Study on Spatial Distribution of OM, N, P in Surface Soil around Lake Chaohu

The concentration of total nitrogen (TN), total phosphorus (TP) and organic material (OM) at sixty grid division in Lake Chaohu basin around the lake was studied, in order to investigate their spatial distribution characteristics. The results showed that the average concentrations of TN, TP and OM were 1027 mg/kg, 483 mg/kg, 1.95%, and their concentrations ranged from 253 mg/kg to 2273 mg/kg, 223 mg/kg to 1173 mg/kg and 0.291% to 5.48%, respectively. The high concentration areas were located at the basins of Tuogao river and Zhao river while the low concentration areas were located at basins of Pai river, Nanfei river and Dianpu river. The concentrations of TN and OM were higher in East part than in West part. The spatial distribution of TN, TP and OM concentrations of the surface soil showed inconsistent with those of the water quality of the inflow rivers and the lake and the TN and TP of lake sediment studied.

Studies on Temporal and Spatial Variations of Phytoplankton in Lake Chaohu

Temporal and spatial variations of the phytoplankton assemblage in Lake Chaohu, a large shallow eutrophic lake in China, were studied from September 2002 to August 2003. A total of 191 phytoplankton species was identified, among which Chlorophytes （101） ranked the first, followed by Cyanophytes （46） and Bacillariophytes （28）. On aver- age over the entire lake, the maximum total algal biomass appeared in June （19.70 mg/L） with a minimum （5.05 mg/ L） in November. In terms of annual mean biomass, cyanobacteria contributed 45.43% to total algal biomass, followed by Chlorophytes （27.14%）, and Bacillariophytes （20.6%）. When nitrate （NOs-N） and ammonium （NH4-N） concentrations dropped in spring, fixing-nitrogen cyanobacterium （Anabaena） developed quickly and ranked the first in terms of biomass in summer. It is likely that dominance of zooplanktivorous fish and small crustacean zooplankton favored the development of the inedible filamentous or colony forming cyanobacteria. The persistent dominance of cyanobacteria throughout all seasons may indicate a new tendency of the response of phytoplankton to eutrophication in Lake Chaohu.

Temporal and spatial changes in nutrients and chlorophyll-a in a shallow lake,Lake Chaohu, China: An 11-year investigation

Temporal and spatial changes of total nitrogen （TN）, total phosphorus （TP） and chlorophyll-a （Chl-a） in a shallow lake, Lake Chaohu, China, were investigated using monthly monitoring data from 2001 through 2011. The results showed that the annual mean concentration ranges of TN, TP, and Chl-a were 0.08-14.60 mg/L, 0.02-1.08 mg/L, and 0.10-465.90 ~tg/L, respectively. Our data showed that Lake Chaohu was highly eutrophic and that water quality showed no substantial improvement during 2001 through 2011. The mean concentrations of TP, TN and Chl-a in the western lake were significantly higher than in the eastern lake, which indicates a spatial distribution of the three water parameters. The annual mean ratio of TN：TP by weight ranged from 10 to 20, indicating that phosphorus was the limiting nutrient in this lake. A similar seasonality variation for TP and Chl-a was observed. Riverine TP and NH4＋ loading from eight major tributaries were in the range of 1.56× 10^4-5.47 × 10^4 and 0.19 × 104-0.51 × 10^4 tons/yr over 2002-2011, respectively, and exceeded the water environmental capability of the two nutrients in the lake by a factor of 3-6. Thus reduction of nutrient loading in the sub-watershed and tributaries would be essential for the restoration of Lake Chaohu.

Study on Nitrogen Forms in Chaohu Lake and Wabu Lake Sediments

Composition and distribution of nitrogen in Chaohu Lake and Wabu Lake sediments were studied.The results showed that the mean total nitrogen content in Chaohu Lake and Wabu Lake was 0.533 g/kg and 0.265 g/kg respectively,and the primary composition of nitrogen was organic nitrogen(94%).The organic index indicated that the organic pollution degree of Wabu Lake was lower than that of Chaohu Lake.

Effects of Environmental Factors on NH_4^+ Release in Sediment from Chaohu Lake

[Objective] The aim of the research was to reveal the influence mechanism of sediment-water exchange of nutrients in Chaohu Lake. [Method] The effects of environmental factors (overlying water, temperature, pH and dissolved oxygen concentration) on NH_4^+ release in sediment from Chaohu Lake were studied under controlled laboratory conditions. [Results] With the rising of temperature and the decrease of NH_4^+ concentration in overlying water, NH_4^+ released from sediment increased significantly. pH had a great effect on NH_4^+ release with a complicated mechanism. The largest release amount of NH_4^+ under anaerobic condition was about 6 times as much as that under aerobic condition. [Conclusion] This research would provide theoretical support for environmental management of Chaohu Lake in the project of leading water from the Yangtze River to Chaohu Lake.

