Speciation of aluminium, arsenic and molybdenum in excessively limed lakes

The possible existence of the potentially toxic oxyanions of Al (Al(OH)₄⁻), As (HAsO₄²⁻), and Mo (MoO₄²⁻) was examined in excessively limed lakes. In-situ dialysis (MWCO 1 kDa) was performed in the surface and bottom waters of two excessively limed lakes (pH 7.1-7.7) and one acidic lake (pH ∼ 5.4). The dialysable metal concentrations were compared to the equilibrium distribution of species as calculated with the geochemical code Visual MINTEQ incorporating the CD-MUSIC and Stockholm Humic models for complexation onto colloidal ferrihydrite and dissolved organic matter. Arsenic and molybdenum in the excessively limed lakes were to a large extent present in the dialysable fraction (> 79% and > 92% respectively). They were calculated to exist as free or adsorbed oxyanions. Most of the Al was observed to reside in the colloidal fraction (51-82%). In agreement with this, model predictions indicated aluminium to be present mostly as colloids or bound to dissolved organic matter. Only a small fraction was modelled as Al(OH)₄⁻ ions. In most cases, modelled values were in agreement with the dialysis results. The free concentrations of the three oxyanions were mostly low compared to toxic levels.     

Psychrotrophic bacteria in sediments from the great lakes

The in vitro growth rates at 0°C of 8 representative psychrotrophs, isolated from Great Lake's sediment, ranged from k values of 0.047-0.022 h⁻¹ and generation times of 14.46-30.69 h. Faster rates were obtained at 15, 20 and 25°C, ranging from k values of 0.205-0.055 h⁻¹ and generation times of 3.38-12.48 h, with the optimum growth rate occurring at either 20°C or higher. Measurement of in situ microbial growth at 0°C in sediment columns by direct microscopy and protein-labelling fluorescent staining showed increases in microbial numbers of 10-fold when the sediment columns were amended with glucose, and 23-fold when amendment was with a more natural supplement, specifically, algal detritus. Determination of the number of viable microorganisms in the sediment columns again showed that considerable increases occurred at 0°C when glucose and detritus were added as substrates. Examination of the types of microbes occurring, during the growth conditions at 0°C when the substrates were added, by microscopy, and isolation of representative microbial types by replica plating showed that different populations responded to the two amendments.     

Unexpectedly high radioactivity burdens in ice-rafted sediments from the Canadian Arctic Archipelago

Unexpectedly high specific activities of (137)Cs (1800-2000 Bq kg(-1) dry weight) have been detected in fine-grained sediments entrained in multi-year sea ice floes grounded in Resolute Bay near the center of the Northwest Passage through the Canadian Arctic Archipelago. These results are remarkable because: (1) the specific activities are about two orders of magnitude higher than average specific activities detected in previous studies of sea ice rafted sediments from the Arctic Ocean, (2) two independent observations of these unexpectedly high specific activities were made several years apart, (3) the sampling site is on the opposite side of the Arctic basin from potential radioactive sources such as disposal and weapons testing sites of the former Soviet Union and nuclear fuel reprocessing sites in western Europe, and (4) the closest compositional match to known geologic source regions is Banks Island, on the western edge of the Arctic Archipelago, although a smaller number of grains from one of the two samples were mineralogically matched to sediments in the Laptev Sea. Consequently, the sediments are probably not from a single distinct source and were likely mixed during sea ice transport. Coupled with previous observations of higher radionuclide specific activities in some sea ice rafted sediments relative to bottom sediments, these new observations indicate that comparatively high as well as variable radioactive contaminant burdens in ice rafted sediments must be common and geographically independent of proximity to known contaminant sources. The mechanisms that would facilitate these unexpected high radionuclide burdens in sea ice are not known and require additional study, as well as investigations of the implications for the transport and fate of contaminants in Arctic sea ice.     

