Experimental study on phosphorus release from sediments of shallow lake in wave flume

Influence of wave on sediment resuspension and nutrients release from sediments, collected from Lake Taihu and Lake Chaohu, was studied in flume experiments. Under strong-wave conditions, concentrations of suspended solids (SS), total phosphorus (TP) and dissolved total phosphorus (DTP) in overlying water were increased significantly following the sediments re-suspension. During the experiments on sediments of Lake Taihu and Lake Chaohu, TP concentrations increased 6 times and 3 times, and DTP concentration increased 100% and 70% more than it in presuspension, respectively. Concentration of soluble reactive phosphorus (SRP) of experiment on sediment of Lake Taihu increased 25%. During the massive sediment suspension, the dissolved phosphorus in pore water and much of the phosphorus adsorbed by the sediment particles were released into overlying water. The phenomena in this wave flume experiment are quite similar to the situation observed in situ of Lake Taihu. The critical wave stresses of sediment re-suspension are nearly equal. The change of concentrations of SS, TP, and SRP was the same as that in situ situation. This study showed that concentrations of TP and SRP in lake water could be increased significantly by wave disturbance. Phosphorus release was significantly enhanced by wave disturbance at the beginning of massive sediment re-suspension, but decreased later.     

Experimental study on phosphorus release from sediments of shallow lake in wave flume

Influence of wave on sediment resuspension and nutrients release from sediments, collected from Lake Taihu and Lake Chaohu, was studied in flume experiments. Under strong-wave conditions, concentrations of suspended solids (SS), total phosphorus (TP) and dissolved total phosphorus (DTP) in overlying water were increased significantly following the sediments re-suspension. During the experiments on sediments of Lake Taihu and Lake Chaohu, TP concentrations increased 6 times and 3 times, and DTP concentration increased 100% and 70% more than it in presuspension, respectively. Concentration of soluble reactive phosphorus (SRP) of experiment on sediment of Lake Taihu increased 25%. During the massive sediment suspension, the dissolved phosphorus in pore water and much of the phosphorus adsorbed by the sediment particles were released into overlying water. The phenomena in this wave flume experiment are quite similar to the situation observed in situ of Lake Taihu. The critical wave stresses of sediment re-suspension are nearly equal. The change of concentrations of SS, TP, and SRP was the same as that in situ situation. This study showed that concentrations of TP and SRP in lake water could be increased significantly by wave disturbance. Phosphorus release was significantly enhanced by wave disturbance at the beginning of massive sediment re-suspension, but decreased later.     

Flood effects on phosphorus immobilisation in a river water filled pit lake—Case study Lake Goitsche (Germany)

Between 1999 and 2002, a former open-cast mine was filled with river water forming the recent Lake Goitsche. During filling initially acid water was neutralised. Phosphorus (P) imported from Mulde River was nearly completely removed from the water column by co-precipitation with iron (Fe) and aluminium (Al) and deposited in the sediment.During extremely high waters of the Mulde River in 2002, a dike breach facilitated a second high import of P into Lake Goitsche with suspended and dissolved matter. The analysis of total phosphorus (TP), however, showed that P again had been eliminated from the water body a few months after the flood event. Sediment investigations before filling with river water, during filling, and after the flood event were used to analyse the process of P immobilisation in a lake with acid mine drainage history.The ratios of Fe to soluble reactive P (SRP) of sediment pore water were up to three orders of magnitudes higher than in natural lakes and can serve as an indicator for potential internal P loading from sediments. The SRP concentrations at the oxic/anoxic boundary were near or below the limit of quantification (< 0.2 μmol/L). Fe and manganese (Mn) redox cycling were responsible for hindering P dissolution from sediment to lake water.Finally it can be stated, that the risk of eutrophication for such a lake seems to be low.     

