Fan Chengxin

The Vertical Distributions of Nitrogen and Phosphorus in the Sediment and Interstitial Water in Taihu Lake and Their Interrelations

The contents of nitrogen and phosphorus and ferrous in the column sediments and their interstitial water were analyzed and compared in the main regions of Taihu Lake in 1998. The results show that the upper layer(0—10cm) contained higher contents in TN and TP and than the lower. And NH 4 N and PO 4 P in the interstitial water are a bit higher in the seriously polluted waters than those in the gently polluted waters. However, those of the lower layers are slightly higher in the gently polluted waters than those in the seriously polluted. It was indicated that there was no distinct corresponding relationships between NH 4 N/PO 4 P contents in the interstitial water and TN/TP contents in the sediments. The ferrous concentration in the interstitial water is distinctly in positive correlation with NH 4 N content ( R =0.9234).

Environmental effect of sediment dredging in lake (I) : the role of sediment dredging in reducing internal phosphorous release

A laboratory experiment was carried out to study the effects of sediment dredging on phosphorus (P) release from lake sediments using incubation of undredged (control) and dredged cores through a year. We found that dredging the upper 30cm layer of the sediment can efficiently reduce the interstitial PO4 3--P concentration and different P forms in the sediment. The P fluxes of the undredged and dredged cores ranged from -237.3 to 3047.6μg/(m2·d) and -143.8 to 14.4μg/(m2·d), respectively. The fluxes of the dredged cores were generally lower than those of the undredged (control) cores, with significant(P<0.05)differences between the fluxes of the dredged and undredged cores occurring between March and October of 2006. The sediment P in the dredged cores had a lower release potential than those in the control cores. Our results suggested that dredging may be a useful approach for decreasing internal P loading in Lake Taihu once the external P loading is effectively controlled in advance.A laboratory experiment was carried out to study the effects of sediment dredging on phosphorus(P)release from lake sediments using incubation of undredged(control)and dredged cores through a year.We found that dredging the upper 30cm layer of the sediment can efficiently reduce the interstitial pO_4(3-)-P concentration and different P forms in the sediment.The P fluxes of the undredged and dredged cores ranged from-237.3 to 3047.6μg/(m~2·d)and-143.8 to 14.4μg/(m~2·d),respectively.The fluxes of the dredged cores were generally lower than those of the undredged(control)cores,with significant(P0.05)differences between the fluxes of the dredged and undredged cores occurring between March and October of 2006.The sediment P in the dredged cores had a lower release potential than those in the control cores.Our results suggested that dredging may be a useful approach for decreasing internal P loading in Lake Taihu once the external P loading is effectively controlled in advance.

Migration mechanism of biogenic elements and their quantification on the sediment-water interface of Lake Taihu:II.chemical thermodynamic mechanism of phosphorus release and its source-sink transition

室内静态模拟不同温度下太湖15个湖区柱状沉积物磷酸根释放,分析了相应表层沉积物形态磷,以及梅梁湾间隙水中相关离子Al（Ⅲ）、Fe（Ⅱ）、Ca（Ⅱ）和PO34-含量的季节变化，研究表明,受陆源影响较大的泥区通常是太湖内源磷的稳定源;而在开敞度较大的湖区,由于表层沉积物胶体的物化吸附,使得温度对底泥磷释放的影响作用减弱,并易产生磷的“内汇”现象;在梅梁湾区成汇区,还加上春夏季藻类的局部超负荷需磷这一控制因素,从而使得太湖大部分泥区在一年中至少发生一次源-汇转换过程，化学热力学分析揭示,Al-P较之Fe-P和Ca-P更易在界面发生溶解可能是太湖表层沉积物Al-P与PO34--P释放速率呈显著相关（r=0，3858＞r1-0，01,n=45）的内在原因，虽然沉积物中Fe-P有较高的释磷潜力,但浅水湖所营造的沉积物表层氧化层和广泛覆盖的无机胶体及粘土矿物的强吸附介质,可能是抑制沉积物中Fe-P释放成为优势的主要因素，估算太湖沉积物-水界面磷的净通量为899，4±573，6t/a,约占太湖磷入湖量的1/4-1/2,其中成汇通量约为-91，2±42，4t/a。

