The influence of pH on phosphate release from lake sediments

pH is believed to be an important regulating factor for the release of phosphate from freshwater sediments. Usually, this is demonstrated in laboratory experiments using intact sediment cores and pH regulation of the overlying water by means of NaOH additions. This technique and a pH regulation technique by means of CO₂-stripping were compared. The first method resulted in a 10-fold increase in release rate at pH 9.5 compared to the rate at pH 8.3. The stripping technique yielded only a doubling of the release rate at pH 9.3. Measurements of pH profiles in the sediment in experiments performed at pH 8.3 and 9.0 proved that the enhanced phosphate release when using NaOH for pH regulation is mainly an artifact caused by an increased alkalinity in the water column and the upper sediment layers, resulting from the NaOH additions.     

Suppression of phosphorus release from lake sediments by the addition of nitrate

An assessment was made of the effectiveness of nitrate in reducing phosphorus release from the anoxic sediments of a small dimictic lake, White Lough, N. Ireland. Laboratory experiments on sediment cores showed that nitrate delayed and reduced phosphorus release with an input of 61 gN m⁻² causing complete suppression. The addition of 24 gN m⁻² of nitrate to the sediment of White Lough resulted in a delay and reduction of phosphorus release similar to that observed in the laboratory core experiments. Sediment release of iron in the lake was also delayed and reduced but manganese release and the rate of hypolimnetic deoxygenation were unaffected by the nitrate addition. Ammonium release rates in the sediment cores and in the whole lake experiment did not vary with nitrate input. Comparing the costs of using nitrate or iron/aluminium salts to suppress sediment phosphorus release indicated that the nitrate method was at least 80% more expensive.     

城市景观水体底泥氮磷释放研究

以城市景观水体的底泥为研究对象,研究了底泥中氮磷的释放规律,以及p H和温度对底泥氮磷释放的影响,结果表明,总氮和总磷的浓度随时间而增加,在前期增加较快;p H值对氮磷也有明显的影响;在较高的温度下促进底泥向水体中释放氮和磷。     

Factors affecting phosphate adsorption to aluminum in lake water: implications for lake restoration

Treatment of lake inlets or lake sediments with aluminum (Al) is being increasingly used for lake restoration but only few studies exist concerning competitive substances that might influence phosphate (PO(4)(3-)) removal from lake water. Therefore, chemical interferences of several ions (magnesium, silicate, chloride and humic acid) on PO(4)(3-) adsorption to Al(OH)(3) were studied. Interference of each ion was studied in artificial lake water, and the complex interactions occurring in natural water were studied in water from 30 Danish lakes at pH 7 in both cases. In the artificial lake water Al:P ratio was high as sediment P-pools were the targets while in the natural lake water Al addition was generally lower as only P present in the water was targeted (i.e. inlet water). The single-ion experiments evidenced that silicate (>200 microM) and humic acids significantly decreased the effectiveness of PO(4)(3-) adsorption to Al(OH)(3) by 10-13% at 450 microM Si and 17% at 1 mM C, respectively. NaCl did not influence adsorption of PO(4)(3-) to Al(OH)(3), however, PO(4)(3-) removal was slightly reduced in seawater, mainly due to the presence of Mg(2+). The studies on interferences in natural lake water showed that as long as the PO(4)(3-) concentration was low (<5 microM), silicate competed with PO(4)(3-) for adsorption sites on Al(OH)(3) but at higher PO(4)(3-) concentrations, color and DOC (as indicators of HA) were the main variables decreasing PO(4)(3-) removal from lake water. Inhibition of PO(4)(3-) precipitation in natural lake water appeared complex and did not allow for a simple calculation of Al dose from the concentration of potentially competitive ions. Recommendation for lake management is therefore still that precipitation assays should be carried out for any type of inlet or lake water prior to Al application.     

