Predicting organic carbon-water partitioning of hydrophobic organic chemicals in soils and sediments based on water solubility

For predicting organic carbon-water partitioning of organic pollutants in soils and sediments, a simple empirical relationship is derived from Raoult's law and fitted to data sets of experimental organic carbon normalized partition coefficients (K(oc)) and aqueous solubilities (S(i)) of 64 hydrophobic organic chemicals (HOCs) from literature including mono- and polycyclic aromatic hydrocarbons, halogenated monoaromatic and alkyl hydrocarbons, and polychlorinated biphenyls. Although over 5 orders of magnitude are covered in sorptivity (logK(oc)), the new relationship (logK(oc)=-0.85 logS(i)-0.55) predicts K(oc) with an average absolute deviation of only 0.23 log units. The relationship between K(oc) and S(i) is inverse and slightly nonlinear. The product of K(oc) times S(i) (=K(oc)( *), which indicates the theoretical maximum contaminant loading at its solubility limit per unit mass of organic carbon) is 0.098kgkg(-1) and 0.012kgkg(-1) for compounds with water solubilities of 1gL(-1) and 1mugL(-1), respectively.     

Phase association of polycyclic aromatic hydrocarbons in the Minjiang River Estuary, China

Persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) are of great concern due to their persistence, bioaccumulation and toxic effects. In this work the levels of 16 priority PAHs were determined in water, pore water, sediment, soil and vegetable samples from Minjiang River Estuary, China. Total PAH concentrations varied from 9.9 to 474 microg/l in water, 82.1 to 239 microg/l in pore water, 112 to 877 ng/g dry wt. in surficial sediments, 128 to 465 ng/g dry wt. in soil and 8600 to 111,000 ng/g dry wt. in Chinese vegetables. Overall, the mean concentrations of PAHs were present in higher levels in pore water than that in surface water, due possibly to higher concentrations of dissolved organic carbon or colloids with which the hydrophobic pollutants were strongly associated. Such a concentration gradient implies a potential flux of pollutants from sediment pore water to overlying water. Contamination was dominated by high molecular mass PAH compounds in all samples, indicating combustion-derived sources (for example, pyrolysis at high temperature). The levels of PAHs in water and vegetable were relatively high in comparison to other studies, although PAHs in sediment and soil were comparable to those found in many other similar environments. The ratios of selected PAHs indicated again that PAHs in Minjiang River Estuary were mainly derived from incomplete combustion of fossil fuel.     

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.     

Mercury and methylmercury concentrations and loads in the Cache Creek watershed, California

Concentrations and loads of total mercury and methylmercury were measured in streams draining abandoned mercury mines and in the proximity of geothermal discharge in the Cache Creek watershed of California during a 17-month period from January 2000 through May 2001. Rainfall and runoff were lower than long-term averages during the study period. The greatest loading of mercury and methylmercury from upstream sources to downstream receiving waters, such as San Francisco Bay, generally occurred during or after winter rainfall events. During the study period, loads of mercury and methylmercury from geothermal sources tended to be greater than those from abandoned mining areas, a pattern attributable to the lack of large precipitation events capable of mobilizing significant amounts of either mercury-laden sediment or dissolved mercury and methylmercury from mine waste. Streambed sediments of Cache Creek are a significant source of mercury and methylmercury to downstream receiving bodies of water. Much of the mercury in these sediments is the result of deposition over the last 100-150 years by either storm-water runoff, from abandoned mines, or continuous discharges from geothermal areas. Several geochemical constituents were useful as natural tracers for mining and geothermal areas, including the aqueous concentrations of boron, chloride, lithium and sulfate, and the stable isotopes of hydrogen and oxygen in water. Stable isotopes of water in areas draining geothermal discharges showed a distinct trend toward enrichment of (18)O compared with meteoric waters, whereas much of the runoff from abandoned mines indicated a stable isotopic pattern more consistent with local meteoric water.     

