Transport of NOM and trace metals through macropores in the Lake Skjervatjern catchment

In the dystrophic Lake Skjervatjern, located at the west coast of Norway, periods with high precipitation coincide with an increase in the concentrations of natural organic matter (NOM) and several trace elements. The lake has no visual inlets, and, during high flow periods, a major part of the drainage follows macropores, entering the lake 10–40 cm below the surface. Water from the lake and the macropores were fractionated according to size by means of a hollow fiber ultra-filtration technique, during two periods with high precipitation. In the macropores, the high molecular weight form of NOM (nominal molecular cut off > 10 kDa) appears to be an important transporting agent for several trace elements that strongly interact with NOM (e.g., Fe, Al, Pb, Sm, La, Ce, and Eu). In contrast, anionic (V and As) and acid sensitive (Mn and Cs) elements were, generally, at a low molecular weight form (nominal molecular cut off < 3 kDa). The latter showed similar or lower concentrations in the macropores compared to the lake water, and NOM were apparently of small importance as a carrier for V, As, Mn, and Cs. Differences in concentration and size distribution of trace elements between the macropores and the lake basins indicate that parts of NOM and associated trace elements that enter the lake in a high molecular weight form, undergo aggregation and gravitational settling and thereby become a part of the lake sediments.     

Association of organic matter, iron and inorganic phosphorus in lake waters

Gel permeation chromatography was used to fractionate ³²PO₄³⁻ labelled components by molecular size in filtered, destabilized lake foam, concentrated lake water, and lake sediment extracts. Evidence is presented for the abiotic formation of organic matter iron inorganic P complexes in lake foam, water and sediments. ³²PO₄^staggered was found to excahnge with low molecular weight, dissolved P fraction, probably an organic matter -Fe- inorganic P complex, but not with a high molecular weight, non-inorganic dissolved reactive P pool, hypothesized to be similar to the dimer. Our experiments suggest that inorganic P binding by high molecular weight organic matter may play a significant role in the P cycle. If the bound P is unavailable to algae and bacteria, the complexes could explain Rigler's (1968) hypothesis that the molybdenum blue technique may overestimate the free orthophosphate concentration by 10–100 times.     

Benthic macroinvertebrates along the soil/water interface of the HUMEX Lake 1989–1991

The taxonomic composition, abundance, and size distribution of benthic macroinvertebrates were studied at the soil/water interface two years before and the first year after the start of artificial acidification of a small catchment and its humic lake. The macroinvertebrate assemblage consisted mainly of predators; dragonflies (Odonata), damselflies (Zygoptera), net-building caddisflies (Polycentropodidae), diving beetles (Dytiscidae), and water bugs (Hemiptera). It is suggested that benthic and planktonic microcrustaceans are important prey for damselflies and that intraguild predation is important for the structure of the community. The typical bog tarn assemblage did not include snails, mussels, or macrocrustaceans, which are algae- and detritus feeders known to be affected by low pH. The only potential herbivores on filaments algae and shredders of coarse detritus were case building caddisflies and the ephemeropteran Leptophlebia vespertina, which were all found in low numbers. If the artificial acidification will eliminate these macroinvertebrates, it will have little impact on attached filaments algae, and on processing of coarse detritus. Although there was a general similarity in taxonomic structure on the two sides, significantly higher numbers of dytiscids (Acilius sulcatus and Ilybius spp.) were consistently found on the experimental side than on the control side through the three years of study. The first year after acidification, the number of Zygoptera was lower on the experimental side than on the control side. The abundance on the control side in this year was, however, also higher than in the previous two years. The size distribution of Coenagrion hastulatum, the dominating zygopteran, showed no difference between lake sides. Significant difference between years indicate, however, that size distribution could be used to detect altered growth conditions.     