Spatiotemporal variations of internal P-loading and the related mechanisms in the large shallow Lake Chaohu

Spatiotemporal variations of P species and adsorption behavior in water column,interstitial water,and sediments were investigated in the large shallow eutrophic Lake Chaohu.Orthophosphate(Ortho-P)and total phosphorus(TP)concentrations were significantly higher in the western part than in the eastern part of the lake,due to different nutrient inputs from the surrounding rivers.Moreover,particulate phosphorus(PP)concentration was in a similar spatial pattern to Ortho-P and TP concentrations,and also showed significantly positive correlation with the biomass of Microcystis,indicating more uptake and store of phosphorus by Microcystis than by other algae.Increase of pH and intensive utilization of P by phytoplankton were the main factors promoting P(especially Fe-P)release from the sediment to interstitial water during the cyanobacterial blooms in Lake Chaohu.Spatial dynamics in TP concentration,P species and adsorption behavior of the sediment,coupled with the statistical analyses,suggested that the spatial heterogeneity of P contents in the sediment was influenced by various factors,e.g.human activities,soil geochemistry and mineral composition.In spite of similar TP contents in the sediments,increase in proportion of Fe-P concentration in the sediment may result in a high risk of P release.

CAUSES AND CONTROL COUNTERMEASURES OF EUTROPHICATION IN CHAOHU LAKE, CHINA

Chaohu Lake, located in the central Anhui Province, is one of the five largest fresh lakes in China. Now it is one of the three most eutrophication lakes in China. The deterioration of its water quality has influenced the sustainable development of society, economy and environment of Hefei City, the capital of Anhui Province. A series of measures have been carried out to control its eutrophication, but it is still serious. On the basis of the lake water quality data from 1984 to 2003, the causes of the eutrophication of Chaohu Lake are analyzed. Studies indicated that the suitable natural conditions and human activities played a crucial role in the process of the eutrophication of Chaohu Lake. A great amount of industrial, agricultural and domestic sewage discharged into the lake is the main cause of eutrophication in the lake. Land use, soil erosion and shoreline collapse destroyed the watershed eco-environment and the terrestrial ecosystem of Chaohu Lake. And the building of Yuxi Gate extends the sluggish of the nutritious substance and speeds up the process of the eutrophication. From the view of systematic engineering and watershed ecology, a series of the countermeasures have been put forward to control the eutrophication.

Assessment of Heavy Metal Pollution in Estuarine Surface Sediments of Tangxi River in Chaohu Lake Basin

A total of 30 surface sediments samples from the estuary wetland of the Tangxi River, Chaohu Lake Basin were obtained and tested. Enrichment factor （EF） and geoaccumulation index （Igeo） as well as multivariate statistical analysis methods including Factor Analysis （FA） and Hierarchical Cluster Analysis （HCA） were applied for the assessment of heavy metal pollution in surface sediments. The results of EF values show that the pollution of copper （Cu） and cadmium （Cd） occurs in the estuarine sediments, and that zinc （Zn）, lead （Pb） and chrome （Cr） may originate from crustal materials or natural weathering process. The mean EF values of the five heavy metals are in the decreasing order： Cu〉Cd）Zn〉Pb〉Cr. Based on the lgeo of target heavy metals, the surface sediments collected from the study area can be approximately categorized as unpolluted with Zn, Pb and Cr, and moderately polluted with Cu and Cd. The degree of heavy metal pollution decreases in the order of Cu〉Cd〉Zn〉Pb〉Cr. Three groups of pollution factors are presented from FA： Zn-TOC, Cu-Cd and Cr-Pb, which respectively accounte for 27.22%, 25.20% and 21.05% of variance. By means of HCA, a total number of seven groups are distinguished from 30 sampling sites. Results indicate that Cu and Cd are the prior controlled pollutants in the estuarine sediments of the Tangxi River.

