Biogeochemistry of Inorganic P, Mn, and Fe in Seasonally
Reduced Soils of the Willamette Valley, Oregon
By
Rex King
A THESIS
submitted to
Oregon State University
Bioresource Research Major
and
International Degree
In partial fulfillment of
the requirements for the
degree of
Bachelor of Science in Bioresource Research
and
Bachelor of Arts in International Degree
December 1997
Bachelor of Science in Bioresource Research thesis of
O
keK 0
l2. 1'117
h
presented on
APPROVED:
Mentor
4-13
Secondary advisor
Co-director of the Bioresource Research' Major
I understand that my thesis will become part of the permanent collection of Oregon State
University, Bioresource Research Program. My signature below authorizes the release of
my project to any reader upon request.
J
(student's name), author
Saturated soils undergo reduced conditions as microorganisms consume
oxygen and require other terminal electron accepting processes for the
mineralization of soil organic carbon. Currently, the soil redox potential has not
been considered as important when sampling these soils for Fe, Mn, and P04.
Since Fe- and Mn-oxides are electron sinks for these reactions, the redox
potential should affect their solubility in the soil. Phosphate solubility, should also
be closely related to redox potential. Current methods for sampling Fe(II), Mn(II)
and P04 under reduced conditions are inadequate since they do not protect the
samples from contamination by 02. The presence of 02 results in oxidation and
subsequent precipitation of Fe-phosphate from solution. The co-precipitation of
Fe-phosphate lowers the amount of P04 and Fe(II) in solution leading to the
conclusions that the concentration of these elements is less than exists in the
natural state.
These reduction and oxidation reactions are occurring in close to 200,000
acres of wetland soils in the southern Willamette Valley. On this scale, the
wetlands play an important role in the non-point sources of phosphorus. The
cyclic nature of reduced conditions on riparian soils of the Willamette Valley, and
its effects on the solubility of Fe, Mn, and P04 is investigated in the second part
of this thesis. Fe and P04 concentrations under dry conditions, representative of
the dry summers, were almost nonexistent. Mn was more soluble under reduced
conditions, but still a fair proportion of the total Mn was soluble even under dry
conditions. Mn and P04 each had a relative redox potential in which their
solubility decreased when the soil redox potential passed below their respective
arbitrary value. This suggesting that at lower redox potentials, these ions formed
new insoluble minerals.
3
Table of Contents
Page
ABSTRACT ............................................................
I
TABLE OF CONTENTS ....................................................................................... 3
LIST OF FIGURES ............................................................................................... 4
LIST OF APPENDICES ....................................................................................... 5
INTRODUCTION .................................................................................................. 6
METHODS AND MATERIALS ............................................................................. 8
SOILS MICROCOSM EXPERIMENT ..................................................................................................... 8
FIELD EXPERIMENT ......................................................................................................................... 9
RESULTS ...........................................................................................................11
EVALUATION OF CLOSED-HEADSPACE WELL PERFORMANCE .......................................................... 11
FIELD EXPERIMENT ....................................................................................................................... 17
Redox potentials
Cumulative Soluble Nutrients ........................................................................................................... 21
Soil Protiles
25
Three Dimensional Graphical Representations .............................................................................29
CONCLUSIONS AND DISCUSSION ................................................................. 35
BIBLIOGRAPHY ................................................................................................ 36
List of Figures
Figure
Ewe
1.
Dissolved 02 and redox measurements for microcosms .............................. 12
2.
Lemmon's soil reactor experiment ................................................................ 14
3.
Redox potentials for soil, open and closed head-space wells ...................... 16
4.
Fe(l1), P04, NO3 concentrations and redox potentials for the center transect
at the Lake Creek watershed; Julian day 154 (1997) ............................... 17
5.
Schematic diagram representing the sub-surface stratigraphy of a transect at
the Lake Creek Site ................................................................................. 18
6.
Redox potentials for the Agricultural Site ...................................................... 19
7.
Redox potentials for the Transitional Site ..................................................... 20
8.
Redox potentials for the Riparian Site .......................................................... 21
9.
Cumulative Fe(ll) concentrations for the three sites ..................................... 22
10. Cumulative Mn(II) concentrations for the three sites ................................... 23
11. Cumulative P04 concentrations for the three sites ...................................... 24
12. Concentration profiles for Fe(II) at the three sites for day 487 ..................... 26
13. Concentration profiles for Mn(II) at the three sites for day 487 .................... 27
14. Concentration profiles for P04 at the three sites for day 487 ....................... 28
15. Concentration profiles for Fe(II) for the three sites over one year ............... 30
16. Concentration profiles for Fe(l1) for the three sites over two years .............. 31
17. Concentration profiles for Mn(II) for the three sites over one year ............... 32
18. Concentration profiles for P04 for the three sites over one year .................. 34
List of Appendices
Page
Appendix 1: Soil P04 Concentration Profiles ..................................................... 37
Appendix 2: Soil Fe(II) Concentration Profiles ................................................... 41
Appendix 3: Soil Mn(II) Concentration Profiles .................................................. 45
Appendix 4: International Degree Experience ................................................... 49
Introduction
Wetlands and riparian zones play an important role in the processing of N,
S, trace metals, and degradation of pesticides. In wet soil ecosystems, water fills
soil pores, thus dramatically slowing the transport of 02. When oxygen is
unavailable because of soil saturation, the microorganisms must use other
terminal electron acceptor processes to ensure their survival. The maximum
amount of biogeochemical energy is obtained through aerobic respiration (02)
followed by denitrification (NO3), oxide reduction (Mn(IV) and Fe(III)), sulfate
reduction (SO4), and finally methanogenesis (HCO3) (Patrick, 1992). As Fe(II)
and Mn(IV) oxide minerals dissolve, inorganic P and trace metals may be
released. Thus the reduction process can exert an important influence on the
water quality aspects of riparian zones and wetlands.
Biogeochemically mediated redox reactions play an important role in
controlling the solubility of P04 containing minerals (Ponnamperuma, 1972). One
of the dominant pools of P is in the form of an Fe(lll)-PO4. Inorganic phosphate
is released as the microorganisms reduce the Fe(III) to Fe(II). Inorganic
phosphate may then become soluble in the soil and more easily absorbed by
plants. Under oxidizing conditions (e.g. well-drained soil), P04 forms mineral
solids with Fe(III) and therefore becomes immobile. Based on the discussion
above, it is likely that P04 may be much more soluble in wet soils than currently
believed. There is no quantitative data available on the annual reductive
dissolution of Fe, Mn, and associated P04 at the landscape level (Stumm, 1992).
This thesis addresses the question of the temporal dynamics of Fe, Mn, and P04
of the some poorly-drained soils of the Willamette Valley. These processes have
important implications in the leaching of P04 into streams, degradation of
chlorinated pesticides, and behavior of trace metals.