Efficiency of the activated carbon filtration in the natural organic matter removal

The removal and transformation of natural organic matter were monitored in the different stages of the drinking water treatment train. Several methods to measure the quantity and quality of organic matter were used. The full-scale treatment sequence consisted of coagulation, flocculation, clarification by flotation, disinfection with chlorine dioxide, activated carbon filtration and post-chlorination. High-performance size-exclusion chromatography separation was used to determine the changes in the humic substances content during the purification process; in addition, a UV absorbance at wavelength 254 nm and total organic carbon amount were measured. A special aim was to study the performance and the capacity of the activated carbon filtration in the natural organic matter removal. Four of the activated carbon filters were monitored over the period of 1 year. Depending on the regeneration of the activated carbon filters, filtration was effective to a degree but did not significantly remove the smallest molar mass organic matter fraction. Activated carbon filtration was most effective in the removal of intermediate molar mass compounds (range 1,000-4,000 g/mol). Regeneration of the carbon improved the removal capacity considerably, but efficiency was returned to a normal level after few months.     

Acid deposition and watershed characteristics in relation to lake chemistry in northeastern Minnesota

The relationship between lake sensitivity to atmospheric acidic inputs and the neutralization capacity of watersheds is examined for 267 lakes in northeastern Minnesota. Three water chemistry/sensitivity measures (color, sulfate, and alkalinity) are correlated with variables representative of precipitation and sulfate inputs, hydrology, and the acid neutralization capacity of various watershed components. An ordinal scale for ranking bedrock and surficial deposit neutralization capacity is presented. The watershed variables found to account for the largest percentages of the variability in measured color, sulfate, and alkalinity levels are determined. Color is strongly related to the presence of peat or marsh and hydrologic renewal time, whereas sulfate is primarily related to atmospheric deposition, evaporative concentration, bedrock type, and the presence of coniferous forest. Variation in alkalinity is the most difficult of the water chemistry measures to explain; for headwater lakes, atmospheric sulfate input, water renewal time, the presence of deciduous forest, and the weatherability of underlying bedrock determine much of its variability. The results illustrate important averaging properties of watersheds from small headwater systems to large drainages and the difficulty in obtaining correlations for some water quality measures (e.g., alkalinity) when some variables, such as soils and land cover, are available only as large-area averages.     

The effect of acidification on abiotic interactions of dissolved humic substances, iron and phosphate in epilimnetic water from the humex Lake Skjervatjern

The responses to pH of abiotic interactions between dissolved humic substances, iron and phosphate were investigated by examining redistributions of ⁵⁵FeCl₃ and ³²PO₄³⁻ added to epilimnetic lakewater from Lake Skjervatjern. The simultaneous movement of ⁵⁵Fe and ³²P to fractions of 10 000–20 000 and > 100 000 Daltons nominal molecular weight, as indicated by Sephadex gel filtration, diminished in response to decreasing pH. Variations in transformations to larger molecular size fractions with incubation time revealed by gel filtration were erratic, but indicated that transformations of added ⁵⁵Fe and ³²P are complete after circa 24 h. Movement of ³²P to particle size fractions (>0.2 μm) was not dependent on pH, whilst transformations of ⁵⁵Fe to material of particle size increased as pH was lowered. Precipitation of added ⁵⁵Fe and ³²P was minimal at all pH values tested. Responses of precipitation losses to pH were not coincident for both radionuclides.     

Modeling long-term attainable soil organic carbon sequestration across the highlands of Ethiopia

Environment, Development and Sustainability - The objectives of this study across the highlands of Ethiopia were: (i) to characterize the association between soil organic carbon (SOC) stocks and...     

An assessment of toxicity in profundal lake sediment due to deposition of heavy metals and persistent organic pollutants from the atmosphere

A Tier I Sediment Ecological Risk Assessment of profundal lake sediment contaminated by diffuse pollution of heavy metals and POPs deposited from the atmosphere was completed. The concentrations of seven heavy metals and four groups of POPs (OCs, PCBs, PAHs, PBDEs) were determined in the profundal sediment of ten lakes in the United Kingdom and two sediment toxicity tests completed (chironomid survival and emergence and cladoceran survival and reproduction). The results showed that around half the lakes are at least moderately contaminated by Pb, Zn, Cd, As and PAHs deposited from the atmosphere and the toxicity quotient suggests that the contaminants of concern are Pb, As and PAHs, and not the other metals nor OCs and PCBs. There was toxicity in the sediment of four of the lakes. The Probable Effect Concentration Quotient values indicated that metals in the sediments of Scoat Tarn, Agden Reservoir and Llyn Llagi were likely to be responsible for the laboratory toxicity found in these lakes, with PAHs also contributing in Agden Reservoir.     

