Will an increased greenhouse impact in Fennoscandia give rise to more humic and coloured lakes?

Abstract

A large-scale increase in the discharge of humic material in rivers, as well as a darkening of Swedish lakes during the last 15 years, are illustrated and discussed. Increased precipitation was responsible for the greatest changes, but a marked part (10–40%) of the increase in river transport of coloured material was independent of discharge. Possible explanations for this increase may be: increased ground water level leading to increased runoff in superficial soil levels, a flow in direct contact with the organic soils; humus fractions in these layers may also be rich in iron resulting in more coloured water; increased primary production giving rise to increased amounts of litter and humic material; reduced capacity of soils to absorb organic matter because of acidification; and effects of modern forest management.

Models of global climate predict a doubling of atmospheric-CO₂, an increase in mean annual temperature of up to 1.5 to 4.5 °C, and in Fennoscandia possibly an increase in precipitation. The factors responsible for the observed large-scale change in humus flux may be strengthened by the increasing greenhouse impacts, and may result in more humic and coloured lakes in Fennoscandia during the next century.