Hydrophysical aspects of oxygen regime formation in a shallow ice-covered lake

Long-term observational data on a small, shallow Lake Vendyurskoe (Karelia) were used to analyze the space and time dissolved-oxygen dynamics in winter. Biochemical consumption was found to play a leading role in the reduction of dissolved-oxygen concentration in lake water in winter. The total decrease in the amount of dissolved oxygen since the beginning of under-ice period until mid-April was shown to amount to one third of the initial value. The year-to-year variations in winter oxygen consumption are ~10%, suggesting the process to be stable in the years of observations. The rate of oxygen consumption and variations in dissolved oxygen content of lake water in winter were evaluated. The analysis and literary data allow us to conclude that the hydrophysical processes taking place in shallow lakes in winter have a considerable effect on their oxygen regime.     

Impact of light regimes on productivity patterns of benthic microbial mats in an antarctic lake: a modeling study

Filamentous cyanobacteria often dominate benthic microbial communities of antarctic lakes and usually exhibit saturation of photosynthesis at light intensities approximately 100 microEinst m-2 s-1. Incident light regimes are controlled by ice and snow accumulations overlaying water columns during much of the year. Thus, light availability to microbial mats is often below saturation intensity and is strongly influenced by modest changes in climatic factors. A model of net primary production for benthic mat communities of the subantarctic Sombre Lake, Signy Island, was developed (1) to evaluate depth-specific productivities of mat communities, (2) to test the relative importances of model parameters to mat production, and (3) to explore the potential impacts of climate change on mat production as manifested through changes in light regime. Simulated rates of net primary production corresponded to observations on a daily basis (approximately 1-4 micrograms C fixed mg-1 ash-free DW of mat d-1) but were an order of magnitude lower than estimates of net annual production based on field measurements (< or = 3 vs. 11-45 g C m-2 yr-1, respectively). Close examination suggested that the simulated values were more plausible. A detailed sensitivity analysis of model behavior revealed that variations in the time of ice and snow melt in spring accounted for 40-60% of the total variation in model behavior, emphasizing the importance of climatic factors to net primary production of mat communities and the sensitivity of mat production to climate change.     

Interpretation of metal profiles in a sediment core from lake geneva: metal mobility or pollution

The transition elements Mn, Fe, Co, Zn, Cu and Cr together with Pb and P were determined in three sequential extractions of sediment and in the pore water of a 35-cm sediment core from Lake Geneva. A high percentage of the mobile Mn, Fe, P, Co, Pb and Zn was extracted in the first (inorganic) fraction, whereas the mobile Cu and Cr were mostly found in the second (organic and sulfide) fraction. Mn was subject to recycling with solubilization from the surface sediment to the oxic bottom water where it was precipitated. Highly enriched Co and P values were observed in the top few mm of the sediment resulting from post depositional solubilization with upward migration and precipitation with oxi-hydroxides at the sediment surface. The slower increase of Cu, Zn and Pb concentrations towards the sediment/water interface are the result of an increase of anthropogenic sources over the past decades. A further increase in Pb in the first cm of the core is believed to be related to the freshly precipitated Mn oxi-hydroxides.     

Sediment profiles of less commonly determined elements measured by Laser Ablation ICP-MS

Anthropogenic influences on trace element profiles in dated sediments from estuaries have been often documented, with the vast majority of studies focusing on a short list of high-abundance trace elements. Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) provides a new approach that minimizes sample preparation and contamination while yielding data on a much larger list of elements simultaneously. We present concentrations and enrichment factor profiles for 22 elements at a locality that is 50 km southeast of Baltimore, the principal industrial city on Chesapeake Bay. Samples representing deposition over almost the entire 20th century were obtained from two archived cores collected 20 years apart. The following elements exhibit profiles consistent with a strong anthropogenic influence, i.e. enrichment after 1920 followed by decline after ca.1980, possibly reflecting increased regulatory efforts: Mn, Co, Cu, Zn, Ag, Cd, In, Sn, Sb, Te, Tl, Pb and Bi. As expected, the redox-sensitive elements: Mo, Re and U have similar profiles to one another. Previously, the potentially hazardous elements, Ag, In, Sb, Te, Tl and Bi, have been measured only rarely in estuarine sediments and never in Chesapeake Bay. Our discovery that their profiles track those of well-known pollutants underscores a need to investigate their sources, transport and biogeochemical behavior. Several rarely determined trace elements, Ga, Ge and Nb, exhibit trendless profiles, as do the major elements, Ti and Fe.     

