Mass balance models of phosphorus in sediments and water

Models are presented in order of progressively more complex spatial resolution in which the effects on the sediment-water interactions are emphasized. For simple models, the diagnostic approach of calculating the net settling and return of total phosphorus is demonstrated with data from Lake Erie. For more complex models, the effects of interbasin transport and vertical mixing are shown to be important in determining the pathways of the sediment-released or sediment-bound phosphorus in the water column.     

湿地沉积物对磷的吸附-解吸动力学模型概述

介绍了常用的吸附-解吸动力学模型(Freundlich方程、Langmuir方程及Temkin模型),分析比较了不同模型之间的相互关系,对目前国内外关于磷吸附-解吸动力学模型研究进行了简要概述,介绍了不同模型的统一表达形式,并提出应加强对不同类型湿地中沉积物对磷的吸附-解吸过程及其动力学模型、对吸附-解吸过程的长期监测和不同环境因子间的交叉效应研究等建议,以深化对动力学模型的认识,从净化机理层面充分理解湿地生态系统的运行机制.     

Release of phosphorus from sediments in Lake Biwa

Two sulfur-mediated reactions are resulting in the eutrophication of Lake Biwa, Japan. The iron (II) phosphate mineral vivianite is dissolving in sulfide-enriched sediments that in places results in porewater concentrations of phosphate exceeding 3 mg l⁻¹. The dissolution of phosphate is evident in profiles of total phosphorus where zones of dissolution and a zone of precipitation in the most oxic surface sediments are visible. At times sulfate reduction in these surface sediments results in pH values as high as 9.9, which can dissolve phosphate adsorbed to iron (III). This release of phosphorus from sediments is at least partially responsible for the recent appearance of blue-green algal blooms. Received: August 4, 2000 / Accepted: March 19, 2001     

杭州西湖北里湖沉积物氮磷内源静态释放的季节变化及通量估算

通过采集北里湖不同季节的柱状芯样,在实验室静态模拟沉积物氨氮(NH+4-N)和可溶解性磷酸盐(PO3-4-P)的释放,同时研究了沉积物间隙水中NH+4-N及PO3-4-P的垂直分布特征.结果表明,沉积物间隙水NH+4-N随深度的增加有上升的趋势,PO3-4-P随深度的增加呈先升后降的趋势.氮、磷营养盐在沉积物—水界面均存在浓度梯度,表明存在自间隙水向上覆水扩散的趋势.沉积物NH+4-N在春季、夏季、秋季、冬季的释放速率分别为0.074 mg·m-2· d-1、0.340mg· m-2· d-1、0.087 mg· m-2· d-1、0.0004 mg·m-2·d-1,pO3-4-P的释放速率则分别为0.340 mg·m-2·d-1、0.518 mg·m-2·d-1、0.094 mg·m-2·d-1、-0.037 mg· m-2·d-1.不同采样点表现出明显的季节和空间差异性,释放速率表现为夏季＞春季、秋季＞冬季.根据静态模拟出的不同季节下内源氮、磷释放速率计算,全湖内源氮、磷营养盐的贡献分别为0.0037、0.0057t/a.该研究可为北里湖富营养化及内源污染的治理提供基础数据.     

Different patterns of phosphorus release from lake sediments in laboratory experiments

The phosphorus release from surface sediments of eight lakes, mainly shallow lakes in agricultural areas, was studied in laboratory batch experiments with additions of acetate and/ or nitrate. The lake sediments could be separated into three categories. Some sediments did not release phosphorus under any conditions. The second category showed a high phosphorus release rate when acetate was added, in order to stimulate bacterial activity and oxygen consumption. The addition of nitrate, only, stabilized the redox conditions and prevented phosphorus release. This pattern followed the classical theories of Einsele and Mortimer. The third sediment category released phosphorus up to some level which remained constant throughout the experiment, and was independent of acetate and/or nitrate additions.Several extraction procedures and adsorption-desorption experiments were performed in order to characterize the sediment phosphorus and thus explain the different behaviours of the three sediment categories.     

Nitrogen fluxes from marine sediments: quantification of the associated co-occurring bacterial processes

Different models for calculate on of di-nitrogen fluxes using ¹⁵NO₃ tracers were tested for their congruence with experimental data obtained with marine sediment samples. The co-occurence of nitrification as source of substrate and the simultaneous N₂ production from denitrification and/or Anammox were taken into account as well as nitrous oxide production in the total denitrification rate. The results highlighted that isotope technique provides a powerful tool to evaluate, in the same experimental set up, the rates of total N₂ fluxes: denitrification and/or Anammox if it is carefully applied and its limitations, mainly the range of ¹⁵NO₃ inputs are adapted to the studied samples and the linearity of the kinetics of the products checked.     