Sediment-water exchange of Vibrio sp. and fecal indicator bacteria: implications for persistence and transport in the Neuse River Estuary, North Carolina, USA

In estuaries, frequent resuspension and deposition of sediment complicate bacterial transport model development by transporting particle-attached bacteria and possibly inducing bacterial responses, such as growth, degradation, or changes in attachment. In order to better characterize these dynamics, observations were made in the Neuse River Estuary (NRE) using the combination of an in situ sampler to monitor the water column and sediment cores to monitor sediment concentrations. Two allochthonous bacteria, Escherichia coli (EC) and Enterococcus sp. (ENT), were selected as proxies for fecal contamination from stormwater runoff. Vibrio sp. (VIB), native to the NRE, was also observed as an autochthonous bacterial group that includes potentially pathogenic species. Two sampling periods were identified as dominated by different suspension types: runoff and resuspension. Despite this difference, several bacterial measures remained comparable between sampling periods. In bottom water, VIB concentration was correlated with salinity and ENT concentration was correlated with turbidity. Differences were observed for EC, where higher concentrations were found in hypoxic waters and sediment during the resuspension period. In the sediment, EC and VIB concentrations significantly increased following the passage of Hurricane Ophelia in September 2005. Throughout this study, all bacterial groups showed evidence of persistence in sediment, suggesting that sediment resuspension represents a significant source of bacteria to the water column.     

PAH fluxes in the Laja Lake of south central Chile Andes over the last 50 years: evidence from a dated sediment core

This paper reports the occurrence of polyaromatic hydrocarbons (PAHs) deposition inferred from a sediment core of an Andean lake in south central Chile. Sediments were carefully collected from one of the deepest section of the lake and sliced every 1 cm. The samples were analyzed for PAHs, (137)Cs, (210)Pb, organic carbon and grain-size. The stratigraphic chronology and the sedimentation rates were estimated using the sedimentary signature left by the (137)Cs and (210)Pb fallout as temporal markers. PAHs were quantified by HPLC-fluorescence detection (HPLC-Fluorescence). 15 priority EPA PAHs were analyzed in this study. Based on these results, PAH deposition over the last 50 years was estimated (a period characterized by an important intervention in the area). PAH concentration ranged from 226 to 620 ng g(-1) d.w. The highest concentrations of PAHs were found in the core's bottom. The PAH profile is dominated by the presence of perylene indicating a natural source of PAH. In addition, two clear PAH deposition periods could be determined: the most recent with two-four rings PAHs, the older one with five-seven rings predomination. Determined fluxes where 71 to 972 microg m(-2) year(-1), dominated by perylene deposition. PAH levels and fluxes are lower compared to the levels found in sediments from remote lakes in Europe and North America. It is concluded that the main source of PAHs into the Laja Lake sediments are of natural origin.     

PAH and metal mixtures in New Orleans soils and sediments.

The purpose of this study is to determine the degree of PAH contamination and the association of PAHs with inorganic substances in soils and sediments of New Orleans. Bonnet Carré Spillway (BCS) (n = 5) provides modern baseline data, while urban soil samples (CTY) (n = 27) and sediment samples from Bayou St. John (BSJ) (n = 11) provide experimental data for New Orleans. Soil samples were collected from the top 2.5 cm of the surface, air-dried, and sieved (2 mm). Sediments samples were collected with a Wildco-Ekman bottom dredge, air-dried and finely ground. Accelerated solvent extraction (ASE) was used to release PAHs from the samples and analysis was conducted with gas chromatography-mass spectrometry (GC-MS). Metals were extracted using a 5:1 ratio of 1 mol/L nitric acid (room temperature) for soil and sediment samples, shaken for 2 h, centrifuged (1000 x g for 15 min) and filtered. Metal analysis was done by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Mann-Whitney tests show PAH differences (P < 0.001). Ranking of total PAHs is, BSJ sediments (10.3 mg/kg) > CTY soils (3.7 mg/kg) > BCS alluvium (0.28 mg/kg). The sum of the metals are similar for BSJ sediments (698 mg/kg) and CTY soils (679 mg/kg) and significantly lower for BCS (189 mg/kg). Manganese of these samples is similar for each site. For paired samples, Pearson Product Moment Correlation tests reveal that many PAHs are strongly associated with each other at all locations. For BCS alluvium and BSJ sediments, total PAHs are not significantly associated with total metals. For CTY, most pairs of metals are significantly associated, and total soil PAHs are strongly associated with total soil metals (correlation 0.78, P = 4.9 x 10(-4)). The linear model, total soil PAH = 136.3 + 6.25 (total soil metals) forms the basis for a predicted PAH map of New Orleans. Previous empirical research demonstrates an association between soil lead and children's lead exposure. This study indicates that PAHs are part of the soil mixture of accumulated substances and by-products of industrial society that presents exposure potential in cities.     