沉水植物驱动的水环境钙泵与水体磷循环的关系

水体磷循环是水柱和对应的沉积物中发生的各种非生物和生物的磷迁移转化过程.与此同时,沉积物中钙通过沉水植物吸收和转运,从该类植物的叶面释放至水柱中,释放的Ca2+与水柱中的CO23-一起形成碳酸钙.在这一过程中,水柱中少量溶解性磷分配在碳酸钙中形成CaCO3-P共沉淀,导致水体中可溶性磷向难溶性磷转化,这种由沉水植物驱动的水环境钙泵在水体磷循环中发挥着重要作用.研究证明,沉水植物菹草叶面上有CaCO3-P共沉淀的形成,且这种共沉淀的含磷量变化范围很宽.另一方面,新近沉积物中钙与磷的沉淀物存在一个由聚磷酸盐向磷灰石逐渐演变过程,而沉水植物叶面上的含磷共沉淀作用是否也存在由聚磷酸盐向磷灰石的变质过程,该过程在沉水植物生长期间是否发生关系到沉水植物除磷效果值得深入研究.本文从水体磷循环概述、钙在水体磷循环中的作用和沉水植物驱动的水环境钙泵假说及其在水体磷循环中的意义等方面综述了钙在水环境中的迁移对水体磷循环的贡献.     

非稳沉采煤沉陷区沉积物-水体界面的氮、磷分布及迁移转化特征

以淮南后湖非稳沉采煤沉陷区沉积物-水体界面为研究对象,分析该湖未开发区(A区)、水产养殖区(B区)和水生蔬菜种植区(C区)3个功能区上覆水-间隙水-沉积物体系中氮、磷分布及其迁移特征.结果表明,氮、磷在不同水体界面的分布差异较大.其中上覆水中氮、磷浓度表现为A区B区C区;间隙水中氮、磷分布差异不显著,然而各功能区间隙水的氮、磷浓度明显高于上覆水,氮、磷主要由间隙水向上覆水中移动;沉积物中氮、磷含量以C区最高.后湖采煤沉陷区水体表现出氮污染、磷限制的现象.     

The effects of particle breakage and abrasion—from simulated fluvial transport,on phosphorus sorption by two soils

Phosphorus sorption studies were carried out on particle size fractions of soils collected from the walls of gullies through a granitic and a sedimentary soil, as well as on particle size classes derived from breakage and abrasion of the 500 to 1400 μm components of these soils. Sorption of phosphorus by the particle size classes of the sedimentary soil was much greater than those of the granite soil, and this also applied to the particles derived from breakage and abrasion. For the original sedimentary soil, sorption of phosphorus by the particle size components was strongly associated with the iron content and less strongly associated with the aluminium content and this also applied to the particles derived from breakage and abrasion. For the granitic soil these relationships were much less precise. A period of vigorous mixing, after 165 hours of gentle mixing, caused release of a proportion of the sorbed phosphorus from all particle sizes of the original granitic soil and for most of the breakage/abrasion derived particles. The released phosphorus was re‐sorbed during a subsequent 48 hour period of settling. Relationships were evident between labile P and sorbed P for the particle size classes of the soils and treatments tested. Because particle size, lithology of the transported sediments and flow dynamics affect the distribution of phosphorus between water and sediments, they can also be expected to effect bio‐availability of phosphorus. Particle breakage and abrasion during sediment transport is another factor likely to influence the bio‐availability of P. Copyright © 1999 John Wiley & Sons, Ltd.     

贵州红枫湖沉积物磷赋存形态及沉积历史

采集了云贵高原深水湖泊红枫湖现代沉积物未受扰动的柱状样品,通过分析不同形态沉积磷在沉积剖面上的分布特征,并结合沉积物样品柱的210Pb、137Cs年代学研究结果,揭示了红枫湖现代沉积过程中不同形态沉积磷的早期成岩改造的时间变化序列,以及沉积磷外源输入负荷的历史变化.采用Ruttenberg法分析沉积磷的地球化学赋存形态,研究表明,红枫湖沉积物中有机磷和铁结合态磷是沉积磷的主要赋存形态,分别占沉积全磷的60%和28%.沉积磷在垂直剖面上的分布特征显示,红枫湖现代沉积过程中,沉积磷在最终埋藏前可能发生非常剧烈的形态转化和再迁移,尤其是有机磷和铁结合态磷的成岩改造可能是湖泊系统磷循环质量平衡的重要方面.年代学数据同时表明,近年的人为活动导致湖泊系统(包括沉积物)磷负荷的显著增加.     

