Jiang Jiahu

China's lakes at present: Number, area and spatial distribution

Based on 11004 satellite images from CBERS CCD and Landsat TM/ETM, changes in the spatial characteristics of all lakes in China were determined following pre-established interpretation rules. This dataset was supported by 6843 digital raster images (1:100000 and 1:50000), a countrywide digital vector dataset (1:250000), and historical literature. Comparative data were corrected for seasonal variations using precipitation data. There are presently 2693 natural lakes in China with an area greater than 1.0 km2, excluding reservoirs. These lakes are distributed in 28 provinces, autonomous regions and municipalities and have a total area of 81414.6 km2, accounting for ∼0.9% of China’s total land area. In the past 30 years, the number of newly formed and newly discovered lakes with an area greater than 1.0 km2 is 60 and 131, respectively. Conversely, 243 lakes have disappeared in this time period.

The characteristics of flood responses to the restoration of polders on Dongting Lake, China

Abstract The serious shrinkage of Dongting Lake in China has led to the deterioration of its flood diversion and storage capacity, and now flood disasters have become more frequent. A lake restoration strategy is proposed in order to relieve flood-prone areas. However, flood movement is a dynamic process, so that approaches neglecting the hydrodynamics cannot accurately represent flood responses to restoring polders to a lake in a complex river basin. Here, a coupled one-dimensional and two-dimensional hydrodynamic model was applied to investigate flood responses to restoring polders to Dongting Lake under the conditions of the 1998 flood event. Quantified flood reduction effects show that the characteristics of flood responses vary significantly with the management option chosen. Appropriate strategies of lake restoration are suggested according to different flood responses. Polders of type II, which favour flood discharge, should be restored in order to streamline flood conveyance. Considering the ecological requirements of the lakes and wetlands, type I polders far from main flows can be partially restored, resulting in evacuation of residents to safe areas but keeping the cultivation.

Nitrogen and phosphorus forms and release risks of lake sediments from the middle and lower reaches of the Yangtze River

Cluster analysis, principal component analysis and correlation matrix analysis were used to analysis the nitrogen and phosphorus release risks from sediments in 18 lakes located in the middle and lower reaches of the Yangtze River, as well as the nitrogen and phosphorus forms and related geochemical parameters from sediments, pore waters and overlying waters. The ecological difference of macrophyte and algae dominated lakes was the main reason of the difference of nitrogen and phosphorus release. The release risks were well correlated with the iron-bound phosphorus (FeP), algae available phosphorus (AAP), total nitrogen (TN), total phosphorus (TP) in sediment, the content of nitrogen and phosphorus in overlying and pore waters, porosity and organic matter content of surficial sediment. The AAP and FeP was the main phosphorus forms deciding the phosphorus release risk and other forms were in less effect on it due to the lower contents or lower transformation ability. The sediment organic phosphorus was not directly related to the phosphorus release risks but remarkably positively correlated to organic matter contents in sediment.

Two-dimensional numerical simulation of hydrodynamic and pollutant transport for Lake Poyang

The present study aims to develop a mathematical model for analyzing and predicting the hydrodynamic and water quality in one large lake(Lake Poyang) with great and rapid stage fluctuation,the complex topography and geometry,the complicated connectivity of narrow channels and depressions inside the lake,the frequently switch between exposed grass beach and water.Based on the two-dimensional shallow water equations and pollutant transport equations,the coupled two-dimensional hydrodynamic and pollutant transport model is developed.The unstructured finite volume method is applied to discretize the equations.The normal water mass,momentum and pollutant fluxes are computed by the HLLC solver.The water front moving boundary is identified automatically by the judgment of the latest water stage.It makes the model be capable of simulating the complex flow regime and the dynamic of pollutant transport in the lake with drying and wetting processes.The hydrodynamic model is calibrated by the water regime of the year 1998.Based on the calibrated hydraulic parameters,the hydrodynamic and water quality(CODMn and ammonia) from January to October in 2008 are simulated by the proposed model.The time series data of measured water stage,CODMn and ammonia,and remotely water extent of CBERS data are both used to validate the results of computation in time and space.The results indicate that the model has the capability to model the flows dynamic and the pollutant transport in this kind of lake.

Characteristics of nitrogen loss via runoff from typical land uses in hilly area of Tianmuhu Reservoir watershed

A large number of forests have been shifting into tea plantation with the continuously promoting of agricultural comprehensive development in the hilly area of Tianmuhu Reservoir watershed,so it is urgent to know how tea plantation expansion influence nitrogen loss.Three experimental natural plots were delineated on tea plantation,secondary pine forest and bamboo forest to study nitrogen loss characteristics via runoff from typical land uses in hilly area of Taihuhu upstream watershed,so as to achieve measured parameters of nitrogen loss via runoff for evaluating the water environmental impact of agricultural comprehensive development in hilly area.TN concentrations in surface runoff of tea plantation,secondary pine forest and bamboo forest were 11.25,2.83 and 3.60 mg/L,respectively,mainly in dissolved form.As to subsurface runoff,they were 27.16,3.59 and 1.06 mg/L,respectively,and were mainly made up of DIN for tea plantation and secondary pine forest,especially as nitrate,while DON for bamboo forest.The plot scale surface runoff coefficients of tea plantation,secondary pine forest and bamboo forest were all less than 0.03,so that subsurface runoff was the major source of runoff.Nitrogen loss was raised heavily with the expansion of tea plantation.The loss rate was 103.08 kg N /(ha·a),which was 7.6 and 23.2 times the loss rate of secondary pine forest and bamboo forest,and 86.7%-99.7% of the total load was lost via subsurface runoff.Subsurface runoff should be paid attention to on prevention and control the nitrogen loss via runoff of tea plantations,and besides reducing fertilizer application,the combination of construction of bamboo buffers at the toe of tea plantation slopes and ponds at the outlet of drainage,so as to prevent and control nitrogen loss via runoff by intercepting nitrogen in situ,is also considerable.

