Nitrate mobilization during the melt season in Central Spitsbergen

Although Arctic soils store approximately half of the global nitrogen stock, research on nitrogen and its integration into active biochemical cycles is limited. Climate warming, which is amplified in the polar regions and particularly on Svalbard, is leading to a deepening of the active layer of permafrost and an increase in rainfall. It is also causing shifts in groundwater, surface water and, glacial meltwater flow rates, pathways, and discharge to fjords. These substantial hydrological changes are expected to increase nitrogen mobilization through two distinct pathways: (1) by introducing inorganic nitrogen (i.e. nitrate, nitrite and ammonium) through increase in runoff, which can be taken up by primary producers and (2) by unlocking large amounts of frozen organic nitrogen, which can be remineralized into inorganic nitrogen. Since nitrite and ammonium are highly biologically labile and only persists for a short period of time before being converted into nitrate, the latter is expected to be the dominant specie of mobilized nitrogen. Increased availability of nitrate in Arctic environments has an important influence on climate change: (1) directly through the potential emission of nitrous oxide (a greenhouse gas ~300 times more potent than carbon dioxide on the 100-year timescale), which is a by-product of denitrification in saturated groundwater or (2) indirectly through hydrologic export of nitrate to fjord ecosystems, which can in turn, increase net consumption and thus carbon dioxide production. Yet, our understanding of nitrate mobilization within the zone of transition between terrestrial and aquatic ecosystems is limited, especially on Svalbard where the complexity of these systems is supplemented by glacial-periglacial interactions. The objective of this project is to explore the role of increased nitrogen in an Arctic ecosystem by identifying and characterizing terrestrial nitrogen hotspots and assess the fate of nitrate.