Effect of organic carbon on release
of phosphorus from agricultural soil
settled on anoxic bottom
is regulated by
coupled cycles of carbon, iron, sulphur and phosphorus
Jouni Lehtoranta
SYKE/Marine Research Centre
15.6.2017
External P loading - from calsium to iron
Phosphorus fertilizers from
apatite
About 20% of the phosphorus
is consumed as food, 80% is lost
3km
150m deep
Diffuse loading
Point source
Waste waters
J. Lehtoranta
Sergey Gratsev
Kuva: Sirkka Tattari
Paimionjoki
Kok. P
250 µg l−1
PP
DRP
DUP
Lepsämänjoki
Kok. P
150 µg l−1
PP
DRP
Yläneenjoki
Kok. P
160 µg l−1
PP
DRP
DUP
What happens to phosphorus bound to field soil when it is eroded
to coastal waters and is settled on the anoxic bottom waters
with different trophy?
Soil erosion
Pathways of organic matter oxidation
in bottom sediments
Reduction reaction
Formula
Depth in sediment
oxic
Aerobic respiration
CH2O + O2  CO2 +H2O
mm
anoxic
Denitrification
5CH 2O + 4NO3- + 4H+ 5CO2 + 2N2 + 7H2O
mm
anoxic
Manganese reduction
CH2O + MnO2 + 4H+ CO2 + 2Mn2+ + 3H2O
cm
anoxic
Iron reduction
CH2O + 4FeOOH + 8H+ CO2 + 4Fe2+ + 7H2O
cm
anoxic
Sulfate reduction
2CH 2O + SO42- + 2H+ 2CO2 + H2S + 2H2O
m
anoxic
Methanogenesis
CH3COO- +CH4 + CO2
m
HCO3- + 4H 2 + H+ CH4 + 3H2O
Canfield and Thamdrup 2009, Geobiology 7: 385-392
One element is missing Phosphorus
J. Lehtoranta
Pathways of organic matter oxidation
oxic
Reduction reaction
Formula
Depth in sediment
Aerobic respiration
CH2O + O2  CO2 +H2O
mm
anoxic
Geobacter
metallireducens
Denitrification
5CH 2O + 4NO3- + 4H+ 5CO2 + 2N2 + 7H2O
anoxic
Manganese reduction
CH2O + MnO2 + 4H+ CO2 + 2Mn2+ + 3H2O
cm
anoxic
Iron reduction
CH2O + 4FeOOH + 8H+ CO2 + 4Fe2+ + 7H2O
cm
anoxic
Sulfate reduction
2CH 2O + SO42- + 2H+ 2CO2 + H2S + 2H2O
m
anoxic
Methanogenesis
CH3COO- +CH4 + CO2
m
Desulfovibrio
vulgaris
mm
HCO3- + 4H 2 + H+ CH4 + 3H2O
Field soil Fe(III) is sensitive towards redox-processes in mineralization
Phosphorus starts react on redox-reactions
J. Lehtoranta
Significance of sulphate
Lehtoranta, Ekholm, Pitkänen 2009. Ambio 38:303-308
Lehtoranta & Ekholm 2013 Vesitalous 2: 40-42
Up-stream thinking: Recipient is anaerobic brackish bottom sediment
and eroded field soil settles and faces anaerobic microbial processes there
Standard field soil
Sandy clay
(60–1000 mg )
80 ml filtered
Gulf of Finland water
Incubation:
• At dark
• (a) +10 °C, (b) +8 °C
• (a) 308 d, (b) 745 d
Natrium acetate
(0.375–24 mg C)
Pasi Valkama
10 µl sediment
Lehtoranta, J., Ekholm, P.,
Wahlström, S. Tallberg, P. and Uusitalo, R.
2015 AMBIO 44 Suppl 2: 263–273
Not redoxsensitive
Al
µg/L
Ca
mg/L
K
mg/L
Na
mg/L
Si
mg/L
P
mg/L
Gulf of
Finland
water
3
67
47
830
1.45
0.04
No added C
3
78
43
843
2.95
0.72
Added C
3
70
45
887
2.61
1.81
Redox-sensitive
Mn
Fe
mg/L mg/L
SO4
S2mg/L mg/L
Gulf of Finland
water
0.01
0.01
320
0
No added C
0.83
3.07
318
0
Added C
0.37
0.14
193
8.78
Added C
No added C
Coupling of carbon, sulphur, iron and phosphorus
4
SO4 4
(mM) 3
2
1
0
y = -24x + 3,7
R² = 0,91
SO42- (mM)
3
2
0,00
0,05
0,10
0,15
TP (mM)
1
0
0
Fe 0,14
(mM) 0,12
0,10
Fe
10
1,6
HS1,4 (mM )
1,2
1,0
0,8
0,6
0,4
0,2
0,0
HS-
0,08
0,06
0,04
0,02
0,00
0
10
20
C (mg)
30
C (mg)
20
30
Dissolution of Fe and P
P
Fe
P
P
H2S, HS-
Mn2+ Fe2+
FeS
High dose organic C
Small amount of organic C
Lehtoranta, Ekholm, Wahlström, Tallberg and Uusitalo 2015
AMBIO 44 Suppl 2: 263–273
O2
NO3,
Mn(IV),
Fe(III),
SO4
CO2
Photo: Ilkka Heikkinen, Inkoo
Seija
Hällfors
Conclusions
• Iron oxides offer ecosystem service for aquatic
systems by binding phosphorus originating from
apatite
• Level of organic carbon together with the availability
of iron and sulphate regulate the release of field soil
bound phosphorus
• Coupling of carbon, sulphur, iron, and phosphorus
driven by microbial processes in sediments challenge
present water protection measures
P
Phosphorus
30.974
6/16/2017
Petri Ekholm
Photos: Ekholm
15
Lay out: Erika Varkonyi/SYKE
16