Subjects -> PALEONTOLOGY (Total: 43 journals)
Showing 1 - 21 of 21 Journals sorted by number of followers
Journal of Quaternary Science     Hybrid Journal   (Followers: 31)
Quaternary Science Reviews     Hybrid Journal   (Followers: 26)
Quaternary Research     Full-text available via subscription   (Followers: 19)
Palaeontology     Hybrid Journal   (Followers: 17)
Palaeogeography, Palaeoclimatology, Palaeoecology     Hybrid Journal   (Followers: 13)
Boreas: An International Journal of Quaternary Research     Hybrid Journal   (Followers: 13)
Peer Community Journal     Open Access   (Followers: 12)
Geologica Saxonica     Open Access   (Followers: 11)
Historical Biology: An International Journal of Paleobiology     Hybrid Journal   (Followers: 9)
Facies     Hybrid Journal   (Followers: 9)
Journal of Vertebrate Paleontology     Full-text available via subscription   (Followers: 8)
Journal of Paleontology     Hybrid Journal   (Followers: 8)
Paleobiology     Full-text available via subscription   (Followers: 6)
Alcheringa: An Australasian Journal of Palaeontology     Hybrid Journal   (Followers: 6)
EvoDevo     Open Access   (Followers: 5)
Journal of Paleolimnology     Hybrid Journal   (Followers: 5)
European Journal of Protistology     Hybrid Journal   (Followers: 5)
Fossil Record     Open Access   (Followers: 5)
Paleoceanography and Paleoclimatology     Full-text available via subscription   (Followers: 5)
Swiss Journal of Palaeontology     Hybrid Journal   (Followers: 4)
Annales de Paléontologie     Full-text available via subscription   (Followers: 4)
Paläontologische Zeitschrift     Hybrid Journal   (Followers: 4)
Paleontological Journal     Full-text available via subscription   (Followers: 4)
Geobios     Full-text available via subscription   (Followers: 4)
Palaeontographica A     Full-text available via subscription   (Followers: 3)
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen     Full-text available via subscription   (Followers: 3)
International Journal of Speleology     Open Access   (Followers: 3)
Quaternaire     Open Access   (Followers: 3)
Palaeoworld     Hybrid Journal   (Followers: 3)
Marine Micropaleontology     Hybrid Journal   (Followers: 2)
Rivista Italiana di Paleontologia e Stratigrafia (Research In Paleontology and Stratigraphy)     Open Access   (Followers: 1)
Vertebrate Anatomy Morphology Palaeontology     Open Access   (Followers: 1)
Palynology     Hybrid Journal   (Followers: 1)
Novitates Paleoentomologicae     Open Access   (Followers: 1)
Annals of Carnegie Museum     Full-text available via subscription   (Followers: 1)
Review of Palaeobotany and Palynology     Hybrid Journal   (Followers: 1)
PaleoBios     Open Access   (Followers: 1)
Zitteliana     Open Access  
Ameghiniana     Open Access  
Papers in Palaeontology     Hybrid Journal  
Spanish Journal of Palaeontology     Open Access  
Open Quaternary     Open Access  
Ichnos: An International Journal for Plant and Animal Traces     Hybrid Journal  
Revue de Micropaleontologie     Full-text available via subscription  
Comptes Rendus Palevol     Open Access  
Similar Journals
Journal Cover
Journal of Paleolimnology
Journal Prestige (SJR): 1.019
Citation Impact (citeScore): 2
Number of Followers: 5  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1573-0417 - ISSN (Online) 0921-2728
Published by Springer-Verlag Homepage  [2469 journals]
  • Effects of climate change and nutrient concentrations on carbon sources
           for zooplankton in a Tibetan Plateau lake over the past millennium

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      Abstract: Abstract Autochthonous and allochthonous organic carbon (OC) are important carbon sources for zooplankton in lakes, and changes in the abundance and proportions of those sources may affect zooplankton community composition and lake ecosystem function. Nevertheless, long-term changes in assimilation of autochthonous and allochthonous carbon by zooplankton and associated climate- and environment-related forcing mechanisms have rarely been studied. We used a sediment record of cladoceran remains and geochemical variables from Lake Jirentso on the Tibetan Plateau to track long-term changes in sources of carbon for cladocera over the past ~ 950 years. High cladoceran:diatom accumulation rate ratios during the cold Little Ice Age indicated that cladocerans assimilated more allochthonous OC that was released from glaciers and frozen soils to replenish their food supply, a consequence of low primary production in the lake. In contrast, low cladoceran:diatom accumulation rate ratios during the Current Warm Period indicated that cladocerans utilized more autochthonous OC. Less autochthonous OC was available for cladocerans during the Medieval Warm Period than during the Current Warm Period. The total accumulation rate of cladocerans was significantly correlated with the annual mean air temperature, total phosphorus, and the organic carbon to nitrogen ratio in the sediment core. Recent warming and sharply increased nutrient inputs affected the cladoceran and diatom assemblages, further inducing a shift in the diet of zooplankton towards more recently produced OC. The sediment record from Lake Jirentso, which represents the last ~ 950 years of deposition, spanned an ideal time window for assessing historical changes related to the impacts of climate and nutrients on zooplankton carbon sources.
      PubDate: 2022-10-01
       
