Bathymetry and Limnological Conditions
0
N a vicu la
100
Cyclotella
Depth (cm)
DIATOM RECORD OF HOLOCENE LAKE
LEVEL AND MOISTURE VARIABILITY IN
THE NORTHERN RUBY MOUNTAINS,
NEVADA
Starratt, Scott W., U.S. Geological Survey,
345 Middlefield Road, Menlo Park, CA 94025
0
0
1
1
S e lla p h o ra
poor preservation
200
300
poor preservation
400
4 65
7
2
2
3
3
4
4
5
5
6
6
7
7
8
18
500
3. Castle Lake
4. Lamoille Lake
5. Upper Dollar Lake
6. Lower Dollar Lake
7. Angel Lake
60
80 100
0
5
10
15
20
25
0
2
4
6
8
10 12
0
0 .2 0 .4 0 .6 0 .8
1
Chrysophyte Stomatocyst/
Diatom Ratio
The diatom flora in Favre Lake contains both planktonic and benthic diatoms. The Fragilaria
complex (containing representatives of the genera Fragilaria, Neofragilaria, Pseudostaurosira,
Staurosira, and Staurosirella) is the dominant component of the flora through most of the high
abundance of this group indicates that nutrient levels were relatively high (at least mesotrophic).
This change in abundance may be related to the greater area of shallow shelf available for
colonization as lake levels rose. The flora at the bottom of the core is more diverse and more
equitably distributed suggesting lower nutrient levels. The lower abundance of planktonic taxa
such as Cyclotella, suggests that the lake is too shallow to support large populations of this
group. Intervals of increased chrysophyte stomatocyst abundance relative to diatoms appear
to indicate intervals of poor preservation.
9
8 .6
8 .2
pH
7 .8
Denotes lower lake levels during the middle Holocene
20
The basins in this study are in Cambrian and Ordovician calcitic marble and Mesozoic granitic
and minor metamorphic rocks which is a factor in the pH and alkalinity of the lakes. Both lakes
are continuous cold polymictic lakes, with significant stratification in late summer. Temperature
profiles to a depth of almost 8 m include the epilimnion and the upper part of the metalimnion.
The warmer surface water and shallower epilimnion-metalimnion boundary (~3 m) in Favre Lake
may be due the more extensive shallow shelf surrounding most of the lake. The shift in pH in
Favre Lake is indicative of a higher (mesotrophic) nutrient level than Liberty Lake (oligotrophic).
This is supported by the diatom floras present in the lakes. The higher pH in Favre Lake may
also be due to productivity on the shelf. The lower pH below 4 m may be due to the concentration
of organic acids in the deeper water which diminish the concentration of HCO3-.
SHALLOW (<2m deep)
INTERMEDIATE (10-20 m deep)
Castle Lake
Lamoille Lake 6-VIII-08
Lamoille Lake 2-X-07
Upper Dollar
Liberty Lake shore
Angel Lake
Lower Dollar
nit-tot
pin-tot
nav-tot enc-tot
cym-tot
lut-spp pin-bor
stu-tot epi-tot
gom-tot lut-mut
ast-for
ach-tot
tab-flo
han-amp
sel-tot pse-tot
amp-tot
dip-tot
fra-tot
Favre Lake
str-tot
0
DEEP (>20 m deep)
LL2 Liberty Lake
LL5 Liberty Lake
LL4 Liberty Lake
LL6 Liberty Lake
cyc-tot
LL1 Liberty Lake
LL3 Liberty Lake
-20
-60
Achnanthes
1. Favre Lake
2. Liberty Lake
40
Favre
Lake
2
1
3
Location map showing the Ruby Mountains.
Inset shows study sites:
20
C ym b ella
D ip lo n e is
Percent of Total Assemblage
8
16
14
12
10
Te m p e r a t u r e ( o C)
0
PC2
Study Sites
D e pt h ( m)
Fragilaria
The north-central Great Basin is affected by bimodal precipitation sources, dominated by winter
(November-February) precipitation from the eastern Pacific Ocean augmented by late spring (MayJune) convectional precipitation. Reconstruction of past moisture variability has proven difficult due
to the limited paleoclimate records and the effect of lake (depth, bathymetric profile) and local watershed (elevation, aspect, bedrock geology) characteristics.