Predicting the transfer of radiocaesium from organic soils to plants using soil characteristics

A model predicting plant uptake of radiocaesium based on soil characteristics is described. Three soil parameters required to determine radiocaesium bioavailability in soils are estimated in the model: the labile caesium distribution coefficient (kd1), K+ concentration in the soil solution [mK] and the soil solution-->plant radiocaesium concentration factor (CF, Bq kg-1 plant/Bq dm-3). These were determined as functions of soil clay content, exchangeable K+ status, pH, NH4+ concentration and organic matter content. The effect of time on radiocaesium fixation was described using a previously published double exponential equation, modified for the effect of soil organic matter as a non-fixing adsorbent. The model was parameterised using radiocaesium uptake data from two pot trials conducted separately using ryegrass (Lolium perenne) on mineral soils and bent grass (Agrostis capillaris) on organic soils. This resulted in a significant fit to the observed transfer factor (TF, Bq kg-1 plant/Bq kg-1 whole soil) (P < 0.001, n = 58) and soil solution K+ concentration (mK, mol dm-3) (P < 0.001, n = 58). Without further parameterisation the model was tested against independent radiocaesium uptake data for barley (n = 71) using a database of published and unpublished information covering contamination time periods of 1.2-10 years (transfer factors ranged from 0.001 to 0.1). The model accounted for 52% (n = 71, P < 0.001) of the observed variation in log transfer factor.     

Constructing a spatially-resolved database for modelling soil organic carbon stocks of croplands in European Russia

This paper describes the conception and construction of a geographic information system (GIS) for use in modelling changes in soil organic carbon stocks in European Russia. A GIS of croplands for European Russia was constructed to allow the RothC and CANDY models, and a statistical model of humus balance, to estimate how soil carbon stocks change in time. The soil map of Russia, the database of soil properties, the map of administrative division, the land use map, the climatic grid, the map of natural and agricultural zoning and an economic database serve as a basis for this system. A map and database of homogeneous units, for maximum accuracy and minimum uncertainty, was created. Homogeneous characteristics are the parameters required for modelling. In the course of this work, the sources of errors in the database and the possible ways of improving calculation accuracy were determined and are described. The methods used and decisions taken in constructing this database are applicable to other studies in which GIS databases need to be constructing from disparate sources.     

Burial of terrestrial and marine organic carbon in Jiaozhou Bay: different responses to urbanization

Organic geochemical proxies (OC, OC/TN, δ¹³C, and lignin oxidation products) were measured in a 271 cm long sediment core collected from central Jiaozhou Bay, northern China, to study the response of terrestrial and marine organic carbon burials to the surrounding urbanization. Terrestrial organic carbon content was constantly low from the bottom of the core to ~150 cm depth, indicating a stable and low level of terrestrial input before urbanization. Thereafter, it increased up to ~20 cm depth, suggesting that increased human activities and land-use changes during urbanization likely enhanced the flux of terrestrial organic carbon to the bay. Overall, 5–38% of the total organic carbon was terrigenous, which was derived from a mixture of woody and non-woody angiosperms and moderately degraded. Marine organic carbon content did not increase notably during urbanization. It increased from the bottom of the core to ~180 cm and stayed at high levels until it decreased in the top 20 cm. It was affected by multiple factors, including grain size and nutrient composition. These results demonstrate the different influences of urbanization on terrestrial and marine organic carbon cycles and suggest the importance of discriminating between these two organic carbon pools in the reconstruction of their historical changes.     

