With this study, we plan to investigate the difference in the concentrations of zinc
between the inlet and outlet of the Radford University wetland. If a difference in
concentrations exists this would support the effectiveness of the wetland as a tool of
sequestration. The null hypothesis is that there is no significant difference between the
inlet and outlet concentrations.
Conductance and pH Testing Method
Small glass jars were used to collect water samples at random locations in the vicinities
of the inlet and the outlet. The water was placed in a graduated cylinder and tested using
a field pH and conductance probe. A total of 3 sets of ten samples were taken, each set
consisting of two groups of 5 samples from each of the inlet and the outlet.
Soil Collection Method
10 samples were collected from the inlet and outlet using a standard forestry knife to dig
3-6 inches into the soil. . Locations for each sample were randomly selected and
recorded. Samples were placed in whirltek collection bags for transportation back from
the field to the lab. Soils were spread thinly out on newspaper and left dry.
Soil Digestion Method
The 10 soil samples were left out for one week to dry. An approximate sample of 0.5
grams was taken from 8 of the 10 soil, 4 from each inlet and outlet (Actual sample
weights are listed in Table 1). 10 mL of 16 M nitric acid was added to each of the 8 eight
samples in a specific container used for the Digestion Microwave. A 2ppm zinc standard
and a spike of 10ml of 16 M nitric acid were created as samples 9 and 10, respectively.
The containers were numbered and placed in the carousel.
The microwave was set at a temperature of 175 degrees Celsius. The samples were
placed in the microwave for 15 minutes. The container was removed from the carousel
and opened under a fume hood due to excess nitrous monoxide gas that is released.
Next, the contents of each sample were separately poured through a filter and into an
individual flask for each sample. The color of the samples was a bold yellow color. The
filtered contents were diluted using 140ml of distilled water. Test tubes were filled with
each samples solution and numbered accordingly.
Absorbance Spectrometer Method
An Atomic Absorbance Spectrometer was used to determine the concentration of zinc in
the solutions resulting from the soil digestion. First a standard solution was used by the
Spectrometer to create a standard curve of absorbance versus concentration. This was
accomplished by emitting a particular amount of light at a standard wavelength, known to
be absorbed by zinc, and allowing it to pass through a known concentration sample and
recording the amount of light that passes thorough freely. By taking the amount of light
passing through and subtracting it from the amount emitted you are able to calculate the
amount of light that was actually absorbed. This was done for an array of concentrations
and was used to find the relationship between absorbance and concentration and is shown
in Figure 1. A best fit line was inserted into the graph.
Next, the 10 samples for the soil digestion microwave are run though the Atomic
Absorbance Spectrometer to find the absorbance of each sample. Using the formula
produced by the line of best fit, the absorption values were converted to parts per million
(ppm) within the solution. Finally, the concentration of the solution was converted to the
concentration in the soil. Averages of the concentrations were taken for the inlet and the
outlet and compared.
0.7
Abs (214.9 nm)
0.6
y = 0.4403735x - 0.0013009
R2 = 0.9969619
0.5
0.4
0.3
0.2
0.1
0
-0.1
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
ppm
Figure 1: Calibration curve of Absorbance vs. Concentration created by the
Atomic Absorbance Spectrometer
DATAFILE DESCRIPTION:
zincconcentrations-11162006-wojdak.doc
a. Soil collection date: 09/11/2006
Time of soil collection: 14:30 – 16:00
Water collection dates: 09/11/2006; 09/18/2006; and 09/25/2006
Times of water collections: 14:30 – 15:30; 14:00 – 14:45; 14:30 – 15:15
Location: Various sites within sites 49 – 46 in the inlet section of the wetlands and sites
12-15 in the outlet section of the Radford University Wetland.
b. PI– Jeremy Wojdak
Pollution Biology – BIOL 392
Soil zinc concentrations at the input and output of the Radford University wetland
c.
Column 1 – Sample
Data are nominal. Each sample is given a unique identifier, arbitrarily, starting with 1.
