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1.
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2.
Outburst floods from glacier‐dammed lakes are major events associated with glacier thinning and volume reduction. This paper investigates jökulhlaups emanating from the glacier‐dammed lake Øvre Messingmalmvatn at Rundvassbreen, an outlet glacier of the Blåmannsisen ice cap in northern Norway. Since 2001, the lake has several times been observed to drain suddenly, causing jökulhlaup outbursts into the pro‐glacial lake Rundvatnet. Varve analysis and lead‐210 (210Pb) dating were used to date sediment cores taken from Rundvatnet. It was found that sedimentation from jökulhlaups is recognizable in the lake as distinct sand layers embedded in the varved silt‐clay sequence which represents the normal lake sedimentation. Sand fractions were carried in suspension because of the extreme hydraulic conditions of jökulhlaups. The thickest sand layer was deposited during the 2001 jökulhlaup which lasted three days and had a total volume of 40 ×106 m3. Jökulhlaups were also recorded in 2005, 2007, 2009, and 2010; they each resulted in a sand layer. Annual sediment accumulation in Rundvatnet increased up to 10‐fold during the years with jökulhlaup outburst floods, from a normal value of 1–2 mm yr?1 to 8–10 mm yr?1. Five other jökulhlaups were identified from the 1910–1930 sedimentation interval, in addition to those observed in 2001–2010; there appear to have been none for 70 years during 1931–2000. Each jökulhlaup was preceded by a period when the glacier thinned to a critical volume and could no longer withstand the hydrostatic pressure of Øvre Messingmalmvatn; consequently a tunnel developed beneath the glacier, leading to a jökulhlaup. Statistical analyses of the correlations between the pro‐glacial sedimentation rate and temperature and precipitation suggested that although climate conditions are expected to influence sedimentation in the pro‐glacial catchment, a host of other interacting factors moderate the availability and delivery of sediment to the pro‐glacial system, making the processes responsible for changes in pro‐glacial sedimentation to remain uncertain. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

3.
Small‐scale heterogeneities and large changes in hydraulic gradient over short distances can create preferential groundwater flow paths that discharge to lakes. A 170 m2 grid within an area of springs and seeps along the shore of Shingobee Lake, Minnesota, was intensively instrumented to characterize groundwater‐lake interaction within underlying organic‐rich soil and sandy glacial sediments. Seepage meters in the lake and piezometer nests, installed at depths of 0·5 and 1·0 m below the ground surface and lakebed, were used to estimate groundwater flow. Statistical analysis of hydraulic conductivity estimated from slug tests indicated a range from 21 to 4·8 × 10?3 m day?1 and small spatial correlation. Although hydraulic gradients are overall upward and toward the lake, surface water that flows onto an area about 2 m onshore results in downward flow and localized recharge. Most flow occurred within 3 m of the shore through more permeable pathways. Seepage meter and Darcy law estimates of groundwater discharge agreed well within error limits. In the small area examined, discharge decreases irregularly with distance into the lake, indicating that sediment heterogeneity plays an important role in the distribution of groundwater discharge. Temperature gradients showed some relationship to discharge, but neither temperature profiles nor specific electrical conductance could provide a more convenient method to map groundwater–lake interaction. These results suggest that site‐specific data may be needed to evaluate local water budget and to protect the water quality and quantity of discharge‐dominated lakes. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

