A Quantitative Analysis
of Biochar’s Effects on Plant Growth in Contradistinctive Mine Site Soils
M.C.
Arcomano, L.M. Buchheim, L.B. Grigsby
Department of the
Sciences: Animas High School
Abstract
After
years of mining the now abandoned sites located in the southwestern Colorado
San Juan Mountains are a serious pollution hazard as mine tailings (materials
left after extraction of ores, mostly metals) are removed by erosion, causing
toxic metals to dissolve in nearby rivers which has a dangerous effect on
aquatic life. The revegetation of contaminated soils is an effective method to
contain mine tailings such as toxic metals through root uptake and metal
precipitation thus preventing exposure of such to erosion. This paper
investigates the effects of biochar as soil amendment for plant growth applied
at different concentrations.
Soil samples collected from mine sites
near Silverton, Colorado were amended with biochar at different concentrations
(0%, 10%, 20%, 30%) and planted with seeds. The results of the experiment
conducted showed significant impacts biochar had on plant growth at all
concentrations, with the highest average improvement (plant height) at 30%
concentration of biochar. However, experimental flaw connected to technical as
well as human error caused doubt to fall on the accuracy of our data. Thus, the
exact effect of biochar at certain concentrations will require a re-performance
of the experiment.
Keywords:
Biochar; Mine Tailings; Soil Remediation; San Juan Mountains
1. Introduction
Biochar
is a porous residue resulting from pyrolyzing biomass at high temperature and
minimal oxygen, characterized by its low density, high surface area as well as
high carbon content (Rajkovich 2010). It is also thought to contain important
plant nutrients which however has not been sufficiently investigated (Lehmann and
Joseph 2009). Resulting from those properties, which are highly dependent on
source material as well as pyrolysis temperature, is its ability to sorb
organic as well as inorganic contaminants, thus decreasing bioavailability of
such within soil (Beesley et al. 2011). These beneficial properties have made
biochar the subject of many investigations on its specific characteristics as a
soil amendment (Graber et al. 2010; Park et al. 2011). Also, biochar, in contrast to fresh organic
residues, does not notably increase CO2 production when added to
soil (Beesley and Marmiroli 2010). Although there are many advantages some of
which are listed above, down sides to using biochar have been found such as the
retention of plant nutrients and an increase in arsenic mobility which may
limit vegetation (Beesley et al. 2011). Combinations of biochar and other
amendments such as compost and manure have been suggested to be the most
successive way to remediate soils (Beesley et al. 2011).
The
San Juan Mountains in southwestern Colorado are the location of many abandoned
gold and silver mines. Erosion causes mine tailings (the materials left after
the extraction of ores from the mine, mostly metals) to spread over tens of
hectares (Mendez et al. 2008) and dissolve in rivers, such as the Animas River (Fellet
et al. 2011). This pollution is more exactly a decrease of pH and a higher
concentration of toxic metals in the water affecting aquatic life as well as
nearby communities. Stabilizing re-vegetation does not occur after tens to
hundreds of years because of the high amount of toxic metals in the soil such
as arsenic, cadmium, copper, manganese, lead and zinc. The lack of micro- and
macronutrients also hinders revegetation (Mendez et al. 2008). This
investigation was initiated with the goal of decreasing acid mine drainage by
adding biochar to contaminated mine sites which is thought to decrease the
amount of mobilized metals in the soil (Park et al. 2011) thus letting less
toxic materials leave the site and enter waters. Additionally, biochar is
believed to improve conditions for plants to grow and stabilize the site which
can contribute to the remediation of the sites by also decreasing metal
mobilization through plants sorbing contaminants onto roots and causing the
precipitation of metals to forms less soluble such as metal carbonates and metal sulfides (Mendez et
al. 2008). One factor to be considered
was at which concentration in the soil biochar caused the most improvement of
plant growth. In order to answer this question we designed an experiment which
we expected to show the advantage of re-vegetation biochar offers at different
concentrations (10%, 20%, 30% by volume) compared to non-amended soil,
expressed in improved plant growth measured by height after the addition of
seeds.
2. Materials and Methods
In
order to find the effects of biochar as a soil amendment we designed an
experiment which would allow us to evaluate the growth response of perennial
vegetation to biochar amendment. Soil samples taken from five different mine
sites, “Bonner” (BON), “Across from Bonner” (AfB), “Road Cut” (RC), “Brooklyn”
(BRK) and “Joe John” (JJ) (12 samples per site, 3 samples per concentration, 60
total samples) were planted and observed under grow light in order to analyze
differences in plant height at varying concentrations of biochar. The experiment
was conducted from January until March 2012. The time frame chosen had no
reason significant to the experiment.
