PNNL-13501 - Pacific Northwest National Laboratory

Totoal Organic Carbon (%)
30
25
20
15
10
5
y = 6.431LOG(x) - 1.028
r = 0.566
0
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320
A 3-year-old eelgrass meadow established initially in
low-organic-content sand in a large (9.5-m diameter) tank
at the Marine Sciences Laboratory in Sequim,
Washington, showed total organic carbon levels 74%
greater than a sand-only control. The sand in the eelgrass
tank was within the range of total organic carbon (mean
=1.04%) found in natural meadows.
Spectral Measurements
Approximate Marsh Age (yrs)
Figure 3. Total organic carbon versus marsh age
An Analytical Spectral Devices FieldSpec®
spectroradiometer was used to measure spectral
reflectance of plants in the mesocosm treatments between
350 and 2500 nm. The reflectance signatures of various
treatments, as well as clipped live biomass and dead,
senescent material were collected.
We applied several indices routinely used to measure crop
stress and photosynthetic function, including normalized
difference vegetation index) (Rouse et al. 1973), the rededge
vegetation stress index (Merton 1998), and the
photosynthetic reflectance index (Gamon and Serrano
1997). The most promising index for future work appears
to be the photosynthetic reflectance index which has been
explored as an indicator of photosynthetic radiation use
efficiency. Gamon and Serrano (1997) tested the index
across functional types (annual, deciduous perennial, and
evergreen perennial) and found a significant correlation
between photosynthetic reflectance index and net CO2
uptake and radiation use efficiency measured by gas
exchange, as well as by a fluorescence-based index of
photosystem II photochemical efficiency.
Our data are representative in some cases of waterstressed
plants. Our relatively high photosynthetic
reflectance index values are also indicative of plants in a
shaded environment, rather than representative of full sun
environment.
Automated Gas Flux Mesocosm
The mesocosm test chamber was constructed in the
Marine Sciences Laboratory greenhouse (Figure 4). The
apparatus consisted of a Plexiglas tank divided into four
0.25-m 3 chambers. Each chamber was provided a 2-inch
diameter opening at the top of the chamber, a 0.3-inch
drain hole in the floor of the chamber, and a 0.25-inch gas
flow line out of each chamber 6 inches above the bottom
(floor).
Figure 4. Prototype automated gas flux chamber
The test chamber is connected by four gas lines to a CO2
analysis system. The configuration of the system is as
follows:
• The configuration of the pumping consists of a
vacuum pump to draw the sample through the
system. The flow rate is regulated by four needle
valves. The volume of gas through the system is
measured by four Cole Palmer flow meters. The gas
flow from the chambers is directed to the test
equipment via four three-position solenoid valves.
• The solenoid valves are controlled by a
programmable micro controller that is programmed
to sample each chamber for 2 minutes every 1 hour.
The duration and delay between samples is programselectable.
The microcontroller is also programmed
to activate a Fluke data logger after each chamber is
Earth System Science 205