Co-Authored with James F.
Abstract:
In our
investigation, we examined the effects of elevated levels of calcium on a forest
ecosystem. In the Hubbard Brook Experimental Forest Watershed One, scientists
added large amounts of calcium in the form of wollastonite into the first
sector, or watershed, of the forest. Our hypothesis was that this calcium, in
its ionized form, precipitates out of the forest stream with ions naturally
present in the water. We theorized that this precipitation could affect the pH
a nearby stream by reacting with acidic or basic ions, such as HSO4-
or OH-, thereby pulling the ions out of solution. We also
postulated that these extreme levels of calcium would be toxic to plant life,
affecting leaf chemistry and potentially having adverse effects on the plants' function,
possibly leading to plant death. Additionally, as a result of increased plant
death and solids precipitating out of solution, we expected to see increased
sediment buildup in a nearby stream. We were unable to investigate this
particular hypothesis as adequate data was not recorded after calcium addition.
However, we were able to examine the increased biomass of the forest floor,
which we believed might correlate with the calcium addition. For our
analysis, we analyzed stream chemistry, leaf chemistry, and forest floor mass
of both the control and calcium-enhanced watersheds. We found clear effects in
leaf chemical levels of Ca, Mg, Mn, K, and P after calcium addition. Leaf
calcium increased, leaf magnesium decreased upon addition, leaf manganese
increased to compensate for increased calcium, leaf potassium decreased upon
addition, and leaf phosphorous decreased upon addition. We also noted
clear increases in the chemical levels of Ca, PO4, SiO2,
SO4, and pH in the stream chemistry after calcium. Finally, we
observed a significant increase in forest floor mass that possibly correlated
with calcium addition and precipitation.
Introduction:
The purpose
of this lab was to examine the effects of calcium on forest ecosystems using
data gathered in the Hubbard Brook experiment.
We compared various attributes of forest watershed one before and after
the addition of calcium to the system.
We also compared several attributes of forest watershed one, with the
addition of calcium, and forest watershed three, the control watershed. We theorized that calcium cations from the
introduction of wollastonite, a calcium compound with the molecular formula
CaSiO3, would precipitate out of the water with other, naturally
occurring anions. We believed that this
increased precipitation could result in increased sediment buildup in the
river. Additionally, we believed that
the excessive levels of calcium in the environment could be detrimental to the
biological function and health of the trees.
We conjectured that the trees would have increased levels of calcium,
increased levels of other chemicals involved in calcium processing, and
decreased levels of absorption of other necessary chemicals, owing to calcium
oversaturation in the soil. We used
several sets of data to study these hypotheses.
We graphed the average thickness of soil and topsoil before and after
the calcium addition, we graphed the increased and decreased presences of
various substances in the trees’ leaves, and we charted the stream chemistry of
the rivers in watershed one and watershed three. We could not graph the sediment buildup owing
to the fact that sediment yield data was not gathered past 1999.
Results:
The above graph shows the
average total thickness of forest floor mass before the addition of calcium to
the watershed. 98 plots were surveyed
eight times each. The mean of the
overall thicknesses was found to be approximately 8.0, the median thickness was
found to be approximately 7.0, and the mode of the set was found to be
approximately 5.4.
The above graph shows the
average thickness of the top layer (Oie) of forest floor mass before the
addition of calcium to the watershed. 98
plots were surveyed eight times each.
The mean of the overall thickness was found to be approximately 3.7, the
median thickness was found to be approximately 3.4, and the mode of the series
was found to be approximately 3.6.
The above graph shows the
average total thickness of forest floor mass after the addition of calcium to
the watershed. 98 plots were surveyed
eight times each. The mean of the
overall thicknesses was found to be approximately 8.2, the median thickness was
found to be approximately 8.2, and the mode of the set was found to be
approximately 4.8. The mean and the
median both show a significant increase form the pre-calcium addition levels,
meaning that there was possibly some precipitation of solid from the calcium
addition.
The above graph shows the
average thickness of the top layer (Oie) of forest floor mass after the
addition of calcium to the watershed. 98
plots were surveyed eight times each.
The mean of the overall thickness was found to be approximately 4.3, the
median thickness was found to be approximately 3.9, and the mode of the series
was found to be approximately 3.5. The mean and the median both show a
significant increase form the pre-calcium addition levels, meaning that there
was possibly some precipitation of solid from the calcium addition.
