|
The mean annual transfer (loss and retention) of nitrogen in a river system was estimated using a
conceptual approach based on water surface area and runoff. Two different approaches for the calculation
of water surface area were applied to determine riverine nitrogen retention in four European catchments,
ranging between 860–14,000 km2 in area, and differing considerably in the proportion and distribution of
surface waters, specific runoff and specific nutrient emissions. The transfer rate was estimated sequentially
as either the mean value for the total catchment, on a sub-catchment scale, or considering the distribution of
water surface area within a sub-catchment. For the latter measure, nitrogen retention in larger lakes was
calculated separately. Nitrogen emissions modelled with MONERIS and HBV-N were used to calculate
nitrogen river loads and compare those with observed loads. Inclusion of the proportion of water area within
a sub-catchment improved modelled results in catchment with large lakes in sub-catchments, but not where
there was a homogenous distribution of surface waters among sub-catchments.
|
