Natural Lake Sediments Research Articles

Turnover of lake sediments treated with sediment microbial fuel cells: a long-term study in a eutrophic lake

Sediment microbial fuel cells (SMFCs) have previously been successfully used to reduce phosphate release from the sediments of eutrophic lakes. In this study, we investigate the risk that SMFCs stimulate sediment decomposition with the unwanted side effect being the release of legacy pollutants stored in sediments. Electrode pairs (16 m2 each) were installed in a eutrophic lake in Denmark and the electricity production was monitored over more than a year at three electrode fields. Equations were derived that allow calculation of the substrate turnover by the SMFCs from the working potential, the open circuit potential, and the external resistance of the SMFCs. The resulting turnover data suggest that the decomposition of the sediment is only slightly expedited by the SMFCs, and that the decomposition process is not significantly stimulated by the type of SMFCs installed in the lake. The measured maximum power density with stainless steel electrodes in the lake sediment was 0.9 mW/m2, which was sufficient to reduce P outflux from sediment. At this power density, the decomposition half-life of the lake sediment (top 5 cm) is calculated to be 277 years, which is only about 10% of natural lake sediment decomposition half-lives. Higher power densities are not necessary for P fixation but inadvertently increase the risk that legacy pollutants buried in the sediment are released.

Toxicity of Mining-Contaminated Lake Sediments to Lumbriculus variegatus

Boreal lakes with soft water and low buffering capacity are susceptible to excess ion loading resulting from metal mining. The impact of two Finish mining sites in downstream lakes was assessed with a chronic sediment toxicity test using a laboratory-reared freshwater Lumbriculus variegatus (Oligochaeta). The test organisms were exposed to mining-contaminated natural lake sediments and hypolimnion water (HLW) or artificial freshwater (AFW) as overlying water in two independent experimental setups. In both test setups, growth and reproduction of L. variegatus were lower in sediments from the lakes receiving high amount of mining effluents from the mines nearby. In the biomining site, the main contaminants in the recipient lakes were the ore metals Ni and Zn, while in the lakes affected by the conventional underground mine, they were Cu and Zn. These metals accumulated in L. variegatus especially in the setup with natural HLW above the sediment. Growth and reproduction were lower in the HLW than in the AFW setup. The mining-contaminated sediments did not support optimum growth or reproduction of L. variegatus in comparison to the local reference sediments. Decline of pH in the unbuffered natural sediments brought up challenges in the assessment of metal-contaminated lake sediments with high sulfur content, and a need to develop new tools for their risk assessment.

Simulating a Spill of Diluted Bitumen: Environmental Weathering and Submergence in a Model Freshwater System.

The main petroleum product transported through pipelines in Canada is diluted bitumen (dilbit), a semiliquid form of heavy crude oil mixed with natural gas condensates to facilitate transport. The weathering, fate, behavior, and environmental effects of dilbit are crucial to consider when responding to a spill; however, few environmental studies on dilbit have been completed. We report on 11-d-long experimental spills of dilbit (Cold Lake Winter Blend) in outdoor microcosms meant to simulate a low-energy aquatic system containing natural lake water and sediments treated with low (1:8000 oil:water) and high (1:800 oil:water) volumes of dilbit. In the first 24 h of the experiment, volatile hydrocarbons quickly evaporated from the dilbit, resulting in increased dilbit density and viscosity. These changes in dilbit's physical and chemical properties ultimately led to its submergence after 8 d. We also detected rapid accumulation of polycyclic aromatic compounds in the water column of the treated microcosms following the spills. The present study provides new information on the environmental fate and behavior of dilbit in a freshwater environment that will be critical to environmental risk assessments of proposed pipeline projects. In particular, the study demonstrates the propensity for dilbit to sink under ambient environmental conditions in freshwaters typical of many boreal lakes. Environ Toxicol Chem 2019;38:2621-2628. © 2019 SETAC.

