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Explaining the recent changes in
agricultural nutrient load in Finland
Katri Rankinen, Petri Ekholm, Hannu
Rita, Heidi Sjöblom, Ljudmila Vesikko
21.7.2015
Petri Ekholm, SYKE
Research question
Is it possible to estimate
• quantity
• development
• contributing factors
of agricultural nutrient load based on
national river monitoring data?
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Data
● National monitoring data from 22 rivers
○ Southern and western Finland
○ ⅓ of agricultural land in Finland
○ Total P, Total N, Flow
● Years 1985–2006 divided into 4 periods
○ I = 1985–1989
○ II = 1990–1994
○ III = 1995–1999, 1st Programme period
○ IV = 2000–2006, 2nd Programme period
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Petri Ekholm, SYKE
CTN
(µg l−1)
Approach
Step 1: Estimating daily concentrations, C, from flow, Q
”Pointsource
component”
C a
b
 cQ
Q
”Basic component”
Q
(m3 s−1)
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Petri Ekholm, SYKE
Approach
Step 2: Riverine nutrient fluxes, L
Ld 
C  Q  86400
1000000
Ly
Step 3: Source apportionment
L Agr  ( L y  L Mun  L Ind  L Pop  L For )  Area
Step 4: Explaining spatial differences and temporal changes
L Agr = β1 X 1 j + β 2 X 2 j+...  β 2 X 2+ α
Step 5: Analysis of development: 1985-2006 flow used for all
the periods
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Factors related to ”agricultural” P load
(LP, kg km−2 y−1)
1.
2.
3.
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●
●
LP = 1.6 × Field-% − 3.6, r2 = 0.57
LP = 1.4 × Field-% − 2.2× Lake-% − 9.0, r2 = 0.70
LP = 1.4 × Field-% + 1.7× Lake-% + 92 × Runoff − 22, r2 = 0.73
Increase in LP : soil-test P, r2 = 0.81
Decrease in LP : fallow, r2 = 0.74
No effect on LP : P in manure
Regional analysis
● Southern Finland: Grassland appears to decrease LP
● Western Finland: Grassland increases LP
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Regional differences
Southern Finland
● P losses high and correlate with TSS losses
Western Finland
● P losses, and correlation with TSS losses, lower
● Soil P decreased from Period III to Period IV
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Factors related to ”agricultural” N load
(kg km−2 y−1)
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●
●
LN = 16 × Field-% −20 × Lake-% + 900 × Runoff, r2 = 0.87
Increase in LN : N in manure, r2 = 0.88, fields on organic soils , r2 = 0.88
No effect on LN : N deposition
Regional analysis
● Western Finland: Grassland, soil temperature, N balance increases LN
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Change in ”agricultural” load 1985–2006
Phosphorus
Nitrogen
The Kalajoki
The Perhonjoki
No change
Western Finland
Southern Finland
No change
No data
No data
Change in ”agricultural” load 1985–2006 (2011)
The Kalajoki
3658 km2
Lakes 1.9%
Fields 15%
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Petri Ekholm, SYKE
Conclusions
Approach
● Allows the use of national monitoring data
● Gives a several-year average load for a larger area
● Relatively robust, if sampling strategy remains unchanged, sensitive
to outliers
● Cannot separate agricultural load from natural background
”Agricultural” load
● P load decreased (especially in Ostrobothnia), N load increased in
2000s
● P: fertilizer use and animal numbers decreased
● N: increase in temperature, clearing of new field, manure handling?
The analysis is currently being expanded in the project
● Larger number of sites
● Larger set of explaining variables
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