Advances in IRIS Technology for Wetland Soil Assessment...and J. P. Megonigal, (Eds). Methods in...
Transcript of Advances in IRIS Technology for Wetland Soil Assessment...and J. P. Megonigal, (Eds). Methods in...
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w w w . e n s t . u m d . e d u
Martin C. Rabenhorst
Advances in IRIS Technology for Wetland Soil Assessment
Delaware Wetlands ConferenceJanuary 29, 2020
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?
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Identification and Delineation
• Hydrology
• Vegetation
• Soils
Also Restoration
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Restoration Performance Standards(What are the metrics?)
• Hydrological Monitoring– Relatively straightforward– Multiple technologies available
• Vegetation – direct observation– Various indices available
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Restoration Performance Standards• What do we do for Soils?
– Standards almost non-existent
– When present, often tied to morphological field indicators • Useful in evaluating natural systems
– Because they form slowly, and they persist
• Not appropriate for created or restored mitigation wetlands– Because they form slowly, and they persist
• Is there an alternative?
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-500
-300
-100
100
300
500
700
4 5 6 7 8
Megonigal, J. P. and M. C. Rabenhorst. 2013. Reduction–Oxidation Potential and Oxygen. Pp 71-86. In R. DeLaune, R. Reddy, C. R. Richardson, and J. P. Megonigal, (Eds). Methods in Biogeochemistry of Wetlands. Soil Science Society of America Book Series No. 10, Madison, WI.
Perhaps more realistic
NTCHS-TS
IRIS Technology(Indicator of Reduction In Soil)
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IRIS Technology began as . . . Tubes
• Fe Oxide paint is applied to ½ inch schedule 40 PVC tubing while the tube is on a lathe device to ensure an even distribution of the paint.
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• Pilot hole made for each IRIS
tube
• IRIS Tubes inserted into the soil
• The soil becomes anaerobic
• Microbes oxidizing OM seek
alternate e- acceptors
• Fe oxides on IRIS tubes utilized
as e- acceptors
• As Fe(III) in paint is reduced to
Fe(II), it dissolves
• Zones where Fe paint has been
removed is visible and can be
documented and quantified.
Fe(OH)3 + 3H+ + e- ---> Fe2+ + 3H2O Soluble
+3
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Typically 5 replicates per plot
Soil Redox Conditions are Notoriously Variable
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Documenting and measurement of coating removal
• The Challenge – Obtaining 2 dimensional information from a 3 dimensional object!
Mylar grids (+/- 3%)
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Documenting and measurement of coating removal
• The Challenge – Obtaining 2 dimensional information from a 3 dimensional object!
Mylar grids (+/- 3%)
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Summary of Strengths/Benefits
• Documents soil biogeochemical processes (reduction)
• Relatively easy to use (in contrast to measureing Eh).
– Install for 1 month, extract, measure.
• Integrates conditions over one month (not a snapshot)
• Conceptually simple
• Can view vertical changes within the soil
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Challenges/Issues that have emerged with IRIS Tubes
1) Accurate Data - difficulty in acquiring a 2 dimensional image from a 3 dimensional cylindrical structure;
2) abrasion or scratching of the tubes during transport or upon installation (especially in sandy or dense soil conditions);
3) Issues with storage and expense of shipping and transport due to their size and weight;
4) general environmental/sustainability concerns related to using large quantities of non-reusable plastic tubing.
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IRIS Innovation #1 – Films• Lightweight flexible coated PVC film is deployed
using a polycarbonate tube.
• The films . . . .
– Are flat, can be scanned or photographed for analysis
– Are lightweight and low volume
• The tube . . . .
– facilitates the installation of the film into the soil,
– protects the film during transport and installation,
– is 100% reusable.
• The Innovation
– figuring out how to deploy flexible films!
