Skalaproblematikk. Tar vi de riktige valg? Har vi forstått prosessene? Hvorfor bedres ikke vannkvalitet tross tiltak JOHANNES DEELSTRA, PER STÅLNACKE Bioforsk Soil and Environment Division, Norway.
Innhold/temaer som tas opp Skala problematikk Hydrologi og nedbørsfelt størrelse Stømningsveier Effekter av arealbruk, gjødsling, topografi, mm Klima Andre NHR2010-Stavanger
Østersjøen Verdens sykeste hav Østersjøen En kvart blir karakterisert som død hav. Hvorfor?? Jordbruket bidrar mye med næringsstoffer NHR2010-Stavanger
Large drop in commercial fertiliser use in Eastern Europe (60-90%) 140 Latvia Nitrogen fertiliser application (kg/ha) 120 100 80 60 40 20 0 1961 1966 1971 1976 1981 1986 1991 1996 NHR2010-Stavanger Hva var effekten av nedgang i gjødselbruk
Nitrogen runoff Overall statistically significant downward trend for nitrogen in 20 stations for Estonia No downward trend for Latvia Phosphorus runoff No clear trends for phosphorus in Estonia. (except in four rivers) Clear downward trends in Latvia NHR2010-Stavanger
Between catchment variability in N-losses (5-year mean) from 35 small agricultural catchments (12 to 2000 ha) NHR2010-Stavanger Hvorfor disse forskjeller? Er det på grunn av landbrukspraksis, gjødsling, mm strømningsveier grøftedistans topografi Vagstad, Stålnacke et al., (2004)
Jordtap og tiltak i landbruk, høsthvete, Øsaker. Rute 2: Høstharvet + sådd høstkorn SS-kons: 1110 mg/l Rute 3: Direktesådd høstkorn SS-kons: 5 mg/l 2 3 4 Rute 4: Høstpløyd + sådd høstkorn SS-kons: 5820 mg/l 16.09.04-05.10.04 NHR2010-Stavanger (Foto: R. Skjevdal) 105 mm nedbør (16 sept- 5 okt sådato : 10 Sept
Skuterud, soil tillage status 31. December 100 % 80 % sådd harvet 60 % pløyd 40 % 20 % stubb med fangvekst stubb 0 % eng 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Trend analyses on TP loss, Skuterud/Mørdre Ruteforsøk viser klare effekter av tiltak Hvorfor måler vi ikke effekter av tiltak? Skala???( rute forsøk -> nedbørsfelt) NHR2010-Stavanger environmental science & policy 11 (2008)
Avrenning og tap av næringsstoffer avr(mm) SS TP TN % dager 50 26 12 16 23 90 118 66 80 106 100 365 365 365 365 Skuterud nedbørsfelt (4.5 km 2 ) Utfordringer når det gjelder vannprøvetaking
Avrenning og tap av næringsstoffer Lena (181 km 2 ) runoff TN TP % dager 50 38 38 24 90 174 166 132 100 365 365 365 Skuterud (4.5 km 2 ) runoff TP TN % dager 50 26 16 23 90 118 80 106 100 365 365 365
Karakteristisk for mindre nedbørsfelter er den store døgnvariasjon i avrenning, fraværende i store nedbørsfelt Ting skjer veldig fort i mindre felt
spec. disch 1 catchment day hr Räpu 0.6 0.7 Rägina 0.4 0.5 Mellupite 1 1.2 Skuterud 2.9 5.7 Mørdre 1.7 2.8 Kolstad 1.4 2.4 Høgfoss 1.3 1.5 Lena 1.3 1.5 1 specific discharge (l s -1 ha -1 ); Spesifikk avrenning og skala In mindre Norske nedbørsfelter, stor dag variasjon i vannføring. Betydelig mindre variasjon i store nedbørsfelt Scale issue!!!! Specific discharge, calculated on average daily and hourly discharge values respectively for Skuterud(4.5 km^2) and Høgfoss(300 km^2) High resolution data important for design effects of climate change
Hydrological pathways and erosion. Runoff generation caused by freeze/thaw cycles in combination with snowmelt/precipitation How will this develop under climate change? Increased freeze/thaw periods?