东洞庭湖沉积物覆水后磷形态变化及其释放量

研究干燥覆水后低流速条件下东洞庭湖沉积物中磷的形态变化及释放量,可以为轻度富营养化湖泊中磷的生物地球化学循环提供基础数据,为季节性湖泊內源营养盐的迁移转化规律研究、內源营养盐的释放风险评价提供理论依据.本文采集处于干湿交替状态的东洞庭湖表层沉积物,利用室内模拟装置,研究风干沉积物低流速条件下覆水后沉积物及上覆水中磷的形态变化.结果表明,低流速覆水后东洞庭湖沉积物中的磷向上覆水及大气中迁移释放,上覆水中磷的释放量随覆水时长增大,释放速率随覆水时长减小,上覆水流速和磷释放量相关性显著.上覆水循环过程中释放到上覆水中的溶解态有机磷比溶解态活性磷更容易吸附于颗粒物而转化为颗粒态磷.覆水后沉积物中各形态有机磷、无机磷及磷的生物有效性均发生转变,覆水初期沉积物中无机磷向有机磷转化,磷的生物可利用性增大;上覆水循环过程中有机磷向无机磷转化,磷的生物可利用性减小;覆水后沉积物的无机磷的主要组分由铝磷转变为铁磷,有机磷的主要组分有从中活性有机磷向活性有机磷转变的趋势.     

水丝蚓(Tubificid worms)扰动对磷在湖泊沉积物-水界面迁移的影响

为探讨水丝蚓(Tubificid worms)扰动对磷在湖泊沉积物-水界面间迁移的影响,选取太湖梅梁湾与大浦口两富营养化湖区为研究对象,通过室内培养实验,利用Rhizon间隙水采样器等技术,研究了水丝蚓扰动对太湖沉积物-水界面理化性质及溶解活性磷(SRP)在界面通量的影响.结果表明水丝蚓扰动能够增大表层沉积物含水率、氧化还原电位,减小间隙水中Fe2+浓度.水丝蚓没有显著改变梅梁湾间隙水中SRP浓度,同时促进了梅梁湾沉积物中SRP向上覆水的释放;但水丝蚓显著减小了大浦口间隙水中SRP浓度,并抑制了大浦口沉积物中SRP向上覆水的释放.水丝蚓扰动对磷在沉积物-水界面间迁移的不同影响可能是由沉积物中Fe2+含量差异较大造成的.     

Estimation of internal nutrient release in large shallow Lake Taihu,China

Based on field investigation of wave, sediment suspension and the changes in nutrient concentration of the water column in Lake Taihu, China, we proposed two release models to quantify nutrient release under static and dynamic conditions, respectively. Under static conditions, nutrient release from sediments to the overlying water mainly depends on chemical diffusion induced by concentration gradient, in which the nutrient release is controlled by the temperature, dissolved oxygen concentration in the sediment-water interface, oxidation-reduction potential and the concentration difference between porewater and overlying water. Under dynamic condition (or disturbed condition), both dissolved and particulate nutrients in sediments are released into the water column because of wind-induced sediment suspension. The amount of nutrient release under dynamic conditions is larger than that under the static condition. The release of dissolved nutrients, however, does not increase because the wind induced turbulence made oxidation of metallic elements such as Fe (ferric iron), Mn which are capable of precipitating soluble reactive phosphate (SRP). Under dynamic conditions, therefore, the release of total phosphorus (TP) increases dramatically but the release of SRP is close to those under static conditions. In sediments of Lake Taihu, high Fe content leads to a high ratio of Fe to P contents in sediments (Fe:P ratio). Under dynamic conditions, therefore, nutrient release is controlled by the intensity of disturbance, sediment consolidation and nutrient content in sediments. As for dissolved nutrients, especially SRP, the release is also controlled by the intensity of dynamic re-oxidation, Fe content in sediments and nutrient concentration gradient between porewater and overlying water. Based on these two release modes, the release flux in Lake Taihu has been estimated. In the static condition (i.e. laboratory experimental condition), total release of NH₄ ⁺-N for whole lake is ca. 10,000 ton/a, and PO₄ ^3?-P is ca. 900 ton/a. In the dynamic condition, nutrient release following sediment suspension was estimated according to three different intensities of wind forcing which were defined as “calm” (wind speed is less than 2 m/s), “gentle” (wind speed is greater than 2 m/s and less than 6 m/s) and “gust” (wind speed is greater than 6 m/s). The release rate in the condition of “calm” was estimated in terms of the nutrient release in the laboratory experimental static condition; whereas the release rate in conditions of “gentle” and “gust” was estimated in terms of measurement during sediment resuspension conducted in flume experiments. With the observation of wind velocity and frequency in 2001, each type of wind forcing took the frequency of 12%, 82% and 6% for “calm”, “gentle” and “gust”, respectively. The yearly release of nitrogen was 81,000 ton and phosphorus was 21,000 ton, which is about 2–6 folds of annual external loading, respectively.     