In this thesis I explored two hypotheses:
1. When sampling shallow reduced soil ground water for soluble Fe(II),
Mn(lI), and P04, the water sample must be protected from oxidation.
Failure to exclude 02 will result in the oxidation of Fe, resulting in the
precipitation of Fe, P and other metals.
Current methods of sampling soils and shallow soil ground waters for
Fe(II), Mn(II), and P04 do not exclude oxygen from entering the system that is to
be sampled. When sampling soils that are under reduced conditions, care must
be taken to prevent oxygen from entering either the sampled soil or the water
samples. If oxygen was allowed to enter, the samples may show lower amounts
of minerals and nutrients than are truly present in the soil.
2. Concentrations of KCI/HCI extractable Fe(II), Mn(ll), and P04 in poorly
drained soils of the Willamette Valley are low during the summer, but
steadily increase as the soil become saturated and peak in the early
spring when the temperatures are warm, and the soil is still saturated.
The Willamette Valley is characterized as a xeric moisture regime. The
soils experience cycles of dry summers and wet winters and springs. This
annual wetting and drying cycle results in interesting soil biogeochemical
conditions. Study of the cyclic nature of biogeochemical reduction in these soils
may lead to an understanding of their role in water and soil quality. This
knowledge may lead us to make changes in the way we manage these soils.
Methods and Materials
Soils Microcosm Experiment
Three controlled soil microcosms were created in 19 L buckets. Each
bucket was filled half-full with surface soil (0-20 cm) collected from a mesic Typic
Alpaqualf (Dayton series) at the Lake Creek West site. The effect of the amount
and chemical nature of organic amendments was tested; microcosm A served as
a control and received no extra source of carbon, 1 kg C
M-2
corn straw was
added to microcosm B and microcosm C was given 1 kg C m2 calcium acetate
(CaC2H3O2). A standard 5 cm diameter piezometer, equipped with an internal
platinum electrode, was inserted to a depth of 20 cm in each soil microcosm.
Two additional platinum electrodes were placed directly in the soil at depths of 5
and 15 cm. Water was added to the microcosms until there was 5 cm of
standing water above the soil surface. The water level was maintained at that
level for the duration of the experiment. Water was continuously pumped
(-100 mLh"1) from inside the piezometer to the standing water surface to ensure
that the water in the piezometer was at least somewhat equivalent to the soil
solution.
The experiment was initiated on July 5, 1995 and lasted for eight weeks.
Redox potentials (mV vs. SHE), and dissolved oxygen concentrations (mg 02 L )
were taken five times weekly. Dissolved oxygen was determined using a
polarographic dissolved oxygen probe. Redox potentials were determined by
connecting the platinum electrodes to a voltmeter and a reference electrode
placed in the standing water of the microcosm. Redox measurements were
converted to values equivalent to the standard hydrogen electrode (SHE) by
addition of the reference electrode potential to the measured laboratory value.
During the initial phase of experiment, no attempt was made to exclude 02 from
the piezometers and the water within. This type of well is referred to as an open
head-space well. On day thirty of the experiment, N2 gas was bubbled into the
piezometers to limit the transport of 02 into the piezometers. This phase of the
well performance is referred to as a purged head-space well. After two weeks
the flow of N2 gas was stopped to determine the rate of 02 diffusion into the soil
microcosm.
Field Experiment
Three sites representing differing soil biogeochemical regimes were
chosen along a gradient of soil drainage (water table levels). The agricultural site
was located in the somewhat poorly drained soil of the field (Holcolmb series, a
fine montmorillonitic mesic Mollic Albaqualf); a transitional site was located at the
interface between the agricultural and the riparian soils. The riparian site was
located in the poorly drained soil (Dayton series, a fine, montmorillonitic mesic
Typic Albaqualf) 20 m from the creek. Approximately 60 m separate the three
sites.
Soils samples were taken bimonthly at depths of 0 to 15 cm, 15 to 30 cm,
30 to 45 cm, and 45 to 60 cm using a soil probe. Immediately after collection,
while still in the field, soil samples were cut in half, perpendicular to the profile.
One-half of the sample was placed into a sampling cup to be dried. The other
half was again divided in half perpendicular to the profile. One portion (-8-12 g)
was placed into a preweighed 50 mL centrifuge tube containing 20 mL of an
extracting solution of 1 M KCI / 0.1 M HCI. While the remaining quarter was
placed into another 50mL centrifuge tube and mixed with 1 M ammonium fluoride
at pH 3 (Bray II Solution) (Bhiyan, 1995).
After returning from the field, the tubes were again weighed and placed on
a shaker for 16 hrs in the dark. The soil slurry extracts were centrifuged at 2000
x g (5000 rpm) for 20 minutes. Ten ml aliquots were decanted off and stored in a
refrigerator prior to analysis. The remainder of the supernate was decanted off
the soil and discarded. The soil was rinsed three times with tap water to
entrained salts and acid prior to the drying process. The soil was then placed
into a sampling cup, air dried, and dry soil mass determined.
The concentrations of Fe(II), total Fe, ortho-PO4, NH4, and NO3 in the
extracts were measured by flow injection analysis. Extractable Mn was
determined by atomic absorption spectroscopy.
Redox potentials were measured on a weekly schedule. Sites were
chosen on a transect parallel to the soil sampling area, but about 5 m away to
prevent the redox electrode sites from being disturbed by the soil sampling.
Each site had six platinum electrodes. The agricultural site had three electrodes
at depth 25 cm and three at depth 45 cm, while the riparian and transitional sites
each had three electrodes at depth 15 cm, and three at depth 45 cm. Redox
measurements were taken using a voltmeter and a reference electrode placed in
a hole in the soil that when dry was filled with tap or creek water that contained
ions to complete the electrical circuit through the soil. Redox measurements
were converted to values equivalent to the standard hydrogen electrode (SHE).
Results
Evaluation of Closed-Headspace Well Performance for the Soil
Microcosm Experiment
Differences in the respective redox potentials between the microcosms (A-
C) were not significant. Apparently adequate soil carbon was already present so
that the added carbon sources for microcosms B and C made little or no
perceivable impact in redox potential when compared to the control (microcosm
A). Averaged values (microcosm A-C) for the redox potentials and dissolved 02
content are plotted in Figure 1.
I
Microcosm Experiment
400
2
1-1
= 300
1.5
> 200
E
-J
100
1
0
0
E
N
0
a-
0
-100
0.5
-200
-300
0
10
0
20
40
30
50
60
Time (days)
-- Wells
Figure 1.
Bottles
--Ar- Oxygen -Q- Soils
Dissolved 02 and redox measurements for microcosms
The average daily values for the soil redox potentials revealed a clear
trend in the biogeochemical process of reduction. At the beginning of the
experiment, the soil redox potential started at just above +50 mV (SHE), and
dropped to a minimum value of approximately -225 mV after approximately three
weeks. The redox value reached an equilibrium value of approximately -175 mV
after five weeks.
