An Investigation in the Carbon Sequestration Potential of soil under wet and dry soil conditions

WordPress Portfolio Website link : https://harrietlucysmith.wordpress.com/portfolio/carbon/

Aim :

The aim of this study is to investigate the carbon sequestration potential of soil/ substrate under wet and dry soil conditions.

Hypothesis

H0 : There will be no difference between the different soil/ substrate conditions and the amount of carbon dioxide that they release ( the variance between the three groups are all equal) H1 : There will be a significant difference between the different substrate conditions and the amount of carbon dioxide, released from the soil and adsorbed by the soda-lime

Introduction

Within the last decade, approximately 33.7% of anthropogenic CO2 emissions have been

removed from the atmosphere through the terrestrial carbon sink ( Keenan et al 2018). This

has generated interest in the carbon sequestration potential of soils to provide as a method

of climate change mitigation ( IPPC 2013, Amundson 2018). Carbon sinks function through

biogeochemical cycles, via the microbial activity within the soil ( Grogan 1998), these natural

cycles are interlinked through the physical, chemical and biological transformations that

occur in the Earths System Therefore the physical climate system and biogeochemical

cycles are very much interconnected ( Broecker 2012). However it is also recognised as a

process that could result in feedbacks that could accelerate climate change over the 21st

century’ ( Melillo 2002). Thus the process of carbon sequestration is a key part in the models

of terrestrial carbon budgets and models of ecosystem carbon cycling ( Grogan 1998)

The effectiveness of these terrestrial sinks and soils carbon sequestration potential depends

on how the current and future patterns of carbon flux not only respond to changes within the

climate system (Lal 2004, Smith 1998, Brocker 2012, Biskaborn 2019 ), but also the to the

changes in atmospheric emission dynamics induced through anthropogenic activity ( Figure

0.1, Ballantyne 2012, Melillo 2002). For example, it has been noted that carbon- land flux

patterns, under the influence of changing climate, have the ability to accelerate global

warming, through processes such as permafrost thawing (Biskaborn 2019) or the drying of

peatlands (Gabbattiss 2019, Ojanen 2010, Natural England 2010) which redistributes long

term terrestrial stored carbon into the atmosphere as CO2, and therefore could be a

significant factor of future climate change, (Melillo, J. 2002,) through positive feedback

mechanisms ( Broecker 2012) Understanding the relationship between terrestrial carbon

sink capacity, the earths carbon budget, and changes within the earths atmosphere system

is crucial to the development of future climate mitigation models and land management

policies. ( Smith, 1998, IPPC 2013)

Method:

Within this investigation, the CO2 flux of wet and dry soils was assessed over a 5 week

incubation period, using the ‘ soda lime method’, adapted from (Sohi and Cross 2011 ). This

is a very common method for measuring soil respiration due to the efficiency in which the

soda-lime reacts with carbon dioxide that passes through the air ( Kieth and Wong 2006) .

Soda lime is conformed of calcium hydroxide (80%), water (15%), and a catalysts: sodium

hydroxide (5%) ( Freeman 2013) Soda lime absorbs about 19% of its weight in carbon

dioxide, hence 100 g of soda lime can absorb approximately 26 L of carbon dioxide

( Freeman 2013) Soda lime is able to absorb CO2 due to the NaOH ( sodium hydroxide). The

chemical reactions involved in the soda lime absorption/ neutralization of CO2 from the

atmosphere follows these reactions ( Grogan 1998)

The theory behind this method is that the mass CO2 emitted within a sealed environment

( in this case a sealed chamber containing soil) is reflected in the increase of soda lime dry

mass during the incubation period ( Grogan 1998). However within these reactions as shown

in the equations above, water has been produced in the process. This water is adsorbed by

the soda lime, and therefore air drying the soda lime was important in order to get a true

value of the increase in CO2 absorption.

Method / Justification Limitation and Caution Control

Date of lab work ( 23.09.2019) 6 of the same glass crucibles were weighed individually to find out their mass (g) before adding the soda lime. A metal spatula was used to measure approximately 1g of dry Soda Lime into each crucible ( Figure 1A)The mass of each ‘crucible + Soda Lime’ was reweighed to confirm the starting weight

Caution must be taken when handling the Soda Lime due to being highly corrosive to eyes and skin and irritating ( Dineshkumer at al 2016)

Measured starting weights of Soda Lime varied slightly – inconsistent measuring ( max 1.056g – min 0.0861g)

Any changes in Soda Lime would be interpreted in SI unit (g) by calculating the ‘relative change’ to overcome the differences in starting weight

6 of the same sealed plastic chambers were used to create the closed system environments

