Holocene variability in hydrology, vegetation, fire, and eolian activity in the Nebraska Sand Hills, USA

Abstract

This study combined multiple aquatic and terrestrial proxies, including diatoms, pollen, grain size, and bulk-sediment chemistry to reconstruct the history of three lake sites located in the central Sand Hills of Nebraska, USA. Long-term changes in effective moisture are evident at all sites, with significant changes occurring at ~6000, ~4000, and ~ 2000 cal. yr BP. Both aquatic and terrestrial indicators suggest that effective moisture was low between 10,000 and ~6000 cal. yr BP, and that this time interval was the driest period of the Holocene. The dominance of benthic and tychoplanktic diatom taxa indicates relatively shallow lake-level, high sand influx indicates moderately high eolian activity, and the pollen assemblage suggests xeric grasslands with abundant mud flats. About 6000 cal. yr BP, all three sites experienced an increase in effective moisture. Lake-level rise is indicated by increases in planktic and tychoplanktic diatoms relative to benthic taxa, while greater abundance of grass pollen and charcoal, and decreased eolian flux indicate stabilized dunes with dense vegetation sufficient to fuel local fires. A significant hydrologic shift recorded at all sites occurred at ~4000 cal. yr BP. This event was characterized by substantial lake-level rise, yet decreased grass cover and fire frequency, and increased eolian activity. Water-table rise may have been caused by a combination of factors including: (1) formation of dune-dams that blocked old drainage channels, (2) reduced grass cover and hence reduced evapotranspiration, and (3) changes in the frequency and duration of drought. The most likely cause(s) of the differential response of the terrestrial and aquatic systems at this time is not clear, none-the-less the late Holocene was not nearly as dry as the interval prior to 6000 cal. yr BP. The last ~2000 yr were characterized by several short-term fluctuations in lake level, including an interval of drought between 950 and 750 cal. yr BP, coincident with increased eolian activity during the latter part of the Medieval Climatic Anomaly.

Chronology of dune development in the White River Badlands, northern Great Plains, USA

“…Multiproxy studies (Shuman and Marsicek, 2016) for multilatudinal North America also show rapid changes in hydroclimate from approximately 9.3 to 8.2 ka. Studies of interdunal lakes in the NSH (Schmieder et al, 2013;Schmieder et al, 2011) indicate that 10 ka to 6 ka was the driest Holocene period on the Great Plains. This prolonged dry period was followed by shorter drought periods from 4 ka to 3 ka, at 1.5 ka to 1.2 ka, and at 1.0 ka to 700 a (Schmieder et al, 2013;Schmieder et al, 2011).…”

“…Studies of interdunal lakes in the NSH (Schmieder et al, 2013;Schmieder et al, 2011) indicate that 10 ka to 6 ka was the driest Holocene period on the Great Plains. This prolonged dry period was followed by shorter drought periods from 4 ka to 3 ka, at 1.5 ka to 1.2 ka, and at 1.0 ka to 700 a (Schmieder et al, 2013;Schmieder et al, 2011). Tree ring data (Cook et al, 2010) also show a dry period for the Great Plains lasting from approximately 1.2 ka to 700 a, and another period of drought lasting from approximately 650 to 550 a, followed by generally wetter conditions.…”

“…The LIA is less well defined than the MCA, but Mann et al (2009) state that the coldest period occurred between 1400 and 1700 CE, or approximately 600-300 a. Evidence of the MCA megadroughts and LIA droughts is preserved in tree rings (Cook et al, 2007;Cook et al, 2010;Cook et al, 2004), lake sediments (Fritz et al, 2000;Hobbs et al, 2011;Laird et al, 1996;Schmieder et al, 2013;Schmieder et al, 2011), and incised stream channels (Burkhart et al, 2008) throughout the region. White River Badlands aeolian and loess deposits (shaded), adapted from United States Geological Survey 1:5,000,000 scale surficial deposit map (Soller and Reheis, 2004).…”

Complex disturbance‐driven reactivation of near‐surface sediments in the largest dunefield in North America during the last 200 years

“…Without a direct measure of long-term vegetation cover, existing research in the Central Great Plains and prairie grasslands (e.g. Milchunas et al, 1989;Biondini et al, 1998;Forman et al, 2001;Mangan et al, 2004;Stubbendieck, 2008;Grassini et al, 2010;Mangan et al, 2004;Milchunas et al, 1989;Schmieder et al, 2011Schmieder et al, , 2012Stubbendieck, 2008) has identified levels of historical precipitation, grazing, wildfire and land use changes as key factors that affect levels of vegetation. Records of these parameters are gathered from a range of instrumental and archival datasets providing information on precipitation, land use change, wildfire occurrence and regional drought.…”

Late Holocene Climate Change and the Origin of the “Figurine Complex” In Grand Canyon, Arizona

“…For example, wetter conditions are implied from cave speleothems in New Mexico and Idaho (Polyak and Asmerom 2001;Lundeen et al 2013) as well as charcoal deposits in alluvial fans in New Mexico (Frechette and Meyer 2009). However, lake and other sediment records in Arizona and Nebraska indicate the opposite with drier conditions present by 4000 BP (Waters and Haynes 2001;Miao et al 2007;Schmieder et al 2012). It is likely then, that the increased variability in ENSO events and climatic patterns caused alternating wet and dry conditions to occur more frequently.…”