Spatial variations of surface water chemistry and chemical denudation in the Erdalen drainage basin, Nordfjord, western Norway

摘要

This study conducted over an investigation period of six years (2004-2010) focuses on spatial variation in chemical components of drainage water from sub-areas within a confined drainage basin of 79.5 km2 (Erdalen drainage basin, inner Nordfjord, western Norway) for detection of spatial diversity and relation to environmental factors. The Erdalen drainage basin is homogenously composed of gneisses, which is reflected in a homogenous relative (as a percentage) chemical composition of surface water across the entire drainage basin system. At the same time, the mean annual TDS values of surface water sampled in creeks draining defined subsystems within Erdalen show a rather high spatial variability. The main controls of this spatial variability are (i) differences in slope deposit/regolith thickness, (ii) differences in slope angle, (iii) differences in areal regolith cover, (iv) differences in vegetation cover, (v) differences in snow cover and ground frost conditions, and (vi) differences in elevation (m a.s.l.). Altogether, the mean annual TDS values in Erdalen are rather low, which can be explained by (i) the shallow thickness of regolith across the very steep drainage basin, (ii) the small percentage of surface areas showing a significant cover of regolith, (iii) the cool climate in the fjord landscape of western Norway and (iv) the weathering resistance of the predominant gneisses within Erdalen. The annual chemical denudation rates in Erdalen are in a similar range of magnitude to rates published for numerous other cold environment catchments worldwide. Despite the rather low mean annual TDS values, chemical denudation is a comparably important and spatially very variable denudational process and should therefore not be neglected when studying slope development as well as slope- and catchment-wide denudation rates and mass budgets in this kind of steep, mountainous cold climate drainage basins.