The study compared nitrate levels in a lake and river in Puerto Rico over 5 days. Samples collected in the morning and evening were analyzed. Nitrate levels in the lake ranged from 0.079 to 0.469 mg/L, lower than the river which ranged from 0.211 to 0.791 mg/L. Both water bodies showed increased nitrate levels after a major precipitation event on April 30th, supporting the hypothesis that rainfall increases nitrate concentration in bodies of water. Higher agricultural activity near the river likely contributed to its elevated nitrate levels.

1. Comparison of the Nitrate Levels in Water Bodies of Puerto Rico
Lysander Borrero and Eduardo Rivera
Abstract
Nitrate is a compound that is found in fertilizers, plants, urine, feces and many other
components. It can be found within the bodies of water; some have a higher concentration than
others. The bodies of water with higher concentration can cause serious diseases like blue baby
syndrome and even different types of cancer. By knowing this information, we collected samples
of water from a lake and a river for a period of five days during the morning and in the evening.
These samples were refrigerated and then analyzed to measure the concentration of nitrate. Our
results showed that the lake the concentrations were lower compared to the rivers, especially
after a precipitation event. In conclusion the nitrates levels rose after the precipitation just like
we stated in our hypothesis. Some of the factors that could have affected our results were the
storage of samples,the location, and agricultural or rural area.
Introduction since plants cannot produce nitrates, people
often use fertilizers, which are mostly
The main purpose of this investigation was
composed of nitrates, to help plants grow.
to measure the levels of nitrates in water
Using a great amount of fertilizers near a
bodies. The nitrate molecule is composed of
water body can eventually end up inside of
one nitrogen atom and three hydrogen
it. If the fertilizers get in the water body, the
atoms. Nitrates are soluble in water at
level of nitrates will rise up. High levels of
standard temperature and pressure. Also,
nitrates on water can affect humans in many
plants use nitrates as building blocks for the
ways. Infants who drink water with high
formation of amino acids and DNA. But
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2. Comparison of the Nitrate Levels in Water Bodies of Puerto Rico
levels of nitrate can develop an acquired Methodology
form of the blue baby syndrome, also called
The samples were taken within a
methemoglibinemia(Austin1999).
period of five days, from April 28th trough
Methemoglobinemia is a blood disorder in
May 2nd, one sample on the morning and
which the protein produced, methemoglobin,
one on the evening. The samples were taken
has very little affinity with oxygen, unlike
from a lake and a river, both located in the
hemoglobin. The problem with this disease
city of Caguas. The specific site of the lake
is that little oxygen reaches the body’s tissue
was in a housing community, called
and gives the infant a blue colored skin.
Hacienda San Jose (figure 1A). The river
Drinking water with high levels of nitrates
from where the sample was taken is called
not only affects infants, but also adults. In
“Rio Caguitas”. This river comes from
adults, nitrates can bind to N-nitroso
Aguas Buenas and passes through Caguas
compounds found in the gastric juices of the
and goes on to other cities. The specific site
stomach. The most common cancers due to
where the sample was taken was in San
high levels of nitrates are stomach cancer
Antonio, very close to some houses (figure
and bladder cancer.
2B). The sample was taken with a cup and
Through the process of our investigation, we then it was stored in a refrigerator
expect that the nitrate levels will rise after a until the nitrate levels were analyzed. The
precipitation event in the lake and the river. dimethylphenol method using TNT 835
Our objective is to measure the levels of (containing sulfuric acid and phosphoric
nitrates in the water bodies after and acid) was performed. Later on, one milliliter
extreme precipitation event. of the sample water was taken and placed
into the vial. Then wetook 200 micro liters
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3. Comparison of the Nitrate Levels in Water Bodies of Puerto Rico
of Solution A (contains isopropanol) and
placed it in the vial also so that later we
Figure 2B
mixed it three timescausing an exothermic
reaction. Later the samples were left for
thirty minutes. After that, the vial was
extremely cleaned so the spectrophotometer
could read it accurately. Then vial was
inserted in the spectrophotometer and it
showed results of the levels of nitrates in the
sample.
