Nitrogen and Sulphur biogeochemistry in a High Arctic glacial watershed: an investigation with isotopic tracers and solute chemistry

This study covered two Arctic summer seasons (2009 and 2010). The first focussed upon temporal dynamics of N and S biogeochemistry, whilst the second study was more focussed upon spatial dynamics. Further lab-based rock dissolution and adsorption experiments were conducted and integrated with stream chemistry data to understand geological controls upon catchment scale N and S biogeochemistry. This study reveals DON as the major component of nitrogen pool (ca. 42-70%) in the snow, followed by NO3ˉ-N (ca. 18-34%) and NH4+-N (ca. 17-24%). However, the composition changes annually. DON largely comes from marine biogenic sources and during the summer plays a major role in subglacial biogeochemical cycling (i.e. a substrate for NO3ˉ-N production). Isotopic evidence suggests that in both subglacial and proglacial streams NO3ˉ-N production and removal processes occur simultaneously. Furthermore, rock dissolution experiments demonstrate that geological nitrogen can be a source of the additional NO3ˉ-N seen in subglacial runoff and proglacial streams. However N content, composition, biogeochemical processes and their detectability in Arctic streams is also variable year to year due to climatic conditions. This study also reveals that; sea-salt, anthropogenic and di-methyl sulphide (DMS)-derived SO4²ˉ are three major sources to Arctic snow SO4²ˉ and their relative fraction vary annually. In the proglacial streams, aerobic biological oxidation of sulphide minerals seems the most plausible SO4²ˉ production mechanism. The ionic data of the subglacial runoff and proglacial streams demonstrate that sulphide oxidation was more important in the subglacial environment than in open proglacial streams. The coupling between sulphide oxidation – calcite weathering was more significant in the proglacial streams.