Diatom-rich sediment formation in lakes

• Main Author: Zahajská, Petra
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Lund University (Media-Tryck) 2021
• Subjects: Earth and Related Environmental Sciences; Silicon; silica; diatom; biogenic silica; lake; sediment; stable Si isotopes; Ge/Si; Yellowstone; Northern Sweden; Subarctic
• Online Access: https://lup.lub.lu.se/record/e2ddb1c9-4e9c-4a51-a213-dad05d1b1446; https://portal.research.lu.se/files/90572608/Petra_Zahajska_complete.pdf

Unicellular photosynthetic golden algae called diatoms are one of the most abundant silicifying organisms. Diatoms take up silicon and build their frustules, in the form of biogenic silica (BSi), which have high preservation potential, and thus are found in sediments. Around 27 % of the annual dissolved silicon (DSi) delivery from the land to the ocean is retained in lakes and reservoirs in the form of BSi. Therefore, diatom production in lakes creates silicon sinks and influences the Si cycle. However, the processes driving and regulating lacustrine diatom-rich sedimentation are poorly constrained.This dissertation investigates two lakes in very different settings to evaluate the major factors governing diatomrichsediment accumulation. The first study site is a small subarctic, high-latitude lake, Lake 850 in Northern Sweden, and the other study site is in the hydrothermally active and DSi-rich Yellowstone Lake in Yellowstone National Park, Wyoming, U.S.A.The study of the recent Si cycle in Lake 850 revealed the importance of groundwater input to the lake’s Si budget. Groundwaterbrings 3 times more DSi compared to the stream inlet and thus is the main source of DSi for diatom production. Low sedimentation rates in the last 150 years are responsible for BSi accumulation as high as 20 dry weight%. The Holocene sedimentary record shows that the lake had low detrital input throughout the last 7400 years, likely due to low-reliefgeomorphology and a stable environment in the lake’s watershed. The stable Si isotopes of fossil diatoms suggest a stable DSi supply for the lake, where only the relative proportion of stream influx and groundwater influx of DSi are driving isotopic changes. The BSi accumulation in the sediment of Lake 850, as high as 46 dry weight% throughout the Holocene, is driven by a combination of sufficient DSi supply from groundwater and the stream inlet, low detrital input and good preservation of diatoms in the sediment.In Yellowstone Lake the importance of hydrothermal vents bringing DSi into the ...