Journal articles: 'Alpine lake sediments' – Grafiati (2024)

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We compare fossil pollen and stomate assemblages in 29 lake sediment surface samples from mountainous regions in northwestern Canada to characterize the relationship between modern vegetation, and pollen and stomate deposition. Modern pollen spectra were dominated by arboreal taxa originating from lower elevation sites. Pinus pollen frequently reached 30% of the pollen sum, regardless of elevation. Alpine-tundra vegetation has lower pollen abundance, even in the alpine-tundra zone, where it dominates the sparse vegetation cover. Fossil stomates were observed in all but one site where trees currently exist in the vicinity of the lake, while no stomates were found in the sediments from alpine-tundra sites. The highest concentration of stomates occurred in lake sediments from closed-canopy forested areas. Our data suggest that different boreal forest types may be differentiated based on pollen assemblages and that the presence of stomates clearly distinguishes vegetation zones dominated by arboreal vegetation from alpine-tundra zones where trees are not present.Key words: pollen, conifer stomates, treeline, Pacific Northwest.

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The ecological equilibrium of water reservoirs may differ from that of natural lakes. We questioned this difference by analysing the sediments of a small oligotrophic Alpine lake, whose management was modified for hydroelectric production since 1976. Corne Lake is formed by a shallow depression connected to a deep depression. The hydropower management induced water level fluctuations (+2 m in summer; −8 m in winter) that emptied the shallow depression during the winter months and promoted the erosion of littoral soils and tributary channel sediment and the sedimentation in the deep depression. The sediment of the original lake was a low-density organic mud. The sediment composition varied according to 3 phases, which chronology is debated. During a first phase we measured an increase in the ratio of Diatom/Chrysophycea and bioavailable P, as well as a decrease in the C/N ratio and bulk radiocarbon age of the sediment, suggesting a trophic surge. A second phase was characterised by a high rate of mineral sedimentation, an increase of benthic diatom genera in the deep depression of the lake and acidophilic diatoms in the shallow depression. In the third phase covering the last upper cm of the cores, the sediment tended to return to its initial composition, but the algae community differed from its initial state. We suggest that the management of Alpine lakes as reservoirs induce long-term ecological changes in relation to water level fluctuations and littoral habitats degradation.

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Hesperodiaptomus arcticus, a predatory calanoid copepod, was eliminated from two alpine lakes within 6 years of stocking with salmonids. Using historical and contemporary Zooplankton and fish data, sediment analysis for diapausing eggs, and experiments on predation of Gammarus lacustris on diapausing eggs of H. arcticus, we assess the fate of these populations 35 years after fish stocking. In Pipit Lake, in which the trout introduction failed within 21 years, we propose that H. arcticus recovered as a result of hatching of diapausing eggs held in the sediments. In Snowflake Lake the diapausing egg bank was exhausted prior to the loss of the fish population 25 years after first stocking and H. arcticus recovery did not occur. Experimental studies indicate that G. lacustris predation on diapausing eggs probably occurs within the sediments. Combined with a 10-fold difference in G. lacustris density between Snowflake and Pipit lakes the results of the predation experiments imply that G. lacustris had a strong negative impact on the abundance of diapausing eggs held in Snowflake Lake sediments and therefore reduced the ability of the population to recover following perturbation.

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ABSTRACT Small sub-alpine glacial lakes are often targeted as Holocene paleoclimate archives, but their evolution as landforms and depositional basins is understudied. At June Lake in the eastern Sierra Nevada of California (USA), bathymetry, surface sediment composition, and seismic stratigraphy are studied to assess the modern sedimentary system and gain insight into the basin's origins. A basin-wide seismic survey reveals sublacustrine morphological features that attest to the role of ice in scouring the June Lake basin, including a prominent abraded bedrock shoal and an adjacent overdeepened depression. The seismic survey reveals four acoustically distinct stratigraphic units that reflect the history of sedimentation following glacial scouring. The youngest of these is represented in the recovered lacustrine core records as hemipelagically deposited, organic-rich, laminated diatomaceous oozes alternating with coarse tephra beds. The organic-rich oozes are characterized by low carbon and nitrogen stable-isotope values and occur in profundal areas of the modern lake floor. These sediments suggest an algae-dominated productivity regime and preservation of organic matter at depth. With no perennial streams entering June Lake, surface-sediment grain-size distribution and geochemistry are controlled by water depth and basin morphology. Additional modern facies types include poorly sorted coarse detrital landslide deposits below steep basin walls and volcaniclastic sandy gravel in windward littoral areas. These data provide a modern facies model for sedimentation in ice-scoured, hydrologically closed sub-alpine lakes and a baseline for future paleoclimate studies using June Lake sediment cores.

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AbstractTatra’s lakes are vulnerable ecosystems and an important element of the alpine landscape. Mainly some shallow lake basins succumb to intense detritus sedimentation, fine fractions of material from the catchment area or to the overgrowing of water level by vegetation. In this paper, changes and dynamics of the 12 Tatra’s lake shorelines that were selected based on the detailed mapping of their extent are pointed out. Changes were assessed by accurate comparisons of historical and current orthophoto maps from the years 1949, 1955 and 2015 – and therefore, based on the oldest and the latest relevant materials. Due to the overgrowing of lakes caused by vegetation, their water surface decreased from −0.9% up to −47.9%, during the examined period. Losses were caused by the overgrowing of open water surface by the communities of sedges and peat bogs. The most significant dynamics of the shorelines during the last decades were reached by those lakes, into which fine sediments were simultaneously deposited by means of mountain water coarse. These sediments made the marginal parts of the lake basins shallower and accelerated rapid expansion of vegetation to the detriment of the open water surface. The overgrowing of shallow moraine lakes lying in the vegetation zone is a significant phenomenon of the High Tatras alpine landscape. It leads to their gradual extinction, turn into peat bogs and wet alpine meadows.