The effect of frozen storage of open-ocean seawater samples on the concentration of dissolved phosphate and nitrate

Filtered seawater samples which were stored at −20°C in containers of different surface area to volume ratios were analysed for the effects of surface adsorption of nitrate and phosphate during storage for a maximum of 24 months. The results for nitrate showed no significant change in concentration over the duration of the experiment. However, the concentration of phosphate steadily decreased in samples stored for longer than 4 months. The loss of phosphate after this time cannot be explained at present, but this study showed that it was not due to the effects of surface adsorption.     

The effect of changes in nitrate concentration in drinking water on methemoglobin levels in infants

For a five‐day period infants consuming powdered milk formula made up with tap water were exposed to water of controlled nitrate content. There was a significant rise in MetHb levels above normal in most children after the first day of exposure to high nitrate water (108 mg/1 NO3). This was followed by some indication of a drop in MetHb levels despite the continued exposure and finally a return to normal levels when the exposure to nitrates stopped. No clinical signs of methemoglobinemia developed. The possible existence of an adaption mechanism is suggested but requires further elucidation.     

Effects of light on sediment nutrient flux and water column nutrient stoichiometry in a shallow lake

The effects of light and temperature on nutrient cycling (silica (Si), nitrogen (N) and phosphorus (P)) between sediments and water in a shallow eutrophic lake (Loch Leven, Scotland), and consequent effects on water column nutrient stoichiometry, were assessed using a series of intact sediment core incubation experiments. Estimates of actual seasonal dark and light P-fluxes were assessed using 24-h incubations. Sediment-P uptake was observed in spring (7 degrees C) and release in autumn (12 degrees C) and summer (17 degrees C), with the highest release rates ( approximately 17 mgPO4-Pm(-2) sediment surface area d(-1)) occurring in summer. In a longer (21-day) experiment in which the effects of light (light (n=6) and dark (n=6)) and temperature (five 4-day cycles to represent: 7 degrees C-->13 degrees C-->23 degrees C-->13 degrees C-->7 degrees C) on water column nutrient concentrations were assessed, PO(4-)-P, total P (TP), SiO2 and total silica (TSi) concentrations in the water column were all significantly higher under dark conditions (ANOVA, alpha=0.05). NH4-N (ammonium N) water column concentrations were observed to be higher under dark conditions at low temperatures and higher under light conditions following a high-temperature (23 degrees C) treatment. No significant light effects were observed for water column total N (TN) concentration. Flux estimates for all nutrients measured are given. In terms of water column nutrient stoichiometry, TN:TP ratio was significantly higher under light conditions, TSi:TN was significantly lower under light conditions, and TSi:TP did not vary significantly between the dark and light treatments. The main processes acting to regulate diffusive nutrient release appeared to be photosynthetic elevation of bottom water pH and dissolved oxygen concentration (both significantly higher under light conditions) and direct microalgal sequestration. Thus, a feedback mechanism exists in recovering shallow lakes where benthic microalgae can affect the stoichiometry (to favour P/Si limitation) of the plankton, and also of the main source of nutrients back to the sediments via the disproportionate regulation of sediment P, Si and N release.     

Impacts of runoff from sulfuric soils on sediment chemistry in an estuarine lake

The impact of runoff from sulfuric soils in the heavily drained Cudgen Lake floodplain, eastern Australia on water quality and downstream coastal lake sediments has been examined. The oxidation of sulfidic soils and the transformation into sulfuric soils leads to changes not only in the upper soil profile but also affects drainage water quality and the chemistry of bottom sediments in receiving waters. Oxidation transforms the soil from a sink for sulfur and metals to a significant source for downstream environments. Sulfuric soils within the Cudgen Lake catchment contain 9.18 x 10(5) mol H+ per hectare as well as elevated concentration of metals (e.g. Al, Fe, Mn) and sulfate. These products of sulfidic soil oxidation are transported efficiently from the soil profile by the constructed drainage network and into the downstream lake system. The acid volatile sulfur (AVS), chromium reducible sulfur (CRS), total sulfur, organic carbon, and reactive iron contents present in the solid phase of the lake sediments are reported. The AVS/CRS, DOP and DOS values observed in the lake sediments show that natural monosulfide formation in the near surface sediments has been enhanced due to increased inputs of organic matter, sulfate, ferrous iron and other metals following development of the catchment. There are elevated concentrations of metals (e.g. As, Al, Cd, Cr, Hg, Zn and Pb) in the upper layer of monosulfidic lake sediments compared with the underlying pyritic sediments some of which exceed sediment quality guidelines. These metals could be released by dredging or through re-suspension during high flow conditions or enter the food chain.     

