Long-term variability of oxygen and mineral phosphorus concentrations in Lake Dal’nee (Kamchatka)

Many-year data on the concentrations of O₂ and mineral phosphorus in a fattening-spawning water body for the Pacific salmon (red salmon) are presented; the seasonal and year-to-year dynamics of these con-centrations are analyzed. It is found that the lake water mass features a high concentration of O₂, the upper 20-m layer being most aerated. It is shown that the year-to-year variability of the concentration of O₂ dissolved in the lake water depends on the amount of organic matter coming with groundwater and surface runoff. The oxygen and phosphorus regimes of the lake at low and abundant entries of puberal red salmon for spawning are considered.     

Quantitative reconstruction of the lake water paleotemperature of Daihai Lake, Inner Mongolia, China and its significance in paleoclimate

By measuring Sr/Ca ratios of the ostracod shells (Limnocthere cf. inopinata) in sediments of the Daihai Lake, and combined with Sr²⁺/Ca²⁺ ratios of the lake water, this paper obtained paleosalinity of the lake water. Vaporizing experiment of the lake water in laboratory showed that there was a quantitative relationship between salinity and oxygen isotope. Using this relationship, oxygen isotope values of the paleo-lake water were calculated. By measuring the oxygen isotope of the authigenic carbonate in the lake’s sediments, and in combination with the oxygen isotope values of the paleo-lake water, the paleotemperature of the lake water was calculated. Finally, based on these proxies, the paleoclimate in the lake basin was explored.     

Chemical evidence of water movements in the deepest part of Lake Leman (Lake Geneva)

Regular surveys of bottom water chemistry (SiO₂, O₂, Fe, Mn) have been carried from 1978 to 1986 in the deepest 30 m of Lake Léman (max. depth 309 m) including interface waters sampled with a Jenkins Mortimer corer. When compared to normal chemical gradients near bottom, i.e. O₂ decrease and SiO₂ increase, three types of anomalies (lens, interface, and behaviour) have been observed on O₂ and SiO₂, the most sensitive chemical species. These anomalies were found throughout the year, in several stations of the deepest part of the lake and even along the slope of the lake basin. Major anomalies (O₂ + 3 to 10 mg ·l^–1; SiO₂ -1 to 2 mg·l^–1) were generally found at the sediment water interface and may extend 10–20 m above the sediment and last 10 weeks. Others marked lens anomalies could be observed for 3 to 4 months. Several mechanisms are probably responsible for this injection of surface waters along the lake slope (accumulation of turbid water on lake banks after severe windstorms; river density currents due to temperature and/or turbidity difference with lake waters). These water-inputs do not represent important volumes ( 1% total lake volume) but, when occuring at the interface, they ensure a sufficient oxygen level to prevent diffusion of phosphate and ammonia from pore waters when winter lake overturns do not reach bottom layers (from 1972 to 1980). Complete overturns, as observed in 1980/81, are connected with major interface anomalies (bottom O₂ moves up from 2 to 10 mg·l^–1) occuring before surface mixing reaches the deepest layers.     

Dual effects of precipitation and evaporation on lake water stable isotope composition in the monsoon region

We present the results of a 3‐year monitoring programme of the stable isotope composition of lake water and precipitation at Taozi Lake, in the East Asian monsoon region of China. Our aims were to reveal the spatiotemporal pattern of variation of stable isotopes in a small closed‐basin lake and to quantitatively determine the impacts of precipitation and evaporation on the stable isotope composition of lake water under a humid monsoon climate. In the time domain, the stable oxygen isotopic ratio of the lake water (δ¹⁸O_L) exhibited substantial seasonal and interannual variations, but the isotope variations between different precipitation events substantially exceeded seasonal and interannual variations. Compared with the stable isotopes in precipitation, δ¹⁸O_L was substantially positive and d_L was negative. In the space domains, the lake water was homogeneously mixed. Indicated by statistic analyses, precipitation plays a dominant role in dynamic of the lake stable isotope during precipitation events of relatively large magnitude, whereas the effect of evaporation is dominant during smaller precipitation events. Results advance our understanding of the stable isotope change rule in the process of lake water evaporation, and it is helpful to identify the climatic significance recorded in stable isotopic compositions of lake bottom sediments.     

