Browsing by Subject "paleolimnology"

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    The Holocene History of Lake Kivu (East Africa): New perspectives from new cores
    (2014-07) Votava, Jillian Emilia
    Lake Kivu lies at the heart of East Africa&lsquos rift lakes in a volcanically active region. Hydrothermal seeps impose a complex stratification regime with heated, high-salinity waters entering below 280 m water depth. Previous detailed studies of fossil diatoms and mineralogy of the sediment record suggest this hydrothermal activity began 5,000 years BP. Unfortunately, dating bulk organic matter of these original cores was problematic due to dissolved volcanogenic CO2. This study offers a new chronology and a detailed perspective on the limnologic history of Lake Kivu through investigation of carbonates and bulk organic matter from sediment cores recovered in 2012 and 2013. A Holocene history was compiled by 14C dating of recovered terrestrial macro fossils from a deep, central basin core, and by 210Pb geochronology of recent sediments from a near shore core. Water levels in Lake Kivu rose during the African Humid Period (AHP) pluvial from 12 ka to 5 ka. Authigenic CaCO3 deposition began around 4.2 ka in the deep, main basin with all subsequent carbonate intervals composed of endogenic aragonite. A solute budget reveals that most of the Ca2+ ion is supplied at depth via the hydrothermal seeps and suggests that this sub-lacustrine input was initiated just prior to onset of carbonate deposition. Stable isotopic analyses of δ13Caragonite and δ13COM both indicate slight enrichment beyond the expected kinetic fractionation and above other East African lakes suggesting volcanogenic influence on water column DIC began around 4.2 ka. Some of the alternating intervals of carbonate deposition and cessation in the late-Holocene, and associated δ18Oaragonite enrichment, coincide with records of drought from nearby Lake Edward, such as at the AHP termination, at 2 ka, and during the Little Ice Age. This suggests a climate overprint on the predominantly volcanogenic record of carbonate sedimentation in Lake Kivu.
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    Paleolimnological Investigation Of The St. Louis River Estuary To Inform Area Of Concern Delisting Efforts
    (2016-08) Alexson, Elizabeth
    The St. Louis River Estuary (SLRE) has a long history of human development since Euro-American settlement ~200 years ago. Due to degradation from logging, hydrologic modification, industrial practices, and untreated sewage in the region including two developing cities (Duluth, MN and Superior, WI), the Environmental Protection Agency (EPA) designated the SLRE as an Area of Concern in 1987. Prior to 1987, actions had begun to restore water quality including the enactment of the Clean Water Act in 1972 and startup of the Western Lake Superior Sanitary District (WLSSD) in 1978 to help remove some beneficial use impairments (BUIs). A better understanding of the historical significance of these contributions over the years is necessary to help document both progress and knowledge gaps related to water quality. Therefore, a paleolimnological study of the SLRE was initiated. Various paleolimnological indicators (pigments, diatom communities, and diatom-inferred phosphorus) were analyzed from six cores taken throughout the estuary and western Lake Superior. Reductions in eutrophic diatom taxa such as Cyclotella meneghiniana and Stephanodiscus after 1970 in certain cores suggest a recovery of water quality over the last 40 years. However, in cores taken from estuarine bay environments, persistence of eutrophic taxa such as Cyclostephanos dubius and Stephanodiscus binderanus indicate continuing nutrient loading and increased production. Sedimentary pigments indicate increases in cyanobacteria in some bays over the last two decades. Diatom model-inferred phosphorus and contemporary monitoring data suggest some of the problems associated with excess nutrient discharges have been remediated, but modern conditions (internal phosphorus loading, changing climate) may be contributing to ongoing water quality problems in some locations. The integrated biological, chemical, and physical indicators from the sediments will aid agencies in determining where to target resources and BUI removal efforts.