Suppression of phosphate liberation from sediment by using iron slag

In order to suppress the phosphate liberation from sediment to sea water, several suppressing materials such as four kinds of iron slag, river and sea sands, and glass bead were tested. The sediment and sea water were sampled from Hiroshima Bay which seemed to be a eutrophicated area. The suppressing materials were covered on the surface of sediment, and sea water was introduced in the aquarium. The concentrations of phosphate, sulfide and dissolved oxygen were measured during the incubation period under the condition of anaerobic state. The suppressing effects of slags, sea and river sands were compared with that of glass bead used as control materials, and the suppression efficiencies were measured. The suppression efficiency of glass bead was 54.1%, and those of slag-2, -3 and -4 were 97.3, 96.1 and 98.8%, respectively. The suppression efficiency depended on the amounts of slag used, and about 85% of liberated phosphate were suppressed by slag-3 of 7.5 kg m⁻². The sulphide ion generated under anaerobic state reacted with some metals on the surface of slags and sands, and the dissolution of precipitated phosphate (Fe-P, Al-P and Ca-P) was suppressed by formation of metal sulfide on the surface of slags and sands. The suppression mechanisms on phosphate liberation, such as covering, chemical and adsorption effects were proposed and discussed. The suppression by slag was mainly carried out by the adsorption effect, in addition to the covering effect.     

Effect of oxygen concentration on the rates of denitratification and denitrification in the sediments of an eutrophic lake

The effect of oxygen concentration on the rates of denitratification and denitritification was investigated by the acetylene inhibition method during initial 1-h incubation period after preculture under complete anaerobic conditions for wide ranges of nitrate and nitrite concentrations using sediment sample collected from a highly eutrophic lake. A maximum denitratification rate of 4 μmol (g-dry mud)^?1 h^?1 was obtained under anaerobic conditions. The denitratification rate was found to be a decreasing function of the oxygen concentration below 60 μM. Approximately the same rate was observed for denitritification in the range below 30 μM O₂. Beyond 30 μM O₂, this rate dropped to the half of the maximum, and remained almost constant until a critical oxygen concentration was attained. The critical concentration, above which denitritification was suppressed thoroughly, depended on nitrite concentration.     

Removal of nitrate from effluent following discharge on surface water

The loss of nitrate nitrogen over a 800-m long reach of canal was studied in a field experiment during a 20-days period. The nitrate originated mainly from sewage effluent. Fifty-six percent of the nitrate had disappeared during its flow through the 800-m long reach, where the average retention time was 1.7 days. The average rate of nitrate disappearance during the 20-day period was 913 mg NO₃⁻-N m⁻² day⁻¹. Laboratory experiments with undisturbed water-sediment profiles from the canal showed that the disappearance of nitrate was caused mainly by denitrification in the sediment. Increased knowledge of this phenomenon may lead to an effective and cheap means in inducing denitrification.     