Methan- und Sauerstoffhaushalt im mesotrophen Lungernsee

Prealpine Lake Lungern shows in spite of low primary production rates (120 g C/m². year) and full winter overturns a complete oxygen depletion in the deepest hypolimnion (65–70 m below surface) towards the end of summer stagnation. Periodical examinations of O₂- and CH₄-concentrations, CH₄-oxidation rates and temperature in the water column during 1975/76 enabled an O₂-balance of Lake Lungern. The direct measurement of the CH₄-flux at the sediment-water-interface and of the CH₄-concentrations in sediment cores as well as the determination of the age of methane bubbles lead to the conclusion, that the hypolimnic oxygen depletion is partly due to the oxidation of fossile methane penetrating the lake from below.      

Untersuchungen über die Bodenfauna des Litorals im eutrophierenden Sempachersee

The Sempachersee (Switzerland), a facultatively oligomictic lake with visibility measuring according to Secchi of between 1.3 m and 12.9 m, is characterized by an oxygen minimum of 4 mg O₂/l in the metalimnion in autumn and an almost total lack of oxygen in the greatest depths of the lake. Phosphate-phosphorus is used up in the trophogenic zone and is found in quantities of between 20 and 24 μg/l during the overturn period. Nitrate-nitrogen concentrations of between 0.55 and 0.6 mg/l are also present during overturn. Phanerogamic growth along the shore is sparse; the variety of animal species as well as the respective number of organisms are limited although the reason for this has not been determined.      

Geochemistry of the magmatic–hydrothermal system of Kawah Ijen volcano, East Java, Indonesia

Samples from Kawah Ijen crater lake, spring and fumarole discharges were collected between 1990 and 1996 for chemical and isotopic analysis. An extremely low pH (<0.3) lake contains SO₄–Cl waters produced during absorption of magmatic volatiles into shallow ground water. The acidic waters dissolve the rock isochemically to produce “immature” solutions. The strong D and ¹⁸O enrichment of the lake is mainly due to enhanced evaporation at elevated temperature, but involvement of a magmatic component with heavy isotopic ratios also modifies the lake D and ¹⁸O content. The large Δ_SO4–S⁰ (23.8–26.4‰) measured in the lake suggest that dissolved SO₄ forms during disproportionation of magmatic SO₂ in the hydrothermal conduit at temperatures of 250280°C. The lake δ¹⁸O_SO4 and δ¹⁸O_H2O values may reflect equilibration during subsurface circulation of the water at temperatures near 150°C. Significant variations in the lake's bulk composition from 1990 to 1996 were not detected. However, we interpret a change in the distribution and concentration of polythionate species in 1996 as a result of increased SO₂-rich gas input to the lake system.Thermal springs at Kawah Ijen consist of acidic SO₄–Cl waters on the lakeshore and neutral pH HCO₃–SO₄–Cl–Na waters in Blawan village, 17 km from the crater. The cation contents of these discharges are diluted compared to the crater lake but still do not represent equilibrium with the rock. The SO₄/Cl ratios and water and sulfur isotopic compositions support the idea that these springs are mixtures of summit acidic SO₄–Cl water and ground water.The lakeshore fumarole discharges (T=170245°C) have both a magmatic and a hydrothermal component and are supersaturated with respect to elemental sulfur. The apparent equilibrium temperature of the gas is 260°C. The proportions of the oxidized, SO₂-dominated magmatic vapor and of the reduced, H₂S-dominated hydrothermal vapor in the fumaroles varied between 1979 and 1996. This may be the result of interaction of SO₂-bearing magmatic vapors with the summit acidic hydrothermal reservoir. This idea is supported by the lower H₂S/SO₂ ratio deduced for the gas producing the SO₄–Cl reservoir feeding the lake compared with that observed in the subaerial gas discharges. The condensing gas may have equilibrated in a liquid–vapor zone at about 350°C.Elemental sulfur occurs in the crater lake environment as banded sediments exposed on the lakeshore and as a subaqueous molten body on the crater floor. The sediments were precipitated in the past during inorganic oxidation of H₂S in the lake water. This process was not continuous, but was interrupted by periods of massive silica (poorly crystallized) precipitation, similar to the present-day lake conditions. We suggest that the factor controlling the type of deposition is related to whether H₂S- or silica-rich volcanic discharges enter the lake. This could depend on the efficiency with which the lake water circulates in the hydrothermal cell beneath the crater. Quenched liquid sulfur products show δ³⁴S values similar to those found in the banded deposits, suggesting that the subaqueous molten body simply consists of melted sediments previously accumulated at the lake bottom.     

