This podcast was moderated by Water for Food Podcast, host Frances Hayes. It was presented by Arindam Malakar, a researcher with the Nebraska Water Center, and Marie Krausnick, assistant general manager for Nebraska’s Upper Big Blue Natural Resources District (NRD).
“While nitrate levels in some areas have decreased in
the Upper Big Blue NRD, there has been an overall increase of 54% in the
district.”
Nitrate is indicated as a
water contaminant that can have significant negative health effects. When I
worked for a county health department collecting private water system samples
from newly drilled wells, we would use a strip to test for the presence of
nitrates/nitrites. As this was not in a farming area, nitrate was never an
issue. I only saw one sample that even registered the presence of nitrate,
although it was too low to be of any concern.
“Excess nitrate in drinking water can cause adverse
health effects, particularly in infants and vulnerable populations, as too much
nitrate in the body makes it harder for red blood cells to carry oxygen.”
The vadose zone is the
interval between plant roots and the top of the water table. The vadose zone is
also considered to be the interval between the surface of the Earth and the
groundwater table. It is the interface and conduit between the ground surface
and the groundwater table. Contaminants from the surface may remain in the
vadose zone for many years and decades. Long-term studies are necessary for
determining how contaminants move through the vadose zone. Contaminants can
move through a porous vadose zone, such as sand, in 3 to 6 years, but movement
through loam and clay soils is much slower.
Both biological and chemical
reactions take place in the vadose zone. Knowing these reactions can point to
remediation methods that will be successful.
The Nebraska Water Center
takes soil cores. Nitrates are a chief contaminant in Nebraska due to
agriculture. This includes manure applications for growing crops as well as
manure from grazing animals, manure ponds, CAFO feeding operations, etc. Vadose
zone soil core collection began in the 1980s, and nitrate profiles can be
developed for the vadose zone. The cores can reach about 100 feet in depth. The
results of newer cores are compared to older ones in the same areas to develop
an idea of how nitrates move and change in the vadose zone. Geoprobes are used
to collect samples and then bring them back to the lab for analysis. They also
collect groundwater samples from monitoring wells. The monitoring program
involves rechecking areas after five years.
One thing to determine is how
fast groundwater and its contaminants move through the vadose zone. Modeling
helps fill in the gaps between samples. Sampling and modeling lead to the
prediction of groundwater quality. Nitrates are often oxidized to ammonium, and
measuring them can be helpful in that the ammonium has less of a negative effect
on groundwater quality. These reactions can be tweaked by speeding them up with
recharge treatments utilizing beneficial microbes. Irrigation techniques and
volumes can affect nitrate contamination.
Vadose zone studies track
nitrate loading and nitrate speed moving through it. Recharge studies are also
required to know how fast groundwater moves from the surface to the aquifer.
Natural Resource Districts
(NRDs) in Nebraska are based on watersheds rather than counties. There are 12
areas of responsibility. There are 17 NRD districts in the state, but also
subdistricts. Emphases vary based on geographic location and whether or not the
Ogallala aquifer is present in the area. The Upper Big Blue NRD collaborates
with the Nebraska Water Center and the University of Nebraska-Lincoln on
groundwater studies focused mainly on nitrate contamination. Other contaminants
besides nitrate are also observed in the vadose zone project, including
uranium, which is present in the state.
NRDs utilize their
groundwater management plans and sample yearly, multiple times a year, or every
three years, depending on results. A certain level of nitrate concentration
triggers more sampling. There is a need to know the farmers’ fertilization and
irrigation details. Agricultural, biochemical, and health researchers are also
partnered in.
Using water well data and
vadose sampling together is useful to determine the nitrate loads in the vadose
zone that are headed to the aquifer, and comparing it to the current
groundwater quality. Land management practices need to be known and tweaked
when necessary. They also collect some pore water samples. If they can connect
specific land management practices to contamination, then they can know
contamination-increasing practices vs. those that do not increase contamination.
Till vs. no-till is one example of practices that might affect groundwater
quality. In that case, tilling leads to more nitrate contamination
The state utilizes a credit
system that is devised to decrease nitrate loads. One is to utilize the nitrate
in the vadose zone by pumping it back up to be reused as fertilizer.
Nebraska has about 40 years
of vadose zone sampling. Aside from nitrate, as noted, other contaminants are
studied. These include other forms of nitrogen that may be formed in the vadose
zone. Nitrate loss and leaching need to be better understood. The state is
ahead of nearby states in nitrate studies. Nebraska has a comprehensive and
holistic approach that exceeds that of other states, especially its long-term
vadose zone research, which other states are utilizing to better understand
their own vadose zone issues. Vadose zone research is also picking up around
the world, with China, New Zealand, and the EU leading with papers being
published. Earlier studies focused more on how quickly nitrate moved through
the vadose zone. More recent focuses have been on co-contamination, including
nitrogen and nitrate reaction byproducts. The data is shared publicly. The
Nebraska Water Center has an interactive map where specific data can be pulled
up by site. It is linked in the Nebraska Vadose Zone link below in the
references.
Nebraska Vadose Zone Program
References:
The
Vadose Zone - A Critical Indicator for Nebraska Groundwater Quality: Daugherty
Water for Food Podcast, Episode 44. July 30, 2025. Daugherty Water for Food Podcast: 44
- The Vadose Zone - A critical indicator for Nebraska groundwater quality
Vadose
Zone. University of Nebraska-Lincoln. Nebraska Water Center, Nebraska Vadose Zone | Nebraska
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