Effects of variants of target surpluses on the quality of surface water in the Netherlands

Publication

This study explores the effects of a number of variants for target N and P surpluses on the ecological state (eutrophication) of surface waters for the purpose of informing policy-makers.

Surpluses of N and P indcate the difference between inputs via purchased fertilisers, animal feed and animal manure, and N and P outputs via crop and animal products as well as export of animal manure. Target surpluses of N from 300 to 40 kg per ha per year, depending on soil type and land use, and of P from 40 to 1 kg P2O5 per ha per year (equivalent to 17.5 to 0.4 kg of P per ha per year), were examined.

A sequence of models has been used to explore the effects of variants of target N and P surpluses on the discharge of N and P from agricultural activities to surface waters, and on N and P concentrations in rivers, freshwater lakes, streams, ditches and the marine coastal zone. The results indicate that lowering target N and P surpluses will decrease the discharge of N and P from agricultural activities into surface waters and also the N and P concentrations in these waters. However, the mean decrease in N and P concentrations in surface waters is relatively low (less than proportional), given the relatively high mean decreases in target N and P surpluses in agriculture.

This relatively small improvement has been attributed to such factors as: (i) surpluses of N decrease less on average in areas were surface-water loading is large, (ii) P discharge to surface waters is primarily determined by the soil P status and groundwater level, and only indirectly by P surplus, and (iii) seepage of N- and P-rich seepage water from marine sub-soils, contribute greatly to surface-water loading. Lowering target N and P surpluses combined with additional measures (like dredging P-rich sediments, flushing ditches with water low in nutrients, and decreasing discharges from other sources) is argued to be necessary to improve the ecological state of surface waters.

Authors

Oenema O , Liere E van , Stam GJ , Blois CJ de , Prins TC (eds)

Specifications

Publication title
Effects of variants of target surpluses on the quality of surface water in the Netherlands
Publication date
30 September 2002
Publication type
Publication
Publication language
Dutch
Product number
90900