  • An isotope, elemental, and n-alkane baseline for organic matter sources in
           sediments of high-altitude lakes in the Uinta Mountains, Utah, USA

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      Abstract: Abstract This research provides a critical baseline for chemical and macromolecular characteristics of organic matter (OM) sources in high-elevation lake sediments. Such studies are essential for accurate paleoenvironmental interpretation of organic matter characteristics, particularly in mountain regions where steep environmental gradients lead to spatially variable OM inputs among lakes. We analyzed the carbon- and nitrogen-isotope compositions (δ13CTOC, δ15NTN), and total organic carbon to total nitrogen atomic ratios (TOC:TN), of whole tissues of modern vegetation, lichen and algae from Uinta Mountain lakes, along with the abundances and carbon- and hydrogen-isotope compositions of n-alkanes (δ13Cn-alkane, δ2Hn-alkane). TOC:TN can be used to distinguish between aquatic and terrestrial sources, but the differentiating values are higher in the Uinta Mountains than in low-elevation regions. Chain lengths of n-alkanes are more useful than n-alkane isotope compositions for differentiating between terrestrial and semi-aquatic sources in the Uinta Mountains. The ratio of n-alkanes C23 to C27 in mountain lake sediment OM can be used to detect inputs from coniferous krummholz trees and may serve as a proxy for treeline position. We used the isotope data from n-alkanes to calculate the carbon-isotope fractionation between atmospheric carbon dioxide and the n-alkane C23 (ɛbulk), and the hydrogen-isotope fractionation between source water and the n-alkane C25 (ɛwater). These fractionation factors, and the isotope compositions of n-alkanes extracted from lake sediments, suggest that the δ13C of atmospheric CO2 was − 7.0 ± 2‰ and the δ2H of precipitation was − 133 ± 7‰ at ~ 1400 CE in this region. These calculations demonstrate potential applications of our results for obtaining additional paleoclimatic information from paleolimnological organic matter archives.
      PubDate: 2022-09-16
       
  • Evidence of large water-level variations found in deltaic sediments of a
           tropical deep lake in the karst mountains of the Lacandon forest, Mexico

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      Abstract: Abstract Lake Tzibaná is one of the largest (1.27 km2) and deepest (Zmax = 52 m) karstic lakes in the UNESCO’s Biosphere Reserve “Nahá-Metzabok” and in the Lacandon Forest, southeastern Mexico. It archives sediments from multiple sources and the inflowing Nahá River forms deltaic deposits. In 2019, the water level in Lake Tzibaná declined by ~ 15 m, persisting for 4 months and exposing the Nahá River Delta. A geophysical profile on the exposed delta revealed an accumulation of ~ 20 m of such deposits. Three sediment outcrops from an inactive channel in the Nahá River Delta, which ranged in height from 0.6 to 1.43 m, were sampled and a multi-proxy analysis of biological remains and geochemical variables was conducted. Four facies were observed: (1) massive-coarse sand, (2) fine sand, (3) dark leaf litter and (4) massive silty clay, each characterized by specific microcrustacean, testate amoebae and diatom taxa. Six dark leaf litter horizons were radiocarbon dated and revealed a complex depositional history including inverted ages making the establishment of an age model difficult. Nevertheless, past lake-level changes and the formation of the four facies match three characteristic water-level stages, which can also be observed on recent satellite images: (1) Massive-coarse sand deposits, with compositional and sedimentological characteristics of a shoreline environment and fluvial lateral banks, were formed during large-magnitude reductions in the lake level, similar to the one in 2019, (2) Interbedded layers of fine sand and dark leaf litter, currently found in low-energy fluvial environments, were formed during shorter and less pronounced decrease intervals, and (3) Massive silty clay, with distinctive microorganisms from low-energy lacustrine environments, is deposited during high water-level stages, when the delta is covered by water. Our findings illustrate how hydrological changes alter sedimentary dynamics in deltaic areas of lakes. Despite the complexity of their depositional processes, deltaic records can serve as a complementary source of paleolimnological information to records from distal zones due to their sensitivity to variations in water level, especially during extreme and prolonged desiccation events. Future research should attempt to combine evidences from deltaic and sediment sequences from deeper zones of Lake Tzibaná to reconstruct water-level variations during the entire Holocene. Understanding past lake-level reductions is not only relevant for the local indigenous communities but also crucial for the conservation of this ecosystem of international importance.
      PubDate: 2022-09-13
       
  • Early to Middle Holocene hydroclimate changes in the Guern El Louläilet
           depressions, Algerian Sahara

