scholarly journals Diatom ecological response to deposition of the 833-850 CE White River Ash (east lobe) ashfall in a small subarctic Canadian lake

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e6269
Author(s):  
Scott J. Hutchinson ◽  
Paul B. Hamilton ◽  
R. Timothy Patterson ◽  
Jennifer M. Galloway ◽  
Nawaf A. Nasser ◽  
...  
Keyword(s):  
Aquatic Biota ◽  
Ecological Communities ◽  
Tephra Layer ◽  
Diatom Assemblages ◽  
Radiocarbon Dates ◽  
White River ◽  
Ash Fall ◽  
Subarctic Lake ◽  
Lake Waters ◽  
The City

A <5 mm thick volcanic ashfall layer associated with the White River Ash (east lobe [WRAe]) originating from the eruption of Mount Churchill, Alaska (833-850 CE; 1,117–1,100 cal BP) was observed in two freeze cores obtained from Pocket Lake (62.5090°N, −114.3719°W), a small subarctic lake located within the city limits of Yellowknife, Northwest Territories, Canada. Here we analyze changes in diatom assemblages to assess impact of tephra deposition on the aquatic biota of a subarctic lake. In a well-dated core constrained by 8 radiocarbon dates, diatom counts were carried out at 1-mm intervals through an interval spanning  1 cm above and below the tephra layer with each 1 mm sub-sample represented about 2 years of deposition. Non-metric Multidimensional Scaling (NMDS) and Stratigraphically Constrained Incremental Sum of Squares (CONISS) analyses were carried out and three distinct diatom assemblages were identified throughout the interval. The lowermost “Pre-WRAe Assemblage (Pre-WRAeA)” was indicative of slightly acidic and eutrophic lacustrine conditions. Winter deposition of the tephra layer drove a subsequent diatom flora shift to the “WRAe Assemblage (WRAeA)” the following spring. The WRAeA contained elevated abundances of taxa associated with oligotrophic, nutrient depleted and slightly more alkaline lake waters. These changes were only apparent in samples within the WRAe containing interval indicating that they were short lived and only sustained for a single year of deposition. Immediately above the WRAe horizon, a third, “Post-WRAe Assemblage (Post-WRAeA)” was observed. This assemblage was initially similar to that of the Pre-WRAeA but gradually became more distinct upwards, likely due to climatic patterns independent of the WRAe event. These results suggest that lacustrine environments are sensitive to perturbations such as deposition of ash fall, but that ecological communities in subarctic systems can also have high resilience and can recover rapidly. If subsampling of the freeze cores was carried out at a more standard resolution (0.5–1 cm) these subtle diatom ecological responses to perturbation associated with the WRAe depositional event would not have been observed. This research illustrates the importance of high-resolution subsampling when studying the environmental impact of geologically “near instantaneous” events such as episodic deposition of ashfalls.

scholarly journals Presencia de hormonas esteroides en el lago Titicaca y agua potable, Puno (Perú)

2021 ◽  
Vol 23 (4) ◽  
pp. 193-199
Author(s):  
Walter Zamalloa-Cuba ◽  
◽  
Sirleith Siomara Condori Canaza ◽  
Olivia Magaly Luque Vilca ◽  
Valdemar Luiz Tornisielo ◽  
...  
Keyword(s):  
Steroid Hormones ◽  
Aquatic Ecosystems ◽  
Extraction Method ◽  
Solid Phase ◽  
Steroid Hormone ◽  
Aquatic Biota ◽  
Lake Titicaca ◽  
Lake Waters ◽  
The City ◽  
Endocrine Alterations

