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  • Print publication year: 2011
  • Online publication date: May 2011

13 - Nitrogen flows from European regional watersheds to coastal marine waters

from Part III - Nitrogen flows and fate at multiple spatial scales

Summary

Executive summary

Nature of the problem

Most regional watersheds in Europe constitute managed human territories importing large amounts of new reactive nitrogen.

As a consequence, groundwater, surface freshwater and coastal seawater are undergoing severe nitrogen contamination and/or eutrophication problems.

Approaches

A comprehensive evaluation of net anthropogenic inputs of reactive nitrogen (NANI) through atmospheric deposition, crop N fixation, fertiliser use and import of food and feed has been carried out for all European watersheds. A database on N, P and Si fluxes delivered at the basin outlets has been assembled.

A number of modelling approaches based on either statistical regression analysis or mechanistic description of the processes involved in nitrogen transfer and transformations have been developed for relating N inputs to watersheds to outputs into coastal marine ecosystems.

Key findings/state of knowledge

Throughout Europe, NANI represents 3700 kgN/km²/yr (range, 0–8400 depending on the watershed), i.e. five times the background rate of natural N2 fixation.

A mean of approximately 78% of NANI does not reach the basin outlet, but instead is stored (in soils, sediments or ground water) or eliminated to the atmosphere as reactive N forms or as N2.

N delivery to the European marine coastal zone totals 810 kgN/km²/yr (range, 200–4000 depending on the watershed), about four times the natural background. In areas of limited availability of silica, these inputs cause harmful algal blooms.

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