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      Abstract: Abstract Fossil diatoms and litho-stratigraphic changes in the Guern El Louläilet depressions, NW of the Great Western Erg, Algeria, were analysed to infer paleoenvironmental changes in the northern Algerian Sahara during the Early and Middle Holocene. Analysis was based on calcareous diatomite collected from four outcrops within the depressions. The diatom flora consists of brackish and epiphytic taxa, such as Epithemia argus, with percentages of some freshwater and planktonic species, mainly Cyclotella distinguenda. Results provide evidence for two Holocene lacustrine episodes related to the African Humid Period. The first episode (Early to Middle Holocene) was characterized by abrupt development of shallow-water conditions, with extensive littoral zones and evaporative periods that coincided with high salt concentrations in warm, alkaline water (swampy conditions). A second episode (Middle to Late Holocene'), with brackish water and alkaline conditions, coincided with a decline in lake water level that is attributed to drier conditions. Our findings are consistent with those of other studies from the area and demonstrate similar environmental changes occurred after 9300 cal yr BP at sites within the region. The main drivers of the African Humid Period were the northward shift of the Intertropical Convergence Zone (ITCZ) and expansion of summer monsoonal rains. Our study sites were located in the northern Sahara, where variations in the position of the Intertropical Convergence Zone (ITCZ) did not affect rainfall. Early and Middle Holocene climate fluctuations detected in this study may have been caused by intensification of winter precipitation in the south-central Mediterranean and its penetration southward.
      PubDate: 2022-09-09
       
  • Historical reconstruction of sediment accumulation rates as an indicator
           of global change impacts in a tropical crater lake

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      Abstract: Abstract Lakes are effective sentinels of global change owing to their sensitivity to land-use changes and climate variability in their catchment. Santa María del Oro Lake (SAMO, NW Mexico) is of interest both for global change studies and as a natural resource to sustain the economy of local communities. Four sediment cores were used to evaluate the temporal variations of sediment accumulation, under the hypothesis that changes in sediment input are mostly driven by anthropic activities developed in the lake surroundings. Radiocarbon (14C) dating of SAMO sediments was precluded by a large and variable reservoir effect, inducing an age offset of ~ 4000 years. Well-constrained chronologies over the past century were obtained by 210Pb dating, corroborated by the stratigraphic markers 137Cs, 239+240Pu, and 14C-fraction modern. Geochemical, magnetic susceptibility, and meteorological data were used to elucidate the main controls of sedimentation processes in the lake. Mass accumulation rates were high, likely because of the natural vulnerability of catchment soils to hydric and aeolian erosion. The highest values, observed towards the lakeshore, were attributed to the influence of seasonal runoff from the surrounding steep hills, and the proximity of human settlements and agricultural fields. Mean mass accumulation rates increased with time (from 0.03 ± 0.01 g cm−2 year−1 between 1900 and 1950, to 0.14 ± 0.10 g cm−2 year−1 after the 1950s), although the most recent values were comparable to the mean values during the pre-1950 period. Accumulation maxima across the lake, occurring mostly since the 1980s, concurred with precipitation minima and were related to terrigenous pulses associated with soil erosion, likely favored by lower soil humidity and the occurrence of wildfires during dryer years. Controls on the development of human settlement and agriculture practices should be included in the long-term environmental management plans for the conservation of the lake resources.
      PubDate: 2022-09-08
       
  • Ecological impacts of N-deposition in a remote, high-elevation lake in the
           Three River Headwaters Region, Qinghai-Tibetan Plateau

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      Abstract: Abstract This study provides a new record of nitrogen (N) deposition and ecological response at a remote, high-elevation lake within the ecologically fragile Three River Headwaters Region, northwest China, from the early 20thCentury to the past decade. A multi-proxy investigation of a lake sediment core including analyses of chironomids (non-biting midge), lake sediment geochemistry (δ15N, δ13C, TN, TOC, OC:TN), pollen, non-pollen palynomorphs and 210Pb-dating. Results were compared with regional pollution forcings, including fertiliser application, atmospheric nitrate and dust deposition, and a localised multiscale air quality modelling system for N-deposition. Our data reflect a mesotrophic lake for the majority of the 20th Century with minimal anthropogenic impact. A shift in the lake conditions is evident after 1985 with increased nutrient enrichment. Low δ15N, OC:TN and increasing TN values, together with an increase in chironomid taxa associated with eutrophic conditions and macrophytes are exhibited in the record, particularly since 2002. These changes are consistent with nutrient loading causing a change in trophic status. Redundancy analysis (RDA) and partial RDAs verified TN as an important driver behind the shift in chironomid community composition in recent decades, explaining 22.2% of the variance on its own and 16.9% with other environmental variables partialled out. While temperature change since 1960 was not a primary control on the chironomid community of Lake Bander, a step-change increase in summer temperatures since the 1990s coincided with the disappearance of cold stenotherms from the record and seems to have exacerbated the shift to more productive conditions. This study highlights the reach of airborne N from modern agricultural and industrial activity to remote locations, and demonstrates the utility of palaeolimnological techniques as part of modern ecosystem assessment for conservation.
      PubDate: 2022-09-03
       
  • Response of lake water nutrient condition to anthropogenic activities from
           1871 to 2013 in the Jiuzhaigou World Natural Heritage Site, China

