Explaining the recent changes in agricultural nutrient load in Finland Katri Rankinen, Petri Ekholm, Hannu Rita, Heidi Sjöblom, Ljudmila Vesikko

Research question Is it possible to estimate quantity development 29.4.2019 Petri Ekholm, SYKE Is it possible to estimate quantity development contributing factors of agricultural nutrient load based on national river monitoring data?

Data National monitoring data from 22 rivers 29.4.2019 Petri Ekholm, SYKE 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

”Diffuse-source component” CTN (µg l−1) Approach Step 1: Estimating daily concentrations, C, from flow, Q 29.4.2019 Petri Ekholm, SYKE ”Point- source component” ”Diffuse-source component” ”Basic component” Q (m3 s−1)

Approach Step 2: Riverine nutrient fluxes, L 29.4.2019 Petri Ekholm, SYKE Step 3: Source apportionment Step 4: Explaining spatial differences and temporal changes Step 5: Analysis of development: 1985-2006 flow used for all the periods

Factors related to ”agricultural” P load (LP, kg km−2 y−1) 29.4.2019 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 Petri Ekholm, SYKE

Regional differences Southern Finland 29.4.2019 Petri Ekholm, SYKE 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

Factors related to ”agricultural” N load (kg km−2 y−1) 29.4.2019 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 Petri Ekholm, SYKE

Change in ”agricultural” load 1985–2006 Phosphorus Nitrogen The Kalajoki The Perhonjoki No change Western Finland No change No data Southern Finland No data

Change in ”agricultural” load 1985–2006 (2011) The Kalajoki 3658 km2 Lakes 1.9% Fields 15%

Conclusions Approach Allows the use of national monitoring data 29.4.2019 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 Petri Ekholm, SYKE