Endogenic development of sediments in a eutrophic lake

Sedimentation in the Gouet reservoir (France), measured for 2 years at 8 stations, was maximal during summer, when river inputs were minimal. Physical and chemical conditions in the deposits indicate that the endogenous part of sedimentation was about 70% and resulted from significant diatom production. The high sedimentation rate on the bottom was favoured by the funnel morphology of the reservoir, the chronic lack of oxygen in the water column, and the repeated copper sulfate treatment. The former river meanders of the reservoir were the preferential deposit sites.     

241Am dating of lake sediments

²⁴¹Am derived from decay of fallout ²⁴¹Pu is now frequently detected in analyses of lake sediments by low-background gamma assay, and offers an alternative to weapons test ¹³⁷Cs in dating recent sediments at those sites where the ¹³⁷Cs record has been degraded by post-depositional mobility or obliterated by Chernobyl fallout. Calculations of the in-growth of ²⁴¹Am from ²⁴¹Pu indicate a nominal distribution broadly similar to that of ¹³⁷Cs, with the maximum ²⁴¹Am activity occuring in fallout dating from 1963. Results from a number of sites suggest that ²⁴¹Am is significantly less mobile in lake sediments than ¹³⁷Cs, and that its distribution in cores reflects more closely the fallout record. Since further decay of existing weapons debris will increase ²⁴¹Am concentrations by about 24% over the next 40 years, ²⁴¹Am is likely to play an increasingly important role in assessing the validity of ²¹⁰Pb dates at sites with varying sediment accumulation rates.     

Determination of nitrite in lake sediments

Abstract

An evaluation of nitrite determination in marine lake sediments has shown that spectrophotometric measurements can be in error due to light scattering by colloidal (<0.2 μm) matter in extract solutions and incomplete nitrite recovery. The scatter error can be minimised by using uncoloured extract in the reference beam but precision at low levels remains poor (RSD 25 to 100%). Recovery tests on ‘spiked’ sediment indicated that optimum retrieval (～85%) occurred with 30 minute mixing with 0.2 M NH₄Cl, using a sediment to extractant ratio of 1:30. To counter this variable, calibration based on standard addition to sample suspensions is recommended. Modified procedure proposed is suitable for measuring up to 10 μg g^?1 of nitrite N; the lake sediments tested contained <100 ng g^?1     

Terrestrial organic matter biomarkers as tracers of Hg sources in lake sediments

Terrestrial organic matter (TOM) plays a key role in mercury (Hg) dynamics between watersheds and lakes. In this study we attempts to determine the role of TOM source and quality and not only quantity, in the fate and transport of total Hg (T-Hg) to boreal lakes. Integrating the watershed complexity is a daunting task. Within the scope of this project, we characterized this organic matter at a molecular level in order to determine Hg transfer conditions to the sediments. We sampled ten lakes in the Quebec boreal forest. In each lake, we took a sediment core at the deepest point in addition to analyzing T-Hg and a set of terrigenous biomarkers in recent sediments. Our results show no relationship between TOM quantity and T-Hg concentration in lake sediments. However, [T-Hg] variation is well explained by the increase of 3,5Bd/V ratios (R²?=?0.84; p?<?0.0002) and the decrease of C/V ratios (R²?=?0.5; p?<?0.0227). Our study shows that TOM source and quality are determinant for Hg loadings in lake sediments. More precisely, increasing TOM derived from humified soil horizons explains most of Hg level variation within sediments.     

River and lake sediments as sources of infective Frankia (Alnus)

Exudation of carboxylic anions and protons by plant roots plays an important role in mobilizing soil P under P-deficiency conditions. The objective of this work was to quantify short-term (6 h) carboxylate and H⁺ exudation by tomato roots in response to P concentration (0, 0.1, 0.5 and 1.0 mt M P) in nutrient solution (C_p). The exudation rate of tri- and dicarboxylates decreased exponentially with increasing C_p, from 0.3 to 0.03 mol plant^–1 6h^–1. At low C_p the predominant exudates were fumarate, citrate and succinate, while at C_p=0.5 and 1.0 mt M the prevalent anions were succinate and citrate. The solution pH declined sharply as C_p was lowered from 0.1 (pH=4.2) to 0 mt M P (pH=3.7).     

Viable endospores of Thermoactinomyces vulgaris in lake sediments as indicators of agricultural history

Bacteria of the genus Thermoactinomyces form endospores with an extreme longevity in natural habitats. We isolated Thermoactinomyces sacchari from 9,000-year-old varved (annually laminated) sediment; thus, T. sacchari is probably one of the oldest known living organisms. More importantly, we tested and verified the hypothesis that there is a relationship between concentrations of dormant, viable endospores of T. vulgaris in lake sediments and the extent of agriculture in the catchments of the lakes. In surface sediments, low concentrations were recorded in forest lakes and the concentrations increased with increasing areas of cultivated land around the lakes. In varved sediment cores from three lakes, we found a temporal relationship between records of T. vulgaris endospores and the pollen of plants indicating agriculture. Endospores were very rare in sediments deposited before agriculture, ca. 1100 A.D. From then to between 1300 and 1700 A.D., a period with restricted cultivation, low but more regular rates of accumulation of endospores were recorded. High endospore accumulation rates were found with the subsequent agricultural expansion. This investigation confirms suggestions that this bacterium could be used as a paleoindicator for agricultural activity and be complementary to pollen analyses. Viable bacteria in continuous records of lake sediments are also potential material for evolutionary studies.     