Wind-wave affected phosphate loading variations and their relationship to redox condition in Lake Taihu

Variation of wind speed and the physico-chemical parameters, such as dissolved phosphate, ferrous and manganese in lake water were observed on site. Together with the chemistry analysis and simulated experiment in lab, the change of phosphate concentration in lake water was analyzed. The variation of ferrous/phosphate ratio explained that along with the enhancement of wind-wave effect and the oxidation ability of lake water, the effects of co-precipitation and removal of dissolved phosphate and iron in the lake water were reinforced. The ferrous/phosphate ratio in pore water was less than 2.0, demonstrating that the dissolved phosphate can be released into the overlying water. But, in the lake water, the stability of phosphate was controlled by the water dynamics. The phosphate release experiment showed that molecular release was only part of the whole and the direct discharge of phosphate in the pore water was also a part. The mineralization and biological process of suspended particulates in the water may be another important reason for the whole phosphate loadings.

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.

Migration Mechanism of Biogenic Elements and Their Quantification on the Sediment-water Interface of Lake Taihu: I.Spatial Variation of the Ammonium Release Rates and Its Source and Sink Fluxes

采集柱状芯样，室内静态模拟不同温度下太湖沉积物铵态氮释放．结果表明，经面积加权，5℃、15℃和25℃下氮的交换速率分别为-16．0±17．6mg／(m^2·d)、12．6±6．9mg／(m^2·d)和34．1±20．8mg／(m^2·d)，不同湖区其释放速率差异极大．受外源污染影响较大的水域，氮释放量随温度的升高而增加；受死亡残体沉降和分解影响明显的草藻型湖区，氮的年释放通量较大．全太湖沉积物-水界面NH4^+-N的年净通量为9960．3±4960．0t，其中成汇的通量值约为-911±637．9t／a，大部分泥区在一年中至少经过了一次的源-汇转换过程。The ammonium release of core samplers in Lake Taihu were simulated at different tempera-tures.The results showed that the area-weighed nitrogen exchange rates in the conditions of5℃,15℃,and25℃are-16.0±17.6mg/(m 2 · d),12.6±6.9mg/(m 2 · d),and34.1±20.8mg/(m 2 · d),respectively.But the ammonium fluxes were quite different among the sediments from different lake aveas.In respect of the waters that were greatly influenced by external pollution source,there was a positive correlation be-tween the ammoniumexchange amount and temperature.In the areas where there are more algal gather-ing and macrophyte growth,the annual release fluxes of nitrogen were usually greater because of being impacted with deposition of biological detritus on the surficial sediment.The ammonium exchange amount,on the whole lake,was estimated to be about9960.3±4960.0t/a,of which the sinking flux was about-911±637.9t/a.There appeared source-sink transition at least once in most of the sediment ar-eas.

Quantitative simulative method of sediment resuspension in Lake Taihu

Concerns on ecological effects of sediment resuspension are on the rise because the sediments in shallow lakes are frequently disturbed by winds.However,few methods could be suitable for supporting its related study. In this paper,Y-shape apparatus for simulating sediment resuspension was used to study vertical distribution of sus- pended sediments in water column and their total suspended amounts driving by different wind speed in Chang- dougang Harbor,southern Lake Taihu.The results showed that the relationship between the total suspended amount of sediments in water column(T)and the motor rotation frequency(n)could be expressed by T=19.77 exp(n/ 2.61)-71.7.Based on the total suspended amounts in water column under field wind conditions,quantitative re- lationships were achieved among the simulated hydrodynamic conditions,the total suspended amounts of sediments and the field wind conditions.According to the correspondent frequency of motor rotation to field wind speed in Lake Taihu from October 2004 to October 2005,the total suspended amounts of sediments were estimated at 159, 230 and 425 g/m~2 for field light,moderate and strong winds,respectively.The estimated amounts,together with the vertical distribution of suspended sediments in water column,were consistent with those observed under field conditions.The Y-shape apparatus was thus recommended for use in studying the ecological effects of sediment re- suspension in shallow aqueous system.

