NUTRIENTS - Marine Pollution: What Everyone Needs to Know - page 30

developed coastlines for unknown reasons. Small-scale exper-
iments have shown that nutrient addition results in a decrease
in the ratio of plant roots to shoots, an increase in above-ground
tissues, a change in plant species composition, and increased
vulnerability of plants to herbivores. Linda Deegan and a
team of scientists working on entire tidal creeks added nutri-
ents to the water coming into a marsh on rising tides, similar
to nutrient-enriched estuaries, and compared the responses
with control creeks over nine years. As expected, plants grew
smaller roots because nutrients were easier to find, and the
decomposition of organic matter in the soil increased because
the extra nutrients enabled bacteria to break it down more
easily. But other results were unexpected. After a few years,
cracks formed in the banks of the high-nutrient creeks, which
then collapsed down into the creeks—eventually turning the
vegetated marsh into a mudflat, which is less productive and
does not provide equivalent habitat for fish and wildlife. The
loss of roots and organic matter reduced the stability of the
creek-bank soils, leading to the collapse of creek banks and the
eventual conversion of salt marsh into mudflat. These results
demonstrate the value of long-term field studies and show that
salt marshes have a finite ability to absorb nutrients before
they themselves are damaged.
How widespread is eutrophication?
Reports of marine and coastal hypoxic areas or dead zones
have been increasing in recent years, with increased popula-
tion growth, urbanization, and expansion of agriculture. The
World Resources Institute has compiled maps and identified
415 areas around the world that are experiencing eutrophi-
cation, but there are many areas where there is not enough
information to determine the extent of eutrophication or
identify sources of the nutrients. The increase in reports of
hypoxic areas may also be due in part to more scientists look-
ing for them. Many areas in the United States and Europe