say nutrients are destroying Lake Victoria
Lake Victoria, the
world's second-largest freshwater lake, is being slowly destroyed
by nutrients carried in soil from deforested land, About 30 million
people depend on the lake for their livelihoods.
Satellite remote sensing
technology used by the Kenya-based International Center for Research
in Agroforesty to study land soil types around the nearly 27,000-square-mile
lake detected a flow of sediments whose water-dissolved nutrients
stimulate the growth of aquatic plants.A dramatic plume of nitrogen-and-phosphorous-rich
sediments feed the water hyacinth As the water hyacinths grow nourished
with sediments from the shores of Uganda, Kenya and Tanzania, they
starve more fish and plankton of oxygen and sunlight.
b. ALGAE LINKED TO
The growth of algae
and associated toxins may be causing a wave of alligator deaths
in Florida. Many species of blue-green algae release chemicals
toxic to the nervous system and liver of animals. Some scientists
believe algae may also be linked to non-cancerous tumors being found
on sea turtles. The increase in algae has worsened in the past years
and is caused by runoff of fertilizers, sewage, and other nutrients
into the water system.
Every year, soil microorganisms
"fix" 140 million tons of nitrogen, thereby enabling plants
to grow and flourish. When plants die, some of that nitrogen is
recycled back into the atmosphere. This process of moving nitrogen
from one form to another is called the nitrogen cycle, and it's
essential to all life.
People are part of this cycle too. We need nitrogen, and we get
it from our food both plants and animals. But we are also
changing the cycle, it's causing tremendous amounts of pollution
to our air and water.
The problem is that people are fixing vast quantities of nitrogen
and releasing it into the environment. In fact, humans now release
almost twice as much available nitrogen every year as do
About one-quarter of
this amount is released through burning fossil fuels, which creates
nitrogen oxides, compounds that can cause smog, global warming,
and acid rain. But the majority of humanity's excess nitrogen comes
from synthetic nitrogen fertilizer used on farmers' fields.
Synthetic fertilizer was first developed in 1913, but its use really
took off in the 1960s during the "green revolution," which
doubled worldwide grain production. Synthetic fertilizer enhances
plant production by boosting the amount of fixed nitrogen available
in the soil.
Today we use so much
of this fertilizer that excess nitrogen is leaching into groundwater,
lakes, rivers, and coastal waters. This leaching removes important
nutrients from the soil, reducing its fertility. It also pollutes
groundwater and can cause an excessive growth of plant life in surface
water, leading to oxygen depletion.
How big a problem is it? About 60 percent of streams sampled
in the United States show some signs of excess nitrogen loading.
The World Water Council, an independent association of water scientists
and engineers, recently reported that more than half of the world's
biggest fresh-water lakes are threatened by pollution or drainage
are also affected. The Gulf of Mexico, for example, contains a notorious
oxygen-depleted "dead zone" caused by agricultural runoff
from the Mississippi River. In sum, ecologists at the recent nitrogen
conference say that the negative impact of excess nitrogen in the
environment ranks right up there with global warming.
But can we dump less
nitrogen into the environment without hurting food and energy production?
It certainly seems that way. Already, clean air laws in many countries
have helped stabilize the production of nitrogen oxides from burning
fossil fuels. Europe leads the way, with plans to reduce them
by 40 percent in the next decade.
Reducing nitrogen leaking from farmer's fields has so far not been
as successful. Fertilizer is cheap and farmers would rather apply
too much, rather than too little, to ensure a bountiful crop. But
studies show that precision application of fertilizers can reduce
the amount of runoff and have little impact on crop yields. For
example, a study on the Mississippi River basin published in the
journal Nature found that reducing fertilizer use by just 12 percent
would reduce nitrogen runoff by 33 percent.
An Assessment of Its Threat to Amphibian Survival
Modification of an
abstract from a paper by Jeremy David Rouse,1 Christine A. Bishop,1
and John Struger
The potential for nitrate
to affect amphibian survival was evaluated by examining the areas
in North America where concentrations of nitrate in water occur
above amphibian toxicity thresholds.
of nitrate in watersheds throughout North America range from <
1 to > 100 mg/L. Of the 8,545 water quality samples collected
from states and provinces bordering the Great Lakes, 19.8% contained
nitrate concentrations exceeding those which can cause sublethal
effects in amphibians. In the laboratory lethal and sublethal
effects in amphibians are detected at nitrate concentrations between
2.5 and 100 mg/L. Furthermore, amphibian prey such as insects and
predators of amphibians such as fish are also sensitive to these
elevated levels of nitrate. From this we conclude that nitrate concentrations
in some watersheds in North America are high enough to cause death
and developmental anomalies in amphibians and impact other animals
in aquatic ecosystems. In some situations, the use of vegetated
buffer strips adjacent to water courses can reduce nitrogen contamination
of surface waters. Environ Health Perspect 107:799-803 (1999). [Online
31 August 1999]