Nutrient Transport Modelling in the Daugava River Basin - DiVA Portal
Nutrient Transport Modelling in the Daugava River Basin - DiVA Portal
Nutrient Transport Modelling in the Daugava River Basin - DiVA Portal
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period. Nitrogen loads are underestimated for this period, especially dur<strong>in</strong>g peak flows.When it comes to phosphorus <strong>the</strong> model greatly underestimates monthly loads for both<strong>the</strong> calibration period and <strong>the</strong> validation period.a) Streamflow, calibration periodb) Streamflow, validation periodReportedModelledcm/monthton/month121086420Apr9314000120001000080006000400020000Apr94Apr95Apr96Apr97Apr98c) Nitrogen load, calibration periodApr99cm/monthton/month12108642025000200001500010000Apr80Apr8150000Apr82Apr83Apr84Apr85Apr86Apr87d) Nitrogen load, validation periodApr88Apr89Apr93Apr94Apr95Apr96Apr97Apr98Apr99Apr80Apr81Apr82Apr83Apr84Apr85Apr86Apr87Apr88Apr89e) Phosphorus load, calibration periodf) Phosphorus load, validation periodton/month10008006004002000ton/month6005004003002001000Apr93Apr94Apr95Apr96Apr97Apr98Apr99Apr80Apr81Apr82Apr83Apr84Apr85Apr86Apr87Apr88Apr89Figure 6. Reported and modelled values of monthly means of streamflow,nitrogen loads and phosphorus loads from <strong>the</strong> <strong>Daugava</strong> <strong>River</strong> for <strong>the</strong> calibration period(19932000) and <strong>the</strong> validation period (19801990).The model output is monthly means of loads and streamflow, but s<strong>in</strong>ce <strong>the</strong> purpose of<strong>the</strong> model is to estimate longterm loads it is of <strong>in</strong>terest to see how well <strong>the</strong> modelpredicts yearly means. In figure 7 <strong>the</strong> reported and modelled yearly means ofstreamflow and nutrient loads are presented. The model seems to estimate yearlystreamflow quite well, both for <strong>the</strong> calibration period and <strong>the</strong> validation period. Thereare, however, tendencies towards a higher variance for modelled yearly flows than forobserved yearly flows. Yearly nitrogen loads are well estimated by <strong>the</strong> model for <strong>the</strong>calibration period, but for <strong>the</strong> validation period nitrogen loads are underestimated.15