Determination of total phosphorus in lake sediments

Several methods are in use to measure total phosphorus in lake sediments making cross-study comparisons tenuous, and may lead to potential errors in calculating other phosphorus fractions. Four methods in common use in the limnological literature were compared using sediments spanning a range of organic content from 2 to 35% C. No significant differences were found in within-lake comparisons, although a method using persulfate oxidation was highly variable, and this variability was correlated with organic content suggesting inconsistent oxidation. The other methods (combustion, acid digestion with HClO₄, H₂SO₄ + H₂O₂) gave uniformly small variances.     

Characterization of carbonaceous particles from lake sediments

Spheroidal carbonaceous particles produced by high temperature combustion of coal and oil are found in high concentrations in lake sediments from areas of high acid deposition. The sediment record of these particles showing the onset of industrialisation correlates well with the record of acidification as indicated by diatom analysis. To find sources of the atmospheric deposition affecting a lake and its catchment, characterisation of the carbonaceous particles is necessary. A reference data set of particle chemistries from coal and oil power stations was produced using EDS generated data of 17 elements. Using multivariate statistical techniques, the most important elements for the coal/oil separation were identified and incorporated into a linear discriminant function which allocated fuel type with > 97% accuracy. Application of this technique to surface sediments in Scotland shows the influence of oil burning from outside the region, higher areas located on the east coast and in the south-west of the country. When applied to a full sediment core, the history of coal and oil combustion affecting the lake is seen and correlates well with known coal and oil consumption figures. Consequently this method could be used to add extra dating levels to sediment cores. The technique has been extended to include peat particles and could potentially be used on those from brown coal, lignite and oil shale combustion.     

Viable endospores of Thermoactinomyces vulgaris in lake sediments as indicators of agricultural history.

Bacteria of the genus Thermoactinomyces form endospores with an extreme longevity in natural habitats. We isolated Thermoactinomyces sacchari from 9,000-year-old varved (annually laminated) sediment; thus, T. sacchari is probably one of the oldest known living organisms. More importantly, we tested and verified the hypothesis that there is a relationship between concentrations of dormant, viable endospores of T. vulgaris in lake sediments and the extent of agriculture in the catchments of the lakes. In surface sediments, low concentrations were recorded in forest lakes and the concentrations increased with increasing areas of cultivated land around the lakes. In varved sediment cores from three lakes, we found a temporal relationship between records of T. vulgaris endospores and the pollen of plants indicating agriculture. Endospores were very rare in sediments deposited before agriculture, ca. 1100 A.D. From then to between 1300 and 1700 A.D., a period with restricted cultivation, low but more regular rates of accumulation of endospores were recorded. High endospore accumulation rates were found with the subsequent agricultural expansion. This investigation confirms suggestions that this bacterium could be used as a paleoindicator for agricultural activity and be complementary to pollen analyses. Viable bacteria in continuous records of lake sediments are also potential material for evolutionary studies.     

Turnover of DNA-P and phospholipid-P in lake sediments

Identifying and quantifying the forms of phosphorus (P) in lake sediments is a prerequisite for understanding lake trophic status and possible exports of P downstream. Organic P is one of the most important P forms found in the sediment, where orthophosphate diesters, including DNA and phospholipids, represent a degradable P pool that can support primary production and eutrophication. In this study, sediment cores from the eutrophic Lake Erken and the oligotrophic Lake Ånnsjön, both in steady state regarding long-term P input revealed trends in the degradation of DNA-P and PL-P with sediment depth. Comparisons were performed based on the differentiation of essentially permanent or recalcitrant P and temporary, potentially mobile P for the respective fractions. The temporary P pool was defined as the part of the total P pool calculated for values higher than the level at which the measured P concentration converged to a constant value and the recalcitrant pool was defined as the difference between the total and the temporary. The temporary diester-P pool comprised over 20 % of the total temporary P in Lake Erken and around 4 % in Lake Ånnsjön. The decrease in P concentrations with depth was more rapid for DNA-P compared to PL-P in both lakes, suggesting that DNA-P has a more prominent role in internal loading. The study shows that P mobilization potential can be different for different P fractions, which is important when assessing their contribution to internal loading of P within an aquatic system.     

Efficient separation of subfossil Chironomidae from lake sediments

Electron transport system (ETS) activity, CO₂ evolution, O₂ consumption, N₂-fixation (C₂H₂ reduction) and methanogenesis were appropriately measured in aerobic and anaerobically incubated sediment at 4, 10 and 20 ° C to better characterize these activities under different incubation conditions. ETS activity was always higher in the aerobically incubated sediment at all three incubation temperatures, whereas (C₂H₂ reduction was always greater in the anaerobic sediment. Carbon dioxide evolution was detected only in the aerobic sediment at 10 and 20 ° C but not at 4 ° C. Methane evolution in anaerobic sediment increased gradually with an increase in the incubation temperature.     

