ABSTRACT
A small land area comprised of distinct agricultural
and suburban areas was monitored over a period of three days in order to
ascertain the relative contribution of each land use type on nitrate loading
of streams. One site near an urban area was also sampled for comparison
purpose. While time and transportation constraints made a more extensive
investigation impossible, some interesting data was collected. Two different
nitrate test kits were compared with respect to ease of use and potential
reliability of the results returned by each test. Even though considerably
more extensive testing is needed, the data showed some correlation between
nitrate found and type of land use employed in each specific area.
DISCLAIMER
As an informational note to the general reader, the authors would like
to explain the context in which this project is presented. If you
have entered our page via an indirect route, please be aware that the purpose
of this work was to investigate, first hand, some methods of selecting,
sampling, and performing field based analyses on water samples for environmental
investigation and monitoring. This activity was performed for the
purpose of more clearly understanding, and communicating to students, the
process skills necessary to begin an ongoing environmental monitoring program
at our home location. This work should not be regarded as a water
quality study for actual environmental analysis.
INTRODUCTION
THE NITRATE ISSUE
Nitrate levels in water sources
have been increasing over the last several years, and many areas of
the country have been identified as nitrate
risk areas. Reportedly, the issue of nitrate
contamination of water has grown over the past 30 or so years from
a local to regional scope and will, if not reduced, progress toward a continental
scale [1].
This increase in nitrate levels is problematic
because nitrate poses a health risk to both humans
and animals.
One health issue of concern is the occurrence of methemoglobinaemia,also
called blue-baby syndrome. In this case, ingested nitrate is presumed to
be involved in the conversion of hemoglobin to methemoglobin resulting
in impaired oxygen-carrying capacity of the blood. Infants
are more susceptible to the resulting cyanosis than adults, hence,
the "blue-baby" label.
Additionally, there is concern over the contribution of water nitrate
level to both eutrophication of fresh water and possible increases in risk
of stomach cancer although the links to the latter seems rather weak at
this time [1]. Connections between nitrate pollution and other
cancers and miscarriage
have been reported. Clearly, the monitoring and control of nitrate
pollution is a serious issue which must be addressed.
TESTING FOR NITRATE
A number of direct tests can be employed in the determination of nitrate
from the direct absorption of the analyte itself, to the reaction of nitrate
with chromotropic acid or brucine and subsequent spectrophotometric detection
of a colored reaction product. These methods as well as fluorimetric, chemiluminescent,
and electrochemical methods have been reviewed [2] but the highly technical
nature of these procedures precludes their general use.
The more common method, which is employed by the
field kits used in this project, is an indirect method involving the reduction
of nitrate to nitrite and subsequent diazotization of the nitrite produced.
The diazo compound is then coupled to another organic molecule to form
a colored azo dye which can be measured spectrophotometrically. The generally
encountered procedure uses cadmium, which is a hazardous substance, as
the reductant . Recently, kits using zinc or nitrate reductase have been
offered, providing non-hazardous options for nitrate monitoring. In as
much as the color intensity of the dye is proportional to nitrite rather
than nitrate, readings will reflect total nitrite in the sample whether
it was produced from nitrate or not. Results should, therefore, be corrected
for any nitrite already present in the sample prior to analysis.
PURPOSE The purpose
of this work is two fold: first, to determine the relative effect of agricultural,
suburban and urban land use on nitrate levels in streams, and second, to
compare different field testing kits available for nitrate monitoring.
The question to be answered here is whether or not there is a difference
in the contribution to nitrate concentration in streams by different types
of land use. Our working hypothesis is that urban and suburban lands show
a higher contribution to nitrate loading in streams than agricultural lands,
because agricultural practice would favor limiting fertilization to the
minimum level required by the particular crop under cultivation in order
to minimize costs and increase profits from crop sales.
MATERIALS All
chemicals were obtained as prepackaged, commercially available test kits
and used per enclosed manufacturers directions.
Kit #1: InQuest Nitrate FS, Ohmicron Environmental Diagnostics Inc.,
Newtown, PA
Kit #2: CHEMets Nitrate Test Kit (#K-6902) Chemetrics
Inc, Calverton, VA
PROCEDURE
A study site was selected which contained both agricultural
land and developed suburban areas. The nature of the Princeton area precluded
the study of large, purely agricultural areas since most outlying lands
had been developed to one extent or another, leaving a mix of housing areas
interspersed with smaller agricultural areas. The site chosen for the present
project was, by necessity, small. The location was selected because not
only were there distinctly agricultural and developed areas, but the entire
site was drained by the same stream system. The three creeks could each
be sampled near its respective head water. Two of the creeks joined together
and flowed into the third. Additionally, one small housing area was drained
into a small wetland area allowing for a possible comparison of levels
above and below this wetland area. An additional sample site was chosen
at the lower end of a channel flowing through a large cultivated area.
