Phosphorus fractions in sediment profiles and their potential contributions to eutrophication in Dianchi Lake

Dianchi Lake is a eutrophic lake in southwestern China. Sediment and the bottom water samples were taken from six sites in the east, west, south, north and center of the lake, respectively, in December 2002. Total phosphorus (TP) concentrations in sediments were high and reached a maximum value of 6.66 g/kg. There was a soluble reactive phosphorus (SRP) concentration gradient at the sediment–water interface. In the present study, sediment P was divided into loosely adsorbed P (NH₄Cl-P), redox-sensitive P (BD-P), metal oxides bound P (NaOH-P), calcium bound P (HCl-P), and organic P (Org-P). At three of the six sites selected, the concentrations of different P forms in sediments followed the order: NaOH-P, Org-P>HCl-P>BD-P>NH₄Cl-P in the profile, and in the southern lake the order was HCl-P>NaOH-P, Org-P>BD-P>NH₄Cl-P in the top 15 cm layers of the sediments. The sediment profiles showed that different forms of P had an increasing trend upward toward the sediment surface. There is a considerable potential for release from the sediment into the overlying water and sediment P could be the dominant factor determining the trophic status of the lake if the external load is reduced. An erratum to this article can be found at     

不同干燥方式对湖泊沉积物磷提取的影响

以滇池5个典型区域表层沉积物为例,研究了自然风干、低温烘干和真空冻干等3种干燥方式对沉积物中磷的形态含量及其生物有效性测定的影响。结果表明：烘干、风干过程促进了沉积物有机磷的降解转化和微生物磷的释放,导致有机磷的含量偏低,总磷含量却比冻干高。各形态磷受不同干燥方式的影响程度不同,风干样品中BD-P较高,冻干样品中NaOH-rP含量最高,NH4Cl-P、HCl-P、残渣磷（Residual-P）由于含量较低或其化学性质比较稳定而差异不大。冻干样品中生物可利用磷分别比风干、烘干高26.7%、20.2%,表明冻干处理能较为真实地反映沉积物中磷的组成特征,是比较理想的样品干燥方式。各形态含量顺序为：藻类可利用磷（AAP）〉NaHCO3可提取磷（Olsen-P）〉水溶性磷（WSP）〉易解吸磷（RDP）。沉积物中Olsen-P与NH4Cl-P、BD-P、NaOH-rP、活性磷及上覆水体总磷水平呈显著正相关,因此可作为评价滇池沉积物磷的生物有效性的重要指标。     

Phosphorus fractions and bioavailability in relation to particle size characteristics in sediments from Lake Hongfeng, Southwest China

Information on the chemical composition of phosphorus (P) fractions in sediments is fundamental to understanding P bioavailability and eutrophication in lake ecosystems. Phosphorus fractions and its bioavailability in sediments cores of Lake Hongfeng, southwest China, were investigated using a chemical sequential extraction scheme. Relationships between P fractions, P bioavailability and particle sizes were discussed. P fractions concentrations were ranked in the order: Residual-P > NaOH–rP > NaOH–NRP > HCl–P > BD–P > NH₄Cl–P, and all of them decreased with increasing sediment depth. Statistical analysis showed that concentrations of bioavailable P (BAP) which includes the NH₄Cl–P, BD–P, NaOH–rP and NaOH–NRP fractions ranged from 404.68 to 1,591.99 mg/kg and accounted for 26.8–71.8 % of the concentrations of total phosphorus (TP) in the top 5 cm sediments, whereas in the whole sediment cores, their concentrations ranged from 239.70 to 1,591.99 mg/kg and accounted for 26.8–76.0 % of TP. The results suggested that the sediments were a large potential source of P for algae blooms in Lake Hongfeng. Phosphorus fractions and their potential bioavailability were influenced by the sediment particle sizes, especially the bioavailability of the NH₄Cl–P fraction, which was strongly affected by the presence of fine particle sizes in the sediments.     