Characteristics and Effects of Inorganic Nitrogen in East Water-source and Inflow Rivers of Chaohu Lake

[Objective] To study the characteristics and effects of inorganic nitrogen in east water-source and inflow rivers of Chaohu Lake. [Method] The speciation and distribution characteristics of dissolvable inorganic nitrogen （DIN） in east water-source and inflow rivers of Chaohu Lake were investigated, and their effects on water qual- ity were examined. [Result] The concentrations of NH3-N and NO2--N were the high in flood season, and low in non-flood season, while the concentration of NO3--N pre- sented the opposite trend; the concentration of NO3--N was the highest in Shuangqiao estuary, where the pollution was the worst. DIN in Zhegao estuary and Xiaozhegao estuary was mainly caused by domestic sewage and industrial wastewaters; surface runoff and pollution from ships contribute the most to the DIN content in Shuangqiao estuary. [Conclusion] This study provided basic data and theoretical basis for the control and management of eutrophication in Chaohu Lake.

On the horizontal distribution of algal-bloom in Chaohu Lake and its formation process

Based on the remote sensing images of algae, the present work analyzes the horizontal distribution characteristics of algal blooms in Chaohu Lake, China, which also reveals the frequency of algal blooms under different wind directions. Further, an unstructured-grid, three-dimensional finite-volume coastal ocean model （FVCOM） is applied to investigate the wind-induced currents and the transport pro- cess to explain the reason why algal blooms occur at the detected places. We first deduce the primary distribution of biomass from overlaid satellite images, and explain the formation mechanism by analyzing the pollution sources, and simulating the flow field and transportation process under prevailing wind over Chaohu Lake. And then, we consider the adjustment action of the wind on the corresponding day and develop a two-time scale approach to describe the whole formation process of algae horizontal distribution in Chaohu Lake. That is, on the longer time scale, i.e., during bloom season, prevailing wind determines the primary distribution of biomass by inducing the characteristic flow field; on the shorter time scale, i.e., on the day when bloom occurs, the wind force adjusts the primary distribution of biomass to form the final distribution of algal bloom.

Dynamic Assessment on Regional Eco-environmental Quality Using AHP-Statistics Model—A Case Study of Chaohu Lake Basin

An indicator system closely connected with eco-environment, in which indicator involves in such fields as society, economy, resources, environment and ecology, is first proposed for eco-environmental quality assessment. Then, a hierarchical model with four levels is established by virtue of these indicators and attributes. In the model, weights of indicators and attributes are determined by combining Delphi method with the Analytic Hierarchy Process (AHP) and a statistic method is used to eliminate the influences arising from the differences in dimension and magnitude of indicators. On these grounds, an AHP-statistics model is provided for regional eco-environmental quality assessment. As a case, such AHP-statistics model is utilized in the dynamic analysis of regional eco-environmental assessment in Chaohu Lake basin. Study results show that natural environmental quality in the watershed was in the declining state while social environmental quality was in a markedly improved situation from 1996, and the synthetic eco-environmental quality was gradually and slowly improved under the common influences of both natural and social environmental factors. Example of application testified the capacities of above methodology to evaluate the real and dynamic state of regional eco-environmental quality.

Forecast of Flood in Chaohu Lake Basin of China Based on Grey-Markov Theory

Flood is one kind of unexpected and the most common natural disasters, which is affected by many factors and has complex mechanism. At home and abroad, there is still no mature theory and method used for the long-term forecast of natural precipitation at present. In the present paper the disadvantages of grey GM (1, 1) and Markov chain are ana- lyzed, and Grey-Markov forecast theory about flood is put forward and then the modifying model is developed by making prediction of Chaohu Lake basin. Hydrological law was conducted based on the theoretical forecasts by grey system GM (1, 1) forecast model with improved Markov chain. The above method contained Stat-analysis, embodying scientific approach, precise forecast and its reliable results.

CAUSES AND COUNTERMEASURES FOR CHAOHU LAKESHORE COLLAPSE

By interpreting the remote sensing data of aerial photos and satellite images in different time, combining with field investigation, landform and water level observation, collecting data of weather, hydrology in Chaohu Lake, Anhui Province from 1957 to 2003, the reasons for collapse of Chaohu lakeshore were analyzed. The results are as follows: 1) The collapse of the Chaohu lakeshore is controlled macroscopically by two sets of north-east and the north-west faults, and the degree of collapse is determined microcosmically by lithology. 2) The constant change of water level, resulting from precipitation, wind speed and its direction, is one of the main reasons for intermittence collapse. 3) The soil and water loss or mud and sand filling up, resulting from artificial factors, such as inconsequence control of Chaohu sluice or irrational agricultural and industrial activities, etc., can uplift the lake′s bed and drive water level up. The high water level also results in the collapse. Judging from the above mentioned reasons for the collapse, we have proposed some countermeasures: 1) Putting the lakeshore slope protection project such as stone and cement mortar into practice, and upstream slope should be 1∶2.5 or 1∶3, some parts of them should be 1∶4, if they were not stable. The back slope, which is from Gui Mountain to Zhongmiao Temple, should be 1∶1.5-1∶3. 2) Constructing a greenbelt for the lakeshore, planting some vegetation such as osier, bulrush and poplar, to resist waves between the high and the low water level. 3) Controlling Chaohu Lake water level scientifically. Corrosion of lakeshore that contains gravel clay and ferruginous-manganese concretionary structures, can decrease at low water level. 4) Renovating Chaohu Lake drainage area, strengthening the administration and supervision, breaking regionalism and establishing special administration organization.