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      Abstract: Abstract Over the past century, lake degradation has increased around the world. Jiuzhaigou World Natural Heritage Site in southwestern China has been experiencing water nutrient enrichment, accelerated swamping, and algal biomass increases. These problems are likely associated with enhanced local anthropogenic activities over the past decades. In this study, radioactivities of 137Cs and 210Pb, diatoms, and nutrient accumulation rates in a lake sediment core from Tiger Lake in Jiuzhaigou World Natural Heritage Site were used as proxies to reconstruct a > 100-year record of environmental change to understand the extent and temporal variability of anthropogenic effects on lake water nutrients. Diatom communities reveal four distinct phases, relating to documented local human activities including (a) Primitive agriculture from 1871 to the mid-1930s, (b) Opium cultivation—logging from the mid-1930s to the mid-1970s, (c) Large-scale logging—the beginning of tourism from the mid-1970s to the early 1990s, and (d) Tourism development from the early 1990s to 2013. Nutrients in the lake (including total organic carbon, total nitrogen, and total phosphorus) steadily increased from 1871 until the late 1990s, declined from the late 1990s to the mid-2000s, and increased rapidly after the mid-2000s. Our data suggest that (a) Opium cultivation, deforestation, and tourism development led to the increase of lake nutrients and primary productivity, (b) Ecological protection measures taken from 1999 to 2004 effectively controlled water pollution, and (c) Post-2005 intensification of tourism further accelerated water quality deterioration. Additional monitoring and mitigation strategies are needed to further reduce nutrient input. Global studies suggest that while water quality of lakes in protected area is better than that of other lakes, care is still required to ensure that tourism activities do not inadvertently increase lake water nutrients.
      PubDate: 2022-08-26
       
  • A diatom-based paleolimnological re-assessment of previously polymictic
           Lake Opinicon, Ontario (Canada): crossing an ecological threshold in
           response to warming over the past 25 years

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      Abstract: Abstract Long-term changes in diatom community composition provided important insights into how multiple stressors affected shallow, macrophyte-dominated Lake Opinicon, Ontario (Canada) over the past ~ 200 years. A previous paleolimnological study of a sediment core collected in 1995 found that diatom responses to numerous large-scale cultural disturbances since the early nineteenth century were moderate in comparison to pronounced diatom responses to similar disturbances in nearby deeper lakes within the Rideau Canal system. The abundance of macrophytes in shallow and previously polymictic Lake Opinicon likely played an important role in maintaining a stable, clear-water equilibrium state. We examined diatom assemblages from a sediment core collected in 2019 to re-assess whether Lake Opinicon maintained its resistance to change over the past ~ 25 years. Despite numerous, intense early nineteenth and twentieth century cultural disturbances in Lake Opinicon’s catchment (complete deforestation, flooding with the construction of the Rideau Canal), the highest rate of diatom compositional change occurred only in the past ~ 25 years, when planktonic diatoms became prevalent for the first time in the lake’s postglacial history. This recent shift in assemblage composition is not explained by nutrient enrichment, as total phosphorus concentrations, measured since the 1970s, have declined significantly. The first appearance of zebra mussels (~ 1990s) and significant increases in Secchi depth broadly co-occurred with the diatom assemblage shift, but precipitous declines in mussel populations since 2013 and a continued increase in planktonic diatom taxa suggest the impact of this invasive species was modest. Instead, changes in diatom assemblage composition were strongly related to increasing regional air temperatures. Limnological monitoring indicated that, over the past few decades, previously polymictic Lake Opinicon has experienced increasingly longer and more stable periods of thermal stratification that are consistent with observed trends in regional warming and reduced wind speed. These water column changes, which accompanied reduced ice cover duration, would have provided favourable conditions for planktonic diatom growth. We conclude that the nature and high rate of diatom compositional change over the past ~ 25 years signifies that an ecological threshold was crossed in response to warming and changes in lake thermal structure.
      PubDate: 2022-08-22
       
  • Climate change and nutrient enrichment altering sedimentary diatom
           assemblages since pre-industrial time: evidence from Canada’s most
           populated ecozone

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      Abstract: Abstract Lakes worldwide are under threat by a myriad of environmental stressors that have been increasing in number and magnitude. These stressors can be regional such as climate change, or local such as nutrient-rich runoff, invasive species, and road salt contamination, to name but a few. To protect lake ecosystems from further deterioration, we need long-term data to define pre-disturbance baselines and to identify stressors that are causing the greatest ecological changes. Paleolimnology is an effective approach to reconstruct limnological history, providing an important window into past changes. Here, we applied paleolimnological tools to explore the pre-industrial and contemporary diatom assemblage changes of 27 lakes located in the most populated ecozone in Canada, the Mixedwood Plains. We also examined a full sediment core for Lac des Chicots (Southern Québec), aiming to disentangle the impacts of natural versus anthropogenic interactions and to assess their relative effects on the lake’s biotic structure. Our ordination analysis suggests that the Mixedwood Plains lakes have experienced varying lake-specific ecological changes over the past ~150 years, with two major trends across most study lakes: (1) a prevalent increase in planktic species, and (2) a rise in mesotrophic/eutrophic taxa in lakes receiving high human impacts. Our case study of Lac des Chicots identifies ecological impacts from both historical natural events and recent human activities, such as cultural eutrophication and climate warming. Overall, our study demonstrates that lakes in the Mixedwood Plains ecozone have experienced marked ecological changes that are mainly associated with human impacts.
      PubDate: 2022-08-21
       