Selenium concentration, speciation and behavior in surface waters of the Canadian prairies

Similar to the San Joaquin Valley of California, the Canadian prairies are underlain with seleniferous shale and have recently witnessed a significant expansion in irrigated agriculture. The irrigated acreage in the prairies is expected to further increase due to global warming and changes in human use patterns. This raises concerns over potential selenium (Se) contamination in prairie surface waters and risk of adverse biological effects. To test the potential for elevated Se in the prairies, Se concentrations and speciation were examined in surface water, sediments, and sediment porewater in three water bodies in southern Manitoba, Canada, along a north-south transect with a gradient of irrigation and agricultural activities. A selenite addition experiment was also performed in mesocosms in a prairie wetland to assess the risk of increasing Se loading to the prairie waters. Overall, our results indicate that Se concentrations in the prairie waters of southern Manitoba are presently low except during the snowmelt season, that Se speciation is dominated by selenate which is of lower toxicity than selenite, and that if additional selenite is discharged into the prairie waters, it will be quickly removed from the surface water to the sediment. The low Se risk in the Canadian prairies is attributed to high soil drainability and relatively small scale of irrigation at present. The Se problem as being experienced in central California is thus unlikely to occur in surface waters of the Canadian prairies, although Se contamination in ground water is possible should the irrigated acreage continue to increase.     

Polycyclic Aromatic Hydrocarbons (PAHs) in urban topsoils: Concentration and source analysis in Xuzhou,China

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic pollutants in urban environments and are considered as the priority pollutants by the US Environmental Protection Agency (EPA). In this study, surface soils (0–10 cm) samples from 41 sampling sites in Xuzhou (China) were collected and analysed for 16 EPA priority polycyclic aromatic hydrocarbons via gas chromatograph/mass spectrometry (GC-MS). Total PAHs concentrations were in the range of 526 to 8612 ng/g with a mean of 2468 ng/g. Total PAHs concentrations were compared to guideline and results showed that nearly all urban soils in our study can be classified as heavily contaminated (>1000 ng/g). Carcinogenic PAHs were detected in relatively high concentrations and contributed 40.2% of the total PAHs in the urban soils. Multivariate statistical analysis including cluster analysis and factor analysis were performed and grouped the 16 PAHs under 2 clusters, which could indicate that the PAHs had different origins. The values of PAHs isomer indicated that vehicular emission might contribute to the soil PAHs in urban topsoils. The carcinogenic potency of PAH compounds was calculated and was found to be insignificant at the present level of emissions in Xuzhou.     

Mass balance for polycyclic aromatic hydrocarbons in the urban watershed of Le Havre (France): transport and fate of PAHs from the atmosphere to the outlet

Polycyclic aromatic hydrocarbon (PAH) concentrations have been monitored simultaneously in ambient air, bulk atmospheric deposition and runoff waters during one year in a small urban watershed of the Seine river basin (France). PAH fluxes from the atmosphere to the outlet of the urban watershed have been calculated to establish a mass balance for PAHs. PAH flux in runoff waters was 5.2 kg km(-2) yr(-1) while PAH atmospheric deposition was 0.21 kg km(-2) yr(-1). The comparison between atmospheric input and output by runoff has shown the importance of street deposits that appeared to be the most important source of PAHs for surface waters in urban areas. PAH profiles in the various compartments showed the fate of PAHs in the air-water system: proportion of carcinogenic PAHs was more important in runoff waters (35%) than in bulk atmospheric deposition (22%) and air (6%).     

