Chesapeake Bay Acidification
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5
W
ORKSHOP
O
VERVIEW
We sought to engage a range of experts from both the regional and national stage. Participants (see
below) included experts in carbon chemistry, biogeochemistry, and hydrodynamic modeling of
Chesapeake Bay, many from academic and research institutions. We also received input from experts
engaged in a variety of coastal and Chesapeake Bay observing systems, as well as scientific contributors
from various related state, regional and federal efforts. Representatives of the U.S. Integrated Ocean
Observing Program (IOOS) and NOAA’s Ocean Acidification Program attended as did representatives of
NGOs. The sections on
Steering Committee
and
Participants
provide the complete list of workshop
attendees. Importantly, the workshop participants provided a broad range of experience and information
on various aspects of coastal ocean acidification, including ongoing efforts to investigate and monitor
carbon chemistry in other coastal regions such as the Pacific Northwest and New England Coasts.
The workshop consisted of several short presentations to put a focus on what is known about carbonate
chemistry in coastal ecosystems and Chesapeake Bay in particular, and a series of discussions that were
guided by a set of charge questions. Presentations summarized research, environmental monitoring and
modeling efforts, as well as contemporary and historical water quality measures that inform our current
state of knowledge with regard to carbonate chemistry dynamics and acidification in Chesapeake Bay.
C
HARGE
Q
UESTIONS
A series of charge questions was posed to help stimulate and guide discussion in the workshop.
Charge Question A - What is currently known about acidification of Chesapeake Bay?
When compared with open oceans and growing data sets in coastal settings such as Puget Sound and the
Gulf of Maine, very little attention has been given to Chesapeake Bay. Nevertheless, retrospective
analyses of pH data from the Chesapeake Bay Program’s historical data set (1984-2008) indicate
significant spatial variation with respect to changes in pH, including across salinity zones in the mainstem
of the Bay’s tributaries. Rates of pH change apparently far exceed those directly attributable to
atmospheric CO
2
rise (Waldbusser et al., 2011). These historical pH data are dominated by daytime
measurements, when photosynthesis can raise pH through the fixation of CO
2
, so must be interpreted with
some degree of caution. Partial pressure measurements of CO
2
in the Rhode River, a mesohaline reach of
Chesapeake Bay, taken once a minute over more than two years (2012-2014, Miller unpublished data)
reveal strong diurnal swings in pCO
2
/pH. CO
2
concentrations decline during the day due to
photosynthetic activity (increasing pH), and rebound at night from benthic respiration (decreasing pH,
Miller unpublished data). These diurnal patterns vary strongly across seasons because of temperature
effects on biological activity. For example, the acidifying effects of respiration diminish substantially
during the cold winter months. In the Rhode River, pCO
2
/pH also shows strong spatial variability, much
of which can be traced to tidal saltmarshes that deliver water high in pCO
2
and total alkalinity on falling
tides.
Recent carbonate chemistry measurements from the Delaware Bay and main stem of Chesapeake Bay
(Cai unpublished data, Salisbury unpublished data) suggest that the upper portions of these bays are likely
sources of CO
2
(net heterotrophic) and the lower portions are CO
2
sinks (net autotrophic). These results
are especially interesting considering recent reviews that suggest that estuaries are believed generally to
be strong sources of CO
2
(Cai, 2011; Borges & Abril, 2011).