  • Trends in sedimentary charcoal shapes correspond with broad-scale land-use
           changes: insights gained from a 300-year lake sediment record from eastern
           Virginia, USA

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      Abstract: Abstract Sedimentary charcoal is a useful fire proxy. Recent advances in the morphological and morphometric analyses of individual charcoal particles have enabled more nuanced paleofire interpretations. However, many uncertainties exist regarding the linkages of these particle characteristics with fuel type burned. Further, most of this proxy development research has been conducted in northern boreal biomes, which poses questions as to its universality. In this paper, we leverage a 300-year sediment record from a mill pond in southeastern Virginia, USA. Historical events and land-use changes are well constrained in Williamsburg, allowing us to compare our data with these known boundary conditions to (1) make inferences about the fuel sourcing of certain charcoal morphotypes, and (2) identify the potential controls of several charcoal morphometric characteristics. We found that the morphology and morphometry of particles in the Matoaka sediments changed in response to broad-scale shifts of historical land use and population. Prior to the American Revolutionary War (ca. 1780 CE), charcoal morphologies indicative of agricultural burning coincided with agricultural and local population expansion. Immediately preceding the American Civil War (1780–1865 CE), charcoal in Lake Matoaka recorded reforestation driven by depopulation and economic depression. After the fall of the Confederacy (ca. 1865 CE), changing charcoal morphologies reflected increased population and urban development. This increase became especially pronounced in the early 1900s, but lasted until the modern. Additionally, shifts of charcoal morphologies potentially reflect increased coal combustion. Comparison of these historical variations with morphotype shifts shows that Types M and S/B charcoal, types defined by their geometric shapes and exhibition of structure, are likely sourced from burning herbaceous fuels. However, we find that the variability of morphometric characteristics makes it unlikely that other morphologies are sourced from sole fuel types. Lastly, we propose three additional morphotypes, Types AI (angular and irregular shaped particles), E (irregular, complex shaped particles), and T (triangular particles), to an existing charcoal morphological key for application in the SE USA. Overall, this research underscores the need for more work calibrating paleofire methodologies in the SE USA.
      PubDate: 2022-08-09
       
  • Surface sediment composition and depositional environments in tropical
           Lake Sentani, Papua Province, Indonesia

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      Abstract: Abstract Tropical Lake Sentani in the Indonesian Province Papua consists of four separate basins and is surrounded by a catchment with a very diverse geology. We characterized the surface sediment (upper 5 cm) of the lake’s four sub-basins based on multivariate statistical analyses (principal component analysis, hierarchical clustering) of major element compositions obtained by X-ray fluorescence scanning. Three types of sediment are identified based on distinct compositional differences between rivers, shallow/proximal and deep/distal lake sediments. The different sediment types are mainly characterized by the correlation of elements associated with redox processes (S, Mn, Fe), carbonates (Ca), and detrital input (Ti, Al, Si, K) derived by river discharge. The relatively coarse-grained river sediments mainly derive form the mafic catchment geology and contribution of the limestone catchment geology is only limited. Correlation of redox sensitive and detrital elements are used to reveal oxidation conditions, and indicate oxic conditions in river samples and reducing conditions for lake sediments. Organic carbon (TOC) generally correlates with redox sensitive elements, although a correlation between TOC and individual elements change strongly between the three sediment types. Pyrite is the quantitatively dominant reduced sulfur mineral, monosulfides only reach appreciable concentrations in samples from rivers draining mafic and ultramafic catchments. Our study shows large spatial heterogeneity within the lake’s sub-basins that is mainly caused by catchment geology and topography, river runoff as well as the bathymetry and the depth of the oxycline. We show that knowledge about lateral heterogeneity is crucial for understanding the geochemical and sedimentological variations recorded by these sediments. The highly variable conditions make Lake Sentani a natural laboratory, with its different sub-basins representing different depositional environments under identical tropical climate conditions.
      PubDate: 2022-08-05
       
  • Decoupling of chemical and biological recovery from acidification in a
           montane lake, Vermont, USA

