,mainly the flood and drought,were likely to cause vegetation succession from wetland ecosystems to terrestrial or aquatic ecosystems; 3) Artificial lake / river control projects had the same impact with water level fluctuations in theory,however,the matching mitigation strategies provide valuable references for maintaining ecological diversity and stability. The potential aspects to be attached importance in the future of the research are as follows: quantitative models based on mechanisms,differentiating impacts caused by anthropogenic and natural driving factors,simulating the water level fluctuations in laboratories and the tracking attention on the long-term impact of artificial lake / river control projects.

Discharge capacity analysis on Lake Poyang

The recently frequent low water level in Lake Poyang attracted wide public attention. As an open lake,Lake Poyang is naturally connected with the Yangtze River via the Hukou Waterway. The interactions between the Yangtze River and the Lake Poyang are directly affected by the flow characteristics of the Hukou Waterway. The discharge capacity is introduced to represent the ability to convey water away using the hydraulic approach. The discharge capacity and its change is investigated here. Results show that: The discharge capacity was stable before 2000s and thereafter it rapidly increased. Its remarkable increase altered the interaction between the Yangtze River and Lake Poyang,leading to the recent severe drought regime. Large-scale sand dredging in Lake Poyang is attributed to be the cause of this increase. The management for sand dredging should be strengthened for conserving the water resources in Lake Poyang.

Temporal and spatial variations of water level and its driving forces in Lake Dongting over the last three decades

Located in the subtropical humid monsoon climate zone, Lake Dongting is significantly experiencing hydrological regime changes at temporal and spatial scales. In this paper, the data of water level at six stations (Chenglingji, Lujiao, Yingtian, Yang⁃ liutan, Nanzui, Xiaohezui) in Lake Dongting and streamflow of Sankou, Sishui, Chenglingji, Yichang, Luoshan stations were col⁃ lected to study the temporal and spatial variations of water level in Lake Dongting. Both water level and streamflow data are daily observation from 1985-2014. Water level of the lake was calculated by Thiessen Polygon. Wavelet analysis, cluster analysis and geostatistics were used to reveal temporal and spatial variations of water level in Lake Dongting. Results indicate that the water level shows typical seasonal features, and its annual fluctuation has multiscale of 28 a and 22 a in Lake Dongting. There are two clusters of the spatial distribution pattern in Lake Dongting, one is Xiaohezui, Nanzui, Yangliutan (Group 1), and another is Chenglingji, Lujiao, Yingtian (Group 2) . The magnitude of spatial autocorrelation in different periods is wet season > retreating season > rising

Characteristics of the changing seasonal water regime in Lake Dongting and their response to the change of river-lake water exchange in recent 30 years

The adjustment of river-lake water exchange will cause water regime of lake to change and threat the sustainable development of social economy and ecology. In this paper,based on daily observation data of water level and water discharge from 1981 to2012 at Chenglingji Station,Nanzui Station in Lake Dongting,Yichang Station and Luoshan Station in the main reaches of the Yangtze River,the characteristics of the changing water regime in Lake Dongting and their response to the changes of river-lake water exchange were analyzed by means of unit root test,analysis of variance and the comparison of stage-discharge curve. The results suggestted that the water regime in Lake Dongting showed periodic characteristics during 1981 to 2012. The period of 1981-2002 was viewed as relatively stable phase. Mean water level decreased 0. 43 m in 2003-2012. In the flood season,water level of Lake Dongting decreased 0. 60 m. In the retreating season,water level fell 1. 49 m. In the dry season,water level rose 0. 18 m. The change of water level was not significant in the rising season. The dry season may be early in consideration of 2. 03 m drop in October. The changes of hydrological regime were related to changes of river-lake water exchange: In the flood season,flow diversion at the three outlets reduced and the lake level dropped. In the retreating season,reduced flow diversion at the three outlets coupled with stepping up outflow intensified lake water withdrawal. In the dry season from January to March,outflow slowed down and the lake level rose.