7STSM report for COST Action: ES1308, ClimMani
By PhD Jesper Riis Christiansen
Title: Using SkyGas to quantify interactive effects of carbon and nitrogen supply on CO2, CH4 and N2O fluxes
Reference: ECOST-STSM-ES1308-200415-058942
STSM dates: from 20-04-2015 to 24-04-2015
Summary
The novel automated system, SkyGas developed at University of York, was set up to measure spatiotemporal
variability of CO2, CH4 and N2O exchange between the soil and atmosphere under paired treatments of glucose
and NH4NO3 addition. Five levels of each element were used and including all possible interactions between
the two it resulted in 25 treatment combinations. Treatments were randomly distributed in each of five blocks
giving a total of 125 flux measurement points. Fluxes were followed over a period of 4 days.
Introduction
The purpose of this STSM was to test a novel greenhouse gas flux measurement method for field studies using
static flow-through chambers. Experimental manipulation studies of biogeochemical fluxes in the field, such as
greenhouse gases, have used the randomized block design. This design often has room for relatively few
replicates due to a labor intensive setup and operation. Furthermore, for every treatment in the experiment,
the possible interactions with other treatments must be included. This puts a restraint on the number of
treatments and replicates that can be studied due to constraints on time and available resources. The
shortcoming of this approach becomes evident considering the complexity of climate change and the
uncertainty of the magnitude and direction of changes in for example soil moisture and how this may affect
greenhouse gas fluxes. Thus, there is a call towards being able to study the response of greenhouse gas fluxes
to multiple levels of one or several treatments.
A viable way forward is automation of the chamber flux measurements. The usefulness of automatic chambers
has long been recognized, but current state-of-the-art systems currently allow a maximum capacity of 16
multiplexed chambers. However, greenhouse gas fluxes are notoriously heterogeneous in space emphasizing
the need for a high spatial coverage of fluxes. Coupled with multiple levels of perhaps several treatments the
requirement is rapid replication of GHG fluxes in many measurement points. SkyGas represents a prototype of
such a system.
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SkyGas
A)
B)
Fig. 1 A) The experimental setup of the SkyGas system at University of York. Each collar was 20 cm in diameter and
inserted 8-10 cm in the ground. B) close up of the SkyGas chamber. A double leveling system ensured that the chamber
was always level when being deployed on top of collars and weights stabilized the chamber in windy conditions and under
movement.
The SkyGas system is a novel automated system to measure exchange of greenhouse between the soil and the
atmosphere in two-dimensions. SkyGas utilizes the “fly-by-wire” technology that is well known from sports
events to remotely control cameras. The SkyGas was in this study programmed to fly to preset measurement
points arranged in a regular grid (Fig. 1A). This requires that the exact XYZ coordinates are known. This was
achieved in this study by manually adjusting the positioning system.
A closed chamber was suspended in four wires connected to motors that control the horizontal and vertical
position (Fig. 1B) by pulling the wires. At measurement the chamber was lowered over a collar and the CO2, CH4
and N2O concentration in the chamber headspace was recorded. The chamber was connected to an Isotopic
N2O analyzer (Los Gatos Research Inc., CA, USA) for N2O concentrations and a DLT-100 Fast Methane Analyzer
(Los Gatos Research Inc., CA, USA) for CH4 and CO2 concentrations. The chamber enclosure was 180 seconds
with 120 seconds of chamber headspace purge in between measurements. Thus, a flux measurement for one
chamber was in total 500 seconds.
The experiment
The STSM was originally intended to investigate interactive effects of nitrogen and soil moisture content.
However, during the STSM several rain events hampered the establishment of a soil moisture gradient. Instead
it was chosen to investigate the effects of different glucose and nitrogen levels instead as both factors are well
known to affect the microbial processes and gas formation/consumption in the soil. We used five levels of each
treatment and all possible interactions. This resulted in 25 distinct treatment combinations.
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Table 1 Application levels of nitrogen and glucose. Nitrogen was added in the form of NH4NO3.
Treatment
Nitrogen
Glucose
#
(kg N ha-1)
(g L-1)
0
N0
0
G0
0
1
N1
30
G1
20
2
N2
60
G2
40
3
N3
90
G3
60
4
N4
120
G4
80
To accommodate an adequate replication of treatments we used a randomized block design with five blocks 15 where treatments were randomly distributed in each respective block. This necessitated installing 125 collars
within the study site (Fig. 1A).
The nitrogen and glucose treatments were added to the collars by aqueous solution. 500 mL solution was
evenly distributed within each collar immediately (1-4 hours) prior to start of the SkyGas system. 500 mL was
found to be the smallest volume of water that would result in an even distribution of the solution within the
collar. Furthermore, we intended to initiate denitrification and 500 mL of solution did increase the soil
moisture content to an optimum range for denitrification to take place.
The blocks were laid out according to the time they were measured by the SkyGas system. Block 1 was
measured first, then 2 and so forth. The resulting experimental layout is shown in the map below (Fig. 2). The
chambers were placed 50 cm apart in both directions. The SkyGas was programmed to measure every other
chamber from south to north starting in the southwestern corner of the experimental plot at chamber 1 then
29, 57, 2, 30, 58 and so forth.
With a total measurement time of 500 seconds for each collar, one cycle of measurements including all 125
collars took 37500 seconds or almost 10.5 hours. The system was started Thursday April 30th at 7 PM and
stopped Monday, May 4th at 12 PM. This resulted in approximately 8.5 cycles of measurements over 4 days,
e.g. the CO2, CH4 and N2O
exchange was on average
measured 8.5 times per
chamber.
Fig. 2 Map of the
experimental layout with
treatments. The five blocks
are represented by collars,
treatments by the bold text
within circles and chamber
number in italics.
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Future work
At the current time the SkyGas flux data has not been processed. The pre-analyses processing is still being
developed by me and Phil Ineson and the sheer amount of data (1 Hz sampling frequency the 9 cycles of
measurements generated over 345000 lines of data for each gas, respectively) requires development of data
management scripts in SAS or R language.
In the near future the initial work with flux calculations will commence and we plan that the experimental work
of this STSM will result in one or two publications as one independent experimental paper and a theoretical
paper concerning alternative experimental designs in climate change experiments where the SkyGas data can
be used as proof-of-concept to test sampling strategy and power analyses.
All in all it was a pleasure to visit Professor Phil Ineson in York. And while my stay was relatively short I learned
a lot about the newest technology in greenhouse gas research and I am confident that my STSM have helped to
generate new, useful data for the scientific community.
May 14, 2015 Frederiksberg, Denmark
Jesper Riis Christiansen
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