Progress and prospect in formation of black bloom in Lake Taihu: A review

This paper reviews studies on formation of the black bloom in Lake Taihu in recent years,with reference to abroad relevant research results about the phenomenon of black spots and hypoxia. A comprehensive summarization focuses on the sensory characteristics and description of the black bloom,the hypoxia and pollution effect,the material and meteorological factors,the microbial and sediment role,the genetic conditions and formation-disappearing processes and so on. We can conclude that the black bloom and its definition are induced from the basic properties,under appropriate weather and terrain conditions,with large amounts of algae or aquatic macrophyte accumulated in local waters for a long time. With interactions of microorganisms and sediments,the accumulated mass can form border distinguishable,removable black stinky,and can led to phenomena of extreme pollution,which result in water quality deterioration and some biological death. Finally,potential future development is proposed in terms of new technologies and new means,e. g. supplying mechanism of active ingredients from sediment,threshold determination of key parameters,stability mechanism of blackening and odor-causing substances.

The Response of Macrophytes to Nutrients and Implications for the Control of Phytoplankton Blooms in East Taihu Lake, China

When macrophytes are growing in the eutrophicated aquatic ecosystem, the vegetation induces important effects to the water quality and phytoplankton concentrations in the water which affected by macroscopic physical, chemical and biological processes and the effects are the results of direct and indirect interactions of the aquatic plants and water body. The interactions between macrophytes, nutrients and phytoplankton blooms were examined in the water and sediments of a shallow, eutrophic and typical East Taihu, China. The importance of macrophytes as a sink for nutrients, and the inhibitory effect of macrophytes on phytoplankton bloom potential were assessed through three different seasons. Luxuriant aquatic plants growth in this system led to decrease available nutrients for phytoplankton and prevented bloom development. Uptake of N and P by aquatic plants accounted for a major portion of the observed N and P loss from the water column and sediments. Luxury uptake of N and P were indicated by high biomass and tissues N and P concentrations, indicating the capacity of macrophytes to act as a nutrient sink in midsummer. Dissolved inorganic N (DIN) and soluble reactive phosphorous (SRP) in water were reduced in midsummer in the presence of macrophytes. The use of macrophytes to reduce the nutrients in water system and thereby inhibit freshwater phytoplankton blooms should be considered as an effective management strategy in shallow eutrophicated lakes. As aquatic macrophytes also develops considerable indirect effects that could have a vital impact than the direct uptake the nutrients into the plant biomass.

Effects on nitrogen and phosphorus distribution in interstitial water and sediment-water nitrogen and phosphorus release with growing of submerged macrophytes

Effect with growing of submerged maerophytes on NH_4~+ -N and PO_4~(3-)-P concentration in the interstitial water was studied by using undisturbed core samples in Lake Talhu,and analyzed the relationship between biomas- ses of submerged macrophytes and amount of nitrogen and phosphorus release.The results showed that concentration of NH_4~+ -N from 0-5 cm in interstitial water was gradually reduced by the biomasses increase of submerged macro- phytes,and amount of nitrogen release is distinctly negative correlated with biomasses of submerged macrophytes; The PO_4~(3-) -P concentration in interstitial water change was me peak tendency by the growing of submerged macro- phytes,indicating that there was no distinct corlationships between amount of phosphorus release and biomasses of submerged macrophytes.There mingt exisf different biogeochemcal mechanism of the absorption of nitrogen and phosphorus by submerged macrophytes.