Significance of phosphorus in lakes and coastal water sediments and benthos

The dynamics of availability of sediment phosphorus to the overlying water depends on P concentration of interstitial water which in turn depends on the redox intensity and the affinity of the solid sediment phases for P. In lakes and coastal waters substantial fractions of P become irretrievably deposited into the sediments, but in lakes the seasonal sequence of P release to the water from the sediments—after spring and fall overturn, preceding periods of massive algal growth—and of P binding to the sediments—prevailing during the later parts of the stagnation period—tends to facilitate algal blooms in shallow waters. With increasing depth of the lake the net removal of P from the water by the sediments becomes preponderant and the quantity of P released from the sediments to the epilimnion becomes small relative to other fluxes.Diffusional transport of P through interstitial water has been determined experimentally for various sediments; these results are compared with observed transfer rates across the sediment water interface in lakes and coastal waters.There are essentially the following ways for P to be deposited: (1) Adsorption of P on clays; (2) burying of detrital P; (3) chemical precipitation of apatite; and (4) diagenetic replacement of calcite (e.g. skeletal carbonate) by substitution of carbonate by phosphate. Accumulation of P, regenerated from detritus as it occurs most extensively in shallow waters and under conditions of counter-current systems (estuaries), does not in itself lead to an increase in the relative apatite saturation because the regeneration of one P atom is accompanied by an increase in acidity caused by the formation of ca. 106 CO₂ molecules. In order to exceed the critical ion product, the excess of CO₂ must be lost or neutralized. Such conditions are encountered in areas of upwelling, where excess CO₂ is lost to the atmosphere and under reducing conditions where denitrification and SO₄²⁻ reduction consume hydrogen ions.A simplified steady state model will be used to depict that the dynamics of P transformations—especially the rate of regeneration of P from phytoplankton, benthos, detritus, and sediments and the rate of supply of soluble P to the algae—are more important in determining productivity than is the concentration of P or the P-reserve.     

Mercury empirical relationships in sediments from three Ontario lakes

Total mercury (THg), methyl mercury (MeHg), total organic carbon (TOC), sediment bulk density (SBD), redox potential (Eh) and percent fines measurements were made on sediment cores collected along transects from littoral to profundal depths in Harp, Dickie, and Blue Chalk lake located on the Canadian Shield near Dorset, Ontario, Canada to determine whether empirical relationships exist among these sediment properties.MeHg was positively correlated with THg in all sediments with a MeHg:THg ratio (0.004 ± 0.004) comparable to other uncontaminated profundal lakes. MeHg, MeHg:THg and TOC decreased with sediment depth within the core for all lakes, whereas THg only showed a decrease in Harp Lake. MeHg:THg ratio in surficial sediments was positively correlated with Eh and negatively correlated with TOC [MeHg:THg = − 0.009 ? TOC (%) + 0.001 ? Eh (mV) − 1.902, p = 0.026]; whereas THg was positively correlated with TOC [log THg (ppb) = 0.026 ? TOC (%) + 1.400, p < 0.0001].     

Metal content of charcoal in mining-impacted wetland sediments

Charcoal is well known to accumulate contaminants, but its association with metals and other toxic elements in natural settings has not been well studied. Association of contaminants with charcoal in soil and sediment may affect their mobility, bioavailability, and fate in the environment. In this paper, natural wildfire charcoal samples collected from a wetland site that has been heavily contaminated by mine waste were analyzed for elemental contents and compared to the surrounding soil. Results showed that the charcoal particles were enriched over the host soils by factors of two to 40 times in all contaminant elements analyzed. Principal component analysis was carried out on the data to determine whether element enrichment patterns in the soil profile charcoal are related to those in the soils. The results suggest that manganese and zinc concentrations in charcoal are controlled by geochemical processes in the surrounding soil, whereas the concentrations of arsenic, lead, zinc, iron, phosphorus, and sulfur in charcoal are unrelated to those in the surrounding soil. This study shows evidence that charcoal in soils can have a distinct and important role in controlling contaminant speciation and fate in the environment.     