Soil
samples we had collected from mine sites in the area of concern as well as the
biochar to be used were sieved to a particle diameter of <2mm. The soil was
then distributed evenly with a measured volume of 200ml into 3.5 in containers.
Biochar was added at concentrations of 0% (as control), 10%, 20% and 30% by
volume to four groups of each three replicates for each treatment. The biochar
was mixed together with the soil entirely so that an even allocation of both
ingredients could be reached. We recommend that each container be labeled
appropriately, that is providing an indicator of the biochar concentration as
well as a number, letter or symbol in order to assure clear identification of
each sample. Before the addition of seeds the samples were equilibrated with
water for 24 hours. The seed mix used in this experiment came from Southwest
Seed Inc. Per container we planted one gram of seed mix as well as four lupine
seeds, carefully tilling them into the samples. After the seeds had been
planted, the containers were covered for 72 hours in order for the seeds to
germinate. To ensure that environmental influences on the seeds were as
constant and equal for all samples as possible, the seeds were grown for 55
days under grow lights which we knew to be the only light sources as we placed
the samples under a table covered with lightproof cloth. Once a week, we
watered them with 100ml of tap water and let each sample drain; the leachate
was disposed of. On the same day the average height of vegetation in each
container was estimated using a ruler as orientation. Values were recorded in a
table according to each sample’s ID (composed of e.g. the concentration and a
specific number for each sample). This process was repeated until the duration
of 55 days and thus the end of the experiment was reached. After this trial,
the samples including the vegetation were disposed of.
At
the end of the experiment, after all data points had been collected, we
analyzed the results to find central tendencies the experiment indicated, such
as average height of all samples or how the heights measured at different
concentrations of biochar in the soil compared to each other. As we had
performed the experiment using three replicates for each concentration of
biochar it seemed appropriate to work with average values calculated from those
replicates. A variety of different graphs could be created using plant height,
the most important of which can be found in the following “Results” section.
3. Results
Summarized
in the following section are the most important data collected and analyzed
during the experiment performed. The data collected, which omits values
collected after February 22nd, shows definite however not large
differences in plant height depending on treatment. Including all sites, the 0%
treatment resulted in an average height of 35.1mm. The highest increase was
found at a concentration of 30% (39.7mm). Oddly, at 10% biochar plant height
was larger than at 20%, where the average actually dropped below 35.1mm (Table
1).
There
is some unusualness in our experiment where the average plant heights of a
certain treatment decrease as time goes on, instead of increasing. Only at a
concentration of 0% there is no drop in plant height. While the 10% and 30%
treatments show only one drop in plant height on February 22nd, 20%
shows an oddly high value on February 1st. After this date the
values seem to normalize again, increasing steadily (Figure 1).
In JJ the
highest plant growth happened with 30% biochar, while in BON the highest plant
growth occurred when there was 0% biochar. BRK showed little difference between
20% and 30% biochar, and AFB and RC showed an odd decrease and then increase in
height as biochar percentage increased (Figure 2).
At
a concentration of 30% our data indicate the highest average height (all sites
considered) with a value of 39.7 mm. There is an odd drop of height at 20%
compared to the value at 10% concentration. With an average height of 34.4 mm
this value is even below the control sample with no biochar at all added
(Figure 3).
BRK
showed significantly low values at all concentrations, however with large
increase of plant growth after the addition of biochar. The highest average
height was measured at a concentration of 20% biochar (Table 2; Figure 2/4).
|
Avg. height by site and concentration
|
|
Concentration
|
|||
|
Site
|
0
|
10
|
20
|
30
|
|
AFB
|
37.7
|
46.3
|
33.3
|
49.0
|
|
BON
|
65.7
|
62.3
|
40.3
|
40.3
|
|
BRK
|
7.0
|
11.3
|
24.0
|
20.7
|
|
JJ
|
31.1
|
29.3
|
49.0
|
53.3
|
|
RC
|
33.8
|
40.0
|
23.3
|
29.2
|
|
Total
|
35.1
|
37.9
|
34.4
|
39.7
|
|
Average height by
date and concentration
|
Concentration
|
||||
|
Date
|
0
|
10
|
20
|
30
|
|
1/27/2012
|
6.66
|
17.66
|
19.66
|
38.75
|
|
2/1/2012
|
30.3
|
35.33
|
44.58
|
33.666
|
|
2/6/2012
|
41.9
|
43.66
|
30.53
|
42.2
|
|
2/13/2012
|
45.1
|
48.66
|
38.66
|
46
|
|
2/22/2012
|
51.2
|
44
|
40.66
|
37.083
|
|
Total
|
35.1
|
37.9
|
34.4
|
39.7
|
|
|
|||
|
|||
Average Height as Compared to Treatment, Site
and Sample ID
|
4. Discussion
Looking
at the results of the experiment performed we can see that the addition of
biochar at all concentrations affected plant growth in different amounts.