Sediment phosphorus fractions and profile distribution at different vegetation growth zones in a macrophyte dominated shallow Wuliangsuhai Lake,China

Sediment phosphorus (P) fractions and profile distribution at submerged macrophyte growth zone, emergent macrophyte growth zone and open-water zone were studied in Wuliangsuhai Lake, China, as well as the correlations among water content, grain size, and organic matter and P fractions. Among the three surveyed zones, the highest concentrations of most P forms occurred in the surface sediment and the lowest between a depth of 12 and 22 cm, except HCl-P and NaOH-P. Sediment phosphorus was mainly associated to inorganic forms (>50%) in three surveyed areas, and the highest value of inorganic phosphorus (IP) in the surface sediment was obtained from submerged macrophyte growth zone. Submerged and emergent macrophytes increased the IP content by 107 and 44 μg/g, respectively, in the surface sediment compared with open-water zone. Vertical profiles of IP in the three surveyed zones showed that the concentrations decreased from surface to 12 cm depth and then increased. There was a similar trend in the sediment profiles of organic phosphorus (OP) and total phosphorus (TP), but the highest concentration of OP and TP in surface sediment was obtained from the emergent macrophyte growth zone. Compared with open-water zone, the emergent macrophyte increased TP content in surface sediment by 1.73 times to 1,320 μg/g, while submerged macrophyte enhanced TP content in the surface sediment by 1.13 times to 865 μg/g. It was observed that in macrophyte growth zones, a strong linear correlation existed between organic matter and OP (r > 0.98), and the maximum concentrations of OP were present in the areas with maximum concentrations of organic matter. Results show that, although rooted macrophyte could uptake directly P from sediments, it is responsible for increasing the internal P loading especially OP by reducing current velocities, attenuating wave energy and generating organic residue in Wuliangsuhai Lake.     

南四湖及主要入湖河流沉积物中磷的赋存形态研究

应用沉积物磷形态SMT提取方法,分析了南四湖及主要入湖河流丰水季节表层沉积物、独山湖及微山湖区沉积岩芯中磷的含量及形态组成变化,研究了磷的埋藏演化过程与人为污染特征.结果表明,老运河表层沉积物中磷的含量最高,为13068.3 mg/kg,以OP及NaOH-P为主,其富集系数分别为6.5和9.0,主要是与来自济宁市的废水污染有关.其余表层沉积物以HCl-P为主;受人为污染的影响,NaOH-P、OP产生一定程度的富集,其富集系数分别为1.0.3.7、1.3～6.0;部分沉积物中高含量的有机质加重了OP的富集.独山湖及微山湖沉积岩芯中以HCl-P和OP为主;20世纪60年代末期以来,随着湖泊生产力的提高及早期成岩过程中有机质的矿化分解,独山湖及微山湖沉积岩芯中TOC含量自下而上呈指数增加,这也导致了沉积物中OP的增加;独山湖及微山湖沉积岩芯6～0 cm和5～0 cm较高的OP及NaOH-P含量,指示了20世纪80年代中期以来磷的人为污染过程.     

湖泊蓝藻水华生态灾害形成机理及防治的基础研究

湖泊具有供水、渔业、旅游、维持区域生态系统平衡等功能,是支撑我国经济和社会发展的重要资源之一。但是近30年来,湖泊富营养化所导致的蓝藻水华频繁暴发,生态灾害事件频发,严重影响湖泊功能的发挥, 制约区域经济可持续发展。针对国家在保障区域水安全和生态安全、保护人民健康及建设和谐社会等方面的重大需求,国家重点基础研究发展计划项目“湖泊蓝藻水华生态灾害形成机理及防治的基础研究”于2008年7月正式立项。项目拟解决的关键科学问题包括：①湖泊蓝藻水华主要衍生污染物的形成机理、迁移转化规律和毒理效应;②蓝藻水华导致湖泊生态系统结构变化和功能退化的机理;③蓝藻水华生态灾害评估及调控机理。针对上述科学问题,项目以蓝藻水华污染物的产生、湖泊生态系统结构与功能的响应以及生态灾害的评估与调控为研究主线,重点开展以下几个方面的研究：①蓝藻水华衍生污染物的产生及其环境过程;②蓝藻水华衍生污染物的毒理效应与生态和健康风险;③蓝藻水华导致湖泊生态系统结构变化与功能退化的关键过程和机制;④蓝藻水华灾害治理和调控的的技术原理和途径。项目的实施和完成将为我国湖泊蓝藻水华生态灾害的预防与控制提供理论和技术原理支撑。     

