Chesapeake Bay Acidification
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6.
The Long-term goal should be to successfully quantify and attribute carbonate chemistry dynamics
to particular drivers such as elevated atmospheric CO
2
, changes in river discharge to the Bay,
changes in the pH of ocean water mixing into the Bay, or water column processes such as
photosynthesis and respiration.
7.
Shore-based pCO
2
measurements indicate strong influences of diurnal and tidal cycling, as well as
strong seasonal variation. Temporal and spatial variability can be orders of magnitude higher than
in the open ocean. Seasonal and interannual dynamics need to be placed in a long-term context
through observation with the goal of understanding how such patterns may be trending through
time.
8.
Sources of total alkalinity, a measure of a water body’s ability to resist change in pH with
changing CO
2
concentrations, need identification and quantification. Alkalinity-generating
biogeochemical processes such as sulfate reduction are widespread in Chesapeake Bay and
hydrologically coupled tidal saltmarshes. It is likely that tidal wetland soil processes control
outwelling of alkalinity and pCO
2
from marshes to adjacent estuaries, and tidal marsh outwelling
is important at local and regional scales.
9.
Efforts should be made to determine the need and feasibility of “weather-” versus “climate-”
quality measurements (as defined in the Blue Ribbon Panel report) for characterizing and
quantifying carbonate chemistry/acidification in Chesapeake Bay over time and space.
10.
Caution should be exercised when considering making direct measurements of pH in many
reaches of Chesapeake Bay that fall within the oligohaline to lower polyhaline salinity zones (0-20
psu). First, pH probes have been designed specifically for use in fresh water or marine water of
salinity ≥20 psu. Likewise, spectrophotometric/dye pH methods are similarly constrained. At
present, the accuracy of pH measurement in waters of 1-20 psu is not well characterized. Second,
changing ionic strength (correlated with changing salinity) may adversely affect pH measurements
due to differences from calibration solution ionic strength. Third, the physical and chemical
influences of biofouling may adversely affect field deployed pH probes, resulting in drift or poor
operation. Continued efforts to develop reliable pH measurements should be sought.
11.
Although there are some technical obstacles in measuring pH in estuarine settings, pH is an
important parameter in the carbonate system and continued refinement of pH technology is much
needed. Given the uncertainty surrounding pH measurement in the Bay (past and present), any
program on estuarine acidification should also measure pCO
2
, TCO
2
, and total alkalinity, all of
which are readily available for determining carbonate chemistry. However, the extent and effect of
non-carbonate alkalinity on carbonate chemistry calculations should be formally determined.
Direct real-time measurements of pCO
2
are taking place in Chesapeake Bay and should be
expanded, as measurement of this parameter may avoid a common over-estimation error
associated with calculating pCO
2
from pH and alkalinity (Abril et al., 2014).
12.
Instrumentation, both shore-based and vessel-based, needs to be considered. Opportunities to co-
locate carbonate chemistry measuring devices with existing water quality stations and cruise
opportunities should be explored.
13.
Current Chesapeake Bay biogeochemical models do not include information on carbonate
chemistry; however, as inorganic carbon budgets begin to emerge, these parameters should be
added to existing models, especially those being used to understand dissolved oxygen dynamics.