According to our results, at a concentration of 30% of biochar the highest
impact on plant height (on average) could be measured. Due to the malfunction
of our lighting however, we were forced to assume that data collected after the
incident (which applies to all data points collected after the 22nd
of February) might not represent reliable information. Thus, we compared our
whole data set to a set which excludes data points collected after the
incident. All data considered, the results indicate a decrease of plant growth
at any concentration of biochar compared to un-amended soil. As this
contradicts with findings described in several other peer-reviewed journals
(Graber et al. 2010; Park et al. 2011) we decided not to use post-incidental
data. The set resulting from those data points seems to be more accurate as it
shows improvement in plant growth (that is, increased average plant height) at
all concentrations of biochar compared to the un-amended soil samples. With
disregard to data collected after the 22nd of February we can prove
our hypothesis that biochar does have a positive effect on plant growth
expressed in an increase of plant height. It is questionable if the measured
differences depending on concentration are actually as close as they appeared
in our experiment due to the fact that measurements were taken by approximately
60 different individuals which certainly had an effect on the accuracy of the
data. Interestingly, plant growth measured by height did not seem to correlate
to the concentration of biochar in a consistent pattern: Although there was an
increase in plant height between 0% biochar and 10% biochar, a decrease of
plant growth which went below the value of the un-amended soil samples could be
found at a biochar concentration of 20%. However, at a concentration of 30%,
biochar caused the highest effect in plant growth with the highest average
plant height measured. Since previous research has found the optimal
application rate of biochar to be at 2% (Rajkovich 2008) it seems unlikely that
our results should be considered accurate. Thus, it seems reasonable to
re-perform the experiment in order to determine the effects of concentration on
plant growth based on more reliable data. In order to reach higher accuracy of
data, crucial changes should be made, the most important ones being a reduction
in the number of individuals collecting data should as well as improved
technology assuring the consistency of independent variables such as lighting.
A prolongation of the experiment in order to attain a bigger set of data might
also be beneficial considering the great effect the two omitted data points
after the incident had on our overall results.
5. Conclusion
It
is clear that the addition of biochar to soils has an impact on vegetation
which makes it very valuable as a soil amendment to be used to efficiently
remediate contaminated soils such as abandoned mine sites. The question
remaining is to what degree the concentration of biochar affects plant growth
and what the concentration is at which the greatest improvement of plant growth
can be found. Due to several factors influencing the potential inaccuracy of
our data we cannot confidently assort what our results indicate regarding this
important question. Thus, it would certainly be beneficial to repeat the experiment,
avoiding the inaccuracies which occurred during ours.
Acknowledgements
We
would like to express special gratitude to Animas High School for support with
equipment as well as working space. Furthermore, our experiment could not have
been conducted without the opportunity of collecting soil samples in abandoned
mine sites which was given to us by the Mountain Studies Institute. Last but
not least, we would like to thank Steve Smith for the invaluable knowledge and
awareness we have gained through this process.
References
Beesley,
L., Marmiroli, M., 2010. The Immobilization
and retention of soluble
arsenic, cadmium and zinc by biochar.
Environmental Pollution 159, 474-480.
Beesley,
L. et al, 2011. A review of biochars’
potential role in the remediation,
revegetation and restoration of
contaminated soils. Environmental Pollution 159, 3269- 3282.
Fellet, G. et al 2011. Application
of biochar on mine tailings: Effects
and perspectives for land reclamation. Chemosphere
83, 1262-1267.
Graber, E. et al, 2010. Biochar impact
on development and productivity of pepper and tomato grown in fertigated soilless media. Plant
& Soil 337, 481- 496.
Lehmann, J., Joseph, S., 2009. Biochar
for Environmental Management: Science and Technology. Routledge, London.
Mendez, M., Raina, R., 2008. Phytostabilization of Mine Tailings
in Arid and Semiarid Environments – An Emerging Remediation Technology.
Environmental Health Perspectives 116,
278-283.
