The volcanic acidification of glacial Lake Caviahue,Province of Neuquen,Argentina     

Johan C. Varekamp 《Journal of Volcanology and Geothermal Research》2008

Lake Caviahue (northern Patagonia, Argentina) is a large glacial lake acidified by volcanic fluids from Copahue volcano. The lake and the feeding rivers were sampled annually from 1997 till early 2006, including the eruptive period of 2000. Lake Caviahue waters evolved over time, with the most concentrated waters in 2000 during the eruptive period, followed by gradual dilution that was interrupted by renewed acidification in 2003–2004. Inversion of the lake water data and application of a dynamic non-steady state model for the lake provides our best quantitative estimates for the variation in element fluxes over the 9-year period. The model flux results agree well with most of the measured fluxes. The Copahue hydrothermal system had gently declining element fluxes between 1997 and mid-1999, although the lake was still becoming more concentrated. About 2–3 months before the 2000 eruption, element fluxes increased strongly, but the hydrothermal fluxes almost shutoff directly after the main eruptive events. The fluxes of several elements recovered post-2001, with an increase in element fluxes in 2003–2004; the lake became more dilute between 2004 and 2006. The intrusion of new magma into the hydrothermal system just prior to the 2000 eruption led to enhanced water rock interaction, with higher concentrations of the rock forming elements in the fluids, and the hot spring flow rate increased as a result of the higher pressure in the reservoir. The fluids became saturated in alunite and jarosite, and they were already saturated with anhydrite. Precipitation of these minerals possibly led to a decreased permeability of the hydrothermal reservoir, leading to the strongly reduced element fluxes just after the eruption. In addition, K, Al and S were retained in the newly precipitated minerals as well, further diminishing their export. The acidification in 2003–2004 may have resulted from a new small intrusion of magma or resulted from seismic activity that created new permeability and fresh rock surfaces for water rock interaction. The volcano is a significant source of toxic trace elements such as F, As, B and Li as well as a nutrient (P) for the local watershed. Monitoring of the hydrothermal fluids in the river that drains Copahue, especially the S/Cl, Mg/Cl and Mg/K values as well as the magnitude of the element fluxes would provide the best information for eruption forecasting for this volcano.  相似文献   

Competition between benthic and pelagic microalgae for phosphorus and light – long-term experiments using artificial substrates     

Annika Pasternak  Helmut Hillebrand  Sabine Flöder 《Aquatic Sciences - Research Across Boundaries》2009,71(2):238-249

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The Stanley unconformity in Lake Huron basin: evidence for a climate-driven closed lowstand about 7900 <Superscript>14</Superscript>C BP,with similar implications for the Chippewa lowstand in Lake Michigan basin     

C. F. M. Lewis  C. W. HeilJr.  J. B. Hubeny  J. W. King  T. C. MooreJr.  D. K. Rea 《Journal of Paleolimnology》2007,37(3):435-452

J.L. Hough in 1962 recognized an erosional unconformity in the upper section of early postglacial lake sediments in northwestern Lake Huron. Low-level Lake Stanley was defined at 70 m below present water surface on the basis of this observation, and was inferred to follow the Main Algonquin highstand and Post-Algonquin lake phases about 10 ¹⁴C ka, a seminal contribution to the understanding of Great Lakes history. Lake Stanley was thought to have overflowed from the Huron basin through the Georgian Bay basin and the glacio-isostatically depressed North Bay outlet to Ottawa and St. Lawrence rivers. For this overflow to have occurred, Hough assumed that post-Algonquin glacial rebound was delayed until after the Lake Stanley phase. A re-examination of sediment stratigraphy in northwestern Lake Huron using seismic reflection and new core data corroborates the sedimentological evidence of Hough’s Stanley unconformity, but not its inferred chronology or the level of the associated lowstand. Erosion of previously deposited sediment, causing the gap in the sediment sequence down to 70 m present depth, is attributed to wave erosion in the shoreface of the Lake Stanley lowstand. Allowing for non-deposition of muddy sediment in the upper 20 m approximately of water depth as occurs in the present Great Lakes, the inferred water level of the Stanley lowstand is repositioned at 50 m below present in northwestern Lake Huron. The age of this lowstand is about 7.9 ± 0.3¹⁴C ka, determined from the inferred ¹⁴C age of the unconformity by radiocarbon-dated geomagnetic secular variation in six new cores. This relatively young age shows that the lowstand defined by Hough’s Stanley unconformity is the late Lake Stanley phase of the northern Huron basin, youngest of three lowstands following the Algonquin lake phases. Reconstruction of uplift histories for lake level and outlets shows that late Lake Stanley was about 25–30 m below the North Bay outlet, and about 10 m below the sill of the Huron basin. The late Stanley lowstand was hydrologically closed, consistent with independent evidence for dry regional climate at this time. A similar analysis of the Chippewa unconformity shows that the Lake Michigan basin also hosted a hydrologically closed lowstand, late Lake Chippewa. This phase of closed lowstands is new to the geological history of the Great Lakes. This is the ninth in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M Lewis were guest editors of this special issue.  相似文献   

