Lake Sediment Pore Water Research Articles

Characteristics of Pore Water Dissolved Organic Nitrogen in the Sediment of Erhai Lake Basin, China

The distribution of Erhai Lake sediment pore water DON followed the pattern of middle (1.449 mg/L) > south (0.828 mg/L) > north (0.266 mg/L), with the highest concentrations being found in the least polluted areas. The sediment pore water DON mainly contained hydrophilic substances and substances derived from microbial sources. Most of these were integrated into humic acid-like substances (∼78%), which benefited for reducing sediment DON releasing risk. There were more chains in Erhai Lake sediment pore water DON, with a small number of aromatic substituents. The characteristics of DON components were suggested to be related to human activities.

Distribution character of localized iron microniche in lake sediment microzone revealed by chemical image.

DGT (diffusive gradients in thin films) technique and LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) for heterogeneous distribution of the soluble labile iron (Fe) at submillimeter resolution in lake sediment porewater are reported. The soluble labile Fe species include ion and labile organic complexes. The chemical images in two dimensions (2D) for DGT concentration of Fe (CDGT(Fe)) are investigated for Fe remobilization character. There are 902 CDGT(Fe) values between 1000 and 2000 μg L-1, 463 values between 2000 and 3000 μg L-1, and 112 values over 3000 μg L-1 in all chemical maps. Based on the linear correlation relationships between CDGT (Fe) and total Fe (TFe), total organic carbon (TOC), acid-volatile sulfide (AVS), Eh, concentrations of the soluble reactive phosphorus (P) (SRP), and soluble labile trace metals (Zn, Cu, Pb, and Zn) in a vertical 1D profile of sediment or porewater, Fe release mechanisms are mainly due to the reductive Fe release from iron oxyhydroxides and the decomposition of organic matter in algae biomass and deep sediment layer. It can be used to explain the formation mechanisms of Fe microniches in chemical maps with heterogeneous character to a great extent. CDGT(Fe) peak flux in the center of Fe microniche and the low CDGT (Fe) at the edge of a microniche are due to the formation of the insoluble iron sulfide and the abundant acid-volatile sulfide (AVS) in sediment. The verified co-remobilization of the soluble labile Fe and trace metals or SRP in sediment porewater can be used to predict their simultaneous release from Fe microniches with the large CDGT (Fe) peaks. The different kinds of Fe microniche zones and hot spots from sediment/water interface (SWI) to deep sediment correspond to the formation mechanisms of microniches mentioned above. Moreover, some narrow Fe microniche zones with the large CDGT (Fe) across chemical maps are due to the desorption of Fe(II) from the freshly formed oxide on Myriophyllum verticiilatur roots, which are located at sites of microniche zones.

Influence of dissolved organic matter (DOM) characteristics on dissolved mercury (Hg) species composition in sediment porewater of lakes from southwest China

The origin and composition of dissolved organic matter (DOM) in porewater of lake sediments is intricate and decisive for fate of pollutants including mercury (Hg). While there are many reports on the relationship between dissolved organic carbon concentration (DOC) and mercury (Hg) concentrations in aquatic systems, there are few in which DOM compositional properties, that may better explain the fate of Hg, have been the focus. In this study, porewaters from sediments of three lakes, Caihai Lake (CH), Hongfeng Lake (HF) and Wujiangdu Lake (WJD), all located in southwest China, were selected to test the hypothesis that DOM optical properties control the fate of Hg in aquatic ecosystems. Porewater DOM was extracted and characterized by UV–Vis absorption and fluorescence spectroscopy. A two end-member (autochthonous and allochthonous DOM) mixing model was used to unveil the origin of DOM in porewaters of the three lakes. Our results show a higher input of terrestrial DOM in the pristine lake CH, as compared to lakes HF and WJD lakes, which were both influenced by urban environments and enriched in autochthonous DOM. While the relationships between the concentrations of DOC and the different chemical forms of Hg forms were quite inconsistent, we found important links between specific DOM components and the fate of Hg in the three lakes. In particular, our results suggest that allochthonous, terrestrial DOM inhibits Hg(II) availability for Hg methylating micro-organisms. In contrast, autochthonous DOM seems to have been stimulated MeHg formation, likely by enhancing the activity of microbial communities. Indeed, DOM biodegradation experiments revealed that differences in the microbial activity could explain the variation in the concentration of MeHg. While relationships between concentrations of DOC and Hg vary among different sites and provide little information about Hg cycling, we conclude that the transport and transformation of Hg (e.g. the methylation process) are more strongly linked to DOM chemical composition and reactivity.