The concentration of dissolved 02 in the well pore water followed the
same trend as redox potential. The concentration of oxygen started at around 1
mg 02 L-1 and steadily decreased to a value near zero. Both the soil redox
I
potentials and 02 profiles appeared to follow a logarithmic path with time,
indicative of a biological rate process.
The initial aqueous piezometer redox potential of +350 mV (SHE) dropped
to a minimum value of just less than zero on around day 20 before stabilizing at
approximately +100 mV. This was almost 300mV more positive than the soil
values. This large difference in redox potential suggest there is something
different about the chemical and physical environment of soil pores as sampled
in open head-spaced wells when compared to actual soil pores. The most likely
explanation is that the open head-spaced wells act as a large pore or a conduit
for the transport of 02 into the water in the piezometer. The presence of 02
would be expected to oxidize the piezometer water leading to the higher redox
potentials and lower values of soluble Fe, Mn, and P04N2 gas was bubbled through the piezometers on day 32 of the experiment
and the redox potentials in the piezometers decreased to that of the soil
electrodes on day 40. On Day 43 of the experiment the N2 gas was turned off,
and the redox potential in the piezometers returned to just under +100 mV, in just
one day. This suggests that 02 transport is a rapid process. The redox potential
in the piezometers after that day fluctuated due to the formation of an iron oxide
crust on the free water surface inside the piezometers. The crust broke
periodically allowing oxidation of the piezometers. This formation and destruction
of the iron oxide crusts caused the erratic, but predictable, behavior of the redox
potentials after that point.
During the last week of the experiment, it was hypothesized that a small
sampling well, completely sealed from the atmosphere and initially purged with
N2, would be able to reproduce the same effect as was being observed in the
purging of the piezometers with N2. A small bottle with perforations to allow
water flow, a redox electrode, and a sampling tube was buried in each
microcosm. Electrode measurements confirmed this hypothesis (Figure 1).
Redox potentials started above +100 mV (SHE) and decreased to almost the
redox potential of the soil.
450 T
3
350 -
r
-
2.5 c
11
250
2
1.5 EL
150
V
50
E
-50
U-
-150
0
100 200 300 4C0 500 600
700
time (hr)
I- Eh
Figure 2.
- Fe(I I 'l
,., phosphate l
Lemmon's soil reactor experiment
Water samples from the microcosm experiments oxidized much more
rapidly than we expected. I therefore abandoned the use of these data and drew
inferences from Lemmon's (1995) experiment performed in a soil reactor (Figure
2). Redox potentials were controlled and the concentration of water soluble iron
and phosphates were determined at selected time intervals. She found that the
concentration of Fe(II) and ortho-PO4 were negatively correlated to the redox
potential. Applying this to my microcosm experiment, I would expect that the
concentrations of Fe(II) and ortho-P04 in the soil pores would be higher than the
open piezometers as the result of the lower redox potentials. After the
piezometers were purged with N2, the concentrations of Fe(II) and ortho-P in the
piezometers should have become more similar to the concentrations of Fe(II) and
ortho-P in the saturated soil pores where 02 diffusion is limited.
These two observations are supported by the formation of Fe(III) mineral
oxide crust in the piezometers after the N2 bubbling was turned off. The results
of this experiment were further confirmed in the field studies (Baham et al. 199X).
They installed purged head-space wells at the Lake Creek West site, there were
three transects with six sampling piezometers along each transect. Each site
had an Ar-gas purged head-space well with redox electrode, and an open
piezometer with redox electrode. Soil redox electrode values were also
measured at each site. The redox potentials of the open piezometers rarely went
below +250 mV (SHE), while the Ar-gas purged head-space wells at times were
less than 0 mV (Figure 3). Again, as in the microcosm experiment, the difference
between open and purged head-space wells was as much as 250 mV. The
redox potentials of the soil electrodes was closer to the purged head-space wells
redox values than to those measured in the open head-space wells.
>
600
E
M iddle Transect
Purged Wells
I
O pen W ells
soil
w
IL
-100
9
10
I1
12
13
Well Number
Figure 3.
Redox potentials for soil, open and closed head-space wells
Solution sampled from the purged head-space wells across the middle
transects show results similar to Lemmon's experiment. When the redox
potential is high (oxidized conditions), the concentrations of Fe(II) and ortho-P
are low (Figure 4). When redox potentials were lower, higher concentrations of
Fe(II) and ortho-P were observed. Nitrates, which are also terminal electron
donors before Fe(lll) followed the opposite trend as would be expected, other
than piezometer number 7 which had a lower level of nitrate that would be
expected.
10-2
350
300
10-4
iii
250
an
a,
l e-5
0
1e-7
6
7
8
1
10
11
12
13
Well Number
Figure 4. Fe(ll), P04, NO3 concentrations and redox potentials for the center transect at the
Lake Creek watershed; Julian day 154 (1997)
Field Experiment
Redox potentials
Soil morphology and edaphic characteristics play an important role in
understanding the results of the field experiment at the Lake Creek field site
(Figure 5). The Dayton soil series underlied much of the riparian zone. This soil
had a Bt horizon of very low hydraulic conductivity which restricted the vertical
movement of water through the soil. Ponding of water during the rainy season is
common. As a result, the Dayton soil was considered to be a poorly drained soil.
The agricultural soil was identified as the Holcomb soil and did not have the
same restrictive layer. Although the soil at the agricultural site was a somewhat
poorly drained soil, the water table is usually much lower and drops much more
rapidly than the water table in the riparian zone. The soil in the transitional zone
+-North
Agricultural Site
(Site')
Lake Creek
Transitional Site
Riparian Site
(Site 3)
(Site
T
Burn
60m
m
2QBi
Figure 5. Schematic diagram representing the sub-surface stratigraphy of a transect at the Lake
Creek Site
was also a Holcomb soil, however the difference between the agricultural and
transitional zones was that the transitional zone was uncultivated and allowed to
grow naturally. Natural vegetation can provides a conduit for the flow of 02 to
the rhizosphere (Engelaar, 1995). This process can lead to the oxygenation and
thus higher redox potentials in the soil horizon where active plant growth occurs
(Kludze, 1994).
I have observed that vegetation grows slowly at the riparian site in the
early spring, which in most years is saturated until June. Vegetation appears to
grow the fastest at the Transitional site, while vegetative growth at the
agricultural site was somewhere between the transitional and riparian sites.
These characteristics of the different sites act in concert to yield differences in
the redox potentials of the sites over time.
Agricultural Site
700
•
-0
p
Shallow Electrode
Deep Electrode
S
w
0
300
0.
200
X
o
c
•
100
•
0
j
;1
S...
-100
-200
300
350
400
450
500
550
Julian day
Figure 6.
