Example of Applying Hydric Soil
Technical Standard (HSTS)

This lecture reinforces the
concepts explained in the
previous lecture.
Introduction
This lecture provides an example of the application of the Hydric Soil
Technical Standard (HSTS) used to make hydric soil determinations
based on Data. Two types of data are analyzed for Anaerobic
Conditions and if one of these two data set pass the HSTS, the soil is
considered to have been proven to meet the Anaerobic Conditions
part of the HSTS. One type of data is analyzed for Saturated
Conditions and if it passes the HSTS, the soil is considered to have
been proven to meet the Saturated Conditions part of HSTS. Both the
Anaerobic Conditions part of the HSTS and the Saturated Conditions
part of HSTS must be met for the soil to be considered hydric. In situ
pH and precipitation data are also needed to apply the HSTS.
“Normal” precipitation is explained again.
Proposal to NTCHS
An individual has requested that the NTCHS
revise Indicator S6, Stripped Matrix, (Hurt, et
al. 2002) from “A layer starting within 15 cm
…” to “A layer starting within 20 cm …” The
rest of the indicator requirements remain the
same.
Data were collected to determine validity of
proposed revision.
Soil Profile Description
0-5 cm 60% 10YR 5/2 and
40% 10YR 2/1 sand
5-12 cm 75% 10YR 2/1 and
25% 10YR 5/2 sand
12-17 cm 60% 10YR 5/2 and
40% 10YR 2/1 sand
17-35 cm 60% 10YR 5/2,
20% 10YR 7/1, and 20%
10YR 6/2 sand (Indicator S6,
Stripped Matrix)
Site that was instrumented.
On-site Features
• Precipitation data
were collected
• Dry-wet-dry
cycle for this area is
October to April
“Normal” Precipitation
For the purposes of applying the HSTS the definition of
“Normal” precipitation is the average monthly
precipitation (50%) + 20%. This would be the 30-70%
probability of occurrence. Another way to express this
range is that during any given 10 years of precipitation
data collection on the average for any given month 4 of 10
years would have precipitation within this range for that
month; 3 would have lower and 3 would have higher
precipitation for that or any month.
“Normal” Precipitation
In order to be able to apply data collected (Eh, dye, and
saturation data) to the HSTS on-site precipitation have to
fall within the 30-70% range during the dry-wet-dry cycle
for the area.
Therefore for this site data would be collected for the
months of October through April and if the precipitation
falls within the 30-70% range, then the other data can be
used to see if the HSTS is met.
In the following slide data collected at this site are
presented for the October, 2000 through April 2001 period
and plotted along with the 30 and 70% probability
(NRCS, National Water and Climate Center).
On-site Precipitation Data vs "Normal" Precipitation
200
180
1-12 below represent the months of
January through December respectively
160
Precipitation (mm)
140
120
100
80
60
40
20
0
1
2
3
4
5
Norm Low (30%)
6
2000
7
2001
8
9
10
Norm High (70%)
11
12
Checking Normal Precipitation
From the data shown on the previous slide we see that
precipitation data collected for the period of October,
2000 through April 2001 fall between the 30 and 70 %
probability of occurrence (the height of the green bars for
2000 and the blue bars for 2001 are between the heights
of the red and yellow bars).
On-site precipitation data is compared with the data from
the nearest weather station. These data (30-70%) are
available at
http://www.wcc.nrcs.usda.gov/water/wetlands.html for
thousands of weather stations nationwide.
Dry-Wet-Dry Cycles
Dry-wet-dry cycles are not only a function of
precipitation but also a function of
evapotraspiration and snow melt.
Evapotraspiration is a function of the types
and amounts of plants present, wind velocity,
air temperature, and amount of water in the
soil. Local soil/wetland scientists should be
consulted if necessary.
Anaerobic Conditions and
Saturated Conditions Data
Anaerobic Conditions are verified by Platinum Electrode
Data or Alpha-Alpha-Dipyridyl Data. Saturated
Conditions are verified by Piezometer Data. Data
presented represent the most reduced and saturated
periods. Data presented are for March 1, March 8, and
March 15. Three consecutive weakly reading is the
minimum requirement; two is not enough. If only two
consecutive weakly reading are reported the NTCHS
could interpret the data as representing 8 days (March 1 March 8) and the HSTS requires 14 days of data for
comparison.
5 Platinum electrodes
were installed at 12.5
cm as measured from
the mineral soil surface
(because soils are
sandy and no muck
was present).
For most loamy or
clayey soils the depth
would have been 25
cm.