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AbstractThe geologic setting of the Ziegler Reservoir fossil site is somewhat unusual — the sediments containing the Pleistocene fossils were deposited in a lake on top of a ridge. The lake basin was formed near Snowmass Village, Colorado (USA) when a glacier flowing down Snowmass Creek Valley became thick enough to overtop a low point in the eastern valley wall and entered the head of Brush Creek Valley. When the glacier retreated at about 155–130 ka, near the end of Marine Oxygen Isotope Stage 6, the Brush Creek Valley lobe left behind a moraine that impounded a small alpine lake. The lake was initially ~ 10 m deep and appears to have been highly productive during most of its existence, based on the abundant and exquisitely preserved organic material present in the sediments. Over time, the basin slowly filled with (mostly) eolian sediment such that by ~ 87 ka it contained a marsh or wetland rather than a true lake. Open-water conditions returned briefly between ~ 77 and 55 ka before the impoundment was finally breached to the east, establishing ties with the Brush Creek drainage system and creating an alpine meadow that persisted until historic times.

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Twenty-two new radiocarbon ages from Skagit valley provide a detailed chronology of alpine glaciation during the Evans Creek stade of the Fraser Glaciation (early marine oxygen isotope stage (MIS) 2) in the Cascade Range, Washington State. Sediments at sites near Concrete, Washington, record two advances of the Baker valley glacier between ca. 30.3 and 19.5 cal ka BP, with an intervening period of glacier recession about 24.9 cal ka BP. The Baker valley glacier dammed lower Skagit valley, creating glacial Lake Concrete, which discharged around the ice dam along Finney Creek, or south into the Sauk valley. Sediments along the shores of Ross Lake in upper Skagit valley accumulated in glacial Lake Skymo after ca. 28.7 cal ka BP behind a glacier flowing out of Big Beaver valley. Horizontally laminated silt and bedded sand and gravel up to 20 m thick record as much as 8000 yr of deposition in these glacially dammed lakes. The data indicate that alpine glaciers in Skagit valley were far less extensive than previously thought. Alpine glaciers remained in advanced positions for much of the Evans Creek stade, which may have ended as early as 20.8 cal ka BP.

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AbstractThe rhyolitic Lake Tapps tephra was deposited about 1.0 myr ago, shortly after culmination of the early phase of the Salmon Springs Glaciation in the Puget Lowland. It is contained within sediments that were deposited in ponds or lakes in front of the reteating glacier. An herb-dominated tundra existed in the southern Puget Lowland at that time. Lake Tapps tephra is most likely the product of an eruption that in part was phreatomagmatic. It forms an early Pleistocene stratigraphic marker across the southern sector of the Puget Lowland and provides a link between Puget lobe sediments of the Cordilleran Ice Sheet and sediments deposited by Olympic alpine glaciers.

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Lake sediments from four sites in the southwest Yukon Territory, Canada, provided paleotemperature records for the past 2000 yr. An alpine and a forest site from the southeastern portion of the study area, near Kluane Lake, and another alpine-forest pair of lakes from the Donjek River area located to the northwest yielded chironomid records that were used to provide quantitative estimates of mean July air temperature. Prior to AD 800, the southwest Yukon was relatively cool whereas after AD 800 temperatures were more variable, with warmer conditions between ~ AD 1100 and 1400, cooler conditions during the Little Ice Age (~ AD 1400 to 1850), and warming thereafter. These records compare well with other paleoclimate evidence from the region.

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Reflectance spectroscopy has made it possible to rapidly and nondestructively assess the chlorophyll content of plants and natural waters. However, to date this approach has not been applied to chlorophyll and chlorophyll derivatives preserved in lake sediments. Here, we explore the relationships between visible-near-infrared spectral properties of lake sediments and measured pigment concentrations for lakes that have been exposed recently to anthropogenic nitrogen deposition. Down-core decreases in pigment concentrations and changes in reflectance properties effectively chronicle increases in whole-lake primary production since 1950. Specifically, reflectance spectra of sediments from four alpine lakes in Rocky Mountain National Park (Colorado Front Range, USA) preserve salient troughs near 675 nm that covary in magnitude with concentrations of chlorophyll a and associated pheopigments. The area of the trough in reflectance between 600 and 760 nm best explains the sum of total chlorophyll a and its derivatives (r2 = 0.82, n = 23, P < 0.01). This result suggests that chlorophyll a preserved in lake sediments can be remotely sensed using a simple index derived from reflectance spectroscopy, thus providing a new paleolimnological strategy for rapid exploratory assessments of changing lake trophic status.

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Abstract. Mediterranean Alpine populations are particularly exposed to natural hazards like floods and earthquakes because of both the close Mediterranean humidity source and the seismically active Alpine region. Knowledge of long-term variability in flood and earthquake occurrences is of high value since it can be useful to improve risk assessment and mitigation. In this context, we explore the potential of a lake-sediment sequence from Lago Inferiore de Laures in Valle d'Aosta (Northern Italy) as a long-term record of past floods and earthquakes. The high-resolution sedimentological study revealed 76 event layers over the last ca. 270 years; 8 are interpreted as most probably induced by earthquakes and 68 by flood events. Comparison to historical seismic data suggests that the recorded earthquakes are strong (epicentral Medvedev–Sponheuer–Kárník (MSK) intensity of VI–IX) and/or close to the lake (distance of 25–120 km). Compared to other lake-sediment sequences, Lago Inferiore de Laures sediments appear to be regionally the most sensitive to earthquake shaking, offering a great potential to reconstruct the past regional seismicity further back in time. Comparison to historical and palaeoflood records suggests that the flood signal reconstructed from Lago Inferiore de Laures sediments represents the regional and (multi-)decadal variability of summer–autumn floods well, in connection to Mediterranean mesoscale precipitation events. Overall, our results reveal the high potential of Lago Inferiore de Laures sediments to extend the regional earthquake and flood catalogues far back in time.

