Why investigate mountainous woodland?

Although the Alps seem to be a major sink for long-range transported POPs, this environmental risk has hardly been recognised so far.

Pollutants reach these remote areas over hundreds, or thousands, of kilometres by long-range atmospheric transport. Obviously, mountains form a distinct physical barrier on this route. They also receive more precipitation which washes out airborne pollutants. Lower air temperatures further the condensation of the less volatile substances.

Among the various mountain ecosystems, woodland has been chosen for MONARPOP because forests are not only a valuabe - and vulnerable - ressource, they are also subject to even higher pollutant inputs than, eg, grassland. One reason is the rough canopy structure, particularly that of the coniferous stands found at higher altitudes. Canopy roughness filters out particulate contaminants and enhances the infiltration of gaseous pollutants. Moreover, the waxy needle surfaces trap such chemicals which, like POPs, are chemically affine to fatlike substances. The POPs reach the forest floor through litterfall but also by direct deposition and accumulate in the humus layer.

The Grasshopper Effect

is thought to be a key mechanism for the extraordinary range of POP pollution: the volatility of POPs depends on temperature. When temperatures decrease, more airborne POPs will be deposited to the earth's surface. However, during a seasonal rise in temperature this depositions may revolatilise and enter the atmosphere for another "hop" away from their original source. Through several of these cycles, POPs eventually reach even the remotest regions of our globe.

"Diurnal mountain winds, in connection with enhanced deposition at higher elevations caused by low temperatures and high precipitation rates, conspire to make mid-latitude mountains become convergence zones for selected persistent organic chemicals."

G L Daly & F Wania:
Organic Contaminants in Mountains
(DOI: 10.1021/es048859u)

POPs are not the only menace to the Alps (see UNEP mountain watch report). The Alps Convention protects this unique European landscape.

POPs elsewhere: AMAP keeps an eye on POPs in the Arctic.