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Reconstructing recent limnological history often relies on lead-210 dating to accurately ascribe a chronology to a sediment
profile. In Lake Okeechobee, Florida, a large, shallow subtropical lake that may experience severe mixing, multiple dating
methods are required to confirm that conformable sedimentation has been preserved and that the assumptions of the 210Pb method are satisfied. This study uses stratigraphic profiles of heavy metals, 137Cs, PCBs and pollen as independent dating markers to validate the sediment chronology as determined by 210Pb for three cores from the central mud zone of the lake. Unsupported 210Pb and most dating markers show distinct concentration/depth profiles, suggesting that the sediments have not been severely
mixed for at least the last 75 years. Onset and maximum activity of the radioisotope 137Cs in the cores coincides with the 210Pb-dated interval of 1945–1970. This agrees well with the known timing of atmospheric deposition of 137Cs that resulted from above-ground nuclear testing during late 1940s until 1963. Sediment core profiles of atmospherically
deposited metals such as Zn and Pb, which reflect regional increases during industrialization and decreases after regulation
in the 1970s, exhibit expected concentration increases and peaks coinciding within 5–15 years of the predicted 210Pb dates. Uranium, a contaminant in some phosphate fertilizers, shows large concentration increases at core depths dated to
be about 1950 by 210Pb, matching the intensification of agriculture after WWII. PCBs, which are expected to peak in the early 1970s, were measured
in one core, and the observed peak corresponds to a 210Pb date of about 1960. Pollen makers were unable to verify specific events, but increases in disturbance taxa and declines
in native types correspond generally with the expected dates assigned by 210Pb dating. Conformity between the 210Pb defined dates and independent markers of < ±15 years confirm that Lake Okeechobee sediments do preserve a sequential and
reliable stratigraphic history of the lake, useful for reconstructing past limnological conditions. 相似文献
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Shawn P. Schottler Jason Ulrich Patrick Belmont Richard Moore J. Wesley Lauer Daniel R. Engstrom James E. Almendinger 《水文研究》2014,28(4):1951-1961
Rivers in watersheds dominated by agriculture throughout the US are impaired by excess sediment, a significant portion of which comes from non‐field, near‐channel sources. Both land‐use and climate have been implicated in altering river flows and thereby increasing stream‐channel erosion and sediment loading. In the wetland‐rich landscapes of the upper Mississippi basin, 20th century crop conversions have led to an intensification of artificial drainage, which is now a critical component of modern agriculture. At the same time, much of the region has experienced increased annual rainfall. Uncertainty in separating these drivers of streamflow fuels debate between agricultural and environmental interests on responsibility and solutions for excess riverine sediment. To disentangle the effects of climate and land‐use, we compared changes in precipitation, crop conversions, and extent of drained depressional area in 21 Minnesota watersheds over the past 70 years. Watersheds with large land‐use changes had increases in seasonal and annual water yields of >50% since 1940. On average, changes in precipitation and crop evapotranspiration explained less than one‐half of the increase, with the remainder highly correlated with artificial drainage and loss of depressional areas. Rivers with increased flow have experienced channel widening of 10–40% highlighting a source of sediment seldom addressed by agricultural best management practices. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Wilhelm Schottler 《International Journal of Earth Sciences》1931,22(3-4):161-168
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DeWeese Nichole E. Favot Elizabeth J. Branstrator Donn K. Reavie Euan D. Smol John P. Engstrom Daniel R. Rantala Heidi M. Schottler Shawn P. Paterson Andrew M. 《Journal of Paleolimnology》2021,66(4):389-405
Journal of Paleolimnology - The spiny water flea (Bythotrephes cederströmii), a freshwater crustacean considered to be the world’s best-studied invasive zooplankter, was first recorded... 相似文献
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W. Schottler 《International Journal of Earth Sciences》1916,7(1-2):95-96
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