The above graph shows the
effects of increased calcium concentration on leaf biochemistry. Data was gathered on three different tree
species, balsam fir (ABBA), red spruce (PIRU), and white or paper birch
(BEPA). (Hubbard Brook, Watershed 1
Temporal Canopy Leaf Chemistry) The
calcium was added in the year 2000.
(Hubbard Brook, Watershed 1 Temporal Canopy Leaf Chemistry) After this year, there is a significant
increase in the calcium concentration in parts per million, which correlates
with our hypothesis.
The above graph shows the
concentration of magnesium in parts per million in leaves as a function of time
(before and after the addition of calcium into the system). As expected, for most tree species the amount
of magnesium absorbed upon the addition of calcium decreased. Two years after the addition of the calcium,
the trees with the most significant absorption loss had returned to previous
levels of magnesium concentration, perhaps making up for a magnesium
deficit.
The above graph shows the
concentration of manganese in parts per million in leaves as a function of time
(before and after the addition of calcium into the system). Manganese is an element that is essential to
calcium absorption. (University of
Maryland Medical Center, 2011) The uptake of manganese correlating with an
uptake of calcium shows that the leaves have been oversaturated with calcium
and need excessive amounts of other ions to process it.
The above graph shows the
concentration of potassium in parts per million in leaves as a function of time
(before and after the addition of calcium into the system). Potassium is an element that is essential to
plant growth; along with calcium it is key to the growth of young and
developing plants. (Fromm, 2010) For ABBA and PIRU species, the initial flood
of calcium apparently reduced the plants’ abilities to absorb potassium. This effect seemed also to be present in BEPA
plants, though it should be noted that they made rapid recovery, and soon the
potassium levels were much, much higher than in pre-calcium addition plants.
The above graph shows the
concentration of phosphorous in parts per million in leaves as a function of
time (before and after the addition of calcium into the system). Phosphorous is an element that is key to
sustained plant growth (Baribault, 2012).
For all species, the initial flood of calcium apparently reduced the
plants’ abilities to absorb phosphorous.
However, the BEPA species quickly rebounded to levels above the initial
pre-calcium levels, possibly to make up for a phosphorous deficit.
The above graph shows the stream chemistry of
watershed three, the control watershed.
This graph shows one large noticeable spike in PO4 levels,
around 400 months.
The above graph shows the stream chemistry of
watershed one, the watershed with calcium added. This graph also shows one noticeable spike in
PO4 levels around 400 months, however its spike is larger than that
of the control. This could possibly be
attributed to the calcium addition and some dissolved precipitate in the
stream.
The above two graphs show the trends of stream
chemistry for watersheds three and one, respectively. The levels of SiO2 initially
increased before leveling out in watershed one, yet in watershed 3 there was no significant trend. This initial increase
could be linked to the presence of calcium.
The levels of Ca were significantly higher in watershed one, as would be
expected. The levels of SO4
were slightly elevated with calcium, yet both watershed three and watershed one
showed a general downward trend over time, indicating that there may be some
larger environmental factor affecting the levels. The pH was elevated with calcium addition, as
would be expected (calcium is a naturally basic substance).
Discussion:
After analyzing the data from the Hubbard Brook watersheds,
we found several correlations between calcium addition and changes in leaf
chemistry, stream chemistry, and forest floor mass over time. The above
graphs demonstrate the correlation between elevated calcium levels and
alterations in plant chemistries.
The first four graphs show an increase in forest floor mass
after the addition of calcium. This increase may be related to elevated
levels of calcium leading to toxicity in some plants. These plants would
die and turn into detritus, which would increase the mass of the forest
floor.
The next five graphs delineate the changes in leaf chemistry of calcium,
magnesium, manganese, potassium, and phosphorous. The addition of calcium
in the watershed environment leads to an expected increase of calcium in the
leaves themselves. We not this effect in all of the three plant species
studied. When we analyzed the levels of magnesium, we found a general
reduction in the levels of magnesium for all three plant species, noted at the
year 2000 for BEPA and ABBA and approximately one year later for PIRU.
This effect is likely the result of excessive calcium saturation of the soil,
which could prevent the plants from drawing other ions from the soil.