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Abstract. A novel proxy for continental mean annual air temperature (MAAT) and soil pH, the MBT/CBT-paleothermometer, is based on the temperature (T) and pH-dependent distribution of specific bacterial membrane lipids (branched glycerol dialkyl glycerol tetraethers – GDGTs) in soil organic matter. Here, we tested the applicability of the MBT/CBT-paleothermometer to sediments from Lake Cadagno, a high Alpine lake in southern Switzerland with a small catchment of 2.4 km2. We analysed the distribution of bacterial GDGTs in catchment soils and in a radiocarbon-dated sediment core from the centre of the lake, covering the past 11 000 yr. The distribution of bacterial GDGTs in the catchment soils is very similar to that in the lake's surface sediments, indicating a common origin of the lipids. Consequently, their transfer from the soils into the sediment record seems undisturbed, probably without any significant alteration of their distribution through in situ production in the lake itself or early diagenesis of branched GDGTs. The MBT/CBT-inferred MAAT estimates from soils and surface sediments are in good agreement with instrumental values for the Lake Cadagno region (~0.5 °C). Moreover, downcore MBT/CBT-derived MAAT estimates match in timing and magnitude other proxy-based T reconstructions from nearby locations for the last two millennia. Major climate anomalies recorded by the MBT/CBT-paleothermometer are, for instance, the Little Ice Age (~14th to 19th century) and the Medieval Warm Period (MWP, ~9th to 14th century). Together, our observations indicate the quantitative applicability of the MBT/CBT-paleothermometer to Lake Cadagno sediments. In addition to the MWP, our lacustrine paleo T record indicates Holocene warm phases at about 3, 5, 7 and 11 kyr before present, which agrees in timing with other records from both the Alps and the sub-polar North-East Atlantic Ocean. The good temporal match of the warm periods determined for the central Alpine region with north-west European winter precipitation strength implies a strong and far-reaching influence of the North Atlantic Oscillation on continental European T variations during the Holocene.

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Abstract. A novel proxy for continental mean annual air temperature (MAAT) and soil-pH, the MBT/CBT-paleothermometer, is based on the temperature (T) and pH-dependent distribution of specific bacterial membrane lipids (branched glycerol dialkyl glycerol tetraethers – GDGTs) in soil organic matter. Here, we tested the applicability of the MBT/CBT-paleothermometer to sediments from Lake Cadagno, a small high-alpine lake in southern Switzerland with a small catchment of 2.4 km2. We analysed the distribution of bacterial GDGTs in catchment soils and in a radiocarbon-dated sediment core from the centre of the lake, covering the entire Holocene. The composition of bacterial GDGTs in soils are almost identical to that in the lake's surface sediments, indicating a common origin of the lipids. Consequently, their transfer from the soils into the sediment record is undisturbed, apparently without any significant alteration of their distribution through in situ production or early diagenesis of branched GDGTs. The MBT/CBT-inferred MAAT-estimates from soils and surface sediments are in good agreement with instrumental values for the Lake Cadagno region (~0.5 °C). Moreover, downcore MBT/CBT-derived MAAT-estimates match in timing and magnitude other proxy-based T-reconstructions from nearby locations for the last two millennia. Major climate anomalies recorded by the MBT/CBT-paleothermometer are, for instance, the Little Ice Age (~14th to 19th century) and the Medieval Warm Period (~10th to 14th century). Together, our observations confirm the applicability of the MBT/CBT-paleothermometer to Lake Cadagno sediments. Consistent with other T-records from both the Alps and from the subpolar NE-Atlantic, our lacustrine paleotemperature record indicates Holocene MAAT-variations with an apparent cyclicity of ~2 kyr. The good temporal match of the warm periods determined for the S-Alpine region with NW-European winter precipitation strength implies a strong and far-reaching influence of the North Atlantic Oscillation on continental European Holocene T-variations.

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The article presents the results of diatom analysis of bottom sediment cores of Lake Shchuchye located in the northern part of the Khibiny Mountains. Data of radiocarbon dating of lacustrine sediments and comparison with previously published sections of lake sediments in the Kola Peninsula suggest that the accumulation of sediments in Shchuchye Lake began during the final stages of deglaciation in the early Holocene and continued uninterruptedly until the present time. Changes in the composition of diatom associations in sediments reflect alterations in the hydrodynamic regime of the lake associated with the isolation from the Goltsovoye Lake, influence of Kunyok River runoff, evolution of vegetation and weathering processes in the catchment area. We used concentration, variety and composition of species and distinguished 8 separate zones of diatoms. Climate changes in the Holocene are reflected directly in the change of the percentage of indicator species, and indirectly through changes in pH, etc. The early Holocene rise of temperature began in this region later than in the sea coastal area. It may reflect the pecularities of deglaciation, namely — late melting of alpine glaciers. Along with the evolutionary environmental changes some catastrophic events are reflected in the sediments of the Shchuchye Lake. For example, in early stages, there the yield of big quantity of terrigenous deposits into the lake was revealed produced by mud flows and erosion from slopes covered by scarce vegetation at that time. Mudflow processes probably led to the formation of a clear interlayer of terrigenous material in the biogenic sediments in the upper part of the section.

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The diatom analysis of the Holocene sediments of Pustoye and Chernoe lakes revealed 37 taxa of diatoms of two classes, five orders, eighteen families and twenty-five genera with a low degree of similarity of species composition (39%) and differences in the ecological priorities of the diatoms according to the leading abiotic factors – salinity and pH. Lake Chernoe is characterized by a greater number of species (26), the presence of halophilic species, as well as the prevalence of indicators of alkaline reaction of the environment. A feature of Lake Pustoye is the complete absence of halophilic forms and the predominance of species that prefer an acidic water reaction. A greater number of planktonic species was characteristic of Lake Chernoe due to the greater depths of this karst reservoir. According to the geographical location in these lakes, arcto-alpine species are noted.

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Abstract. The record of past environmental conditions and changes archived in lacustrine sediments serves as an important element in paleoenvironmental and climate research. A main barrier in accessing these archives is the undisturbed recovery of long cores from deep lakes. In this study, we have developed and tested a new, environmentally friendly coring tool and modular barge, centered around a down-the-hole hydraulic hammering of an advanced piston coring system, called the Hipercorig. Test beds for the evaluation of the performance of the system were two periglacial lakes, Mondsee and Constance, located on the northern edge of the Alpine chain. These lakes are notoriously difficult to sample beyond ∼ 10 m sediment depths due to dense glacial deposits obstructing deeper coring. Both lakes resemble many global lake systems with hard and coarse layers at depth, so the gained experience using this novel technology can be applied to other lacustrine or even marine basins. These two experimental drilling projects resulted in up to 63 m coring depth and successful coring operations in up to 204 m water depth, providing high-quality, continuous cores with 87 % recovery. Initial core description and scanning of the 63 m long core from Mondsee and two 20 and 24 m long cores from Lake Constance provided novel insights beyond the onset of deglaciation of the northern Alpine foreland dating back to ∼ 18 400 cal BP.

