HR: 0800h
AN: B51D-0245    [Abstracts]
TI: Latest Pliocene and Quaternary diatom floras of the Lake Tahoe basin, California and Nevada, USA
AU: * Starratt, S W
EM: sstarrat@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AB: Despite an active research program at Lake Tahoe, few attempts have been made to understand the conditions that existed within the watershed prior to European contact. A greater understanding of the Quaternary history of the basin would not only benefit local stakeholders, but would also enhance the knowledge of the entire Truckee River system. Lake Tahoe has been called one of the most oligotrophic lakes in the world. Historically, the lake has contained low levels of phosphorus (5 �g/L) and nitrogen (100 �g/L). As a result, the abundance of phytoplankton and zooplankton is also low. Over the past century anthropogenic inputs have caused parts of the lake to become seasonally mesotrophic. The impact of climate variability on the nutrient load in the lake is poorly known. Detailed analysis of the pre-European contact record is necessary in order to unravel the complex interaction between natural and human inputs to the watershed. Dredge samples collected from slump blocks and surface sediments in the deep basin and surface samples collected at a number of sites around the margin of Lake Tahoe have been analyzed for diatoms and chrysophyte stomatocysts. The deep lake basin diatom flora is dominated by planktonic, oligotrophic, alkaliphilic taxa such as Cyclotella bodanica and C. ocellata. Planktonic and obligate planktonic taxa ( Aulacoseira distans, Fragilaria crotonensis, Stephanodiscus spp.) found close to shore and benthic taxa are representative of oligotrophic to eutrophic conditions ( Frustulia rhomboides, Tetracyclus glans, Achnanthes minutissima, Epithemia spp., Rhopalodia gibba, Meridion circulare). Several samples of diatomaceous sediment collected near Tahoe City, California, on the west side of the lake, contain taxa that are representative of shallow, more eutrophic conditions and at least one of these samples contains late Pliocene taxa ( Tertiarius sp., Pliocaenicus sp.), which suggests that at least locally, the lake at that time was shallower and was subject to a higher influx of nutrients.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1845 Limnology (0458, 4239, 4942)
DE: 4239 Limnology (0458, 1845, 4942)
DE: 4942 Limnology (0458, 1845, 4239)
DE: 4944 Micropaleontology (0459, 3030)
SC: Biogeosciences [B]
MN: Fall Meeting 2005