化学连续提取法对太湖沉积物中磷的各种形态测定

为确定太湖沉积物中磷的各种形态含量,本文应用SMT 连续提取法对太湖梅梁湾表层沉积物样品和淡水沉积物标准物质BCＲ --684 中磷的各种形态进行测定。结果表明SMT 法具有一定的适用性和准确性。太湖沉积物中磷形态测定结果表明无机磷是太湖沉积物中磷的主要赋存形态,占总有效磷的 59. 22%,无机磷含量中非磷灰石态磷含量为139 μg /g,大于磷灰石态磷含量113 μg /g。     

Seasonal and spatial changes in water and sediment quality variables in Bafa Lake

The brackish Bafa Lake located in the southwestern part of Turkey is under stress because of both natural and untreated wastewater effluents. The purpose of this research is to determine spatiotemporal distributions of some physicochemical variables in water column (temperature, salinity, pH, conductivity, dissolved oxygen, NH₄–N, NO₂–N, NO₃–N, oPO₄–P, TPO₄–P, chlorophyll-a, total suspended solids) and sediment (TN, TC, TOC, TP) and their relationships at coastal stations. In the water column, nitrate and phosphate concentrations showed seasonal variations with high values recorded in winter period. Ammonium was determined as a main source of TIN component. During summer period, a large amount of total phosphorus was found as dissolved organic form. However, in the winter period, inorganic phosphate levels increased at sampling stations. N limitation was a common feature throughout the lake where P-limitation was only observed in summer period. The total phosphorus levels which showed hypereutrophic condition at the western part of the lake changed between 1.55 and 4.99 μM and did not remain in the range for uncontaminated condition. In the lake sediment, a strong relationship was found between TOC and TC levels. Generally, the mean TOC concentrations constitute small amount of TC values in the sampling stations. The results also indicated that a strong correlation exists between TOC and TN values, and TN was greatly regulated by organic sources. In the lake, TOC:TN ratios changed between 5 and 13; the ratio greater than 10 could be an indicator of algal and land plant sources mixing as an organic matter.     

Phosphorus Cycling in a Freshwater Estuary Impacted by Cyanobacterial Blooms

The availability of reactive phosphorus (P) may promote cyanobacterial blooms, a worldwide increasing phenomenon. Cyanobacteria may also regulate benthic P cycling through labile organic input to sediments, favouring reduced conditions and P release, ultimately acting as self-sustainment mechanism for the phytoplankton blooms. To analyse P–cyanobacteria feedbacks and compare external versus internal loads, we investigated P cycling in the Curonian Lagoon, a freshwater estuary with recurrent summer blooms. At two sites representing the dominant sediment types, we characterised P pools and mobility, via combined pore water analysis, calculation of diffusive exchanges and flux measurements via sediment core incubations. Annual P budgets were also calculated, to analyse the whole lagoon role as net sink or source. Muddy sediments, representing nearly 50 % of the lagoon surface, displayed higher P content if compared with sandy sediments, and most of this pool was reactive. The muddy site had consequently higher pore water dissolved inorganic phosphorus (DIP) concentrations maintaining high diffusive gradients. However, measured fluxes suggested that both sediment types were mostly P sinks except for a large DIP regeneration (nearly 30 μmol m^?2 h^?1) recorded at the muddy site during an intense cyanobacteria bloom. Such internal regeneration had the same order of magnitude as the annual external P load and may offset the net annual DIP sink role of the estuary. It may also prolong the duration of the bloom. Our results suggest that positive feedbacks can regulate N-fixing cyanobacteria blooms and internal P recycling, through either diffusive fluxes or sediment settling and resuspension.     