Sediment diffusive fluxes of Fe,Mn, and P in a eutrophic lake: Contribution from lateral vs bottom sediments

Water column data and porewater profiles are used to study the chemical evolution with time and with depth of a eutrophic lake. By using different approaches, diffusion fluxes for dissolved iron, manganese and phosphate are calculated and used to describe the processes occurring at the sediment-water interface as well as in the hypolimnion of the lake. These data are used in the elaboration of a qualitative model to describe the chemical behaviour of the sedimentary interface of an anoxic lake with emphasis on the Fe/P/S system. Acorona model is proposed to explain the evolution with time of the diffusion process by estimating the relative contribution of bottom and lateral sediment surfaces to the total fluxes of dissolved elements diffusing from the sediment to the overlying water. As the hypolimnion becomes more anoxic, it has been observed that lateral sediment surfaces (16 to 10 meters in depth) represents a larger supplier of diffusing dissolved components than the bottom sediment portion (bottom to 18 meters).     

Hydrocarbons in a wilderness lake

The hydrocarbons found in Green Lake, Ontario, Canada, are believed to be of natural origin coming from plant and animal organisms.     

Interactions between groundwater seepage and sediment porewater sulphate concentration profiles in lake anna,Virginia

Most sulphur diagenesis models predict that SO₄^2- concentrations decrease exponentially with increasing sediment depth and are lower than that of the overlying water throughout the sediments. Low SO₄^2- concentrations (less than 0.2 mM) are common in the sediments of Lake Anna that receive acid mine drainage; however, sediment with as much as 20 mM SO₄^2- at about 20cm below the sediment surface is also seen in this section of the lake. A decision tree was proposed to investigate the cause of the high SO₄^2- concentrations at depth (HSD) in the sediment. The first possibility proposed was that an increase in the quantity of groundwater flowing through Lake Anna sediments may increase groundwater advection of SO₄^2- or oxygen which would induce sulphide oxidation. This hypothesis was tested by measuring groundwater flow. HSD profiles were found in a discrete region of the lake; however, stations having these profiles did not have higher groundwater flow than other sites sampled. Alternate explanations for the HSD profiles were that the region in which they occurred had: (1) unusual sediment chemical compositions; (2) a different source of regional groundwater, or (3) a lateral intrusion of high SO₄^2- groundwater. There were no differences in sulphide and organic matter concentrations between the two regions. The area which has HSD in the sediment covers a large area in the middle of the lake, so it is unlikely that it has a unique source of regional groundwater. The third alternative was supported by the fact that in all three sample years, HSD stations were located in the preimpoundment stream channel, which is a likely lateral flow path for groundwater containing high SO₄^2- concentrations.     

Oxygen patchiness in a lake

The presence and extent of small scale vertical structure in dissolved oxygen were investigated in a tropical Australian lake. At a 9 m deep site an extremely high oxygen patch appeared near the bottom boundary. Light levels reaching the bottom boundary during the life of the patch exceeded 10 µEinst m^–2 s^–1. The patch remained for 1.5 h before gradually reaching ambient oxygen levels. The patch's disappearance coincided with decreasing light levels during the late afternoon. Differences in the extent of oxygen vertical patchiness between deep (16 m) and shallow (9 m) sites were also observed. At the deep site, the distribution of oxygen steps over the water column coincided largely with the distribution of temperature steps. This indicates the dominance of physical processes at that site. At the shallow site, marked vertical patchiness in oxygen was observed with no similar patchiness in temperature. This indicates the prevalence of biological and chemical processes.     

