3.4.6.2. Development and Application of Water Resource Scenarios
Water resource scenarios have been developed at different time and space scales.
For example, projections to 2025 on the basis of national water resource monitoring
data have been reported by Shiklomanov (1998). Model-based projections of water
use and availability to 2025 at the river basin scale have been made by Alcamo
et al. (2000), assuming a BAU scenario and two alternative, normative scenarios
that focus on water conservation. Some results of these scenario exercises are
shown in Table 3-3. Among the most developed scenarios
of water quality are model-based scenarios of acidification of freshwaters in
Europe (e.g., NIVA, 1998). More general normative scenarios describing rural
and urban access to safe drinking water by 2025 and 2050 are presented by Raskin
et al. (1998). Scenarios of water availability have been applied in several
climate change impact studies. Most of these are in the water resources sector
and are reported in Chapter 4. However, they are increasingly
being applied in multi-sectoral and integrated assessments (e.g., Strzepek et
al., 1995).
3.4.7. Scenarios of Marine Pollution
3.4.7.1. Reference Conditions
Marine pollution is the major large-scale environmental factor that has influenced
the state of the world oceans in recent decades. Nutrients, oxygen-demanding
wastes, toxic chemicals (such as heavy metals, chlorinated hydrocarbons, potential
endocrine-disrupting chemicals, and environmental estrogens), pathogens, sediments
(silt), petroleum hydrocarbons, and litter are among the most important contaminants
leading to degradation of marine ecosystems (Izrael and Tsyban, 1989; GESAMP,
1990; Tsyban, 1997). The following ranges of concentrations of heavy metals
are characteristic of open ocean waters: mercury (0.3-7 ng l-1),
cadmium (10-200 ng l-1), and lead (5-50
ng l-1); levels of chlorinated hydrocarbons are a
few ng l-1. Chemical contaminants and litter are found
everywhere in the open ocean, from the poles to the tropics and from beaches
to abyssal depths. Nonetheless, the open ocean still remains fairly clean relative
to coastal zones, where water pollution and the variability of contaminant concentrations
are much higher (often by one to two orders of magnitude; specific values depend
on the pattern of discharge and local conditions).
3.4.7.2. Development and Application of Marine Pollution
Scenarios
Data characterizing the state of the marine environment have been obtained
through national as well as international monitoring programs in recent decades,
and analysis of tendencies may serve as an initial basis for developing environmental
scenarios. At present, expert judgment appears to be the most promising method
of scenario development because modeling methods are insufficiently developed
to facilitate prediction.
In qualitative terms, trends in marine pollution during the 21st century could
include enhanced eutrophication in many regions, enhancement of exotic algal
blooms, expanded distribution and increased concentration of estrogens, invasion
of nonindigenous organisms, microbiological contamination, accumulation of pathogens
in marine ecosystems and seafood, and increases of chemical toxicants (Izrael
and Tsyban, 1989; Goldberg, 1995).
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