Ammonia adsorption and nitritation in sediments derived from the Three Gorges Reservoir,China

The influences of suspended particles (SPs) on NH₄ ⁺ adsorption and nitritation occurring in the water system of the Three Gorges Reservoir (TGR) were evaluated in this study. The results indicated that the adsorption of NH₄ ⁺ was significantly affected by the SPs concentration under the conditions typically present in the TGR. The amount of ammonia adsorbed per unit weight of suspended particles was inverse proportional to the concentration of suspended particles. However, the influences of the particle size and the organic matter concentration existing in SPs were insignificant under the experimental conditions. The effects of suspended particles on nitritation were determined by the use of ammonia-oxidizing bacteria (AOB) strain SW16, identified as Nitrosomonas nitrosa, which was isolated from sediment samples of the TGR. Suspended particle concentration in water–sediment solution played an important role in the nitritation process. The rate of nitritation enhanced with the increase of the suspended particle concentration. It was found that the critical factor controlling ammonia oxidizing rate was the AOB biomass resulting from the AOB growth rate. Moreover, results demonstrated that both particle size and organic matter content showed little effect on the nitritation process under the experimental conditions.     

Importance of terrestrially-derived,particulate phosphorus to phosphorus dynamics in a west coast estuary

Allochthonous inputs of suspended particulate matter from freshwater environments to estuaries influence nutrient cycling and ecosystem metabolism. Contributions of different biogeochemical reactions to phosphorus dynamics in Tomales Bay, California, were determined by measuring dissolved inorganic phosphorus exchange between water and suspended particulate matter in response to changes in salinity, pH, and sediment redox. In serum bottle incubations of suspended particulate matter collected from the major tributary to the bay, dissolved inorganic phosphorus release increased with salinity during the initial 8 h; between 1–3 d, however, rates of release were similar among treatments of 0 psu, 16 psu, 24 psu, and 32 psu. Release was variable over the pH range 4–8.5, but dissolved inorganic phosphorus releases from sediments incubated for 24 h at the pH of fresh water (7.3) and seawater (8.1) were similarly small. Under oxidizing conditions, dissolved inorganic phosphorus release was small or dissolved inorganic phosphorus was taken up by particulate matter with total P content <50 μmoles P g^?1; release was greater from suspended particulate matter with total phosphorus content >50 μmoles P g^?1. In contrast, under reducing conditions maintained by addition of free sulfide (HS^?), dissolved inorganic phosphorus was released from particles at all concentrations of total phosphorus in suspended particulate matter, presumably from the reduction of iron oxides. Since extrapolated dissolved inorganic phosphorus release from this abiotic source can account for only 12.5% of the total dissolved inorganic phosphorus flux from Tomales Bay sediments, we conclude most release from particles is due to organic matter oxidation that occurs after estuarine deposition. The abiotic, sedimentary flux of dissolved inorganic phosphorus, however, could contribute up to 30% of the observed net export of dissolved inorganic phosphorus from the entire estuary.     

Prospective scenarios for water quality and ecological status in Lake Sete Cidades (Portugal): The integration of mathematical modelling in decision processes

