Ocean urea fertilization for carbon credits poses high ecological risks

Abstract

The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best. The potential for growth of toxic dinoflagellates is also high, as many grow well on urea and some even increase their toxicity when grown on urea. Many toxic dinoflagellates form cysts which can settle to the sediment and germinate in subsequent years, forming new blooms even without further fertilization. If large-scale blooms do occur, it is likely that they will contribute to hypoxia in the bottom waters upon decomposition. Lastly, urea production requires fossil fuel usage, further limiting the potential for net carbon sequestration. The environmental and economic impacts are potentially great and need to be rigorously assessed.

The Challenge of Bioenergies: An Overview

“…The stimulation of fish production by increasing phytoplankton biomass through CO 2 injection into specific ocean localities has also been proposed (Markels & Barber, 2001). However, ocean fertilization has been severely challenged because it would eventually destroy the local ecosystem (Bertram, 2010;Glibert et al, 2008).…”

Relationship between induced phytoplankton blooms and the structure and dynamics of the free-living heterotrophic bacterial community

“…In the U tanks, urea was added as an organic nitrogen source. Our interest in the urea addition arose be cause it has been suggested that urea enrichment could preferentially lead to the dominance of cyano bacteria, pico eukaryotes and dinoflagellates (Glibert et al 2008, and references therein). We observed an increase in dinoflagellates towards the end (Table 2), and Synechococcus reached values higher than in the other treatments from Day 5 to Day 9 (Fig.…”

“…Diatom growth has been reported to be dependent on silica availability (e.g. Allen et al 2005), and urea is thought to potentially select for some cyanobacteria and dinoflagellates because they have been found to preferentially use this molecule as a nitrogen source (Glibert et al 2008, Solomon et al 2010. Other algae are adapted to low nutrient concentrations, and they might bloom after oppor-tunistic species have depleted nutrients.…”

Implications of large-scale iron fertilization of the oceans

“…Ocean fertilization with nutrients is one of 2 potential methods of using the ocean to mitigate atmospheric CO 2 concentrations that have received both wide media interest (Young 2007) and considerable scientific scrutiny (Boyd et al 2007, Glibert et al 2008. (The other method is deep ocean CO 2 disposal; Parks 1999, Brewer et al 1999, Tamburri et al 2000.…”