4.
Microbial activity, abundance and biomass, and biogeochemical cycling of iron, sulphur and carbon were studied in the extremely acidic (pH 2.5-4.3), meromictic, nutrient-rich pit lake Cueva de la Mora in Spain. The goal was to find out (1) if the relatively high nutrient content influenced plankton abundance in the water column and alkalinity-producing microbial processes in the sediments compared to other acid pit lakes, and (2) if sediments in the shallow, mixed and the deep, stagnant parts of the lake exhibited differences in microbial activities and geochemical sediment composition related to meromixis. We hypothesised that redox cycling was more intense in the mixed part and higher amounts of reduced components would accumulate in the stagnant part. Especially phytoplankton biomass, CO2 production, and sulphate reduction were indeed higher than reported from typical acid pit lakes and were rather within the range of neutral or weakly acidic lakes, which can be attributed to the relatively high nutrient contents of Cueva de la Mora. Even in the monimolimnion, anaerobic processes occurred mainly in the sediments. Sediments from the mixed and stagnant parts of the lake differed markedly in their biogeochemistry. Mixolimnetic sediments showed high iron and sulphate reduction rates, and they appeared to undergo substantial recycling, as supported by reactive Fe, relation between gross sulphate reduction rate and net accumulation of reduced sulphur, and viable counts of iron and sulphur bacteria. Monimolimnetic sediments exhibited lower anaerobic microbial activities, and surprisingly they accumulated more Fe(II) than mixolimnetic sediments, but less reduced sulphur and carbon. This might be explained by a strong separation of the two water bodies, resulting in comparably less input of energy (light) and allochthonous matter into the monimolimnion. Regarding the total extent of alkalinity-generating microbial processes, their net effect is not sufficient to neutralise the lake within decades.  相似文献   

5.
This study was motivated by an interest in understanding the potential effects of climate change and glacier retreat on late summer water temperatures in alpine areas. Fieldwork was carried out between July and September 2007 at Place Lake, located below Place Glacier in the southern Coast Mountains of British Columbia. Place Lake has an area of 72 000 m2, a single inlet and outlet channel, and an approximate residence time of 4 days. Warming between the inlet and outlet of the lake ranged up to 3 °C and averaged 1.8 °C, which exceeds the amount of warming that occurred over the 1 km reach of Place Creek between the lake outlet and tree line. Over a 23‐day period, net radiation totalled about 210 MJ·m–2, with sensible heat flux adding another 56 MJ m‐2. The latent heat flux consumed about 8% of the surface heat input. The dominant heat sink was the net horizontal advection associated with lake inflow and outflow. Early in the study period, temperatures between the surface and 6‐m depth were dominantly at or above 4 °C and were generally neutral to thermally stable, whereas temperatures decreased with depth below 6 m and exhibited irregular sub‐diurnal variations. The maximum outflow temperature of almost 7 °C occurred in this period. We hypothesize that turbidity currents associated with cold, sediment‐laden glacier discharge formed an underflow and influenced temperatures in the deeper portion of the lake but did not mix with the upper layers. Later in the study period, the lake was dominantly well mixed with some near‐surface stability associated with nocturnal cooling. Further research is required to examine the combined effects of sediment concentrations and thermal processes on mixing in small proglacial lakes to make projections of the consequences of glacier retreat on alpine lake and stream temperatures. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

6.
Organic matter mineralisation in the hypolimnion of an eutrophic Maar lake   总被引：2，自引：0，他引：2  
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7.
The biogeochemistry of methane in the sediments of Lake Caviahue was examined by geochemical analysis, microbial activity assays and isotopic analysis. The pH in the water column was 2.6 and increased up to a pH of 6 in the deeper sediment pore waters. The carbon isotope composition of CH4 was between − 65 and − 70‰ which is indicative for the biological origin of the methane. The enrichment factor ε increased from − 46‰ in the upper sediment column to more than − 80 in the deeper sediment section suggesting a transition from acetoclastic methanogenesis to CO2 reduction with depth. In the most acidic surface layer of the sediment (pH < 4) methanogenesis is inhibited as suggested by a linear CH4 concentration profile, activity assays and MPN analysis. The CH4 activity assays and the CH4 profile indicate that methanogenesis in the sediment of Lake Caviahue was active below 40 cm depth. At that depth the pH was above 4 and sulfate reduction was sulfate limited. Methane was diffusing with a flux of 0.9 mmol m− 2 d− 1 to the sediment surface where it was probably oxidized. Methanogenesis contributed little to the sediments carbon budget and had no significant impact on lake water quality. The high biomass content of the sediment, which was probably caused by the last eruption of Copahue Volcano, supported high rates of sulfate reduction which probably raised the pH and created favorable conditions for methanogens in deeper sediment layers.  相似文献   