The design of alternative strategies for water and ecological quality protection at the Lake Verde of Sete Cidades should be coupled with the assessment of future trophic states. Therefore, a mathematical model was developed to make prospective scenarios to reduce the risk of environmental degradation of the lake, and a modified Psenner scheme was used to characterize P distribution in the sediments. The model was able to describe thermal stratification, nutrient cycling (P, NH₄ and NO₃), dissolved O₂, and phytoplankton dynamics in the water column and adjacent sediment layers. Internal P recycling, resulting from thermal stratification and sediment anoxia, was identified as the main cause for the increase of P concentration in the hypolimnion followed by slow transfer to the epilimnion (about 20 μg/L annual average). Cyanobacteria blooms during spring were explained by the availability of P and increased water temperature verified during this season. The most sensitive model parameter was sediment porosity. This parameter has a direct effect in dissolved O₂ and P profiles and also in phytoplankton biomass. Finally, different water quality restoration scenarios were identified and their effectiveness assessed. Without the adoption of remediation measures (scenario control), Lake Verde water quality would deteriorate with annual average concentrations of total P and phytoplankton biomass (dry matter) reaching 34 μg/L and 2 mg/L, respectively, after 10 years of simulation. The reduction of P loads (scenario PORAL) into the lake would improve water quality comparatively to the scenario control, reducing the annual average concentrations of total P from 34 μg/L to 26 μg/L and of phytoplankton from 2 mg/L down to 1.4 mg/L after 10 years of simulation. In scenario sediments, corresponding to a decrease in the organic content of the sediments, a reduction in the concentrations of total P and phytoplankton is expected in the first two years of simulation, but this effect, would be attenuated throughout the years due to organic matter sedimentation. The best strategy is obtained by combining external and internal measures for P remediation. Finally, it is recommended that the model be used to integrate the results of water quality monitoring and watershed management plans.     

Phosphorus transport in shallow groundwater in peri-urban Kampala, Uganda: results from field and laboratory measurements

To understand Phosphorus (P) sources and transport processes in the subsurface in Bwaise III Parish, Kampala, P attenuation and adsorption capacities of soils were studied in situ and from laboratory measurements. Relationships between sorption parameters and soil matrix properties, rates and mechanism of the adsorption process and soil P fractions were also investigated. P was generally higher in the wet than the dry season, but for both seasons, the maximum was 5 mgP/l. P transport mechanisms appeared to be a combination of adsorption, precipitation, leaching from the soil media and by colloids with the latter two playing an important role in the wet season. The sorption process comprised two phases with the first stage rate constants being about fourfold those of the second stage. The Langmuir isotherm described the sorption data well (R ² ≥ 0.95) with the second soil layer exhibiting the highest sorption maximum (C _max) (average value 0.6 ± 0.17 mgP/gDW). The best prediction of C _max had organic carbon, Ca, available P and soil pH. Residual P consisting mostly of organics was the main fraction in all the layers followed by inorganic HCl-P and NaOH-P in the top and middle layers, respectively. Loosely bound P (NH₄Cl-P) was the least fraction (<0.4% of total P) in all layers indicating the high binding capacity of P by the soils. The study results suggest that P dynamics is related to Ca, Fe and organic carbon content of the soils.     

Phosphorus Cycling and Burial in Sediments of a Seasonally Hypoxic Marine Basin

Recycling of phosphorus (P) from sediments contributes to the development of bottom-water hypoxia in many coastal systems. Here, we present results of a year-long assessment of P dynamics in sediments of a seasonally hypoxic coastal marine basin (Lake Grevelingen, the Netherlands) in 2012. Sequential phosphorus extractions (SEDEX) and X-ray absorption spectroscopy (XAS) indicate that P was adsorbed to Fe-(III)-(oxyhydr)oxides when cable bacteria were active in the surface sediments in spring. With the onset of summer hypoxia, sulphide-induced dissolution of the Fe-(III)-(oxyhydr)oxides led to P release to the pore water and overlying water. The similarity in authigenic Ca-P concentrations in the sediment and suspended matter suggest that Ca-P is not formed in situ. The P burial efficiency was ≤ 32%. Hypoxia-driven sedimentary P recycling had a major impact on the water-column chemistry in the basin in 2012. Water-column monitoring data indicate up to ninefold higher surface water concentrations of phosphate in the basin in the late 1970s and a stronger hypoxia-driven seasonal P release from the sediment. The amplified release of P from the sediment in the past is attributed to the presence of a larger pool of Fe-bound P in the basin prior to the first onset of hypoxia. Given that P is not limiting, primary production in the basin has not been affected by the decadal changes in P availability and recycling over the past 40 years. The changes in P dynamics on decadal time scales were not recorded in sediment profiles of total P or organic C/total P.     

