K. Coastal Acidification

Drivers & Stressors Condition of the bay human connections

K. Coastal Acidification

Coastal Acidification Varies Seasonally, Daily, Jerry Monkman, Ecophotography.com
and Among Locations in Casco Bay

Scientists Are Investigating Local Patterns and Causes of Acidification

why it matters Dissolved Carbon Dioxide Rises
over the Summer and Fall
Lobsters, clams, and many other marine species build their
shells out of carbonate minerals that they extract from 1000
seawater. Acidification of the water can make it more difficult
for them to build their shells, or even cause shells to dissolve. 500
Four out of every five dollars in Maine fisheries comes from Corrected pCO2 (mAtm) Year
shell-building species. Lobster represents about 75 percent
of the fisheries' total value, and clams, oysters, urchin, and Jan 2015
scallops account for another five or six percent. Feb 2016
Mar 2017
In offshore waters, the primary cause of acidification is carbon Apr 2018
May
dioxide (CO₂) from the atmosphere dissolving into the water. Jun
Jul
One quarter of the carbon dioxide released to the atmosphere Aug
Sep
by human activity annually is absorbed by the ocean, making Oct
Nov
ocean acidification a global concern. Near the coast, however, Dec

other localized sources such as rivers and nutrient pollution

are major contributors to acidification, which refers to changes Carbon dioxide levels in the Bay (temperature-corrected) are at their
lowest in the spring, and climb steadily through the fall. Levels are
in not only pH but also availability of carbonate ions. Coastal above atmospheric concentrations (~ 400 µAtm) most of the year.

acidification interacts with other environmental stressors like

climate change, invasive species, and poor water quality to

affect the ecosystem. 7

status &6trends pH Decreases from Summer to Fall

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conditions corrosive enough to dissolve carbonate 8.25pH Year
minerals like clam shells. Scientists from the University of 8.00
New Hampshire, with funding through Casco Bay Estuary 7.75 Jan 2015
Partnership, have monitored coastal acidification near Feb 2016
Southern Maine Community College (SMCC) in South Mar 2017
Portland for five years. The monitoring reveals seasonal Apr 2018
and daily variations reflecting biological activity in the May
ecosystem. Carbon dioxide levels fluctuate seasonally 7.50 Jun
and daily, in synchrony with cycles of photosynthesis, Jul
respiration, and decomposition. In late summer and fall, Aug
levels of carbon dioxide hit their peak, pH drops, and Sep
acidification reaches levels of concern. For most of the year, Oct
levels of carbon dioxide dissolved in the Bay's waters are Nov
higher than atmospheric levels, meaning the Bay seldom Dec
absorbs carbon dioxide from the atmosphere.
At SMCC, pH shows a clear seasonal pattern, dropping over the
course of the year by as much as a half of a pH point. pH is measured
on a logarithmic scale, so that difference in pH represents a change in
acidity by a factor of 3.

25 casco BAY estuary partnership