太湖入、出湖湖区磷的特征及其影响因素分析

为进一步了解人类活动及环境因子对太湖磷污染的贡献,揭示磷在太湖不同介质中的迁移转化规律,本文以太湖主要入湖湖区竺山湖、西部沿岸区、南部沿岸区和主要出湖湖区东太湖为对象,调查了表层水、上覆水、间隙水和沉积物中总磷(TP)分布的概况,分析了不同介质中磷的交换特征及其影响因素. 结果表明,表层水和上覆水TP浓度基本相当,平均值均为0.10 mg/L,上覆水和间隙水TP差异较大,间隙水平均浓度约为上覆水的7倍,表层沉积物TP含量为474~2160 mg/kg. 在本研究水域中,TP具有较强的沉积物吸附特性,沉积物作为“汇”的特征明显强于其“源”的特征,且磷的留存能力高度依赖于铁浓度. 空间分布上,入湖湖区磷污染程度明显高于出湖湖区,竺山湖和西部沿岸区存在较大的底泥污染释放风险,但竺山湖外源污染影响较内源污染更加突出,应列为当前太湖磷治理重点关注的区域,建议以控源截污作为竺山湖周边区域的治理重点. 西部沿岸区需注重外源和内源污染同步控制. 南部沿岸区周边区域需妥善处理好未来经济发展与废水排放负荷的关系.     

氧化还原条件对红枫湖沉积物磷释放影响的微尺度分析

选取贵州红枫湖为研究对象,在实验室条件下模拟了自然、好氧和厌氧条件下沉积物内源磷的释放过程,联合应用微电极技术和沉积物磷形态分析对沉积物—水界面开展了微尺度观测与研究.结果表明,厌氧条件下红枫湖沉积物总磷含量显著降低,且主要是NaOH提取态磷(NaOH-P)和残渣态磷(rest-P)含量降低所致,厌氧条件下沉积物孔隙水中磷酸盐浓度明显升高,而好氧条件下沉积物孔隙水磷酸盐浓度显著降低,反映厌氧条件显著促进了红枫湖沉积物磷释放.厌氧条件下沉积物内部溶解氧浓度下降、硫还原活动增强可能是导致NaOH-P释放的主要原因.O_2浓度的降低加速了沉积物还原作用并产生大量H2S,进而与二价铁离子形成硫化亚铁沉淀,最终导致NaOH-P(Fe-P)释放到孔隙水中.好氧条件向厌氧条件的转换可通过改变沉积物内部pH值分布和微生物活动促使rest-P释放:厌氧条件下,厌氧微生物不仅可以消耗硫酸根产生H_2S,导致pH值降低,还可消耗有机质,将有机磷转变为无机磷.上述研究结果表明,沉积物—水界面氧化还原环境可影响沉积物氧渗透深度、pH值分布、微生物活动、硫循环以及有机质降解过程,进而控制沉积物磷的形态转化与释放.联合应用微电极技术和沉积物磷形态分析对湖泊沉积物—水界面开展微尺度观测研究是揭示沉积物内源磷释放机制与控制因素的有效途径.     