8.
Spatial variability of recent lacustrine sedimentary structures and sedimentation rates are examined for Green Lake, a morphologically complex lake basin of the southern Coast Mountains, British Columbia. A dense, 100 m grid sampling scheme was used for sediment coring within the 2 km2 lake basin. Deltaic, massive, weakly laminated, and varved sediment sequences are identified within the sediment record. Spatial patterns among these sedimentary deposits are related to within‐lake sediment transfer processes, morphometric controls, and the extent of post‐depositional mixing by bioturbation. Unconformities, turbidites, and cohesive slump failure deposits, observed within the contemporary varve sequences, could all be correlated with major flooding events in the catchment area and direct anthropogenic disturbances along the shoreline. There is an overall, non‐linear decrease in sedimentation rates with increasing distance from the lake inflows; however, this pattern is disrupted in deep water sites of intervening lake sub‐basins where locally higher accumulation rates are observed. Spatial sedimentation patterns are quantitatively described by an empirically‐derived model. Systematic variations in the model parameters are observed for different lake sub‐regions and are associated with changing sediment transfer dynamics between proximal and distal sub‐basin settings. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

9.
This study investigates the consequences of flocculation for sediment flux in glacier‐fed Lillooet Lake, British Columbia based on density, fractal dimension, in situ profiles of sediment concentration and size distribution, and settling velocity equations presented in the literature. Sediment flux attributed to macroflocs during the late spring and summer accounts for a significant portion of sediment flux in the lake, equivalent to at least one‐quarter of the average annual sediment flux. Fine sediment is reaching the lake floor faster in flocs than occurs if settling as individual grains. This flux varies both spatially and temporally over the observation period, suggesting a link between deposition via flocculation and the properties of bottom sediments. Macrofloc flux increased through June, reached a peak during July, and then declined into August. Macrofloc flux was greatest in the distal end of the first basin, approximately 10 km from the point of inflow. Relatively high excess densities (～0·1 g cm–3 at 500 µm) for flocs in situ are consistent with a composition dominated by inorganic primary particles. Microlaminations within Lillooet Lake varves have been linked by earlier workers to discharge events, and the action of turbidity currents, emanating from the Lillooet River. While turbidity currents undoubtedly occur in Lillooet Lake, these results demonstrate flocculation as an adjunct process linking discharge, lake level, macrofloc flux, bulk density and microlaminations. In situ measurements of sediment settling velocity in glacier‐fed lakes are required to better constrain flux rates, and permit comparison between flocculation in lacustrine environments with existing studies of estuarine, marine and fluvial flocculation. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

10.
Supra‐glacial lakes and ponds can create hotspots of mass loss on debris‐covered glaciers. While much research has been directed at understanding lateral lake expansion, little is known about the rates or processes governing lake deepening. To a large degree, this knowledge gap persists due to sparse observations of lake beds. Here we report on the novel use of ground penetrating radar (GPR) surveys to simultaneously collect supra‐glacial lake bathymetry and bottom composition data from Spillway Lake (surface area of 2.4 × 105 m2; volume of 9.5 × 104 m3), which is located in the terminus region of the Ngozumpa Glacier in the Khumbu region of the Nepal Himalaya. We identified two GPR bottom signals corresponding to two sedimentary facies of (1) sub‐horizontal layered fine sediment drape and (2) coarse blocky diamict. We provide an understanding of the changes in subaqueous debris distribution that occur through stages of lake expansion by combining the GPR results with in situ observations of shoreline deposits matching the interpreted facies. From this, we present an updated conceptual model of supra‐glacial lake evolution, with the addition of data on the evolving debris environment, showing how dominant depositional processes can change as lakes evolve from perched lakes to multi‐basin base‐level lakes and finally onto large moraine‐dammed lakes. Throughout lake evolution, processes such as shoreline steepening, lakebed collapse into voids and conduit interception, subaerial and subaqueous calving and rapid areal expansion alter the spatial distribution and makeup of lakebed debris and sediments forcing a number of positive and negative feedbacks on lake expansion. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

