Arthropod Fallout and Nutrient Transport: A Quantitative Study of Alaskan Snowpatches

Abstract

Arthropod fallout was sampled during the summers of 1971 and 1972 on snowpatches at the IBP Tundra Biome site at Eagle Summit Alaska (65028'N, 45023'W) at an altitude of about 1100 m. Diptera dominated the fallout numerically (61%), followed by Hymenoptera (28%), Coleoptera (4.4%), and Heteroptera (1.2%). Peak fallout occurred in early June, and diminished to zero in early September. Greatest fallout biomass, which occurred in midJune and in early July, was composed largely of alate ants. The mean rate of arrival on the snow surface mid-June through mid-July was 1.5 mg dry wt m-2 * day-l. Eight species of bird which breed in the vicinity of Eagle Summit utilized the snowfield insect fallout as a food source. On the basis of elemental analyses made on snowpatch insects it is estimated that rates of deposition during mid-June to mid-July are carbon, 0.7 mg * m-2 * day-1; nitrogen, 0.15 mg m-2 - day-1; phosphorus, 0.008 mg ? m-2 . day-1. Assuming imported insects from lower altitudes comprised 70% of the total fallout, at least 21.3 mg carbon m-2, 4.3 mg nitrogen m-2, and 0.25 mg phosphorus m-2 were imported during the period mid-June to late August 1972. The significance of arthropod fallout on snowfields as a source of nutrient is discussed.