Constructing functional models from biophysically-detailed neurons

Improving biological plausibility and functional capacity are two important goals for brain models that connect low-level neural details to high-level behavioral phenomena. We develop a method called “oracle-supervised Neural Engineering Framework” (osNEF) to train biologically-detailed spiking neural networks that realize a variety of cognitively-relevant dynamical systems. Specifically, we train networks to perform computations that are commonly found in cognitive systems (communication, multiplication, harmonic oscillation, and gated working memory) using four distinct neuron models (leaky-integrate-and-fire neurons, Izhikevich neurons, 4-dimensional nonlinear point neurons, and 4-compartment, 6-ion-channel layer-V pyramidal cell reconstructions) connected with various synaptic models (current-based synapses, conductance-based synapses, and voltage-gated synapses). We show that osNEF networks exhibit the target dynamics by accounting for nonlinearities present within the neuron models: performance is comparable across all four systems and all four neuron models, with variance proportional to task and neuron model complexity. We also apply osNEF to build a model of working memory that performs a delayed response task using a combination of pyramidal cells and inhibitory interneurons connected with NMDA and GABA synapses. The baseline performance and forgetting rate of the model are consistent with animal data from delayed match-to-sample tasks (DMTST): we observe a baseline performance of 95% and exponential forgetting with time constant τ = 8.5s, while a recent meta-analysis of DMTST performance across species observed baseline performances of 58 − 99% and exponential forgetting with time constants of τ = 2.4 − 71s. These results demonstrate that osNEF can train functional brain models using biologically-detailed components and open new avenues for investigating the relationship between biophysical mechanisms and functional capabilities.     

Effect of temperature on phosphorus sorption to sediments from shallow eutrophic lakes

The availability of phosphorus (P) in lakes is dependent on the sorption characteristics of the underlying sediments. Temperature is a crucial factor affecting the P sorption in sediments. The objective of this study was to evaluate the effect of temperature on sorption of P by sediments from two eutrophic lakes. The study was carried out using short-term batch experiments at 4, 20 and 30 °C. Phosphorus sorption kinetics, isotherms, fractionation and desorption were investigated. The P sorption was dependent on sediment type and temperature (p < 0.001). The Mei sediments showed a higher sorption rate and sorption capacity than Hua sediments. The P sorption kinetics were best described by a pseudo second order model (R² > 0.97). Activation energies derived from the kinetics rate constant indicated that P sorption onto the two sediments was controlled by a diffusion process. For both sediments, Freundlich model fit the P sorption isotherms well and the calculated apparent sorption heat was 6.37 kJ mol⁻¹ for Mei sediments and 8.67 kJ mol⁻¹ for Hua sediments. This indicated that P sorption onto both sediments was endothermic. Adding P significantly increased the soluble and loosely bound P (S/L-P), aluminum-bound P (Al-P) and iron-bound P (Fe-P) (p < 0.05). The amount of Al-P and Fe-P was markedly higher at 30 °C than at 4 °C (p < 0.05). Subsequent P desorption indicated that adsorbed P was highly labile, in particular for Hua sediment. The degree of P mobility that occurred during sediment sorption was inversely related to the temperature at the time of sorption. A significant relationship (R² = 0.978) between phosphorus sorption maximum and oxalate-extractable Fe and Al at different temperatures reflects that the amorphous contents of Fe and Al are responsible for the temperature effect on P sorption.     

A new device for collection of interstitial water from wetland sediments

A sampler for collection of interstitial water from wetland sediments is described. It differs from other sampling devices because it does not have to be filled with solution to facilitate diffusion, it does not have to be removed from the wetland to collect samples, and it can be used to draw repeated samples over time from identical locations. The device facilitates in situ measurement of a wide range of abiotic parameters such as electrical conductivity, redox potential, and pH in wetland sediments. The device has application in ecological investigations of sediment-borne wildlife diseases, studies of benthic invertebrates, measurement of nutrient exchange, and other aspects of wetland ecology.     

A new sampler for collection of interstitial water from sandy sediments

An inexpensive, easily constructed apparatus for collecting interstitial water from sandy substrates is described and evaluated against two other devices. Results indicate that these samplers yield comparable dissolved oxygen determinations, but vary in terms of repeatability, efficiency, construction complexity and sturdiness.     

