Page 277 - Materials Chemistry, Second Edition

4.5 Impact Categories, Impact Indicators and Characterisation Factors 261

A recommendation for one or the other indicator model cannot be provided at
present.

4.5.2.6 Eutrophication
Eutrophication can best be translated as over-fertilisation or excess supply of
nutrients. The impact category eutrophication is listed in every LCA but at closer
look poses some difficulties. 252)
The substances that cause eutrophication cannot be generally referred to as
pollutants as such, rather as plant nutrients. Its surplus implies as a first impact
a forced photosynthetic increase of biomass (growth of plants, especially algae). A
change of this supply causes changes in the spectrum of species in an ecosystem.
An important secondary impact in water bodies is the consumption of oxygen
by means of bacteriological degradation of dead biomass. A strong increase of
growth of algae induces more extinct biomass at the bottom of the water body with
subsequent decay and can completely change the character of, for example, a lake
or estuary: a formerly clean lake with drinking water quality can evolve into water
with an anoxic (free of oxygen) depth layer. The reduction of the oxygen content
changes the composition of species. In extreme cases an anaerobic ecosystem that
is not desirable evolves.
The impact assessment can be differentiated between aquatic eutrophication
(eutrophication in the original sense) and terrestrial eutrophication or over-
fertilisation. 253) GaseslikeNO and NH (terrestrial eutrophication) and substances
x 3
in the effluent of waste water sewage plants, which have not been completely
decomposed or removed, are considered as well as untreated waste water entries
into water bodies (aquatic eutrophication).
4.5.2.6.1 Aquatic Eutrophication An entry of nutrients into water bodies can
occur both by the water path and by air.
The most important nutrients for plants are the elements phosphor and nitrogen in
a resorbable nutrition compound, primarily as water soluble salts. Gaseous nitrogen
from the air can only be used by some ‘specialised’ plants like legumes in symbiosis
with nodule bacteria. The impact assessment only considers compounds suited
for uptake by plants and only these must be integrated into the inventory. Other
elements important for plant nutrition like potassium, copper (high concentrations
are toxic!) and other trace elements are not integrated into the impact assessment.
Phosphor is the limiting 254) element in most fresh water bodies (surface water like
lakes and rivers as well as groundwater) whereas in seawater generally nitrogen
is the limiting element. Estuaries and brackish waters can be either P- or N-
limited. Terrestrial ecosystems are mostly N-limited. These differences can only be

252) Kl¨ opffer and Renner (1995), Udo de Haes (1996), Udo de Haes et al. (1999a,b, 2002), Finnveden
and Potting (1999, 2001), Guin´ ee et al. (2002), Potting et al. (2002), Norris (2002), Sepp¨ al¨ a et al.
(2006) and Toffoletto et al. (2007).
253) ‘Fertilisation’ should not be misunderstood in an agricultural (intended) context, although
agricultural wastes, increased run-off, and so on can (unintended) contribute to eutrophication.
254) If a shortage of a limiting element occurs even an overdose of other substances necessary for
growth cannot produce biomass. The same applies for special amino acids in the food of animals.