Distribution and geochemical processes of boron in the multimedia of Lake Qinghai, China

Abstract Lake Qinghai on the Qinghai-Tibet plateau is the largest lake in China. This study investigated the concentration and geochemical processes of boron (B) in lake water, lake sediment and river samples collected from Lake Qinghai and the Buha River. In addition, lake sediment pore water samples were analyzed. The concentrations of B and major ions, including K+, Na+, Ca2+, Mg2+, Cl− and SO42−, were analyzed in all the water samples. The average concentration of B was 0.07 mg L−1, 6.37 mg L−1, 12.79) mg L−1 and 59.42 mg kg−1 for river water, lake water, pore water, and sediment, respectively. There were significant (p

High-resolution profiles of trace metals assessed by DGT techniques in lake sediment porewaters

The technique of diffusive gradients in thin films (DGT) was applied to obtain high-resolution vertical profiles of trace metals in sediment porewater of a eutrophic lake, Lake Chaohu. All sampling sediments were under anaerobic conditions with Eh values below 0, the redox potential profile in M4 was relatively stable, and higher Eh values in M4 than that in M1 were observed due to hydrodynamic effects. Fe, Mn and As exhibited closely corresponding profiles due to the co-release of Fe and Mn oxides and the reduction of As. Higher Fe and Mn concentrations and lower As concentrations were observed in M1 of the western half-lake than those in M4 of the eastern half-lake due to different sources and metal contamination levels in the two regions. Cu and Zn showed increasing concentrations similar to Mn and Fe at 1–2 cm depth of sediments, while DGT measured Co, Ni, Cd and Pb concentrations decreased down to 3–4 cm in the profiles. Co, Ni, Cu, Zn, Cd and Pb showed insignificant regional concentration variances in the western and eastern half-lakes. According to the R(CDGT/Ccentrifugation) values, the rank order of metal labilities decrease as follows: Fe (>1) > Cu, Pb, Zn (>0.9) > Co, Ni, Cd (>0.3) > Mn, As (>0.1).

A reusable electrochemical biosensor for highly sensitive detection of mercury ions with an anionic intercalator supported on ordered mesoporous carbon/self-doped polyaniline nanofibers platform

In this paper, a reusable electrochemical biosensor was developed for highly sensitive detection of mercury ions (Hg2+) using an anionic intercalator, which was based on Hg2+-induced conformational change of a thymine-rich, single-stranded DNA (ssDNA) supported on the platform of ordered mesoporous carbon (OMC) and self-doped polyaniline (SPAN) nanofibers. In the presence of Hg2+, the mercury-specific oligonucleotides were induced and folded into hairpin structure through mismatched thymine-Hg2+-thymine (T-Hg2+-T) base pairs from random coils. Then, the indicators intercalated into the hairpin structure and increased electric signal. OMC and SPAN nanofibers possessed excellent electrical conductivity which synergistically accelerated electron transfer and greatly improved the efficiency of electrochemical reaction at the electrode interface. Meanwhile, SPAN nanofibers strongly adhered to the electrode surface and attached rod-like OMC homogeneously and firmly, which provided a stable platform for DNA immobilization. Under the optimal conditions, the detection limit (LOD) for Hg2+ was 0.6 fM (S/N=3). Furthermore, the biosensor could be easily regenerated by cysteine for cyclic utilization. Some environmental samples including lake sediment pore water and tap water were analyzed by the developed biosensor, the relatively satisfactory results indicated that it provided a green and promising strategy for detection of trace Hg2+ in the practical application.

Improved Method for the Quantification of Methane Concentrations in Unconsolidated Lake Sediments.

There is conclusive evidence that the methods most commonly used to sample methane (CH4) dissolved in the pore water of lake sediments produce results that are likely to be affected by gas loss or gas exchange with the atmosphere. To determine the in situ amount of CH4 per unit mass of pore water in sediments, we developed and validated a new method that combines techniques developed for noble-gas analysis in pore waters with a standard headspace technique to quantify the CH4 present in the pore space in dissolved and gaseous form. The method was tested at two sites: Lake Lungern, where CH4 concentrations were close to saturation; and Lake Rotsee, where CH4 concentrations are known to exceed saturation and where CH4 bubble formation and gas ebullition are commonly observed. We demonstrate that the new method, in contrast to the available methods, more reliably captures the total amount of CH4 per unit mass of pore water consisting of both dissolved and free CH4 (i.e., gas bubbles) in the pore space of the sediment.

