The Haber Bosch-harmful algal bloom (HB-HAB) link

Large-scale commercialization of the Haber–Bosch (HB) process is resulting in intensification of nitrogen (N) fertilizer use worldwide. Globally N fertilizer use is far outpacing that of phosphorus (P) fertilizer. Much of the increase in N fertilizers is also now in the form of urea, a reduced form of N. Incorporation of these fertilizers into agricultural products is inefficient leading to significant environmental pollution and aquatic eutrophication. Of particular concern is the increased occurrence of harmful algal blooms (HABs) in waters receiving nutrient enriched runoff. Many phytoplankton causing HABs have physiological adaptive strategies that make them favored under conditions of elevated N : P conditions and supply of chemically reduced N (ammonium, urea). We propose that the HB-HAB link is a function of (1) the inefficiency of incorporation of N fertilizers in the food supply chain, the leakiness of the N cycle from crop to table, and the fate of lost N relative to P to the environment; and (2) adaptive physiology of many HABs to thrive in environments in which there is excess N relative to classic nutrient stoichiometric proportions and where chemically reduced forms of N dominate. The rate of HAB expansion is particularly pronounced in China where N fertilizer use has escalated very rapidly, where soil retention is declining, and where blooms have had large economic and ecological impacts. There, in addition to increased use of urea and high N : P based fertilizers overall, escalating aquaculture production adds to the availability of reduced forms of N, as does atmospheric deposition of ammonia. HABs in both freshwaters and marginal seas in China are highly related to these overall changing N loads and ratios. Without more aggressive N control the future outlook in terms of HABs is likely to include more events, more often, and they may also be more toxic

Global hindcasts and future projections of coastal nitrogen and phosphorus loads due to shellfish and seaweed aquaculture

A model was developed to estimate nitrogen and phosphorus budgets for aquaculture production of crustaceans, bivalves, gastropods, and seaweed, using country production data for the 1970–2006 period from the Food and Agriculture Organization and scenarios based on the Millenium Assessment for 2006–2050. Global production of crustaceans (18% yr−1), molluscs (7.4%), and seaweed (8%) increased rapidly during the 1970–2006 period. Scenarios indicate that annual nutrient release from all shellfish (crustaceans, bivalves, and gastropods) aquaculture will rapidly grow from 0.4 to up to 1.7 million tonnes of nitrogen and from 0.01 to 0.3 million tonnes of phosphorus between 2006 and 2050. The nitrogen and phosphorus releases from global freshwater shellfish aquaculture will increase from 1% of river export in 2006 to up to 6% in 2050. Marine shellfish production is an important contributor to nutrient loading of coastal seas, particularly in Eastern Asia. Nitrogen (7% of marine aquaculture + river export in 2006 and up to 19% in 2050) and phosphorus (12% in 2006 and up to 30% in 2050) releases from Chinese marine shellfish aquaculture are important and growing contributors to total nutrient inputs to coastal seas. Production of crustaceans and bivalves causes changes in nutrient stoichiometry and increasing reduced and organic nitrogen forms, which are of concern because of their preferential use by some harmful algae. Nutrient withdrawal by seaweed is projected to increase rapidly over the coming decades. To overcome effects of increasing nutrient release from shellfish production, integrated systems that include seaweed may play an important role in reducing this nutrient load