Abstract:There are many heavily sediment-ladden rivers in China, with high sediment concentration and a large quantity of sediment load. The reservoir sedimentation problems in those rivers are so serious that the amount of sediment deposited in the reservoir is great and the rate of sedimentation is accelerated. According to the statistics, up to the end of 1981? a total amount of 11.5×10¹⁰ m³ of sediments were approximately accumulated in the reservoirs, and 14.2% of the design capacity was lost. The average annual loss in capacity for storage reservoirs reaches 2.3 percent, the highest in the world. Silting of impounding lakes not only has an effect on the benefits of the reservoirs and seriously threatens the life of reservoirs, but also entails many environmental problems not fully anticipated at the time of planning of the reservoir, which calls for the Chinese scientific-technical personnol to pay high attention to and make great efforts in research on the methods of minimizing sediment deposition. In this paper, the situalion of rcservior deposition in China will be described. The main content is as follows:1) the characteristics of hydrology and sediment of rivers; 2) the seriousness of reservoir sedimentation in China; 3) problems caused by reservoir deposition; 4) the methods of minimizing sediment deposition etc.

Abstract:Inflow/outflow is one of the main styles of water currents in lakes, which affects pollutant diffusion and transportation?sand scouring and sediment, and lake density field variation through water exchanging. A numerical model of two-dimension and open-boundary is proposed in accordance with the features of Hongze Lake in this paper. The model is used to study the course of in-flow/outflow, which is engaged in numerical experiment for the characteristics of Huaihe flow through the lake.

Abstract:Up to now, three-dimension (3-D)finite difference models have been extensively used to simulate water current in coastal areas, lakes and reservoirs. The explicit time integration method is used in many of such mcxiels and thus the time step size is limited by the well-known CFL stability criterion. A three-dimension implicit finite difference model for wind-driven water current in a lake is developed in this paper. Stress terms, pressure terms and Corilic terms in the governing equations are represented implicitly in the model, and through analysing the stability of difference scheme, it is discovered that time step size of the scheme is essentially independent of CFL criterion. The proposed model is thus valuable in reducing compute time. The proposed model is first validated by a particular case where analytic solution is available in comparison with difference solution of the model, and then it is used to simulate wind-drivern water current in Moshui Lake. The real case shows that the calculated results of the mcxiel are rational and available, and can describe better the structural characteristic of wind-driven water current in a lake.

Abstract:Seven cores of recent sediments were obtained in Yangcheng I.ake, among which 102cm-core YCl and 55cm-core YC3 in the western part of the lake kept undisturbed. The core profile is divided into 3 lithological beds which are separated by 2 long-term sedimentation hiatus, namely upper bed A of sapropel, middle bed B of silty clay, and lower bed C of sticky silty clay (so called "hard earth bed"). ¹⁴C, ²¹⁰Pb, water content, grainsize? magnetic susceptibility, nutrient elements, metal elements (both total and liable facies), stable isotope of organic carbon and fossil pigments were analysed. Chronic stratigraphic study demonstrates that beds A, B and C belong respectively to the deposits of Late Pleistocene, Holocene and about recent 100 years. The environmental characteristics of every bed are described as follows. Bed C:Reworked fluvial sediments, in which lower values of TOC, TN, pigment content, CD/TC and heavy metals and higher values of C/N, δ¹³C, allogenic metals (Al, Na, Mg, Ca and Ti) manifest more intense erosion of catchment land, lower primary productivity and eu-trophic state. Bed B:Lacustrine sediments, of which every environmental proxy sits between beds A and C. Bed A:Lacustrine sediments, of which higher values of TOC, TN, pigment content, CD/TC and heary metals and lower values of C/N, δ¹³C and allogenic metals show enhanced primary productivity and eutrophication of the lake. Detailed analysis of the beds demonstrates slightly higher pollution coefficient of Cu, Co, Zn, Cr, Ni in 0-2cm on surficial sediments. In the accumulation rate profile, the accumulation of many heavy metals is increased gradually upwards, extensively since the 1970s. The accumulation rate of nutrient elements and pigments also indicate more intense lake eutrophication since the 1970s-1980s.

