INFERENCE OF NITROGEN CYCLING IN 3 WATERSHEDS OF NORTHERN FLORIDA, USA, BY MULTIVARIATE STATISTICAL-ANALYSIS

Nitrogen in fresh waters of three rivers in northern Florida-the Apala chicola-Chattahoochee-Flint (ACF) River system, Ochlockonee (Och), and Sopchoppy (Sop)-is inferred to be derived mostly from atmospheric dep osition. Because the N:P mole ratios in the rivers are nearly three ti mes higher than the Redfield ratio for aquatic photosynthesis, N is sa turated in the ecosystems, not a limiting nutrient, although it may be chemically transformed. Absolute principal component analysis (APCA), a receptor model, was applied to many years of monitoring data for Ap alachicola River water and rainfall over its basin in order to better understand aquatic chemistry of nitrogen in the watershed. The APCA mo del describes the river water as mainly a mixture of components with c ompositions resembling fresh rain, aged rain, and groundwater. In the fresh rain component, the ratio of atmospheric nitrate to sulfate is c lose to that in rainwater, as if some samples had been collected follo wing very recent rainfall. The aged rain component of the fiver water is distinguished by a low NO3-/SO42- ratio, signifying an atmospheric source but with most of its nitrate having been lost or transformed. T he groundwater component, inferred from its concentration to contribut e on average about one fourth of the fiver water, contains abundant Ca 2+ but no detectable nitrogen. Results similar to ACF were obtained fo r Sop and Och, though Och exhibits some association of NO3- with the C a2+-rich component. Similar APCA of wet precipitation resolves mainly components that represent acid rain, with NO3-, SO42-, and NH4+, and s ea salt, with Na+, Cl-, and Mg2+. Inland, the acid rain component is r elatively more prominent and Cl- is depleted, while at atmospheric mon itoring sites nearer the coastal region sea salt tends to be more prom inent.