Redox potentials for the Agricultural Site
Redox potentials declined for both the shallow and deep electrodes from
+450 mV (SHE) on Julian day 325 (mid-November, 1995) to about an average of
+50 mV by Julian day 425 (end of February 1996) (Figure 6). From Julian day
425, the value for the electrodes climbed steadily back to the soil's usual dry
potential of around +500 (SHE). The shallow electrodes maintained lower redox
potential values for a longer time period and their mean values climbed more
slowly. The shallow electrode did not reach the usual dry redox potential by the
time the experiment ended on Julian day 525 (May 17). A reasonable
explanation for higher redox potentials in the deeper horizons is that the soil was
managed so that the majority of the soil organic matter was near the surface of
the soil. Therefore, the lower horizons supported little biogeochemical activity
and were not as great a sink for 02 and hence the redox potentials were higher.
2
Transitional Site
700
j
600
500
(0
04
E
Shallow Electrode
Deep Electrode
400
0
CL
x
0
p
300
200
100
a)
0
-100
ii,
-200
0
450
Ad
400
Julian day
Figure 7.
Redox potentials for the Transitional Site
The deeper soil electrode readings at the transitional site (Figure 7) were
lower (more reduced) than the agricultural site. The redox potential remained
near zero mV (SHE) until Julian day 490 (May 1). This was probably the result of
a proceedingly higher water table level in moving towards the intermittent stream.
The rapid growth of vegetation, in early April, pumped oxygen into the shallower
soil horizons resulting in a increase in redox potential for the shallow electrode.
The lowest redox potential values were observed at the riparian site
(Figure 8). This is evidently the result of a relatively high water table coupled to a
warming of the soil in spring while the soils are still saturated. The redox
potential of both the shallow and the deep electrodes decreased until Julian day
500 (May 1) with a final low of around -100 mV (SHE). Redox potentials below
+200mV were low enough to result in significant reductive dissolution of the soil
Fe- and Mn- oxide minerals.
Riparian Site
700
600
:o
500
Shallow Electrode
Deep Electrode
400
o ...
300
200
100
0
-100
-200
300
450
400
Julian day
Figure 8. Redox potentials for the Riparian Site
Cumulative Soluble Nutrients
The cumulative amounts of each KCI/HCI extractable Fe(II). Mn(II), P04,
NO3, and NH4 in units of g M-2 integrated to the sampling depth of 60 cm was a
useful measure for interpreting overall effects on biogeochemical reduction.
Examination of these values against a backdrop of the redox potentials on a
temporal scale revealed the recognizable trends between the sites.
The highest concentrations of extractable Fe(II) produced by reductive
weathering was approximately 600 g m2 Fe(II) for the riparian site on Julian day
-440(- April 10, 1997) (Figure 9). The agricultural site, which was the most welldrained and had the highest redox potentials, produced less than 100 g m-2
Fe(I1).
r,
!
Fe(II) Agricultural Site
600
500
400
300
200
100
700
600
500
400
300
200
100
0
-100
-200
0
350
300
400
450
Julian day
!l
Fe(II) Transitional Site
700
600
500
400
300
200
100
600
500
400
300
200
100
0
V.
-100
-200
E
0
300
350
400
450
500
550
Julian day
ra
Fe(II) Riparian Site
700
600
500
400
300
200
100
0
-100
-200
IN
600
500
400
300
200
100
0
300
350
400
450
500
550
Julian day
40
Shallow Electrode
Deep Electrode
IF a (11)
Figure 9.
Cumulative Fe(ll) concentrations for the three sites
The time course trends for Mn were similar to those for Fe(II). This was
reasonable, since both Fe and Mn would be expected to originate from an oxide
mineral source. When the redox potential of the soil initially declined, the
concentration of extractable Mn(II) increased. At some point however, Mn(II)
Mn Agricultural Site
m
C
m
0
0
0
O
m
700
600
500
400
300
200
100
360
320
280
240
200
160
120
80
40
0
-100
-200
0
300
350
450
400
500
550
Julian day
Mn Transitional Site
m
C
al
0
0.
0
V
a,
700
600
500
400
300
200
360
320
280
240
200
160
100
120
P
80
-10:
40
-200
0
Julian day
Mn Riparian Site
a
C
m
0
0.
0
0
V
700
360
320
280
240
200
190
120
80
40
600
500
400
300
200
100
0
-100
-200
0
300
350
400
450
500
550
Julian day
. Shallow Electrode
0 Deep Electrode
-- M n
Figure 10. Cumulative Mn(ll) concentrations for the three sites
concentrations decreased as the soil continued to become more deeply reduced
(Figure 10). This suggests the formation of a mineral (e.g. MnS(s) or MnHPO4(s))
which is not completely soluble in the extracting solution. Another trend that is
important to clarify is the observed greater values of extractable Mn(ll) at the
transitional site than at the riparian site. Krebs et al. (1997), also found that
I
PO4 Agricultural Site
m
I
700
600
500
400
300
200
c
m
0
a
X
0
a,
1e
14
12
10
100
6
0
4
-100
-200
2
E
a-
8
a-
0
Julian day
PO4 Transitional Site
m
700
c
600
500
400
300
200
100
al
0
a.
X
0
v
ai
16
14
12
10
8
E
aa-
6
0
4
100
2
-200
0
Julian day
PO4 Riparian Site
a,
c
m
0
0
X
0
V
a,
700
600
16
500
400
300
200
100
12
10
14
E
8
a-
6
0
4
-100
-200
2
0
Julian day
41- Shallow Electrode
O Deep Electrode
t P0.
Figure 11. Cumulative P04 concentrations for the three sites
extractable Mn was low at the riparian site. However, the riparian site had the
highest amount of Mn extracted when expressed as a percentage of the total soil
Mn when compared to the transitional and agricultural sites. Therefore, much of
the manganese at site three had weathered and transported out of the soil via
"reductive dissolution."
The cumulative exchangeable phosphate concentration increased as the
soil became reduced and decreased as the redox potentials returned to more
oxidized conditions (Figure 11). However, the largest amount of ortho-P was
found in the soil of agricultural site. This observation points to a large input of
phosphorus through fertilization. The cumulative concentrations of extractable P
at the riparian site were lower than at the transitional site; most likely due to the
riparian site being more weathered than either the agricultural or the transitional
sites.
Soil Profiles
Once the cumulative trends were understood, it then became important to
understand the concentration gradient of Fe(II), Mn(II), and ortho-P04 in a soil
profile. When looking at a concentration profile for a given day, it was instructive
to know the redox potential for that day. Julian day 487 (April 20, 1997) was a
particularly interesting profile from which to discuss to the differences in redox
potentials for the three different sites.
