Sunday, July 3, 2016

Saving the Bay = Saving the Planet

In addition to sequestering carbon, biochar's capacity for reducing nutrient leaching from cultivated land makes it an especially valuable weapon against global warming around estuaries like the Chesapeake Bay. Other measures are necessary, but in terms of longevity, they are band-aids compared to biochar.  Biochar can throw global warming a one-two punch when prodigiously applied in the Chesapeake's watershed. The carbon sequestration aspect is pretty straightforward, but the nutrient leaching/global warming connection needs more explanation.

In spring and summer, the Chesapeake Bay, due to seasonal changes in its upper and lower water density profiles, is a storehouse of methane-generating detritus in its cold, dense, oxygen-starved lower strata. As hurricane season swings into full gear in mid-summer, a strong storm can bring about the phenomenon know as wind set-up which pushes water level higher on the western shore of the bay and an upwelling of water from the lower layer, pulling methane from the underneath the pycnocline and bringing it to the surface.
From Chesapeake Bay: Introduction to an Ecosystem, Chesapeake Bay Foundation, 1995.
Research by Laura Lapham, Lauren Gelesh, Kathleen Marshall, and +William Boicourt published in February under the title "Methane concentrations increase in bottom waters during summertime anoxia in the highly eutrophic estuary, Chesapeake Bay, U.S.A.", hypothesizes that the methane in the sediment begins to escape into the water and collects under the pycnocline where conditions are anoxic enough to prevent it from oxidizing into more benign substances. When a storm comes through before the methane has a chance to mix with upper layers in the cooling autumn, the sudden upwelling of this methane sends a portion of it into the atmosphere.

We already know that estuaries throughout the world contribute something like 3% of total methane to the atmosphere without the large pulses just described. In such an event, however, the Chesapeake Bay (the U.S.A.'s largest estuary) could almost double that figure, were all the sub-pycnocline gas bubbles to escape. Hurricanes and tropical storms have impacted my Maryland home near the Bay about once every three years, of late. It is worth considering that major storms in late summer, when methane buildup is at its peak, may cause methane bursts of this magnitude.

To grasp the magnitude of such an event, let's say just one-third of the Bay's methane inventory were to bubble out during a major storm in mid-August. That would be 47 times the amount released over a 100 day period in the Aliso Canyon natural gas leak!  (Aliso Canyon incident emitted 0.1 Tg. - the largest such leak ever in the U.S.  Based on annual total worldwide CH4 emissions of 469 Tg, a 1% increase from Chesapeake Bay would be 4.7 Tg.)

We cannot shift the burden of climate change to ocean estuaries and blame the Chesapeake Bay for emitting all these greenhouse gases. These episodes would not occur if the Chesapeake Bay were in a healthy condition in which the lower strata maintained adequate oxygen year-round. This is anthropogenic and the cause is mainly excess nutrients and uncontrolled runoff. The tendency of storm intensity to increase as global temperatures warm also gives this punishing sequence of events a positive feedback quality. To stop it, we need to not only think about how to reduce the concentration of atmospheric CO2, but also how to clean up the water draining into our major estuaries.

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