Chesapeake Bay Acidification
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1
E
XECUTIVE
S
UMMARY
Scientists forecast that open ocean pH will continue to decline by 0.1 to 0.4 units, but such forecasts for
estuaries and coastal oceans are far more challenging due to dramatic spatial and temporal variation in the
processes that control pH. Chesapeake Bay is an intensively studied estuary that is well understood in
terms of nutrient chemistry, hydrodynamics, ecology and fisheries, but poorly understood from the
perspective of pH, the carbonate chemistry that largely controls pH, and the sensitivity of marine biota to
pH change. This report is the outcome of a workshop focused on acidification in Chesapeake Bay, the
goal of which was to assess the state of the relevant scientific knowledge. It is anticipated that this first
step will be followed by engagement with the management community and stakeholder groups such as
the aquaculture industry, culminating in the establishment of a Chesapeake Bay Acidification Network.
The carbonate chemistry of Chesapeake Bay and similar estuaries worldwide is highly sensitive to the
chemistry of tributaries (rivers and streams), the terrestrial watersheds that feed into tributaries, and
therefore human activities on land. Land use in Chesapeake Bay varies from agriculture to urban
development across small distances and is constantly changing, creating complex spatial and temporal
patterns that are certain to influence Bay acidification. Overlaid on spatial and temporal variation in
climate, ocean pH, and Bay sediments, it is clear that an estuarine acidification observing network in
Chesapeake Bay requires a high density of spatial and temporal observations. Fortunately, the
infrastructure developed over several decades to monitor the chemical and biological health of
Chesapeake Bay can be leveraged to address this newly emerging biogeochemical perturbation, a
phenomenon that shares mechanistic links with nutrient eutrophication. The most efficient strategy for
capturing key sources of spatial and temporal variation is to add acidification observing platforms across
the full suite of existing Bay water quality observation assets, including shore-, vessel-, and buoy-based
sampling stations. This goal will require cooperation among county, state and federal agencies and
academic institutions, another area where the Chesapeake Bay already has extensive experience.
Scientists working in Chesapeake Bay have begun to work on estuarine acidification, providing a
framework for the design of an observing network. For example, total alkalinity in major tributaries such
as the Susquehanna and Potomac has been rising in recent decades, perhaps due to human activities; it
appears that upper portions of the Bay are likely sources of CO
2
while lower portions are CO
2
sinks; and
it is clear that tidal wetlands are point sources of CO
2
-enriched water and perhaps alkalinity to the Bay.
Finally, academic institutions have been developing and testing the sensor technology required to build a
highly resolved acidification observation network.
The information gaps to be filled by a Chesapeake Bay Acidification Network are large, requiring a
process for setting priorities. The workshop identified four goals that will advance our capacity to forecast
Bay acidification: (i) determine Bay-wide patterns of pH, pCO
2
, dissolved inorganic carbon, total
alkalinity and CO
2
fluxes at the air-water interface, with sufficient resolution to capture temporal (daily,
seasonal, annual) and spatial (sub-watershed) variation, (ii) understand the biogeochemical and physical
controls on pH-relevant chemical fluxes across the key interfaces of land:estuary, ocean:estuary, and
sediment:water column, (iii) link the carbonate system to biological processes in the water column such as
photosynthesis and respiration, and (iv) determine the sensitivity of Bay biota to natural variation in Bay
carbonate chemistry and acidification-driven changes thereof.
The workshop posed several questions to guide the planning of a Chesapeake Bay Acidification Network
(CBAN): Is elevated atmospheric CO
2
an important driver of Bay pH? How important are the fluxes that
cross ecological subsystem boundaries to estuarine pH? Does CBAN need to capture short-term (e.g.
weather-scale) and long-term (e.g. climate-scale) variation in order to forecast acidification trends? How
can existing Bay observing networks and expertise be leveraged to address acidification? Which
