|
Nitrates in
forest streams, because elevated levels may indicate changes in
forest functioning and/or increased inputs from the atmosphere, and
can impair water quality. (Figs. 1, 2,
3)
Soil properties,
because the chemical, physical, and biological properties of soil determine
its capability to supply water and nutrients for plant growth. (Fig.
4)
Nitrate concentrations
in forest streams are generally low relative to drinking water standards
(10 parts per million) and are generally much lower than those in urban
or agricultural areas.
Nitrates
In Forest, Urban
& Agricultural Streams (1)
Technical
Note |
Nitrate
Concentrations
In Forest Streams (2)
Technical
Note |
|
 |
 |
Available
nitrogen is low in most forest soils and is often the factor that
most limits plant growth. As a result of competition among trees,
plants, and soil microbes, nitrogen is retained, and concentrations
in forest streams are usually low.
|
| Source:
USGS National Water Quality Assessment |
| |
Source:
USGS National Water Quality Assessment |
|
Nitrate
Concentrations In Forested Watersheds
(Mid-Atlantic states) (3)
Technical Note |
|
 |
This
study of 346 watersheds found that watersheds with a higher proportion
of forest area generally have lower concentrations of nitrates¾a
common pollutant¾than do similar watersheds with less forest area. |
| Source:
US Environmental Protection Agency |
|
| Soil
Properties (4) |
 |
| The capability
of a soil to support plant growth depends on its chemical, physical,
and biological properties. These properties are affected by natural
processes, soil management practices, and other human influences.
Changes in soil chemical properties that indicate nutrient depletion
by tree harvest and acidic deposition have been reported at some
research sites but not others |
|
STATUS
OF DATA & OTHER NOTES
|
No consistent
or comprehensive national information is available on forest soil
properties, and we did not select a specific measure for reporting
on these properties. Soil monitoring is difficult because intensive
sampling is needed to account for natural variability. Good information
on long-term changes in soil conditions has come from a limited
number of research sites.
Data in 1
and 2 are from a continuing monitoring program (the U.S. Geological
Survey [USGS] National Water Quality Assessment, or NAWQA), which
will expand in coverage over time. The stream nitrate data in
Figure 3 are from the Mid-Atlantic region and may not represent
conditions in all forests. These data are from a U.S. Environmental
Protection Agency research project.
Because the
focus of this report is on ecosystem conditions, and not on stresses
that may affect an ecosystem, this page DOES NOT include information
on stressors such as acid rain or atmospheric deposition of nitrates,
sulfates, or other chemicals.
Please see
the Technical
Notes at the back of this book for additional information.
|
|
