Wet and dry deposition of phosphorus into Lake Huron

Abstract

The deposition rates for wet, dry, and integrated fallout of P to the southern portion of Lake Huron were determined. Samples were analyzed for water-soluble, acid (pH =2) soluble, and insoluble (bound) P. The term ‘available P’ was used to indicate the sum of the water- and acid-soluble fractions of P in each type of input. Of the integrated fallout samples, approximately one-third was present as available P. The deposition rate for dry fallout of available P was determined to be 1.7 ng cm −2 day −1 . The wet deposition rate was estimated to be 2.2 ng cm −2 day −1 for available P. Total fallout of available P, determined from shore-based integrated fallout collectors, was calculated to occur at a rate of 6.5 ng cm −2 day −1 . The difference between the wet-plus-dry deposition and the integrated deposition rates has been ascribed to the contamination of integrated fallout collectors by local sources (roads, agricultural activity, etc.) though attempts were made to minimize this problem. The presence of large quantities of biological material (pollen, algae, insect larvae) accounted for a large fraction of the difference observed, especially in the spring months.