|Characterisation Method Name:|
|Contributions to EF(ne)|
|Principal Method Name:|
|EDIP:nutrient enrichment potential|
|Nutrient enrichment is an impact on ecosystems from substances containing nitrogen (N) or phosphorus (P). As a rule, the availability of one of these nutrients will be a limiting factor for growth in the ecosystem, and if this nutrient is added, the growth of algae or plants will be|
increased. In aquatic ecosystems this can cause the occurrence of situations without oxygen in the bottom strata due to the increased algal growth and subsequent breakdown of algae at the bottom. On land, ecosystems poor in nutrients such as raised bogs, commons and heathlands are gradually disappearing as a result of addition of nitrogen.
Society's emissions of nitrogen to the aquatic environment are blamed especially on the agricultural use of fertilizers, but oxides of nitrogen from combustion processes are also of significance for both aquatic and
terrestrial ecosystems. The most significant sources of emission of phosphorus are sewage treatment plants for urban and industrial effluents and leaching from agricultural land.
The nutrient enrichment is an impact which affects the environment on both local and regional scales.
1 Determine which compounds contribute to nutrient enrichment
For a compound to be regarded as contributing to nutrient enrichment, it must contain nitrogen or phosphorus in a form which is biologicaly available.
Free nitrogen is not regarded as a contributor to nutrient enrichment even if it is available for certain bacteria and algae. This is because emission of N, has no additional fertilizing effect, inasmuch as the greater part of the atmosphere already consists of free nitrogen. Nutrient enrichment can be caused by emissions to air, water and soil. The list of potentially nutrient enriching compounds is very long but in practice most compounds occurring in the inventory of the product system will be in the list of equivalency factors in right side screen.
2 Calculate the nutrient enrichment potential
There is no internationally accepted system of equivalency factors for nutrient enrichment which can be used in calculation of its potential. As the environmental impact as here defined is attributed to addition of N- or P-containing nutrients, it is, however, easy to develop a system of equivalency factors, as the equivalency factor must simply show the
compound's content of N or P.
It is possible to operate with two potentials for nutrient enrichment, one for each of the two nutrients N and P. It will be an advantage to treat N and P separately if an assessment is subsequently to be made of whether the contributions to nutrient enrichment are to be accorded major or little weight on the basis of site-specific considerations. The weight accorded nutrient enrichment depends on whether the nutrient
which is added is the limiting one in the ecosystem in question. This can only be decided if the contributions from compounds containing N and P are treated separately in the calculation of their potentials.
It is also possible for the sake of simplicity to operate with only one
potential for nutrient enrichment. The two nutrient enrichment potentials must then be combined, which requires an assumption of a fixed relative strength of the contributions from N and P which must be independent of the type and sensitivity of the ecosystem which is exposed. As there are on average about 16 times as many nitrogen atoms as phosphorus atoms in aquatic organisms, a strength of 16 is used for P relative to N
when their impact potentials are aggregated into one. As for several of the other
potential environmental impacts, the potentials for nutrient enrichment are expressed as an equivalent quantity of a reference substance. If the two nutrients are treated separately, the reference substances are simply nitrogen and phosphorus. If they are combined in one impact potential, the latter is expressed as an equivalent quantity of nitrate, NO3.
As noted, all substances containing N or P are potential contributors to nutrient loads. Compounds other than those for which equivalency factors are given here may therefore occur in the inventory. If this is the case, it is easy to calculate equivalency factors for them. The method is
given in Hauschild & Wenzel (1997c).
|Henrik Wenzel, Michael Hauschild and Leo Alting (1997 ): Environmental assessment of products Vol. 1 Methodology, tools and case studies in product development London Chapman & Hall|
|Geographical range is Global|
|Characterisation Parameter||Category Indicator||Impact Indication Principle||Aspect||Substance||Quantity||Unit||Notes|