Emerging Role of Atmospheric Nitrogen Deposition in Coastal Eutrophication: Biogeochemical and Trophic Perspectives

Abstract

Approximately half of the world's oceanic primary production originates in coastal waters which are often nitrogen (N) limited and sensitive to externally supplied N. Among anthropogenically generated N sources, atmospheric deposition of N (ADN) (as wet- and dryfall) contributes 10–50% of the total external N load at present (20–100 mmol N∙m⁻²∙yr⁻¹), and this will increase. At current levels, atmospheric N inputs lead to a significant enhancement of CO₂ fixation and chlorophyll a production. ADN may play a central role in mediating "new" production in coastal oceans downwind of emissions. Alterations in productivity, nutrient flux, and trophic changes have recently been documented from the Baltic and North seas, the Northwest Atlantic seaboard, and the Western Mediterranean. The recently noted "epidemic" of toxic and nuisance phytoplankton blooms is possibly due to accelerating nutrient loading inshore, especially from atmospheric sources. A need exists to spatially and temporally evaluate, quantify, and potentially manage this nutrient-production interaction on regional and larger synoptic scales. Aircraft- and satellite-based multiband ocean color remote sensing (SeaWiFS) will help characterize and link the spatial-temporal interactions of this (and other) "new" nutrient inputs with biogeochemical and trophic changes in coastal and offshore waters.