Synthetic Methane-Consuming Communities from a Natural Lake Sediment.

The factors and processes that influence the behavior and functionality of ecosystems inhabited by complex microbiomes are still far from being clearly understood. Synthetic microbial communities provide reduced-complexity models that allow an examination of ecological theories under defined and controlled conditions. In this study, we applied a multiphasic approach to study synthetic methane-oxidizing communities and species interactions as proxies to the natural communities. Our results confirm that, under selective pressures, natural-sediment communities of high complexity simplify rapidly, selecting for several major functional guilds, the major partners in methane oxidation being the Methylococcaceae methanotrophs and the Methylophilaceae methylotrophs, along with minor but persistent partners, members of Burkholderiales and Flavobacteriales As a proof of concept, we established minimalist synthetic communities that were representative of the four functional guilds to demonstrate the dependency of the non-methane-utilizing species on the methanotrophs as the primary carbon-providing species. We observed that in communities consisting of multiple representatives of the key guilds, members of the same guild appeared to compete for resources. For example, when two methanotrophs of the same family were present, the two expressed similar key methanotrophy pathways and responded similarly to changing environmental conditions, suggesting that they perform a similar keystone function in situ Similar observations were made for the Methylophilaceae However, differences were noted in the expression of auxiliary and unique genes among strains of the same functional guild, reflecting differential adaptation and suggesting mechanisms for competition. At the same time, differences were also noted in the performances of partners with specific metabolic schemes. For example, a mutant of Methylotenera mobilis impaired in nitrate utilization behaved as a more efficient cooperator in methane consumption, suggesting that the loss of function may lead to changes in communal behavior. Overall, we demonstrate the robust nature of synthetic communities built of native lake sediment strains and their utility in addressing important ecological questions while using a simplified model.IMPORTANCE The metabolism of methane is an important part of the global carbon cycle. While deciphering the community function and the potential role of the different functional guilds is very difficult when considering native complex communities, synthetic communities, built of species originating from a study site in question, present a simplified model and allow specific questions to be addressed as to carbon, nitrogen, and other nutrient transfer among species in a controlled system. This study applies an ecophysiological approach, as a proof of principle, to an already well-studied model system, contributing to a better understanding of microbial community function and microbial ecosystem processes.

Hydrogen Peroxide Treatment of Natural Lake Sediment Prior to Carbon and Oxygen Stable Isotope Analysis of Calcium Carbonate

AbstractThe carbon and oxygen stable isotope ratios (δ13C and δ18O) of authigenic and biogenic lacustrine carbonates are commonly used as past climate proxies, and these carbonates are often preserved within organic‐rich bulk sediment. We measured the δ13C and δ18O of carbon dioxide evolved from fine‐grained crystalline calcite and biogenic aragonite, mixed with natural organic‐rich lake sediment. We found that if the ratio of total inorganic carbon (TIC) to total organic carbon (TOC) in lacustrine bulk sediment is low, then organic compounds evolve detectable CO2 during phosphoric acid digestion, leading to an “organic bias” in the measured δ13C and δ18O. We tested the effect of oxidative pretreatment of the bulk sediment with acidic or alkaline hydrogen peroxide (H2O2), at a range of temperatures. Pretreatment with acidic H2O2 not only had a negligible effect on the TIC/TOC but also resulted in dissolution and reprecipitation of carbonate, and a consequent “treatment bias” that was particularly strong for δ18O. Oxidation with alkaline H2O2 removed a greater proportion of organic material, with no evidence for carbonate dissolution at temperatures of ≤50 °C. The δ13C and δ18O values obtained from sediment treated with alkaline H2O2 at 50 °C were both accurate and precise, even for sediment with very low initial TIC/TOC. Our results show that it is possible to obtain accurate δ13C and δ18O values from carbonates preserved within organic‐rich lacustrine sediment, suitable for use in paleoclimate reconstructions.