11.
Several sediment cores were collected from two proglacial lakes in the vicinity of Mittivakkat Glacier, south‐east Greenland, in order to determine sedimentation rates, estimate sediment yields and identify the dominant sources of the lacustrine sediment. The presence of varves in the ice‐dammed Icefall Lake enabled sedimentation rates to be estimated using a combination of X‐ray photography and down‐core variations in 137Cs activity. Sedimentation rates for individual cores ranged between 0·52 and 1·06 g cm−2 year−1, and the average sedimentation rate was estimated to be 0·79 g cm−2 year−1. Despite considerable down‐core variability in annual sedimentation rates, there is no significant trend over the period 1970 to 1994. After correcting for autochthonous organic matter content and trap efficiency, the mean fine‐grained minerogenic sediment yield from the 3·8 km2 basin contributing to the lake was estimated to be 327 t km−2 year−1. Cores were also collected from the topset beds of two small deltas in Icefall Lake. The deposition of coarse‐grained sediment on the delta surface was estimated to total in excess of 15 cm over the last c. 40 years. In the larger Lake Kuutuaq, which is located about 5 km from the glacier front and for which the glacier represents a smaller proportion of the contributing catchment, sedimentation rates determined for six cores collected from the centre of the lake, based on their 137Cs depth profiles, were estimated to range between 0·05 and 0·11 g cm−2 year−1, and the average was 0·08 g cm−2 year−1. The longer‐term (c. 100–150 years) average sedimentation rate for one of the cores, estimated from its unsupported 210Pb profile, was 0·10–0·13 g cm−2 year−1, suggesting that sedimentation rates in this lake have been essentially constant over the last c. 100–150 years. The average fine‐grained sediment yield from the 32·4 km2 catchment contributing to the lake was estimated to be 13 t km−2 year−1. The 137Cs depth profiles for cores collected from the topset beds of the delta of Lake Kuutuaq indicate that in excess of 27 cm of coarse‐grained sediment had accumulated on the delta surface over the last approximately 40 years. Caesium‐137 concentrations associated with the most recently deposited (uppermost) fine‐grained sediment in both Icefall Lake and Lake Kuutuaq were similar to those measured in fine‐grained sediment collected from steep slopes in the immediate proglacial zone, suggesting that this material, rather than contemporary glacial debris, is the most likely source of the sediment deposited in the lakes. This finding is confirmed by the 137Cs concentrations associated with suspended sediment collected from the Mittivakkat stream, which are very similar to those for proglacial material. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

12.
The significance of organic matter origin for carbon oxidation via sulfate and iron reduction in the sediments of three acid mine lakes is analyzed. Carbon reactivity was estimated by fitting first‐order expressions to measured rates. Carbon oxidation rates via sulfate and ferric iron reduction ranged from 3.4 to 4.7 mmol m–2 d–1 and resembled those reported for freshwater lakes. The estimated reaction constants increased from about 10–3 a–1 at the interface to the former mine grounds to 0.05 to 0.2 a–1 at the current sediment‐water interface. Aquatic organic matter accounted for an estimated 45...75% of total carbon oxidation rates while it amounted only to about 5...14% of the total organic matter that had been deposited. The results of this study suggest that in highly acidic mine lakes the reactivity of the deposited organic matter can rapidly increase after flooding, enhancing carbon oxidation and internal neutralization rates in the sediments.  相似文献   

13.
The dustfall (DF) and mass sedimentation rate (MSR) in Lake Alchichica, Central Mexico, were studied from June 2006 to June 2008. DF ranged between 0·11–0·93 g m?2 d?1 in the warm and rainy season and 0·54–1·21 g m?2 d?1 in the cold and dry season. MSR varied from 0·52–2·40 g m?2 d?1 in the stratification season to 1·14–5·07 g m?2 d?1 in the circulation season. The timing of the highest fluxes of DF and MSR is most likely a product of several factors coinciding during the cold and dry season: (a) availability of dust sources and the presence of strong winds (>7·5 m s?1) in the DF case, and (b) the circulation period of the lake and the availability of nutrients in the MSR case. As expected, the DF in Alchichica was high and similar to that found in other arid and semi‐arid areas. However, the MSR was higher than that reported for other oligotrophic lakes. Particles captured in the aerial traps consisted mainly of detrital minerals; in contrast, particles found in the water traps were mostly biogenic and, to a lesser extent, detrital minerals. The MSR was one to seven times higher than the DF. In spite of the oligotrophic status of Lake Alchichica, the large size of the settled phytoplankton (autochthonous, waterborne) is what leads to the high MSR, which surpasses the DF (allochthonous, airborne) derived from whirlwinds originating in easily eroded terrains that are characteristic of arid/semi‐arid areas. Our results indicate that caution must be taken in considering that the DF amount measured through DF collectors located at the lake shore does actually represent the DF entering into the lake. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

