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PROPOSED
MEASURES: PLANT GROWTH & PRODUCTIVITY
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Concentration
of chlorophyll, as a measure of the amount of algae in coastal waters.
Algae form the basis for coastal food chains but can also be over-abundant,
which creates problems. (Fig. 1)
Concentration
of dissolved oxygen. Oxygen needed by fish and other animals can
be depleted when excess algae accumulate and decompose. Ideally, this
indicator would be reported as the percentage of water (by volume) in
an estuary that is either low in oxygen or completely without oxygen.
(Fig. 2)
No national statements
can be made using the available data.
| Remote
Sensing of Chlorophyll (1) Technical
Note |
 |
| Source:
National Aeronautics and Space Administration and NOAA’s National
Ocean Service |
|
The concentration
of chlorophyll is a measure of the amount of algae in coastal
waters. Algae are a normal component of coastal and marine waters,
but human activities are increasing the levels of nitrogen and
phosphorus (key plant nutrients) above historical baselines, resulting
in increased algae growth, or eutrophication. Eutrophication often
has negative consequences; for example, decaying algae can use
up oxygen, resulting in fish kills and habitat degradation. Chlorophyll
concentrations can also be used to estimate primary productivity
- the rate at which solar energy is converted to algae.
When algae
bloom and die, their decomposition depletes the water of oxygen,
especially near the bottom and in poorly flushed estuaries. The
stars on the map indicate estuaries in which low dissolved oxygen
poses a significant concern, as identified by experts participating
in a national survey by the National Ocean Service.
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| Example:
Area of Gulf of Mexico Low-Oxygen Zone (2) Technical
Note |
 |
| Source:
Modified from Rabalais et al 1998 |
|
The
Gulf of Mexico exhibits an extreme case of hypoxia, or low-oxygen
conditions, with an area nearly 5,000 square miles affected in
1998.
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STATUS
OF DATA & OTHER NOTES
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No consistent
and comprehensive national information is available on chlorophyll
concentrations in estuaries. Satellite remote sensing can detect
chlorophyll levels in some bodies of water but not in estuaries,
where problems often occur, and there is little monitoring of
local conditions.
No consistent
and comprehensive national information is available on oxygen
concentrations in coastal and ocean waters. Information on the
Gulf of Mexico low-oxygen zone is provided as an extreme example
of this problem; the area of low oxygen was approximately the
size of Connecticut in 1998. The NOAA National Eutrophication
Survey, which was the source of the information identifying estuaries
with hypoxia problems (the stars on the remote sensing image),
was based on survey and interview analysis with local and national
experts. Thus, it represents the best scientific judgment, not
the results of a comprehensive monitoring program.
Please see
the Technical
Notes for additional information.
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