湖泊沉积物中磷酸盐氧同位素前处理方法对比

磷酸盐氧同位素(δ~(18)OP)是一种有效的磷源示踪方式.由于湖泊沉积物的组成十分复杂,必须对样品进行除碳处理和纯化处理.本文对目前应用较为广泛的几种前处理方法进行比较,包括NaClO处理和H_2O_2处理等除有机碳方法,以及Blake法和Mc Laughlin法等纯化方法,以期获得适用于湖泊沉积物磷酸盐氧同位素的前处理方法.结果表明:(1)NaClO处理可以保证较高的无机磷提取效率,同时能有效地减少无机磷提取液中有机质含量,且对不同形态磷的破坏较小;H2O2对有机质的去除效果不稳定,且处理后样品磷形态之间发生转化,显著增加了提取的无机磷浓度.(2)Blake法和Mc Laughlin法分别采用磷钼酸铵(APM)+磷酸铵镁(MAP)沉淀和Ce PO4沉淀对样品进行纯化.在纯化处理湖泊沉积物过程中,Blake法优于Mc Laughlin法,主要体现为有机质去除率高,并且磷的回收率较为稳定.(3)经Blake法纯化丹麦Nordborg湖沉积物样品得到的Ag_3PO_4中C、N含量低于Mc Laughlin法且重现性好.本文结合NaClO法与Blake法的优点,建立了一种适合湖泊沉积物的磷酸盐氧同位素前处理方法:首先用2.5%NaClO对沉积物样品进行除碳预处理,然后对磷酸盐提取液依次通过氢氧化镁共沉淀(MAGIC)、APM+MAP沉淀、阳离子交换树脂处理,最后生成Ag3PO4沉淀.     

Modeling the depletion of dissolved oxygen in a lake due to algal bloom: Effect of time delay

We propose and analyze a non-linear mathematical model for algal bloom in a lake to account for the delay in conversion of detritus into nutrients. It is assumed that there is a continuous inflow of nutrients in the lake due to agricultural run off. The model involves four variables, namely nutrient concentration, algal population density, detritus density and dissolved oxygen concentration. The dynamics of the model is studied in terms of local stability analysis and Hopf-bifurcation analysis. It is found that the positive equilibrium of the model may switch from stability to instability to stability, and eventually instability sets in under certain conditions. The numerical simulation is performed to support the analytical results.     

Solute transfer across the sediment surface of a eutrophic lake: I. Porewater profiles from dialysis samplers

Porewater profiles often are used to identify and quantify important biogeochemical processes occurring in lake sediments. In this study, multiple porewater profiles were obtained from two eutrophic Swiss lakes using porewater equilibrators (peepers) in order to examine spatial and seasonal trends in biogeochemical processes. Variability in profile shapes and concentrations was small on spatial scales of a few meters, but the uncertainty in calculated diffusive fluxes across the sediment surface was, on average, 35%. Focusing of Fe and Mn oxides toward the lake center resulted in systematic increases in porewater concentrations and diffusive fluxes of Fe²⁺ and Mn²⁺ with increasing water depth; these fluxes are postulated to be regulated by the pH-dependent dissolution of reduced-metal phases. Despite higher concentrations of inorganic carbon, NH ₄ ⁺ , Si and P in pelagic compared to littoral sites, diffusive fluxes of these substances across the sediment surface increased only slightly or not at all with increasing water depth. Porewater profiles did reveal temporal changes in Fe²⁺, Mn²⁺, Ca²⁺ and Mg²⁺ that were an indirect result of the large, seasonal changes in seston deposition, but no clear seasonal variations were found in diffusive fluxes of nutrients across the sediment surface. The intense mineralization occurring at the sediment surface was not reflected in the porewater profiles nor in the calculated diffusive fluxes. Calculated diffusive fluxes across the sediment surface resulted from decomposition occurring primarily in the top 5–7 cm of sediment. Diffusive fluxes from this subsurface mineralization were equal to the solute release from mineralization occurring at the sediment-water interface. Buried organic matter acts as a memory of previous lake conditons; it will require at least a decade before reductions in nutrient inputs to lakes fully reduce the diffusive fluxes into the lake from the buried reservoir of organic matter.     