Soil organic carbon dynamics of croplands in European Russia: estimates from the “model of humus balance”

The Model of Humus Balance was used to estimate the influence of climate effects and changing agricultural practices on carbon (C) levels in soddy–podzolic soils in the Russian Federation for the years 2000–2050. The model was linked with a spatial database containing soil, climate and farming management layers for identification of spatial change of C sequestration potential. Analysis of relationships between C, soil texture and climate indicated that compared with a business-as-usual scenario, adaptation measures could increase the number of polygons storing soil organic carbon (SOC) by 2010–2020. The rate of possible C loss is sensitive to the different climate scenarios, with a maximum potential for SOC accumulation expected in 2030–2040, thereafter decreasing to 2050. The effect is most pronounced for the arid part of the study area under the emission scenario with the highest rate of increase in atmospheric CO₂ concentration, supporting findings from the dynamic SOC model, RothC. C sequestration during the study period was permanent for clay and clay loam soils with a C content of more than 2%, suggesting that C sequestration should be focused on highly fertile, fine-textured soils. We also show that spatial heterogeneity of soil texture can be a source of uncertainty for estimates of SOC dynamics at the regional scale. Figures in color are available at     

Role of allochthonous carbon in the energy of terrestrial invertebrate communities at different distances from the Black Sea and a freshwater lake (Isotopic Evidence)

Isotopic analysis has become an important tool in the study of lateral links between ecosystems. The isotopic composition of carbon in terrestrial and aquatic primary producers can differ significantly, which provides an opportunity to identify the “marine” or “freshwater” carbon in the tissues of terrestrial animals. We measured the isotopic composition of C and N in tissues of soil invertebrates and estimated the proportion of “aquatic” carbon in the energy budget of terrestrial food webs at different distances from the Black Sea and a freshwater lake. Terrestrial predators are actively subsidized with carbon from the Black Sea to distance of up to about 50 m. The carbon subsidy from the freshwater lake is significant in the zone extending no farther than the forest border (ca. 15 m). Thus, the effect of allochthonous organic matter on terrestrial communities in both cases manifests itself only in a relatively narrow coastal strip.     

Radiocarbon and stable carbon isotope compositions of chemically fractionated soil organic matter in a temperate-zone forest

To better understand the role of soil organic matter in terrestrial carbon cycle, carbon isotope compositions in soil samples from a temperate-zone forest were measured for bulk, acid-insoluble and base-insoluble organic matter fractions separated by a chemical fractionation method. The measurements also made it possible to estimate indirectly radiocarbon ((14)C) abundances of acid- and base-soluble organic matter fractions, through a mass balance of carbon among the fractions. The depth profiles of (14)C abundances showed that (1) bomb-derived (14)C has penetrated the first 16cm mineral soil at least; (2) Delta(14)C values of acid-soluble organic matter fraction are considerably higher than those of other fractions; and (3) a significant amount of the bomb-derived (14)C has been preserved as the base-soluble organic matter around litter-mineral soil boundary. In contrast, no or little bomb-derived (14)C was observed for the base-insoluble fraction in all sampling depths, indicating that this recalcitrant fraction, accounting for approximately 15% of total carbon in this temperate-zone forest soil, plays a role as a long-term sink in the carbon cycle. These results suggest that bulk soil organic matter cannot provide a representative indicator as a source or a sink of carbon in soil, particularly on annual to decadal timescales.     

Determination of Cs in the water system of a pre-Alpine lake

The aim of this study was to measure the ¹³⁷Cs activity derived from the Chernobyl accident in the water system of Lake Wallersee, a pre-Alpine lake in Austria within an area highly contaminated by the Chernobyl fallout.     

