Hydrological processes, nutrient and soil loss in small agricultural catchments, models and the WFD

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Hydrological processes, nutrient and soil loss in
small agricultural catchments, models and the WFD
Johannes Deelstra Bioforsk, Norway.
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What did we do and why?

• What is so special with hydrology in small
  catchments when compared to larger catchments?
• Is hydrology in countries in Northern and Western
  Europe different from that in Southern Europe?
• Do smaller catchments need any special
  consideration when considering hydrology, soil -
  and nutrient losses?

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Location of catchments
Agricultural environmental monitoring programme
(JOVA), similar programs in Latvia and Estonia
Quantifying runoff, nutrient and soil loss
Catchments represent different agricultural
practices and climate
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Some catchment characteristics
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Runoff and nutrient loss
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Characteristic for runoff generation is strong
seasonality in runoff
During growing season very little runoff
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Especially for Norwegian catchments, yearly
runoff and nutrient loss is generated in only
limited number of days
An example for the Skuterud catchment, Norway
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Subsurface drainage and nutrient and soil loss
Subsurface drainage systems contribute
significantly in nutrient loss
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Characteristic for many catchments is the large
in-day variation in runoff
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This variation can be expressed through a
flashiness index, showing the rate of change
- based on average daily discharge values - based
on hourly discharge values (in-day variation)
day
hour (in- day variation)
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Which factors might affect runoff generation?

• The size of the catchment is important
• In addition are soil types important
• The share of agricultural land is important
• It is believed that subsurface drainage systems
  have a significant influence on runoff generation

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Runoff generation, scale and subsurface drainage
Has subsurface drainage an impact on soil loss?
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Runoff generation processes

• In humid, temperate climates, surface runoff is
  often generated through saturation from below
• One of the reasons for subsurface drainage
  systems in many European countries is to drain
  excess water from the rootzone, thereby
  preventing surface runoff
• In this case also erosion generation processes
  need special consideration
• Especially in small catchments, large variation
  in runoff over short time periods occur, this
  most likely having a large effect on nutrient and
  soil loss (energy)
• An additional aspect to be taken into
  consideration is the winter, with freezing soils,
  snow development and freeze/thaw cycles
• To be able to give advice on best management
  practices, among others simulation models,
  capable to these handle processes are needed.

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Do we have models to deal with those situations

• Several models are testet in a Norwegian
  catchment
• SWAT (water balance, nutrient and soil loss)
• The SWAT model has also been applied in Norway as
  part of EuroHarp and Striver, two EU projects
  (large scale)
• The model is tested now in Skuterud
• DRAINMOD, developed at NCSU (Skaggs) simulating
  subsurface drainage/surface runoff/nitrogen
  dynamics
• HBV model (hydrology)
• INCA model (hydrology, nutrient dynamics)
• SOIL/SOIL_NO and COUP (hydrology,nitrogen) have
  been tested (developed by SLU)
• WEPP (Water erosion prediction model) tested on
  small plots

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Hydrological processes, nutrient and soil loss in
small agricultural catchments, models and the WFD

• Only when we have models which simulate the
  dominating flow generating processes and there
  affect on nutrient and soil loss under our
  prevailing climatic conditions we can be
  successful in implementing the WFD