Evaluation of volcanic gas analysis from surtsey volcano, iceland 1964–1967

Methods used previously to remove compositional modifications from volcanic gas analyses for Mount Etna and Erta'Ale lava lake have bean employed to estimate the gas phase composition at Nyiragongo lava lake, based on samples obtained in 1959. H₂O data were not reported in 11 of the 13 original analyses. The restoration methods have been used to estimate the H₂O contents of the samples and to correct the analyses for atmospheric contamination, loss of sulfur and for pre- and pest-collection oxidation of H₂S, S₂, and H₂. The estimated gas compositions are relatively CO₂-rich, low in total sulfur and reduced. They contain approximately 35–50% CO₂ 45–55% H₂O, 1–2% SO₂, 1–2% H₂., 2–3% CO, 1.5–2.5% H₂S, 0.5% S₂ and 0.1% COS over,he collection temperature range 102° to 960° C. The oxygen fugacities of the gases are consistently about half an order of magnitude below quartz-magnetite-fayalite. The low total sulfur content and resulting low atomic S/C of the Nyiragongo gases appear to be related to the relatively low f_O2 of the crystallizing lava. At temperatures above 800°C and pressures of 1–1.5 k bar, the Nyiragongo gas compositions resemble those observed in primary fluid inclusions believed to have formed at similar temperatures and pressures in nephelines of intrusive alkaline rocks. Cooling to 300°C, with f_O2 buffered by the rock, results in gas compositions very rich in CH₄ (50–70%) and resembling secondary fluid inclusions formed at 200–500°C in alkaline rocks. Below 600°C the gases become supersaturated in carbon as graphite. These inferences are corroborated by several reports of hydrocarbons in plutonic alkaline rocks, and by the presence of CH₄-rich waters in Lake Kivu — a lake on the flanks of Nyiragongo volcano.     

A sensitivity analysis of lake water level response to changes in climate and river regimes

Lake water level regimes are influenced by climate, hydrology and land use. Intensive land use has led to a decline in lake levels in many regions, with direct impacts on lake hydrology, ecology and ecosystem services. This study examined the role of climate and river flow regime in controlling lake regimes using three different lakes with different hydraulic characteristics (volume-inflow ratio, CIR). The regime changes in the lakes were determined for five different river inflows and five different climate patterns (hot-arid, tropical, moderate, cold-arid, cold-wet), giving 75 different combinations of governing factors in lake hydrology. The input data were scaled to unify them for lake comparisons. By considering the historical lake volume fluctuations, the duration (number of months) of lake volume in different ‘wetness’ regimes from ‘dry’ to ‘wet’ was used to develop a new index for lake regime characterisation, ‘Degree of Lake Wetness’ (DLW). DLW is presented as two indices: DLW₁, providing a measure of lake filling percentage based on observed values and lake geometry, and DLW₂, providing an index for lake regimes based on historical fluctuation patterns. These indices were used to classify lake types based on their historical time series for variable climate and river inflow. The lake response time to changes in hydrology or climate was evaluated. Both DLW₁ and DLW₂ were sensitive to climate and hydrological changes. The results showed that lake level in high CIR systems depends on climate, whereas in systems with low CIR it depends more on river regime.     

