VARIATIONS OF WEEKLY ATMOSPHERIC DEPOSITION FOR MULTIPLE COLLECTORS AT A SITE ON THE SHORE OF LAKE OKEECHOBEE, FLORIDA

Eight wet/dry precipitation collectors were modified to house four add itional dryfall collectors and one bulk precipitation collector to sam ple atmospheric deposition for 12 weeks in a small area on the southwe stern shore of Lake Okeechobee; sample contamination, primarily by ins ects, reduced the comparison to the last nine weeks. The deposition wa s determined for Ca2+, Na+, Cl-, and SO4(2-) and nutrients including t otal phosphorus, orthophosphate, total ammonia plus organic nitrogen, and nitrite plus nitrate. In general, deposition was lower and less va riable in wet precipitation than in bulk precipitation. The higher var iability of the bulk precipitation was attributed to local contaminati on, particularly by dust and insects. Each wet/dry precipitation colle ctor was fitted with dryfall collectors that consisted of the dry-side bucket on a wet/dry collector, which was preloaded with distilled and deionized water, and four glass dish collectors; two of the glass dis hes were preloaded with water and the other two remained dry. The depo sition to the dry dish collectors was not comparable in adjacent colle ctors for any constituent; however, the deposition in the adjacent wat er-loaded dishes was comparable for most major constituents, except nu trients. A comparison of Ortho-P deposition with Total-P indicated tha t the P collected by the dryfall collectors was predominantly reactive , which also was reflected in the bulk deposition, whereas that in the wet deposition was mostly nonreactive. The large variability in depos ition of P among the bulk and dryfall collectors suggests that alterna tive methods must be used to evaluate the P sources and processes of a tmospheric transfer.