Depth profiles of radiocarbon and carbon isotopic compositions of organic matter and CO2 in a forest soil

Depth profiles of the specific activities of (14)C and carbon isotopic compositions (Delta(14)C, delta(13)C) in soil organic matter and soil CO(2) in a Japanese larch forest were determined. For investigating the transport of CO(2) in soil, specific activities of (14)C, Delta(14)C and delta(13)C in the organic layer, and atmospheric CO(2) in the same forest area were also determined. The specific activity of (14)C and Delta(14)C in the soil organic matter decreased with the increase in depth of 0-60cm, while that of soil CO(2) did not vary greatly at a soil depth of 13-73cm and was more prevalent than that of atmospheric CO(2). Peaks of specific activities of (14)C appeared at the depth of 0-4cm and Delta(14)C values were positive in the depth range from 0 to 15cm. These results suggest that the present soil at a depth of 0-4cm had been produced from the mid-1950s up until 1963, and the bomb C had reached the depth of 15cm in the objective soil area. The delta(13)C in the soil organic matter increased at the depth of 0-55cm, while that of soil CO(2) collected on 8 November 2004 decreased rapidly at the depth of 0-13cm and only slightly at the depth of 53-73cm. By combining the Delta(14)C and delta(13)C of the respective components and using the Keeling plot approach it was made clear that the entering of atmospheric CO(2) showed a large contribution to soil CO(2) at the depth of 0-13cm and a negligible contribution at the depth of 53-73cm for soil air collected on 8 November 2004. Respiration of live roots was presumed to be the main source of soil CO(2) at the depth of 53-73cm on 8 November 2004.     

Source of radium in a well-water-augmented Florida lake

A study of the lake waters of Saddleback Lake, Florida was undertaken with the goal of determining the source of elevated radium activities in the lake. Four radium isotopes, (226)Ra, (228)Ra, (223)Ra and (224)Ra, were measured and activities of all the four radium isotopes were substantially greater in the well water used to augment the lake as compared to the lake waters. In the surface water, radium activities were highest close to the well used for augmentation in the initial sampling. Activities initially decreased with time after augmentation from the well ceased. The (223)Ra/(226)Ra activity ratio decreased during the first month of sampling and closely followed an exponential decay curve based on the (223)Ra decay constant. Trends in the activities and the (223)Ra/(226)Ra activity ratios support the conclusion that the well used to augment the lake was the dominant source of (223)Ra and (226)Ra to Saddleback Lake during this study. The (224)Ra/(226)Ra activity ratio did not follow the expected trend of exponential decay based on the (224)Ra decay constant. While the augmentation well supplied some (224)Ra, these results suggest that there must be an additional source of (224)Ra to the lake. The most likely additional source of (224)Ra appears to be the ingrowth of (224)Ra on the sediment within the lake from (228)Ra (via (228)Th).     

Impact of woody encroachment on soil organic carbon and nitrogen in abandoned agricultural lands along a rainfall gradient in Italy

Land use changes represent one of the most important components of global environmental change and have a strong influence on carbon cycling. As a consequence of changes in economy during the last century, areas of marginal agriculture have been abandoned leading to secondary successions. The encroachment of woody plants into grasslands, pastures and croplands is generally thought to increase the carbon stored in these ecosystems even though there are evidences for a decrease in soil carbon stocks after land use change. In this paper, we investigate the effects of woody plant invasion on soil carbon and nitrogen stocks along a precipitation gradient (200?C2,500?mm) using original data from paired experiment in Italian Alps and Sicily and data from literature (Guo and Gifford Glob Change Biol 8(4):345?C360, 2002). We found a clear negative relationship (?0.05%?C?mm^?1) between changes in soil organic carbon and precipitation explaining 70% of the variation in soil C stocks after recolonization: dry sites gain carbon (up to +67%) while wet sites lose carbon (up to ?45%). In our data set, there seem to be two threshold values for soil carbon accumulation: the first one is 900?mm of mean annual rainfall, which separates the negative from the positive ratio values; the second one is 750?mm, which divides the positive values in two groups of sites. Most interestingly, this threshold of 750?mm corresponds exactly to a bioclimatic threshold: sites with <750?mm mean annual rainfall is classified as thermo-mediterranean sites, while the ones >750?mm are classified as mesomediterranean sites. This suggests that apart from rainfall also temperature values have an important influence on soil carbon accumulation after abandonment. Moreover, our results confirmed that the correlation between rainfall and trend in soil organic carbon may be related to nitrogen dynamics: carbon losses may occur only if there is a substantial decrease in soil nitrogen stock which occurs in wetter sites probably because of the higher leaching.     

