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1.
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2.
A geochemical survey carried out in November 1993 revealed that Lake Quilotoa was composed by a thin (14 m) oxic epilimnion overlying a 200 m-thick anoxic hypolimnion. Dissolved CO2 concentrations reached 1000 mg/kg in the lower stratum. Loss of CO2 from epilimnetic waters, followed by calcite precipitation and a consequent lowering in density, was the apparent cause of the stratification.The Cl, SO4 and HCO3 contents of Lake Quilotoa are intermediate between those of acid–SO4–Cl Crater lakes and those of neutral-HCO3 Crater lakes, indicating that Lake Quilotoa has a ‘memory’ of the inflow and absorption of HC1- and S-bearing volcanic (magmatic) gases. The Mg/Ca ratios of the lake waters are governed by dissolution of local volcanic rocks or magmas, but K/Na ratios were likely modified by precipitation of alunite, a typical mineral in acid–SO4–Cl Crater lakes.The constant concentrations of several conservative chemical species from lake surface to lake bottom suggest that physical, chemical and biological processes did not have enough time, after the last overturn, to cause significant changes in the contents of these chemical species. This lapse of time might be relatively large, but it cannot be established on the basis of available data. Besides, the lake may not be close to steady state. Mixing of Lake Quilotoa waters could presently be triggered by either cooling epilimnetic waters by 4°C or providing heat to hypolimnetic waters or by seismic activity.Although Quilotoa lake contains a huge amount of dissolved CO2 (3×1011 g), at present the risk of a dangerous limnic eruption seems to be nil even though some gas exsolution might occur if deep lake waters were brought to the surface. Carbon dioxide could build up to higher levels in deep waters than at present without any volcanic re-awakening, due to either a large inflow of relatively cool CO2-rich gases, or possibly a long interval between overturns. Periodical geochemical surveys of Lake Quilotoa are, therefore, recommended.  相似文献   

3.
Temperature profiles in summer (February/March 1990) were measured in 24 lakes along a latitudinal transect from central Chile (32° S) to Patagonia (47° S), and on Easter Island (27° S). The lakes of the temperature zone, between 47° S and 38° S, are warm monomictic with surface and deep-water temperatures ranging from 12 °C to 21 °C and from 5.5 °C to 10 °C respectively. The heat content per unit area in midsummer was found to vary with lake area. The local stability of stratification (N 2) varied by more than two orders of magnitude, declining with increasing latitude, altitude, and depth. The lakes can be classified according to morphometric and temperature characteristics, mixing depth, stability of stratification and glacial turbidity. Lago General Carrera (463 m) was found to be almost as deep as Lago Nahuel Huapi (464 m), which is considered to be the deepest lake in South America.  相似文献   

4.
In Lake Baldegg, Switzerland (surface area 5.3 km2, maximum depth 66 m) the analysis of data from moored instrument systems (atmospheric boundary layer, lake temperature distribution, bottom currents) was correlated to the long-term development of vertical mixing as seen from profiles of natural isotopes (radon-222, tritium and helium-3) and chemical species. The investigation shows: 1. Vertical mixing coefficients below 25 m are small. Consequently the vertical concentration distribution of sediment emanating species in the deep hypolimnion is controlled by the bottom topography. 2. Renewal of deep hypolimnic water is significant even during stratification. 3. Weakly damped internal waves characterize the internal dynamics during stratification. 4. Horizontal bottom currents play an important role in the hypolimnion mixing and can be correlated to internal waves during stratification.  相似文献   

5.
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, Stot=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–Se 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.  相似文献   

6.
In most lakes eutrophication is linked to an excessive input of phosphorus. Lake restoration by reduction of P-input (external measure) has led to a considerable drop of the P-concentration in all major Swiss lakes as well as in many other lakes. Internal restoration measures such as artificial mixing, drainage of hypolimnetic water, flushing, aeration, biomanipulation and others serve to improve and accelerate the response of a lake to external measures. For the case of Lago di Lugano, a simple two-box model is employed to demonstrate that a reduction of the P-input to about 25% of the present values is necessary to reach the P-criterion (P-concentration below 30 µg/l). Internal measures could possibly accelerate the extremely slow response of the northern basin.  相似文献   

