Comparisons of Nutrients Exported From Greenlandic Glacial and Deglaciated Watersheds

摘要

Recent work demonstrates extensive nutrient exports from outlet glaciers of the Greenland Ice Sheet. In comparison, nutrient exports are poorly defined for deglaciated watersheds that were exposed during ice retreat and retain reactive comminuted glacial sediments. Nutrient exports from deglaciated watersheds may differ from glacial watersheds due to their longer exposure times, more mature chemical weathering, and ecosystem succession. To evaluate nutrient exports from glacial and deglaciated watersheds, we compare discharge and dissolved (<0.45 mu m filtered) nutrient concentrations in two glacial and six non-glacial streams in southwestern and southern Greenland. Glacial streams have orders of magnitude greater instantaneous discharge than non-glacial streams but their specific discharges are more similar, differing by up to a factor of 10. Compared with non-glacial streams, filtered water of glacial streams have on average (1) higher inorganic nitrogen (DIN) and PO4 concentrations, lower Si concentrations, and Fe concentrations that are not statistically different; (2) higher DIN and PO4 but lower Si specific yields; and (3) lower DIN/PO4, Si/DIN, and Fe/PO4 ratios, but indistinguishable Fe/DIN. Maximum specific yields occur in early melt season prior to maximum solar radiation for non-glacial streams, and in mid-melt season as solar radiation wanes for proglacial streams. Impacts to coastal ecosystems from nutrient exports depend on suspended sediment loads and processing in the estuaries, but landscape exposure during glacial terminations should decrease DIN and dissolved PO4 and increase dissolved Si exports, while increased meltwater runoff associated with future warming should increase DIN and dissolved PO4 and decrease dissolved Si exports.