Mixture of commercial herbicides based on 2,4-D and glyphosate mixture can suppress the emergence of zooplankton from sediments

It is generally assumed that zooplankton can recolonize lakes that have been exposed to pesticides, via their dormant egg banks. Hitherto, few studies have evaluated the relative importance of dormant egg bank recruitment in the re-establishment of zooplankton communities in the presence of pesticide. This study investigated the effects of commercial products Bratt® (a.i. 2,4-D), Roundup® (a.i. glyphosate) and their mixture on the emergence (abundance and taxon richness) of dormant zooplankton egg banks from natural lake sediment. Sediment samples were collected from the surface sediment (<10 cm depth) in four lakes in Southeast São Paulo, Brazil. We performed a hatching experiment, in which natural lake sediments containing dormant eggs were exposed separately to Bratt® (applied concentrations ranging from 0.30 to 20 mg L−1), Roundup® (0.28–8.5 mg L−1), and combined mixtures of all concentrations, plus one control (non-exposure to formulated herbicides) for a period of 28 days. All tested concentrations of Bratt®, Roundup® and their mixture reduced the abundance and taxon richness of emerging zooplankton (except 2 mg L−1 of Bratt®). This effect was more pronounced in rotifers. In comparison, there were no negative effects on the emergence of microcrustaceans. These findings suggest that commercial products Bratt®, Roundup® and their mixture can suppress the emergence of rotifers, thereby influencing zooplankton recruitment potential in lakes impacted by the presence of these commercial herbicides. Our results stress the importance of the need for additional studies to assess the effects of pesticides on dormant egg banks.

Biogeochemistry of methanogenesis with a specific emphasis on the mineral-facilitating effects

The Earth surface contains various oxic and anoxic environments. The later include natural wetlands, river and lake sediments, paddy field soils and landfills. In the last few decades, the biogeochemical cycle of carbon in anoxic environments, which leads to the production and emission of methane, a potent greenhouse gas in the atmosphere, has drawn great attentions from both scientific and public sectors. New organisms and mechanisms involved in methanogenesis and carbon cycling have been uncovered. Interspecies electron transfer is considered as a crucial step in methanogenesis in anoxic environments. Electron-carrying mediators, like H2 and formate, are known to play the key role in electron transfer. Recently, it has been found that in addition to the conventional electron transfer via chemical mediators, direct interspecies electron transfer (DIET) can occur. In this Review, we describe the ecology and biogeochemistry of methanogenesis and highlight the effect of microbe-mineral interaction on microbial syntrophy. Recent advances in the study of DIET may pave the way towards a mechanistic understanding of methanogenesis and the influence of microbe-mineral interaction on this process.

Bridging between litterbags and whole-ecosystem experiments: a new approach for studying lake sediments

&lt;p&gt;Nearshore sediments have a major influence over the functioning of aquatic ecosystems, but predicting their response to future environmental change has proven difficult. Previous manipulative experiments have faced challenges controlling environmental conditions, replicating sediment mixing dynamics, and extrapolating across spatial scales. Here we describe a new approach to manipulate lake sediments that overcomes previous concerns about reproducibility and environment controls, whilst also bridging the gap between smaller microcosm or litterbag experiments and whole-ecosystem manipulations. Our approach involves submerging moderate-sized (~15 L) artificial substrates that have been standardised to mimic natural sediments within the littoral zones of lakes. We show that this approach can accurately mirror the absolute dissolved organic carbon concentrations and pH of pore water, and to a lesser degree inorganic carbon concentrations, from natural lake sediments with similar organic matter profiles. On a relative basis, all measured variables had similar temporal dynamics between artificial and adjacent natural sediments. Late-summer zooplankton biomass also did not differ between natural and artificial sediments. By offering a more realistic way to manipulate freshwater sediments than previously possible, our approach can improve predictions of lake ecosystems in a changing world.&lt;br /&gt;&lt;br /&gt;&lt;img src="/public/site/images/ttaccini/88x31.png" alt="" /&gt; &lt;br /&gt;This work is licensed under a &lt;a href="https://creativecommons.org/licenses/by/4.0/" target="_blank"&gt;Creative Commons Attribution 4.0 International&lt;/a&gt;.&lt;/p&gt;