Most of the extractable Fe(II) was concentrated in the upper horizons
(Figure 12). This is the result of greater biological mineralization of carbon
coupled to Fe reduction under limited 02 conditions (i.e., saturated soil with a
high water table). Since the redox potentials at the agricultural site were quite
high, it was not surprising to find high concentrations of extractable Fe(II), nearly
three orders of magnitude smaller than the riparian site. The transitional site,
Riparian Site
Transitional Site
Agricultural Site
0
0
0
-10
-10
-10
-20
-20
E
w
-30
-30
-30
CL
CL
a)
a,
0
-40
0
-40
-60
-60
0.0
0.5
1.0
1.5
mg Fe(ll)/ Kg soil
2.0
-40
-50
-50
-50
-20
0
U
-60
0
50
100 150 200 250
mg Fe(ll)/ Kg soil
0
500
1000
1500
mg Fe(ll)/ Kg soil
Figure 12. Concentration profiles for Fe(H) at the three sites for day 487
however, had a lower redox potential in the lower horizon than in the upper
horizon. As mentioned earlier, this was due most likely to the pumping of oxygen
into the soil by plant roots. The highest concentration for Fe(II) at the transitional
site occurred in the 15 to 30 cm layer. Since the shallow electrode was placed at
15 cm, it becomes apparent that the plant roots were mostly only to a depth of
about 15 cm and therefore only pumped oxygen down to about that depth. The
lack of extractable Fe(II) below 30 cm, even though the redox potential in that
region was quite low, was due to the fact that there was little reducible Fe in that
region. At the riparian site, the extremely low redox potential was fairly constant
throughout the entire profile. As a result, Fe(II) concentrations in the riparian site
are the highest of all the sites.
Riparian Site
Transitional Site
Agricultural Site
0
0
0
-10
-10
-10
-20
-20
-20
E
E
U
U
-30
n
0a)
-40
-50
-30
-30
n.
a)
0
-40
-50
-60
-50
-60
0
100
200
mg Mn/ Kg soil
300
-40
-60
0
100 200 300 400 500
0
mg Mn/ Kg soil
100
200
300
mg Mn/ Kg soil
Figure 13. Concentration profiles for Mn(11) at the three sites for day 487
Mn was more susceptible to reductive weathering than Fe. The surface
riparian soil profile showed a lower concentration of extractable Mn(II) than
subsurface soils as a result of the intense reductive weathering (Figure 13). The
amount of exchangeable Mn was a moderate percentage of the total pool of Mn
under even fairly oxidized conditions, whereas, Fe(ll) was almost nonexistent at
similar redox potentials. This means that even when the soil is completely dry, a
fairly large fraction of the Mn remains in the extractable pool. For this reason, the
largest amount of extractable Mn(II) was found at the surface of the soil at the
transitional site, which had a much higher redox potential.
2
Although trends in concentration of inorganic P04, which are released
when Fe-P04 minerals are reduced, tend to follow similar trends as extractable
Fe(II), other factors have considerable influence (Figure 14). Considerations for
fertilization and plant uptake of ortho-P04 must be made in order to fully
understand the soil profiles. Both these considerations are extremely important
to understand the profile at the agricultural site. Unlike either Fe(ll) or Mn(II),
Agricultural Site
Riparian Site
Transitional Site
0
0
0
-10
-10
-10
-20
E -20
-30
E
-20
:
-30
U
U
-30
CL
Q.
m
m
-40
-40
-40
-50
-50
-50
-60
-60
-60
0
5
10
15
20
mg PO4/ Kg soil
0
2
4
6
8
10
mg P04/ Kg soil
0
1
2
3
mg PO4/ Kg soil
Figure 14. Concentration profiles for P04 at the three sites for day 487
ortho-P04 was more highly concentrated at the Agricultural site. Extractable P04
is also higher in the subsurface horizons of both the agricultural site and the
transitional site due to plant uptake in the upper horizons and possible
differences in parent materials.
2
Three Dimensional Graphical Representations
Three dimensional graphical representation of extractable Fe(II), Mn(ll),
and P04 concentrations for temporal scales which encompass the entire reduced
season can provide some interesting perspectives on reductive dissolution.
These graphs represent interpolated smoothed fits to the triplet data. The actual
surface generated by the 3-D numerical fitting routine (Sigma Plot) is not
intended to represent an exact concentration. However, since only the trends
are important, these assumptions are acceptable. The highest concentrations
and the longest duration of Fe(II) occurred in the riparian soil profile (Figure 15).
Conversely, the agricultural site had the lowest concentration of Fe(II) of all three
sites and had shortest duration of it's presence. This was exactly what would be
expected based on the proposed hypotheses.
30
A ricultural Site
400-
1C''200 I-/-L"-rim 2?`Tz
300
104 i
y.
MO-loo
30
-`T-44peP
lv
60-50
Julian day
Transitional Site
1500
1200
900,
600
300
-rr' ,r"-' "Y 4V 301h lGml
K}-T -
JUllan day
Riparian Site
2
c ,vv
-y
2000
1500
3
Co
10001( `- -'f>f', x
5001
1_`
_;
;<
100
0-3 4 cm1
Julian day
Figure 15. Concentration profiles for Fe(//) for the three sites over one year
When viewed over a two year period (Baham et al., 1997) the same trends
for iron at the different sites were again reproduced making the annual cyclic
biogeochemical nature of the soils clearly visible (Figure 16).
Agricultural Site
400 k
300 i
200
-4
C0
100
0
[An
I
j.11
10
0
Julian day
Transitional Site
2000
1500
ca
1000
500
01
tG
0
N
0
Julian day
g
ian Site
n
0
L_
CLI
2400
1600
8001
0
Julia -cl
Figure 16. Concentration profiles for Fe(11) for the three sites over two years
Extractable Mn(ll) followed a similar trend as Fe(ll), but the proportion of
manganese that was extractable when dry was much higher than for Fe, even
when the soil was dry. Therefore, the effects of redox potential were not as
obviously apparent (Figure 17). As mentioned earlier, the apparent lower
concentrations of extractable Mn(II) at the riparian site than the transitional site
must be attributed to the more intense reductive weathering.
ricultural Site
l if
I
Transitional Site
i
Julian day
Julian clay
Figure 17. Concentration profiles for Mn(11) for the three sites over one year
Phosphorus also followed the same overall trends as Fe(II) and Mn(II), at
the agricultural and transitional sites (Figure 18). These same trends continued
in the riparian site until the redox potentials went well below zero. At low redox
3
potentials, the concentration of extractable P04 decreased markedly. This
suggests the possible formation of vivianite, an Fe(II)-PO4 mineral (Lindsay
p.179). As redox potentials decreased, Fe(Ill) comprised in a mineral with P04
reduced to Fe(II), and the mineral was dissolved. Further reduction caused the
solubility of vivianite to decrease.