Hydrogen emissions from Erebus volcano, Antarctica

The continuous measurement of molecular hydrogen (H₂) emissions from passively degassing volcanoes has recently been made possible using a new generation of low-cost electrochemical sensors. We have used such sensors to measure H₂, along with SO₂, H₂O and CO₂, in the gas and aerosol plume emitted from the phonolite lava lake at Erebus volcano, Antarctica. The measurements were made at the crater rim between December 2010 and January 2011. Combined with measurements of the long-term SO₂ emission rate for Erebus, they indicate a characteristic H₂ flux of 0.03?kg s^–1 (2.8?Mg? day^–1). The observed H₂ content in the plume is consistent with previous estimates of redox conditions in the lava lake inferred from mineral compositions and the observed CO₂/CO ratio in the gas plume (～0.9 log units below the quartz–fayalite–magnetite buffer). These measurements suggest that H₂ does not combust at the surface of the lake, and that H₂ is kinetically inert in the gas/aerosol plume, retaining the signature of the high-temperature chemical equilibrium reached in the lava lake. We also observe a cyclical variation in the H₂/SO₂ ratio with a period of ～10?min. These cycles correspond to oscillatory patterns of surface motion of the lava lake that have been interpreted as signs of a pulsatory magma supply at the top of the magmatic conduit.     

Geochemistry of the acid Kawah Putih lake, Patuha Volcano, West Java, Indonesia

Kawah Putih is a summit crater of Patuha volcano, West Java, Indonesia, which contains a shallow, 300 m-wide lake with strongly mineralized acid–sulfate–chloride water. The lake water has a temperature of 26–34°C, pH=<0.5–1.3, S^tot=2500–4600 ppm and Cl=5300–12 600 ppm, and floating sulfur globules with sulfide inclusions are common. Sulfur oxyanion concentrations are unusually high, with S₄O₆²⁻+S₅O₆²⁻+S₆O₆²⁻=2400 – 4200 ppm. Subaerial fumaroles (<93°C) on the lake shore have low molar SO₂/H₂S ratios (<2), which is a favorable condition to produce the observed distribution of sulfur oxyanion species. Sulfur isotope data of dissolved sulfate and native sulfur show a significant ³⁴S fractionation (ΔSO₄–S_e of 20‰), probably the result of SO₂ disproportionation in or below the lake. The lake waters show strong enrichments in ¹⁸O and D relative to local meteoric waters, a result of the combined effects of mixing between isotopically heavy fluids of deep origin and meteoric water, and evaporation-induced fractionation at the lake surface. The stable-isotope systematics combined with energy-balance considerations support very rapid fluid cycling through the lake system. Lake levels and element concentrations show strong seasonal fluctuations, indicative of a short water residence time in the lake as well.Thermodynamic modeling of the lake fluids indicates that the lake water is saturated with silica phases, barite, pyrite and various Pb, Sb, Cu, As, Bi-bearing sulfides when sulfur saturation is assumed. Precipitating phases predicted by the model calculations are consistent with the bulk chemistry of the sulfur-rich bottom sediments and their identified mineral phases. Much of the lake water chemistry can be explained by congruent rock dissolution in combination with preferential enrichments from entering fumarolic gases or brines and element removal by precipitating mineral phases, as indicated by a comparison of the fluids, volcanic rocks and lake bed sediment.Flank springs on the mountain at different elevations vary in composition, and are consistent with local rock dissolution as a dominant factor and pH-dependent element mobility. Discharges of warm sulfate- and chloride-rich water at the highest elevation and a near-neutral spring at lower level may contain a small contribution of crater-lake water. The acid fluid-induced processes at Patuha have led to the accumulation of elements that are commonly associated with volcano-hosted epithermal ore deposits. The dispersal of heavy metals and other potentially toxic elements from the volcano via the local drainage system is a matter of serious environmental concern.     