Denitrification kinetics of high nitrate concentration water: pH effect on inhibition and nitrite accumulation

The effect of pH variation, within the range 6.5, 7.0, 7.5, 8.5 and 9, on activated sludge denitrification of a synthetic wastewater containing 2700 mg/l NO₃-N was examined using bench-scale Sequencing Batch Reactors. Two major effects were observed. One, at pH values of 6.5 and 7.0, denitrification of a synthetic wastewater containing high nitrate levels was significantly inhibited. Two, denitrification was achieved at higher pH values of 7.5, 8.5 and 9.0, but the accumulation of nitrite increased significantly as mixed liquor pH increased with peak values of 250, 500 and 900 mg/l NO₂-N, respectively. As the pH rose, the specific rate of nitrate reduction increased. At the same time the specific rate of nitrite reduction increased in the absence of nitrate. In the presence of nitrate the specific rate of nitrite reduction remained constant, and the degree to which nitrite reduction increased in the absence of nitrate was a function of increasing pH. While increasing pH from 7.5 to 9.0 affected nitrite intermediate accumulation, the overall time for complete denitrification (reduction of both NO⁻₃ and NO⁻₂) was similar for the pH values of 7.5, 8.5 and 9.     

Temporal and spatial variation of phosphate distribution in the sediment of a free water surface constructed wetland

This study was aimed at determining the spatial and temporal variation of P distribution in sediment of an artificial wetland for sewage and industrial wastewater treatment, and the fraction that is potentially involved in the P exchange processes. Influent, effluent, macrophytes and sediment at the inlet, middle and outlet areas were sampled over 24 months. The P-fractionation in sediment was performed following the EDTA method. Eichhornia crassipes and Typha domingensis removed P efficiently when cover was high, but E. crassipes caused anoxic conditions. The increase in cover of T. domingensis may contribute to attain oxic conditions and to improve P removal. When macrophytes are not present or when cover is low, sediment seems to increase removal efficiency. A significant increase in the concentration of the fraction of Fe(OOH) approximately P and mainly that of CaCO(3) approximately P can be observed at the inlet. High pH, Ca(2+) and CO(3)(-)(2) concentrations in the influent suggest that P co-precipitates together with CaCO(3). Therefore, it seems that CaCO(3) approximately P represents the main precipitating mechanism. However, mineralization of organic matter maintained the sediment at a pH range lower than the high values prevailing in the influent. CO(3)(-)(2) could undergo partial dissolution and the released i-P(diss) could be readsorbed onto the Fe(OOH) approximately P fraction. Since the environment for P retention (high pH, Fe, Ca and ionic concentrations) is largely provided by the influent, the wetland may be expected to continue retaining P as far as the composition of the influent is maintained and there are available adsorption sites in the sediment.     

Effect of precursor concentration on the characteristics of nanoscale zerovalent iron and its reactivity of nitrate

Differing precursor concentrations, 1.0, 0.1, and 0.01 M FeCl(3) x 6H(2)O, were performed to produce nanoscale Fe(0) and the results were discussed in terms of the specific surface area, particle size and electrochemical properties. The results indicated that the nanoscale Fe(0) prepared by 0.01 M FeCl(3) had absolutely reduced in size (9-10nm) and possessed the greatest specific surface area (56.67 m(2) g(-1)). These synthesized nanoscale Fe(0) particles were attempted to enhance the removal of 40 mg-NL(-1) unbuffered nitrate solution. The first-order degradation rate constants (k(obs)) increased significantly (5.5-8.6 times) with nanoscale Fe(0) prepared by 0.01 M precursor solution (Fe(0.01 M)(0)). When normalized to iron surface area concentration, the specific rate constant (k(SA)) was increased by a factor of approximately 1.7-2.4 using Fe(0.01 M)(0) (6.84 x 10(-4) L min(-1) m(-2) for Fe(0.01 M)(0), 4.04 x 10(-4) L min(-1) m(-2) for Fe(0.1 M)(0) and 2.80 x 10(-4) L min(-1) m(-2) for Fe(1 M)(0)). The rise of reactivity of the reactive site on the Fe(0.01 M)(0) surface was indicated by the specific rate constant (k(SA)) calculation and the i(0) value of the electrochemical test.     