Phosphate removal in acidified and limed lake water

Biotic and abiotic removal of phosphate from lake water from the acidified Lake Gårdsjön as well as immediate changes in these processes upon liming were tested in laboratory experiments. Phosphate was added and analyses of particulate material from both sterilized and nonsterilized series permitted determinations of biotic uptake as the difference between the series. In the original lake water (pH 4.7) biotic uptake largely dominated phosphate removal and abiotic precipitation was of minor importance.In the limed series at pH 7.2 the results had changed and abiotic precipitation dominated the phosphate removal and biotic uptake was strongly reduced. Of the analysed metals, Ca, Mn, Fe and Al, only Fe and Al occurred in the particulate material. The coprecipitation of phosphate and iron was probably due to adsorption on iron hydroxide at both pH values. The nature of phosphorus-aluminium precipitates is largely unknown but different possible complexes are discussed as well as the relative importance of iron and aluminium precipitates.Application of the results in relation to the ongoing lake liming and phosphorus fertilization are discussed.     

Characterization of bottom sediments in lakes using hydroacoustic methods and comparison with laboratory measurements

The acoustical properties of bottom sediments in two lakes were shown to be strongly correlated with clay content, organic C and total N concentrations, and other important sediment properties. The fractal dimension of the bottom echo was more strongly correlated with sediment physical and chemical properties than energy-based measures. The fractal dimension was also related to rates of PO₄-P and NH₄-N release from intact sediment cores and sediment oxygen demand. Measurements made at 430-kHz were more sensitive to differences in sediment properties than 201- or 38-kHz. Hydroacoustic measurements allow rapid assessment of properties important in lake restoration and water resource management.     

Horizontal and vertical variability of mercury species in pore water and sediments in small lakes in Ontario

Mary Lake, St. George Lake, and Philips Lake are located in the Greater Toronto Area, Ontario, Canada. These lakes are relatively small and have no direct inflow and outflow channels. Mercury (Hg) input to the lakes comes mainly from atmospheric deposition. Sediment cores from the points of the maximum lake depth and surface sediment samples from the points of maximum lake depth to the bank of each lake were collected in October 2005. Total and methyl mercury concentrations in the pore water and sediments of these samples were determined. In these small lakes with high organic content, there was no correlation between organic content and total mercury (THg) in the samples throughout the entire sediment cores while strong positive correlation between these two parameters was observed in all the surface sediments. Compared with typical methylmercury (MeHg) depth-profiles of sediment cores in other studies, where MeHg concentrations and methylation rates decreased sharply with increasing depth, MeHg distributions in the sediment cores in this study showed that MeHg might have been produced not only in the upper sediment but also in the deeper sediments, which resulted in a larger MeHg reservoir in the sediment. Organic matter, to some extent, affected MeHg distributions in the samples throughout the entire sediment cores. Concentrations of MeHg in all the surface sediments, however, were not controlled by organic matter, whereas they were largely a function of water column depths. Total mercury concentrations in pore water were relatively homogenous in both the sediment cores and surface sediment while MeHg in pore water generally deceased with increasing depth in the sediment cores and increasing distance from the centre of the lakes in surface sediments. Methylmercury contributed 1% to 76% of THg in the pore water samples. Concentrations and distributions of MeHg in overlying water and sediment-surface water in Mary Lake and St. George Lake suggested that both in situ production of MeHg in lake water and the release of MeHg from sediment contributed to high MeHg in deep anoxic water.     

大连湾表层沉积物中汞的赋存形态与生物可利用性研究

为了解大连湾沉积物中汞的赋存形态和生物可利用性,对大连湾表层沉积物中总汞(THg)和甲基汞(Me Hg)的含量进行了分析,并采用选择连续提取法对表层沉积物中汞的赋存形态进行了研究,探讨了沉积物中汞的赋存形态与甲基汞的关系。结果表明:大连湾表层沉积物中总汞和甲基汞的平均含量分别为95.1、0.71 ng/g,甲基汞占总汞的比例(甲基化率)为0.76%,与自然背景值相比,沉积物中总汞含量明显受到了人类活动的影响;大连湾表层沉积物中各赋存形态汞比例的平均值由小至大依次为水溶态汞(Hg-w)(3%)<胃酸溶解态汞(Hg-h)(10%)<硫化物结合态汞(Hg-s)(24%)<有机结合态汞(Hg-o)(31%)<强络合态汞(Hg-e)(32%),Hg-e、Hg-o和Hg-s为主要存在形态;沉积物中Hg-w、Hg-h和Hg-o与甲基化率呈正相关,显示Hg-w、Hg-h和Hg-o具有较高的生物可利用性。研究表明,采用选择连续提取法进行沉积物中汞赋存形态的研究,对了解沉积物中汞的生物可利用性具有较好的指示意义。     