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.     

Physico-chemical Limnology of Lake Naini Tal,Kumaun, Himalaya (U. P.), India

The monomictic lake at a height of 1937 m, having an area of 48 ha, a mean depth of 16 m and a maximum depth of 27 m, is subjected to such an intensive use in its drainage area that the lake became eutrophicated. The spatial-temporal distribution of important physico-chemical criteria is represented for a period of two years. The depth of visibility varies between 0.4 m (March) and 2 m (June). The thermal stratification keeps up from March to November; therefore in the deep water zone a typical oxygen depletion and an enrichment of PO₄? P (26 μg/l) and of N_inerg (940 μg/l) occur. The pH-value lies in the alkaline range and shows a significantly positive correlation with primary production and temperature and a negative correlation with the carbonate content. Also the oxygen concentration is positively correlated with the primary production and temperature. During stagnation, the sediment/water contact zone is free of oxygen for ca. 70 % of the area.     

太湖有色可溶性有机物(CDOM)对COD及BOD5的指示意义

化学需氧量(COD)、五日生化需氧量(BOD_5)及溶解性有机碳(DOC)是指示湖泊水质的重要指标,然而上述指标测定通常耗费大量时间、试剂及人力物力且排放大量有害废液.有色可溶性有机物(CDOM)是溶解性有机物(DOM)中可以强烈吸收光谱中的紫外光和可见光的部分,数据测定耗时短、方便快捷,且样品处理过程环境友好,能在很大程度上反映湖泊水质.本研究基于2016年2、5和8月在太湖均匀布设的32个采样点进行样品采集,运用光谱吸收与三维荧光-平行因子分析(EEMs-PARAFAC)探究太湖CDOM的光谱吸收和荧光组分,探讨CDOM光谱指标对湖泊BOD_5、COD及DOC浓度等湖泊环境质量指标的可替代性.结果表明:(1)运用EEMs-PARAFAC方法解析出3种荧光组分:类腐殖酸C1、类酪氨酸C2和类色氨酸C3.(2) COD和BOD_5和DOC在空间上呈现出相似的分布趋势,不同水期的最高值均出现在竺山湾和梅梁湾,由西北湖区至中部敞水区、东南湖湾递减.(3)在不同水期,COD、BOD_5、DOC浓度和C1组分均表现为丰水期极显著大于枯水期和平水期,a_(254)在丰、平、枯水期间无显著性差异,最大值出现在丰水期;C2与C3组分均在枯水期和平水期极显著大于丰水期.(4)在不同水文时期,COD、BOD_5和DOC浓度均与a_(254)、类腐殖酸C1呈显著正相关,丰水期太湖COD、BOD_5和DOC浓度与CDOM光谱指标的线性相关性要优于枯水期和平水期.(5) CDOM光谱指标在不同水文时期均能很好地替代COD、BOD_5和DOC等作为反映太湖水体中有机物污染程度及湖泊水质的指标.     

太湖流域降雨和湖水酸根阴离子长期变化及其环境意义

为揭示太湖流域降雨和湖水酸根阴离子长期变化特征及环境意义,通过历史数据收集和采样分析,对太湖流域降雨和湖水中的SO₄^2-、NO₃^-变化特征和来源进行了研究.结果表明：自1990s以来太湖流域降雨中SO₄^2-呈显著下降趋势,年平均下降率为0.28 mg/（L·a）;NO₃^-浓度却呈显著上升趋势,年平均增长率为0.05 mg/（L·a）,降雨中氮污染呈现加重的趋势.与之相反,湖水中SO₄^2-呈显著上升趋势,年平均增长率为1.24 mg/（L·a）;NO₃^-浓度却呈显著下降趋势,年平均下降率为0.02 mg/（L·a）.30年以来,太湖水体SO₄^2-/NO₃^-比值不断升高,远高于降水SO₄^2-/NO₃^-比值.研究认为：流域SO₂排放引起的酸沉降是湖水SO₄^2-浓度增长的最重要原因,但氮氧化物排放并未引起湖水NO₃^-浓度升高,说明太湖流域对大气沉降的氮氧化物有滞留作用,而太湖水体是流域大气沉降硫酸盐的重要汇.综合治理太湖流域酸性物质排放对防止太湖水体酸化和治理富营养化都具有重要意义.     