Relationship of brines in the Kinnarot Basin, Jordan‐Dead Sea Rift Valley

AbstractElement ratios and water stable isotopes reveal the presence of only two independent deep brines in the Kinnarot Basin, Israel: the evaporite dissolution brine of Zemah‐1 and the inferred Ha’on mother brine (HMB) with low and high Br/Cl ratios, respectively. HMB is considered to be a representative of the Late Pliocene evaporated Sedom Sea. The freshwater‐diluted evaporation brine emerges as Ha’on brine on the eastern shore of Lake Tiberias and is also identified in the pore water of lake sediments. HMB is converted into Tiberias mother brine (TMB) by dolomitization of limestones and alteration of abundant volcanic rocks occurring along the western side of the lake. The Ha’on and Tiberias brines, both characterized by high δD and δ18O values, are similar in Na/Cl and Br/Cl ratios but are dissimilar in Br/K ratios because these brines were subjected to different degrees of interactions with rocks and sediments. Excepting the brine from KIN 8, all brines from the Tabigha area including the nearby off‐shore Barbutim brine are related to the TMB. The brine KIN 8 and all brines from the Fuliya and Hammat Gader areas are related to the HMB. The brine encountered in wildcat borehole Zemah‐1 is generated by halite‐anhydrite/gypsum dissolution and is independent from the HMB system.

Characteristics and distribution of low molecular weight organic acids in the sediment porewaters in Bosten Lake, China

The composition and vertical profiles of low molecular-weight organic acids (LMWOAs) and the contribution of them to dissolved organic matter (DOM) in sediment porewaters in Bosten Lake, Xinjiang, China were investigated. The results showed that total concentration of LMWOAs was up to 94.5 μmol/L and their proportion in DOM was 5.6%, suggesting that LMWOAs were important chemical components in DOM in lake sediment porewaters. Among the seven LMWOAs, pyruvic and acetic acid had the highest concentrations with 26.30 and 8.31 μmol/L, accounting for 51.4% and 14.92% of LMWOAs, respectively. Trifluoroacetic and sorbic acid had the lowest concentrations, indicating that the compositions of LMWOAs in relative reducing environments were largely different from those reported in glacier, atmosphere and soils. The concentrations of lactic, acetic, formic, sorbic and oxalic acid decreased with increasing depth, probably relating to stronger microbial activities in the initial stage of early diagenesis. Trifluoroacetic acid was mainly anthropogenic with its concentration, showing a diffusive trend from the surface to bottom sediments. The concentrations of lactic acid and nitrate generally showed a consistent profile. The increasing concentration of pyruvic acid in the vertical profile was just opposite to that of sulfate, revealing a significant negative relationship between them. Oxalic acid remained constant except for an obvious peak at 6 cm depth. The results indicated the diversities in sources and behaviors for various LMWOAs during early diagenesis in sediments.

Miniaturized photometrical methods for the rapid analysis of phosphate, ammonium, ferrous iron, and sulfate in pore water of freshwater sediments

Pore water analysis is a challenge for routine analysis methods, because of the small sample volume available and large sample numbers required for a high spatial resolution. To overcome the restrictions of established methods, this study presents a miniaturized photometrical method for the rapid analysis of phosphate, ammonium, ferrous iron, and sulfate in pore water of lake sediments. The method can cope with large sample sets (> 1000) and minimizes the sample volume to about 250 µL. Standard photometric methods were modified for the use of microtiter plates (microphotometry), which allow the simultaneous determination of up to 100 samples by a microtiter plate reader. The advantage of this analytical technique is the minimal sample consumption, which enables new approaches for pore water sampling and analysis on a microscale level. In combination with a 2‐dimensional dialysis sampler, it is now possible to obtain spatial patterns of pore water concentrations (SRP, NH4+, Fe2+, SO42−) with a high vertical and lateral resolution (9 mm). This approach shows the common 1‐dimensional view of pore water profiles to be insufficient. Furthermore, the application examples yield new insights on lateral heterogeneity as well as nutrient mobilization and redox processes associated with the formation of microzones around biogenic structures, such as roots or macrofaunal burrows.

Seasonal variations in pore water and sediment geochemistry of littoral lake sediments (Asylum Lake, MI, USA).

BackgroundSeasonal changes in pore water and sediment redox geochemistry have been observed in many near-surface sediments. Such changes have the potential to strongly influence trace metal distribution and thus create seasonal fluctuations in metal mobility and bioavailability.ResultsSeasonal trends in pore water and sediment geochemistry are assessed in the upper 50 cm of littoral kettle lake sediments. Pore waters are always redox stratified, with the least compressed redox stratification observed during fall and the most compressed redox stratification observed during summer. A 2-step sequential sediment extraction yields much more Fe in the first step, targeted at amorphous Fe(III) (hydr)oxides (AEF), then in the second step, which targets Fe(II) monosulfides. Fe extracted in the second step is relatively invariant with depth or season. In contrast, AEF decreases with sediment depth, and is seasonally variable, in agreement with changes in redox stratification inferred from pore water profiles. A 5-step Tessier extraction scheme was used to assess metal association with operationally-defined exchangeable, carbonate, iron and manganese oxide (FMO), organic/sulfide and microwave-digestible residual fractions in cores collected during winter and spring. Distribution of metals in these two seasons is similar. Co, As, Cd, and U concentrations approach detection limits. Fe, Cu and Pb are mostly associated with the organics/sulfides fraction. Cr and Zn are mostly associated with FMO. Mn is primarily associated with carbonates, and Co is nearly equally distributed between the FMO and organics/sulfide fractions.ConclusionThis study clearly demonstrates that near-surface lake sediment pore water redox stratification and associated solid phase geochemistry vary significantly with season. This has important ramifications for seasonal changes in the bioavailability and mobility of trace elements. Without rate measurements, it is not possible to quantify the contribution of various processes to natural organic matter degradation. However, the pore water and solid phase data suggest that iron reduction and sulfate reduction are the dominant pathways in the upper 50 cm of these sediments.

