View of runoff, also called nonpoint source pollution, from
a farm field in Iowa during a rain storm. Topsoil as well as farm fertilizers
and other potential pollutants run off unprotected farm fields when heavy rains
occur.
Credit: Lynn Betts/U.S. Department
of Agriculture, Natural Resources Conservation Service
Dangerous
nitrate levels in drinking water could persist for decades, increasing the risk
for blue baby syndrome and other serious health concerns, according to a new
study published by researchers at the University of Waterloo.
Nitrogen
fertilizer applied to farmers’ fields has been contaminating rivers and lakes
and leaching into drinking water wells for more than 80 years. The study,
published this week in a special issue of the journal Environmental Research Letters,
reveals that elevated nitrate concentrations in rivers and lakes will remain
high for decades, even if farmers stop applying nitrogen fertilizers today.
The
researchers have discovered that nitrogen is building up in soils, creating a
long-term source of nitrate pollution in ground and surface waters.
“A
large portion of the nitrogen applied as fertilizer has remained unaccounted
for over the last decades,” said Nandita Basu, a professor in the Department of
Earth and Environmental Sciences and Civil and Environmental Engineering. “The
fact that nitrogen is being stored in the soil means it can still be a source
of elevated nitrate levels long after fertilizers are no longer being applied.”
Their
paper presents the first direct evidence of a large-scale nitrogen legacy
across the United States’ Mississippi River Basin.
Forced
to invest millions of dollars to upgrade their water treatment plants, Des
Moines Water Works, Iowa’s largest drinking water utility, is currently suing
three upstream counties for failing to address harmful surface-water nitrate levels
that are more than twice the US federal drinking water standard.
Such
nitrate concentrations are likely to remain stubbornly high, according to the
Canadian research team.
Professor
Basu and her group analyzed long-term data from over two thousand soil samples
throughout the Mississippi River Basin to reveal a systematic accumulation of
nitrogen in agricultural soils. In many areas, this accumulation was not
apparent in the upper plow layer, but instead was found from 25-100 cm beneath
the soil surface
“We
hypothesize that this accumulation occurred not only because of the increased
use of fertilizers, but also increases in soybean cultivation and changes in
tillage practices over the past 80 years,” said Kim Van Meter, a doctoral
student in the Department of Earth and Environmental Sciences in the Faculty of
Science.
Their
modeling results suggest that this nitrogen legacy could still be leaching into
waterways more than three decades after nitrogen is no longer being applied to
fields.
Similar
to phosphorus, nitrogen is a limiting nutrient for plants and when applied as
fertilizer helps increase crop yields.
Unfortunately
when too much nitrogen is added, the excess enters waterways, causing hypoxic
conditions such as the Gulf of Mexico’s massive dead zone and threatening
drinking water quality. Exposure to excessive nitrate in drinking water causes
serious health problems, including Methemoglobinemia or blue baby syndrome in
infants.
Since
the 1970s, farmers and policymakers alike have worked hard to reduce the amount
of fertilizer leaking from agricultural fields to groundwater and nearby lakes
and streams. Yet in some rural areas, nitrate levels have been found to be more
than ten times the drinking water standard.
“The
presence of this legacy nitrogen means it will take even longer for best
management practices to have a measurable benefit,” said Professor Basu, also a
member of the Water Institute. “If we’re going to set policy goals, it’s
critical we quantify nitrogen legacies and time lags in human impacted
landscapes.”
https://www.sciencedaily.com
No comments:
Post a Comment