Metal contamination in sediments from a desalination plant effluent outfall area

To assess the impact of seawater desalination effluent discharges on the receiving water body, the outfall area of a small desalination facility on the northwestern coast of the Arabian Gulf (Saudi Arabia) was investigated for metal contamination. Sediment samples were collected from a 6 x 6 km2 area and were analyzed for metal concentrations. Cadmium, cobalt, copper, mercury, vanadium, iron, phosphorus and zinc were very high in the sediment samples from the immediate vicinity of the outfall, and decreased progressively away from it. Contour maps of elemental concentrations confirm the above conclusions. Barium and chromium showed a decreasing trend towards the outfall, but this could be related to drilling activities in a nearby oil field (barium and chromium were high in the drilling mud). Concentrations of nickel, lead, and titanium exhibited no general trend in the sediment samples.     

Rain water leachates of heavy metals in road surface sediments

Samples of street surface and roadside gutter sediments within a separately sewered catchment in N.W. London have been analysed for heavy metal contamination. Particle size distributions are presented and the removal efficiency of metal species demonstrated for various street cleaning procedures. Laboratory sorption and desorption studies are described and solution concentrations are obtained for Pb, Cd and Mn.Solubility curves are typically variable with time with Mn showing the strongest tendency to attain equilibrium. No obvious dependence of metal concentrations on grain size is readily apparent although Cd tends to desorb more rapidly from size fractions greater than 250 μm.     

Metal fractionation study on bed sediments of River Yamuna, India

The pollution of aquatic ecosystem by heavy metals has assumed serious proportions due to their toxicity and accumulative behavior. The toxicity and fate of the water borne metal is dependent on its chemical form and therefore quantification of the different forms of metal is more meaningful than the estimation of its total metal concentrations. In this study fractionation of metal ions on bed sediments of River Yamuna has been studied to determine the eco-toxic potential of metal ions. The investigations suggest that copper have a tendency to remain associated with residual, reducible and carbonate fractions. The Risk Assessment Code reveal that about 30-50% of lead at most of the sites exist in exchangeable fraction while 30-50% of cadmium at almost all the sites is either exchangeable or carbonate bound and therefore comes under the high risk category and can easily enter the food chain. Most of the copper is in immobile fraction at Delhi while at other sites, a sizable portion (10-30%) is found in carbonate fraction thus posing medium risk for the aquatic environment. Fractionation pattern of zinc shows low to medium risk to aquatic environment.     

Organochlorinated pesticide multiresidues in surface sediments from Beijing Guanting reservoir

For the analysis of organochlorine pesticides (OCPs) in sediments and water, a multiresidue analysis method based on gas chromatography with electron capture detection (GC/ECD) was developed. Solid-phase extraction (SPE) using Oasis HLB cartridges was also applied in sample extraction. Mean recoveries were satisfactory with 72-103% and 71-103% for water and sediment, respectively. Twenty-one OCPs were analyzed in water and surface sediment samples from Beijing Guanting reservoir. Total concentrations of 21 OCPs were 16.7-791 ng/l (mean 234 ng/l), 275-1,600 ng/l (mean 644 ng/l), 5250-33,400 ng/kg (mean 13,000 ng/kg) in surface water, pore water and sediment (dry weight), respectively. P, p'-DDE, delta-HCH, aldrin, gamma-HCH and beta-HCH are the most abundant compounds in water while p, p'-DDE, o, p'-DDT, beta-HCH, delta-HCH, p, p'-DDT and aldrin accounted for about 85% of total 21 OCPs in sediment in Beijing Guanting reservoir. Concentrations of OCPs were high both in water and sediment samples in Beijing Guanting reservoir for municipal water supply. The data provides information on the levels and sources of OCPs in Guanting reservoir. The study indicated that measures should be taken to decrease OCPs residues in order to improve the quality of municipal water supply in Beijing.     

