Variations in the nitrate concentration of glacial runoff in Alpine and sub-Polar environments

Abstract

Abstract Variations in the NO^ content of glacial runoff arise from the routing of snowmelt through the hydroglacial system. Where there is little contribution of distributed system drainage (water which has spent prolonged periods at the glacier bed) to runoff, such as at the Austre Braggerbreen, Svalbard, NO3 concentrations show a rapid, exponential decline as the snowpack becomes progressively leached. There is also little association of NO3 with discharge throughout the ablation season. Where there is a contribution of distributed system drainage to runoff, such as at the Haut Glacier d'Arolla, Switzerland, the decline in NOJ concentrations occurs more gradually throughout the ablation season, reflecting the temporary storage of NO J -rich waters at the glacier bed. There is also an inverse diurnal association of N01 concentrations with discharge, arising from the dilution of snowmelt with icemelt. The disappearance of NO J from runoff at the Haut Glacier d'Arolla on certain occasions may be due to microbiological activity. INTRODUCTION One of the major sources of NO to hydroglacial systems is snowmelt (Tranter et al., 1993). This is particularly true during the thaw, when the first fractions of snowmelt may contain high concentrations of all soluble ions (Johannessen & Henriksen, 1978). Nitrate is a bio-essential nutrient in the snow-glacier ecosystem, but given the relative youth of snow-glacier ecology, it is not yet clear whether N or P is limiting. Of the NO 3 released during the spring thaw, some is utilized by snow biota (Jones & Deblois, 1987), some may be utilized in subglacial ecosystems and the remainder is exported in glacial runoff. Glacial runoff is typically turbid, with concentrations of mainly silt-sized material (Fenn & Gomez, 1989) in the region of 200 to > 5000 mg l