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National Environmental Research Institute • Department of Freshwater Ecology
Can we foresee the impact ofclimate change on runoff, nutrientlosses, river morphology andecology in Denmark
Brian Kronvang, Søren E. Larsen and Niels B. OvesenDepartment of Freshwater ecology
NERI, Denmark
A CONWOY contributionwww.conwoy.ku.dk
National Environmental Research Institute • Department of Freshwater Ecology
Potential impacts on the linked
catchment, river, floodplain and lake system
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National Environmental Research Institute • Department of Freshwater Ecology
Hindcasting of precipitation andriver hydrologyHypothesis• Mean annual precipitation has changed during the
last century.• River discharge will reflect these changes both
annually, seasonally and in the case of extremes(peak flows, droughts).
• A gradient in precipitation and hence changes indischarge can be expected across Denmark.
• Changes in land use during the last century (arableland, drainage, urban areas, groundwaterabstraction) could counteract or accelerate theclimate signal on river hydrology.
National Environmental Research Institute • Department of Freshwater Ecology
Investigated:
5 climate stations(red)
17 river stations(blue)
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National Environmental Research Institute • Department of Freshwater Ecology
Period CatchmentArea
(km2)Western JutlandBrede Å 1921-2001 290Ribe Å 1934-2001 675Skjern Å 1920-2001 1055Northern JutlandLindenborg Å 1925-2001 214Lindholm Å 1917-2001 106Årup Å 1936-2001 105Uggerby Å 1917-2001 153Eastern JutlandGudenå, Åstedbro 1917-2001 184Gudenå, Tvilum 1917-2001 1282Århus Å 1919-2001 119FunenOdense Å 1917-2001 302Brende Å 1918-2001 71ZealandSaltø Å 1918-2001 64Tude Å 1932-2001 148Harrested Å 1921-2001 16Suså, Holløse 1934-2001 763Åmose Å 1920-2001 292Tryggevælde Å 1917-2001 129
National Environmental Research Institute • Department of Freshwater Ecology
Other factors than climateinfluencing changes in runoff
• Land use changes during last century(drainage, urban development, agriculture,forest).
• Changes in drinking water and irrigationwater consumption.
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National Environmental Research Institute • Department of Freshwater Ecology
Daily mean discharge 1920-2001Stream Tryggevælde (Zealand)
National Environmental Research Institute • Department of Freshwater Ecology
Daily mean discharge 1920-2001Skjern river (western Jutland)
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National Environmental Research Institute • Department of Freshwater Ecology
Udvikling i årlig gennemsnitsnedbør forDanmark (øverst), samt årsafstrømningeni henholdsvis Skjern Å (midt) og Tude å(nederst).
National Environmental Research Institute • Department of Freshwater Ecology
Changes inannualprecipitationfrom 1931-60 to1961-1990
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National Environmental Research Institute • Department of Freshwater Ecology
Changes in annualprecipitation at 5climate stationsand runoff forDanish riversduring a 75 yearperiod.
*Significant(p≤0.05)
National Environmental Research Institute • Department of Freshwater Ecology
Trend i nedbør over året vedforskellige målestationer
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National Environmental Research Institute • Department of Freshwater Ecology
Trend i måneds middelafstrømningen i 10 vandløb
National Environmental Research Institute • Department of Freshwater Ecology
Trend i måneds maksimumafstrømningen i 10 vandløb
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National Environmental Research Institute • Department of Freshwater Ecology
Trend i måneds minimumsafstrømningen i 10 vandløb
National Environmental Research Institute • Department of Freshwater Ecology
Hindcast 1920-2001 (rød) ogfremskrivning (blå) 2001-2080 for ændringi måneds middel afstrømning i to vandløbfor perioden 1920-
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National Environmental Research Institute • Department of Freshwater Ecology
River morphology and sedimenttransportHypothesis
• River morphology will adjust to changes in climateand hydrology.
• Adjustments will take place during and for a periodfollowing climate and hydrological changes beforethe river again will be in a dynamic equilibrium.
• Sediment transport will increase due to highererosion and transport capacity/competence.
• Bank and bed erosion will increase.• Substratum composition will change.
