Sticking to the topic of acidification…I’ve encountered some research on acidification of the world’s oceans and how this may be impacting on the way nitrogen is cycled within them.
An article appearing in Proceedings of the National Academy of Sciences (PNAS) by Beman et al. (2010) details how the quantity of anthropogenic carbon dioxide dissolved in the oceans, and the acidification that occurs as a consequence, has impacted the microbially mediated biogeochemical processes that are so vital to the response of the earth system to environmental change.
Beman et al. state that microbial nitrification (a process where ammonia is oxidised to nitrite and then nitrates by two different groups of microbes) decreased at all of the 6 sites analysed, in both the Pacific and Atlantic oceans, when ocean pH was experimentally reduced. Based on their experimental data, Beman et al. believe that that ocean acidification could reduce nitrification rates by 3–44% within the next few decades; they say that this will affect oceanic nitrous oxide production, reduce supplies of oxidised nitrogen in the upper layers of the ocean, and fundamentally altering nitrogen cycling in the sea.
Beman et al. state that microbial nitrification (a process where ammonia is oxidised to nitrite and then nitrates by two different groups of microbes) decreased at all of the 6 sites analysed, in both the Pacific and Atlantic oceans, when ocean pH was experimentally reduced. Based on their experimental data, Beman et al. believe that that ocean acidification could reduce nitrification rates by 3–44% within the next few decades; they say that this will affect oceanic nitrous oxide production, reduce supplies of oxidised nitrogen in the upper layers of the ocean, and fundamentally altering nitrogen cycling in the sea.
The point about reduced production of nitrous oxide is an interesting one, as it is a potent greenhouse gas (298 times more impact 'per unit weight' than CO2 over a 100 yr period, according to the IPCC) and the ocean is already a significant emitter to the atmosphere. However, there is a chance that this may be offset by other changes, such as increased contributions on nitrogen to the ocean.
Marine food webs can also be affected. Acidification could produce a competitive shift away from ammonia-oxidising organisms, this would result in less nitrate being produced and ammonia would instead be converted into other forms such as regenerated ammonium. An increase in ammonium based primary production would cause a cascade of complex effects throughout marine food webs.
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