A niche model to predict Microcystis bloom decline in Chaohu Lake, China

Cyanobacterial blooms occur frequently in lakes due to eutrophication. Although a number of models have been proposed to forecast algal blooms, a good and applicable method is still lacking. This study explored a simple and effective mathematical-ecological model to evaluate the growth status and predict the population dynamics of Microcystis blooms. In this study, phytoplankton were collected and identified from 8 sampling sites in Chaohu Lake every month from July to October, 2010. The niche breadth and niche overlap of common species were calculated using standard equations, and the potential relative growth rates of Microcystis were calculated as a weighted-value of niche overlap. In July, the potential relative growth rate was 2.79 (a.u., arbitrary units) but then rapidly declined in the following months to -3.99 a.u. in September. A significant correlation (R=0.998, P<0.01) was found in the model between the net-increase in biomass of Microcystis in the field and the predicted values calculated by the niche model, we concluded that the niche model is suitable for forecasting the dynamics of Microcystis blooms. Redundancy analysis indicated that decreases in water temperature, dissolved oxygen and total dissolved phosphorus might be major factors underlying bloom decline. Based on the theory of community succession being caused by resource competition, the growth and decline of blooms can be predicted from a community structure. This may provide a basis for early warning and control of algal blooms.

Spatial Distribution of Archaeological Sites in Lakeshore of Chaohu Lake in China Based on GIS

There are about 19 Neolithic Age sites and 120 Shang-Zhou dynasties sites in the western lakeshore of Chaohu Lake,Anhui Province,China.Based on sites data,topographic data,drainage maps,administrative maps and SPOT5 remote sensing data,spatial analysis methods were introduced into the archaeology of Chaohu Lake Basin with Geographic Information System(GIS).The spatial analysis methods include:1) Point Density Analysis with density model to acquire the shift of the sites;2) Distance Analysis to reveal the spatial structure of the sites;3) 3D Analysis based on Digital Elevation Model to get micro-geomorphologic features of the sites;and 4) Buffer Analysis to discover the relationship between the sites and rivers.The results indicate that the archaeological sites spread from the western lakeshore of Chaohu Lake gradually to the northwest,later to the south,and then symmetrically spread.Controlled by productive forces and other factors,ancient people preferred to reside in those places near water,or in plain and fertile land,which resulted in linear and decentralized distribution of the sites,and presented such disciplines as river valley directivity,terrace directivity and soil directivity.This paper indicates that the distribution of archaeological sites was influenced earlier by natural elements and later by human elements in the study period.The research is important for the integration of GIS and archaeology.

General Thinkingon the Management of Blue Algae Outbreak in the Taihu Lake,the Chaohu Lake and the Dianchi Lake

Among the Chinese lakes with the problem of eutrophication, the Taihu Lake, the Chaohu Lake and the Dianchi Lake have the worst cases of blue algae outbreak, which happen every year. Other lakes also have problems of blue algae outbreak at various degrees. However, some lakes don＇t have such problems. Practices have shown that through comprehensive management, the problem can be basically eliminated or significantly alleviated. ＂Water bloom＂ and blue algae outbreak have different connotation. The major factors affecting blue algae outbreak are sources of pollutants and ecological environment. Experiences are summed up and a new thinking on its management is developed： resolving the problem of blue algae is fundamental to lake management and development goals should be clearly set forth so as to eventually build a healthy aquatic ecosys- tem. The problem of blue algae can＇t be fully tackled by solely relying on the management of eutrophication but only by combining efforts of reducing the amount of blue algae and the management of eutrophication. The number of reduced blue algae should be larger than that of naturally prolifera- ted algae so as to alleviate and eliminate the problem of blue algae outbreak. Various engineering and technical measures and relevant protective procedures should be carried out in a scientific and proper manner. The total amount of nitrogen and phosphorous entering the lake either from point-source or non-point source pollution should be substantially reduced. Controlling the source of pollution and intercepting pollutants are the bas- ic measures. Wastewater treatment plant is the largest point source pollution in the future and adequate plants should be built with improved emission standards. Meanwhile, other measures including fishing out blue algae, diverting water, dredging, ecological restoration and expanding reed zone, should be implemented to alleviate the problem of eutrophication and eventually eliminate the problem of blue algae outbreak.