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24” (60 cm) 50 cm
0.010” (10 mil; 0.25 mm) Rigid Vinyl Film
3”
IRIS Innovation #1 – Films
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Loading films into delivery tubes
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Deployment of films
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Pilot hole Tube with film inserted into pilot
hole
Tube removed and film
expanded to pilot hole
Top (Plan) View
Film Expands
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Example #1
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-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
0 50 100
De
pth
(cm
)
Percent Removed
Individual Films
00004B.jpg 00007B.jpg
00008B.jpg 00011B.jpg
00013B.jpg Mean
Median Threshold
0-30cm Depth
30
15 cm contiguous zone within the upper 30 cm showing maximum removal
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30
-50
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-30
-25
-20
-15
-10
-5
0
0 50 100
Dep
th (c
m)
Percent Removed15 cm Running Averages
Individual Films15 cm Running Averages
00004B.jpg 00007B.jpg
00008B.jpg 00011B.jpg
00013B.jpg Mean
Median Threshold
Depth of Interest
% Removal
15 cm Zone 39.6 15.4 42.1 24.7 23.7
Y Y≥30%
30
Do a majority (3/5) have ≥30% paint removed?
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Example #2
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-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
0 50 100
De
pth
(cm
)
Percent Removed
Individual Films
00017B.jpg 00018B.jpg
00021B.jpg 00022B.jpg
00025B.jpg Mean
Median Threshold
0-30cm Depth
30
15 cm contiguous zone within the upper 30 cm showing maximum removal
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-50
-45
-40
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-30
-25
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-10
-5
0
0 50 100
Dep
th (c
m)
Percent Removed15 cm Running Averages
Individual Films15 cm Running Averages
00017B.jpg 00018B.jpg 00021B.jpg 00022B.jpg 00025B.jpgMean
% Removal
15 cm Zone 35.5 46.0 68.6 38.0 22.0
Y Y Y Y≥30%
30
Do a majority (3/5) have ≥30% paint removed?
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IRIS Innovation #2 – Mn Coating
-200
0
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400
600
800
1000
1200
4 5 6 7 8
Eh
pH
O2-H2O
NO3-N2
birnessite - Mn+2
pyrolucite - Mn+2
NTCHS-TS
Ferrihydrite - Fe+2
Goethite - Fe+2
(OR
P)
Stiles et al 2010.
The Problem
More easily/quickly reducedBetter indicator of important processes?
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3”
Solution Achieved• Two years in the lab
• Lot’s of testing
FeMn
Rabenhorst, M. C. and K. A Persing. 2017. A Synthesized Manganese Oxide for Easily Making Durable Mn-Coated IRIS Tubes. Soil Sci. Soc. Am. J. 81:233–239. doi: 10.2136/sssaj2016.10.0348Rabenhorst, M.C. and J. Post. 2018. Manganese Oxides for Environmental Assessment. Soil Sci. Soc. Am. J. 82:509-518 doi:10.2136/sssaj2017.08.0256.
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Zone 1 Fe Zone 2 Fe Zone 3 Fe Zone 1 Mn Zone 2 Mn Zone 3 Mn
Example Data
-100
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-40
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0
20
40
3/27 4/3 4/10 4/17 4/24
De
pth
(cm
)
Low
Mid
High
-50
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-30
-20
-10
0
10
0 10 20 30Days
March 27 - April 24
Zone 1
Zone 2
Zone 3
cm
cumulative days
saturated
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Ongoing Testing of Mn-Coated IRIS
• Multiple sites
– Multistate project (VA, MD, DE, WV, PA, MA, RI, WY)
– Multiple projects in Maryland
– Projects coordinated with COE (VA, PA)
• Multiple years
• Currently Analyzing and Synthesizing Data
• Hoping to prepare a summary and proposal later this year
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IRIS Technology - Summary• Documents actual wetland soil processes (functional
assessment) A reasonable soil performance standard– Shows wetland soils are doing what they are supposed to do– Microbially reduction of Fe oxides (and now Mn oxides)
• Becoming more commonly used – moved from the periphery into mainstream in hydric soils studies
• The appeal:– Ease of use– Conceptual simplicity– Approval of by the NTCHS (Fe-coated devices) – Some regulatory agencies (MDE; beginning to be recognized by COE)
• New Developments– System for delivering PVC films
• addresses issues/problems with IRIS tubes
– Advent of Mn Oxide coatings • more closely related to some important environmental/ecosystem services
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Stop by Poster #29
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Thank You
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