The presence of steroid hormones in lake waters causes contamination of aquatic ecosystems, which may cause endocrine alterations in the organisms that inhabit them. Moreover, many of these waters are purified and distributed to populations located around the lake. Therefore, these effects could be repeated in humans consuming the water. This study reports the presence of steroid hormone residues in the waters of the inner bay of Lake Titicaca and drinking water in the city of Puno (Peru). The solid phase extraction method was used for sample preparation, and the analyses were developed in an HPLC-DAD system. Results show maximum concentrations of steroid hormones estrone (E1) 1.56, 17 β- estradiol (E2) 2.27, 17 α- ethinylestradiol (EE2) 13. 88 ng L-1 respectively. These concentrations vary at the different monitoring points, and their presence could cause ecotoxicological effects to the endemic aquatic biota that inhabit this part of the lake. At the same time they also could affect the health of the human population that consumes this water

scholarly journals Late-Holocene diatom community response to climate driven chemical changes in a small, subarctic lake, Northwest Territories, Canada

The Holocene ◽  
2021 ◽  
pp. 095968362110032
Author(s):  
Paul B Hamilton ◽  
Scott J Hutchinson ◽  
R Timothy Patterson ◽  
Jennifer M Galloway ◽  
Nawaf A Nasser ◽  
...  
Keyword(s):  
Iron Age ◽  
Biological Diversity ◽  
Regional Climate ◽  
Natural Aging ◽  
Community Response ◽  
Warm Period ◽  
Ice Age ◽  
Diatom Assemblages ◽  
Subarctic Lake ◽  
Over Time

The paleolimnological record of diatoms and climate, spanning the last 2800 years, was investigated in a small subarctic lake (Pocket Lake) that from AD 1948 to 2004 was contaminated by gold smelting waste. An age-depth model was constructed using a combination of 210Pb, 14C, and tephra to determine a 2800 year history of lake ontogeny (natural aging), biological diversity, and regional climate variability. Diatoms form six strong paleoecological assemblages over time in response to changes in local hydrological and sedimentological conditions (including metals). Selected environmental variables explained 28.8% of the variance in the diatom assemblages, with Fe, Ca, and sediment end member distribution being important indicators. The diatom assemblages correlated to the Iron Age Cold Epoch (2800–2300 cal BP), Roman Warm Period (2250–1610 cal BP), Dark Age Cold Period (1500–1050 cal BP), Medieval Climate Anomaly (ca. 1100–800 cal BP), and the Little Ice Age (800–200 cal BP). The disappearance of Staurosira venter highlights the change from the Iron Age Cold Epoch to the Roman Warm Period. After deposition of the White River Ash (833–850 CE; 1117–1100 cal BP), transition to circumneutral conditions was followed in tandem by a transition to planktic influenced communities. Ten discrete peaks of Cu, Pb, and Zn were observed and attributed to soluble mobility from catchment soils through enhanced seepage and spring snowmelt. The prominent metal spikes were aligned with increases in Brachysira neoexilis. Downward mobilization of arsenic and antimony from contaminated surficial sediments highlight the problem of post depositional industrial contamination of paleosediments. Results demonstrate that paleoclimatic changes in the region, modulated by solar radiation, impacted temperature and precipitation in the lake catchment, influencing temporal shifts in diatom ecology. Changes in diatom taxa richness provided valuable information on the relative influence of water quality (planktic taxa) and sediment input (benthic taxa). The diatom assemblage succession also provides evidence that natural aging over time has played a role in the ecological evolution of the lake.

scholarly journals New Perspectives on Migration into the Tlajinga District of Teotihuacan: A Dual-Isotope Approach

2021 ◽  
pp. 1-21
Author(s):  
Gina M. Buckley ◽  
Rebecca Storey ◽  
Fred J. Longstaffe ◽  
David M. Carballo ◽  
Kenneth G. Hirth ◽  
...  
Keyword(s):  
Oxygen Isotopes ◽  
Human Remains ◽  
Past Research ◽  
Urban Center ◽  
Radiocarbon Dates ◽  
Future Studies ◽  
Dual Isotope ◽  
West Mexico ◽  
New Finding ◽  
The City