Impacts of regional warming on long‐term hypolimnetic anoxia and dissolved oxygen concentration in a deep lake

Although few reports have described long‐term continuous anoxia in aquatic systems, Lake Ikeda in Japan experienced such conditions in the hypolimnion from 1990 to 2010. The present study aimed to assess temporal fluctuations in the lake's thermal stability from 1978 to 2011 to understand the influence of regional climate change on hypolimnetic anoxia in this lake. Because complete vertical mixing, which supplies dissolved oxygen (DO) to the hypolimnion, potentially occurs on February, we calculated the Schmidt stability index (S) in February and compared it with hypolimnetic DO dynamics. Vertical water temperature profiles were calculated using a one‐dimensional model, and calculated temperatures and meteorological data were used to analyse annual fluctuations in water temperatures, thermocline depth, meteorological variables and S. We estimated that mean annual air and volume‐weighted water temperatures increased by 0.028 and 0.033 °C year^?1, respectively, from 1978 to 2011. Between 1986 and 1990, S and water temperature increased abruptly, probably due to a large upwards trend in air temperature (+0.239 °C year^?1). We hypothesize that a mixing regime that lacked overturn took effect at this time and that this regime lasted until 2011, when S was particularly small. These results demonstrate that abrupt climate warming in the late 1980s likely triggered the termination of complete mixing and caused the 21‐year period of successive anoxia in Lake Ikeda. We conclude that the lake response to a rapid shift in regional climate conditions was a key factor in changing the hypolimnetic water environment and that thermal stability in winter is a critical environmental factor controlling the mixing regime and anoxic conditions in deep lakes. Copyright © 2014 John Wiley & Sons, Ltd.     

The most acidified Austrian lake in comparison to a neutralized mining lake

This study investigated two mining lakes located in the north of Lower Austria. These lakes arose 45 years ago when open cast lignite mining ceased. The lakes are separated by a 7-m wide dam. Due to the oxidation of pyrite, both lakes have been acidified and exhibit iron, sulphate, and heavy metal concentrations several orders of magnitude higher than in circumneutral lakes. The water column of both lakes is divided into two layers by a pronounced chemocline. The smaller mining lake (AML), with pH close to of 2.6, is the most acidic lake in Austria, whereas flooding with stream water and by drainage from the surrounding fields neutralized the adjacent larger pit lake. The goal of our study was to investigate the effect of flooding on its physical, chemical and biological properties, in comparison to the pristine AML. Even relative to other extremely acidic lakes, the flora and fauna in the AML was reduced and composed of only two flagellate, one ciliate, and one rotifer species. The simplified pelagic food web in the mixolimnion consisted of heterotrophic bacteria, the mixotrophic flagellates Chlamydomonas acidophila and Ochromonas sp., the ciliate Oxytricha sp., and the rotifer Cephalodella sp. The latter two are as yet undescribed new species. The heliozoan Actinophrys sp. that may act as top predator occurred only in low abundance. The euglenid Lepocinclis buetschlii formed a stable deep chlorophyll maximum (DCM) at 7 m depth. Highest cell numbers of L. buetschlii in the DCM exceeded 10⁸ L^?1. The neutralized mining lake harboured higher plankton diversity similar to that of natural circumneutral lakes. A peak of at least 16 different phytoplankton taxa was observed during summer. The zooplankton consisted of several copepod species, daphnids and other cladocerans, and at least six different rotifer species. Several fish species occurred in the neutralized lake. Although the effect of non-permanent flooding was largely sustainable, interannual fluctuations of the pH affected the plankton community and reduced its species diversity.     

