Effects of light and oxygen on the uptake and distribution of phosphorus at the sediment-water interface

Effects of oxygen and light on the uptake and distribution of phosphorus at the sediment-water interface were investigated in this study. The experimental water and sediment samples were collected from East Taihu Lake, China. The results show that phosphorus can be taken up from the overlying water to the sediments with high nutrient loading in both anoxic and aerobic conditions. The transformation between different phosphorus fractions in the sediments and in the overlying water was observed. Effects of dissolved oxygen on the phosphorus distribution at the sediment and overlying water interface were mainly due to the inorganic processes, while effects of light were mainly due to the biological activity. This study indicates that oxygen concentration had a predominant control on the distribution and uptake of phosphorus in the sediments, and light had obvious effect on the dissolved inorganic phosphorus (DIP) concentration in the overlying water.     

Effects of light intensity and water temperature on oxygen release from roots into water lettuce rhizosphere

The oxygen release rate into the rhizosphere by a floating aquatic plant-water lettuce-was determined under various light intensities (0.0-1.2x10(5)lx) and water temperatures (10-35 degrees C). The net specific oxygen release rate was expressed by a model equation comprising the gross oxygen release rate and the rhizosphere respiration terms. Experimental and simulated results show that the net specific oxygen release rate increased with light intensity up to the optimal value, but slight inhibition by higher light intensities was observed at 10-20 degrees C. With increased water temperature, the respiration rate became larger than the gross oxygen release rate. The maximum net specific oxygen release rate of 11.0-12.5mg-O(2)kg-wet(-1)h(-1) was obtained at the optimal condition of about 25 degrees C and 9.0x10(4)-1.1x10(5)lx. The net oxygen release rate was negligible at 35 degrees C at any light intensity because the respiration rate was much greater than the gross oxygen release rate into the rhizosphere.     

Degradation of chlorophenols in soil, sediment and water at low temperature

Chlorophenol degradation was studied under aerobic conditions in soil, sediment and water. Ortho-chlorophenol, p-chlorophenol and 2,4-dichlorophenol were degraded by soil and sediment microorganisms at 0°C and 4°C. Metachlorophenol and pentachlorophenol were also degraded, but to a lesser extent. Stream-water microorganisms were only able to degrade 2,4-dichlorophenol at 20°C. None of the other chlorophenols examined were degraded by stream-water microorganisms at 0 or 20°C. The addition of some chlorophenols stimulated aerobic, and to a lesser extent, anaerobic microbial growth in sediment incubated at 0°C. A decrease in the concentration of some chlorophenols was noted in both sterile and non-sterile stream water at 0 and 20°C; which could not be explained by microbial contamination, photodecomposition or volatilization.     

Temporal and spatial distributions of phosphine in Taihu Lake, China

Phosphine is a natural gaseous carrier of phosphorus in its geochemical cycles, and it might be of importance to the phosphorus balance of eutrophic lakes. Phosphine concentration levels in Taihu Lake, a typical shallow eutrophic lake in China, were intensely investigated in this work. Results show that in the period of 2002 the variation of phosphine concentration in the atmosphere near Taihu Lake is significant, with a maximum value 2.85 pg/l. Concurrent sampling of phosphine in surface and bottom water of the lake had no distinct change. The mean concentration of phosphine in the water ranged from 1.92 to 3.01 pg/l. Approximately 84-90% of the phosphine was removed from lake water during passage of the sample through a 0.45 microm pore size filter, i.e. the average phosphine concentrations of filtered lake water in all sampling locations were from 0.37 to 0.40 pg/l with the highest value 0.73 pg/l and the lowest 0.08 pg/l, whereas phosphine concentrations in unfiltered samples were 5-9 times higher. Phosphine levels in lake sediments were positively correlated with different contamination of the samples. The concentration levels of phosphine were also higher in severe polluted sites. The local average values of the phosphine concentrations were from 21550 to 563,100 pg/kg. Its highest value was 919,238 pg/kg at 6# site (Zhihu harbor), a severely polluted sampling site.     

Lake restoration by hypolimnetic Ca(OH)2 treatment: impact on phosphorus sedimentation and release from sediment

A whole-lake hypolimnetic Ca(OH)₂ addition, that induced calcium carbonate precipitation, combined with deep water aeration has been applied to eutrophic Lake Luzin, Germany during 1996-1998. In this study we investigated the dynamic of phosphorus and its binding forms in seston and sediment before and during the treatment. The sedimentation rates of phosphorus increased within three years of induced calcite precipitation. The phosphorus binding forms shifted to the calcite-bound phosphorus in the settling matter. The increase of calcite-bound P in the settling material did not coincide with the maximum induced CaCO₃-precipitation caused by the hypolimnetic addition of Ca(OH)₂. An impact of chemicals additions and pH on phosphorus binding forms in seston and surface sediments has been studied in laboratory experiments with sediment core incubations and slurry experiments.Laboratory studies showed that the lowest phosphorus flux from sediment was related to the experiment with pH = 7 in overlaying water adjusted with Ca(OH)₂. The adjusting of pH with Ca(OH)₂ leads to a lower P flux of 2.3 mg P m⁻² d⁻¹, while the highest P-flux is attributed to the experiment with the pH which was adjusted with NaOH. Phosphorus fraction which reflects phosphorus binding on carbonates in surface sediments increased within one year of treatment, enhancing the phosphorus retention capacity of sediments.     