This source was not shown as a stream and it was not possible to trace
it to its source. Finally, a site on the Stony
Brook, near the power plant on the Princeton campus was chosen for
purposes of urban vs suburban/rural comparison.
All streams were accessible by road, and samples
were taken at crossings on each stream. Water was dipped from the stream
with a 250 ml polyethylene wide mouth bottle and capped immediately. Each
bottle was rinsed thoroughly on site prior to sample collection.
Samples were analyzed according to the manufacturer's instructions
included with each kit. In general, this involved an initial step to dissolve
a solid reagent containing the reductant to reduce nitrate to nitrite followed
by the addition of a solution reagent to form the azo dye on which the
colorimetric determination was based. This second step required a wait
period that must be consistent, as the color intensity of the dye was time
dependent as well as analyte concentration dependent. The wait time depended
upon the particular kit used. In our case, 3 minutes for kit #1 and 10
minutes for kit #2. The simple and rapid procedure used with the InQuest
kit (kit #1) enabled samples to be analyzed at the time of collection.
The more complex and time consuming nature of the CHEMet kit (kit #2) required
samples to be stored until a more suitable location
could be used for analysis. This delay was kept as short as possible to
minimize sample degradation over time. Samples were refrigerated in the
case of any delay of more than one hour between sampling and analysis(which
occurred on day two).
 |
 |
 |
| This shady location was surrounded by woods and lush vegetation |
The most significant thing about this site was the heavy growth of
cattails,suggesting scrubbing of NO3 |
One of 2 samples taken as the creek crossed Cold Soil rd. was located
next to an agricultural site. |
SITE DESCRIPTIONS
SITE #1 Keefe Road: Creek crossing. Originates in area north
west of site. Primarily agricultural.
SITE #2 Van Kirk/T of Trees (upper): Storm drainage into
small wetlands. Drains empty into middle part of wetlands (where
road crosses). This site is upstream of lower wetlands area.
SITE #3 Van Kirk/T of Trees (lower); Storm drainage below
(downstream) of small wetlands.
SITE #4 Van Kirk West: Creek crossing. Heads in an agricultural
area just north of site.
SITE #5 Van Kirk East: Creek crossing. Heads
in suburban area just north east of site. Appears to head in a pond
in the midst of a small housing development.
SITE #6 Carter Road: Stream crossing. Represents confluence
of all creeks sampled.
SITE #7 Cold Soil Road: Creek crossing. Stream runs
through a relatively dense suburban area. Site is approximately at
center of development area.
SITE #8 Cold Soil Road #2 Sunny Slope Farm: Appears to be
a canal/drainage area
SITE #9 Stony Brook: Site on Stony Brook--Princeton campus near
lot #23. Used for urban comparison.
RESULTS
Time and vehicular access constrained sampling activities to a three day
period. Numeric raw data were measured as nitrate-nitrogen and are summarized
in the table below:
DATA COLLECTION RESULTS
|
SITE
|
DAY 1
|
DAY 2
|
DAY 2
|
DAY 3
|
DAY 3
|
|
|
INQUEST KIT (ppm)
|
INQUEST KIT (ppm)
|
CHEMETRICS KIT (ppm)
|
INQUEST KIT (ppm)
|
CHEMETRICS KIT (ppm)
|
|
1
|
2
|
1
|
1
|
1
|
1
|
|
2
|
1
|
0.75
|
1
|
1
|
1
|
|
3
|
0.5
|
--
|
0.2
|
--
|
0.2
|
|
4
|
< 0.5
|
0.75
|
0.8
|
<0.5
|
0.3
|
|
5
|
0.5
|
--
|
--
|
no sample
|
no sample
|
|
6
|
2
|
1
|
0.9
|
1
|
0.9
|
|
7
|
1
|
1
|
0.9
|
0.75
|
0.9
|
|
8
|
2
|
1.5
|
1
|
1
|
0.9
|
|
9
|
2.5
|
1.5
|
1
|
1.5
|
1.2
|
|
|
|
|
|
|
Note: The CHEMetrics kit was not available on day one so
only InQuest data are available for the first day. On day 3, sample site
#5 was dry so no sample could be collected. A dash (-) indicates no color
development was observed during the nitrate test.
