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respectively, affecting groundwater via percolation and surface water via runoff and
leaching processes, and of ammonia emitted to air and deposited on land nearby.
Oxides of nitrogen may be emitted from incineration processes. Point sources in the
form of wastewater treatment plants for households (e.g. from polyphosphates in
detergents) and industry as well as fish farming are important sources of phosphorus
and nitrates. Apart from man-made emissions, natural sources include leaching and
runoff of nitrogen and phosphates. The natural addition of nutrients to terrestrial
areas is believed to consist mainly of atmospheric deposition of oxides of nitrogen
and ammonia while some natural plant species also possess the ability to fixate
atmospheric nitrogen.
Emissions of organic materials can lead to oxygen consumption by bacteria
degrading this organic matter and thus contributing to oxygen depletion similarly to
what is observed as a result of the nutrient enrichment of lakes and coastal waters.
However, this is a primary effect and is strictly speaking not part of the nutrient
enrichment mechanism. Therefore, emissions of BOD (biological oxygen demand—
substances which consume oxygen on degradation) or COD (chemical oxygen
demand) may additionally be characterised by some LCIA methods considering
oxygen depletion (hypoxia) in water as a common midpoint for both mechanisms.
Most LCIA methods are currently based on the N/P ratio and typically do not
classify BOD or COD as contributing to nutrient enrichment and thus eutrophica-
tion. In large parts of the industrialised world organic matter emissions are only of
local significance in watercourses and for occasional emissions of untreated effluent.
10.9.4 Existing Characterisation Models
The essential evolutions during the last decade were related to improved fate
modelling, distinguishing P-limited (freshwater) and N-limited (marine) ecosys-
tems, introduction of a midpoint effect factor in the more recent methods, and
characterisation models becoming global and spatially more detailed.
Midpoint LCIA methods usually propose units in P- and N-equivalents such as kg
3
P-eq or kg PO 4 -eq and kg N-eq or kg NO 3 -eq. For endpoint characterisation
2
most models use Potentially Disappeared Fraction of species (PDF) in [m years],
except LIME which uses Net Primary Productivity (NPP) loss. For further details
see Chap. 40 and Hauschild and Huijbregts (2015).
10.10 Photochemical Ozone Formation
This impact category appears under a number of different names in the various
LCIA methods: (tropospheric) ozone formation, photochemical ozone formation or
creation, photo oxidant formation, photosmog or summer smog. There are minor