14.
The mechanisms which controls the fixation and/or release of P in sediment of an extremely acidic lake（pH = 2.0 to 3.0） and its response to the influence of eutrophic urban waste water were investigated.The results,in the chemical composition,in the mineralogy of the sediment and in the material as obtained from sediment traps,show that the lake sediments are mainly volcanic material reflecting volcanic features of the basin.The sedimentation rate calculated for the lake(2.5×10-2 mg m-2 day-1) was higher than that observed in other similar glacial lakes in both Andean Patagonia and also elsewhere in the world.The Total Phosphorus concentration in sediments was higher than figures reported by other authors for mining acid lakes,and the main fraction of P was found associated with organic matter.There was no control by Fe or Al on P,because both are in solution at pH < 3.0.It was concluded that changes in the natural input of nutrients（derivatives of Copahue volcano fluid,the discharge of sewage,or basin run-off） are responsible for a high concentration of SRP and N-NH4+ in the lake.Laboratory experiments showed that sediments have no ability to retain phosphorus and a continuous release of P from the sediments into the water column was observed.The assays where the pH was artificially increased showed that the P still remains in solution until at least pH 7.0.It was concluded that changes in the natural input of nutrients due to:1) the volcanic fluids,2) the increase in sewage charges,or 3) surface runoff upstream,maintain a high trophic state with high concentrations of dissolved P and N-NH4+,although the threshold of neutral pH in the lake is exceeded.This study will enable a better understanding about of the mechanism of release/fixation of phosphorus in acidic sediments in order to assist in making decisions regarding the conservation and management of this natural environment.  相似文献   

15.
To ascertain the influence of hydrological boundary conditions on acidity fluxes in lakes influenced by acid mine drainage, acidity budgets were developed for two sediments in areas of differential groundwater inflow (approx. 1 L m?2 d?1 and 10 L m?2 d?1). In both sediments iron was deposited as schwertmannite leading to iron(III) enriched sediments (3.9…6.2 mmol g?1, referred to dry weight). Compared to the surface water, the inflowing groundwater had higher pH (4.5 vs. 3), ferrous iron (6…20 mmol L?1 vs. 0.8…2.0 mmol L?1), and sulfate (5…60 mmol L?1 vs. 8…13 mmol L?1) concentrations. The inflow changed the sediment pore water chemistry and triggered a further increase in pH to above 5.5. In both sediments acidity generation in the surface water (10…30 mol m?2 a?1) strongly prevailed over acidity consumption in the sediments (> ?0.6 mol m?2 a?1). With advective groundwater inflow, however, more acidity was consumed due to TRIS formation (?0.12 mol m?2 a?1 vs. ?0.017 mol m?2 a?1), iron carbonate burial (upper estimate: ?0.14 mol m?2 a?1 vs. ?0.022 mol m?2 a?1), and unspecific ferrous iron retention (?0.39 mol m?2 a?1 vs. ?0.08 mol m?2 a?1). Also, less acidity was generated due to schwertmannite transformation (?2.4 mol m?2 a?1 vs. ?0.11 mol m?2 a?1). The acidity balance of internal processes in the sediment with groundwater inflow was negative, whereas it was positive in the other sediment. The study demonstrates that in acidic and iron rich lakes the hydrological boundary conditions strongly affect geochemical processes as subsumed in acidity fluxes.  相似文献   