Validation of an updated fractionation and indirect speciation procedure for inorganic arsenic in oxic and suboxic soils and sediments

A sequential extraction procedure (SEP) for the speciation analysis of As(III) and As(V) in oxic and suboxic soils and sediments was validated using a natural lake sediment and three certified reference materials, as well as spike recoveries of As(III) and As(V). Many of the extraction steps have been previously validated making the procedure useful for comparisons to similar previous SEP studies. The novel aspect of this research is the validation for the SEP to maintain As(III) and As(V) species. The proposed five step extraction procedure includes the extraction agents (NH4)2SO4, NH4H2PO4, H3PO4 + NH2OH·HCl, oxalate + ascorbic acid (heated), and HNO3 + HCl + HF, targeting operationally defined easily exchangeable, strongly sorbed, amorphous Fe oxide bound, crystalline Fe oxide bound, and residual As fractions, respectively. The third extraction step, H3PO4 + NH2OH·HCl, has not been previously validated for fraction selectivity. We present evidence for this extraction step to target As complexed with amorphous Fe oxides when used in the SEP proposed here. All solutions were analyzed on ICP-MS. The greatest concentrations of As were extracted from the amorphous Fe oxide fraction and the dominant species was As(V). Lake sediment materials were found to have higher As(III) concentrations than the soil materials. Because different soils/sediments have different chemical characteristics, maintenance of As species during extractions must be validated for specific soil/sediment types using spiking experiments.

Imaging the movement of toxic pollutants with 2D electrical resistivity tomography (ERT) in the geological environment of the Hoa Khanh Industrial Park, Da Nang, Vietnam

This study presents the results of a geophysical survey undertaken by 2D electrical resistivity tomography (ERT) along two traverses. The study was conducted between an industrial park (IP) and a residential area bounding the Hoa Khanh Industrial Park, Da Nang, Vietnam. The first traverse, 300 m long, which is at the boundary between the industrial park and Bau Tram Lake, includes 504 measured data points. The second traverse, which includes 189 measured data points, is 200 m in length and runs alongside the boundary between Bau Tram Lake and the residential area. Bau Tram Lake is located between the IP and the residential area and acts as a natural boundary. After discarding noisy data points, the data were processed using the commercial software Res2dinv which creates a 2D visual section of the resistivity distribution below surface using a finite difference algorithm and the method of least squares inversion. The result of an inversion, which is a simulated 2D resistivity image of the subsurface or Electrical Resistivity Tomogram (ERT), showed the formation characteristics and geological structure along the first traverse from surface to 39.4 m in depth, including two overlapping geological layers with indistinctive local boundaries. The resulting image illustrates the amalgamation of anthropometric transported soil and rocks with local lake material, brought into the lake from other areas, to fill up the lake with rock and improve the engineering foundation for the construction of the industrial park buildings. The research results show that the main components of the second geological layer on both sides of the survey area have the same electrical signature associated with black mud and sand and represent the natural lake sediments. The inferred groundwater level identified in the electrical imagery and two boreholes corresponds approximately to the water level in Bau Tram Lake. At a depth of approximately 10 m along both traverses, the groundwater in Bau Tram Lake and the surrounding residential areas is contaminated by electrolytes and heavy metals. Furthermore, the groundwater inside the industrial park contains a significant amount of industrial electrolytes (with a high probability of chemicals such as KCl, NaCl) and heavy metal contamination (with a high probability of elements such as Pb, Hg, Zn) at a greater density than measured in the residential areas. This suggests that Bau Tram Lake acts as a filter to strongly reduce the movement of these toxic substances from seeping into the groundwater below the residential area.