34
Ag ricultural Site
Julian day
Transitional Site
Julian clay
Riparian Site
Julian aay
Figure 18. Concentration profiles for PO,, for the three sites over one year
3
Conclusions and Discussion
In general, the experiments supported the proposed hypotheses. It is often
common, especially in the Willamette Valley, to sample soils for nutrients that are
susceptible to redox reactions in soils that are under reduced conditions. At
these times, it is important to sample in a way that prevents oxygen from
interfering as well as to protect the samples themselves from oxidation in order to
have samples which are truly representative of the soils from which they have
been taken. Unprotected sampling can cause the nutrients to become insoluble,
leading the researcher to believe there was less soluble nutrients than what
actually existed in the soils.
Certain nutrients in poorly drained soils undergo cyclic periods of changing
solubility following quite closely the cycling change in redox potentials of these
soils. Linking these effects with vegetative growth call for serious considerations
for amounts and timing of fertilization, especially for phosphorus and possibly for
nitrates and other nutrients as well as in soils that are linked to climatic redox
reactions. Phosphorus has been considered to be mostly insoluble in well
drained soils, reconsideration of this paradigm for poorly drained soils clearlynee
more study to understand the possible linkage to groundwater and stream
pollution.
Bibliography
Baham, J., R. Krebs, S. M. Griffith. 1998. Soluble P, Fe(II), and Mn(II) in
Shallow Anoxic Groundwater Collected from Purged and Open
Piezometer Wells. American Journal of Soil Science. (in prep.)
-
Baham J., R. King, R. Krebs, S. M. Griffith. 199_. Changes in Fe and Mn
Oxide Mineralogy in Poorly drained Agricultural and Riparian Sites. Soil
Science. (in prep.)
Bhiyan, L. R., J. E. Sedberry Jr. 1995. Apparent Phosphorus Fixation by
Selected Soils of Louisiana. Communications in Soil Science and Plant
Analysis. V.26 (1/2) p. 21-34
Engelaar W. M. H. G., J. C. Seymens, H. J. Lambroek, C. W. P. M. Blom. 1995.
Preservation of Nitrifying Capacity and Nitrate Availability in Waterlogged
Soils by Radial Oxygen Loss from Roots of Wetland Plants. Biology A
Fertility of Soils. V. 20 p. 243-248
Kludze H. K., S. R. Pezeshki, R. D. Delaune. 1994. Root Oxygenation and
Growth in Baldcypress in Response to Short-Term Hypoxia. Canadian
Journal of Forest Research. April v. 24 p. 804-809
Krebs, R., J. Baham, S. M. Griffith. 1998. Seasonal Transformations of Fe- and
Mn-oxides at a Poorly-drained agricultural and Riparian Soil. Environ. Sci.
Technol. (in prep.)
Lindsay, W. L. 1976. Chemical Eauilibria in Soils. John Wiley and Sons, New
York
Patrick W. H. Jr., A. Jugsuinda. 1992. Sequential Reduction and Oxidation of
Inorganic Nitrogen, Manganese, and Iron in Flooded Soils. Soil Society of
America Journal. v56 n4, p. 1071-1073
Ponnamperuma, F. N. 1997. Chemistry of Submerged Soils. Adv. Agron. 24:
29-96
Stumm W., B. Sulzberger. 1992. The Cycling of Iron in Natural Environments,
Considerations based on Laboratory Studies of Heterogeneous Redox
Processes. Geochimica et Cosmochimica Acta. v56 n8, p. 3233-3252
3
Appendix 1:
Julian day 365
Site 1
E
Soil P04 Concentration Profiles
0
0
-10
-10
-10
-20
E
-30
0 -40
-30
a
a)
0 -40
-50
-50
-60
-60
CL
0)
0.0
0.5
E
-20
U
CL
0
-40
-60
0.5
0
1.0
Site 3
Site 2
0
0
0
-10
-10
-10
-20
E
E
-20
-20
o(D -30
O -40
a -30
0 -40
-30
n
N
0 -40
-50
-50
-50
-60
2
4
6
8
10 12
0
mg PO4/ Kg soil
E
CL
2
1
0
-10
-10
-10
E
-30
CL
a)
-20
0
E
-20
-30
am
-30
a)
0 -40
0
-50
0
-40
0
2
4 6 8101214
mg P04/ Kg soil
-40
-50
-50
-60
8
Site 3
Site 2
0
0
6
mg P04/ Kg soil
0
-20
4
2
0
3
mg P04/ Kg soil
Julian day 395
Site 1
0
-60
-60
0
2
1
mg PO4/ Kg soil
mg PO4/Kg soil
Julian day 375
Site 1
-30
-50
0.0
1.0
-20
cu-
mg PO4/ Kg soil
E
Site 3
Site 2
0
-60
-60
0.6
0.8
1.0
mg PO,/ Kg soil
0
1
2
3
4
5
6
mg PO4/ Kg soil
7
3
Julian day 404
Site 1
E
0
Site 3
Site 2
0
0
-20
E
0
ZQ -30
a)
0 -40
-20
I
-30
a
0 -40
-40
-50
-50
-50
-60
-60
-60
0
10
5
15
0
20
Julian day 425
0
0
-10
-10
-10
E -20
E -20
-30
n -30
0
-50
E
n
0
-40
-60
20
10
0
30
-20
-30
-40
-60
0
mg PO4/ Kg soil
2
6
4
8
0
10
Site 3
Site 2
0
0-
2
1
mg PO4/ Kg soil
mg PO4/ Kg soil
Julian day 440
Site 1
8
-50
-50
-60
6
Site 3
Site 2
0
D -40
4
2
mg PO4/ Kg soil
mg PO4/Kg soil
mg PO4/ Kg soil
Site 1
0
4
3
2
1
0
-10
E
0
0E -20
-20
-30
Q
CL
E
-20
n
m
-30
U