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Lake O'Hara (subalpine) and Opabin Lake (alpine) are situated directly adjacent to a high section of the Continental Divide in the central Canadian Rocky Mountains. Core samples recovered from the lakes show a consistent stratigraphy comprising gyttja and underlying inorganic clastic sediments. The gyttja contains Bridge River (2350 years BP) and Mazama (6800 years BP) tephras and is separated from the lower clastic sediments by a sharp, conformable contact. Radiocarbon dates obtained from conifer needles, extracted from directly above the contact, indicate that deglaciation had proceeded upvalley from the O'Hara basin priorto ca. 10 100 years BP. Preliminary palaeobotanical and macrofossil data suggest that a Pinus–Abies forest with lesser Picea was established in the vicinity of Lake O'Hara by this time. Consequently, the minimum age of moraine systems situated downvalley from Lake O'Hara is Late Wisconsinan.Mean annual sedimentation rates were derived from sediment thickness data from 14 Lake O'Hara and 2 Opabin Lake cores. Averaged total sedimentation rate values from the Lake O'Hara cores are 0.13 mm/year (post-Bridge River), 0.13 mm/year (Mazama – Bridge River) and 0.05 mm/year (11 000 years BP – Mazama). Averaged total sedimentation rate values from the Opabin Lake cores are 0.19 mm/year (post-Bridge River), 0.07 mm/year (Mazama – Bridge River), and 0.06 mm/year (8530 years BP – Mazama). Higher total sedimentation rates in post-Bridge River sediments of Opabin Lake are presumably related to climatic conditions associated with more extensive upvalley ice during the last ca. 2300 years. Highly variable sedimentation rate data obtained from the Lake O'Hara cores suggest that the use of sedimentation rate data as a proxy record of upvalley glacial activity is inappropriate in the Lake O'Hara setting where inflowing glacial stream systems are interrupted by upvalley lake basins.Aspartic acid D/L ratios were derived from bulk gyttja samples of known age from seven Lake O'Hara and one Opabin Lake core. In all but two cases, aspartic acid D/L ratios increase consistently with respect to sediment age. The increasing downcore trends in the aspartic acid D/L ratios suggest the possibility of using amino acid data from bulk gyttja samples as a check for reworking in cases where chronostratigraphic markers are absent.

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AbstractAlthough lake tsunamis constitute a rare peril, they have repeatedly occurred in peri-alpine lakes in the past. There are several documented historical examples of landslide-triggered tsunamis in Swiss lakes. However, fundamental information and workflows to rapidly quantify the lacustrine tsunami hazard for multiple lakes are missing so far. The fact that the shorelines of major peri-alpine lakes are densely populated underlines the need for a hazard assessment. Detailed assessments require high-resolution geophysical, geotechnical and sedimentological data, and considerable computation time. Due to the involved data acquisition and calculation efforts, such assessments are mainly conducted as detailed case studies for single lakes. We present a workflow for a rapid first-order estimation of the landslide-triggered tsunami hazard along the shores of peri-alpine lakes. A crucial step is the identification of potential tsunami sources. Unstable slopes are mapped automatically, based on parameters that are derived from past studies. Such parameters include the bathymetry and derived parameters, and type, characteristics and thickness of the sediments. Wave amplitudes are estimated with existing predictive equations, based on the constructed maps of potentially unstable slopes. The results may be used for focusing more detailed, lake-specific tsunami-hazard assessments in respective areas.

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Sediment cores recovered from alpine and subalpine lakes up to 250 km apart in northern British Columbia contain five previously unrecognized tephras. Two black phonolitic tephras, each 5–10 mm thick, occur within 2–4 cm of each other in basal sediments from seven lakes in the Finlay River – Dease Lake area. The upper and lower Finlay tephras are slightly older than 10 220 – 10 560 cal year B.P. and likely originate from two closely spaced eruptions of one or two large volcanoes in the northern Cordilleran volcanic province. The Finlay tephras occur at the transition between deglacial sediments and organic-rich postglacial mud in the lake cores and, therefore, closely delimit the termination of the Fraser Glaciation in northern British Columbia. Sediments in Bob Quinn Lake, which lies on the east edge of the northern Coast Mountains, contain two black tephras that differ in age and composition from the Finlay tephras. The lower Bob Quinn tephra is 3–4 mm thick, basaltic in composition, and is derived from an eruption in the Iskut River volcanic field about 9400 cal years ago. The upper Bob Quinn tephra is 12 mm thick, trachytic in composition, and probably 7000–8000 cal years old. A fifth tephra occurs as a cryptotephra near the top of two cores from the Finlay River area and is correlated to the east lobe of the White River tephra (ca. 1150 cal year B.P.). Although present throughout southern Yukon, the White River tephra has not previously been documented this far south in British Columbia. The tephras are valuable new isochrons for future paleoenvironmental studies in northern British Columbia.

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Abstract. The deposition of dust has recently increased significantly over some regions of the western US. Here we explore how changes in dust deposition have affected the biogeochemistry of two alpine watersheds in Colorado, US. We first reconstruct recent changes in the mass accumulation rate of sediments and then we use isotopic measurements in conjunction with a Bayesian mixing model to infer that approximately 95% of the inorganic fraction of lake sediments is derived from dust. Elemental analyses of modern dust indicate that dust is enriched in Ca, Cr, Cu, Mg, Ni, and in one watershed, Fe and P relative to bedrock. The increase in dust deposition combined with its enrichment in certain elements has altered the biogeochemisty of these systems. Both lakes showed an increase in primary productivity as evidenced by a decrease in carbon isotopic discrimination; however, the cause of increased primary productivity varies due to differences in watershed characteristic. The lake in the larger watershed experienced greater atmospheric N loading and less P loading from the bedrock leading to a greater N:P flux ratio. In contrast, the lake in the smaller watershed experienced less atmospheric N loading and greater P loading from the bedrock, leading to a reduced N:P flux ratio. As a result, primary productivity was more constrained by N availability in the smaller watershed. N-limited primary productivity in the smaller watershed was partly ameliorated by an increase in nitrogen fixation as indicated by reduced nitrogen isotopic values in more contemporary sediments. This study illustrates that alpine watersheds are excellent integrators of changes in atmospheric deposition, but that the biogeochemical response of these watersheds may be mediated by their physical (i.e. watershed area) and chemical (i.e. underlying geology) properties.