Sediment and hydro biogeochemistry of Lake Nainital, Kumaun Himalaya, India

The picturesque Nainital Lake, in the Uttarakhand state of India, is one of the major tourist attractions in the northern part of India. The increasing tourism and population around these lakes are a major concern for the ecology and good sustenance of the lakes. The present study is aimed to understand the behaviour of nutrients and metals in the sediment and their association with chemical forms in the lake. The study was accomplished by studying the water, interstitial water and sediments for major oxides, nutrients and metals in the lake. The different chemical forms of phosphorus and metals in the sediments were done using sequential extraction procedures. The water chemistry (Ca + Mg:Na + K) and the sediment chemistry (CIA and Al₂O₃/K₂O) show that the rocks in the catchment area play an important role in the geochemistry of the lake. The metals in the water also show that the Tallital basin is more polluted than the Mallital basin, may be due to the influence of Bus station. The high concentration of chloride, NH₄, SO₄ and metals in the sediment water interface and the interstitial water shows denitrification, sulfidisation and sulfide oxidation in the anoxic bottom water. The sediment composition shows that the phosphorus in the water is sequestered as carbonate flour apatite, and the metals precipitate as carbonate. The geo- accumulation index shows that the metals zinc, cobalt and nickel show moderate polluted nature than other metals. In general, the lake is less affected by anthropogenic activities. The chemical processes undergoing within the lake, like sulfidisation and sulfide oxidation, oxide dissolution and denitrification and organic matter degradation play an important role in the remobilization of the metals from the lake sediments.     

Effects of calculation procedure and sampling site on trap method estimates of sediment resuspension in a shallow lake

Resuspension estimates given by two different trap methods in a shallow lake were compared. The sensitivity of the methods to errors in estimates of gross sedimentation and organic fraction of trapped material was explored. The methods were label method, in which resuspension is estimated by determining the organic fraction of surface sediment, suspended seston and trapped material, and SPIM/SPM method, where the relationship between settling particulate inorganic matter (SPIM) and total settling particulate matter (SPM) is used. During the whole 111 day study period, according to the label method, at a sheltered station 1949 g m⁻² dry weight of sediment was resuspended, whereas SPIM/SPM gave an estimate of 1815 g m⁻². The difference in the estimates was probably due to mineralization loss of organic material in the traps during the two week exposure periods. Sensitivity analysis showed that of the two methods, the label method was more sensitive to variations in the organic content of trapped material. At a wind-exposed station, the total amounts of resuspended matter given by the label method and by the SPIM/SPM method were 4966 g m⁻² and 4971 g m⁻², respectively. Due to wind effects, escape of trapped material took place, which caused underestimation of gross sedimentation and compensated the effects of mineralization loss to diminish the difference between the methods. Of the two methods, the SPIM/SPM method seems thus more suitable for lakes, where bacterial activity is high. If cyanobacterial blooms take place, the label method is probably more reliable, providing that the exposure time of sediment traps is kept adequately short.     

The effects of fertilizer applications on runoff loss of phosphorus

The phosphorus index (PI) can be used to effectively identify areas with high risks of phosphorus losses. Manures and fertilizers are important source factors for the establishment of the PI system. An artificial precipitation experiment was performed to evaluate phosphorus losses with the applications of different types of fertilizers and manures. The results showed that the total phosphorus (TP) losses in runoff followed the order of ammonium phosphate monobasic (NH₄H₂PO₄), ammonium hydrogen phosphate ((NH₄)₂HPO₄), monobasic potassium phosphate (KH₂PO₄), chicken manure, and cattle manure with surface application of these fertilizers and manures. The order was slightly changed to NH₄H₂PO₄, KH₂PO₄, (NH₄)₂HPO₄, chicken manure, and cattle manure with incorporation application under the same rainfall condition. Both the methods and the rate of manure application can affect the amounts of phosphorus in water and particles of runoff. More than 90 % of TP in runoff were lost through suspended particles. Manure application had a significant contribution to the P load in runoff.     