Sunlight‐induced carbon dioxide emissions from inland waters

AbstractThe emissions of carbon dioxide (CO2) from inland waters are substantial on a global scale. Yet the fundamental question remains open which proportion of these CO2 emissions is induced by sunlight via photochemical mineralization of dissolved organic carbon (DOC), rather than by microbial respiration during DOC decomposition. Also, it is unknown on larger spatial and temporal scales how photochemical mineralization compares to other C fluxes in the inland water C cycle. We combined field and laboratory data with atmospheric radiative transfer modeling to parameterize a photochemical rate model for each day of the year 2009, for 1086 lakes situated between latitudes from 55°N to 69°N in Sweden. The sunlight‐induced production of dissolved inorganic carbon (DIC) averaged 3.8 ± 0.04 g C m−2 yr−1, which is a flux comparable in size to the organic carbon burial in the lake sediments. Countrywide, 151 ± 1 kt C yr−1 was produced by photochemical mineralization, corresponding to about 12% of total annual mean CO2 emissions from Swedish lakes. With a median depth of 3.2 m, the lakes were generally deep enough that incoming, photochemically active photons were absorbed in the water column. This resulted in a linear positive relationship between DIC photoproduction and the incoming photon flux, which corresponds to the absorbed photons. Therefore, the slope of the regression line represents the wavelength‐ and depth‐integrated apparent quantum yield of DIC photoproduction. We used this relationship to obtain a first estimate of DIC photoproduction in lakes and reservoirs worldwide. Global DIC photoproduction amounted to 13 and 35 Mt C yr−1 under overcast and clear sky, respectively. Consequently, these directly sunlight‐induced CO2 emissions contribute up to about one tenth to the global CO2 emissions from lakes and reservoirs, corroborating that microbial respiration contributes a substantially larger share than formerly thought, and generate annual C fluxes similar in magnitude to the C burial in natural lake sediments worldwide.

Determination of the total and extractable fraction of Ni in lake sediments and natural waters of San Luis (Argentina) by FAAS using a simple solid phase extraction system

An on-line nickel preconcentration and determination system implemented with flame atomic absorption spectrometry (FAAS) was developed. The nickel was retained on the inner walls of a column filled with ethyl vinyl acetate (EVA). The EVA was used as sorbent material for on-line solid-phase extraction (SPE) in the absence of complexing agent. The effects of sampling volume, elution conditions, sample pH and flow rate on the Ni extraction were studied. The analytical efficiency parameters obtained with this methodology were: enrichment factor (EF) of 46 times for a preconcentration time of 120s, the limit of detection (LOD) was 3.78μgL−1, and the precision for six replicate determinations (repeatability conditions) at 20μgL−1 Ni concentration was 4.38% relative standard deviation. The sampling frequency for the proposed system was about 20samples/h. The optimized procedure was applied to the determination of Ni in natural water and lake sediment samples.

Combined dynamics of mercury and terrigenous organic matter following impoundment of Churchill Falls Hydroelectric Reservoir, Labrador

Sediments from two recently (40 years) flooded lakes (Gabbro lake and Sandgirt lake) and an unflooded lake (Atikonak lake) were sampled to investigate the effects of reservoir impoundment on mercury (Hg) and terrigenous organic matter (TOM) loading in the Churchill Falls Hydroelectric complex in Labrador, Canada. Lignin biomarkers in TOM, which exclusively derive from terrestrial vegetation, were used as biomarkers for the presence and source origin of TOM—and for Hg due to their close associations—in sediments. In the two flooded Gabbro and Sandgirt lakes, we observed drastic increases in total mercury concentrations, T-[Hg], in sediments, which temporally coincided with the time of reservoir impoundment as assessed by 210Pb age dating. In the natural Atikonak lake sediments, on the other hand, T-[Hg] showed no such step-increase but gradually and slowly increased until present. T-[Hg] increases in lake sediments after flooding were also associated with a change in the nature of TOM: biomarker signatures changed to typical signatures of TOM from vegetated terrestrial landscape surrounding the lakes, and indicate a change to TOM that was much less degraded and typical of forest soil organic horizons. We conclude that T-[Hg] increase in the sediments of the two flooded reservoirs was the result of flooding of surrounding forests, whereby mainly surface organic horizons and upper soil horizons were prone to erosion and subsequent re-sedimentation in the reservoirs. The fact that T-[Hg] was still enriched 40 years after reservoir impoundment indicates prolonged response time of lake Hg and sediment loadings after reservoir impoundments.