Assessing the impact of swales on receiving water quality

Swales are one type of sustainable drainage system (SuDS) which contribute to the management of water quality in receiving waterbodies. Using a semi-quantitative approach, an impact assessment procedure is applied to the residual water quality that is carried forward to surface waters and groundwaters following treatment within a swale. Both volumetric and pollutant distributions are considered as stormwater passes through the swale system. The pollutant pathways followed by TSS, nitrate, chloride, metals (Cd, Cu, Pb, Zn) and polyaromatic hydrocarbons (PAHs) are determined for a swale receiving highway runoff. For TSS, metals and PAHs between 20% and 29% of the total mean influent pollutant load is predicted to be directed to infiltration through the underlying soils compared to between 4% and 16% of chloride and nitrate. Although surface water impacts are deemed possible, the discharges of swales to groundwaters are assessed to represent a negligible impact for effectively maintained systems.     

Polycyclic aromatic hydrocarbons (PAHs) and organochlorines (OCs) in bottom sediments of the Guba Pechenga,Barents Sea,Russia

Surface sediment samples from the Guba Penchenga and adjacent areas: Varangerfjord, Guba Malaya Volokovaya and Guba Bol'shaya Volokovaya (south-western Barents Sea) collected in March-April 1997 were analysed for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), chlorinated pesticides: p,p'-DDT, p,p'-DDE, p,p'-DDD, alpha- and gamma-HCH, and hexachlorobenzene (HCB). Mean summation operator PAH (sum of the two- to six-ring PAHs) concentration in sediments from the Guba Pechenga (1481 ng/g dry wt.) was significantly higher than in sediments from adjacent areas (252 ng/g dry wt.), where PAH contamination levels were similar to reported for unpolluted sediments of the northern Norway fjords and open parts of the Barents Sea. Differences between HCB levels as well as summation operator HCH (sum of alpha- and gamma-HCH) levels found in Guba Pechenga sediments and adjacent area sediments were not significant. Concentrations of these contaminants varied in ranges 0.28-1.76 and 0.05-0.68 ng/g dry wt., respectively, and were consistent with literature data on PAH levels in sediments from the northern Norway harbours, Kola Bay (Russia) and south-eastern part of the Barents Sea. Average total DDT concentration in Guba Pechenga sediments (10.5 ng/g dry wt.) was one and 2-3 orders higher than those found in sediments from the Pechora Sea and from the seas of eastern Arctic, respectively, however, it was comparable with DDT levels reported for harbours of northern Norway and Kola Bay. Significant difference between total DDT levels in Guba Pechenga and in the adjacent areas (mean 1.8 ng/g) was found. Among compounds of DDT family, p,p'-DDT isomer prevailed in all sediment samples indicating a possible local 'fresh' DDT source. Mean summation operator PCB (sum of PCB-28, 31, 52, 101, 118, 105, 153, 138, 156, 180, 209) concentration in the Guba Pechenga sediments (12.8 ng/g dry wt.) was significantly higher than in sediments of adjacent areas (2.1 ng/g dry wt.), but it was lower in comparison with summation operator PCB levels reported for the northern Norway harbours and Kola Bay sediments. The highest levels of contaminants were found in sediments collected close to the Liinakhamari harbour. The origin of both PAHs and OCs in the Guba Pechenga sediments is a combination of local sources and long-range transport from lower latitudes.     

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.     

A study of the cycling of manganese and other elements in a seasonally anoxic lake, Rostherne Mere, U.K.

The vertical distribution of sulphate, dissolved sulphide, alkalinity, pH, total iron and manganese, Fe(II) and Mn(II) and humic substances was monitored for a year in a seasonally anoxic lake, Rostherne Mere, U.K. During summer stratification Mn(II), probably of sediment origin, accumulated in the hypolimnetic bottom waters to a concentration of 50μm. Release occurred in two stages and appeared to be related to the supply of organic material to the sediment. No ferrous iron or dissolved sulphide were detected in the water column, although they were measured in the interstitial waters of the sediment. Ferrous sulphide formation in the sediment controls the iron(II) and dissolved sulphide concentrations and so minimises the concentration gradients at the sediment-water interface. Electron acceptors other than oxygen are capable of oxidising ferrous and sulphide ions in the water column. pH and alkalinity were the only other chemical components to show appreciable variation with depth, reflecting the biological processes of photosynthesis, respiration and decomposition. Iron and humic substances simultaneously increased in the surface waters after a major flood indicating that they are both present in the solution in contact with the soils of the catchment.     

