Biology Reference
In-Depth Information
prevent pregnancy,” says scientist Ben Greenfield of the San Francisco Es-
tuary Institute. “The bay, and every waterway in the world, is becoming
this petri dish that all these things are leaching into at very low concentra-
tions, and we're starting to see some stresses on the fish and wildlife.”
Sadly, nature doesn't always cooperate with humanity's best intentions.
The processes at work in such a large water system complicate cleanup. In
the past, for example, rivers were constantly adding new layers of sedi-
ment eroded from upstream to the bottom of the bay. As a result, a lot of
contaminants—which naturally attach themselves to sediment particles—
got buried and immobilized, or “sequestered,” semipermanently within
bay mud. However, since dams have trapped the supply of sediments from
upstream, the bay floor has started to erode. When long-buried contami-
San Pablo
Bay
Suisun Bay
Rivers
Central Bay
South Bay
Lower South
Bay
0
20 miles
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0.11
0.12
Map 7. Distribution of total methyl mercury, the most bioavailable and toxic form of
this heavy metal, in water in San Francisco Bay, measured in nanograms per liter
(ng/L). Plots based on 75 data points collected from 2006 to 2008 as part of the
Regional Monitoring Program conducted by the S.F. Estuary Institute. (S.F. Estuary
Institute)