Chemical characteristics of the crater lakes of Popocatetetl, El Chichon, and Nevado de Toluca volcanoes, Mexico     

M. A. Armienta  S. De la Cruz-Reyna  J. L. Macías 《Journal of Volcanology and Geothermal Research》2000,97(1-4)

Three crater lakes from Mexican volcanoes were sampled and analyzed at various dates to determine their chemical characteristics. Strong differences were observed in the chemistry among the three lakes: Nevado de Toluca, considered as dormant, El Chichón at a post-eruptive stage, and Popocatépetl at a pre-eruptive stage. Not surprisingly, no influence of volcanic activity was found at the Nevado de Toluca volcano, while the other volcanoes showed a correlation between the changing level of activity and the evolution of chemical trends. Low pHs (<3.0) were measured in the water from the active volcanoes, while a pH of 5.6 was measured at the Nevado de Toluca Sun lake. Changes with time were observed at Popocatépetl and El Chichón. Concentrations of volcanic-gas derived species like Cl⁻, SO₄²⁻ and F⁻ decreased irregularly at El Chichón from 1983 until 1997. Major cations concentrations also diminished at El Chichón. A 100% increase in the SO₄²⁻ content was measured at Popocatépetl between 1985 and 1994. An increase in the Mg/Cl ratio between 1992 (Mg/Cl=0.085) and 1994 (Mg/Cl=0.177) was observed at Popocatépetl, before the disappearance of the crater lake in 1994. It is concluded that chemical analysis of crater lakes may provide a useful additional tool for active-volcano monitoring.  相似文献   

The hazards of eruptions through lakes and seawater     

L. G. Mastin  J. B. Witter 《Journal of Volcanology and Geothermal Research》2000,97(1-4)

Eruptions through crater lakes or shallow seawater, referred to here as subaqueous eruptions, present hazards from hydromagmatic explosions, such as base surges, lahars, and tsunamis, which may not exist at volcanoes on dry land. We have systematically compiled information from eruptions through surface water in order to understand the circumstances under which these hazards occur and what disastrous effects they have caused in the past. Subaqueous eruptions represent only 8% of all recorded eruptions but have produced about 20% of all fatalities associated with volcanic activity in historical time. Excluding eruptions that have resulted in about a hundred deaths or less, lahars have killed people in the largest number of historical subaqueous eruptions (8), followed by pyroclastic flows (excluding base surges; 5) tsunamis (4), and base surges (2). Subaqueous eruptions have produced lahars primarily on high (>1000 m), steep-sided volcanoes containing small (<1 km diameter) crater lakes. Tsunamis and other water waves have caused death or destroyed man-made structures only at submarine volcanoes and at Lake Taal in the Philippines. In spite of evidence that magma–water mixing makes eruptions more explosive, such explosions and their associated base surges have caused fewer deaths, and have been implicated in fewer eruptions involving large numbers of fatalities than lahars and tsunamis. The latter hazards are more deadly because they travel much farther from a volcano and inundate coastal areas and stream valleys that tend to be densely settled.  相似文献   

Factors affecting clarity of freshwater lakes in Brandenburg, Germany     

Jens Pfannkuche  Jens Meisel  Olaf Mietz   《Limnologica》2000,30(4):311-321

In the German State Brandenburg, water clarity and the concentrations of the water quality components chlorophyll a, seston and gelbstoff were measured in 27 lakes. Correlation analysis showed, that spectral beam attenuation at 662 and 514 nm was mainly dependent on changes in chlorophyll a concentrations. In the UV-channel at 360 nm, beam attenuation depended mostly on gelbstoff.

Multiple linear regression provided a direct model of beam attenuation at 514 nm with the inputs of inorganic seston, chlorophyll a and gelbstoff. The specific beam attenuation coefficients were comparable to other natural waters around the world. An inverse model is presented, from which gelbstoff and chlorophyll a could be predicted with some accuracy from the inputs of beam attenuation coefficients at 514 and 360 nm. However, it became obvious that biological variability put major constraints on the predictive capacity of both the direct and the inverse model.