Factors contributing to the internal loading of phosphorus from anoxic sediments in six Maine, USA, lakes

Phosphorus (P) is the limiting macronutrient for primary production in most lakes. Seasonal anoxia in the hypolimnion of lakes has been strongly correlated with internal P loading to the water column. Gravimetric sediment cores were collected before and after the onset of anoxia in six Maine (USA) lakes during the summer of 2003. This study investigates the relative importance of P sequestration by aluminum hydroxide (Al(OH)3(s)), and ferric (oxy)hydroxide (Fe(OH)3(S)) dissolution with subsequent P release in lakes with varying trophic status. Two lakes, Pennesseewassee and Highland, are oligotrophic. The remaining lakes, China, Cobbosseecontee, Webber and Salmon, have varying levels of productivity. Sediment P, Al and Fe in the top 10 cm were extracted sequentially using ammonium chloride (NH4Cl), bicarbonate-dithionite (BD), and sodium hydroxide (NaOH) at 25 degrees C. The results suggest that a sediment [NH4Cl-Al+BD-Al+NaOH25-Al]:[NH4Cl-Fe+BD-Fe] molar ratio >3 and a sediment [NaOH25-Al]:[NH4Cl-P+BD-P] molar ratio >25 predict low P flux from sediments during the development of anoxia, as proposed by Kopácek et al. [Kopácek J, Borovec J, Hejzlar J, Ulrich K, Norton S, Amirbahman A. Aluminum control of Phosphorus Sorption in Lake Sediments. Environ Sci Technol 2005; 39: 8784-8789.], despite the development of anoxia in and the release of Fe(II) from the hypolimnia of the two study lakes. However, when these molar ratios are not exceeded the model does not adequately describe sedimentary P flux. The application of the model proposed by Kopácek et al. to Cobbosseecontee Lake suggests that its sediment may be a source of P to the water column. However, water column data indicate little to no sedimentary P flux. Therefore, the lack of P flux may be attributed to the absence of Fe(III) reduction in the Cobbosseecontee Lake sediment or perhaps to the slow diagenesis of organically-bound P.     

Mercury cycling between the water column and surface sediments in a contaminated area

Mercury cycling in the water column and upper sediments of a contaminated area, the Largo do Laranjo, Aveiro (Portugal), was evaluated after determination of reactive and non-reactive mercury concentrations in the water column and pore waters of sediments, collected in several places of this bay. In the water column, reactive mercury concentrations varied between 10 and 37 pmol dm(-3), the highest values being observed near the mercury anthropogenic source. However, reactive mercury was a narrowly constrained fraction of the total mercury, making up only 4-16% of the total, showing evidence of the importance of dissolved organic matter on mercury transport. In sediments, higher concentrations of mercury were also determined near industrial discharges. Results indicate the existence of an equilibrium between solid and liquid phases, determined by solid sediment/pore water distribution coefficients. Much of the mercury present in the solid fraction is associated with organic matter (r=0.837) and iron oxyhydroxides (r=0.919), but as oxides begin to dissolve in reduced sediments and organic matter decays, the adsorbed mercury is released. In fact, the mercury concentrations in pore waters of those contaminated sediments largely exceeded the values determined in the water column. As molecular diffusion may contribute to the dissolved mercury distribution in the overlying water column, this phenomenon was evaluated. However, the pore waters of Largo do Laranjo do not enrich the water column substantially in terms of reactive and non-reactive mercury. In fact, pore waters can contribute only to 0.2% and 0.5% of the reactive and non-reactive mercury present in the water column, respectively, showing that as long as mercury is being incorporated in sediments, it stays in stable forms.     

Distributions of total mercury and methylmercury in surface sediments and fishes in Lake Shihwa, Korea

The concentrations of total mercury (THg) and methylmercury (MeHg) in the sediments of Lake Shihwa, an artificial salt lake in Korea located near two large industrial complexes, were determined to investigate the state of Hg contamination in the lake sediments and the effect of local Hg source. THg and MeHg concentrations in the sediments, monitored for 2 years, ranged from 0.02 to 0.28 µg g^− 1 and ≤ 0.026 to 0.67 ng g^− 1, respectively. The overall distribution of Hg in lake sediments showed higher values near industrial complexes and in the central part of the lake. However, the correlations between Hg and environmental factors, such as organic material (OM) content, and acid volatile sulfide (AVS), were weak and did not clearly explain the variation in Hg distribution. The spatial distribution of sediment Hg and monthly precipitation data during the sampling period showed that the amount of runoff following rain events and water gate operation may be additional important factors regulating Hg level and distribution in lake sediments. The levels of THg in fish species in this lake ranged from 9.8 to 35 ng g^− 1, suggesting that the bioavailability of sediment Hg in the lake may be low. Although the THg concentrations in Lake Shihwa sediment were lower than those in other foreign study sites, they were higher than in neighboring coastal regions, and are constantly increasing. This result indicates that the nearby industrial complexes may be the major source of Hg found in the sediments of Lake Shihwa.     

