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Integrated Nitrogen Catchment model (INCA) was applied successfully to simulate
nitrogen concentrations in the River Lee, a northern tributary of the River
Thames for 1995-1999. Leaching from urban and agricultural areas was found to
control nitrogen dynamics in reaches unaffected by effluent discharges and
abstractions; the occurrence of minimal flows resulted in an upward trend in
nitrate concentration. Sewage treatment works (STW) discharging into the River
Lee raised nitrate concentrations substantially, a problem which was compounded
by abstractions in the Lower Lee. The average concentration of nitrate (NO3)
for the simulation period 1995-96 was 7.87 mg N l-1. Ammonium (NH4)
concentrations were simulated less successfully. However, concentrations of
ammonium rarely rose to levels which would be of environmental concern.
Scenarios were run through INCA to assess strategies for the reduction of
nitrate concentrations in the catchment. The conversion of arable land to
ungrazed vegetation or to woodland would reduce nitrate concentrations
substantially, whilst inclusion of riparian buffer strips would be unsuccessful
in reducing nitrate loading. A 50% reduction in nitrate loading from Luton STW
would result in a fall of up to 5 mg N l-1 in the reach directly
affected (concentrations fell from maxima of 13 to 8 mg N l-1 ,
nearly a 40 % reduction), whilst a 20% reduction in abstractions would reduce
maximum peaks in concentration in the lower Lee by up to 4 mg l-1
(from 17 to 13 mg N l-1, nearly a 25 % reduction),.
Keywords: modelling, water quality, nitrogen, nitrate, ammonium, INCA,
River Lee, River Thames, land-use. |