Biogeochemical cycling in an organic-rich coastal marine basin. 5. Sedimentary nitrogen and phosphorus budgets based upon kinetic models,mass balances,and the stoichiometry of nutrient regeneration

The rapid rates of sediment accumulation (~ 10–20 cm/yr) in the recently formed Cape Lookout Bight, North Carolina, have resulted in the deposition of approximately 157 moles of carbon, 14 moles of nitrogen and 1.3 moles of phosphorus, per square meter annually. The metabolism of the organic matter in these anoxic sediments is dominated by sulfate reduction and fermentation reactions. Sedimentary nitrogen and phosphorus budgets are estimated using 3 related approaches: 1) a kinetic model of solid phase diagenesis; 2) direct measurements of nutrient burial and regeneration; and 3) nutrient recycling rates estimated from annual rates of sulfate reduction and the SO₄:NH₄ and SO₄:PO₄ stoichiometry of nutrient regeneration. The mass balances derived agree reasonably well and indicate that approximately 30% of the total nitrogen and 15% of the total phosphorus deposited in these sediments are recycled. The kinetics of nutrient regeneration are rapid. The mean residence time for recycled nutrients within the sediment is 4 to 6 months for nitrogen and 1.5 to 2 years for phosphorus. Nearly 60% of the total nitrogen regeneration and 90% of the total phosphorus regeneration occur during the 4 month summer period of June through September. Nitrogen regeneration, like carbon, appears to be controlled by the microbially-mediated metabolism of labile organic matter. The greater asymmetry and lower percent turnover in phosphorus cycling is apparently due to changes in its solubility under oxidized and reduced conditions and selective regeneration prior to deposition.     

Phosphorus dynamics and corn growth under applications of corn stalks biochar in a clay soil

Biochar prepared from corn stalks is used as a source of phosphorus in this study. The hypotheses were to investigate effects of biochar applications in clay soil on availability, changes of phosphorus pools and maximum adsorption of phosphorus as well as corn growth. The soil was placed in plastic pots with each contains 3 kg of this soil. Biochar was added at levels of 0 (control), 6.5 (B₁), 19 (B₂), and 38 (B₃) g pot^?1. In this experiment, the pot was planted with corn (Zea mays). The results of this study revealed that the biochar application enhanced available phosphorus (Olsen-P) from 11.51 to 17.10 mg kg^?1. Adding biochar significantly increased the amount of NH₄Cl-P, NaHCO₃-P_o, and NaOH I-P_o fractions (p?≤?0.05), but it significantly decreased HCl-P_i fraction (p?≤?0.05). Addition of biochar at the highest level increased the fresh and dry matter productions by up to about 75 and 48.7%, respectively, compared to the control. The phosphorus uptake by corn plants significantly increased with increasing levels of biochar. The removal efficiency (% sorption) and maximum adsorption (b) of phosphorus increased with increasing level of biochar addition compared to control. Consequently, it is recommended to add biochar produced from corn stalks to the soil in order to substitute phosphate fertilizers.     

滇池湖泊沉积物中甘油二烷基甘油四醚脂的组成特征

以云贵高原浅水湖泊—滇池作为研究对象,在对湖心一个63 cm沉积物柱样的有机质总体及分子有机地球化学研究的基础上,对沉积物有机质中甘油二烷基甘油四醚脂（GDGTs）组成进行了测定。研究结果表明,滇池湖泊沉积物中具有丰富的GDGTs,且以反映陆相土壤来源的支链类GDGTs为主。该沉积柱样中支链类GDGTs的环化指标（CBT）和甲基化指标（MBT）揭示出:1）整个沉积阶段滇池流域土壤的pH值主要介于7.5~8.2,相对中、下部层段,上部层段pH值呈现略微减小的趋势;2）基于CBT/MBT重建的滇池流域内年平均气温呈现由早期的温暖潮湿气候逐渐向寒冷干燥气候变化,近来又有所回暖的变化过程,这可以很好地解释该沉积柱中、下层段记录的总体有机质主要特征的演化规律。