-30
a)
0 -40
0 -40
0 -40
-50
-50
-50
-60
-60
(D
0
1
2
3
4
5
mg PO,,/ Kg soil
6
-60
0
1
2
3
4
5
mg PO4/ Kg soil
6
0
1
2
3
4
5
mg PO4/ Kg soil
6
3
Julian day 453
Site 1
0
0
-10
-10
-10
E -20
0
a
a)
Site 3
Site 2
0
E -20
E -20
0
0
-30
a()
-30
Q
-30
a)
0 -40
0 -40
0 -40
-50
-50
-50
-60
-60
0
20
10
-60
0
30
Julian day 473
8
0.0
10
-10
-10
-10
E
-20
s
-30
E
ta
0
U
CL
a)
a)
D -40
0
-50
a)
0
-40
20
10
-30
-40
0 2 4 6 81012
30
mg P04/ Kg soil
Site 1
-20
-60
-60
0
0
0
0
0
-10
-10
-10
E -20
-20
-30
-30
0 -40
-40
-50
-50
-50
-60
-60
E -20
0
-30
Q
a)
0 -40
0
5
10
15
mg PO,/ Kg soil
20
2
34
5
6
Site 3
Site 2
Julian day 487
1
mg P04/ Kg soil
mg P04/ Kg soil
L)
2.0
1.5
-50
-50
-60
1.0
Site 3
Site 2
0
-30
0.5
mg P04/ Kg soil
0
E -20
n
a)
6
0
0
Q
4
mg P04/Kg soil
mg P04/ Kg soil
Site 1
2
-60
0
2
4
6
8
mg P04/ Kg soil
10
0
1
2
mg P04/ Kg soil
3
Site 1
E
Julian day 505
Site 3
Site 2
0
0
0
-10
-10
-10
-20
-20
-30
-30
-30
-40
0 -40
-40
-50
-50
-50
-60
-60
-60
-20
E
U
U
0
2
4
6
8
mg P04/ Kg soil
10
0
1
2
mg P04/Kg soil
3
0
3
6
9
mg P04/ Kg soil
12
Appendix 2:
Soil Fe(II) Concentration Profiles
Julian day 365
Site 1
-10
E
U
E
-20
U
L
a -30
CL
a,
a)
0
-40
-50
0
0
-10
-10
-20
-20
-30
-30
-40
-40
-50
-50
-60
-60
-60
10
0
20
30
40
0
50
Julian day 375
Site 1
-10
0
-10
-10
U
-20
-30
a
-30
n
-30
0
-40
0
-40
a)
a)
-50
-60
-50
-60
-60
10
0
20
30
0
mg Fe(ll)/ Kg soil
500
1000
0
E
-20
U
-30
Q-
1800
0
-10
-10
1200
Site 3
Site 2
0
0
600
mg Fe(ll)/ Kg soil
mg Fe(ll)/ Kg soil
Julian day 395
Site 1
1000
Site 3
0
20
-40
5 00
mg Fe(ll)/ Kg soil
-20
-50
E
0
300
E
()
0
200
Site 2
0
CL
100
mg Fe(II)/Kg soil
mg Fe(ll)/ Kg soil
U
Site 3
Site 2
0
-10
E
-20
U
L
-30
CL
-20
-30
a>
0
-40
-40
-40
-50
-50
-50
-60
-60
0
5
10 15 20 25 30
mg Fe(ll)/ Kg soil
-60
0
500
1000
mg Fe(ll)/ Kg soil
0
600
1200
1800
mg Fe(ll)/ Kg soil
4
Site 1
Julian day 404
0
0
0
-20
E
Site 3
Site 2
E
-20
U
U
C-
-30
Q
-30
N
N
0 -40
0 -40
-50
-50
-60
-60
0
100 200 300 400 500
-50
-60
0
800
0
1200
Julian day 425
Site 3
Site 2
0
200 400 600 8001000
mg Fe(ll)/ Kg soil
mg Fe(ll)/Kg soil
mg Fe(ll)/ Kg soil
Site 1
400
0
0
-10
E
-20
=-
E -20
E
-20
-30
0
y -30
n
0
n
O -40
0 -40
0 -40
-50
-50
-50
0
L
-60
-60
0
10
20
30
-60
0
mg Fe(ll)/ Kg soil
Site 1
-30
200 400 600
0
800
mg Fe(ll)/ Kg soil
mg Fe(ll)/ Kg soil
Site 3
Site 2
Julian day 440
0
0
400 800 1200 1600
0
-10
E
E
-20
0
U
-20
0E
-a--30
-Q-30
t -30
CL
-20
0 -40
0 -40
0 -40
-50
-50
-50
-60
I
0
-60
-60
1000
2000
mg Fe(ll)/ Kg soil
0
1000
2000
mg Fe(ll)/ Kg soil
0
1000
2000
3000
mg Fe(ll)/ Kg soil
Site 1
E
U
Julian day 453
Site 3
Site 2
0
0
0
-10
-10
-10
-20
E
U
E
-20
0
-20
a -30
0 -40
a -30
0 -40
-30
-50
-50
-50
-60
-60
4
0
8
-60
0
16
12
-40
E
Q
Julian day 473
Site 3
Site 2
0
0
0
-10
-10
-10
-20
-30
CD
E
-20
n
0
-30
(D
0 -40
-50
E
0.
(D
-40
0
-50
-60
1
2
4
3
-30
-40
-60
0
mg Fe(ll)/ Kg soil
20
40
60
0
Site 3
Site 2
0
0
300 600 900 1200
mg Fe(ll)/ Kg soil
mg Fe(ll)/ Kg soil
Julian day 487
Site 1
-20
-50
-60
0
300 600 900 1200
mg Fe(ll)/ Kg soil
mg Fe(ll)/Kg soil
mg Fe(ll)/ Kg soil
Site 1
0
200
100
0
-10
E
0
Q
-20
E
-20
E
-20
-30
aa
-30
n
-30
aD
0 -40
0 -40
0 -40
-50
-50
-50
-60
-60
-60
a)
0.0
0.5
1.0
1.5
2.0
mg Fe(ll)/ Kg soil
0
100
200
g P04/ Kg soil
0
400 800 1200 1600
g P04/ Kg soil
Site 1
E
Julian day 505
Site 3
Site 2
0
0
0
-10
-10
-10
-20
E
0
-30
E -20
-20
0
-30
-30
Q-
CL
(D
a)
-40
0 -40
0 -40
-50
-50
-50
-60
-60
-60
0
1
2
mg Fe(ll)/ Kg soil
3
0
100
200
mg Fe(ll)/Kg soil
0
200
400
600
mg Fe(ll)/ Kg soil
45
Appendix 3:
Site 1
0
CL
Soil Mn(II) Concentration Profiles
Julian day 365
0
0
-10
-10
-10
-20
-40
0 -20
m -30
()
0 -40
-50
-50
-30
a)
0
0
0
200
400
a)
0
-60
0
Julian day 375
0
-10
-10
-10
w
-30
a -30
0
-50
200
400
600
0
-10
-10
U
-30
CL
0
-10
20
0
100 200 300 400
mo Mn(ll)/ Kg soil
-20
-30
a -30
-40
0
aD
-40
-50
-60
-60
-60
Site 3
E
-50
-50
mg Mn(ll)/ Kg soil
0
a)
-40
50 100 150 200 250 300
Site 2
0
aD
0
-60
100 200 300 400 500
mg Mn(ll)/ Kg soil
Julian day 395
-20
-40
-50
0
mg Mn(ll)/ Kg soil
Site 1
-20
a)
0
-40
-60
0
150
a -30
-50
-60
CL
0
a)
-40
100
Site 3
Site 2
-20
50
mg Mn(ll)/ Kg soil
0
0
E
0
0
-20
0
100 200 300 400
mg Mn(II)/Kg soil
0
(,
-40
-50
mg Mn(II)/ Kg soil
Site 1
-20
a -30
-60
-60
CL
Site 3
Site 2
0
100 200 300 400
mg Mn(ll)/ Kg soil
0
100
200
300
mg Mn(ll)/ Kg soil
Site 1
E
U
Q
Julian day 404
0
0
0
-10
-10
-10
-20
E
U
-30
E
-20
U
4)
CL
a)
-40
0 -40
-50
-50
-50
-60
-60
-60
0 -40
0
0
200 400 600 800
0
Site 1
200 400 600 800
0
Julian day 425
0
0
-10
-10
-10
E
-20
n
0
-30
U
s
-30
a.