Predictive models for phosphorus retention in wetlands

The potential of wetlands to efficiently remove (i.e., act as a nutrient sink) or to transform nutrients like phosphorus under high nutrient loading has resulted in their consideration as a cost-effective means of treating wastewater on the landscape. Few predictive models exist which can accurately assess P retention capacity. An analysis of the north American data base (NADB) allowed us to develop a mass loading model that can be used to predict P storage and effluent concentrations from wetlands. Phosphorus storage in wetlands is proportional to P loadings but the output total phosphorus (TP) concentrations increase exponentially after a P loading threshold is reached. The threshold P assimilative capacity based on the NADB and a test site in the Everglades is approximately 1 g m^–2 yr^–1. We hypothesize that once loadings exceed 1 g m^–2 yr^–1 and short-term mechanisms are saturated, that the mechanisms controlling the uptake and storage of P in wetlands are exceeded and effluent concentrations of TP rise exponentially. We propose a One Gram Rule for freshwater wetlands and contend that this loading is near the assimilative capacity of wetlands. Our analysis further suggests that P loadings must be reduced to 1 g m^–2 yr^–1 or lower within the wetland if maintaining long-term low P output concentrations from the wetlands is the central goal. A carbon based phosphorus retention model developed for peatlands and tested in the Everglades of Florida provided further evidence of the proposed One Gram Rule for wetlands. This model is based on data from the Everglades areas impacted by agricultural runoff during the past 30 years. Preliminary estimates indicate that these wetlands store P primarily as humic organic-P, insoluble P, and Ca bound P at 0.44 g m^–2 yr^–1 on average. Areas loaded with 4.0 g m^–2 yr^–1 (at water concentrations>150 g·L^–1 TP) stored 0.8 to 0.6 g m^–2 yr^–1 P, areas loaded with 3.3 g m^–2 yr^–1 P retained 0.6 to 0.4 g m^–2 yr^–1 P, and areas receiving 0.6 g m^–2 yr^–1 P retained 0.3 to 0.2 g m^–2 yr^–1. The TP water concentrations in the wetland did not drop below 50 g·L^–1 until loadings were below 1 g m² yr^–1 P.     

Determination of total phosphorus in lake sediments

Several methods are in use to measure total phosphorus in lake sediments making cross-study comparisons tenuous, and may lead to potential errors in calculating other phosphorus fractions. Four methods in common use in the limnological literature were compared using sediments spanning a range of organic content from 2 to 35% C. No significant differences were found in within-lake comparisons, although a method using persulfate oxidation was highly variable, and this variability was correlated with organic content suggesting inconsistent oxidation. The other methods (combustion, acid digestion with HClO₄, H₂SO₄ + H₂O₂) gave uniformly small variances.     

岱海表层沉积物中内源磷的释放

以北方半干旱地区典型内陆封闭湖泊岱海为研究对象,开展了上覆水质及多种环境因子(温度,pH,溶解氧,扰动,光照)对湖泊沉积物内源磷释放的影响研究。结果表明:(1)温度升高有利于内源磷的释放,湖泊水体在温度较高的夏季更易呈现富营养化状态;(2)碱性条件有利于磷的释放,岱海水体属微碱性环境(pH8.8),若水体pH进一步升高,将会造成沉积物内源磷的大量释放;(3)厌氧条件(ρDO0.8mg/L)有利于磷的释放,岱海湖心区水深较深,易形成厌氧环境,因此湖心区内源磷释放强度较浅水区大;(4)强烈扰动有利于磷的释放,这会对浅水区的底质产生较大影响;(5)照度通过底栖藻类的生物作用,间接地限制了沉积物释磷对上覆水中磷浓度的影响。     

Seasonal phosphorus release from exposed,re-inundated littoral sediments of two Australian reservoirs

Water levels in many reservoirs typically fluctuate seasonally, but the effects of re-inundation of exposed sediments on nutrient dynamics in the water column are poorly known. This study concerns the seasonal differences in the potential of sediments from two Australian reservoirs, after having undergone different degrees of in situ desiccation, to release P under aerobic conditions. Differences were determined between biotic and abiotic P release, and results were also examined in relation to sediment chemistry. The two reservoirs, Carcoar Dam and Lake Rowlands, demonstrated different patterns of P release involving an interactive complex of P release mechanisms. Sediment chemistry at the reservoir margins was important because of the higher concentrations of N, P, Fe and Mn in Lake Rowlands. Physical and chemical processes influenced P uptake and release due to desiccation and oxidation of sediments and were of greater importance in Carcoar Dam. Abiotic P release from sterilised sediments was greater than from unsterilised sediments where both biotic and abiotic processes were apparent. Biotic P uptake and release were especially marked in Lake Rowlands where large macrophyte beds provided a rich source of organic matter. Little seasonal difference in P release was detected. The increased P release from dried sediments has ramifications for internal P loading into reservoirs and for the calculation of P budgets. For managers of reservoirs where large expanses of sediment are exposed during drying, it may be better to maintain high water levels, where possible, during the summer by modifying drawdown practices.     