Deconvolution of u channel magnetometer data: Experimental study of accuracy, resolution, and stability of different inversion methods

We explore the effects of sampling density, signal/noise ratios, and position‐dependent measurement errors on deconvolution calculations for u channel magnetometer data, using a combination of experimental and numerical approaches. Experiments involve a synthetic sample set made by setting hydraulic cement in a 30‐cm u channel and slicing the hardened material into ∼2‐cm lengths, and a natural lake sediment u channel sample. The cement segments can be magnetized and measured individually, and reassembled for continuous u channel measurement and deconvolution; the lake sediment channel was first measured continuously and then sliced into discrete samples for individual measurement. Each continuous data set was deconvolved using the ABIC minimization code of Oda and Shibuya (1996) and two new approaches that we have developed, using singular‐value decomposition and regularized least squares. These involve somewhat different methods to stabilize the inverse calculations and different criteria for identifying the optimum solution, but we find in all of our experiments that the three methods converge to essentially identical solutions. Repeat scans in several experiments show that measurement errors are not distributed with position‐independent variance; errors in setting/determining the u channel position (standard deviation ∼0.2 mm) translate in regions of strong gradients into measurement uncertainties much larger than those due to instrument noise and drift. When we incorporate these depth‐dependent measurement uncertainties into the deconvolution calculations, the resulting models show decreased stability and accuracy compared to inversions assuming depth‐independent measurement errors. The cement experiments involved varying directions and uniform intensities downcore, and very good accuracy was obtained using all of the methods when the signal/noise ratio was greater than a few hundred and the sampling interval no larger than half the length scale of magnetization changes. Addition of synthetic noise or reduction of sampling density decreased the resolution and accuracy of all the methods equally. The sediment‐core experiment involved uniform (axial) magnetization direction and strongly varying intensities downcore. Intensity variations are well resolved and directions are accurate to within about 5 degrees, with errors attributable to omission and/or inaccurate calibration of cross terms in the instrument response function.

Diversity of methanogenic archaeal communities in Japanese paddy field ecosystem, estimated by denaturing gradient gel electrophoresis

Diversity of methanogenic archaeal communities in Japanese paddy field ecosystem was evaluated by the denaturing gradient gel electrophoresis (DGGE) after PCR amplification of the 16S rRNA genes (16S rDNAs), sequencing analysis and data evaluation by principal component analysis. Data were obtained from samples collected from the plowed soil layer, rice roots, rice straws incorporated in soil, plant residues (mixture of weeds, rice litters, rice roots, and rice stubbles) in soil, and composing rice straw. The number of bands of DGGE profiles ranged from 12 to 26 with the highest numbers in rice roots and rice straws incorporated in soil. However, the diversity indices based on both the numbers and intensity of bands indicated that the community of the plowed soil layer was the most diverse, even, and stable. Sequencing of the main DGGE bands showed the presence of Methanomicrobiales, Methanosarcinales, Methanobacteriaceae, and Methanocellales. The plowed soil layer included all phylogenetic groups of the methanogenic archaea of the other studied habitats, with prevalence of the members of Methanomicrobiales and Methanocellales. The phylogenetic diversity was compared with that of paddy soils collected in Italy, China, and the Philippines and that of 12 anaerobic environments (fen, waste, coast, permafrost, natural gas field, bovine rumen, riparian soil, termite, ciliate endosymboints, lake sediment, landfill, and seep rumen). The phylogenetic diversity was more similar among paddy soils than with the other anaerobic environments. Probably, the methanogenic archaeal communities of the paddy field soils were characterized by indigenous members and some of the members of the community of the plowed soil layer colonized rice roots, rice straws, and plant residues.