Evaluation of chemical and ecotoxicological characteristics of biodegradable organic residues for application to agricultural land

The use of organic waste and compost as a source of organic matter and nutrients is a common practice to improve soil physico-chemical properties, meanwhile reducing the need for inorganic fertilisers. Official guidelines to assess sewage sludge and compost quality are mostly based on total metal content of these residues. Measurement of the total concentration of metals may be useful as a general index of contamination, but provides inadequate or little information about their bioavailability, mobility or toxicity when the organic residue is applied to the soil. However, ecotoxicity tests provide an integrated measure of bioavailability and detrimental effects of contaminants in the ecosystem. In the present study, three different types of biodegradable organic residues (BORs) have been considered: sewage sludge from municipal wastewater treatment (SS), compost from the organic fraction of unsorted municipal solid waste (MSWC), and garden waste compost (GWC). The BORs were subjected to chemical characterisation and total metal quantification (Cd, Cr, Cu, Ni, Pb and Zn), in order to verify their suitability for land application. Water leachability was determined through the DIN 38414-S4 method, while the modified BCR sequential extraction procedure was used for metal speciation. Ecotoxicity of the BORs was studied by direct and indirect bioassays. Direct toxicity bioassays were: plant growth tests with cress (Lepidium sativum L.) and barley (Hordeum vulgare L.), and earthworm (Eisenia fetida) mortality. On the other hand, indirect exposure bioassays, with leachate from the residues, took into account: luminescent bacteria (Vibrio fischeri), seed germination (L. sativum and H. vulgare) and Daphnia magna immobilization. As far as total metal concentration is concerned, with particular reference to Zn, SS resulted neither suitable for the use in agriculture nor compatible to be disposed of as an inert material into landfill, according to the Directive 1999/31/EC. Zinc in SS was mainly present in exchangeable form (28.5%), appearing as highly bioavailable. As a consequence, SS exhibited either high ecotoxicity effects with the indirect exposure bioassays or significant mortality with the earthworm bioassay. Total content of metals in MSWC allowed its classification as "stabilised biowaste", according to 2nd draft [DG Env.A.2. Working document of Biological treatment of biowaste - 2nd draft. Directorate-General Environment, Brussels, 12th February; 2001. accessed in:http://europa.eu.int/comm/environment/waste/facts_en.htm, at 10/09/2002] while leachate, on the basis of the concentration of these contaminants, could be classified as "inert waste". This residue showed significant ecotoxicity effects with direct exposure bioassays as well as with the luminescent bacteria bioassay. However, it resulted less toxic than SS. Finally, GWC could be classified as a Class 2 compost, with no detectable toxic effects on the organisms used in the bioassays, except for the luminescent bacteria. In this case, an EC(50) of 73.0% was observed. Considering the results, the use of a battery of toxicity test in conjunction with chemical analysis should be suggested, in order to correctly assess possible environmental risks deriving from disposal or land application of biodegradable organic residues.     

Changes in mineral soil organic carbon stocks in the croplands of European Russia and the Ukraine, 1990–2070; comparison of three models and implications for climate mitigation

Three soil carbon models (RothC, CANDY and the Model of Humus Balance) were used to estimate the impacts of climate change on agricultural mineral soil carbon stocks in European Russia and the Ukraine using detailed spatial data on land-use, future land-use, cropping patterns, agricultural management, climate and soil type. Scenarios of climate were derived from the Hadley Centre climate Version 3 (HadCM3) model; future yields were determined using the Soil–Climate–Yield model, and land use was determined from regional agricultural and economic data and a model of agricultural economics. The models suggest that optimal management, which entails the replacement of row crops with other crops, and the use of extra years of grass in the rotation could reduce Soil organic carbon (SOC) loss in the croplands of European Russia and the Ukraine by 30–44% compared to the business-as-usual management. The environmentally sustainable management scenario (SUS), though applied for a limited area within the total region, suggests that much of this optimisation could be realised without damaging profitability for farmers.