Lake_erie_sensor_AGU_2013_presentation

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AGU 2013
B21A-0443
Eddy covariance measurements of carbon, latent and sensible heat fluxes from western Lake Erie
Changliang Shao1,2, Jiquan Chen1,2, Carol Stepien1,2, Housen Chu1, Thomas Bridgeman1,2, Kevin Czajkowski3, Richard Becker1, Zutao Ouyang1 , Ranjeet John1
1Department of Environmental Sciences; 2Lake Erie Center; 3Department Geography and Planning, University of Toledo, OH, USA
email: [email protected]
2. Research Site
N
(c)
RH (%)
100
80
60
PAR (mol m-2d-1)
VPD (kPa)
40
(d)
2
1
0
(e)
60
40
20
0
40
(f)
4.3. Results: Daily CO2 fluxes
2
0
-2
15
10
5
0
4
2
0
-2
-4
11 12 1
2
3
4
5
6
7
8
10
9 10 11 12 1
2
3
4
6
5
7
8
9 10
Year/Month
2
3
4 5 6
2011-12
7
8
9 10 11 12 1
2
Year/Month
3
4 5 6
2012-13
7
8
 Monthly C revealed that Lake Erie served as a carbon sink
in the summer and as a carbon source in winter, in both
years. The site uptake C was 43.8 and 14.6 g C m-2 in the
first and second summers from May through September.
 Annual variation in LE showed a single-peak curve change,
with the annual cumulative ~1765 and 1580 MJ m-2 (i.e.,
evapotranspiration 720 and 645 mm), compared with
annual rainfall of 810 and 740 mm in the first and second
years, respectively.
 There was no seasonal H pattern, matching the daily trend.
Annual cumulative H was 340 and 380 MJ m-2 in the first
and second years, respectively, which is about one quarter
or less than that of the annual LE.
9 10
4.2. Results: Daily energy fluxes
Lake Erie
200
Jan
150
a) Jul
g)
b) Aug
h)
H
LE
100
50
0
200
Feb
150
100
50
0
3. Daily photos
4.5. Results: Driving forces behind LE
200
c) Sep
Mar
i)
150
20
LE (MJ m-2 d-1)
-2
H & LE (W m )
50
0
200
Apr
j)
d) Oct
150
There was no diurnal variation of CO2 flux, even between day
and night. Mean eddy covariance measurements revealed a
small but measurable downward flux from May through
September, in both years. According to the daily mean (see
Table below), the lake acted as a small carbon sink in the
summer and a carbon source in winter, with the efflux rate
varying from -0.45 to 0.98 g C m-2 d-1.
100
50
0
200
e) Nov
May
k)
150
100
15
(b)
(a)
LE=0.26Rg+1.65
r2=0.22
P<0.0001
100
Yearly mean air temperature (Ta), water vapor pressure
deficit (VPD), and photosynthetically active radiation (PAR)
were 10.69 and 10.79 °C, 0.55 and 0.49 kPa, 27.4 and 25.1
mol m-2 d-1 in the first and second years, respectively. Wind
speed (U) was 5.7 and 6.5 m s-1 , with synoptic weather
events driving U, reaching 15.0 m s-1, and providing
substantial turbulent mixing. Relative humidity (RH) varied
little seasonally, having a mean of 70% in both years. Rainfall
(PPT) showed little monthly variability, ranging from 50 to 70
mm from May-Oct in year one, with August having greater
PPT near 100 mm. In year two, PPT reached a high of 100 in
June and 150 mm in July. Total annual rainfall was 810 and
740 mm for the first and second years, respectively.
(c)
6
20
11 12 1
4.1. Results: Micrometeorology
(b)
20
30
0
http://www.glerl.noaa.gov, the same site.
(a)
-2
-1
C (g C m d )
-20
H (MJ m d )
0
LE (MJ m d )
Ta (oC)
20
4
-1
0
4.4. Results: Monthly C and energy fluxes
-2
U (m s-1)
5
(b)
PPT (mm)
Lakes play an important role in determining local, regional,
and even global climate through biophysical and biogeochemical processes. The Great Lakes contain 20% of the
earth’s surface fresh water and are among the most critical
ecosystems that influence water and carbon budgets in
North America. Yet, no conclusions have been reached as to
the carbon and water budgets of any of the Great Lakes due
to the difficulties of collecting observations over open water.
A permanent eddy-covariance (EC) flux station equipped
wireless instruments in western Lake Erie at the NOAA #2
Light buoy – was installed in October 2011 as part of our
NSF Lake Erie Center Sensor Network and has been in
continual operation. Here we report the first two years of
results for carbon dioxide and latent and sensible heat fluxes
from Lake Erie, a Great Lakes site (41.8314N, 83.2006W,
174 ASL) located >12 km offshore.
10
 In 2012, there were no obvious diurnal patterns in latent
heat flux (LE), showing little day and night variation. From
June to October, values were slightly higher at night than
during the day. Maximum values (of 130-150 W m-2 from
April to July) were observed from the afternoon to early
next morning, whereas the minimum (lowest 0-30 W m-2
from January to March) ones occurred from late afternoon
to the early morning.
 Sensible heat flux (H) was at its minimum in the afternoon
(15:00-17:00) and peaked in the early morning (7:00-9:00)
from July-October. The hourly H of the average diurnal
courses varied from -1 W m-2 (July) to 30 W m-2
(September). The diurnal amplitude of H was largest in
spring and in early fall (29 W m-2 in September) and
smaller in July and August (20 W m-2).
-1
(a)
15
-2
1. Introduction
10
5
LE=1.76(U× VPD)+0.74
2
r =0.44
P<0.0001
0
0
5
10
15
20
Rg (MJ m-2 d-1)
25
0
2
4
6
8
10
U × VPD (m s-1 kPa)
Variation in LE is best explained by changes in global solar
radiation (Rg), and VPD multiplied by wind speed. The latter
contributed more.
5. Conclusions
50
H (W m-2)
C (g C m-2 d-1)
2012(May-Sept) 7.82(2.39)
1.28(0.31)
-0.12(0.32)
2013(May-Sept) 6.43(1.65)
1.45(0.47)
-0.04(0.32)
2012(Oct-Apri)
2.68(1.50)
0.69(0.52)
0.42(0.20)
2013(Oct-Apri)
2.83(1.60)
0.78(0.23)
0.57(0.32)
2011-12
4.82(3.21)
0.93(0.53)
0.19(0.37)
2012-13
4.33(2.41)
1.05(0.47)
0.32(0.44)
Period
0
200
f) Dec
Jun
l)
150
100
50
0
0
4
8
12 16 20
0
4
8
Time (hour)
12 16 20 24
LE (W m-2)
 Lake latent heat showed an obvious seasonal pattern, with
obvious greater energy than the sensible heat values, and
the turbulent energy totaling less than 40% of the global
solar radiation; thus water heat storage contributed one half
or more of the input energy.
 From an annual perspective, the lake acted as a carbon
source of 70.8 and 116.1 g C m-2 yr-1 in the first and second
years, respectively, but as a small carbon sink in the
summer during both years.
Acknowledgements:
This study was partially funded by the FSML program of the NSF (1034791), NOAA, and USDAFS.
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