Surface sediment was collected from tarns in the northern Ruby Mountains (Lamoille Lake, 2976
masl, 5.5 ha; Upper Dollar Lake, 2942 masl, ~1 ha, 2 m deep; Lower Dollar Lake, 2937 masl, ~1 ha,
2 m deep; Liberty Lake, 3064masl, 8.5 ha, 33 m deep; Castle Lake, 2980 masl, 5.7 ha, 4.6 m deep;
Favre Lake, 2902 masl, 7.7 ha, 12.0 m deep), and East Humboldt Range (Angel Lake, 2553 masl,
5.2 ha, 9 m deep). The bedrock underlying all the watersheds is early Paleozoic marble and Mesozoic granite and metamorphic rocks. A series of cores were collected in Favre Lake using a modified
Livingstone piston corer. The presence of the Mazama ash in the basal sediment (~4 m below the
sediment/water interface) indicates the record extends to ~7700 cal yr B.P. Between about 7700 and
6000 cal yr B.P. the diatom flora is dominated by a diverse assemblage of benthic species. The remainder of the core is dominated by Fragilaria, suggesting that lake level rose and flooded the shelf
that surrounds the depocenter of the lake. The upper part of the Favre Lake record contains an increase in the abundance of Cyclotella, suggesting an increase in the amount of water entering the
lake from Liberty Lake, where Cyclotella is a significant part of the flora.
Liberty
Lake
Amphora
A. formosa
Cyclotella
Cymbella
Encyonema
Fragilaria
-40
-20
0
PC1
Principal Component Analysis of Generic Abundance
Gomphonema
Navicula
Nitzschia
Pinnularia
Pseudostaurosira
Staurosira
Staurosirella
ach-tot amp-tot ast-for cyc-tot cym-tot enc-tot fra-tot gom-tot nav-tot nit-tot pin-tot pse-tot stu-tot str-tot
Upper Dollar
7.8
0.4
0.0
0.4
6.2
2.4
4.2
1.6
6.4
5.2
17.8
2.4
15.0
8.6
Lower Dollar
4.0
0.4
0.0
0.0
1.8
1.6
2.8
2.4
4.6
4.0
3.4
3.6
52.0
13.2
Lamoille Lake 2-X-0
20.2
1.6
0.0
0.0
0.2
4.8
7.6
0.4
13.0
12.8
0.4
13.6
13.0
7.0
Lamoille Lake 6-VIII12.0
0.8
0.0
1.2
3.8
4.6
5.0
3.0
19.0
9.0
8.0
12.8
2.0
1.0
Castle Lake
6.4
0.6
0.0
0.0
4.6
10.6
1.8
1.8
8.6
15.0
3.6
0.2
28.6
9.0
Liberty Lake shore
5.2
0.0
0.0
14.8
7.2
10.8
5.8
0.6
9.0
24.4
2.4
5.2
3.0
1.0
Liberty Lake LL1
3.4
1.6
0.2
15.0
0.2
0.8
8.0
0.2
2.2
0.8
0.2
2.2
23.6
34.8
Liberty Lake LL2
5.6
2.8
0.0
7.8
0.2
0.2
9.0
0.0
4.8
0.6
0.2
17.4
15.4
26.2
Liberty Lake LL3
3.0
1.2
0.0
17.0
0.0
0.8
11.2
0.0
2.6
0.6
0.4
7.8
20.4
28.6
9.0
24.6
Liberty Lake LL4
11.0
5.8
0.8
17.0
1.0
1.0
6.4
1.6
5.8
2.4
0.0
3.4
Liberty Lake LL5
19.2
3.2
0.0
11.6
0.6
4.0
4.6
0.2
5.8
0.4
0.0
3.2
10.6
25.0
Liberty Lake LL6
15.2
4.0
1.0
15.8
0.2
1.4
10.0
0.2
9.8
0.8
0.2
5.2
7.4
18.2
Favre Lake
1.2
1.2
1.0
4.6
3.4
2.8
11.0
0.0
0.8
0.0
0.2
4.2
15.0
40.2
Angel Lake
20.6
5.8
7.2
0.0
2.6
4.0
17.6
0.2
6.8
11.0
0.0
0.8
16.2
2.8
Diatom images from Diatoms of the United States (http://westerndiatoms.colorado.edu)
Diatom Percent Abundance of Total Assemblage Tabulated by Genera (Except Asterionella formosa). Five most Abundant Genera highlighted.
20