Wt. Sloan et al., A SIMPLE-MODEL OF STREAM NITRATE CONCENTRATIONS IN FORESTED AND DEFORESTED CATCHMENTS IN MID-WALES, Journal of hydrology, 158(1-2), 1994, pp. 61-78
A model is developed specifically for simulating the nitrate concentra
tions in a stream at approximately weekly intervals in an upland fores
ted and a moorland catchment. It is constructed on the basis of observ
ed nitrate concentrations in rain water and in two streams, the Hafren
and the Hore, at Plynlimon, Mid-Wales, where long data records exist.
The Hore catchment has recently undergone extensive deforestation. A
simple regression model relating temperature to stream nitrate concent
rations was capable of simulating the seasonal fluctuations in nitrate
concentration observed in the Hafren. However, this ignores the influ
x of nitrate through wet deposition and is incapable of simulating lan
d-use change. The regression model was developed into a simple dynamic
model which includes a deposition term and a biomass indicator. The e
xtended Kalman filter algorithm was used to estimate the optimum value
s of the parameters and to assess the model structure. The model was a
pplied to both catchments, and the fit between observed and simulated
nitrate concentrations at the Hafren was good. At the Hore, the model
was able to capture the major changes in nitrate concentration through
the deforestation and replanting phases although detailed short-term
dynamics were not well represented. Finally, the model is related, spe
culatively, to processes which are known to occur in most catchments.
This simple model is intended as a step towards the development of sim
ilar but more comprehensive catchment models of stream nitrogen dynami
cs.