Atmospheric deposition of macronutrients by pollen at a semi-remote site in northern Wisconsin

Abstract

Pine pollen concentrations in air at a semi-remote site in northern Wisconsin attained levels of 18 and 25 μ m −3 in late May and early June of 1979 and 1981, respectively. The upper and lower limits for the deposition velocity of pine pollen at this site are approximately 30 and 1.3 cm s −1, respectively. Consequently, the average annual pine pollen flux at this location for 1979 and 1981 was between 8.0 and 0.35 g m −2. Deposition of total phosphorus and organic C by pollen dispersal are about 5–100% and 11–240%, respectively, of the measured bulk atmospheric loading rate in the region. Pine pollen fluxes of water-extractable K are about 10–230% of the average annual wet deposition, while the fluxes of waterextractable NO 3 − and SO 4 −2 by pollen appear to be negligible in comparison to the total atmospheric deposition (wet plus dry deposition) by other particles. The annual pine pollen flux to Crystal Lake, an oligotrophic seepage lake in the region, was estimated to be 6.5 g m −2 during 1981. The deposition of total P by pollen to this lake was 5.8 kg a −1, which is 45 % of the external input of total phosphorus. About 60% of the total P in samples of Pinus strobus and P. resinosa was dissolved reactive P, which is readily available for plant uptake. Because P is the limiting nutrient for many lacustrine systems and pine pollen dispersal coincides with the period of phytoplankton blooms in temperate-region lakes, this episodic input of P may represent an important source for seepage lakes whose external inputs are dominated by atmospheric deposition.