Landscape scale patterns in the character of natural organic matter in a Swedish boreal stream network

摘要

This paper defines landscape-scale patterns in the character of naturalorganic matter (NOM) and tests for relationships to catchment soil,vegetation and topography. The drainage network of a boreal catchment,subcatchment size 0.12–78 km2, in Northern Sweden was sampled inAugust 2002 during a period of stable low water flow. The NOM wascharacterized with UV/Vis spectroscopy, fluorescence, XAD-8 fractionation(%humic substances), gel permeation chromatography (apparent molecularweight), and elemental composition (C:N). The largest spatial variation wasfound for C:N, absorbance ratio, and specific visible absorptivity. Thelowest variation was in fluorescence index, %humic substances and molecularretention time. The variation in total organic carbon (TOC), iron andaluminium concentration was more than twice that of C:N. Between headwaterand downstream sites no significant changes were distinguished in the NOMcharacter. At stream reaches, junctions and lakes little change (<10%) inNOM character was observed. Common factor analysis and partial least squaresregression (PLS) revealed that the spatial variation in surface coverage oflakes and mires could explain some of the variation of TOC and NOM character.Our suggestion is that the mosaic of landscape elements (different amounts ofwater from lakes, forest soil and mires) delivers NOM with varyingcharacteristics to a channel network that mixes conservatively downstream,with possible small changes at some stream reaches, junctions and lakes.