Column 2 – Sample type
Data are nominal. Soil samples are denoted “soil”, laboratory mixtures samples are
denoted “mixtures” and aqueous samples are denoted “water”. Both the aqueous and soil
samples were obtained from the Radford University wetlands. The laboratory “mixture”
sample has different factors that make it up. For sample #9, known as a laboratory
standard, contained only 10 mL’s of nitric acid and no other chemicals, or soil from the
wetland. For sample #10, known as a laboratory Spike, it contained 2 ppm of the zinc
standard chemical, 93 mL’s of distilled water, and 10 mL’s of nitric acid also not
containing no soil from the wetland.
Column 3 – Sample area
Data are nominal. In order to test if zinc concentrations change between the input and the
output of the wetlands, there were specified areas that soil and aqueous solutions were
taken. The input area which was chosen was at the front of the wetlands in areas 49 – 46,
because of how relatively close it is to the input pipe. The output area which was chosen
was at the back area of the wetlands in areas 12 – 15, also chosen because of how
relatively close the area was to the output pipe.
There were 4 soil samples taken from the input section of the wetland and 4 soil
samples that were taken from the output section of the wetlands. Each of the samples was
chosen at random and the area in which they were collected is demonstrated by a nominal
number in the data section. Water samples were chosen the same ways in which the soil
was chosen. Random areas between the selected areas were chosen each week to prevent
bias and their locations are documented in the data. The only difference between the soil
collection process and the water selection process was that, 5 samples of water from the
input and 5 samples of water from the output were taken each week for three weeks
(09/11/2006 – 09/25/2006) when only one sample of soil was taken (09/11/2006).
Column 4 – Sample Mass
Interval data. The soil from the wetlands, once dried, was weighed on a digital scale as
close to .5 grams as possible. The exact amount of soil weight is recorded for further use
in the calculation of the concentration of zinc in the soil. This weight is very important in
later generating the soil concentration because it will show more linear results if you have
the error added on to the value
Column 5 – Absorbance
Data is absolute. Absorption is calculated by an Atomic Absorbance Spectrometer. It
creates a standard curve of absorbance produced by concentration of zinc from the soil
versus concentration of zinc by recording the amount of light that was not absorbed and
subtracting it from the amount emitted to find how much light was actually absorbed.
Absorbance in this category was measured in ppm.
Column 6 – Solution concentration
Data is absolute. The concentration of the solution from the previous column, that is
converted into the concentration of the solution in the soil. This shows the proportion of
the concentration that’s prevalent in the wetland.
Column 7 – Soil concentration
Data is absolute. Column 5 and 6 were used to find the soil concentration. The soil
concentration shows how much zinc variation there is within the eight soil samples that
were obtained on 09/11/2006. These values are within each other’s margins so there is no
significant change in the concentration of zinc in water as it passes through the wetlands.
Column 8 – Reading day
Data is nominal. In the column a 1 indicates that the data was collected on 09/11/2006. In
the column a 2 indicates that the data was collected on 09/18/2006. Finally, in the column
a 3 indicates that the data was collected on 09/25/2006.
Column 9 – Inlet pH
Data are continuous. pH values as read by a YSI 63 pH, temperature, and conductance
probe. The data represents the pH within the inlet portion of the wetlands.
Column 10 – Outlet pH
Data are continuous. pH values as read by a YSI 63 pH, temperature, and conductance
probe. The data represents the pH within the outlet portion of the wetlands.
Column 11 – Conductance of inlet
Data are continuous. Data are values as read by YSI 63 pH, temperature, and
conductance probe, and are expressed in uS/cm at 25C (microsiemens per centimeter at
25 degrees Celsius). These measures are the conductance in the inlet portion of the
wetlands.
Column 12 – Conductance of outlet
Data are continuous. Data are values as read by YSI 63 pH, temperature, and
conductance probe, and are expressed in uS/cm at 25C (microsiemens per centimeter at
25 degrees Celsius). These measures are the conductance in the outlet portion of the
wetlands.
d. Data permissions – anyone can use this data and information collected for any purpose