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The chemistry of the carbonate-free clay-size fraction of Owens Lake sediments supports the use of total organic carbon and magnetic susceptibility as indicators of stadial–interstadial oscillations. Owens Lake records of total organic carbon, magnetic susceptibility, and chemical composition of the carbonate-free, clay-size fraction indicate that Tioga glaciation began ∼24,500 and ended by ∼13,60014C yr B.P. Many of the components of glacial rock flour (e.g., TiO2, MnO, BaO) found in Owens Lake sediments achieved maximum values during the Tioga glaciation when valley glaciers reached their greatest extent. Total organic carbon and SiO2(amorphous) concentrations reached minimum values during Tioga glaciation, resulting from decreases in productivity that accompanied the introduction of rock flour into the surface waters of Owens Lake. At least 20 stadial–interstadial oscillations occurred in the Sierra Nevada between 52,600 and 14,00014C yr B.P. Total organic carbon data from a Pyramid Lake sediment core also indicate oscillations in glacier activity between >39,500 and ∼13,60014C yr B.P. Alpine glacier oscillations occurred on a frequency of ≤1900 yr in both basins, suggesting that millennial-scale oscillations occurred in California and Nevada during most of the past 52,600 yr.

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Alpine environments are particularly sensitive to climate fluctuations and recent changes to their hydrological and ecological components have been documented in mountain ranges around the world. Paleoclimate reconstructions from these regions can improve our understanding of alpine climate change by placing recent observed changes in a long-term context and by improving our ability to accurately predict and model future changes. This research is designed to use lake sediments to reconstruct the glacier history and paleohydrology of the Teton Mountain ecosystem to provide a framework for characterizing the impacts of climate change occurring in Grand Teton National Park. Multiple physical and geochemical parameters contained in sediments from lakes strategically positioned along elevation transects will be used to develop the first continuous records of: 1) alpine glacier fluctuations, including the timing and character of deglaciation, and 2) coupled fire, vegetation and hydroclimate histories spanning the elevation gradient of the Tetons. This work is critical for assessing and managing the ecological impacts of future climate change in this unique ecosystem and for improving our understanding of how changes here are connected to the broader climate system.

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Abstract Past environmental changes in mountain lakes can be reconstructed with the use of subfossil diatoms from post-glacial sediments. This study applied such an analysis to two mountain lakes in the Sudetes Mts. in Poland: Mały Staw (MS) and Wielki Staw (WS). Cores 882 cm long (MS) and 1100 cm long (WS) taken from the centre of each lake in 1982 were used to study the long-term acidification history of these lakes. Changes in vegetation indicate that the initial phase of MS started at the end of the Pleistocene. WS sediments began to accumulate shortly after that, at the beginning of the Holocene. The majority of the diatom assemblages are typical of oligotrophic acidic lakes located in alpine and arctic regions. A pH reconstruction based on diatoms (DI-pH) showed long-term acidification dating to almost the beginning of the lakes’ existence. Natural acidification began after the deglaciation, and the most intensive acidification continued to the end of the mid-Holocene. Through the whole period studied, pH decreased by 1.4 in MS and 0.9 in WS. After a period of relatively stable lake water pH, it decreased rapidly during the last few decades of the 20th century, due to anthropogenic pollution: pH declined by 0.7 in MS and 0.3 in WS. Mały Staw, being shallower, smaller, and with a larger drainage basin than Wielki Staw, is more sensitive to acid deposition; this accounts for the difference in pH.

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Abstract. The deposition of dust has recently increased significantly over some regions of the western US. Here we explore how changes in dust deposition have affected the biogeochemistry of two alpine watersheds in Colorado, US. We first reconstruct recent changes in the mass accumulation rate of sediments and then we use isotopic measurements in conjunction with a Bayesian mixing model to infer that approximately 95% of the inorganic fraction of lake sediments is derived from dust. Elemental analyses of modern dust indicate that dust is enriched in Ca, Cr, Cu, Mg, Ni, and in one watershed, Fe and P relative to bedrock. The increase in dust deposition combined with its enrichment in certain elements has altered the biogeochemisty of these systems. Both lakes showed an increase in primary productivity as evidenced by a decrease in carbon isotopic discrimination; however, the cause of increased primary productivity varies due to differences in watershed characteristic. The lake in the larger watershed experienced greater atmospheric N loading and less P loading from the bedrock leading to a greater N:P flux ratio. In contrast, the lake in the smaller watershed experienced less atmospheric N loading and greater P loading from the bedrock, leading to a reduced N:P flux ratio. As a result, primary productivity was more constrained by N availability in the smaller watershed. N-limited primary productivity in the smaller watershed was partly ameliorated by an increase in nitrogen fixation as indicated by reduced nitrogen isotopic values in more contemporary sediments. This study illustrates that alpine watersheds are excellent integrators of changes in atmospheric deposition, but that the biogeochemical response of these watersheds may be mediated by their physical (i.e. watershed area) and chemical (i.e. underlying geology) properties.

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AbstractLake sediment cores from the Coast Mountains of British Columbia were analyzed using chemical sequential extractions to partition the dominant geochemical fractions of phosphorus (P). The P fractions include mineral P (the original source of bioavailable P), occluded P (bound to soil oxides), and organic P (remains of organic matter). By comparing P fractions of soil and recent lake sediment samples, these fractions are shown to be a valid proxy for landscape-scale nutrient status. Changes in soil development for an alpine watershed (Lower Joffre Lake) are inferred from the P fractions in the basin's outlet lake sediments. Glacially sourced mineral P dominates at the base of the core, but several rapid shifts in P geochemistry are evident in the first ∼3000 yr of the record. The latter indicates an interval of early and rapid soil nutrient maturation from ∼9600 to 8500 cal yr BP and a significant influx of slope-derived material into Lower Joffre Lake. A substantial increase in mineral P occurs at ca. 8200 cal yr BP, consistent with the cold event in the vicinity of the North Atlantic at that time. The more recent record reveals a continual increase in the proportion of mineral P from glacial sources to the lake, indicating a trend toward cooler conditions in the Coast Mountains.