Figure 1A
Results
After the samples were analyzed in
the spectrophotometer, the ranges of nitrate
concentration were revealed. In the lake, the
nitrate concentrations were from 0.079 to
0.469 mg/L, as shown in table 2A. In the
river sample, the range of nitrate
concentrations was from 0.211 to 0.791
mg/L, as shown on table 3B.
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4. Comparison of the Nitrate Levels in Water Bodies of Puerto Rico
Lake Sample (Table 2A) answer this question we did a table (table 4)
where we show you the nitrate levels before
Date Time Nitrate
Results and after a precipitation event. According to
28/abril/2012 9:00 am 0.079 mg/L
28/abril/2012 4:45 pm 0.111 mg/L the USGS (United Sates Geological Survey)
29/abril/2012 7:15 am 0.122 mg/L
29/abril/2012 4:30 pm 0.113 mg/L an extreme precipitation event occurred on
30/abril/2012 9:30 am 0.147 mg/L
30/abril/2012 6:38pm 0.137 mg/L April 30th, 2012 I the afternoon (table 5).
1/mayo/2012 6:47 am 0.137 mg/L
1/mayo/2012 7:03 pm 0.469 mg/L The averages of both water bodies were
2/mayo/2012 9:00 am 0.061 mg/L
2/mayo/2012 6:48 pm 0.258 mg/L taken from April 28th in the morning and
April 30th, which is considered before
precipitation event. Through April 30th
River Sample (Table 3B)
evening and May 2nd evening, the Nitrate
Date Time Nitrate levels rose in the lake sample after the
Results
28/abril/2012 11:35 am 0.303 mg/L extreme precipitation event. Even though it
28/abril/2012 5:32 pm 0.573 mg/L
29/abril/2012 11:45 am 0.211 mg/L wasn’t an extreme difference, as shown in
29/abril/2012 6:01 pm 0.540 mg/L
30/abril/2012 6:28 am 0.628 mg/L table 6A,the nitrate levels rose in the river
30/abril/2012 6:27 pm 0.791 mg/L
1/mayo/2012 6:37 am 0.706 mg/L sample and you can see the difference from
1/mayo/2012 7:12 pm 0.470 mg/L
2/mayo/2012 8:24 am 0.600 mg/L before and after the extreme precipitation
2/mayo/2012 8:21 pm 0.730 mg/L
event, as shown in table 6B. Mainly you can
see that in both tables the nitrate levels did
The average of the concentration of nitrates
rise after the precipitation occurred.
in the river was higher compared to the lake
samples, as shown in table 4. However, the
question is, did the levels of nitrate rose
when a precipitation event occurred? To
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5. Comparison of the Nitrate Levels in Water Bodies of Puerto Rico
Average of Nitrate Concentration (Table 4) Before and After Precipitation Event: Lake
Sample (Table 6A)
USGS Rain Gauge (Table 5)
Before and After Precipitation Event: River
Sample (table 6B)
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6. Comparison of the Nitrate Levels in Water Bodies of Puerto Rico
Discussion levels are higher in that specific body of
water.
In conclusion the nitrate concentration from
the lake sample ranged from 0.079 to Acknowledgments
0.469mg/L and the river sample from 0.211
We will like to thank our mentor Dr. Javier
to 0.769 mg/L. We can find a broader
Arce and the Laboratory Technician Ruby
amount of nitrates in fertilizers, which are
Otero. Also the RISE Program for giving us
commonly used in agricultural areas and
the opportunity to participate in this
since Rio Caguitas is near a rural area, the
research.
fertilizers used near this location can end up
inside the river. However, the lake is not
near to any agricultural areas, so nitrates
from fertilizers do not end inside it. This
meansthat there is a higher probability that
the concentration of nitrates is higher in the
river than in the lake.
For future works, it would be good to take
samples of water when there is a dry out and
after an extreme precipitation event to
measure, analyze and compare the nitrate
levels. Also what would be good is to take
more samples so that we can have more data
and take samples from different sites in the
same body of water to see where the nitrate
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7. Comparison of the Nitrate Levels in Water Bodies of Puerto Rico
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