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Martin C. Rabenhorst

Advances in IRIS Technology for Wetland Soil Assessment

Delaware Wetlands ConferenceJanuary 29, 2020

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Identification and Delineation

• Hydrology

• Vegetation

• Soils

Also Restoration

Restoration Performance Standards(What are the metrics?)

• Hydrological Monitoring– Relatively straightforward– Multiple technologies available

• Vegetation – direct observation– Various indices available

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?

-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)

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.

• 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

Typically 5 replicates per plot

Soil Redox Conditions are Notoriously Variable

Documenting and measurement of coating removal

• The Challenge – Obtaining 2 dimensional information from a 3 dimensional object!

Mylar grids (+/- 3%)

Documenting and measurement of coating removal

• The Challenge – Obtaining 2 dimensional information from a 3 dimensional object!

Mylar grids (+/- 3%)

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

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.

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!

24” (60 cm) 50 cm

0.010” (10 mil; 0.25 mm) Rigid Vinyl Film

3”

IRIS Innovation #1 – Films

Loading films into delivery tubes

Deployment of films

Pilot hole Tube with film inserted into pilot

hole

Tube removed and film

expanded to pilot hole

Top (Plan) View

Film Expands

Example #1

-50

-45

-40

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-30

-25

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-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

30

-50

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-40

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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?

Example #2

-50

-45

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-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

-50

-45

-40

-35

-30

-25

-20

-15

-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?

IRIS Innovation #2 – Mn Coating

-200

0

200

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?

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.

Zone 1 Fe Zone 2 Fe Zone 3 Fe Zone 1 Mn Zone 2 Mn Zone 3 Mn

Example Data

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0

20

40

3/27 4/3 4/10 4/17 4/24

De

pth

(cm

)

Low

Mid

High

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-30

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0

10

0 10 20 30Days

March 27 - April 24

Zone 1

Zone 2

Zone 3

cm

cumulative days

saturated

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

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

Stop by Poster #29

Thank You

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