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Abstract:

Terrestrial paleoclimate archives such as lake sediments are essential for our understanding of the continental climate system and for the modeling of future climate scenarios. However, quantitative proxies for the determination of paleotemperatures are sparse. The relative abundances of certain bacterial lipids, i.e., branched glycerol dialkyl glycerol tetraethers (brGDGTs), respond to changes in environmental temperature, and thus have great potential for climate reconstruction. Their application to lake deposits, however, is hampered by the lack of fundamental knowledge on the ecology of brGDGT-producing microbes in lakes. Here, we show that brGDGTs are synthesized by multiple groups of bacteria thriving under contrasting redox regimes in a deep meromictic Swiss lake (Lake Lugano). This niche partitioning is evidenced by highly distinct brGDGT inventories in oxic vs. anoxic water masses, and corresponding vertical patterns in bacterial 16S rRNA gene abundances, implying that sedimentary brGDGT records are affected by temperature-independent changes in the community composition of their microbial producers. Furthermore, the stable carbon isotope composition (δ13C) of brGDGTs in Lake Lugano and 34 other (peri-)Alpine lakes attests to the widespread heterotrophic incorporation of 13C-depleted, methane-derived biomass at the redox transition zone of mesotrophic to eutrophic lake systems. The brGDGTs produced under such hypoxic/methanotrophic conditions reflect near-bottom water temperatures, and are characterized by comparatively low δ13C values. Depending on climate zone and water depth, lake sediment archives predominated by deeper water/low-13C brGDGTs may provide more reliable records of climate variability than those where brGDGTs derive from terrestrial and/or aquatic sources with distinct temperature imprints.

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APA, Harvard, Vancouver, ISO, and other styles

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Abstract:

Pollen and macrofossil analyses of two radiocarbon-dated lake sediment cores in the upper Peace River district were used to investigate the controversial late-glacial geochronology of the “ice-free corridor.” The basal mineral-rich sediments contain reworked, radiogenically “dead” palynomorphs, as well as intrusive “modern” carbon. Analyses of the basal sediments from Boone Lake show that two 14C ages greater than 12,000 yr B.P. are spuriously old due to contamination by organic matter of Cretaceous age. The data support occlusion or near occlusion of Laurentide and Cordilleran ice in the Peace River area during the late Wisconsinan period. The sediment record began around 12.000 yr B.P. in the ice-dammed and enlarged Boone Lake. An initially open, sedge-dominated cover was invaded by sage, willow, grass, and poplar by 11,700 yr B.P., suggesting that a habitable landscape has existed in the area for at least 12 millennia. The data, however, do not support the ice-free corridor arguments of B. O. K. Reeves (1973, Arctic and Alpine Research 5, 1–16; 1983, In “Quaternary Coastlines and Marine Archaeology: Towards the Prehistory of Land Bridges and Continental Shelves” (P. M. Masters and N. C. Fleming, Eds.), pp. 389–411. Academic Press, New York), who suggests that ice occlusion did not occur in the Peace River Valley during the last 55,000 yr.

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APA, Harvard, Vancouver, ISO, and other styles

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Abstract:

The contamination of aquatic environments by microplastics has been largely documented in the last years, especially in oceans, rivers, and lakes, but their occurrence in remote mountain lakes has been scarcely considered. This work aims to investigate the presence and abundance of microplastics and fibres in a remote, alpine, and uninhabited lake in Switzerland (Sassolo). In this study, the water column as well as the sediments were analysed. The isolation of microplastics and fibres from the samples of the sediment was achieved with a digestion process using H2O2 and a density separation technique with NaI. Classification of microparticles (from 5 mm to 125 μm) was first developed with an optical microscope. Infrared spectroscopy was then used to identify and characterize the chemical nature of the microplastics and fibres. On average, 2.6 microplastics and 4.4 fibres per litre were identified in the water column. On the other hand, the results of the sediment samples revealed significant fibre concentrations compared to plastic microparticles (514 fibres and 33 microplastics per kilogram). The most abundant types of microplastic identified in the samples were composed of polyethylene (PE) and polypropylene (PP). Microplastic and fibre sources were not determined, but it is likely that the number of human activities in this area as well as aerial deposition are contributing to contaminate this remote environment with microplastics and fibres.

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We estimated the net P transport by Gammarus lacustris from the benthic to pelagic regions of a fishless alpine lake and compared it with P regeneration by the entire plankton community. Gammarus lacustris released between 5.2 and 18.1 ng P·L-1·h-1 (adults only and adults plus immatures, respectively) in the pelagic region during nighttime vertical migration. Additional P released into and removed from the water column due to predation on zooplankton was estimated at 1.87 and 2.3 ng P·L-1·h-1, respectively. The net daily regeneration of 52.2-181.4 ng P·L-1·day-1 by the G. lacustris population represented 9.5-32.9% of the total P regenerated by the planktonic community. The majority of the P released by G. lacustris represents "new" P to the pelagic zone because it originated in sediments. We conclude that G. lacustris can represent an important link in benthic-pelagic coupling in oligotrophic mountain lakes.

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Abstract. Lake Iseo is undergoing a dramatic deoxygenation of the hypolimnion, representing an emblematic example among the deep lakes of the pre-alpine area that are, to a different extent, undergoing reduced deep-water mixing. In the anoxic deep waters, the release and accumulation of reduced substances and phosphorus from the sediments are a major concern. Because the hydrodynamics of this lake was shown to be dominated by internal waves, in this study we investigated, for the first time, the role of these oscillatory motions on the vertical fluctuations of the oxycline, currently situated at a depth of approximately 95 m, where a permanent chemocline inhibits deep mixing via convection. Temperature and dissolved oxygen data measured at moored stations show large and periodic oscillations of the oxycline, with an amplitude of up to 20 m and periods ranging from 1 to 4 days. Deep motions characterized by larger amplitudes at lower frequencies are favored by the excitation of second vertical modes in strongly thermally stratified periods and of first vertical modes in weakly thermally stratified periods, when the deep chemical gradient can support baroclinicity regardless. These basin-scale internal waves cause a fluctuation in the oxygen concentration between 0 and 3 mg L−1 in the water layer between 85 and 105 m in depth, changing the redox condition at the sediment surface. This forcing, involving approximately 3 % of the lake's sediment area, can have major implications for the biogeochemical processes at the sediment–water interface and for the internal matter cycle.

