Geoscience Reference
In-Depth Information
Figure 10-3.
Nitrogen oxides (NO
X
) are released by burning gasoline and diesel fuel in vehicles and contribute to
acid rain. Photo by J.S. Aber; Warsaw, Poland.
again into organic matter. In marshes with algal
blooms, pH may exceed 8, in which case ammo-
nium is converted into ammonia (NH
3
) and
released into the atmosphere (Mitsch and Gos-
selink 2007). Under aerobic conditions, ammo-
nium may be converted into nitrite (NO
2
−
) and
then nitrate (NO
3
−
) respectively by
Nitrosomonas
and
Nitrobacter
. Denitrii cation is the further
conversion of nitrate into nitrogen (N
2
) or
nitrous oxide (NO
X
) gases by facultative bacteria
under anaerobic conditions. Nitrogen gas makes
up the largest fraction of the atmosphere (
c
.
80%), so its production has no impact on climate.
Nitrous oxide, however, is a greenhouse gas that
could affect climate.
Human activities have essentially doubled the
amount of nitrogen entering terrestrial and
wetland ecosystems, as result of fertilizer runoff,
nitrogen-i xing crops, and burning fossil fuels
(Fig. 10-3; Mitsch and Gosselink 2007). This
extra nitrogen is a nutrient in wetlands, leading
to eutropic conditions and algal blooms. When
the algae die, oxygen is consumed by the decay
process, and hypoxic (
10.1.3 Phosphorus, potassium and sulfur
Phosphorus, like nitrogen, is also often a limiting
nutrient in wetland habitats, particularly in
northern bogs, fresh-water marshes, and deep-
water swamps (Mitsch and Gosselink 2007). For
example, Everglades saw grass (
Cladium jamai-
cense
) communities are limited by phosphorus
(Charman 2002). Phosphorus is typically bound
in minerals as well as organic litter and peat, but
does not occur in wetland gases. It is not directly
affected by redox conditions, but does interact
with several other elements that affect its avail-
ability for plant growth (Reddy et al. 1999):
• P is i xed as aluminium and iron phosphates
under acidic conditions.
• P bound by calcium and magnesium under
alkaline conditions.
• P is most bioavailable under neutral to
slightly acidic conditions.
Phosphorus is considered to be an essential
element for life in the DNA molecule and adeno-
sine triphosphate, which stores chemical energy.
Arsenic is chemically similar to phosphorus, but
is a well-known poison for most life. Recently a
bacterium from alkaline soil of dry Lake Mono,
California demonstrated the ability to substitute
arsenic for nearly all phosphorus in its body.
The GFAJ-1 strain, a member of the common
<
2 mg/L dissolved oxygen)
conditions result in i sh kills and widespread
“dead zones” in coastal marine waters around
the world. Off the coast of Louisiana, for
instance, the hypoxic zone appears annually
and extends over 15,000 to 20,000 km
2
in many
years (Fig. 10-4).