Pattern of impoundment effects and influencing mechanism of Three Gorges Project on water regime of Lake Dongting

With the operation of Three Gorges Project(TGP),water regime of rivers and lakes downstream of the dam changed with the reservoir regulation.The lowering of water level becomes normal after flood season compared with the years before TGP.Here,the water storage of TGP in 2006 was selected as a case to quantitatively investigate the effects of TGP on water regime of Lake Dongting.We applied the coupled hydrodynamic analysis model for the middle Yangtze River to compute the variation of water regime induced by the water storage.During impoundment,the reduction of the water level and discharge are 1.32m and 466m3/s,respectively,at Chenglingji,the outlet of Lake Dongting.The bottomlands inside the Lake Dongting are exposed ahead of time and the lake area with over 5 inundation days reach to 287 km2.Results also indicate that: 1) the impact of TGP on water regime varied with locations: east Lake Dongting takes the first place,the east of South Lake Dongting and the north of West Lake Dongting second,and the west of South Lake Dongting and the south of West Lake Dongting third.2) The bottomlands which strongly affected by the impoundment are mainly located at East Lake Dongting,South Lake Dongting and the both sides of flood ways.3) Two influencing mechanisms on water regime are identified: one is the increase of the lake discharge induced by the rapid drawdown of the mainstream of the Yangtze River;the other is the reduction of inflow from the Yangtze River via Sankou distributary channels.

Analysis of deposition and erosion of Dongting Lake by GIS

The sediments of the Dongting Lake come from four channels (one of them was closed in 1959), connected with the Yangtze River, four tributaries (Lishui, Yuanjiang, Zishui and Xiangjiang) and local area, and some of them are transported into the Yangtze River in Chenglingji, which is located at the exit of the Dongting Lake, some of them deposit into drainage system in the lake region and the rest deposit into the lake. The annual mean sediment is 166,555xl04t, of which 80% come from the four channels, 18% from the four tributaries and 2% from local area, whereas 26% of the total sediments are transported into the Yangtze River and 74% deposited into the lake and the lake drainage system. Based on topographic maps of 1974, 1988 and 1998, and the spatial analysis method with geographic information system (GIS), changes in sediment deposition and erosion are studied in this paper. By overlay analysis of 1974 and 1988, 1988 and 1998, erosion and sediments deposition areas are defined. The main conclusions are: (1) sediment rate in the lake is larger than erosion rate from 1974 to 1998. The mean deposition in the lake is 0.43 m; (2) annual sediment deposition is the same between 1974–1988 and 1988–1998, but the annual volume of deposition and erosion of 1988–1998 is bigger than that in 1974–1988; (3) before the completion of the Three Gorges Reservoir, there will be 7.82xl08m3of sediments deposited in the lake, which would make the lake silted up by 0.33 m; (4) in the lake, the deposition area is found in the north of the east Dongting Lake, the south-west of the south Dongting Lake, and the east of the west Dongting Lake; while the eroded area is in the south of the east Dongting Lake, the middle of the south Dongting Lake, the west of the west Dongting Lake, as well as Xiangjiang and Lishui river flood channels.

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.

鄱阳湖湿地植物灰化薹草(Carex cinerascens)对不同地下水位的生理生态响应

地下水位在非淹水期对湿地植物的生长影响较大，但目前相关研究十分缺乏.本文选择鄱阳湖典型植被灰化薹草（Carex cinerascens）为研究对象，研究不同地下水位（地下水位埋深10、20、40、80和120 cm）对灰化薹草形态指标、地上生物量和生理指标的影响.结果表明，随着地下水位埋深的增加，灰化薹草的株高、叶长和生物量均显著降低，地下水位10 cm处理组的灰化薹草生物量为0.371±0.017 g，为地下水位120 cm处理组（0.084±0.004 g）的4.4倍；处理组间灰化薹草叶片中超氧化物歧化酶活性、过氧化物酶活性、游离脯氨酸含量和叶绿素含量均存在显著差异，其中游离脯氨酸含量由地下水位10 cm处理组的6.29±0.70 μg/g增加到地下水位120 cm处理组的8.54±1.37 μg/g，表明随着地下水位埋深的增加，灰化薹草面临一定程度的干旱胁迫.灰化薹草的生理生态响应综合表明，地下水位埋深20 cm以内适宜灰化薹草的生长，地下水位埋深80 cm以上的干旱胁迫会阻碍灰化薹草的生长.

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