Atmospheric noble gases in lake sediment pore water as proxies for environmental change

Lake sediment pore water has been proposed as a noble gas archive for paleoenvironmental reconstruction, but appropriate experimental techniques have not been available until recently. Here we present noble gas concentrations measured in the sediment pore water of Lake Issyk‐Kul (Kyrgyzstan) which demonstrate for the first time the value of the sediment pore water archive for paleoclimate reconstruction. The noble gas profiles in the sediment indicate that the salinity of the lake water during the mid‐Holocene was more than twice its present value of 6.0 g/kg, implying a 200‐m lower lake level.

Simultaneous determination of small organic and inorganic anions in environmental water samples by ion-exchange chromatography

Anion-exchange chromatography at elevated pH values is the method of choice for the simultaneous determination of weak and strong low-molecular-mass organic and inorganic acids. These are important species found in the environment where most of them are formed and further degraded, particularly if microbial activities are involved. A step gradient procedure with a weak eluent such as borate on a low-capacity column was developed for the simultaneous one-run one-column determination of most of these types of components in environmental water samples. High selectivity and detection limits below 1 μM were achieved. Other yet unknown coelutions of 3-hydroxybutyrate with fluoride and 2-hydroxybutyrate with propionate were found. The different retention characteristics of a high-capacity column was used to obtain additional evidence to identify interfering components. These separation procedures were used to investigate fog, lake sediment pore water and rain after roof run-offs.

Dissolved Organic Carbon Cycling in Forested Watersheds: A Carbon Isotope Approach

Dissolved organic carbon (DOC) is important in the acid‐base chemistry of acid‐sensitive freshwater systems; in the complexation, mobility, persistence, and toxicity of metals and other pollutants; and in lake carbon metabolism. Carbon isotopes (13C and 14C) are used to study the origin, transport, and fate of DOC in a softwater catchment in central Ontario. Precipitation, soil percolates, groundwaters, stream, beaver pond, and lake waters, and lake sediment pore water were characterized chemically and isotopically. In addition to total DOC, isotopic measurements were made on the humic and fulvic DOC fractions. The lake is a net sink for DOC. Δ14C results indicate that the turnover time of most of the DOC in streams, lakes, and wetlands is fast, less than 40 years, and on the same time scale as changes in acidic deposition. DOC in groundwaters is composed of older carbon than surface waters, indicating extensive cycling of DOC in the upper soil zone or aquifer.

Mobilization of radiocaesium in pore water of lake sediments

THE deposition of large amounts of radiocaesium from nuclear weapons testing and from accidents such as Chernobyl has necessitated study of the fate of these long-lived radioisotopes in the natural environment. Caesium is known to interact strongly with micaceous clay minerals in soils and sediments1–4. Radiocaesium can therefore be removed from the water column in lake systems by settling particles and surface sediments5. This process reduces its mobility and the risk of assimilation by biota. Nevertheless, there are indications that radiocaesium may be mobilized from lacustrine anoxic sediments6. Direct evidence, however, can come only from measurements on pore water from lake sediments, and here we report such measurements. Actual in situsolid/liquid distribution coefficients (Kd values), determined from our data, provide convincing evidence for post-depositional mobilization of particle-bound 137Cs. This is probably caused by ion exchange with NH4+which reaches high concentrations in anoxic pore waters. The pore-water data indicate that radiocaesium is returned to the water column and thus becomes available for uptake by aquatic organisms.

Ancient Ice Islands in Salt Lakes of the Central Andes

Massive blocks of freshwater ice and frozen sediments protrude from shallow, saline lakes in the Andes of southwestern Bolivia and northeastern Chile. These ice islands range up to 1.5 kilometers long, stand up to 7 meters above the water surface, and may extend out tens of meters and more beneath the unfrozen lake sediments. The upper surfaces of the islands are covered with dry white sediments, mostly aragonite or calcite. The ice blocks may have formed by freezing of the fresh pore water of lake sediments during the "little ice age." The largest blocks are melting rapidly because of possibly recent increases in geothermal heat flux through the lake bottom and undercutting by warm saline lake water during the summer.