Heavy metal pollution status in surface sediments of the coastal Bohai Bay

Bohai Bay, the second largest bay of Bohai Sea, largely due to the huge amount of pollutants discharged into it annually and its geohydrologic condition, is considered to be one of the most polluted marine areas in China. To slow down, halt and finally reverse the environmental deterioration of Bohai Sea, some researchers have proposed to connect it with Jiaozhou Bay in the western coast of Southern Yellow Sea by digging an interbasin canal through Shandong Peninsula. In order to assess the heavy metal pollution and provide background information for such a large geoengineering scheme, surface sediments from 42 stations covering both riverine and marine regions of the northwestern coast of Bohai Bay were analyzed for heavy metal content and fractionation (Cd, Cr, Cu, Ni, Pb and Zn). Three empirically derived sediment quality guidelines were used to assess the pollution extent of these metals. The studied metals had low mobility except for Cd at all stations and Zn at some riverine stations. Although a high mobility of Cd was observed, it could hardly cause a bad effect on the environment owing to its low total concentrations. Anthropogenic influence on the accumulation of studied heavy metals in sediments of Bohai Bay was obvious, but their contents were relatively lower to date comparing with some other marine coastal areas that receive important anthropogenic inputs. Taking as a whole, surface sediments of northwestern Bohai Bay had a 21% probability of toxicity based on the mean effects range-median quotient.     

Source characterization using compound composition and stable carbon isotope ratio of PAHs in sediments from lakes, harbor, and shipping waterway

Molecular compositions and compound specific stable carbon isotope ratios of polycyclic aromatic hydrocarbons (PAH) isolated from sediments were used to characterize possible sources of contamination at an urban lake, a harbor, a shipping waterway, and a relatively undisturbed remote lake in the northwest United States. Total PAH concentrations in urban lake sediments ranged from 66.0 to 16,500 microg g(-1) dry wt. with an average of 2600 microg g(-1), which is approximately 50, 100, and 400 times higher on average than PAH in harbor (48 microg g(-1) on average), shipping waterway (26 microg g(-1)), and remote lake (7 microg g(-1)) sediments, respectively. The PAH distribution patterns, methyl phenanthrene/phenanthrene ratios, and a pyrogenic index at the sites suggest a pyrogenic origin for PAHs. Source characterization using principal component analysis and various molecular indices including C2-dibenzothiophenes/C2-phenanthrenes, C3-dibenzothiophenes/C3-phenanthrenes, and C2-chrysenes/C2-phenanthrenes ratios, was able to differentiate PAH deposited in sediments from the four sites. The uniqueness of the source of the sediment PAHs from urban lake was also illustrated by compound specific stable carbon isotope analysis. It was concluded that urban lake sediments are accumulating PAH from sources that are unique from contamination detected at nearby sites in the same watershed.     

辽宁獐岛海滩表层沉积物粒度特征及输运

通过对獐岛海滩的60个表层沉积物样品进行粒度试验,分析了表层沉积物粒度变化特征。研究结果表明:研究区表层沉积物细颗粒与粗颗粒存在明显的分界线,距岸约12 m范围内主要为卵砾、粗砂、中砂(2Ф),12 m以外海滩主要为细砂(2Ф);沉积物平均粒径为2.51Ф,由岸向海逐渐变小,以负偏、宽平峰态为主,分选性较好(σi=0.58)。潮汐和波浪是研究区表层沉积物输送的主要水动力,岬角的存在影响了沉积物粒度的分布,由粒度分布变化趋势推断沉积物输移特征为双向输运,主要以跃移搬运方式为主。