Changing Land-, Sea-, and Airscapes: Sources of Nutrient Pollution Affecting Habitat Suitability for Harmful Algae

Abstract

Globally, nutrient loading to surface waters is large and increasing, with sources from land-based pollution to aquaculture and atmospheric deposition. Spatial differences in amounts and forms of nutrients released to receiving waters are large, with Asia, Western Europe, and North America exporting the highest loads of nutrients, especially of inorganic nitrogen (N). Export of N is increasing more rapidly than that of phosphorus (P) on a global basis, leading to stoichiometrically imbalanced nutrient conditions. Under such conditions, some types of harmful algal blooms (HABs) can thrive. Differences in coastal typology affect the retentive nature of different coastal types, while dam and reservoir constructions have further altered riverine flows and differentially retain different nutrients. A coastal eutrophication index comparing information on the changes in N and P relative to silicon (Si) and modeling projections of future outcomes using several modeling approaches show that the likelihood for increased nutrient pollution and, correspondingly, for continued regional and global expansion of HABs is great.