National Environmental Research Institute • Department of Freshwater Ecology
Regime models for undisturbed Danishstreams in downstream directionStream widthMoraine landscape: w = 4.83Q0.61
Outwash plain: w = 5.59Q0.50
Stream depthMoraine landscape: d = 0.52Q0.47
Outwash plain: d = 0.60Q0.39
Current velocity:Moraine landscape: v = 0.40Q-0.08
Outwash plain: v = 0.30Q0.12
Mernild (2002) MSc Thesis, University of Copenhagen.
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National Environmental Research Institute • Department of Freshwater Ecology
Suspended sediment response toclimate change: an example
Q in m3/s and Css in mg/l
Strongly rising stage: Css = 80 • Q1.72
Winter (Oct-May): Css = 12 • Q1.37
Summer (June-Sept.): Css = 20 • Q0.99
Kronvang (1992) Water Research 26(10).
National Environmental Research Institute • Department of Freshwater Ecology
Nutrient losses
Hypothesis
• Nitrogen leaching will increase due to highermineralization and percolation of water through theroot zone.
• Phosphorus leaching will increase due to highermineralization and percolation of water through theroot zone.
• Phosphorus loss will increase due to increase inoverland flow (PP and DP).
• Phosphorus loss will increase due to increase inbank erosion.
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National Environmental Research Institute • Department of Freshwater Ecology
Climate change impact onnitrogen leaching from root zone
0
20
40
60
80
100
120
140
0 200 400 600 800
Annual percolation of water through root zone (mm)
An
nu
al le
ach
ing
of
nit
rog
en
(kg
N/h
a)
Western Jutland
12 kg N/haIslands
12 kg N/ha
National Environmental Research Institute • Department of Freshwater Ecology
Climate change impact on diffusetotal nitrogen loading of streams
0
5
10
15
20
25
30
35
0 200 400 600 800
Runoff (mm)
Dif
fuse
to
tal N
itro
gen
loss
(k
g N
/ha)
Sandy soilLoamy soil
6.5 kg N/ha4.9 kg N/ha
12
National Environmental Research Institute • Department of Freshwater Ecology
Climate change impact on diffuse totalphosphorus loading of streams
0
0,5
1
1,5
2
2,5
0 100 200 300 400
Annual storm runoff (mm)
Dif
fuse
to
tal P
ho
sph
oru
s lo
ss (
kg P
/ha)
Sandy soilLoamy soil
0.15 kg P/ha
0.25 kg P/ha
National Environmental Research Institute • Department of Freshwater Ecology
Climate change impact on diffusedissolved P loading of streams
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0 200 400 600 800
Annual Runoff (mm)
Dif
fuse
dis
solv
ed in
org
nai
c P
-lo
ss (
kg P
/ha) Western Jutland
0.111 kg P/ha
Islands
0.059 kg P/ha
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National Environmental Research Institute • Department of Freshwater Ecology
Climate change impact on nutrient retention
National Environmental Research Institute • Department of Freshwater Ecology
Lake: 100 ha & 2 m average depth
catchment area = 1000 ha
Q = 400 mm
Q = 200 mm
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National Environmental Research Institute • Department of Freshwater Ecology
Stream ecologyHypothesis• The changing hydrological regime in streams will impact the
spatial and temporal extent of physical habitats and henceinfluence the biotic conditions.
• The more extreme hydrological conditions in streams, bothhigh flow and low flow, will create larger physcial disturbanceswith adverse impacts on the biological structure and diversity.
• Rising stream water temperature will impact the speciescomposition of macrophytes, invertebrates and fish in Danishstreams.
• Indirect impacts on stream ecosystems will also occur causedby changes in catchment pressures (substances), concentrationof dissolved oxygen in stream water, etc.
National Environmental Research Institute • Department of Freshwater Ecology
River, lakes and floodplains
Research under the CONWOY project - WP2• Hindcast of changes in longer time series of daily discharge in a
number of Danish rivers covering the west/east gradients inlandscape and climate.
• Forecasting of changes in river discharge by applyinghydrological models (NAM/MIKE11; MIKE-SHE/MIKE11.
• Analysis of changes in sediment mobilisation and transportapplying erosion models and development of statistical modelsbased on existing sediment concentration data.
• Analysis of changes in nutrient losses applying statistical anddeterministic models.
• Analysis of changes in sediment and nutrient retention applyingcoupled hydrodynamic and nutrient retention model.
• Dating of sediment cores to analyse historical changes insedimentation rates linked to climate/land use changes.