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Abstract:

Late Pleistocene glacial chronologies developed for the Front Range Mountains of Colorado include two or more cirque glacier advances, locally known as the Satanta Peak Advances. Sediment cores were recovered from Sky Pond, an alpine lake (3320 m) located less than 100 m downvalley from a moraine that exhibits late Pleistocene to early Holocene relative age features and appears to correlate to the Satanta Peak deposits. One of the cores penetrated 0.5 m of basal diamict and recovered 3.3 m of overlying sediments that are predominantly gyttja. An accelerator mass spectrometry (AMS) age of 12,040 ± 60 yr14C B.P. was obtained from directly above the basal diamict and is similar to other reported ages for cirque deglaciation in the Front Range Mountains. The lower portion of the gyttja contains an interval of clastic sediments that show characteristics consistent with glacial activity in alpine catchments. Radiocarbon ages obtained from below and near the upper contact of this clastic interval are 11,070 ± 50 and 9970 ± 8014C yr B.P., respectively. An additional AMS age of 10,410 ± 9014C yr B.P. was obtained from within the clastic interval in a second core. The most likely source for this interval of clastic sediments is a moraine situated directly upvalley from Sky Pond, and consequently, it appears that the deposition of this moraine was coeval with the European Younger Dryas event (11,000–10,00014C yr B.P.). Similarities in soil development, weathering features, and altitude between this moraine and the type Satanta Peak moraines suggest that the moraines are correlative. These findings are in agreement with a growing body of evidence that suggests a relatively minor advance of alpine glaciers occurred in the North American Rockies during the Younger Dryas Chron.

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Abstract. Nitrous oxide (N2O) is a potent greenhouse gas, generated through microbial nitrogen (N) turnover processes, such as nitrification, nitrifier denitrification, and denitrification. Previous studies quantifying natural sources have mainly focused on soils and the ocean, but the potential role of terrestrial water bodies in the global N2O budget has been widely neglected. Furthermore, the biogeochemical controls on the production rates and the microbial pathways that produce benthic N2O in lakes are essentially unknown. In this study, benthic N2O fluxes and the contributions of the microbial pathways that produce N2O were assessed using 15N label flow-through sediment incubations in the eutrophic, monomictic south basin of Lake Lugano in Switzerland. The sediments were a significant source of N2O throughout the year, with production rates ranging between 140 and 2605 nmol N2O h−1 m−2, and the highest observed rates coinciding with periods of water column stratification and stably anoxic conditions in the overlying bottom water. Nitrate (NO3−) reduction via denitrification was found to be the major N2O production pathway in the sediments under both oxygen-depleted and oxygen-replete conditions in the overlying water, while ammonium oxidation did not contribute significantly to the benthic N2O flux. A marked portion (up to 15%) of the total NO3− consumed by denitrification was reduced only to N2O, without complete denitrification to N2. These fluxes were highest when the bottom water had stabilized to a low-oxygen state, in contrast with the notion that stable anoxia is particularly conducive to complete denitrification without accumulation of N2O. This study provides evidence that lake sediments are a significant source of N2O to the overlying water and may produce large N2O fluxes to the atmosphere during seasonal mixing events.

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Abstract:

Paleolimnology, bioenergetics modelling, and mesocosm experiments were used to quantify changes in phytoplankton following introduction of trout into fishless alpine lakes in the Canadian Rocky Mountains. During the 1960s, Snowflake and Pipit lakes were stocked with brook (Salvelinus fontinalis), cutthroat (Oncorhynchus clarkii) and rainbow trout (O. mykiss) either singly or in combination. Stocked trout eliminated large invertebrates (Daphnia spp., Hesperodiaptomus arcticus, Gamrnarus lacustris), but the fish died within 15 yr. High performance liquid chromatographic analysis of carotenoids and chlorophylls in sediments inferred that algal abundance increased 4- to 10-fold shortly after fish stocking. In contrast, phytoplankton composition and biomass were constant in nearby, unstocked Harrison Lake, as inferred from fossils. Pigment analysis of mesocosms showed that phytoplankton were sensitive to moderate fertilization: 11 μg P∙L−1 resulted in four- to six-fold increases in algal biomass. Bioenergetics modelling was used to estimate phosphorus (P) excretion from trout. The flux of excreted P was highly correlated (r2 = 0.76, p < 0.0001, N = 12) to changes in algal biomass, as estimated from fossil pheophytin b. Consequently, we infer that nutrient recycling by stocked trout was one of several mechanisms that contributed to increased algal biomass.

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APA, Harvard, Vancouver, ISO, and other styles

APA, Harvard, Vancouver, ISO, and other styles

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Abstract. Nitrous oxide (N2O) is a potent greenhouse gas, generated through microbial nitrogen (N) turnover processes, such as nitrification, nitrifier denitrification, and denitrification. Previous studies quantifying natural sources have mainly focused on soils and the ocean, but the potential role of terrestrial water bodies in the global N2O budget has been widely neglected. Furthermore, the biogeochemical controls on the production rates and the microbial pathways that produce benthic N2O in lakes are essentially unknown. In this study, benthic N2O fluxes and the contributions of the microbial pathways that produce N2O were assessed using 15N label flow-through sediment incubations in the eutrophic, monomictic south basin of Lake Lugano in Switzerland. The sediments were a significant source of N2O throughout the year, with production rates ranging between 140 and 2605 nmol N2O h−1 m−2, and the highest observed rates coinciding with periods of water column stratification and stably anoxic conditions in the overlying bottom water. Nitrate (NO3–) reduction via denitrification was found to be the major N2O production pathway in the sediments under both oxygen-depleted and oxygen-replete conditions in the overlying water, while ammonium oxidation did not significantly contribute to the benthic N2O flux. A significant portion (up to 15%) of the total NO3– consumed by denitrification was reduced only to N2O, without complete denitrification to N2. These fluxes were highest when the bottom water had completely stabilized to a low-oxygen state, in contrast with the notion that stable anoxia is particularly conducive to complete denitrification without accumulation of N2O. This study provides evidence that lake sediments are a~significant source of N2O to the overlying water and may produce large N2O fluxes to the atmosphere during seasonal mixing events.

