Agricultural-Based Food Production Geoenvironment Stressors - Sustainable Practices in Geoenvironmental Engineering - page 184

Atmosphere

Runoff leading to
eutrophication of
surface water

Plant uptake
and denitrification Organic nitrogen

and fertilizers

Contaminated groundwater

+ - -

NH 4 NO 2 NO 3

Aquifer

FIGURE 6.4
Illustration of the nitrogen cycle as it relates to the geoenvironment and farming practices.

be altered through production of nitrogen oxides, which can impact human and ecosystem
health (Figure 6.4). The nitrogen can travel from agricultural ields, to the rivers, streams,
groundwater, and inally to the oceans. The diffusion processes for fertilizers (1 m/year)
are slow. Consequently, groundwater contamination may not be seen until a decade after
a large amount of fertilizer is spread (Chamley, 2003).
Nitrogen from fertilizers can be converted to nitrate before uptake by plants. When this
happens, contamination of rivers, lakes, estuarine, deltaic, or coastal waters can occur, as
shown, for example, in Figure 6.4. Toxic algal blooms (by the dinolagellate Pisteria ) can
result from the eutrophication of estuaries and kill ish via their toxins. Eutrophication
processes also deplete the oxygen in the water, destroying aquatic ecosystems. These
phenomena affect the sustainability of isheries. In the United Kingdom, eutrophication
decreased tourism and the values of waterfront properties by $105 to $160 million/year in
the 1990s and has led to expenditures of $77 million/year to ix the damage (Millenium
Ecosystem Assessment, 2005). Humans can also be affected by shellish poisoning. High
nitrate levels (above 10 ppm) can also lead to methemoglobinenemia (also known as blue-
baby syndrome), abortions, and increased rates of non-Hodgkin lymphoma. Levels above
5 ppm can affect young animals (Pimentel, 1989). Algal blooms initiated by the elevated
nutrient levels lead to (a) disruption of the ecology through oxygen consumption, (b) accu-
mulation of organic content, (c) reduction of water and sediments, (d) asphyxia, and
(e) biota mortality such as plankton and benthos (Chamley, 2003). Inorganic nitrogen levels
in coastal areas have increased by a factor of 2.5 and phosphorus levels by 2, particularly