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      Abstract: Abstract Lakes in the northeast United States are recovering from acidification, but it is unclear if species assemblages will return to pre-acidification conditions, in light of new, interacting climate change pressure. This study explored the impact of past acidification on Beaver Pond, an acid-impaired lake in Vermont, USA. We analyzed long-term seasonal trends in water chemistry data collected by the Vermont Department of Environmental Conservation to assess the extent of acidification and subsequent chemical recovery since the beginning of the monitoring period (1985-present). Biological recovery in acidified waterbodies often lags chemical recovery, as changes in community composition occur at a slower rate. To assess both, we integrated analysis of long-term changes in lake physical and chemical characteristics (pH, dissolved organic carbon, Secchi depth, surface water temperature) with a paleolimnological analysis to analyze shifts in sediment diatom community composition and changes in sediment geochemistry in the past ~ 180 years. Long-term water chemistry analysis indicates that both pH and DOC concentration in Beaver Pond increased over the monitoring period, and that the greatest rate of increase for both variables occurred between 2001 and present. We identified shifts in sediment diatom assemblages from acid-sensitive taxa (D. stelligera, L. affinis) pre-acidification, to acid-tolerant taxa (Eunotia spp.) during acid deposition, and different acid-sensitive taxa (F. rhomboides, B. brebissonii) in the post-acidification recovery period. Together, paleolimnological and modern data in our study indicate that Beaver Pond is experiencing chemical and biological recovery from acid deposition, though diatom communities in the recovery period differ in composition from those in the lake prior to acidification.
      PubDate: 2022-08-05
       
  • A 15,000-yr paleo-environmental record from Lake Chapala, west-central
           Mexico

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      Abstract: Abstract A 27.15-m-long core from Lake Chapala, west-central Mexico (1520 masl) possesses a continuous 15,000-year record of sediment accumulation with abundant diatoms, pollen, charcoal particles, and organic and inorganic carbon. Analyses of multiple sediment variables revealed the lake was deep, dominated by Stephanodiscus niagarae, and was surrounded by temperate forests of Pinus, Quercus, and Alnus in the late Pleistocene (14,700–12,760 cal yr BP). During the Pleistocene-Holocene transition (12,760–9660 cal yr BP), the lake level dropped and a temperate forest of Pinus and Quercus occupied the watershed and was persistently affected by fire. During the earliest Holocene, Quercus nearly disappeared and Pinus, relatively abundant, declined abruptly. Pollen of dry forests became more common, indicating the onset of drier conditions in the region. During the interval from 7500 to 6500 cal yr BP, more humid climate conditions prevailed and abundant Surirella spp. diatom valves were well preserved. Sediments of the time also contain Stephanodiscus niagarae and Ulnaria acus, suggesting deep-water conditions. Between 6500 and 2000 cal yr BP, the lake experienced higher conductivity and longer water residence times. The Pinus and Quercus forests began to be replaced by open vegetation, with Asteraceae and Poaceae dominating the pollen spectrum. Lake level fluctuated, but overall declined. Between the interval of ca. 2 ky to 0.5 cal yr BP basin conditions remained relatively wet. During the last ~ 0.5 kyr BP to present day, the lake level declined and ionic concentration increased, as inferred from representation of planktonic and benthic saline diatom taxa and TIC increases. Numerous micro-tephras are common in this interval; additionally, frequent fires favored the dominance of Poaceae. Paleolimnological records suggest that after the Last Glacial Maximum, Chapala and other lakes of west-central Mexico maintained relatively high water levels. Some records from the region showed evidence of increased humidity beginning ca. 8200 cal yr BP, a consequence of strength intensification in North American Monsoon, associated with ENSO variability and/or tropical cyclones. The record from the last 0.5 cal yr BP in Lake Chapala is similar to records from other lakes in Central Mexico, as it displays a trend toward drier conditions with a more variable precipitation regime.
      PubDate: 2022-08-03
       
  • Correction to: Late Holocene climate change inferred from the lithology
           and chemical stratigraphy of sediment cores from Swan Lake, Nebraska
           Sandhills, USA

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      PubDate: 2022-08-02
       
  • Acid-volatile sulfide and acid-extractable iron sediment profiles do not
           track changes in lake trophic status and atmospheric sulfur deposition

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      Abstract: Abstract Sulfide formation in anaerobic lake sediments depends on supply rates of organic carbon and sulfate. Improvements to wastewater treatment plant effluent quality (e.g., lower total phosphorus (P)) and sulfur emissions can affect sulfide formation rates, which, in turn, can affect metal chemistry including internal iron loading. To determine if these improvements corresponded with sulfide and iron-related signals in sediments over time, acid-volatile sulfide (AVS) and acid-extractable iron accumulation rates were measured in sediment cores of two lakes with anaerobic hypolimnia, the formerly eutrophic, now mesotrophic central basin of Lake Erie, one of the Laurentian Great Lakes, and a small meso-eutrophic moraine lake in southern Ontario, Lake St. George. AVS accumulation rates declined gradually in both lakes after 1980 by 95% and 57%, respectively. Acid-extractable iron accumulation rate profiles were similar to AVS in both lakes, but acid-extractable iron rates were several orders of magnitude larger than AVS rates, hence most of the iron was not chemically associated with AVS. In contrast to the gradual declines in AVS, total P loading to Lake Erie did not decline much after 1980, total P concentrations in Lake St. George remained relatively constant between 1980 and 2014, and sulfate concentration decreases were too small in both lakes to account for the large AVS declines after 1980. Hence, productivity and sulfur emission signals appear to have been overridden by diagenetic processes, which produced similar profiles. Therefore, AVS and acid-extractable iron do not appear to be useful as paleo-indicators of trophic status and sulfate deposition.
      PubDate: 2022-08-01
      DOI: 10.1007/s10933-022-00240-1
       