The city of Teotihuacan (AD 1–550) was a major multiethnic urban center that attracted migrants from as far away as west Mexico and the Maya region. Past research in the Tlajinga district at Teotihuacan using oxygen isotopes from human remains estimated that nearly 30% of the population of Tlajinga 33, a single apartment compound, were migrants. This study takes a dual-isotope approach (87Sr/86Sr and δ18O p ) to reevaluate the proportion of in-migration at Tlajinga and includes data from two additional apartment compounds, Tlajinga 17 and 18 (n = 23). New results indicate that migrants comprised ~45% of the Tlajinga population. Previously acquired radiocarbon dates combined with mortuary and isotope data suggest that immigration to Tlajinga was highest during the first centuries of compound occupation. Nevertheless, migration was a continual process throughout its history. Additionally, a new finding suggests that residents of Tlajinga 33 ingested foods with higher 87Sr/86Sr ratios than did those of Tlajinga 17 and 18. We hypothesize that the incorporation of imported lime for the nixtamalization process skewed the 87Sr/86Sr ratios of human remains, a potentially important finding for future studies at Teotihuacan.

scholarly journals Diachronic modeling of the population within the medieval Greater Angkor Region settlement complex

2021 ◽  
Vol 7 (19) ◽  
pp. eabf8441
Author(s):  
Sarah Klassen ◽  
Alison K. Carter ◽  
Damian H. Evans ◽  
Scott Ortman ◽  
Miriam T. Stark ◽  
...  
Keyword(s):  
Machine Learning ◽  
Demographic History ◽  
Machine Learning Algorithms ◽  
Archaeological Excavation ◽  
13Th Century ◽  
Radiocarbon Dates ◽  
Ancient Civilization ◽  
Demographic Study ◽  
Key Aspects ◽  
The City

Angkor is one of the world’s largest premodern settlement complexes (9th to 15th centuries CE), but to date, no comprehensive demographic study has been completed, and key aspects of its population and demographic history remain unknown. Here, we combine lidar, archaeological excavation data, radiocarbon dates, and machine learning algorithms to create maps that model the development of the city and its population growth through time. We conclude that the Greater Angkor Region was home to approximately 700,000 to 900,000 inhabitants at its apogee in the 13th century CE. This granular, diachronic, paleodemographic model of the Angkor complex can be applied to any ancient civilization.

Pollen diagrams from interior Labrador

1970 ◽  
Vol 48 (11) ◽  
pp. 1957-1975 ◽  
Author(s):  
Alastair Morrison
Keyword(s):  
Primary Succession ◽  
Vegetation Changes ◽  
Bare Ground ◽  
Radiocarbon Dates ◽  
River Watershed ◽  
Pollen Diagrams ◽  
Glacier Ice ◽  
Lake Waters

Six pollen zones can be distinguished in interior Labrador. The earlier zones represent the primary succession of vegetation from bare ground to boreal woodland or forest, which occupied about 500 years between 5700 and 5200 B.P. There have been only minor fluctuations in the nature of the vegetation since 5200 B.P. Radiocarbon dates show that the zones are contemporaneous over that part of the Lake Plateau within the Churchill River watershed, but similar vegetation changes occurred 1000 years earlier in the Kaniapiskau basin, further north, in New Quebec. These two areas must have been freed of a cover of glacier ice or lake waters immediately before 5700 B.P. and 6700 B.P. respectively.

Isotopic and geochemical composition of marl lake waters and implications for radiocarbon dating of marl lake sediments

1983 ◽  
Vol 20 (4) ◽  
pp. 599-615 ◽  
Author(s):  
J. V. Turner ◽  
P. Fritz ◽  
P. F. Karrow ◽  
B. G. Warner
Keyword(s):  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Sediment Cores ◽  
Geochemical Composition ◽  
Radiocarbon Dates ◽  
Southern Ontario ◽  
Suitable Material ◽  
Geochemical Parameters ◽  
Marl Lake ◽  
Lake Waters

