Geomorphology and vegetation drive hydrochemistry changes in two Northeast Greenland streams

Abstract

Climate change is causing drastic landscape changes in the Arctic, but how these changes modify stream biogeochemistry is not clear yet. We examined how catchment properties influence stream nitrogen (N) and dissolved organic carbon concentrations (DOC) in a high-Arctic environment. We sampled two contrasting headwater streams (10-15 stations over 4.8 and 6.8 km, respectively) in Northeast Greenland (74 N). We characterized the geomorphology (i.e., bedrock, solifluction and alluvial types) and the vegetation (i.e., barren, fell field, grassland and tundra types) cover of each subcatchment area draining into each sampling station and collected water samples for hydrochemistry characterization. The two sampled streams differed in geomorphology and vegetation cover in the catchment. Aucellaelv catchment was mostly covered by a 'bedrock' geomorphology (71%) and 'fellfield' vegetation (51%), whereas Kaeerelv was mostly covered by 'alluvial' geomorphology (65%) and 'grassland' and 'tundra' vegetation (42% and 41% respectively). Hydrochemistry also differed between the two study streams, with higher concentrations of inorganic N forms in Aucellaelv and lower DOC concentrations, compared to Kaerelv. The results from the linear mixed model selection showed that vegetation and geomorphology had contrasting effects on stream hydrochemistry. Subcatchments with higher solifluction sheets and limited vegetation had higher nitrate concentrations but lower DOC concentrations. Interestingly, we also found high variability on the production and removal of nitrate across subcatchments. These results indicate landscape controls to nutrient and organic matter exports via flow paths, soil organic matter stocks and nutrient retention via terrestrial vegetation. Moreover, the results suggest that climate change induced alterations to vegetation cover and soil physical disturbance in high-Arctic catchments will affect stream hydrochemistry, with potential effects in stream productivity, trophic relations as well as change of solute export to downstream coastal areas.

Links Between Stream Water Nitrogen and Terrestrial Vegetation in Northeast Greenland

“…Third, in the Zackenberg valley there are vegetated wetlands present, where removal of $${{\text{NO}}_{3}}^{-}$$ via assimilative uptake or denitrification would be expected to be enhanced (e.g., Sirivedhin & Gray, 2006). Although the wetlands vegetation is included in the catchment NDVI, the N and C biogeochemical processes in wetlands may be disproportionally high compared to areas with tundra vegetation (Pastor et al., 2021), thus substantially adding to the patterns of low $${{\text{NO}}_{3}}^{-}$$ but high DON concentration at high catchment NDVI.…”

“…Headwater streams show intimate connectivity to their catchments and are therefore ideal sites for inferring catchments effects on stream water chemistry (Hynes, 1975) or disentangling catchments processes from stream water chemistry (Harms et al., 2016; Kendrick et al., 2018). Studies on small headwater stream catchments rather than only considering large river catchments (Frey & McClelland, 2009; Tank et al., 2023; Toohey et al., 2016) are essential for enhancing the understanding of the mechanistic links between vegetation, hydrological connectivity, and solute runoff (e.g., Khosh et al., 2017; McNamara et al., 2008; Pastor et al., 2021), that eventually are affecting the larger‐scale patterns in solute runoff to rivers and coastal areas. In addition, we conducted the study in NE Greenland, where only two other studies linking catchment characteristics and stream water chemistry exist (Docherty et al., 2018; Pastor et al., 2021).…”

“…Studies on small headwater stream catchments rather than only considering large river catchments (Frey & McClelland, 2009;Tank et al, 2023;Toohey et al, 2016) are essential for enhancing the understanding of the mechanistic links between vegetation, hydrological connectivity, and solute runoff (e.g., Khosh et al, 2017;McNamara et al, 2008;Pastor et al, 2021), that eventually are affecting the larger-scale patterns in solute runoff to rivers and coastal areas. In addition, we conducted the study in NE Greenland, where only two other studies linking catchment characteristics and stream water chemistry exist (Docherty et al, 2018;Pastor et al, 2021). Therefore, this study contributes to a broader understanding of the Arctic region.…”

Catchment-scale thawing and greening decreases long-term nitrogen export in NE Greenland

“…Documenting long-term changes is critical to unlocking linkages between climate-driven changes in terrestrial ecosystems and changing watershed N export. Most studies on riverine nutrient export in the Arctic are short-term, limited to a single summer [9,10,13,33,34] or a few years [35][36][37][38]. Critically, Greenland accounts for approximately 27% of the Arctic landmass, yet research on changing N dynamics, especially at the basin scale, is lacking from this region.…”

“…Critically, Greenland accounts for approximately 27% of the Arctic landmass, yet research on changing N dynamics, especially at the basin scale, is lacking from this region. Several short-term studies from Northeast Greenland have explored nutrient uptake [14,39], linkages between hydrochemistry and vegetation [34], and the role of snow cover in controlling stream chemistry [12]. However, long-term patterns in riverine N export from Greenland, a region in which temperatures are increasing by 0.4 • C per decade [40], have not yet been documented.…”