  • Environmental changes during the past ~ 400 years in alpine Lake
           Son-Kul, central Tien Shan, Kyrgyzstan: evidence from sedimentary lipid
           biomarker records

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      Abstract: Abstract Environmental and ecological changes recorded in lake sediments can provide valuable information about natural versus anthropogenic effects on the environment, especially in alpine lakes, which are commonly regarded as sensitive indicators of both local and global environmental changes. To reconstruct the past ~ 400 years of environmental history of alpine Lake Son-Kul, central Tienshan, Kyrgyzstan, we measured lipid biomarkers (n-alkanes [n-ALKs] and n-alkanoic acids [n-FAs]) and other geochemical variables (total organic carbon [TOC] and total nitrogen [TN]) in a 210Pb- and 137Cs-dated sediment core. Stratigraphic shifts in lipid biomarkers, TOC and TN indicate three principal environmental stages in the lake over the past four centuries. Stage I (~ 1600–1900 AD) was characterized by relatively lower and stable terrestrial organic matter (OM) and limited aquatic primary productivity. A period of shallow-water conditions was revealed by increased abundances in long-chain n-FAs ca. 1775 AD. Stage II (~ 1900–1960 AD) was characterized by increased allochthonous OM inputs, indicating marked development of terrestrial vegetation caused by elevated temperatures. In stage III (~ 1960–2011 AD), allochthonous OM inputs and aquatic primary productivity in the lake increased significantly compared to previous stages. Warm and dry conditions may be responsible for the rapid increase in allochthonous OM inputs and changes in herbaceous plant communities during the interval ~ 1960–1983 AD. A pesticide spill in 1976 caused a reduction in aquatic macrophytes, as recorded by biomarker indexes, e.g. Paq, LPTP. In addition, greater human-mediated nutrient loading was responsible for increasing phytoplankton productivity, especially in recent decades.
      PubDate: 2022-07-21
      DOI: 10.1007/s10933-022-00246-9
       
  • Records of environmental and ecological changes related to excavation in
           varve sediment from Lake Hiruga in central Japan

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      Abstract: Abstract Sub-annual-scale environmental and ecosystem changes since the mid-18th century were reconstructed in a semi-closed lagoon, Lake Hiruga, located along the Sea of Japan in central Japan. Lake Hiruga is one of the Mikata Five Lakes and is connected to Lake Suigetsu through an artificial tunnel, the Saga Tunnel. Analyses of siliceous phytoplankton (diatoms, silicoflagellates, and chrysophyte cysts) and elemental composition (carbon, nitrogen, sulfur) of laminated sediments were conducted to determine the impacts of irregular hazards and anthropogenic tunnel construction on the lagoon ecosystem. In this lagoon, sediment laminae were deposited after the first Saga Tunnel re-excavation in 1844–1848, and the dominant phytoplankton taxa have changed with each re-excavation. The behaviors of total nitrogen, total organic carbon, freshwater diatom taxa, and chrysophyte cysts in Lake Hiruga are strongly affected by tunnel excavation and water gate construction. In addition to anthropogenic effects, the deposits show extreme hazard impacts of the Lake Hiruga ecosystem. The peaks of marine diatom taxa, silicoflagellate abundance, and sulfur content of Lake Hiruga showed close relationships with the local earthquake event. A relatively high sea level in the coast of Sea of Japan by local subsidence induced active seawater exchange with Lake Hiruga around AD 1928–1930. Furthermore, the peaks of freshwater diatom taxa and chrysophyte cyst showed a freshening event of this lake caused by local extreme events, such as continuous flooding around AD 1900.
      PubDate: 2022-07-21
      DOI: 10.1007/s10933-022-00251-y
       
  • Middle to Late Holocene climate, vegetation and sea-level changes in NW
           Tripura, northeast India, based on palynological and mineral magnetic
           evidence

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      Abstract: Abstract The sediment deposits of northwestern Tripura, northeast India, revealed the enhanced proximity to the marginal marine environments, forest cover variations and anthropogenic influences. We infer the palaeo-vegetation and palaeo-environmental conditions between 9900 and 1800 cal B.P. through a 1.80 m deep sediment profile, from the remote location of Charilam, Tripura, using biotic (fossil pollen) and abiotic (mineral magnetism) proxies. The sediment profile recorded warm and humid conditions between 8300 and 6200 cal B.P., which later shifted towards less humid phase until 4900 cal B.P. The lower part of the sediment profile provided evidence of enhanced sea-level in this region, as manifested by mangrove taxa found between 9900 and 4900 cal B.P. But later, these taxa were minimal and thereafter, diminished in the sediments during the Late Holocene (4100–1800 cal B.P.).The occurrence of fewer tree taxa and dominance of larger grass pollen signify the enhancement of anthropogenic activities in the region, during the recent times. The shifts in mineral magnetic content towards fine-grained anti-ferrimagnetic hematite components, as exhibited by relatively high Hard IRM, SIRM/ΧLF, ARM/SIRM ratio and low S–ratio towards the end of the Middle Holocene, resonate with the climate variations concurrent to the vegetation changes. These interpretations lead to the perception of a reduction in the Indian Summer Monsoon (ISM) strength during the Late Middle Holocene. The inception of anthropogenic activities has also induced the changes in the vegetation cover, leading to increased soil erosion and land-use changes during the Late Holocene in the region, which are well observed in the pollen and mineral magnetic records. This study focuses on multi-proxy analyses of the Holocene sediments in this part of northeast India, which has no such previous records.
      PubDate: 2022-07-20
      DOI: 10.1007/s10933-022-00249-6
       