Spatial and vertical distribution of polycyclic aromatic hydrocarbons in mangrove sediments

The distribution and historical changes of polycyclic aromatic hydrocarbons (PAHs) contamination in mangrove sediments in Hong Kong SAR were investigated. Surface sediments (2-3 cm) collected from four mangrove swamps exhibited significant spatial variations in concentrations of total PAH (with SigmaPAHs ranging from 56 to 3758 ng g(-1) dry wt), as well as the composition of 16 USEPA priority PAH compounds. Within a small swamp with an area of 0.68 ha, the total PAH concentrations also differed from sampling site to site, indicating that the PAH contamination is localized and confined to a very small area within the same swamp. Discharges from municipal and industrial wastewater, urban runoff, oil leakage from boats and ships, and accidental oil spill are possible sources of the PAH contamination. The sediment depth profiles reveal that the surface sediment layer (0-5 cm) had lower total PAH concentrations than that in the bottom layer (15-20 cm), and PAH composition also changed with the sediment layers. Based on the estimated annual sediment deposition rate in Hong Kong SAR of around 0.4-0.5 cm, the present findings suggest that the PAH contamination was most serious between 1958 and 1979 but started to decline thereafter. Such decline was probably due to changes in petroleum usage in urban areas and a better control of wastewater discharges from 1980 onwards in this region.     

Runoff erosion and nutrient depletion in five Mediterranean soils of NE Spain under different land use

We investigated the influence of agricultural management and various plant covers related to the period of abandonment on soil properties, erosion and nutrient depletion in a typical Mediterranean area with sandy loam shallow soils. Cultivated soils (CS) with insufficient management, 5 year abandoned soils covered with meadow (A5), 25 year abandoned soils covered with dense scrubs (A25), 50 year abandoned soils covered with cork trees (A50) and soils in a 50 year pine reforested area (P50) were studied over a period of 6 months (May-October 1999). The soils were classified as Lithic Xerorthents. Both the differences in soil properties and response to rainfall events were mainly attributed to the different vegetation types and stages in land management. Principal components analysis (PCA) was performed on the results, by running the overall data determined after five rainfall events. The factors extracted by PCA of the samples by variables matrix represented the response of the environments to different rainfall intensities as a function of management or natural evolution after abandonment. CS environments showed the highest runoff and sediment yield as well as the highest amount of dissolved organic carbon (DOC) and nitrogen in runoff water. The sequence of abandonment (A5, A25 and A50) showed approximately the same runoff production, whereas eroded sediments (ES) and DOC were inversely correlated. Organic carbon in the ES and DOC in runoff water always increased with the period of abandonment, which accounted for consistent nutrient depletion. Nevertheless, the A50 environment (dominated by Quercus suber) showed the best soil properties, whilst the A25 environment with dense cover of Cistus monspeliensis and Calicotome espinosa seemed to cause a worsening effect on the soil's physical and chemical properties. This is probably because these environments are more severely damaged by wild fire occurrence. In terms of sediment yield, the P50 environment followed CS environment, indicating that reforestation followed by insufficient forest management may negatively affect both soil properties and response to the erosive action of rainfall.     

Chemical and ecotoxicological assessment of polycyclic aromatic hydrocarbon--contaminated sediments of the Niger Delta, Southern Nigeria