Abstract:Pollen assemblages of profile ZK₂ (116°12'50"E, 29°44'30"N, 7.83m a. s. 1.) are studied to reconstruct the paleoclimate of Hukou arca, Poyang Lake. According to the pollen diagram, 8 assemblage zones have been distinguished in an ascending order as follows; Ⅰa, Pinus-Quercus-Liqidamber(20.2-17.6m); Ⅰb, Pinus-Cyclobalanoopsis(17.6-16m); Ⅱ, Pinus-Microlepia (16-13.7m); Ⅲa, Pinus-Castaneae-Cyclotbalanoopisis (13.7-11.2 m); Ⅲb, Pinus-Microlepia (11.2-10.5m); Ⅲc, Pinus-CycLobanlanoopsis (10.5-7.5m); Ⅳ, Pinus-Pteris-Gamineae(7.5-2.0 m); Ⅴ, Pinus-Microlepiu (2.0-0m). Based on the above statement, 6 phases of climate fluctuation were shown in the past 4 500 years:4.5~3.8kaB. P., warm and wet; 3.8~3.4kaB. P., cool and little dry; 3.4-3. OkaB. P., warm and little dry;around 3. OkaB. P., cool and wei; 2.8-2.3kaB. P., warm and wcl; 2.3kaB. P.-present, fluctuated frequently.

Abstract:Yangcheng Lake Group is composed of Yangcheng Lake and its surrounding smaller lakes such as Kuncheng Lake, Shengze Lake and Kuilei Lake etc., making up dish-like Yangcheng Lake depression topographically. In the paper the environmental changes of the lake area during Neolithic Age and the formation of the lake group are analyzed through the study on the spatial and temporal geographic distribution of the Neolithic sites as well as the depositional features and animal and plant remains in the strata where the relics exist. The study manifests that Majiabang Culture sites of early Neolithic Age are distributed on mound land or hill foot, showing that the ancients settled mostly on higher land. The phenomenon as well as the pollen assemblages and animal remnants in the relic strata indicated a warmer and wetter climate and broader water area. In Songze Culture Period of middle Neolithic Age the intensively fluctuated climate, frequently changed water area exerted a negative effect on the ancients' living and development. Songze sites reduced and distributed only in thg area of Majiabang sites. During Liangzhu Culture Period of late Neolithic Age the climate got dryer and cooler, the land area got broader and the culture sites increased sharply and filled up the space beyond Majiabang and Songze sites. However, an extensive water transgression in the end of Liangzhu Age broke violently the ancient culture and stop the culture development which would enter the historical civilization. Yangcheng Lake together with the surrounding lakes is formed gradually on the basis of the river course during Song Dynasty resulting from the increased water body, disordered water system, blocked river and the overflowed flood.

Abstract:Although the result of long-time detail ecological monitoring shows that the pollution of water and sediment is serious, there is no acute toxicity to fish in the aquatic ecosystems of Xuanwu Lake. This was proved by toxicity tests(in situ and in laboratory) and simulation tests (simulated the lake water and sediment). The pathogenic bacteria, Aennnonas hydrophila, were isolated from silver and variegated carp of the lake, and is believed to be the responsible pathogen. From the results of determining germ virulence and observing the symptoms of fish inection it can be concluded that the cause of fish eruptive death is a kind of bacteriosis caused by A. hydrophila. The results of comprehensive analyses have drawn the following conclusion. In the summer when the redox shielding level(Eh, +200mV) is close to the surface of the sediment, the introduction of pathogenic bacteria from the sediment into the water occurs readily. The dominant population, Merismopedia, is not a preference bait for fish. On the contrary, it makes fish struggle along on the verge of starvation during the summer. In addition, terrible pollution of water and sediment may not only destroy the antibody systems of fish but also effect the dynamic of pathogenic bacteria. Therefore, this bacteriosis is an environmental disease.

Abstract:This study is dealt with the effects of toxic Microcystis aeruginosa and Microcystin (MCYST) on fishes and Daphnia magna by feeding and intraperitoneal injection. The results suggested were as follows:1. MCYST-LR was pernicious to all of the tested fishes. 1) Grass Carp:mean weight was about 10-12 g. The dosage of injection was about 65-300 μg/kg, LD₅₀ 110 μg/kg; 2) Silver Carp:mean weight 18-20 g, dosage of injection 150-400 μg/kg, LD₅₀ 350 Hg/kg; 3) Tilapia:mean weight 32-35 g, dosage of injection 400-800 μg/kg, LD₅₀ 500 μg/mg. Liver injury was discovered by observing fish liver altrastructure 24hrs after the injection with Microcystins. The liver damage of Grass Carp was more serious than that of the other two fishes. 2. When Silver Carp and Tilapia fed on toxic M. aeruginosa as the only diet, they can be alive for more than 20 days. The toxicity of feces decreased 2-4.5 times respectively compared with that of M. aeruginosa. The absorption spectra and microscope observation of the feces of both fishes reflected that the ability of digesting and absorbing of toxic algae cell and toxin for Tilapia was greater than that of Silver Carp; both fishes had little liver damage by observing their liver ultrastructure, 3. Fed on Micnx'ystis ueruginosa or added with 15 μg/mL MCYST-LR to the medium, Daphnia magna may die 48hrs later. Daphnia magna grew slowly and did not carry eggs when fed on nontoxic M. aeruginosa 8508, showing that Microcystis was not a suitable food for Daph-nia.

