• Virginia’s oyster harvest expanded
ten-fold from 2001 to 2011.
The Chesapeake Bay ecosystem is complex, diverse, and productive. The watershed
is 64,000-square miles and includes parts of
six states and the District of Columbia.
brated models were used to estimate existing
pollution loads and conditions. Finally, various scenarios were run with reduced nitrogen, phosphorus, and sediment pollution.
The pollution limits were set at levels needed for healthy levels of dissolved oxygen and
• Improved survival rates in
Maryland (see page 23 for more).
Scientists use computer models to better
understand complex systems and how best
to manage them. In the case of the Bay pollution limits, EPA and the Bay jurisdictions
used three models—an atmospheric model
that predicts the deposition of nitrogen from
sources like cars and power plants, a watershed model that estimates pollution (from
various sources) coming off the land, and
finally, a water-quality model that predicts
the effects of these pollution loads on water
clarity and dissolved oxygen in the Bay and
• Farm-raised oysters in the Bay
increased more than twenty-fold
in the five years ending in 2010.
The tricky part was fairly allocating those Bay-wide pollution limits. It wouldn’t be fair to set
the same reduction rate for each state, because
some have already done more to reduce pollution. State allocations, therefore, were based
on a percentage of pollution reduction from a
theoretical maximum as opposed to a reduction from current progress.
• Sanctuary bars are being used
to restore oysters’ ecological
role (see page 25 for more on
how this is working in Virginia’s
The first step in establishing the pollution
limits was to calibrate the models. This was
done by comparing the models’ predictions,
for example, of pollution loads, dissolved
oxygen, or water clarity to actual monitoring
data. The models were adjusted, when nec-
essary, to provide the best fit. Next, the cali-
EPA and the Bay states will continue to
update the models with the best available
information. So though the limits currently
are set, they will be reviewed in 2017 to
ensure the use of the best science to restore
this national treasure.
u To learn more about pollution limits, visit
Spring is in the air.
It’s time to dust off the picnic blanket
and enjoy a nice relaxing day with
friends and family.
Shop CBF’s online store and use your
10% member discount code CBFP1-23229.
We have many products to choose from.
CBF just concluded our annual Save
the Bay photo contest, but you can still
participate. Go to cbf.org/photocontest
to vote for your favorite photo in our
Viewers’ Choice Gallery.
The winning photo will be displayed
on our website in early May as well
as in our next Save the Bay magazine.