7.
Reservoirs have to be released when repairing of the dams is necessary. In 1995, two reservoirs in Baden-Württemberg (Germany) of similar age and volume (Lake Herrenbach near Göppingen, 1.0 Mio. m3 and Lake Breitenau near Heilbronn, 2.3 Mio. m3) were emptied. This allowed the singular possibility to investigate the effects of drainage and refilling on the limnochemistry and the phytoplankton biocoenosis of such artificial lakes.Before the drainage of the reservoirs, both lakes showed phosphorus release from the sediment during summer stagnation. Phosphorus values of Lake Herrenbach were regularly higher than those of Lake Breitenau (Lake Herrenbach 88 μg/l, Lake Breitenau 33 μg/l). During release, both lakes indicated higher phosphorus and chlorophyll concentrations as well as rising biomasses. Remarkable differences were observed during refilling of the reservoirs: while Lake Herrenbach showed higher transparency and lower phosphorus concentrations, Lake Breitenau progressed towards eutrophication (total phosphorus during summer 1996: Lake Herrenbach 30 μg/l, Lake Breitenau 55 μg/l). One reason for the reaction of Lake Breitenau was the reduced ground drainage during the refilling, which caused an accumulation of nutrients in the hypolimnion. Another reason was the mineralisation of vegetation which covered great parts of the dry lake sediment. The limnological change of Lake Herrenbach was not as clear but could be caused by the restauration of the pre-reservoir which was drainaged and dredged before the emptying of the main reservoir started as well as many other facts which differed Lake Herrenbach from Lake Breitenau.  相似文献   

8.
Mögliche Massnahmen zur Restaurierung des Sempachersees   总被引：1，自引：1，他引：1  
Since 1954 average orthophosphate and total phosphorus concentrations have increased twenty and eightfold respectively in Lake Sempach. It is demonstrated that the lake is not in steady state with its phosphorus loading and that the net deposition rate of phosphorus is not linearly related to the phosphorus content of the lake. This implies that linear steady state one-box models are unsuitable to describe the phosphorus balance of this lake. Applying a nonlinear dynamic lake model we predict that the defined water quality goals ([P] ⩽30 mg m−3, [O2 ⩾4 mg m−3]) can only be achieved within the next 15 years if the external phosphorus loading is reduced by at least 50% and simultaneously lake-internal measures, such as hypolimnion areation or hypolimnion siphoning are carried into effect.   相似文献   

9.
The medium shallow lake Grimnitzsee (maximum depth: 9.9 m; mean depth: 4.6 m; area: 7.7 · 106 m2) which is situated in the biosphere reserve “Schorfheide-Chorin” in northern Brandenburg (Germany) was studied in 1994 and 1995. A bathymetric map of Grimnitzsee is given for the first time. The lake is usually polymictic although in 1994 and 1995 relatively long summer stratification was observed due to very high global radiation input. Nutrient concentration, light climate, oxygen status, phytoplankton biomass and the species composition of littoral diatoms characterize the lake as eutrophic. Special features deducible from the lake's polymictic character were the multiple development of aerobic or anaerobic strata above the sediment, the fast recovery of silicon concentration in the water column after diatom sedimentation, the importance of resuspension for the success of planktonic diatom populations, and an only moderate correlation between chlorophyll a concentration and light attenuation as well as seston dry weight probably due to the influence of suspended particles.  相似文献   

10.
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11.
Rivers, lakes, and coastal waters are chaotic systems — physical, chemical, and biological parameters influence their development. Each parameter itself is influenced by the system. Human interaction has led to fast eutrophication. Oxygen input and artificial mixing have been considered as tools to overcome the biggest problems of fish kills, algal blooms, and bad odour. The favoured technology for destratification and oxygen input so far is the bubble curtain. This technology has been applied successfully in several cases. But often, this technology could not be implemented because of high investment and operating costs.

Alternatively, the free jet is discussed as an efficient and low investment and operating cost technology. The free jet may transport oxygen-rich water from the surface down into the hypolimnion, thereby destratifying a water system. A free jet entrains on its way down even more oxygen rich and warm epilimnic water. This water will finally — if some mixing with the cold hypolimnic water occurs — be transferred to the metalimnion. The density differences will make this water travel long distances.

The energy input may be very low and the objective must not be to totally overturn a system. A jet started in early spring may help a lake to have a deep enough epilimnion, relatively large in volume in respect to the hypolimnion, and the normal wind will recirculate the water transferring enough oxygen to the deeper part, thus expanding the fish habitat and enabling benthic fauna. Literature also shows that the occurrence of massive algal blooms may be reduced.