This would lower the levels of the aforementioned ions in the leaf chemistry
analysis. We subsequently observed the levels of magnesium in the leaves
increasing after the initial reduction to higher levels than before. We
may attribute this phenomenon to a deficit in magnesium levels from the
blockage, which would cause the plant to overcompensate to restore proper
magnesium levels. The next graph, a plot of manganese levels over time,
showed an increase of manganese absorption. We found in our research that
manganese aids in calcium absorption. Therefore, increased calcium
absorption owing to the elevated calcium levels would elicit an increase in
manganese absorption to allow for proper calcium processing and
integration. We have noted this general increase in the manganese
absorption in all three species of plant studied after the 2000 calcium
addition. All three plant species experienced reduced levels of potassium
at the 2000 calcium addition, probably owing to the introduced calcium blocking
the absorption of other chemicals. We note the BEPA plants seemed to make
a rapid recovery, unlike ABBA and PIRU, which appear to recover at a slower
rate. This recovery may also be the result of a compensation for a
deficiency, similarly to magnesium. Phosphorous absorption is also reduced.
This may be attributed to, as noted above, extreme calcium levels blocking the
absorption of other chemicals. We also note the extreme recovery of the BEPA
plant, perhaps related to compensation for a previous deficiency.
The last graphs refer to stream chemistry. PO4 has its
own graph due to the relatively small scale of the concentrations with regards
to the other chemicals in question. First, we note the clear increase in
calcium levels shown by the graph due to its artificial augmentation by
scientists. This calcium addition in watershed one showed a correlation to
increases in SiO2, pH, and SO4. SiO2 levels
do not show a trend in the control, watershed three, but show a clear increase
linked with the calcium addition. Therefore, the calcium addition probably
caused, through an unknown set of processes, the increased SiO2 levels.
Similarly, pH was largely stable in watershed 3, but rose in watershed one in a
manner tied to the calcium addition. Calcium likely is the cause of this
increase, as we hypothesized. SO4 also increased in this
manner, but we note that it trended generally downward during the measurement
period. This long-term downward trend is likely due to external factors,
perhaps climate change, as the overall trend does not correlate with calcium
levels and is present in both watersheds. However, the short-term increase of
SO4 is strongly correlated with and likely caused by calcium
addition. Finally, PO4 generally trended higher at the calcium
addition at around month 400. This is increase was likely caused by calcium.
Note that there is another relative increase in the PO4 levels at
300 months. As this deviation is present in both graphs and occurs before
addition of calcium, it is likely caused by a larger scale event that would
affect both watersheds, such as a climatological incident.
We do not have any known sources of error because we did not perform the data
taking, although, of course, there is some extent to which there is presumable
error. If we had the necessary data, we would have examined the sediment
buildup as related to increased detritus from calcium toxicity (as indicated by
increased forest floor mass). Another potential project is to find
exactly through what means calcium functions to increase PO4, SiO2,
pH, and SO4. As hypothesized in the abstract, we believed that a
reduction in acidic ions such as HSO4- due to their
precipitating out of solution by reacting with calcium ions. As for the other
compounds, the processes through which they are increased could be chemical
reactions or physical, i.e. calcium toxicity causing increased detritus that
decomposes into some of the above chemicals.
Overall, it seems that the introduction of calcium into a forest ecosystem
results in possible toxicity to trees, precipitation of natural substances, and
significant changes in leaf chemistry. This phenomenon should be examined
further before calcium is implemented in any large-scale projects in forest
biomes.
Works Cited:
Baribault, Thomas W., Richard
K. Kobe, and Andrew O. Finley. "Tropical Tree Growth Is Correlated with
Soil Phosphorous, Potassium, and Calcium, Though Not for Legumes." Ecological
Monographs 82.2 (2012): 189-203. ESA Journals. Ecological
Society of America, 2012. Web. 9 Apr. 2013. <http://www.esajournals.org/doi/abs/10.1890/11-1013.1>.
Fromm, J. "Wood Formation
of Trees in Relation to Potassium and Calcium Nutrition."Tree
Physiology 9 (2010): 1140-147. PubMed. US National Library
of Medicine, National Institutes of Health, 2 May 2010. Web. 9 Apr. 2013. <http://www.ncbi.nlm.nih.gov/pubmed/20439254>.
Hubbard Brook. "Watershed
1 Temporal Leaf Chemistry." Hubbard Brook Ecosystem Study.
LTER Network, n.d. Web. 9 Apr. 2013.
<http://hubbardbrook.org/data/dataset.php?id=45>.
University of Maryland Medical Center.
"Manganese." University of Maryland Medical Center.
A.D.A.M. Inc., 2011. Web. 9 Apr. 2013.
<http://www.umm.edu/altmed/articles/manganese-000314.htm>.
Data from the Hubbard Brook Ecosystem Study Data Sets
http://hubbardbrook.org/data/dataset_search.php
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