Tracing of Peroxidase Activity in Humic Lake Water

An enzyme assay was developed for studies on peroxidase activities in humic lake water. 3,4-Dimethoxybenzyl alcohol (veratryl alcohol, VeraOH) was used as tracer substrate, and peroxidase (EC 1.11.1.7) activity was measured by high-performance liquid chromatography. The chemical stability of VeraOH and its application as peroxidase substrate was tested under light and dark conditions, different hydrogen peroxide (H₂O₂) concentrations and humic matter contents. VeraOH was stable under low UV radiation at in situ conditions in lake water (<0.010...0.25 kJ m^–2 d^–1), laboratory conditions (<0.05...0.30 kJ m^–2 d^–1), and low (1...100 μM) H₂O₂ concentrations. However, peroxides oxidized VeraOH above 1...10 mM H₂O₂ concentration in sterile Millipore-Q and humic lake water. Dark incubations showed little VeraOH oxidation products. The developed peroxidase assay was tested in the growth medium of Phanerochaete chrysosporium and a bacteria isolate (P.M.D. 20.4.3.1) from mesohumic lake Pääjärvi. Peroxidase activities were also measured in natural microbial communities under standard laboratory and under in situ conditions in humic lake water. Incubation times of about 5 to 12 days were usually needed to record significant (P < 0.05) peroxidase activities, in lake waters. In situ peroxidase activities varied in pelagial surface water (0...0.5 m) on a seasonal scale between 74 nmol L^–1 h^–1 and 273 nmol L^–1 (mean: 176 nmol L^–1 h^–1) and within the water column between 110 nmol L^–1 h^–1 and 800 nmol L^–1 h^–1 (mean: 500 nmol L^–1 h^–1) in polyhumic lake Mekkojärvi.     

Characteristics of δ13CDIC in lakes on the Tibetan Plateau and its implications for the carbon cycle

Dissolved inorganic carbon isotope (δ¹³C_DIC) is an important tool to reveal the carbon cycle in lake systems. However, there are only few studies focusing on the spatial variation of δ¹³C_DIC of closed lakes. Here we analyze the characteristics of δ¹³C_DIC of 24 sampled lakes (mainly closed lakes) across the Qiangtang Plateau (QTP) and identify the driving factors for its spatial variation. The δ¹³C_DIC value of these observed lakes varies in the range of ? 15·0 to 3·2‰, with an average value of ? 1·2‰. The δ¹³C_DIC value of closed lakes is close to the atmospheric isotopic equilibrium value, much higher than that in rivers and freshwater lakes reported before. The high δ¹³C_DIC value of closed lakes is mainly attributed to the significant contribution of carbonate weathering in the catchment and the evasion of dissolved CO₂ induced by the strong evaporation of lake water. The δ¹³C_DIC value of closed lakes has a logarithmic correlation with water chemistry (TDS, DIC and pCO₂), also suggesting that the evapo‐concentration of lake water can influence the δ¹³C_DIC value. The δ¹³C_DIC value shows two opposite logarithmic correlations with lake size depending on the δ¹³C_DIC range. This study suggests that the δ¹³C in carbonates in lacustrine sediments can be taken as an indicator of lake volume variation in closed lakes on QTP. Copyright © 2011 John Wiley & Sons, Ltd.     

