Nutrient and Metal Amounts in Permafrost and Active Layer Soils at the Stordalen Mire, Abisko Sweden
We assessed how nutrients, solutes, and metals vary in permafrost soil and in the active layers across four plant communities undergoing permafrost thaw at the Stordalen Mire in Abisko Sweden. We hypothesized that nutrient availability shifts from low nitrogen and phosphorus to high nitrogen and phosphorus amounts across plant communities with increasing thaw depth. Although nutrient availability did not shift from low to high nitrogen and phosphorus across plant communities with increasing thaw depth as hypothesized, nutrient availability immediately increased in the thaw front (rich Sphagnum lawn), and returned to low nitrogen and phosphorus availability in the tall graminoid fen, where permafrost was no longer intact. Despite high amounts of acid digestible phosphorus, available P (Presin) amount was low in the permafrost and tall graminoid fen soils, likely due to P sorption with iron. While permafrost soils had high amounts of nitrogen, phosphorus, and metals, dissolved organic carbon amounts were low.
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We collected soil samples from four plant communities at the Stordalen Mire in Abisko Sweden in early August of 2017. Frozen "transitional" permafrost was collected from the palsa plant community at 33-57 cm depth directly below the active layer to the bottom depth of the permafrost. We collected active layer soil at two depths near the average water table specific to each of the four plant communities (palsa, palsa hollow, rich Sphagnum lawn, and tall graminoid fen). Samples were collected above the permafrost in the palsa, above and below the average water table in the palsa hollows and the rich Sphagnum lawn, and below surface in the tall graminoid fen. Soils were collected from three separate locations of each plant community and permafrost to avoid pseudo-replication. We extracted ammonium (NH4 mg/m2), nitrate (NO3 µg/m2), total dissolved nitrogen (TDN g/m2), dissolved organic nitrogen (DON g/m2), and extractable dissolved organic carbon (DOC g/m2) by shaking fresh soil with 0.5 M K2SO4 on an orbital shaker, and analyzed eluent using automated colorimetry with a Westco Scientific Smartchem200 discrete analyzer, a high temperature catalytic oxidation on a Shimadzu TOC-V with a TNM-1 nitrogen analyzer, and calculated DON by subtracting inorganic N from the total dissolved nitrogen. We measured % carbon and % nitrogen using an Elementar Americas Pyrocube elemental analyzer. We extracted resin-extractable molybdate reactive P (Presin mg/m2) on fresh soils using anion exchange membranes and analyzing eluent on a Smartchem discrete analyzer. We digested dry soil samples with nitric acid hydrogen peroxide digestion for amounts of acid digestible phosphorus (P g/m2), aluminum (Al g/m2), iron (Fe g/m2), copper (Cu mg/m2), manganese (Mn g/m2), molybdenum (Mo mg/m2), vanadium (V mg/m2), and zinc (Zn mg/m2) amounts. We analyzed digest using inductive coupled plasma sector field mass spectrometry. We multiplied nutrient extraction concentrations by the bulk density to calculate areal amounts.