Park, Jin, 2011. Biochar reduces the bioavailability and phytotoxicity of
heavy metals. Plant & Soil 348,
439- 445.
Rajkovich, S, 2010. Biochar as an Amendment to Improve Soil Fertility. College of Agriculture and Life Sciences, Physical Sciences of Cornell University, Honors Thesis.
For chemistry we each wrote letter's to different companies telling them how they could use chemistry to improve one of their products. In our letters we talked about everything from the chemical formula of the product to the type of chemical bond that is used in the product. I wrote to JCPenney about the chemical formula of their earrings, which often causes allergic reactions.
At J. C. Penney’s, there are three different types of earrings to buy, all of which are mixtures and alloys. They are: 18 karat gold, white-gold, and austenitic stainless steel. Unfortunately for your customers, 18 karat gold and white-gold are both rather expensive, and therefore are not an option for many people. Therefore austenitic stainless steel is the only option for your lower income consumers, and it contains the element nickel, which many people are allergic to. Those who have allergic tendencies to nickel then have to buy gold earrings, and if those earrings are too expensive for them, then they can’t wear pierced ears at all. However, austenitic stainless steel can also be made in 18/0 quantities, which means it can be made with .15% carbon, 18% chromium and 81.85% steel. The only difference between 18/0 stainless steel and the regular kind 18/10 (10% nickel) is that in 18/0 there is no nickel and there is a little more steel. In fact, the only reason that nickel is in stainless steel is that it makes it more durable, but, earrings don’t need to be durable, as there is no particular pressure or stain placed upon them.
Both 18/0 and 18/10 stainless steel are hard and strong, although, as I have previously stated, 18/0 stainless steel is less so. Yet, in almost every other aspect they are identical. Neither alloys are good conductors of electricity or are magnetic. They are also both resistant to corrosion, are not easily oxidized and will retain a sharp edge. In addition to that, they share a density of .29 pounds per cubic inch, have a melting point of roughly 1435 degrees Celsius and have an elasticity rate of about 200 GPa. Clearly, the only relevant difference between the two is that one causes painful and disgusting allergic reactions in your customers and the other doesn’t.
Both formations of stainless steel have a metallic bond, which reiterates how alike they are. Metallic bonding is the forces between electrons in the “electron sea” and positively charged metal ions. This bond is very strong, therefore, stainless steel with and without nickel are both very hard to destroy, that’s the reason that so it doesn’t melt except for in extremely high temperatures. The metallic bond is also the reason that stainless steel is shiny, so because of that, the 18/0 stainless steel will have the same aesthetic qualities as the 18/10 variety. Please consider this opportunity to increase your customer satisfaction, by making 18/0 austenitic stainless steel rather than 18/10 austenitic stainless steel which contains the common allergen nickel.
Sincerely,
Amanda Arcomano
This was a very interesting project for me because in it both my academic strength and struggle areas were used to complete the letter. I'm very good at writing, both in creative free form and in a more structured, scientific format. For this project, I was able to use a bit of both, so once I had the information about stainless steel and the earrings, the project became very easy for me; in fact, I finished several days early. As I said above, I did finish this early, so there weren't really any improvements that I would have made if I had more time, because I ended up having way more than enough time. I'm very proud of this project and what I learned from it, and I truly believe that it was the absolute best work that I could do, and therefore would not have made any changes to it.
I learned a great deal throughout this project. It's obvious that I learned a lot about stainless steel, but that isn't very relevant to the class, nor will it help me in future endeavors. The main things that I got out of this project were learning how to do scientific research and getting a better grasp on the concept of chemical bonds. Scientific research is a difficult thing to do, as you have to look everything up several times, so as to make sure that the fact is real. Also, the chemical formula of austenitic stainless steel is an obscure piece of information, therefore it takes a lot of looking and perseverance to find it. I also got a better understanding of chemical bonding, quite simply because it wasn't something that I understood at all, but for this project I needed to understand it, so I was given more of an incentive to ask questions about it.
This quiz is a really good example of the aspect of chemistry that I am best at, math. I really enjoyed this part of the class because it was very simple and logical. To do well on this quiz, all that was required was to memorize several equations. It was something that made a lot of sense on a logical and numerical plane, so I understood it much better than other concepts that are straight chemistry. I really enjoyed using more logic and a small amount of memorization more than memorizing a huge amount of chemistry facts and vocabulary. I did really well on this quiz, in fact, the only reason I didn't get 100% was because I didn't understand what the first question was asking, so I didn't answer it correctly. All in all, this was my favorite topic that I studied in chemistry in this semester.