Radiocarbon dates on organic and calcareous fractions of sediment cores from marl lakes may yield anomalous ages due to the assumption of a constant hardwater correction factor along the sediment sequence. A study of eight marl lakes in southern Ontario that are actively precipitating calcium carbonate was conducted in order to assess those isotopic and aqueous geochemical parameters in modern lakes that may be utilized to estimate the history and extent of variations in the hardwater effect along such sediment sequences. Results show an increase in the δ13C composition of lake DIC (dissolved inorganic carbon) as approach to isotopic equilibrium with atmospheric CO2 occurs. Differences in the extent to which this equilibrium is established also appear responsible for observed differences in the 14C activity of DIC between lakes of as much as 20 pmc (percent modern carbon). These variations have been related to the relative residence times of water in each lake by examination of their corresponding seasonal variations in 18O and 2H content. Consequently δ13C and δ18O of marl and molluscs have been used to identify variations in the hardwater effect along the sediment profile. A profile of radiocarbon dates on marl from Little Lake in southern Ontario shows satisfactory agreement with an independently determined pollen chronology. Where certain criteria are met, marl deposits appear to be suitable material for establishing Quaternary chronology.

Growth and decay of palsas and peat plateaus in the Macmillan Pass–Tsichu River area, Northwest Territories, Canada

1979 ◽  
Vol 16 (7) ◽  
pp. 1362-1374 ◽  
Author(s):  
G. P. Kershaw ◽  
Don Gill
Keyword(s):  
Northwest Territories ◽  
Volcanic Ash ◽  
Late Winter ◽  
White River ◽  
The Past ◽  
Ash Fall ◽  
Tall Plant ◽  
Reduction Of Area ◽  
Crustose Lichens ◽  
Peat Plateaus

Macmillan Pass, at 1350 m asl (above sea level), is located in the Selwyn Mountains at the Yukon–Northwest Territories border (63 °15′N, 130°02′W). This area lies within the discontinuous but widespread permafrost zone. Palsa–peat plateau complexes cover 0.7% of the 235 km2 study area and are found in bog and fen depressions at elevations from 1285–1690 m. Palsa heights range from 0.15–9.75 m and diameters from 3.25–75.0 m; peat plateaus have maximum heights of 2.5 m and maximum diameters of 225 m. Both features are vegetated by Cladina-Betula glandulosa, Cladina-Polytrichum-Cetraria, and crustose lichens-Polytrichum plant communities.Palsas and peat plateaus are windswept during winter. On surfaces which support recumbent (5–15 cm tall) plant communities there was an average of only 7.5 cm of snow during late winter 1978. Snow cover was thinner by a ratio of 1:4 compared to control areas.These permafrost features have formed since the White River volcanic ash fall of 1220 BP. On palsas and peat plateaus this ash occurs at an average depth of 21 cm and has an average thickness of 11.6 cm.Shrinkage and (or) total decay of palsas and peat plateaus has occurred during the past 34 years. In one palsa field this represents a 34% reduction of area whereas in two others, 100%. The areal extent of some peat plateaus has also been reduced.

Spatial patterns of modern diatom distribution and multiple paleolimnological records from a small arctic lake on Baffin Island, Arctic Canada

1996 ◽  
Vol 74 (3) ◽  
pp. 435-449 ◽  
Author(s):  
Alexander P. Wolfe
Keyword(s):  
Late Holocene ◽  
Baffin Island ◽  
Diatom Assemblages ◽  
Arctic Canada ◽  
Habitat Specificity ◽  
Radiocarbon Dates ◽  
Numerous Species ◽  
Sediment Reworking ◽  
Clear Differentiation ◽  
Lake Ontogeny