Estimation of internal nutrient release in large shallow Lake Taihu, China

Based on field investigation of wave, sediment suspension and the changes in nutrient concentration of the water column in Lake Taihu, China, we proposed two release models to quantify nutrient release under static and dynamic conditions, respectively. Under static conditions, nutrient release from sediments to the overlying water mainly depends on chemical diffusion induced by concentration gradient, in which the nutrient release is controlled by the temperature, dissolved oxygen concentration in the sediment-water interface, oxidation-reduction potential and the concentration difference between porewater and overlying water. Under dynamic condition (or disturbed condition), both dissolved and particulate nutrients in sediments are released into the water column because of wind-induced sediment suspension. The amount of nutrient release under dynamic conditions is larger than that under the static condition. The release of dissolved nutrients, however, does not increase because the wind induced turbulence made oxidation of metallic elements such as Fe (ferric iron), Mn which are capable of precipitating soluble reactive phosphate (SRP). Under dynamic conditions, therefore, the release of total phosphorus (TP) increases dramatically but the release of SRP is close to those under static conditions. In sediments of Lake Taihu, high Fe content leads to a high ratio of Fe to P contents in sediments (Fe:P ratio). Under dynamic conditions, therefore, nutrient release is controlled by the intensity of disturbance, sediment consolidation and nutrient content in sediments. As for dissolved nutrients, especially SRP, the release is also controlled by the intensity of dynamic re-oxidation, Fe content in sediments and nutrient concentration gradient between porewater and overlying water. Based on these two release modes, the release flux in Lake Taihu has been estimated. In the static condition (i.e. laboratory experimental condition), total release of NH4 -N for whole lake is ca. 10,000 ton/a, and PO43--P is ca. 900 ton/a. In the dynamic condition, nutrient release following sediment suspension was estimated according to three different intensities of wind forcing which were defined as "calm" (wind speed is less than 2 m/s), "gentle" (wind speed is greater than 2 m/s and less than 6 m/s) and "gust" (wind speed is greater than 6 m/s). The release rate in the condition of "calm" was estimated in terms of the nutrient release in the laboratory experimental static condition; whereas the release rate in conditions of "gentle" and "gust" was estimated in terms of measurement during sediment resuspension conducted in flume experiments. With the observation of wind velocity and frequency in 2001, each type of wind forcing took the frequency of 12%, 82% and 6% for "calm", "gentle" and "gust", respectively. The yearly release of nitrogen was 81,000 ton and phos- phorus was 21,000 ton, which is about 2-6 folds of annual external loading, respectively.     

The role of sediments in the phosphorus cycle in Lake Lugano. II. Seasonal and spatial variability of microbiological processes at the sediment-water interface

P, Fe, Mn, and S species were analyzed in water samples from the sediment-water interface collected at four seasonally different times during the course of a year at two sampling sites in the southern basin of Lake Lugano (Lago di Lugano). The results reveal the strong influence of the biogeochemical processes in the sediment on the chemical composition of the lake water above. Consumption of oxygen and nitrate under oxic to microoxic conditions in the water column as well as sequential release of reduced manganese and iron under anoxic conditions was observed as a direct or indirect consequence of microbially mediated degradation of organic matter. The seasonal pattern observed for the release and the retainment of dissolved reduced iron and manganese correlates well with the one for dissolved phosphate. Iron, manganese and phosphorus cycling are coupled tightly in these sediments. Both sediment types act as sinks for hydrogen sulfide and sulfate. An inner-sedimentary sulfur cycle is proposed to couple iron, manganese and phosphorus cycling with the degradation of organic matter. Nutrient cycling at the sediment-water interface might thus be driven by a microbially regulated electron pumping mechanism. The results contribute to a better understanding of the role of sediment processes in the lake's internal phosphorus cycle and its seasonal dynamics.     

Evaluation of phosphorus bioavailability in El Mex Bay and Lake Mariut sediments

Phosphorus (P) fractions and their bioavailability in the sediments from El Mex Bay and Lake Mariut in Egypt were investigated using different chemical extraction methods. Sodium bicarbonate (NaHCO3) extractable P (Olsen-P) was the largest fraction (14.42%), followed by algal available P (AAP) (3.56%), water soluble P (WSP) (0.79%), and readily desorbable P (RDP) (0.06%) for El Mex Bay. While AAP con-tributed 9.94% to total P in sediments from Lake Mariut, Olsen-P 8.53%, WSP 4.11%, and RDP 0.92%. Summation of the bioavailable P fractions didn't exceed the sediment quality guidelines, and, therefore, P doesn't represent a danger to marine organisms. Correlation coefficients showed that no apparent relations between total P (TP) and iron (Fe), aluminum (Al), and calcium (Ca) in the sediments. Fur-thermore, Fe:P ratio was less than 15 indicting that there was not enough Fe in surface sediments to bind to P at most of the sampling sites. The positive correlation between TP and organic matter (OM) for Lake Mariut and El Mex Bay sediments indicated that the organic matter content of the sediment was a useful predictor of the total phosphorus content. Data from this study constitute a baseline of phosphorus bioavailability in sediments from El Mex Bay and Lake Mariut and could be used as a reference for future studies on the changes of bioavailable and residual phosphorus fractions over time.     