太湖流域含藻原水的处理技术及运行效果研究

针对太湖流域地区的夏季含藻水源水采用了投加高锰酸钾预氧化、高锰酸盐复合药剂(PPC)氧化助凝、聚丙烯酰胺(PAM)助凝、加碱调整pH值、聚硫氯化铝(PACS)混凝和助凝等几种处理方法,并对药剂投加条件等进行了研究.生产试验结果表明,投加高锰酸钾预氧化对藻类和CODMn的最高去除率分别为84.3%和24.1%.烧杯搅拌试验结果表明,PAM强化助凝、加碱调整pH值和PPC氧化助凝三种处理技术对含藻水的处理效果较佳,其作为应急工艺运用到生产上的可操作性较强.     

Regeneration of N, P and Si near the sediment/water interface of lakes from Southwestern China Plateau

Lake water, pore water, and sediments were sampled in both polluted and unpolluted lakes from Southwestern (SW) China Plateau. The results show that although the mechanisms of nutrient regeneration were similar in the polluted and unpolluted lakes, the processes, however, were much stronger in the polluted lakes. Nitrogen regeneration was mainly of organic process. Phosphorus regeneration was essentially controlled by iron redox cycling near sediment/water interface. Nutrient upward fluxes were in the order SiO2 > NH4+ > PO4(3-). This study has significance for further investigating the response of nutrient biogeochemistry to the increasing nutrient levels in aquatic environments.     

Effects of submerged macrophytes on sediment resuspension and internal phosphorus loading in Lake Hiidenvesi (southern Finland)

The effects of submerged macrophytes on sediment resuspension and internal phosphorus loading in the shallow Kirkkoj?rvi basin of Lake Hiidenvesi were studied by sedimentation traps and sediment and water samples. During the 83 d study period, 793 g DW m(-2) of sediment was resuspended within the stand formed by Ranunculus circinatus, Ceratophyllum demersum and Potamogeton obtusifolius. Outside the stand, 1701g DW m(-2) sediment resuspension was measured during the same period. Water turbidity and concentration of suspended solids (SS) were significantly lower within the plant bed compared with the surrounding water area. Despite the higher concentration of inorganic suspendoids, the concentration of chlorophyll a was higher in the open water than within the submerged plant bed, owing to the enhanced nutrient recycling rate in the absence of submerged plants. With the resuspended sediment, 11.8 mg Pm(-2)d(-1) was brought into the water column within the stand and 24.5 mg Pm(-2)d(-1) outside the stand. Within the macrophyte stand, resuspended particles absorbed phosphorus from the water (indicated by the inverse relationship between SS and soluble reactive phosphorus), which was probably connected to the lowered phosphorus concentration of surface sediment due to uptake by macrophytes.     

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.     

The effects of sediment size fraction and associated algal biofilms on the kinetics of phosphorus release

Experiments using flumes containing sediment of three different size fractions, from two sites on the River Tame, investigated the influences of sediment particle size, and an associated biofilm, on sediment-water exchanges in heterogeneous sediment deposits. This is the first study undertaken to understand the kinetics of the release of soluble reactive phosphorus from sediments of natural systems to identify which of the size compartments affected those fluxes most. Samples of fine material (<2 mm), gravel (2-20 mm), and stones (>20 mm) were collected over a period of several weeks and brought to a fluvarium where they were placed in artificial, controlled flow, and flume channels. Synthetic solutions of similar ionic strength to the river were prepared using calcium chloride. Temperature, pH, and dissolved oxygen of the solution overlying the sediment were monitored automatically whilst filtered samples were obtained at 2 h intervals over 48 h. The biomass, expressed as mg m(-2) chlorophyll a, of the algal component of the biofilm from the surface of the sediment was estimated using methanol extraction. Differences in the responses were observed between the sediment size fractions and the two sites, where contaminant concentrations varied. The equilibrium phosphate concentration and a phosphorus transfer index were used to establish that there was a net uptake of phosphorus by all three sediment size fractions, from both sites, at the time of sampling. The kinetic results showed very fast initial reactions of phosphorus release from the larger size fractions with a well-developed filamentous algal growth present implying a different mechanism than diffusion being involved. The stones and associated biofilms also released more phosphorus than the fine fraction, e.g. final release concentrations for the most contaminated site were: fines approximately 2.5 microM, gravel approximately 6.5 microM, and stones approximately 65.0 microM (expressed as soluble reactive phosphorus). Phosphorus fluxes, calculated assuming the concentration of phosphorus in the sediment was less than the equilibrium concentration, were a maximum at the most contaminated site, e.g. fines 6.4 nmol m(-2) s(-1), gravel 27 nmol m(-2) s(-1), and stones 109 nmol m(-2) s(-1) (normalised with respect to the river bed area). These results confirm that sediment having a biofilm and associated particulate material results in a greater flux than fine sediment, which does not support a filamentous biomass. Removal of the fine particulates trapped in the algal growth reduced soluble phosphorus release. These factors demonstrate that both gravel and stone substrates have an important control over the release of soluble reactive phosphorus.