Furthermore, we observed a good correspondence of Secchi depth and the inverse of beam attenuation at 514 nm. The predictions of Secchi depth and chlorophyll a concentration from the inverse model were assessed in perspective of using this instrument instead of laborious chemical analysis for future trophic status classification according to LAWA (Länderarbeitsgemeinschaft Wasser). Predictions of trophic status were principally good when using calibrated models, however, quality of classification critically depended on predictions of chlorophyll a.  相似文献   

An inexpensive, optical (infrared) detector to locate the sediment/water interface in lakes with unconsolidated sediments     

Peter Myers  Claire L. Schelske 《Journal of Paleolimnology》2000,23(2):201-205

Unconsolidated, flocculent sediments that are frequently resuspended by wind action are found in many shallow-water lakes. Collecting sediment/water interface cores in such lakes for paleolimnological study may be problematic because it is difficult to determine the depth to the water/sediment interface. Accurately determining this water depth is necessary to guarantee that a piston corer does not penetrate the sediments prior to the drive and to maximize the core length. A simple instrument constructed with inexpensive, readily available components is described. This infrared floc detector (IFD) is used to sense the increased optical density of unconsolidated sediments as the detector is lowered into a lake. The IFD, in effect, yields a precise as well as an accurate measure of water depth. The depth to the water/sediment interface can be measured with an accuracy of approximately 1 cm, provided surface waters are relatively calm.  相似文献   

Late quaternary paleoclimatic reconstructions for interior Alaska based on paleolake-level data and hydrologic models     

Valerie A. Barber  Bruce P. Finney 《Journal of Paleolimnology》2000,24(1):29-41

Hydrologic models are developed for two lakes in interior Alaska to determine quantitative estimates of precipitation over the past 12,500 yrs. Lake levels were reconstructed from core transects for these basins, which probably formed prior to the late Wisconsin. Lake sediment cores indicate that these lakes were shallow prior to 12,500 yr B.P. and increased in level with some fluctuation until they reached their modern levels 4,000-8,000 yr B.P. Evaporation (E), evapotranspiration (ET), and precipitation (P) were adjusted in a water-balance model to determine solutions that would maintain the lakes at reconstructed levels at key times in the past (12,500, 9,000 and 6,000 yr B.P.). Similar paleoclimatic solutions can be obtained for both basins for these times. Results indicate that P was 35-75% less than modern at 12,500 yr B.P., 25-45% less than modern at 9,000 yr B.P. and 10-20% less than modern at 6,000 yr B.P. Estimates for E and ET in the past were based on modern studies of vegetation types indicated by fossil pollen assemblages. Although interior Alaska is predominantly forested at the present, pollen analyses indicate tundra vegetation prior to about 12,000 yr B.P. The lakes show differing sensitivities to changing hydrologic parameters; sensitivity depends on the ratio of lake area (AL) to drainage basin (DA) size. This ratio also changed over time as lake level and lake area increased. Smaller AL to DA ratios make a lake more sensitive to ET, if all other factors are constant.  相似文献   

Aquatic vegetation dynamics in two pit lakes related to interannual water level fluctuation     

Lilin Zheng  Pengfei Zhan  Jinying Xu  Ligang Xu  Zhiqiang Tan  Xiaolong Wang 《水文研究》2020,34(11):2645-2659

Water regime characteristics have been recognized as critical factors for aquatic vegetation. In this study, we examined changes in aquatic vegetation coverage area in two shallow sub-lakes of Poyang Lake (Bang Lake and Cuoji Lake) during the dry season from 1987 to 2017. The relationships between eight water regime components (annual average water level, annual maximum water level, annual minimum water level, and flooded days at five water levels [11, 13, 15, 17, and 19 m]) and aquatic vegetation coverage area were determined. The most critical water regimes were identified and results demonstrated that aquatic vegetation coverage area in Bang Lake and Cuoji Lake peaked in drier years (2005 and 2009, respectively) with no obvious up or down trend. Water regimes indicating high flow events such as annual maximum water level, flooded days at water level 19 m, and annual average water level were found to be more important for predicting aquatic vegetation. High-flow events appear to be essential for understanding aquatic vegetation dynamics in pit lakes, yet overall the influences of water level fluctuation on aquatic vegetation varied among wetland units of Poyang Lake. This study helps to understand the hydroecological dynamics in connected lakes further and provide a reference for the lake management and protection.  相似文献   

Geophysical and geochemical constraints on the age and paleoclimate implications of Holocene lacustrine cores from the Andes of central Chile          下载免费PDF全文

Rachel J. Tiner  Robert M. Negrini  Jose L. Antinao  Eric McDonald  Antonio Maldonado 《第四纪科学杂志》2018,33(2):150-165

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