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.