Staining of subfossil chironomid head capsules: a method for improving the extraction process from lake sediments and peat

Hydrobiologia - Subfossil chironomids are regarded as a useful biological proxy for palaeoenvironmental research, but picking chironomid head capsules from aquatic sediments is extremely...     

Proteolytic anaerobic bacteria from lake sediments of Antarctica

Amongst twenty five proteolytic bacteria isolated from lake sediment samples of Antarctica, six isolates were selected based on SDS PAGE protein profile and zone of hydrolysis on casein agar at 10 degrees C. Most of the cultures were rod shaped and motile with two showing terminal bulging spores. Isolates grew between 5 degrees C to 37 degrees C and protease was induced in the late log, stationary or death phase. Isolate SPA-3 grew maximally at 10 degrees C and SPA-6 at 37 degrees C while others preferred 20 degrees C-30 degrees C for growth. The growth and protease production on casein, skimmed milk, bovine serum albumin and gelatin varied with the isolates. Acetate was the dominant volatile fatty acid (24-66% of total VFA) produced during hydrolysis of protein substrate.     

Carotenoids in bottom sediments of lake Shira as a paleoindicator for reconstruction of Lake States in Khakassiya,Russia

The concentrations of carotenoids buried in the bottom sediments of Lake Shira (Siberia, Khakassiya) have analyzed for the period of the last 2300 years. The bottom sediments were found to contain carotenoids, which are molecular markers of the corresponding groups of Phototrophic organisms. The bottom sediments of Lake Shira were shown to be a promising object for climate reconstructions of the Late Holocene in southern Siberia.     

Inferred ionic composition and salinity of a Bolivian Quaternary lake,as estimated from fossil diatoms in the sediments

Multiple Linear Regression (MLR) was used to estimate past salinity and ionic composition in sediments of a paleolake in the southernmost Bolivian Altiplano. Modern diatom assemblages were sampled from the subsurface sediments of 14 saline lagoons, and compared quantitatively with fossil assemblages. Only one application of the method is reported: to a Quaternary outcrop located on the border of one of them (Laguna Ballivian). Multivariate analysis was performed on diatom data to check the range of variation of both the fossil and modern flora. It also allowed a reduced set of explanatory variables for regression analysis. Finally, a number of transformations of the chemical variables was computed prior to the regression process in order to stabilize the residuals variance and obtain a good error estimate. Only ten chemical components were studied, but the method could be applied to other palaoenvironmental parameters.     

Shallow lake sediments provide evidence for metapopulation dynamics: a pilot study

The aim of this pilot study is to test the hypotheses that sediment cores can provide evidence for metapopulation dynamics and that these can be linked with site characteristics. We focus on temporal patterns of incidence and abundance of overwintering stages (statoblasts) produced by the freshwater bryozoan Cristatella mucedo, an organism characterised by a metapopulation ecology, in sediment cores retrieved from 18 UK lakes. Runs and goodness-of-fit tests provided evidence for population instability, periods of low abundance and absence, and of asynchrony—all signatures of metapopulation dynamics. Further hypothesis testing indicated that extinction risk is greater in more isolated sites and in sites of smaller size. Absence of statoblasts from the top sections of spatially separated, replicate cores provided independent evidence for extinction in one site. Our study demonstrates how the abundances of sedimentary-bound propagules may be analysed initially for metapopulation dynamics and subsequently how this may lead to working hypotheses regarding the drivers of such dynamics. The sediment archive represents a unique historical record whose potential for characterising metapopulation dynamics has previously been untapped but is broadly relevant for understanding the population biology of freshwater organisms.     

In situ sampling of interstitial water from lake sediments

A sampler with a relatively high resolution has been developed, which allows interstitial water to be obtained from lake sediments at well defined depths, without serious disturbance of sediment structure. Oxidation effects are excluded. Sampling time is in the order of a day. Installation requires little additional equipment. The instrument has been developed for use in shallow lakes.     

Release of metals from polluted sediments in a shallow lake: quantifying resuspension

The contribution of erosion of bed sediment to the load of metals leaving Lake Ketelmeer, a shallow lake in the Netherlands fed by the IJssel branch of the River Rhine, is reported. Transport of suspended matter and associated trace metals was measured using both centrifuges and sediment traps at several locations in the lake. Mass balances of suspended matter and heavy metals were calculated using data from these field measurements.Metal/scandium-ratios were used to identify the source of the suspended matter in the lake. Since the bed sediment is more polluted than the suspended sediment entering the lake, higher metal/scandium-ratios were found for bottom sediment in the lake compared with those for suspended matter entering the lake from the River IJssel. Using the metal/scadium-ratio in suspended matter from the lake, it was calculated that bottom sediments made up 43% of the suspended matter leaving the lake. This implies an erosion flux of bottom sediment of 16 g m^–2 d^–1. For cadmium, mercury, chromium and zinc, this erosion process accounts for more than 50% of the pollutant load leaving Lake Ketelmeer and entering Lake IJsselmeer.