Winter/snowmelt Winter runoff (Øygarden, 2000) January 30 Runoff: 25 mm Soil loss: 2 kg ha - 1 January 31 Runoff: 77 mm Soil loss: 3 050 kg ha -1
Avrenning fra nedbørsfelter Dominerende strømningsveier i et nedbørtsfelt (jordbruk) Overflate avrenning Grøfteavrenning Bidrag grunnvannet NHR2010-Stavanger
Avrenning og tap av næringsstoffer
Variation in discharge can be expressed through a flashiness index, showing the rate of change dag; FI day n q i i= 1 = n i= 1 q q i i 1 pathlength time (døgn variasjon); n FI 1 hr i= = n i q q i hr NHR2010-Stavanger Baker et al. 2004. Journal of the American Water Resources Association 40: 503 522
Flashiness index, subsurface drainage and scale Size Size(ha) (ha) Fihr Fihr Fiday Høgfoss Mørdre 29500 680 0.40 1.54 0.54 0.24 Skuterud Vandsemb dr 450 5 1.84 1.47 0.64 0.57 Mørdre 680 1.54 0.54 Vandsemb Lena Kolstad dr 18100 5308 1.47 0.47 0.94 0.24 0.29 0.64 Lena Kolstad Bye 18100 3084 0.47 0.94 0.79 0.29 0.37 0.24 Kolstad 308 0.94 0.29 Bye Berze Mellupite riverc. 85100 4964 0.79 0.67 0.15 0.37 Mellupite Berze Mellupite c. c. dr. 964 368 12 0.67 1.10 0.51 0.37 Mellupite dr. 12 1.10 0.51 Berze Kasari Berze river c. 85100 264000 368 0.37 0.15 Berze Räpu Berze c. dr 368 2550 76.6 0.30 0.17 0.31 0.37 Berze Rägina dr 76.6 2130 0.30 0.18 0.31 Kasari 264000 0.15 Räpu 2550 0.30 0.17 Rägina 2130 0.30 0.18 1.Based on FI, subsurface drainage systems might have a significant influence on runoff generation (complicated by upscaling, share of non-arable land, others) 2.The size of the catchment is important. The reduction in FI can indicate retention potential. 3.A high FI -> low retention = low nutrient retention (water inn -> water out). 4.Small Norwegian catchments show higher FI compared to Baltic catchments. Reasons; soils, topography subsurface drainage systems/intensity play a major role(?). Norway; L = 8 m; Baltic; L= 20 25 m
Can the FI say something about nutrient and soil loss? Comparison of Estonian and Norwegian catchments Catchment TN-loss TP-loss (kg ha -1 ) (kg ha -1 ) FIhr Skuterud (Nor) 46.3 2.4 1.84 Mørdre (Nor) 21 1.6 1.54 Rägina (Est) 7.9 0.2 0.30 Räpu (Est) 6.7 0.2 0.30 Deelstra and Iital, 2008. Boreal Environment Research
Subsurface drainage systems in agriculture Why do we need them? Artificial drainage necessary because of poor natural drainage conditions Optimal conditions in the rootzone for crop growth Facilitate land preparation in spring/autumn Reduces surface runoff, erosion/p-loss However at the same time a highway for nutrient transport bad functioning subsurface drainage systems can lead to the release of climate gas (N 2 O) drain groundwater level NHR2010-Stavanger
Subsurface drainage systems, an example of the highway Vandsemb, 1992-2004 surface subsurface. N-loss (kg/ha) 2 22 P-loss (kg/ha) 0.6 0.5 SS(kg/ha) 470 90 Runoff (mm) 126 202 Dominating soil; silt Drain spacing, L = 8 10 m Drain depth, d = 0.8 1.0 m bss. Bye, 1994-2007 surface subsurface N-loss (kg/ha) 1.1 29 P-loss (kg/ha) 0.3 0.04 SS(kg/ha) 220 20 Runoff (mm) 14 165 Dominating soil; moraine Few suspended solids through subsurface drainage systems. However, what about clay soils? drain groundwater level
Summarising Small agricultural catchments show in general large diurnal variations in discharge. Factors playing a role seem to be Subsurface drainage system intensity Soils Topography Large catchments show less variation in discharge while in addition having a low FI compared to smaller catchments Time resolution is important to take into consideration, especially in small catchment, important for 1)design purpose, 2)explain nutrient loss processes Understanding the hydrology is important to be able to implement the right mitigation measures against nutrient and soil loss, to deal with the effects of climate change on hydrology and nutrient loss (fe share of subsurface runoff in total runoff/increase drainage intensity?) NHR2010-Stavanger
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