Release rates and biological availability of phosphorus released from sediments receiving aquaculture wastes

Aquaculture is an increasingly significant user of freshwater resources in Scotland. In 1989, the total fish biomass produced in Scottish freshwater amounted to 7000 t. 50% of this total was reared in floating cage systems situated in lochs (lakes). Both solid (mainly in the form of uneaten feeds and faecal matter) and dissolved byproducts of the production cycle enter the limnetic environment untreated. Much solid waste material accumulates directly on the sediments beneath the cage systems. This leads to a localised enrichment in nutrient elements of the sedimentary environment. The experiments served to quantify rates of total phosphorus (TP) and dissolved reactive phosphorus (DRP) release from undercage and control sites, and to relate such releases to the biological availability of the released P. Results indicate significantly higher levels of NH₄Cl-extractable P in sediments affected by waste deposition from fish cages. TP and DRP release, and greater growth of Chla are obtained from undercage cores compared with control sites. No link between extractable-P content of sediments, or release rate and Chla production was established.     

Antarctic glacial history from numerical models and continental margin sediments

The climate record of glacially transported sediments in prograded wedges around the Antarctic outer continental shelf, and their derivatives in continental rise drifts, may be combined to produce an Antarctic ice sheet history, using numerical models of ice sheet response to temperature and sea-level change. Examination of published models suggests several preliminary conclusions about ice sheet history. The ice sheet's present high sensitivity to sea-level change at short (orbital) periods was developed gradually as its size increased, replacing a declining sensitivity to temperature. Models suggest that the ice sheet grew abruptly to 40% (or possibly more) of its present size at the Eocene–Oligocene boundary, mainly as a result of its own temperature sensitivity. A large but more gradual middle Miocene change was externally driven, probably by development of the Antarctic Circumpolar Current (ACC) and Polar Front, provided that a few million years' delay can be explained. The Oligocene ice sheet varied considerably in size and areal extent, but the late Miocene ice sheet was more stable, though significantly warmer than today's. This difference probably relates to the confining effect of the Antarctic continental margin. Present-day numerical models of ice sheet development are sufficient to guide current sampling plans, but sea-ice formation, polar wander, basal topography and ice streaming can be identified as factors meriting additional modelling effort in the future.     

分离自海洋沉积物的四个中国真菌新记录种

报道了分离自渤海沉积物的4个中国真菌新记录种：黄褐隐囊菌Aphanoascus fulvescens、小翅孢壳Emericellopsis minima、弗氏光黑壳Preussia flanaganii和湿生假散囊菌Pseudeurotium hygrophila。其中,隐囊菌属Aphanoascus为中国新记录属。研究菌株保存于中国海洋大学海洋生物标本室（OUCMB）。     

柘林湾表层沉积物中的生物可利用磷

对2002年7月至2003年7月间采集的柘林湾表层沉积物样品中的总磷(TP)、有机磷(OP)及各形态无机磷进行分析。结果表明,各形态磷的空间分布与调查海区沉积物粒径有关,并受沿岸污水排放及近岸养殖排污等人为活动的影响。表层沉积物各形态磷的平面分布基本呈现为湾内(除S1、S7站外)高于湾外的总体趋势。无机磷中以自生磷(Au-P)为主要存在形态,占总磷的47.3%,有机磷(OP)含量次之,占总磷的19.5%,铁结合磷(Fe-P)最低。其中,生物可利用磷(包括Ex-P、Fe-P、OP和部分Au-P)占TP的35.7%~83.0%,在国内外海湾中处于较高水平。     

Two new species ofPichia isolated from slime fluxes of deciduous trees

Two new homothallic species ofPichia, associated with exudates ofPopulus trichocarpa andSalix sp. have been described.Pichia trehalophila sp.n. was isolated from slime exudates in two widely separatedPopulus trichocarpa trees andPichia salictaria sp.n. was isolated from two exudates ofSalix sp. The latter species was previously present as an unidentified strain ofPichia in the culture collection of the Centraalbureau voor Schimmelcultures and had been isolated from a patient in Germany. The natural habitat ofP. salictaria is considered to be in association with willow trees.