16.
Lake eutrophication is a large and growing problem in many parts of the world, commonly due to anthropogenic sources of nutrients. Improved quantification of nutrient inputs is required to address this problem, including better determination of exchanges between groundwater and lakes. This first of a two‐part review provides a brief history of the evolution of the study of groundwater exchange with lakes, followed by a listing of the most commonly used methods for quantifying this exchange. Rates of exchange between lakes and groundwater compiled from the literature are statistically summarized for both exfiltration (flow from groundwater to a lake) and infiltration (flow from a lake to groundwater), including per cent contribution of groundwater to lake‐water budgets. Reported rates of exchange between groundwater and lakes span more than five orders of magnitude. Median exfiltration is 0.74 cm/day, and median infiltration is 0.60 cm/day. Exfiltration ranges from near 0% to 94% of input terms in lake‐water budgets, and infiltration ranges from near 0% to 91% of loss terms. Median values for exfiltration and infiltration as percentages of input and loss terms of lake‐water budgets are 25% and 35%, respectively. Quantification of the groundwater term is somewhat method dependent, indicating that calculating the groundwater component with multiple methods can provide a better understanding of the accuracy of estimates. The importance of exfiltration to a lake budget ranges widely for lakes less than about 100 ha in area but generally decreases with increasing lake area, particularly for lakes that exceed 100 ha in area. No such relation is evident for lakes where infiltration occurs, perhaps because of the smaller sample size. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

17.
Water source and lake landscape position can strongly influence the physico‐chemical characteristics of flowing waters over space and time. We examined the physico‐chemical heterogeneity in surface waters of an alpine stream‐lake network (>2600 m a.s.l.) in Switzerland. The catchment comprises two basins interspersed with 26 cirque lakes. The larger lakes in each basin are interconnected by streams that converge in a lowermost lake with an outlet stream. The north basin is primarily fed by precipitation and groundwater, whereas the south basin is fed mostly by glacial melt from rock glaciers. Surface flow of the entire channel network contracted by ～60% in early autumn, when snowmelt runoff ceased and cold temperatures reduced glacial outputs, particularly in the south basin. Average water temperatures were ～4 °C cooler in the south basin, and temperatures increased by about 4–6 °C along the longitudinal gradient within each basin. Although overall water conductivity was low (<27 µS cm?1) because of bedrock geology (ortho‐gneiss), the south basin had two times higher conductivity values than the north basin. Phosphate‐phosphorus levels were below analytical detection limits, but particulate phosphorus was about four times higher in the north basin (seasonal average: 9 µg l?1) than in the south basin (seasonal average: 2 µg l?1). Dissolved nitrogen constituents were around two times higher in the south basin than in the north basin, with highest values averaging > 300 µg l?1 (nitrite + nitrate‐nitrogen), whereas particulate nitrogen was approximately nine times greater in the north basin (seasonal average: 97 µg l?1) than in the south basin (seasonal average: 12 µg l?1). Total inorganic carbon was low (usually <0·8 mg l?1), silica was sufficient for algal growth, and particulate organic carbon was 4·5 times higher in the north basin (average: 0·9 mg l?1) than in the south basin (average: 0·2 mg l?1). North‐basin streams showed strong seasonality in turbidity, particulate‐nitrogen and ‐phosphorus, and particulate organic carbon, whereas strong seasonality in south‐basin streams was observed in conductivity and dissolved nitrogen. Lake position influenced the seasonal dynamics in stream temperatures and nutrients, particularly in the groundwater/precipitation‐fed north‐basin network. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

18.
The purpose of this study was to examine the historical change in sedimentation rates in lakes that have been impacted by river regulation and agricultural activities in the Ishikari River floodplain. We dated sediment cores using caesium‐137 (137Cs) dating and tephrochronology, and we estimated sediment sources from 137Cs concentrations in the topsoil of representative land covers. We found that, between 1739 and 1963, the distance between the lake and the main river channel and whether or not the lake was connected to the river affected the sedimentation rates. After 1963, agricultural drainage systems were established in the Ishikari River floodplain. The average sedimentation rate before and after the construction of drainage ditches varied between 1–66 and 87–301 mg cm–2 a–1, respectively. The increase in the sedimentation rate after 1963 was caused by the construction of a number of drainage networks, as well as extensive cultivation activity and/or fragmentation of the swamp buffers surrounding the lakes. The 137Cs activities at the surfaces of the lake as well as the catchment‐derived 137Cs contributions and 137Cs inventory in the lake profiles were used to examine the sediment influx from the various drainage areas after the establishment of the drainage system. Our results indicate that the majority of the lake sediments were derived from cultivated areas, and therefore the catchment‐derived 137Cs contribution in the lakes was strongly correlated with the sedimentation rate. The 137Cs inventory across all of the lake profiles was also significantly greater than the atmospheric fallout. We identified a negative correlation between the 137Cs lake profile inventory and the sedimentation rate. This is because the sediment originating from the drainage areas contained low 137Cs concentrations, which diluted the overall concentration of 137Cs in the lake sediment. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