Distribution of mercury in six lake sediment cores across the UK

Six sediment cores, from Lochnagar, Loch Chon and Loch Grannoch in Scotland, Burnmoor Tarn in the English Lake District, Llyn Llagi in the Snowdonia region of Wales and Banbury Reservoir in London, were taken in order to study the distribution of Hg temporally and historically in lake sediments across the UK. These cores were dated using the spheroidal carbonaceous particle technique. The cores show that all sites across the UK have been contaminated by Hg. There is a rapid increase in Hg concentration during the last approximately 200 years at all rural sites. In the 95 year record from Banbury Reservoir in London the sediments show high Hg concentrations (380-840 ngg(-1)) throughout. Inter-site differences in Hg concentrations and profiles may be explained by impacts of afforestation, composition of the sediments and the provenance of the Hg including catchment in-wash influences. For example, catchment contributions result in a sharp peak (1606 ngg(-1)) in the Hg concentration profile in the core taken from Loch Chon in the Trossachs region of Scotland. Mercury fluxes were calculated for the sediment cores and show that over the last few decades these UK sites, except Lochnagar, would fall into the upper range for European rural areas.     

Influence of sediment redox conditions on release/solubility of metals and nutrients in a Louisiana Mississippi River deltaic plain freshwater lake

The influence of sediment redox conditions on solubility of selected metals and nutrients in sediment from a coastal Louisiana freshwater lake (Lake Cataouatche) receiving diverted Mississippi River water was quantified. Sediment redox was cycled step wise in 50 mV increments between oxidized (-200 to +500 mV) and reduced (+500 to -200 mV) conditions. Changes in sediment oxidation/reduction status and pH influenced solubility of both metals and nutrients. When redox potential (Eh) was increased from -200 to +500 mV, sediment pH decreased from 7.1 to 5.7. When the sediment Eh decreased from +500 to -200 mV, pH increased from 5.7 to 7.1. The increase in sediment acidity upon oxidation resulted in the release of the Pb, Ca, Mg, Al, and Zn into solution. The solution concentration of these elements was inversely proportional to Eh (P相似文献   

Effect of water composition, distance and season on the adenosine triphosphate concentration in unchlorinated drinking water in the Netherlands

The objective of our study was to determine whether water composition, distance to the treatment plant and season significantly affect the adenosine triphosphate (ATP) concentration in distributed drinking water, in order to resolve the suitability of ATP as an indicator parameter for microbial regrowth. Results demonstrated that the ATP concentration in distributed water averaged between 0.8 and 12.1 ng ATP L⁻¹ in the Netherlands. Treatment plants with elevated biofilm formation rates in treated water, showed significantly higher ATP concentrations in distributed drinking water and ATP content was significantly higher in the summer/autumn compared to the winter period at these plants. Furthermore, transport of drinking water in a large-sized distribution system resulted in significantly lower ATP concentrations in water from the distal than the proximal part of the distribution system. Finally, modifications in the treatment significantly affected ATP concentrations in the distributed drinking water. Overall, the results from our study demonstrate that ATP is a suitable indicator parameter to easily, rapidly and quantitatively determine the total microbial activity in distributed drinking water.     

Effect of selected metal ions on the photocatalytic degradation of bog lake water natural organic matter

Herein we report the photocatalytic degradation of natural organic matter from a bog lake (Lake Hohloh, Black Forest, Germany) in the presence of 0, 5, and 10 μmol L⁻¹ of added Cu²⁺, Mn²⁺, Zn²⁺ and Fe³⁺. The reactions were followed by size exclusion chromatography with organic carbon detection (SEC-DOC) and by measurements of low molecular weight organic acids. Addition of Cu²⁺ had the largest effect of all four studied metals, leading to a retardation in the molecular size changes in NOM: degradation of the larger molecular weight fraction was inhibited leading to reduced production of smaller molecular weight metabolites. Similarly, addition of Cu²⁺ reduced the production of formic and oxalic acids, and reduced the bioavailability of the partially degraded NOM.