Size Distribution and Spectroscopic Properties of Dissolved Organic Matter in Low Ionic Forest Lakes E-Norway

摘要

Recently there have been major increases in water colour and dissolved organic carbon (DOC) in many forest lakes that serve as drinking water reservoirs in the southern part of Norway. Reduction in sulphate deposition, changes in land use and climate have been put up as explanations to the increased concentration of DOC. Studies in a forest lake area, E-Norway (1983-2005), have shown that increases in water colour and DOC are related to increased amount of precipitation (1). The largest increase in DOC occurred between 1997 and 2001. Furthermore, changed water pathways with increased leaching through the upper forest floor influence the spectroscopic properties of DOM, as DOM are, generally, more coloured (high colour: DOC ratio) at high compared to low flow conditions. Optical properties of water have frequently been used to quantify the concentration of organic carbon. In addition, transmission of light in the water column and lake primary production is highly related to optical properties. Thus, both from analytical and ecological perspectives increased knowledge on factors influencing the spectroscopic characteristics of DOM is needed. The major objective of the present study was to investigate how the size distribution of DOM influences spectroscopic properties (both in the ultra-violet and the visible ranges) of freshwaters in low ionic forest lakes.