  • Planktonic diatom communities in temperate South-Central Chilean lakes
           with a focus on Asterionella formosa and the genus Aulacoseira

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      Abstract: Abstract Paleolimnological records from temperate South-Central Chilean lakes revealed a recent and marked increase in the relative abundances of the key-planktonic diatom species Asterionella formosa and Aulacoseira distans. To better understand these changes, we studied the ecological niches of planktonic diatoms in 42 temperate Chilean lakes (36–43°S). We used morphological analysis of spring and early summer diatom communities, as well as sub-fossil sedimentary assemblages along gradients in mixing regime, light climate, and water chemistry. For Asterionella formosa and the species belonging to the genus Aulacoseira, morphology based enumerations were combined with molecular phylogenies using the 18S rDNA and rbcL genes to determine their taxonomic position and explore potential hidden diversity. Analysis of extant and sub-fossil communities revealed similar patterns, with small Discostella species (D. mascarenica and D. pseudostelligera) and Urosolenia eriensis being characteristic for large, well-mixed lakes, whereas Aulacoseira pusilla (previously erroneously identified as A. distans in Chile) is more dominant in smaller, warmer, and stratified water bodies. This suggests that recent increases in the latter taxon might be related to changes in the physical lake properties in the region, rather than a recent increase in nutrient concentrations. By contrast, Asterionella formosa occurred in lakes with a high Si concentration. Phylogenetic data of the most common species belonging to the genera Aulacoseira and Asterionella showed little evidence for hidden diversity in most of the taxa, except for the Aulacoseira granulata complex. This indicates that the Chilean strains are closely related to populations in the Northern Hemisphere. The results of this study will allow for more accurate diatom-based reconstructions of limnological changes in South-Central Chilean lakes. This is crucial to better understand climate dynamics in the region, as these lakes are known to be sensitive to alterations in windiness and precipitation in response to changes in the intensity and latitudinal position of the Southern Hemisphere Westerlies and the El Niño-Southern Oscillation.
      PubDate: 2022-07-19
      DOI: 10.1007/s10933-022-00247-8
       
  • Late Holocene climate change inferred from the lithology and chemical
           stratigraphy of sediment cores from Swan Lake, Nebraska Sandhills, USA

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      Abstract: Abstract Continuous sediment cores H1 (11.0 m long) and H2 (8.5 m long), collected from Swan Lake, in the Nebraska Sandhills (USA), contain a sandy silt interval between overlying lake gyttja and underlying marsh peat. The marsh peat is a 3-m-thick layer in core H1 and a 1.5-m-thick layer in core H2, with basal ages of ca. 4790 and 4710 cal yr BP, respectively. Peat samples contain up to ~ 61% organic matter (OM) and lack CaCO3 and opal phases. Gyttja extends from 7.6 to 0 m in core H1 and from 6.6 to 0 m in core H2, with estimated basal ages of 3480 and 3530 cal yr BP, respectively. Gyttja samples contained stratigraphically fluctuating relative amounts of OM, precipitated CaCO3, biogenic (ostracod) CaCO3, and diagenetic mineralogical aggregates with CaCO3-opal-A-opal-CT-quartz or opal-A-quartz. OM content in the gyttja ranged from 15.1 to 32.1% and bulk CaCO3 content ranged from 13.5 to 34.6%. Mineralogical aggregates appeared after ~ 2630 cal yr BP in core H1 and after ~ 2590 cal yr BP in core H2, whereas ostracods were found only after ~ 1250 and ~ 1840 cal yr BP in the two cores, respectively. The discrepancy in the timing of ostracod occurrence may be related to environmental differences at the two locations, which are ~ 100 m apart. The sandy silt interval (0.4 m thick) between the peat and overlying gyttja accumulated between ~ 3700 and 3500 cal yr BP. It has relatively low OM (10.3–15.1%) and calcite content (0–6.1%) and no ostracods or mineralogical aggregates. The sandy silt interval possessed a high clastic content (~ 88%), with up to 3.2% Fe, 0.25% Ti, 108 ppm Rb, 105 ppm Zr, 65.5 ppm Cr, 36.6 ppm La, 10 ppm Th, and 2.6 ppm U. The clastic particles and associated metals were deposited by eolian processes during a dry and windy climate episode at the onset of the late Holocene in the Sandhills region.
      PubDate: 2022-07-11
      DOI: 10.1007/s10933-022-00250-z
       
 
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