Assessment of toxic heavy metals in urban lake sediments as related to urban stressor and bioavailability

A suite of heavy metals was monitored at sediments and overlying water in three urban lakes located in Seoul, Korea during spring season 2006. Metals measured were zinc, arsenic, chromium, copper, nickel, and cadmium. All metal concentrations in urban lake sediments were much higher than those in natural lake sediments. Elevated metal levels in urban lake sediments are associated with urban runoff, including street dust polluted by heavy metals. Metals in sediments from urban lakes were extracted with a weak electrolyte solution (0.1 M Ca(NO(3))(2)) to predict the toxicity of metals. Among the six heavy metals studied, Cu was the most extractable, followed by Ni and Zn. Ca(NO(3))(2)-extractable metal recoveries has a good relationship with metal toxicity based on Chironomus riparius bioassay. This study showed that urban stressors such as vehicle emissions could increase the concentration of heavy metals in urban lake sediments. In addition, there is a positive relationship between sediment toxicity by using C. riparius bioassay and Ca(NO(3))(2)-extractability of heavy metals from sediments.

Top-down and bottom-up regulation of planktonic communities in a warm temperate wetland

This field experimental study simultaneously analysed the effects of predation (top-down) and nutrients (bottom-up) on planktonic communities (phytoplankton, zooplankton, heterotrophic nanoflagellates and ciliates) in a warm temperate wetland in South America. The top-down and bottom-up controls were investigated by assessing the impact of omnivorous-planktivorous fish (Jenynsia sp.) and the effects of nutrient input from natural lake sediments, respectively Three treatments and a control were run in triplicate in mesocosms and samples were taken at Days 0, 3, 7 and 15. The control contained all the planktonic components while treatments included all planktonic components plus the addition of either planktivorous fish (F), natural wetland sediments in dialysis bags (S) or both of them (SF). A bottom-up effect due to nutrient release from sediment (mainly total phosphorus) was noticed in treatments S and SF. Phytoplankton abundance increased in all treatments compared with the control. Thus, phytoplankton appeared to be bottom-up controlled while fish exerted a strong predation pressure on zooplankton (top-down), because treatments F and SF showed a marked decrease in mesozooplankton abundance. The results obtained in this study agree with the hypothesis that phytoplankton regulation by zooplankton might be weaker in warm temperate systems than in temperate ones.

The post-depositional accumulation of metal-rich cyanide phases in submerged tailings deposits

Abstract The characterization and accumulation pathway of metal-rich cyanide phases in mine-contaminated Balmer Lake (Ontario, Canada) were assessed through detailed examination of sediment mineralogy and porewater composition. The near-surface deposits in the lake consist of fine-grained calcareous tailings intermixed with natural organic-rich lake sediments. The tailings contain blue to greenish Fe-dominant cyanide that has formed in situ within the tailings. X-ray diffraction confirmed the presence of a mixed ferri/ferrocyanide [ Fe 4 III ( Fe II ( CN ) 6 ) 3 ] , commonly referred to as “Prussian Blue” but it is likely other metal–cyanide complexes are present as evidenced by the distinct colour variations. The cyanide phases occur in up to 1 wt.% as discrete particles and as bedded layers, where the cyanide phases act to cement other siliceous tailings components into a heterogeneous blend. Energy Dispersion X-ray Spectroscopy (EDS) analyses indicate that the authigenic cyanide precipitates contain variable amounts of Ni, Cu and Zn. Quantitatively, the cyanide compounds represent the dominant repository for Cu in Balmer Lake sediments. For Ni and Zn, cyanide associations are secondary in importance to Fe oxyhydroxides. High-resolution porewater profiles and solubility considerations suggest that the formation of the cyanide complexes is a feature of historical (pre-1990) conditions when aqueous cyanide concentrations were higher in the lake.

