Chesapeake Bay Acidification
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3.
How must CBAN be designed in order to best capture Bay’s short term “Weather” variability
and long term “Climate” acidification trends?
Understanding how “coastal acidification” may
change with changing atmospheric pCO
2
requires characterizing both short-term variation (tidal,
diurnal, seasonal cycling and dynamics) and long-term trends (directional shifts across years to
decades). Detecting long term trends requires that data of adequate accuracy and precision be
collected over a long enough period to indicate directional shifts. Such observations are being
carried out in open ocean settings on a global scale (e.g., GOA-ON). However, because
Chesapeake Bay experiences much greater short term temporal fluctuations and spatial variability
in water quality (including its carbonate chemistry) than the open ocean, observations must be far
more dense to capture and resolve local and regional phenomena.
4.
How can existing observing networks (e.g., Eyes on the Bay, MARACOOS) be leveraged and/or
complemented to yield data that addresses acidification in Chesapeake Bay?
The spatial and
temporal coverage of such existing observation can be leveraged by adding new instrumentation to
existing water quality stations and vessel-based sampling cruises. Instrumentation is available to
reliably measure carbonate chemistry parameters such as pCO
2
, TCO
2
, total alkalinity, (although
see discussion of pH measurement in estuaries below). These would be economical add-ons that
take advantage of existing infrastructure (e.g., shore-based stations and possibly buoys) and
expensive vessel time.
5.
What investigators/experts and research programs are active in Chesapeake Bay, either working
directly on carbonate chemistry/acidification or related areas?
This information will be
important for gauging the current capacity and expertise to address acidification. Understanding
who is working on aspects of this issue will be helpful for building collaborations/partnerships and
shoring up deficiencies, perhaps through collaborations with experts outside the region.
6.
Which combinations of carbonate parameters will yield the most reliable data?
Total alkalinity,
pH, pCO
2
, and TCO
2
each can be useful, depending on the goal or question, but each has its own
challenges, especially in estuarine settings. For example, though
pH
would seem to be an obvious
measurement to make, the measurement is compromised by several characteristics of estuarine
system such as heavy biofouling and rapidly changing salinity and ionic strength in both time and
space. Chesapeake Bay presents serious challenges for autonomous deployments of pH probes,
both for glass bulb and solid state versions. Furthermore, pH probes and dye-based
spectrophotometric pH methods have been designed for use in either fresh water or marine water
of ≥20ppt (Dickson, pers. comm.; Yao & Byrne, 2001; Zhang & Byrne, 1996); however, Mosely
et al. (2004) demonstrate spectrophotometric pH measurements across an estuarine gradient. From
this perspective, pH may not yet be a fully reliable parameter to measure in estuarine settings.
Total alkalinity
titration of filtered discrete water samples is traditionally used to determine the
carbonate buffering capacity of water; however, in some coastal waters organic acids such as
humic substances may contribute organic components (non-carbonate alkalinity) to total alkalinity.
Work by Cai et al. (1998) concluded that protonation and deprotonation of humic substances
occurs rapidly in initial stages of fresh and salt water mixing, such that these organic compounds
may not be contributing appreciably to total alkalinity in middle to high salinity bay waters. Partial
pressure of CO
2
(
pCO
2
) is measured accurately via active air:water equilibration in combination
with an infrared gas analyzer (IRGA). Although historically this measurement has required a very
expensive instrument, modern electronics and IRGAs make this a much more accessible parameter
for measurement. pCO
2
has the advantage of being a real time measurement, and one in which the
sensor is not in direct contact with the water. Total dissolved inorganic carbon (denoted as
TCO
2
)
can also be assessed from discrete water samples that are filtered and sealed to prevent gas
exchange with the atmosphere.
