ELEMENTAL MOBILITY THROUGH SMALL TUNDRA WATERSHEDS

Tundra plants and soils may constrain ecosystem response to climate ch ange. To understand these constraints requires integrated studies of b iogeochemical cycling in tundra ecosystems. This paper summarizes a 4- yr irrigation-fertilization experiment designed to evaluate elemental mobility through small tundra watersheds and examines the ''leaky ecos ystem-nutrient hypothesis.'' The irrigation treatment increased elemen tal mobility of Fe and Mn, possibly due to reducing conditions caused by waterlogging. Ammonium and NO3 concentrations remained above backgr ound levels for four field seasons following application of a slow-rel ease NPK fertilizer. Sharp peaks and valleys in NH4 and NO3 concentrat ions over the four seasons suggest slow fertilizer solubilization due to low temperatures and mixing of waters of variable composition. Fert ilizer P showed limited mobility. Soil solutions were saturated with r espect to gibbsite suggesting that a gibbsite-like mineral may control Al solubility in these arctic soils. Comparisons of elemental concent rations among tundra ecosystems indicate that weathering rates are hig hly individualistic, depending critically on soil parent material. Fur thermore, tundra ecosystems are leaky with respect to nutrients, which may have ramifications well beyond the disturbance both with respect to time and space, and bears attention in assessing the future respons e of tundra ecosystems.