Estimation of internal nutrient release in large shallow Lake Taihu,China

Based on field investigation of wave, sediment suspension and the changes in nutrient concentration of the water column in Lake Taihu, China, we proposed two release models to quantify nutrient release under static and dynamic conditions, respectively. Under static conditions, nutrient release from sediments to the overlying water mainly depends on chemical diffusion induced by concentration gradient, in which the nutrient release is controlled by the temperature, dissolved oxygen concentration in the sediment-water interface, oxidation-reduction potential and the concentration difference between porewater and overlying water. Under dynamic condition (or disturbed condition), both dissolved and particulate nutrients in sediments are released into the water column because of wind-induced sediment suspension. The amount of nutrient release under dynamic conditions is larger than that under the static condition. The release of dissolved nutrients, however, does not increase because the wind induced turbulence made oxidation of metallic elements such as Fe (ferric iron), Mn which are capable of precipitating soluble reactive phosphate (SRP). Under dynamic conditions, therefore, the release of total phosphorus (TP) increases dramatically but the release of SRP is close to those under static conditions. In sediments of Lake Taihu, high Fe content leads to a high ratio of Fe to P contents in sediments (Fe:P ratio). Under dynamic conditions, therefore, nutrient release is controlled by the intensity of disturbance, sediment consolidation and nutrient content in sediments. As for dissolved nutrients, especially SRP, the release is also controlled by the intensity of dynamic re-oxidation, Fe content in sediments and nutrient concentration gradient between porewater and overlying water. Based on these two release modes, the release flux in Lake Taihu has been estimated. In the static condition (i.e. laboratory experimental condition), total release of NH₄ ⁺-N for whole lake is ca. 10,000 ton/a, and PO₄ ³⁻-P is ca. 900 ton/a. In the dynamic condition, nutrient release following sediment suspension was estimated according to three different intensities of wind forcing which were defined as “calm” (wind speed is less than 2 m/s), “gentle” (wind speed is greater than 2 m/s and less than 6 m/s) and “gust” (wind speed is greater than 6 m/s). The release rate in the condition of “calm” was estimated in terms of the nutrient release in the laboratory experimental static condition; whereas the release rate in conditions of “gentle” and “gust” was estimated in terms of measurement during sediment resuspension conducted in flume experiments. With the observation of wind velocity and frequency in 2001, each type of wind forcing took the frequency of 12%, 82% and 6% for “calm”, “gentle” and “gust”, respectively. The yearly release of nitrogen was 81,000 ton and phosphorus was 21,000 ton, which is about 2–6 folds of annual external loading, respectively.

     

Phosphorus forms and bioavailability of lake sediments in the middle and lower reaches of Yangtze River

Forms of phosphorus in sediments from 25 lakes in the middle and lower reaches of Yangtze River were analyzed by the sequential extraction procedure. Contents and spatial distrubution of algal available phosphorus (AAP) in sediments of Lake Taihu, the third largest freshwater lake of China, were also studied. Relationships between phosphorus forms in sediment and macrophytes coverage in sample sites, as well as phosphorus forms in sediments and chlorophyal contents in lake water were discussed. Exchangeable form of phosphorus (Ex-P) in surface sediments was significantly positive correlative to total phosphorus (TP), dissolved total phosphorus (DTP) and soluble reactive phosphorus (SRP) contents in the lake water. Bioavailable phosphorus (Bio-P) contents in sediments from macrophytes dominant sites were significantly lower than that in no macrophyte sites. In Lake Taihu, Ex-P content in top 3 cm sediment was highest. However, content of ferric fraction phosphorus (Fe-P) was highest in 4–10 cm. Bioavalilble phosphorus (Bio-P) contents in surface sediments positively correlated to Chlorophyll a contents in water of Lake Taihu with significant difference. Therefore, contents of Bio-P and AAP could be acted as the indicators of risks of internal release of phosphorus in the shallow lakes. It was estimated that there were 268.6 ton AAP in top 1 cm sediments in Lake Taihu. Sediment suspension caused by strong wind-induced wave disturbance could carry plenty of AAP into water in large shallow lakes like Lake Taihu.     