In general, there was very little difference in
readings from site to site on any given day nor was there much change from
day to day at any particular site. There were, however, some interesting
aspects to the data. In comparing sites above (#2) and below (#3) the small
wetland area, consistently lower nitrate concentrations were seen below
the wetland than those seen above the wetland. Higher nitrate levels were
also generally seen at the urban site (#9) than at the rural/suburban sites.
Very little flow was observed at most sample sites.
Weather conditions were hot and dry during the time of this study, in fact,
one site (#5) was actually too dry to sample by day three.
There was reasonable agreement between the two test kits used in the
study. The CHEMetrics kit was the more sensitive of the two, having two
comparators, one for the 1 to 5 ppm nitrate-nitrogen range and another
for the 0 to 1 ppm range. The InQuest kit has only 4 index colors at 0.5,
2.5, 5 and 10 ppm nitrate-nitrogen, making precise determinations difficult.
(InQuest supplies a kit to test in the lower concentration range but one
was not available to us). Samples tested on day 3 with the CHEMetrics kit
did not show a pure pink color but rather an orange tint. This made reading
the color comparator difficult.
CONCLUSIONS
The consistently lower values below the wetland would
seem to suggest some scrubbing of nitrate by the wetland. The higher values
found at the urban site (#9) suggests a larger effect from urban areas
than suburban or agricultural lands. These data, however, must be viewed
with some degree of caution. First, most of the values obtained using the
InQuest kit required an estimate of color intensity between the reference
blocks provided on the chart. Since the concentration difference between
reference blocks was large compared to the change being measured, there
is a large probability of error in these measurements which may be responsible
for part of the change recorded. Second, while the CHEMetrics kit was able
to test to a lower concentration range and had reference standards in smaller
increments, the poor color development was troublesome in accurately reading
the color comparator, possibly leading to erroneous data. Third, the low
flow rate, very dry conditions and general lack of differences in concentration
both site to site and day to day would suggest that little of anything
including water is entering the stream system. It may be expected that
little contribution will be seen regardless of location or type of land
use until climatic conditions become more favorable to nitrate leaching
from the surrounding soil. Further, no evidence of either fertilizing or
irrigation was seen at any location during our time in the field. Certainly,
it will require a much more extensive study over at least a complete seasonal
cycle to resolve these issues.
The comparison of the two test kits was also very
preliminary. The CHEMets kit was as easily used as the InQuest kit. The
InQuest kit was a very quick test requiring about four minutes per test
and has the advantage of being non hazardous as it is zinc rather than
cadmium based. The actual determination of concentration using the supplied
color chart seemed less certain than the color comparator in the CHEMets
kit which, while easier to read, is cadmium based and so required greater
attention to handling and disposal of used reagents. This kit also required
a longer analysis time, about 15 minutes per test. Both kits proved equally
usable in the field and, in spite of the aforementioned uncertainty in
reading, showed good agreement most of the time.
ACKNOWLEDGEMENTS
The authors wish to extend a special thanks to Larry Price and Lisa Bryce
Lewis of the GREEN program
for the gracious loan of the InQuest test kit used in this study.
REFERENCES
1. Nitrate: Processes, Patterns and Management; Burt,T.P. ed.; John Wiley
and Sons, New York; (1993); ch 1
2. Water Anaysis Vol II, Inorganic Species, Part 2; Minear, Roger A
and Keith, Lawrence H., eds.; Academic Press, New York, (1984)
CONTINUING OUR PROJECT AT HOME
As an extension to our Princeton project, we will continue
to carry on research at home through our school's affiliation with the
Ala Wai Canal Watershed Improvement
Project (AWCWIP--see background information following this section).
Our science dept will develop a joint stream profile research project,
funded through a national service
learning grant. We will model the inquiry based research done at Princeton
and extend this project to include a variety of other
water quality measurements. It is our intention to integrate service
learning into the science curriculum and to implement the national standards
at the same time. To comply with the national standards recommendation
using the inquiry method, students will design and conduct scientific investigations.
Students will suggest answers to questions about the stream profile study
such as: why, who, where, when and what they are monitoring. What we learned
at Princeton will allow us to assist students with methodological problems,
recommend use of various technologies, and guide students as they try to
clarify the question, method,controls, and variables. Student inquiries
will culminate in model building.
We will also utilize many of the resources obtained
while at Princeton to achieve the aforementioned. A few of these include
the EPA's Volunteer Monitor's Guide To Quality Assurance Project Plans(QAPP),
GIS and some of the protocols used by the GLOBE and GREEN projects.
