Climate Change and the European Water Dimension - Agri ...

• provide a surface where photolytic degradation of POPs may occur.
It has been estimated that coniferous forests have the largest storage capacity for
POPs (of the different vegetation types), while tropical systems may be areas where
photodegradation occurs most rapidly. Hence, changes in vegetative cover over the
Earth’s surface will alter the dynamics of POPs cycling.
Soils:
Soil is a major environmental reservoir/sink of POPs, either because of direct
applications in urban or agricultural areas, or because all soils receive POPs as a
result of accumulative atmospheric deposition. The soils’ storage capacity for POPs
is strongly influenced by the soil organic matter (SOM) content (and – to a lesser
extent – type), while the degradation rates in soils are affected by the fertility, aerobic
status, moisture content and temperature. The POPs content of global background
soils are positively correlated to their SOM, suggesting: i). that compounds can ‘hop’
between locations until they find soils of higher SOM status, from where they are less
likely to be re-emitted to atmosphere (Meijer et al., 2003; Gouin et al., 2004); and/or
ii). Their rate of degradation in soils is inversely proportional to the SOM content,
perhaps because higher SOM results in lower compound bioavailability. Figure VI.F4
shows how the capacity of surface soils to store an illustrative POP (PCB-153) has
been estimated to vary globally and seasonally – as a function of SOM and
temperature. It can vary over orders of magnitude with location and by about a factor
of 10 seasonally.
Clearly, underlying climate change processes that result in a change in soil use and
management, or a direct change in SOM content, can be expected to influence the
storage capacity and turnover of POPs in this major environmental repository (see
below). Rates of organic matter turnover in soils may also play an important part in
their incorporation into SOM, and rates of degradation. POP half-lives in background
soils are ‘long’ (perhaps decades); it may therefore be anticipated that underlying
changes in soils - occurring over these timeframes as a result of climate change –
may impact global POPs cycles.
Water bodies:
Oceans cover seventy percent of the world’s surface. Some major ‘enclosed’ water
bodies, such as the Baltic Sea, the North American Great Lakes, and the estuaries of
the Atlantic Coast of the USA are areas of the world where the adverse effects of
POPs have been most extensively reported. Water bodies are therefore of critical
importance to the storage, processing and removal of POPs from the global cycle.
There is evidence that the air and open oceans are close to a state of dynamic
equilibrium, with respect to many POPs that undergo air-water gas exchange
(Jaward et al., 2004c; Wodarg et al., 2004). The storage capacity of the surface
oceans is strongly influenced by the phytoplankton, with close coupling of the airdissolved
phase-phytoplankton system (Dachs et al., 2000). Ultimately, the surface
oceans loose POPs to the deeper oceans in association with the C flux. Any factors
that influence the rates of C removal to the deeper oceans, or the rates of primary
productivity of the surface oceans, would potentially be major drivers influencing the
air-surface exchange of POPs. Air-water exchange is enhanced by increases in
biomass (i.e., eutrophication) and thus more eutrophic water bodies may ‘capture’
atmospheric gas phase POPs (Jeremiason et al., 2000, Dachs et al., 2000).
Snow/ice cover:
Snow and ice are efficient scavengers of POPs from the atmosphere, resulting in
their deposition to polar and mountainous environments. On the other hand, snow
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