Connecting Variations in Vegetation and Stream Water Geochemistry along a Deglaciation Transect in western Greenland.

Ice retreat following the last glacial maximum, and the associated changes in landscape, climate, and hydrology, altered  nutrient fluxes off the landscape and fostered the development of new biological communities. The role of feedbacks between the new plant communities and geological processes, such as mineral weathering, are not well understood. Differences in water chemistry between catchments in southwestern Greenland that were deglaciated ~ 7 and 10 kya suggests that nutrient differences cannot be explained solely by abiotic factors alone.  One hypothesis to explain the variation in water chemistry is that plant communities mobilize different nutrients, either by releasing them directly or by differential weathering of the underlying substrates. To test this hypothesis, we first surveyed plant communities using a combination of Floristic Habitat Sampling and modified Point Quarter method in forty-five 1.25 m2 plots across five watersheds in 2022. The watersheds were ~ 150 km apart with one near the ice edge exposed ~6.8 ky ago and the other near the coastexposed ~ 10 ky. ago Using NMDS and ANOSIM (α = 0.05) analyses, we found that species compositions across locations were distinct (stress score = 0.15; p = 1e -04, R = 04025). Next we compared the vegetation distribution data  to elemental concentrations of dissolved nutrients (Li, Mg, Al, P, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Si) from adjacent streams using a Mantel test (method = Spearman, permutation = 9999). The variation in vegetation is correlated with the stream elemental composition data (p = 0.0043). The correlation between the two matrices suggests that either plant community composition drives variation in nutrient concentrations, or plant community and nutrient fluxes may both respond to another environmental variable. To distinguish between these alternatives, we are currently conducting mesocosm weathering experiments to test whether tundra plants vary in their ability to promote biogenic weathering, and whether biogenic weathering is sufficiently enhanced to explain variations in nutrient elements dissolved in streams and vegetation in southwestern Greenland.