Briana Johnson & Paula J. Noble Department of Geological - PowerPoint PPT Presentation

Briana Johnson & Paula J. Noble Department of Geological Sciences & Engineering University of Nevada, Reno

To use paleolimnological proxies to assess the impact of atmospheric nitrogen deposition, land use changes, and climatic variability on Fallen Leaf Lake over the past ~200 years

 Diatoms are unicellular siliceous golden algae that live in any moist habitat  Diatoms in sediment cores can be used to determine past lake level, water chemistry, & paleoecology  They are sensitive to biological, chemical, & physical changes in water  Eutrophication  pH  Salinity/Alkalinity

Anthropogenic Nitrogen Deposition • Beartooth Mountians (Wolf et al. 2001; 2003) • Colorado Front Range (Saros et al. 2003; 2005)  Increasing A. formosa & Fragilaria crotonensis • Lake Tahoe  Increasing F. crotonensis (Byron & Eloranta, 1984)  Increasing shoreline algae and araphid pennate diatoms (Winder & Hunter, 2008) Asterionella formosa Climate Change & Nitrogen Deposition • Arctic Lakes  Discostella spp. & Cyclotella spp. has replaced small benthic taxa (Hobbs et al., 2010)

• Near ultra-oligotrophic (Reuter et al., 1996) • Moderately impacted by homes and motorized activities • Gravity core from lake center taken in 2010 Modified from Kleppe et al., (2011)

Contour Plot of NO 3 0 m 10 m Metalimnion 20 m 30 m 40 m 50 m 6/01/09 7/27/09 6/26/09 8/28/09 9/25/09 09/02/2011 A. formosa comprises a large component of the phytoplankton and is also found in Gilmore Lake.  Is this related to N-deposition?

 Processed the top 10 cm of the ~40 cm sediment core Bolly FLL10 2E-1G-1 in 0.5 cm increments  Completed 200 valve counts of diatoms for 10 samples in the top 10 cm of the core  Identified diatom species present and any species composition changes  Water quality data collected during run-off

Age Model for Bolly 2E-1G-1 Sediment Core Date A.D. 2050 2000 1950 1900 1850 1800 0 1 2 Base of Interval (cm) 3 4 5 6 7 8 9 10 Analyses run at Harmon Research Center by Dan Engstrom .

Sediment Accumulation Rate of Bolly 2E-1G-1 2010 2000 1990 1980 1955 -Dams for reservoir below Lily Lake 1970 Age of Base of Sample Interval 1960 washed away in storm 1950 1940 1938 -Glen Alpine Creek rerouted by 1930 storm near FLL 1920 1910 1908 -Anita Baldwin built 1 st dam at 1900 FLL outlet 1890 1880 1870 1861 -Nathan Gilmore brought cattle to 1860 FLL 1850 1840 1830 1820 1810 0 0.005 0.01 0.015 0.02 Sediment accumulation (g/cm² yr) Analyses run at Harmon Research Center by Dan Engstrom

 The gravity core shows that A. formosa has been persistent since at least 1812  Aulacoseira subarctica has declined over the past 60 years in favor of F. tenera group Asterionella formosa Aulacoseria subarctica Fragilaria tenera group % of Total Valves % of Total Valves % of Total Valves 0.0% 20.0% 0.0% 20.0% 40.0% 0.0% 20.0% 40.0% 0% 10% 20% 0% 20% 40% 0% 20% 40% 2010-2008 2010-2008 2010-2008 2002-1997 2002-1997 2002-1997 1989-1981 1989-1981 1989-1981 1968-1952 1968-1952 1968-1952 1937-1931 1937-1931 1937-1931 1917-1902 1917-1902 1917-1902 1891-1880 1891-1880 1891-1880 1870-1860 1870-1860 1870-1860 1849-1839 1849-1839 1849-1839 1826-1812 1826-1812 1826-1812

Sample Date NH4-N NO3/NO2-N DP-P Sample Location Depth (m) Sampled (ppb) (ppb) (ppb) Secchi Depth (m) Gilmore Lake 0 8/7/2011 5 1 7 Gilmore Lake 10 8/7/2011 2 1 3 Gilmore Lake 20 8/7/2011 1 1 3 13 m (8/7/2011) & 11.5 m (10/15/2011) Gilmore Lake 30 8/7/2011 1 1 5 Gilmore Lake 40 8/7/2011 1 1 4 Gilmore Lake 50 8/7/2011 1 35 4 3.5 m (10/1/2011) Lily Lake 0 6/27/2011 3 21 3 Upper Angora Lake 0 6/27/2011 2 21 3 Upper Angora Lake 5 6/27/2011 2 22 3 6.5 m (6/27/2011) & 6.25 m (10/1/2011) Upper Angora Lake 8 6/27/2011 9 23 2 Upper Angora Lake 10 6/27/2011 24 24 3 Although FLL has higher NO 3 values during spring run-off, data from Gilmore Lake show NO3 may not be coming from the snowpack.

 The sedimentation rate at FLL has increased since 1950 while F. tenera group has increased in and A. subarctica has decreased  A. formosa is not a newcomer; chronic high abundance (5-10%) since 1812  Abundant in Gilmore Lake water column (10/15/2011)  The data does not support anthropogenic N- deposition as a factor in the recent diatom community composition

Fallen Leaf Lake Sediment & Geochemical Analyses  Sediment Core Bolly 2E-1G-1  Carbon & Nitrogen Concentration & Isotopes  Phosphorous Concentration  Diatom Analysis & Ecologic Interpretation Gilmore Lake (Low Impact)  Sediment core - summer 2012

 What other factors may account for chronic A. formosa in FLL & Gilmore Lake?  Land use changes  Climate  Fish manipulations  Are any of the changes seen in FLL also seen in other similar lakes inside and outside of the Tahoe basin?

 LacCore  Bob Karlin - UNR  Laurel Stratton - UNR  Jason Barnes – UNR  U.S. Fish & Wildlife Service  U.S. Forest Service  Sudeep Chandra - UNR  Kerry Howard - UNR  John Kleppe – UNR  Alan Heyvaert - DRI