The extent of environmental contamination and sources of polycyclic aromatic hydrocarbons (PAHs) compounds to sediments of the Niger Delta, Nigeria were assessed using combined chemical analysis and toxicity bioassay techniques. Concentrations of two- to six-ring PAHs of molecular mass 128-278 and toxicity to Vibrio fischeri and Lemna minor are considered in this investigation. Levels of the sum of the 16 USEPA priority pollutant PAHs varied from 20.7 to 72.1 ng/g dry weight. Sediment PAH levels were highest in samples collected from Delta Steel located at the outskirts of Warri, and Quality control centre, Ughelli West; with total PAH concentrations of 72.1 and 67.5 ng/g dry weight, respectively. The overall levels of PAHs in this study are low compared to other regions and reveal moderate PAHs pollution in the sediments of the Niger Delta. Two- and three-ring aromatic hydrocarbons predominated in almost all the sediments, which indicate a petrogenic origin. The sediment total PAH (PAHtot) concentration, normalized to organic carbon content (OC), ranged from 120.2 to 1.99 ng PAHtot/mg OC; and showed distinctively that the sedimentary organic matter of the sample from Delta Steel is highly contaminated with PAHs, and had a value of 120.2 ng PAHtot/mg OC. The toxicity bioassays indicated that the sample collected from Warri Refinery Area (SDWRR) was the most toxic to V. fischeri, with an EC50 value of 0.45 mg sediment equiv./mL test medium; and samples from Ogunu (SDOGN) and Warri Refinery area (SDWRR) showed high toxicity to L. minor, with percent inhibitions of 42.6% and 33.67%, respectively, after 7 days of exposure. The total PAH concentrations showed no correlation with toxicity bioassays, and thereby implied that chemical analysis of PAHs cannot be an indicator of sediment toxicity.     

Natural inactivation of phosphorus by aluminum in atmospherically acidified water bodies

Atmospheric acidification of catchment-lake ecosystems may provide natural conditions for the in-lake control of P cycling. This process is based on the elevated transport of aluminum from acidified soils and its subsequent precipitation in the water body and is described for strongly acidified forest lakes, acidified and circumneutral reservoirs, and a moderately acidified alpine lake. In water bodies with episodically or permanently acidified inflows a pH gradient develops between lake water and tributaries due to: (i) neutralization of acidic inflows after mixing with waters with undepleted carbonate buffering system, and/or (ii) the in-lake alkalinity generation dominated by biochemical removal of NO3- and SO4(2-). With the pH increasing towards neutrality, ionic Al species hydrolyze and form colloidal Al hydroxides (Al(part)) with large specific surfaces and strong ability to bind orthophosphate from the liquid phase. Moreover, Alpart settles and increases the P sorption capacity of the sediment. The presence of Al(part) on the bottom reduces orthophosphate release from sediments after its liberation from ferric oxyhydroxides during anoxia because Al(part) is not sensitive to redox changes. Consequently, the natural in-lake P inactivation may be expected in any water body with elevated Al input and a pH gradient between its inlet and outlet.     

A review of the role of bed deposits in the phosphate eutrophication of lakes and rivers

The distribution of phosphates in fresh waters is briefly discussed and the different phosphorus cycles are mentioned. The chemistry of phosphorus in lakes is reviewed with special reference to the extraction methods used for the fractionation of phosphorus in soils and sediments. The models of the sediment‐water exchange are also discussed together with their environmental implications. The relevant publications on the adsorption by and desorption from sediments, especially clays, are reviewed with special reference to the adsorption mechanism on clays and the oxides of Fe and Al. The important topic of the desorption of phosphate from the relevant minerals and soils is presented with special reference to the effects of the sediment and water parameters affecting the release of phosphate from sediments.     

Distribution of some trace metals in Lochnagar, a Scottish mountain lake ecosystem and its catchment

Anthropogenic trace metals enter the entire ecosystem of Lochnagar solely through atmospheric deposition. Trace metals, including Hg, have been monitored in atmospheric deposition and lake water, and measured in catchment vegetation, aquatic plants and zooplankton, revealing contamination levels in the ecosystem. Furthermore, 17 sediment cores were taken from different areas of the lake. Hg, Pb, Cd, Zn and Cu were analysed in all the cores, which show that the sediments have been heavily contaminated by these trace metals since the 1860s. The distribution of trace metals in the lake sediments was found to be heterogeneous, with concentrations in the surface sediments varying significantly: 110-250 ng/g, 100-360 microg/g, 39-180 microg/g, 0.3-1.9 microg/g and 8-25 microg/g for Hg, Pb, Zn, Cd and Cu, respectively. Trends in the concentration profiles for different trace metals in the same core are different, as are the trends of the profiles for the same metal in different cores. Hence, a single sediment core cannot represent the pollution history of the whole lake. As the soils and sediments contain a high proportion of plant debris and the debris has a high affinity for Hg, resulting in Hg enrichment. Hg was measured in plant debris (> 63 microm) separated from catchment soils and lake sediments. Plant debris may play an important role in storing and transferring Hg in this ecosystem.