Abstract:A survey of food organism is made in Danjiangkou Reservoir which consists of Danjiang Reservoir Region and Hanjiang Rcservir Region during December 1992 and September 1993. The results show that the production of phytoplankton, zooplankton and benthos was 1.5×10⁶ t, 3.0×10⁵ t and 4.48×10⁴ t respectively, a total of 1.845×10⁶ t; the potential fishery production reached 1×10⁴ t, 0.6×10⁴ t and 0.015×10⁴ t seperately, amounting up to 1.615×10⁴ t. Based on the standing crops of phytoplankton and bio-nutrients, the trophic type of Danjiang Reservoir region could be regarded as oligmesotrophic and that of Hanjiang Reservior region to mesotrophic. The fishery development and water quality protection in Danjiangkou Reservoir were also discussed.

Abstract:The present paper deals with the reproduction, feeding habits and growth of salangid fishes Neosalaruc taihuensis and N. oligodontis in the Wanghu Lake, Hubei Province. The survey was conducted from 1992 to 1993 and the results are summarized as follows. The male secondary sexual characters of N. taihuensis emerge in October and those of N. oligodontis in November. Both species spawn in batches. The N. taihuensis spawns from March to June, with an average absolute individual fecundity of 1 506 eggs per female and dominant body-length groups of 56.0 mm to 64.9mm; and for N. oligodontis, from March to May, 569 eggs per female and 35.0mm to 42- 9mm, respectively. Both species feed mainly on Cladocera and Copepoda, with feeding intensities peaking twice, from October to November and from February to April. The juveniles grow fast before June and the adults grow fast between September and November. Erased on the studies, some propagation measures are suggested.

Abstract:Pelecus cultratus and Albumus alburnus are two dominant cyprinid fishes in the open lake of Neusiedler See (Austria). Food resource partioning between two species was studied through June to November, 1994. From June to September, Pelecus and Alburnus preferred cladocerans Dlaphanosoma mongolianum and Leptodora kindti, resulting in a high degree of dietary overlap. In October and November, Pelecus fed mainly on copepod Arctodiaptomus spinosus and insects drifting at the water surface, while Alburnus exclusively consumed insects, and the overlap became minimal. The observed changes in the diet of and overlap between these species were caused by seasonal variation in food abundance and composition, combined with the divergence in foraging profitability of the fishes. Niche segregation was profound in lean-food seasons, and this may be a responsible process of the fishes coexistence.

Abstract:Based on the thermodynamic formulation of Darwin's Theory of Survival of the Fittest, this paper introduces the thermodynamic concept Exergy into an ccadynamic model for lakes as a goal function of some important model parameters, then the ecological properties of lake ecosystem are considered extensively. The changes in model parameters with time are aecomplished by using the modelling procedure of parameter combinations under exergy control, then the changes in the species composition and ecological structure of ecosystem are reflected by the varying parameters. This improvement overcomes the original ecodynamie model's defects of strong rigidity, poor adaptability and inadequate considerations of ecosystem properties. The modelled results of Di-anchi Lake ecosystem have shown that the improved ccodynamic model is satisfactory and practicable.

Abstract:Both the advance in the study of the degradation and rcsioration of eutrophic shallow lakes and the role of biomanipalation in the recovery of damaged lake ecosystems have been reviewed in the present paper. Three models have also been introduced on the decline of submerged macrophytes to interpret the succession of submerged macrophyte communities in the process of eu-trophicatoa of the shallow lakes in the middle and lower reaches of the Changjiang River. Based on the well-dcxrumented references and the researches on the decline and restoration of aquatic vegetation conducted in Donghu Lake of Wuhan during the 8th Five Year Plan period (1991-1995), the ant hors put forward a model.

Abstract:On the basis of general methods for evaluating lake cutrophicalion, the anthor summarized some comprehensive assessment methods for lake eutrophication reported at home and abroad. It is pointed out that the trophic state index should be the major method for evaluating lake eutrophication status, since it could provide a continuous numerical class of lake trophic state and a rigorous foundation of quantitative studies of eutrophication mechanism. After analyzing some determination methods of weight distribution in lhe comprehensive indices, ihe anthor insists that the hierarchical analysis bo quite perfect to determine weights. This paper shows the weight distribution of TSI and its modifiers. Additionally, il is discussed in brief the relations between comprehensive evaluation and other statistical methcxls such as cluster analysis in the last part of this paper.