The impact of the accumulation of algal blooms on reed wetlands in the littoral zones of Chaohu Lake

In a large eutrophic lake,the littoral zone is normally an area with high-density elevated aquatic plant life,including algal blooms,where the presence of reed wetlands allows the accumulation of algae.In this study,the impact of accumulated algal blooms in reed wetlands in the littoral zone s of Chaohu Lake was investigated seasonally from 2018 to 2019.The concentrations of chlorophyll a(Chl a),total nitrogen(TN),and total phosphorus(TP)were much higher in the reed-covered littoral zones(RCLZ)than in the unvegetated littoral zones(ULZ),indicating that more algal biomass was trapped and accumulated in the RCLZ.Algal biomass could be horizontally transported to downwind littoral zones under low wind speeds,favoring the establishment of blooms.Algal accumulation levels were highest in summer due to high water temperatures and algal biomasses.Likewise,the northern littoral zones were conducive to the development of large algal blooms because of the wind pattern.The values of TN,TP,Chl a,and loss on ignition in surface sediments were higher in the RCLZ than in the ULZ.Moreover,the diffusive fluxes of ammonium and soluble reactive pho sphorus were also higher in the RCLZ than in the ULZ.Considering the capability of reed wetlands to trap algae,mechanical salvage and other physical methods should be adopted to eliminate algal biomass when massive blooms accumulate in the RCLZ.

Analysis of Pollution Sources and Countermeasures against Water Pollution in a Small River Basin of Chaohu Lake——A Case Study of the Shiwulihe River

The Shiwulihe River, the inflow river of Chaohu Lake in Hefei City, was taken as an example. Based on the current status of water quali- ty and analysis of pollution sources in the Shiwulihe River, countermeasures and suggestions of controlling water pollution were proposed to provide effective ways for the control of water pollution and restoration of aquatic ecosystem in the Shiwulihe River and other similar rivers flowing into lakes.

Current Situation and Comprehensive Control Measures of Water Environment in the Chaohu Lake

Based on the analysis of current situation of water environment in the Chaohu Lake,general ideas and measures of controlling the water environment were proposed. In respect of control ideas,controlling outbreaks of blue-green algae should be as one of control goals; it is needed to combine reducing the quantity of blue-green algae with decreasing eutrophication level to make the decrease in the quantity of blue-green algae larger than their natural increase until outbreaks of blue-green algae are eliminated; all kinds of techniques should be combined closely,integrated and innovated,and corresponding safeguard measures should be adopted. In respect of control measures,controlling sources of pollution and intercepting pollutants are basic measures,of which improving sewage treatment capacity and standard greatly is a key measure,and actively controlling pollution from large-scale livestock and poultry breeding is one of main measures; rivers polluted heavily should be controlled,and using microorganisms to purify small and moderate rivers can be as one of preferred techniques; blue-green algae should be dredged deeply to reducing their quantity; water should be transferred from the Yangtze River to the Chaohu Lake or the Hauihe River to purify water bodies and increase environmental capacity; reed wetland should be restored on a large scale to increase vegetation coverage from 5% to 20%; dredging should be combined with the elevation of basement of restored reed wetland.

Regional eco-environmental analysis of Yuxi River-Chaohu Lake

Yuxi River-Chaohu Lake water suffers greatly from the ecological problems of eutrophication, high turbidity, organic pollution, disappearance of littoral macrophyte, bank erosion and reduction of economic fishery products. With Micro-cystis dominant, it is a degenerated and weak ecosystem. Its vicious cycling is caused by too much nutrient load, high spring water level and improper management of the water. The point sources of pollution from cities and industries contribute more than 50% of nutrient load. Soil erosion and fertilizer loss from late rice fields are important factors in non-point nutrient load. The disappearing littoral zone can neither give enough protection for the bank nor provide proper habitats for the biota. The feasibility of ' ecological water level proposal' and means to reduce nutrient load are discussed to improve the habitat environment for both the nature and human being.