雅鲁藏布大峡谷格嘎古堰塞湖沉积岩石磁学性质指示的溃决事件

末次冰期时,在雅鲁藏布大峡谷入口处发育了一个古冰川堰塞湖,称为格嘎古堰塞湖.该堰塞湖是认识冰川阻江地貌效应的重要地质证据.古冰川堰塞湖可能会发生多次溃决洪水,通过堰塞湖沉积的分析可以获取堰塞期间的水文事件的信息.本文通过对古堰塞湖沉积39个样品多种磁学参数的详细分析发现,湖相沉积中的砂层低频磁化率（Xlf）为291×10-8m3/kg,泥质沉积的Xlf仅为42×10-8m3/kg;而非磁滞剩磁磁化率（XARM）和饱和等温剩磁（SIRM）的差别则较小.进一步的X-T、Loop和IRM研究以及XARM/Xlf表明,砂层中包含较多的粗颗粒磁铁矿是Xlf较高的主要原因,说明砂层中的磁性矿物没有经过风化破坏,应为近源沉积,并且快速埋藏,指示了溃决事件.本文的结果表明,利用岩石磁学性质以检测古堰塞湖溃决事件是一种可行的新方法.     

OSL dating of past lake levels for a large dammed lake in southern Tibet and determination of possible controls on lake evolution

Fluvio‐lacustrine terraces along Phung Chu (river) on the central southern Tibetan Plateau indicate that a large palaeo‐dammed‐lake formerly existed in this area. Based on landscape survey, optically stimulated luminescence (OSL) dating and sedimentary analyses, this research shows that the Phung Chu was blocked and a dammed‐lake over 2500 km² in size formed before 30 ka ago. OSL dating analysis suggests the fluvio‐lacustrine sediments were well bleached and yield accurate age estimates for two lake drainage events. The first drainage event took place after 30 ka, resulted in river incision and formed a high terrace at 50 m height from the present river level. The second drainage happened after 3.7 ka, resulted in further river incision and formed the second terrace at 25 m height from the present river level. According to the distribution of the fluvio‐lacustrine sediments, active normal faults (particularly the Kharta Fault) in this region and the high gradient slopes after Phung Chu enters the Yö Ri gorge, seismically‐induced landsliding is regarded as highly likely to have been the cause of river blockage and associated formation of a dammed‐lake, although glacial damming is also a possible cause. The volume of drainages from this dammed‐lake may have led to catastrophic flooding and analogous modern lakes represent significant geo‐hazard risks to down‐river human settlements. As dammed‐lakes are special phases in fluvial evolution, often involving river blockage, breakthrough and drastic catchment change, these processes can reveal how tectonic or climatic events modify landforms. However, such tectonic‐derived landform changes can also impact palaeo‐climate of the region. Thus this study has added new evidence regarding the evolutionary history of a dammed lake including its formation, duration, extent and final drainage, which is crucial for understanding its general landscape process mechanisms and for better assessing geo‐hazard risks. Copyright © 2016 John Wiley & Sons, Ltd.     

