For more than 25 years mapping of vulnerable areas to nitrate have been important in Denmark, where more than 60 % of the area are used for intensive agriculture. In the beginning focus was on regulation of nitrate in recharge areas and the protection of ground waters but by the EU Water Framework Directive, the mapping will so be used in the regulation of nitrate to surface waters. Key elements in the vulnerability mapping of nitrate are the redox status of the soils and sediments, including the amount and distribution of reduced compounds that can reduce the surplus of nitrate. These analyses may include measurements of reduced compounds like e.g., pyrite, total organic matter, and ferrous iron, and/or measurement of the total amount of reduced compounds.

For the measurement of the total amount of reduced compounds, a acid solution of cerium(IV) sulphate is used as described by Ernstsen et al. (2005). The method has now been tested on many types of soils and sediments and with very promising results. The presentation will give more detail about the cerium-method, the use and limitations, related to mapping on a scale of cm to km.    

References

Ernstsen, V. , Jørgensen, N. and C.R. Lynge (2005). Method for analyse of reduced compounds  in sediments (in Danish). Miljøprojekt, Nr. 1024. Ministry of Environment, Denmark.