Platinum Electrode Data
Dates:
Mar 1 Mar 8
Electrode #1 = 201 mv 189 mv
Electrode #2 = 233 mv 177 mv
Electrode #3 = 103 mv 100 mv
Electrode #4 = 252 mv 252 mv
Electrode #5 = 189 mv 160 mv
Soil pH was 6.6 on all dates
Mar 15
201 mv
167 mv
113 mv
252 mv
180 mv
Eh/pH Line (-60) for Determining Aerobic and
Anaerobic Conditions with data points for
March 1 are indicated by the arrows
400
Aerobic Conditions Exist
Eh
300
200
Anaerobic Conditions Exist
100
pH 4
pH 5
pH 6
pH 7
pH 8
Data points for March 8 and March 15
indicated by
400
Eh
300
200
100
400
Eh
300
200
100
pH 4
pH 5
pH 6
pH 7
pH 8
Interpretation of Eh/pH Data
Based on the Eh/pH line of 175 mv for pH 7
adjusted for pH with a slope of negative 60
the critical Eh for pH 6.6 would be 199 mv.
Thus Anaerobic Conditions = Eh of < 199 and
Aerobic Conditions = Eh of > 199.
Mar 1: 2 of 5 were Anaerobic
Mar 8: 4 of 5 were Anaerobic
Mar 15: 3 of 5 were Anaerobic
Electrode Data Analysis
Data are not summarized.
Data from each electrode are presented separately.
Data summarization would have been:
Mar 1
196 mv (Anaerobic)
Mar 8
176 mv (Anaerobic)
Mar 15
183 mv (Anaerobic)
Compare the results of summarization Vs. reporting
data from all electrodes. Platinum electrodes often
fail; note that one electrode recorded a value of near
100 (Electrode 3) for each of the three weekly
readings (the electrode may be faulty). By analyzing
all data, suspect data can better be analyzed.
Alpha-Alpha-Dipyridyl Data
and Data Analysis
Dates
Mar 1
Mar 8
Mar 15
Sample #1 Yes
No
Yes
Sample #2 Yes
Yes
Yes
Sample #3 No
Yes
No
Yes = positive reaction in at least 1/2 of the upper
12.5 cm.
No = no positive reaction in at least 1/2 of the
upper 12.5 cm.
2 piezometers were
installed at 25 cm.
2 piezometers were
installed at 100 cm.
An open well to a
depth of 2 m was also
installed.
Saturation Data and Data Analysis
of the two 25 cm Piezometers
Dates:
Piezometer 1
Piezometer 2
Mar 1 Mar 8 Mar 15
Yes Yes Yes
No Yes Yes
Yes = Water in piezometer
No = No water in piezometer
Summary
No*
Yes
Yes
*Water has to be in both piezometers.
HSTS Data Analysis
Dates:
Mar 1 Mar 8 Mar 15
Anaerobic (Eh) No
Yes Yes
Anaerobic (dye) Yes
Yes Yes
Saturated
No
Yes Yes
Has the soil been proven to be hydric?
Is the proposed revision valid?
Does the NTCHS accept the proposed
change to Indicator S6 (Stripped Matrix)?
HSTS Data Analysis
Has this soil been proven to be hydric? This is a 2 part test.
Has the Anaerobic Conditions part of the HSTS been met?
Remember the Eh and dye data are analyzed for Anaerobic
Conditions and if one of these two types of data collected pass the
HSTS, the soil is considered to have been proven to meet the
HSTS.
This soil meets Anaerobic Conditions for at least 14 consecutive
days based on the dye data. This soil does not meet anaerobic
conditions for at least 14 consecutive days based on the Eh data.
The soil meets the anaerobic conditions part of the HSTS
Has the Saturated Conditions part of the HSTS been met?
The soil is not known to be saturated for at least 14 consecutive
days based on the piezometer data; only 8 days.
This soil fails the Saturated Conditions part of the HSTS.
This soil has not been proven to be hydric.
Is the proposed revision valid? NO
Does the NTCHS accept the proposed change to Indicator S6 (Stripped
Matrix)? NO
Literature Cited
Hurt, G.W., P.M. Whited, and R.F. Pringle ( Eds.). 2002.
Field indicators of hydric soils in the United States
(Version 5.0), USDA, NRCS, Fort Worth, TX.
http://soils.usda.gov/soil_use/hydric/field_ind.pdf
National Technical Committee for Hydric Soils. 2001.
Hydric Soil Technical Standard (Technical Note 11).
http://soils.usda.gov/soil_use/hydric/hstn.htm
NRCS, National Water and Climate Center.
(http://www.wcc.nrcs.usda.gov/water/climate/)