Geoecological Characteristics of Lake Seliger

Data of hydrological and hydrochemical observations conducted in August 2000 at Lake Seliger and its major tributaries are presented. The analyzed characteristics included: O₂, H₂S, CH₄, microelements; mineral and organic compounds of P and N, ionic composition components (HCO₃ ^–, Cl^–, Na⁺, K⁺, dry residue, pH; color index, electrical conductivity. Bottom sediment samples were analyzed for microelement concentrations, CH₄, oil hydrocarbons. The influence of the basin on the ecological state of the lake was assessed, and tendencies in the evolution of its ecosystem are analyzed. It is shown that the ecological conditions of the lake has not changed significantly since 1960–1991, however, nutrient concentrations in the lake water was found to increase.     

Time-dependent CO<Subscript>2</Subscript> variations in Lake Albano associated with seismic activity

Lake Albano (Alban Hills volcanic complex, Central Italy) is located in a densely populated area near Rome. The deep lake waters have significant dissolved CO₂ concentrations, probably related to sub-lacustrine fluid discharges fed by a pressurized CO₂-rich reservoir. The analytical results of geochemical surveys carried out in 1989–2010 highlight the episodes of CO₂ removal from the lake. The total mass of dissolved CO₂ decreased from ∼5.8 × 10⁷ kg in 1989 to ∼0.5 × 10⁷ kg in 2010, following an exponential decreasing trend. Calculated values of both dissolved inorganic carbon and CO₂ concentrations along the vertical profile of the lake indicate that this decrease is caused by CO₂ release from the epilimnion, at depth <9 m, combined with (1) water circulation at depth <95 m and (2) CO₂ diffusion from the deeper lake layers. According to this model, Lake Albano was affected by a large CO₂ input that coincided with the last important seismic swarm at Alban Hills in 1989, suggesting an intimate relationship between the addition of deep-originated CO₂ to the lake and seismic activity. In the case of a CO₂ degassing event of an order of magnitude larger than the one that occurred in 1989, the deepest part of Lake Albano would become CO₂-saturated, resulting in conditions compatible with the occurrence of a gas outburst. These results reinforce the idea that a sudden CO₂ input into the lake may cause the release of a dense gas cloud, presently representing the major volcanic threat for this densely populated area.     

Influences of watershed landscape composition and configuration on lake‐water quality in the Yangtze River basin of China

Lake‐water quality is highly dependent on the landscape characteristics in its respective watershed. In this study, we investigated the relationships between lake‐water quality and landscape composition and configuration within the watershed in the Yangtze River basin of China. Water quality variables, including pH, electrical conductivity (EC), dissolved oxygen (DO), Secchi depth (SD), NO₂^?, NO₃^?, NH₄⁺, TN, TP, chemical oxygen demand (COD_Mn), chlorophyll‐a (Chl‐a), and trophic state index (TSI), were collected from 16 lakes during the period of 2001–2003. Landscape composition (i.e. the percentage of vegetation, agriculture, water, urban, and bare land) and landscape configuration metrics, including number of patches (NP), patch density (PD), largest patch index (LPI), edge density (ED), mean patch area (MPA), mean shape index (MSI), contagion (CONTAG), patch cohesion index (COHESION), Shannon's diversity index (SHDI), and aggregation index (AI), were calculated for each lake's watershed. Results revealed that the percentage of agriculture was negatively related to NO₂^?, TN, TP, Chl‐a concentrations, and TSI, while the percentage of urban was significantly correlated with EC, NH₄⁺, and COD_Mn concentrations. Among landscape‐level configuration metrics, only ED showed significant relationships with TN, TP concentrations, and TSI. However, at the class level, the PD, LPI, ED, and AI of agriculture and urban land uses were significantly correlated with two or more water quality variables. This study suggests that, for a given total area, large and clustered agricultural or urban patches in the watershed may have a greater impact on lake‐water quality than small and scattered ones. Copyright © 2011 John Wiley & Sons, Ltd.