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Abstract:

Reconstructing paleo-denudation rates over Holocene timescales in an Alpine catchment provides a unique opportunity to isolate the climatic forcing of denudation from other tectonic or anthropogenic effects. Cosmogenic 10Be on two sediment cores from Lake Stappitz (Austrian Alps) were measured yielding a 15-kyr-long catchment-averaged denudation record of the upstream Seebach Valley. The persistence of a lake at the outlet of the valley fixed the baselevel, and the high mean elevation minimizes anthropogenic impacts. The 10Be record indicates a decrease in the proportion of paraglacial sediments from 15 to 7 kyr cal. BP after which the 10Be concentrations are considered to reflect hillslope erosion and thus can be converted to denudation rates. These ones significantly fluctuated over this time period: lower hillslope erosion rates of ca. 0.4 mm/year dated between 5 and 7 kyr cal. BP correlate with a stable climate, sparse flooding events and elevated temperatures that favoured the widespread growth of stabilizing soils and vegetation. Higher hillslope erosion rates of ca. 0.8 mm/year over the last ~4 kyr correlate with a variable, cooler climate where frequent flooding events enhance denudation of less protected hillslopes. Overall, our results suggest a tight coupling of climate and hillslope erosion in alpine landscapes as it has been observed in other parts of the Alps.

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Abstract:

Abstract Multiple biogeochemical variables in a sediment core from Lake Lugu in southwest China were studied to investigate the effects of regional environmental changes on the ecosystem. Subfossil Cladocera, together with diatom, pollen and geochemical records, were used to examine climate-induced changes in lake ecosystem since the Last Glacial Maximum (30 000–0 cal year BP). Consistency among these biological records indicates that the succession of zooplankton, algae and vegetation changed in response to direct and indirect climatic factors. Alterations in the nutrient supply mediated by climate-induced changes in vegetation and soil processes are likely responsible for the variability of cladocerans. During the Last Glacial Maximum, cladocerans were dominated by littoral taxa (e.g. Alona), indicating an unproductive and oligotrophic lake system. A peak distribution in the pelagic Bosmina highlights the period of increased nutrient availability at 11 500 cal year BP. The ecological changes in Cladocera at 19 000 cal year BP and diatom communities at 18 000 cal year BP reveal independent and indirect responses to nutrient and light conditions induced by solar radiation and increased monsoon intensity across the study region. The palaeoecological archives from Lake Lugu sediments highlight a complex lake ecosystem influenced by both direct and indirect changes corresponding to climate changes and shifts in regional anthropogenic pressure over the last 30 000 years.

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Abstract. High-altitude peat bogs and lacustrine records are very sensitive to climate changes and atmospheric dust input. Recent studies have shown a close relationship between regional climate aridity and enhanced eolian input to lake sediments. However, changes in regional-scale dust fluxes due to climate variability at short scales and how alpine environments were impacted by climatic- and human-induced environmental changes are not completely understood. Here we present a multi-proxy (palynological, geochemical and magnetic susceptibility) lake sediment record of climate variability in the Sierra Nevada (southeastern Iberian Peninsula) over the Holocene. Magnetic susceptibility and geochemical proxies obtained from the high mountain lake record of Laguna Hondera evidence humid conditions during the early Holocene, while a trend towards more arid conditions is recognized since ∼7000 cal yr BP, with enhanced Saharan eolian dust deposition until the present. This trend towards enhanced arid conditions was modulated by millennial-scale climate variability. Relative humid conditions occurred during the Iberian Roman Humid Period (2600–1450 cal yr BP) and predominantly arid conditions occurred during the Dark Ages and the Medieval Climate Anomaly (1450–650 cal yr BP). The Little Ice Age (650–150 cal yr BP) is characterized in the Laguna Hondera record by an increase in runoff and a minimum in eolian input. In addition, we further suggest that human impact in the area is noticed through the record of Olea cultivation, Pinus reforestation and Pb pollution during the Industrial Period (150 cal yr BP–present). Furthermore, we estimated that the correlation between Zr and Ca concentrations stands for Saharan dust input to the Sierra Nevada lake records. These assumptions support that present-day biochemical observations, pointing to eolian input as the main inorganic nutrient source for oligotrophic mountain lakes, are comparable to the past record of eolian supply to these high-altitude lakes.

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Abstract:

AbstractMountain lakes are increasingly impacted by a series of both local and global disturbances. The present study reveals the eutrophication history of a remote subalpine lake (Oberer Soiernsee, Northern Alps, Germany), triggered by deforestation, alpine pasturing, hut construction, tourism and atmospheric deposition, and identifies the intertwined consequences of on-going global warming on the lake’s ecosystem. The primary objective was to disentangle the various direct and indirect impacts of these multiple stressors via down-core analyses. Our multi-proxy approach included subfossil diatom assemblages, carbon and nitrogen stable isotope ratios and subfossil pigments from dated sediments. Shifts within the diatom assemblages were related to variations in trophic state, lake transparency, water temperature and thermal stratification. The organic carbon isotope (δ13Corg) records, the diatom valve density and the pigment concentrations documented the development of primary production and composition. Total nitrogen isotope values (δ15N) are more likely to reflect the history of atmospheric nitrogen pollution than lake-internal processes, also mirrored by the decoupling of δ15N and δ13Corg trends. The composition of sedimentary pigments allowed a differentiation between planktonic and benthic primary production. Concordant trends of all indicators suggested that the lake ecosystem passed a climatic threshold promoted by local and long-distance atmospheric nutrient loadings.

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