19.
Ferric iron reduction was studied in a pilot-scale enclosure experiment for passive biological remediation of an acidic mine pit lake in Lusatia, Germany. The metabolic properties of prokaryotes involved in Fe(III) reduction may be important for the outcome of biological remediation, as chemolithotrophic Fe(III) reduction can counteract the desired pH increase, but heterotrophic Fe(III) reduction will provide the necessary Fe(II) for precipitation of sulfide minerals following sulfate reduction. Therefore, vertical profiles of sediment parameters related to iron and sulfur cycling were determined in conjunction with viable counts of different ferric iron-reducing micro-organisms using selective media. Findings were compared to an untreated reference site. The addition of organic matter stimulated ferric iron reduction and sulfate reduction in the enclosure and led to elevated pH and accumulations of ferrous iron and reduced sulfur compounds. Numbers of neutrophilic heterotrophic Fe(III) reducers increased during treatment, those of acidophilic heterotrophic Fe(III) reducers remained similar, and those of acidophilic chemolithotrophic Fe(III) reducers decreased. Zones of ferric iron-reducing activity corresponded well with microbial depth profiles; however, viable counts of neutrophilic or acid-tolerant Fe(III) reducers must have been underestimated based on the corresponding observed activity levels. Ferric iron reduction by chemolithotrophic acidophiles seemed to be of minor importance, so a lowering of pH values due to Fe(III) reducing activity is unlikely.  相似文献   

20.
Lake sedimentation has a fundamental impact on lake lifetime. In this paper, we show how sensitive calculation of the latter is to the quality of data available and assumptions made during analysis. Based on the collection of a large new dataset, we quantify the sediment masses (1) mobilized on the hillslopes draining towards Lake Tana (Ethiopia), (2) stored in the floodplains, (3) transported into the lake, (4) deposited in the lake and (5) delivered out from the lake so as to establish a sediment budget. In 2012–2013, suspended sediment concentration (SSC) and discharge measurements were made at 13 monitoring stations, including two lake outlets. Altogether, 4635 SSC samples were collected and sediment rating curves that account for land cover conditions and rainfall seasonality were established for the 11 river stations, and mean monthly SSC was calculated for the outlets. Effects of the floodplain on rivers' sediment yield (SY) were investigated using measurements at both sides of the floodplains. SY from ungauged rivers was assessed using a model that includes catchment area and rainfall, whereas bedload and direct sediment input from lake shores were estimated. As a result, the gross annual SY was c. 39.55 (± 0.15) Mt, dominantly from Gilgel Abay and Gumara Rivers. The 2.57 (± 0.17) Mt sediment deposited in floodplains indicate that the floodplains serve as an important sediment sink. Moreover, annually c. 1.09 Mt of sediment leaves the lake through the two outlets. Annual sediment deposition in the lake was c. 36.97 (± 0.22) Mt and organic matter accumulation was 2.15 Mt, with a mean sediment trapping efficiency of 97%. Furthermore, SSC and SY are generally higher at the beginning of the rainy season because soils in cultivated fields are bare and loose due to frequent ploughing and seedbed preparation. Later in the season, increased crop and vegetation cover lead to a decrease in sediment production. Based on the established sediment budget with average rainfall, the lifetime of Lake Tana was estimated as 764 to 1032 years, which is shorter than what was anticipated in earlier studies. The sedimentation rate of Lake Tana (11.7 ± 0.1 kg m?2 yr?1) is in line with the sedimentation rates of larger lakes in the world, like Lake Dongting and Lake Kivu. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

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