It is hoped that our research will assist the state to meet its project
goal, which is: to improve the quality of both surface waters and ground
waters in the drainage basins for Manoa, Palolo, and Makiki Streams, and
in the Ala
Wai Canal through a long term, community-based, public-private program
of non-point source management activities in the watershed. At the same
time, our students will benefit academically by being involved in an open-ended
project through which they will be able to personally experience the process
of scientific work while also seeing a direct impact on their personal
lives. An additional societal component will be provided as students will
have the opportunity to interact with governmental leaders and other adults
in the community.
GLOSSARY
QAPP- Quality Assurance Project Plan is a written document that outlines
the procedures a monitoring project will use to ensure that the samples
collected analyzed, stored and managed are of high enough quality to meet
standards set by EPA.
GIS-(Geographical Information Systems) A linked set of geograhical elements
and a database containing information about those elements.
GLOBE- (Global Learning and Observations to Benefit the Environment)
A worldwide program designed to network teachers, students, and scientists
working together to learn more about the environment.
GREEN (Global Rivers Environmental Education Network) An innovative,
action-oriented approach to education, based on an interdisciplinary watershed
education model.
BACKGROUND INFORMATION ABOUT PROJECT SITE AT HOME
The Ala Wai Canal Watershed drains into a two-mile long,
twelve acre, man-made canal which separates Waikiki from much of urban
Honolulu. The canal was built in the 1920's as a marsh reclamation project
to control mosquitoes and to drain runoff from upper watershed forest reserves
and surrounding urban areas. The Ala Wai Canal has been identified as a
Water Quality Limited Segment, and cannot reasonably be expected to attain
or maintain State Water Quality Standards without additional action to
control nonpoint sources of pollution. Recent literature indicates that
the Ala Wai Canal has high levels of fecal coliform bacteria, nutrients,
lead and copper, pesticides (dieldrin, chlordane, and heptachlor epoxide),
and sediment. In spite of the poor water quality and general condition
of the canal, the Ala Wai continues to be a heavily utilized recreational
waterbed. Fishing, crabbing, and canoeing occur daily in the Ala Wai. It
is commonly understood by state and local governments that the restoration
of water quality to meet the "designated uses" under the State's Water
Quality Standards is urgently needed. In 1994, the State Department of
Health (DOH) and the U.S. Environmental Protection Agency selected the
Ala Wai Canal Watershed as a target watershed for protection. An outreach
coordinator is in the process of being selected(by Sept. 1997) to serve
as a catalyst for community involvement, environmental education, and stewardship
partnership in the Ala Wai Canal Watershed Project. As our school is in
the watershed zone, we intend to participate in the stream monitoring part
of the project. Data that we gather and analyze will be posted to the Woodrow
Wilson website and will also be written up and shared with the service
learning evaluation team next spring.
CORRELATION TO EDUCATIONAL STANDARDS
In accordance with the National
Science Education Standards and Benchmarks for Science Literacy, we
selected those standards which were partially addressed by our current
research. As we expand our project at home, more of the standards
will be addressed. The list below outlines the national standards
we believe our project will have encompassed at completion. The benchmarks
for literacy are provided following the national standards. Note:
as a team of three, each member comes from a different discipline area
and grade level in science. Therefore, input here is individually
listed:
Teaching Standards A, B, and D.
Program Standards D and E
System Standards D and E
Content Standards A, B,E,F, and G
Assessment Standards A,B,C,D, and E
BENCHMARKS:
PHYSICS ORGANIZED BY THEMES
| Content |
Systems |
Constancy |
Patterns of change |
Scale |
Nature&Values of Science |
Models |
Measurement
|
definition of systems |
uncertainty of measurement |
variables & their relationships |
sensitivity to scale/size |
1 world view
2sci. inquiry
3.inq. process |
1.use of models
2.math m. |
Mechanics
|
energy systems |
conservation of energy |
cyclical motion |
graphs
& scales |
1.graphical methods
2.world view |
motion
position
distance |
Materials
|
thermal systems |
1.thermal stability
2.equilibrium |
1.randomness
2.entropy
3.chng state |
1.temp scale
2.surf ten. |
|
thermal energy |
Waves
|
light diffrac.& interference |
|
diffraction & interference |
diffraction effects |
1.light,color,
illumination
2.optics tec. |
light diff. & interference |
| Electricity & Magnetism |
electric charges & transfer |
charge trans.
equil of chg bodies |
|
1.elec.waves
2.spect.anal. |
dev. of electromag. |
electric charges |
| Modern Physics |
|
1.constancy of spectra
2.cons-energy |
|
scales of energies |
1.electronics
2.spectroscopy |
band theory of elec cond. |