Phosphorus forms and bioavailability of lake sediments in the middle and lower reaches of Yangtze River

Forms of phosphorus in sediments from 25 lakes in the middle and lower reaches of Yangtze River were analyzed by the sequential extraction procedure. Contents and spatial distrubution of algal available phosphorus (AAP) in sediments of Lake Taihu, the third largest freshwater lake of China, were also studied. Relationships between phosphorus forms in sediment and macrophytes coverage in sample sites, as well as phosphorus forms in sediments and chlorophyal contents in lake water were discussed. Exchangeable form of phosphorus (Ex-P) in surface sediments was significantly positive correlative to total phosphorus (IP), dissolved total phosphorus (DTP) and soluble reactive phosphorus (SRP) contents in the lake water. Bioavailable phosphorus (Bio-P) contents in sediments from macrophytes dominant sites were significantly lower than that in no macrophyte sites. In Lake Taihu, Ex-P content in top 3 cm sediment was highest. However, content of ferric fraction phosphorus (Fe-P) was highest in 4 - 10 cm. Bioavalilble phosphorus (Bio-P) contents in surface sediments positively correlated to Chlorophyll a contents in water of Lake Taihu with significant difference. Therefore, contents of Bio-P and AAP could be acted as the indicators of risks of internal release of phosphorus in the shallow lakes. It was estimated that there were 268.6 ton AAP in top 1 cm sediments in Lake Taihu. Sediment suspension caused by strong wind-induced wave disturbance could carry plenty of AAP into water in large shallow lakes like Lake Taihu.     

城市浅水型湖泊底泥释磷的通量估算—以南京玄武湖为例

以南京玄武湖为研究对象,通过静态条件下5℃、10℃、15℃、25℃、35℃玄武湖底泥释磷室内实验计算玄武湖释磷速率,得出底泥释磷速率与上覆水温度的关系,进而算出玄武湖北湖每年磷释放量为0．815 t,东南湖每年磷释放量为 1．013t,西南湖每年磷释放量为0．266t．玄武湖每年底泥释磷总量为2．094 t．根据费克定理,建立了间隙水扩散模型,利用模型计算玄武湖北湖每年磷释放量为0．799 t,东南湖每年磷释放量为0．983 t,西南湖每年磷释放量为0．232 t．玄武湖每年底泥释磷总量为2．014t．在不考虑外源污染的情况下,由底泥磷释放造成的内源污染使玄武湖磷浓度年均维持在 0．101 mg/L,超过湖泊富营养化磷标准,因此,在切断外源污染的情况下应采取措施治理磷的内源污染．     

Contributions of phosphatase and microbial activity to internal phosphorus loading and their relation to lake eutrophication

Phosphatase may accelerate the process of lake eutrophication through improving phosphorus bioavailability. This mechanism was studied in three Chinese eutrophic shallow lakes (Lake Taihu, Lake Longyang and Lake Lianhua). Phosphatase activity was related to the concentration of soluble reactive phosphorus (SRP) and chlorophyll a. Stability of dissolved phosphatase in reverse micelles may be attributed to molecular size, conformation and active residues of the enzyme. At the site with Microcystis bloomed in Lake Taihu, dissolved phosphatase activity was higher and more stable in micelles, SRP concentrations were lower in interstitial water, the contents of different forms of phosphorus and the amounts of aerobic bacteria were lower while respiration efficiency was higher in sediments. Phosphobacteria, both inorganic and organic and other microorganisms were abundant in surface water but rare in sediments. Therefore, internal phosphorus may substantially flux into water column by enzymatic hydrolysis and anaerobic release, together with mobility of bacteria, thereby initiating the bloom. In short, biological mechanism may act in concert with physical and chemical factors to drive the internal phosphorus release and accelerate lake eutrophication.