Nutrient Transport Modelling in the Daugava River Basin - DiVA Portal

all cultivated land will have winter crops. In order to simulate such a scenario it wouldbe necessary to divide cultivated land into two categories; cultivated land with wintercrops and cultivated land without winter crops. This way it would be easier to handlescenarios where new agricultural policies affect management practices.6. CONCLUSIONSThe main conclusions that can be drawn from the study are:• Yearly nitrogen loads are fairly well estimated by the model during thecalibration period, but since the loads during the validation period generallywere higher than during the calibration period it was not possible to validate theability of the model to predict nitrogen loads.• The model significantly underestimates phosphorus loads. Possible reasons forthis are that septic systems, which were not included in the model, are a maincontributor to phosphorus loads and that reported point sources areunderestimated.• Modifications of the model need to be done in order to use the model for longtermpredictions. As an example it should be possible to vary the groundwaternutrient concentration with time.• The lack of good quality data makes it difficult to model nutrient loads in partsof the Baltic Sea basin. It should be of high priority to make data more readilyavailable and to create more homogeneous databases for the region. In order todo this successfully cooperation between all the countries in the region isneeded.22