Increased organic carbon concentrations in Estonian rivers in the period 1992–2007 as affected by deepening droughts

Abstract

There are 10,091 km2 of peatlands in Estonia and human activities may have changed the role of northern peatlands from global sinks to global sources of carbon. The aim of this work was to explain the changes in organic carbon exports from eleven Estonian rivers in the period 1992–2007 in terms of land use change, climate change quantified by trends in stream-water discharge and hydrological droughts and reductions in atmospheric sulfate quantified by change in water chemistry. Direct TOC (total organic carbon) measurements had been initiated in 1998. We used CODKMnO4 (permanganate oxygen consumed) as its surrogate for the whole time span (Spearman’s determination coefficient in six small northern Estonian rivers 0.95 > I2 > 0.72; p  2.35; p  0.05). We conclude that the main factor in the increase of organic carbon export is the deepening of droughts driven by climate change, magnified by man-made drainage.