Page 233 - Materials Chemistry, Second Edition

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10.8.4 Existing Characterisation Models

The acidification potential depends both on the potency of the emitted gas and on
the sensitivity of the receiving environment in terms of buffering capacity of the
soils and sensitivity of the ecosystems to acidification as expressed by their critical
load. While the difference between the contributing gases is modest—within a
factor 5–10 across substances, the difference between sensitivities in different
locations can be several orders of magnitudes depending on the geology and soil
characteristics. Early characterisation models were site-generic and only incorpo-
rated the difference in ability to release protons, but newer models incorporate more
and more of the cause–effect chain in Fig. 10.13 and model e.g. the area of
ecosystem in the deposition area that becomes exposed above its critical load. This
requires a site-dependent LCIA approach where the characterisation factor is
determined not just per emitted substance but also per emission location.
Characterisation factors may be expressed as absolute values or as an equivalent
emission of a reference substance which in that case is usually SO 2 . For further
details see Chap. 40 and Hauschild and Huijbregts (2015).

10.9 Eutrophication

10.9.1 Problem

Nutrients occur naturally in the environment, where they are a fundamental pre-
condition for the existence of life. The species composition and productivity of
different ecosystems reflect the availability of nutrients, and natural differences in
the availability of nitrogen and phosphorus are thus one of the reasons for the
existing multiplicity of species and of different types of ecosystems. Ecosystems are
dynamic, and if they are affected by a changed availability of nutrients, they simply
adapt to a new balance with their surroundings. Originally, eutrophication of
aquatic environments, such as rivers or lakes, describes its eutrophic character
(from the Greek word “eu”—good or true, and “trophein”—feed), meaning
nutrient-rich. From the 1970s the term was used to describe the slow suffocation of
large lakes. It now has a meaning close to dystrophic, i.e. poor conditions and low
in oxygen, supporting little life. An aquatic ecosystem in strong imbalance is named
hypertrophic, when close to a natural equilibrium it is called mesotrophic, and when
healthy it is called oligotrophic.
The perhaps most prominent effect of eutrophication in lakes, rivers and the
coastal sea are lower water quality including low visibility or for stronger situations
massive amounts of algae in the surface layers of those waters. Eutrophication
essentially describes the enrichment of the aquatic environment with nutrient salts
leading to an increased biomass production of planktonic algae, gelatinous zoo-
plankton and higher aquatic plants, which results in the degradation of
(organoleptic) water quality (e.g. appearance, colour, smell, taste) and an altered