The oxygen efficiency can be multifold compared to standard technologies.  相似文献   


12.
The weight-specific respiration rate (μl O2 mg−1 AFDW h−1) of three species of leech from Lake Esrom, Denmark, Glossiphonia concolor, G. complanata and Helobdella stagnalis was measured in a closed stirred chamber with a micro electrode. At declining oxygen concentration (mg O2 l−1) all three species expressed moderate ability to regulate respiration, in G. concolor and G. complanata down to 2 mg O2 l−1, in H. stagnalis down to 0.75 mg O2 l−1. Survival in anoxia was measured in closed bottles. The time to 50% survival (LD50) was 30 days in G. concolor at 20 °C and 30 and 4 days in H. stagnalis at 10 and 20 °C, respectively. The results were discussed in relation to habitat and spatial distribution of the three species in the lake.  相似文献   

13.
The fate of inflows into lakes has been extensively studied during summer stratification but has seen relatively little focus during the weak winter stratification, with or without ice-cover. Field observations are presented of groundwater inflow into a shallow bay of a subarctic lake. Atmospheric forcing of the bay during the study period was extremely variable and coincided with spring ice-cover break-up. Two dominant wind regimes were identified; (1) weak wind-forcing (wind speed <5 m s−1 or land-fast ice-cover), and (2) strong wind-forcing (wind speed >5 m s−1 and open water). At a relatively constant temperature of ~3.3°C, the groundwater inflow was closer to the temperature of maximum density than the water in the main body of the lake, which during the observed winter stratification is ~1.2°C. During weak wind-forcing, the stratification within Silfra Bay approximated two-layers as this denser groundwater formed a negatively buoyant underflow. A calculated underflow entrainment rate of 2.8 × 10−3 agrees well with other underflow studies. During strong wind-forcing, the water column out to the mouth of the bay became weakly stratified as the underflow was entrained vertically by wind-stirring. Observed periods of mixing can be predicted to occur when turbulent kinetic energy (TKE) production by wind stirring integrated over the underflow hydraulic residence time in the bay exceeds the potential energy associated with the stratification. A decrease of ice cover, as observed in the studied subarctic lake over the last decade, will result in the underflow being more frequently exposed to the strong wind-forcing regime during winter, thereby altering the winter distribution of groundwater inflow within the lake.  相似文献   

14.
Concentrations of chloride and sulfate and pH in the hot crater lake (Laguna Caliente) at Poás volcano and in acid rain varied over the period 1993–1997. These parameters are related to changes in lake volume and temperature, and changes in summit seismicity and fumarole activity beneath the active crater. During this period, lake level increased from near zero to its highest level since 1953, lake temperature declined from a maximum value of 70°C to a minimum value of 25°C, and pH of the lake water increased from near zero to 1.8. In May 1993 when the lake was nearly dry, chloride and sulfate concentrations in the lake water reached 85,400 and 91,000 mg l−1, respectively. Minimum concentrations of chloride and sulfate after the lake refilled to its maximum volume were 2630 and 4060 mg l−1, respectively. Between January 1993 and May 1995, most fumarolic activity was focused through the bottom of the lake. After May 1995, fumarolic discharge through the bottom of the lake declined and reappeared outside the lake within the main crater area. The appearance of new fumaroles on the composite pyroclastic cone coincided with a dramatic decrease in type B seismicity after January 1996. Between May 1995 and December 1997, enhanced periods of type A seismicity and episodes of harmonic tremor were associated with an increase in the number of fumaroles and the intensity of degassing on the composite pyroclastic cone adjacent to the crater lake. Increases in summit seismic activity (type A, B and harmonic tremor) and in the height of eruption plumes through the lake bottom are associated with a period of enhanced volcanic activity during April–September 1994. At this time, visual observations and remote fumarole temperature measurements suggest an increase in the flux of heat and gases discharged through the bottom of the crater lake, possibly related to renewed magma ascent beneath the active crater. A similar period of enhanced seismic activity that occurred between August 1995 and January 1996, apparently caused fracturing of sealed fumarole conduits beneath the composite pyroclastic cone allowing the focus of fumarolic degassing to migrate from beneath the lake back to the 1953–1955 cone. Changes in the chemistry of summit acid rain are correlated changes in volcanic activity regardless of whether fumaroles are discharging into the lake or are discharging directly into the atmosphere.  相似文献   