a)
0 -40
E
U
-40
-50
-50
-50
-60
-60
-60
100 200 300 400 500
(D
0
mg Mn(ll)/ Kg soil
Site 1
200 400 600 800
0
100
150 200
Site 3
Site 2
Julian day 440
50
mg Mn(II)/ Kg soil
mg Mn(II)/ Kg soil
0
0
300
-20
n -30
0 -40
0
200
Site 3
Site 2
0
-20
100
mg Mn(ll)/ Kg soil
mg Mn(II)/Kg soil
mg Mn(II)/ Kg soil
E
-20
-30
-30
CL
CD
U
Site 3
Site 2
0
-10
E
U
Q
E
-20
U
-30
Q
-20
-30
a)
a)
E
-20
a
a)
-30
U
0 -40
0 -40
0 -40
-50
-50
-50
-60
-60
0
200
400
600
mg Mn(ll)/ Kg soil
-60
0
200
400
600
mg Mn(ll)/ Kg soil
0
50 100 150 200 250
mg Mn(ll)/ Kg soil
47
Site 1
Julian day 453
Site 3
Site. 2
0
0
0
-10
-10
-10
E
E
-30
0 -40
a -30
0 -40
0 -40
-50
-50
-50
-60
-60
CL
0
-20
-20
-20
E
200 400 600 800
-a -30
E
0
Julian day 473
0
0
-10
-10
-10
E
E
0
4-
0 -40
a -30
m
0 -40
-50
-50
CL
U
-30
a)
T
-60
0
100
200
Cl)
-50
-60
0
mg Mn(ll)/ Kg soil
Site 1
E
0
CL
-20
a -30
0 -40
-60
300
100
200
0
300
Site 3
Site 2
0
0
0
-10
-10
-10
0
E
-20
L
nm
-30 IF
0
-40
0
-30
a
a
0 -40
-30
a
0 -40
-50
-50
-60
-60
0
100
200
300
mg Mn(ll)/ Kg soil
200 400 600 800
mg Mn(ll)/ Kg soil
mg Mn(ll)/ Kg soil
Julian day 487
-20
600
Site 3
Site 2
0
-20
400
200
mg Mn(II)/ Kg soil
mg Mn(ll)/Kg soil
-20
0
f
-60
0 100 200 300 400 500
mg Mn(ll)/ Kg soil
Site 1
1
E
I
-20
-50
J-
-60
0 100 200 300 400 500
mg Mn(ll)/ Kg soil
0
100
200
300
mg Mn(ll)/ Kg soil
Site 1
0E
Q
0
0
Julian day 505
Site 3
Site 2
0
0
0
-10
-10
-10
-20
E
-20
E
-30
Q
-30
Q
a)
0
(D
0
-40
-20
U
U
-40
-30
-40
-50
-50
-50
-60
-60
-60
0
100 200 300 400
mg Mn(ll)/ Kg soil
0
200
400
600
mg Mn(ll)/Kg soil
0
100
200
300
mg Mn(ll)/ Kg soil
Appendix 4:
International Degree Experience
This appendix is a summary of my experiences and observations on
Japanese research while in Japan. It is submitted for the partial fulfillment of the
requirements for the International Degree.
During my year stay in Japan from September 1995 to August 1996, I
learned much about the inner workings of the Japanese educational system, and
the research of science in Japan.
The largest difference that I observed between the United States and
Japan was the role universities played in scientific research. A large proportion
of the research in the United States, is performed by professors and their
graduate students. In Japan, however, applied research with economic benefits
is usually reserved to private research institutes, while professors usually pursue
only pure sciences which often have no immediate foreseeable economic
application.
There are several reasons for this difference between the two countries.
One reason is the source of income that professors use to supplement their
university salaries. In the United States, professors fund the summer incomes
through grants to research areas that the government or other industries have
and interest. In Japan, one of the major ways a professor would supplement his
or her income is from the commission on the sales of the textbooks to the
students who enroll in his or her class. Although it is as common for faculty in
Japan to act as consultants for the private sector as in the United States,
Japanese professors maintain an air of "educational purity."
Another reason for the difference in private sector vs. public universitiy
research appears to be the result of the methodology upon which education is
built. Students in the United States are expected to learn by working on an
original research project, thus increasing the knowledge base. However, in
Japan, the graduate student learns through an apprenticeship with the professor,
and is not necessarily expected to work on original research. In this, they are not
expected to make a large contribution to the world of science. In fact, it is
assumed that as students, they lack the knowledge to yet work on their own and
perform in the manner of their American counterparts. In order to be regarded by
science they must work under a professor for several years to slowly gain the
understanding of how science works.
Industries often place higher importance on the reputation a student's
professor or university then the student's academic record. Since it is assumed
that a good professor or university will have students that are able to learn the
tasks required of them during their career with a company.
During the last term of my stay in Japan, I was allowed an inside view of a
professor's laboratory where I spent several hours a week learning technical
Japanese from Dr. Sugiura. Much of my time was also spent learning about his
research and his scientific interests. I found Dr. Sugiura's laboratory to be run in
a manner unlike any that I have ever seen in the United States. First year
graduate students were supervised by upper level students and spent much of
their time doing the menial work of the laboratory. Sometimes they were
interrupted from their work to learn by watching upper level graduate students do
something that the lower level students had never seen or done. Likewise, if Dr.
Sugiura were to use some of the equipment, he would call on all the student to
gather around him while he worked on equipment that even upper classmen
were not allowed to use.
Although this may seem an unlikely way of doing things, as it did to me at
first, it is closely related to the Japanese ideology of education. In the American
system, the student may be essentially equal to the professor with the exception
of lacking the knowledge of the professor. It is for this knowledge and the
professors' willingness to teach the student that the student respects his or her
professor. However in Japan, this difference in knowledge puts the professor
and student on completely different levels. It is expected that the student must
do everything that he of she can to learn as much as possible from the professor.
Any responsibility is then placed upon the student to learn and not the professor
to teach.
This is idea is not restricted to formal education. It is the standard method
through which all knowledge or skill is passed from a master of an art to a
student hoping to someday attain the level of master. It is an idea deeply
ingrained in most Asian countries that have a history of strong Confucian beliefs.
It is for these reasons that industries most often hire private research
institutes to perform any research in which they are interested. And research
performed at universities is often restricted mainly to areas of pure science.