Decomposition of macrophytes in a shallow subtropical lake

Submerged macrophyte detritus is a major component of the organic matter entering shallow lakes. Plant litter decomposition is a complex process that is mediated by microorganisms and some invertebrates. However, the role that aquatic organisms play in the decomposition of macrophytes in shallow subtropical lakes is unclear. This study compared the decomposition rates of Potamogeton pectinatus and Chara zeylanica in a shallow lake (southern Brazil) and assessed the fungal biomass and the macroinvertebrate community associated with the detritus. Aliquots of both species were incubated in litter bags and placed in the lake. After 1, 7, 20, 40, 60, and 80 days of incubation, one set of litter bags was removed from the lake. In a laboratory, plant material was washed for the determination of decomposition rates, chemical characterisation, and quantification of microorganisms and invertebrates. After 80 days of incubation, there was no C. zeylanica detritus, with a decomposition that was four times faster than that of P. pectinatus. The chemical composition was also different between the two detritus, with P. pectinatus showing a higher concentration of nitrogen, phosphorus, organic matter, polyphenols, and carbon. The fungal biomass was similar between the two species. In total, 7502 invertebrates belonging to 27 taxa were sampled in this study. The composition and abundance of invertebrates was different between the two species. In conclusion, the chemical structure of the macrophyte species studied was important for the microorganisms’ and invertebrates’ colonisation. In addition, leaching had an important function in the initial degradation process.     

不同溶解氧水平下湖泊底泥-水界面磷交换影响因素分析

在实验室控制条件下,研究了玄武湖底泥在饱和溶解氧、75%、50%、25%、0%溶解氧水平下底泥-水界面磷交换,探讨了溶解氧对底泥-水界面磷交换的影响途径.结果表明:(1)上覆水溶解氧与玄武湖底泥溶解性磷酸盐、溶解性总磷释放速率呈开口向上的抛物线关系;(2)上覆水溶解氧水平可以决定磷在底泥-水界面交换中的转换方向,而且还影响间隙水中溶解氧扩散深度,25%、50%、75%和饱和溶解氧水平下溶解氧最大扩散深度分别为0.974cm、1.377cm、1.687cm和1.948cm,溶解氧在间隙水中最大扩散深度影响底泥-水界面的磷交换;(3)溶解氧可通过影响底泥-水界面处电位、藻类聚磷作用以及pH来影响底泥-水界面的磷交换.     

Sediment accumulation rates in subarctic lakes: Insights into age-depth modeling from 22 dated lake records from the Northwest Territories,Canada

Age-depth modeling using Bayesian statistics requires well-informed prior information about the behavior of sediment accumulation. Here we present average sediment accumulation rates (represented as deposition times, DT, in yr/cm) for lakes in an Arctic setting, and we examine the variability across space (intra- and inter-lake) and time (late Holocene). The dataset includes over 100 radiocarbon dates, primarily on bulk sediment, from 22 sediment cores obtained from 18 lakes spanning the boreal to tundra ecotone gradients in subarctic Canada. There are four to twenty-five radiocarbon dates per core, depending on the length and character of the sediment records. Deposition times were calculated at 100-year intervals from age-depth models constructed using the ‘classical’ age-depth modeling software Clam. Lakes in boreal settings have the most rapid accumulation (mean DT 20 ± 10 yr/cm), whereas lakes in tundra settings accumulate at moderate (mean DT 70 ± 10 yr/cm) to very slow rates, (>100 yr/cm). Many of the age-depth models demonstrate fluctuations in accumulation that coincide with lake evolution and post-glacial climate change. Ten of our sediment cores yielded sediments as old as c. 9000 cal BP (BP = years before AD 1950). From between c. 9000 cal BP and c. 6000 cal BP, sediment accumulation was relatively rapid (DT of 20–60 yr/cm). Accumulation slowed between c. 5500 and c. 4000 cal BP as vegetation expanded northward in response to warming. A short period of rapid accumulation occurred near 1200 cal BP at three lakes. Our research will help inform priors in Bayesian age modeling.     

Nutrients and organic matter in the surface sediment of a submerged macrophyte zone in a eutrophic lake:Implications for lake management

Little is known about the distribution and risk levels of nutrients and organic matter(OM) in the surface sediment of shallow submerged macrophyte-dominated lakes. In the current study, sixty surface sediment samples were collected from Xukou Bay, a typical submerged macrophyte-dominated zone in Lake Taihu, China. A 60-day degradation experiment of Potamogeton malaianus, a dominant species in the bay,was done in the laboratory. The results demonstrated that the ranges of total nitrogen(TN) and t...