15.
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16.
Using constraints from an extensive database of geological and geochemical observations along with results from fluid mechanical studies of convection in magma chambers, we identify the main physical processes at work during the solidification of the 1959 Kilauea Iki lava lakes. In turn, we investigate their quantitative influence on the crystallization and chemical differentiation of the magma, and on the development of the internal structure of the lava lake. In contrast to previous studies, vigorous stirring in the magma, driven predominately by the descent of dense crystal-laden thermal plumes from the roof solidification front and the ascent of buoyant compositional plumes due to the in situ growth of olivine crystals at the floor, is predicted to have been an inevitable consequence of very strong cooling at the roof and floor. The flow is expected to have caused extensive but imperfect mixing over most of the cooling history of the magma, producing minor compositional stratification at the roof and thermal stratification at the floor. The efficient stirring of the large roof cooling is expected to have resulted in significant internal nucleation of olivine crystals, which ultimately settled to the floor. Additional forcing due to either crystal sedimentation or the ascent of gas bubbles is not expected to have increased significantly the amount of mixing. In addition to convection in the magma, circulation driven by the convection of buoyant interstitial melt in highly permeable crystal-melt mushes forming the roof and the floor of the lava lake is envisaged to have produced a net upward flow of evolved magma from the floor during solidification. In the floor zone, mush convection may have caused the formation of axisymmetric chimneys through which evolved magma drained from deep within the floor into the overlying magma and potentially the roof. We hypothesize that the highly evolved, pipe-like ‘vertical olivine-rich bodies’ (VORBs) [Bull. Volcanol. 43 (1980) 675] observed in the floor zone, of the lake are fossil chimneys. In the roof zone, buoyant residual liquid both produced at the roof solidification front and gained from the floor as a result of incomplete convective mixing is envisaged to have percolated or ‘leaked‘ into the overlying highly-permeable cumulate, displacing less buoyant interstitial melt downward. The results from Rayleigh fractionation-type models formulated using boundary conditions based on a quantitative understanding of the convection in the magma indicate that most of the incompatible element variation over the height of the lake can be explained as a consequence of a combination of crystal settling and the extensive but imperfect convective mixing of buoyant residual liquid released from the floor solidification front. The remaining chemical variation is understood in terms of the additional influences of mush convection in the roof and floor on the vertical distribution of incompatible elements. Although cooling was concentrated at the roof of the lake, the floor zone is found to be thicker than the roof zone, implying that it grew more quickly. The large growth rate of the floor is explained as a consequence of a combination of the substantial sedimentation of olivine crystals and more rapid in situ crystallization due to both a higher liquidus temperature and enhanced cooling resulting from imperfect thermal and chemical mixing.  相似文献   

17.
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18.
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 ΔSO4–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 δ18OSO4 and δ18OH2O 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.  相似文献   

19.
Thermal springs of the Boundary Creek hydrothermal system in the southwestern part of Yellowstone Park outside the caldera boundary vary in chemical and isotopic composition, and temperature. The diversity may be accounted for by a combination of processes including boiling of a deep thermal water, mixing of the deep thermal water with cool meteoric water and/or with condensed steam or steam-heated meteoric water, and chemical reactions with surrounding rocks. Dissolved-silica, Na+, K+ and Ca2+ contents of the thermal springs could result from a thermal fluid with a temperature of 200 ± 20°C. Chloride-enthalpy and silica-enthalpy mixing models suggest mixing of 230°C, 220 mg/l Cl− thermal water with cool, low-Cl− components. A 350 to 390°C component with Cl− ≥ 300 mg/l is possibly present in thermal springs inside the caldera but is not required to fit observed spring chemical and isotopic compositions. Irreversible mass transfer models in which a low-temperature water reacts with volcanic glass as it percolates downward and warms, can account for observed pH and dissolved-silica, K+, Na+, Ca2+ and Mg2+ concentrations, but produces insufficient Cl− or F− for measured concentrations in the warm springs. The ratio of aNa/aH, and Cl− are best accounted for in mixing models. The water-rock interaction model fits compositions of acid-sulfate waters observed at Summit Lake and of low-Cl− waters involved in mixing.The cold waters collected from southwestern Yellowstone Park have δD values ranging from −118 to −145 per mil and δ18O values of −15.9 to −19.4 per mil. Two samples from nearby Island Park have δD values of −112 and −114 per mil and δ18O values of −15.1 and −15.3 per mil. All samples of thermal water plot significantly to the right of the meteoric water line. The low Cl− and variable δD values of the thermal waters indicate isotopic compositions are derived by extensive dilution with cold meteoric water and by steam separation on ascent to the surface. Many of the hot springs with higher δD values may contain in addition a significant amount of high-D, low-Cl−, acid-sulfate or steam-heated meteoric water. Mixing models, Cl− content and isotopic compositions of thermal springs suggest that 30% or less of a deep thermal component is present. For example, the highest-temperature springs from Three Rivers, Silver Scarf and Upper Boundary Creek thermal areas contain up to 70% cool meteoric water and 30% hot water components, springs at Summit Lake and Middle Boundary Creek spring 57 are acid-sulfate or steam-heated meteoric water; springs 27 and 48 from Middle Boundary Creek and 49 from Mountain Ash contain in excess of 50% acid-sulfate water; and Three Rivers spring 46 and Phillips could result from mixing hot water with 55% cool meteoric water followed by mixing of acid-sulfate water. Extensive dilution by cool meteoric water increases the uncertainties in quantity and nature of the deep meteoric, thermal component.  相似文献   

20.
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 fO2 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 fO2 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.  相似文献   

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