The assumption that within-lake, deep-water sedimentary diatom assemblages are relatively uniform and that a single core is sufficient to depict lake ontogeny was tested for a small tarn on the southwestern Cumberland Peninsula of Baffin Island, Northwest Territories. Diatom transport and deposition were evaluated through analyses of periphytic, planktonic, and epipelic habitats. Diatom stratigraphies of four cores were used to test whether or not trends are comparable in different regions of the lake and throughout the Holocene. Among 12 surface-sediment stations, diatom distributions were alternately highly equitable or variable. Valves of evenly distributed genera (Aulacoseira and Achnanthes) are mixed in the water column prior to deposition. This is supported by plankton tow and periphyton samples, which were respectively dominated by Aulacoseira distans (and varieties) and Achnanthes altaica. Conversely, frequencies of several benthic taxa (e.g., Pinnularia biceps, species of Eunotia) varied up to 30% between stations, in patterns unrelated to water depth, and reflecting habitat specificity and minimal transport prior to burial. Of the four cores (38.0–95.5 cm), analysis of the two longest revealed three distinct zones: (i) a zone dominated by species of Fragilaria (> 9000 BP); (ii) a zone containing benthic acidophilic diatoms indicating natural acidification (9000–7000 BP); and (iii) a zone characterized by numerous species of Aulacoseira ranging from the mid to late Holocene. Clear differentiation of the lower two zones was impossible in the shorter cores, and radiocarbon dates suggest that sediment reworking truncated the earliest records of organic sedimentation at these sites. Correspondence analysis facilitated comparisons of the diatom stratigraphies and enabled the evaluation of core reproducibility. Central cores preserve the most useful paleolimnological records in this environment. Keywords: diatoms, paleolimnology, Arctic Canada, Baffin Island.

The Development of a Diatom Database for Inferring Lake Salinity, Western Victoria, Australia: Towards a Quantitative Approach for Reconstructing Past Climates

1997 ◽  
Vol 45 (3) ◽  
pp. 389 ◽  
Author(s):  
Peter A. Gell
Keyword(s):  
Salinity Tolerance ◽  
Salt Lake ◽  
Data Sets ◽  
Diatom Assemblages ◽  
Tolerance Limits ◽  
Data Set ◽  
Lower Salinity ◽  
Western Victoria ◽  
Lake Waters ◽  
Lake Salinity

The development of a modern data set of 156 diatom samples from salt lakes has provided evidence of the tolerance of a large number of taxa to the salinity of lake waters. Thirty taxa have been recorded from 30 or more samples and so have been well characterised. A further 42 taxa have been recorded from 10 or more samples. The lakes sampled range in salinity from the freshwater–oligosaline boundary to well into the hypersaline range, so the upper and lower salinity tolerance limits of many species were investigated. Canonical correspondence analysis of the data set showed that salinity was the most important of the tested parameters influencing the diatom assemblages in the samples. Randomisation tests have provided correlation values between measured and predicted salinity comparable with those gained from other major salt lake diatom data sets, suggesting that this set is a good predictor of lake salinity.

scholarly journals Did the Megafauna Range to 4300 BP in South America?

Radiocarbon ◽  
2001 ◽  
Vol 43 (1) ◽  
pp. 69-75 ◽  
Author(s):  
Alberto L Cione ◽  
Aníbal J Figini ◽  
Eduardo P Tonni
Keyword(s):  
South America ◽  
Buenos Aires ◽  
Bone Sample ◽  
Collagen Content ◽  
Buenos Aires Province ◽  
Radiocarbon Dates ◽  
Fossil Remains ◽  
The Poor ◽  
Bone Preservation ◽  
The City

A date of 4300 ± 90 BP for extinct megafauna in Argentina is discussed. The fossil remains come from the Guerrero Member (area) of the Luján Formation near the city of Luján, Buenos Aires Province. The age of the top of the Guerrero Member is constrained by more than 60 radiocarbon dates obtained from the overlying Río Salado Member of Luján Formation, Las Escobas Formation, and Puesto Callejón Viejo Soil, most of them older than 4300 BP. In view of its low collagen content, the 14C measurement of bone sample from Luján should not be accepted uncritically. Because of the poor bone preservation and the possible introduction of “young” contaminants that were not completely eliminated, the 14C date of 4300 ± 90 BP is not reliable. Both biostratigraphic and 14C dating evidence indicates that the date of 4300 BP for the last representative of extinct megafauna in South America is unsupported.

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