Detection of phosphorus species in sediments of artificial landscape lakes in China by fractionation and phosphorus-31 nuclear magnetic resonance spectroscopy

Phosphorus (P) pollution in the sediments of seven artificial landscape lakes was studied via fractionation and phosphorus-31 nuclear magnetic resonance ( 31P NMR) spectroscopy. The lake sediments accumulated significant amounts of P from supplementation with reclaimed water and from runoff from the golf course lawns. The differences in total sediment P among lakes were correlated to the varied pollution extent from the lawns. One striking feature of the artificial lake sediments was the insufficiency of NaOH-extracted Al, which plays an important role in avoiding internal P release during anoxia. Another characteristic was the dominance of orthophosphate in the NaOH–EDTA extractants of the sediments, due to the heavy external P pollution. Phytate, considered prevalent in many soils and lake sediments, as well as polyphosphates and phosphonates which have appeared in some natural lake sediments, was not detected. The rank order of present biogenic P species was monoester-P > DNA-P > pyrophosphate > lipid-P.

Characteristics and Seasonal Variation of Sediments in Lake Junttiselkä, Pyhäsalmi, Finland

Lake Junttiselka, located in central Finland, has been loaded by effluents from Pyhasalmi Zn–Cu mine since 1962 and also receives Pyhasalmi municipal effluent. A total of 32 top sediment samples (0–2, 2–4, and 4–6 cm) were collected in October 2005 and March 2006 to examine the seasonal variation in sediment composition. Furthermore, two sediment cores of 1 m were taken from the northern and southern parts of the lake (Junttiselka_N, Junttiselka_S) to investigate the sedimentation history. Electrical conductivity (EC) was measured from the sediment in situ, and sediment pH, redox values, and EC were measured in the winter from the top samples. The sediment samples were freeze-dried and multi-element determinations were performed using ICP-MS on nitric acid extracts (EPA 3051, acid soluble fraction, AF) and on ammonium acetate extracts (bioavailable fraction, BF). The composition of crystalline and semi-crystalline fractions (CF) was calculated by the formula CCF = CAF – CBF. Due to the high clay content of till in the catchment area, the Al, K, and Mg concentrations in the natural lake sediments (>49 cm) are greater than the average level in lake sediments of Finland (AF). Soil cultivation has increased the sedimentation of fines, which has further increased Al, K, and Mg concentrations in the lake sediments (49–19 cm). Mine effluents have had the greatest impact on sediment concentrations of Cu and Zn, with the recorded levels of 166 mg/kg and 434 mg/kg (<19 cm), respectively, being nine- and threefold greater than the natural concentration level. Also, Ca and S concentrations are elevated. The electric conductivity of pore water was elevated at a depth of 1 m. Seasonal variation in the composition of Junttiselka top sediments is linked to the oxic/anoxic conditions in the water column during the autumn to winter period. The greatest variation was recorded in the 0–2 cm layer in Junttiselka_S, where CaBF and SBF concentrations were three and sixfold higher in the winter than in the autumn. MgBF, PbBF, SrBF, CrBF, PBF, UAF, and SeAF concentrations also increased in the winter, but MnBF, CuBF, CdBF, CoBF, ZnBF, BaBF, NiBF, FeBF, and AlBF decreased. The seasonal variation in composition was less for CF than for BF, and was also partially different. The most significant difference was an increase in CaCF and SCF concentrations in the winter in Junttiselka_S, with the reverse situation being observed in Junttiselka_N. Furthermore, the FeCF concentration increased in Junttiselka_N. Equimolar variations in Ca and S suggest that the precipitation and dissolution of gypsum is the most notable seasonal process in the top sediment layer. The seasonally precipitated S corresponds to only 1.4% of the total load of S from the mine effluents.