In creating a closed a system environment and measured in the lab, external interactions from biosphere components

The same soil was used within each plastic chamber and filled to an equal level. This limited ( although didn’t

2NaOH (s) + CO2 (g) <---> Na2CO3 (s) + H2O (ads) [1] Ca(OH)2 (s) + CO2 (g) <---> CaCO3 (s) + H2O (ads) [2]

2 x chambers were 2/3rds with soil ( to replicate a dry environment)

2x chambers were 2/3rds filled with soil + 90ml deionized water ( to replicate a wet environment)

2 x chambers were intentionally left without soil ( these were used as a control, to measure the change of Soda Lime without a substrate influence)

have been removed; analysis of the results must consider external factors that would influence the carbon sequestration potential of soils in an open/ natural system (e.g. land use change/ deforestation/ increasing Carbon Dioxide in the atmosphere/ erosion)

Approximated volume of soil used, not measured. This could impact respiration potential ( Keith and Wong 2006)

Water added to the soil in chambers 3 and 4 may have influenced the results also due to the water chemistry

remove) the interference of external factors (other than water content) during the experiment

Deionized water was used in chambers 3 and 4 as which means most of its mineral ions have been removed – although this could have influenced the soil/ isn’t replicable in the natural environment – issue?

A labelled crucible containing Soda Lime of a known weight (g) was inserted into each of the plastic chambers. The chambers were sealed, labelled accordingly and left at room temperature ( 20-24oC) for an incubation period of 35 days ( 5 weeks)( Figure 1B)

The chambers were left near a window, this could have had an impact on the temperature of the soil over this time period due to possibly being in direct sunlight at times during incubation.

Date of lab work 4.11.2019

The crucibles containing Soda Lime were removed from the chambers and reweighed.

The Soda Lime from the chambers with Wet soil were evidently damp, noticeable by the colour and texture (Figure 1C)DURING ANALYSIS : do we know how much CO2 has been absorbed by the water ? partitioning value

Crucible 4 was dried overnight and reweighed (crucible 3 had already been disposed of) in order to remove the adsorbed waterThe effects of the partitioning value between CO2 , soda lime and water was considered during analysis

Data Interpretation

The data within this report was interpreted using descriptive statistical methods such

as reporting the relative frequency of change in mass of soda lime and the associate

within the between each of the variables.

The decision not to use statistical analysis tests such as the ANOVA test or T Test to

describe the variance or difference between the mean values was due to the lack of

data within the small samples sizes and therefore such measures would have been

inappropriate to report ( Montello et al 2013) The lack of data is considered to be a

limitation within the design of this investigation.

Results

Variable Descriptive Interpretation of data

Control (chambers1 and 2)

The chambers holding no soil both show a decrease in their mass of soda lime ( chamber 1; -0.101g and chamber 2; -0.072g). The mean relative change in mass of Soda Lime was -0.011g ±0.002 ( -1.11% ±0.2%) with a range of ( 0.36%)

Dry Soil (Chambers 5 and 6)

The chambers containing dry soil also show a decrease in their mass differencein soda lime ( chamber 5: 0.106g and chamber 6: 0.074g) The mean relative change in mass of soda lime was -0.011g ±0.002 ( -1.17 % ±0.2%) and a range of ( 0.38%). These values are very similar to the % relative change recorded for

the control’ chambers (1 and 2).

Wet Soil (Chambers 3 and 4)

The chambers containing soil with 90ml of water added, showed an increase in mass of soda lime ( chamber 3 : -1.823g and chamber 4 : -0.715g). The mean relative change in mass of Soda Lime was -0.018g ±0.12 ( 18.49% ± 12%).

These chambers showed the largest variation in relative change, ranging from 9.52% increase in chamber 4 and 27.45% increase chamber 3, ( a difference of 17.93%)Figure 2 : (above) : A bar graph to illustrate the changes in mass of soda lime within Contolled, Wet

and Dry chambers before and after incubation period. Figure 3 : (Below) a bar graph to show the relative change in mass of soda- lime between the control, wet and dry soil samples

Air Dried Soilchamber 4)

Interpretation of air dried (AD) Soda Lime mass from chamber 4 alsoshowed an increase in mass difference in soda lime ( -0.149g). The relative change was 0.019g ( 1.99%), a value which is 7.53% lower than the initial recording of soda lime mass change in chamber 4. During the air drying process/ evaporation of water, -0.565g in mass was removed from the Soda Lime. This process of evaporation may have obscured the true value of mass change in Soda Lime . – do we know how much co2 would have been absorbed by the water.

The relative increase value of 1.99% is larger than then relative decrease of soda lime mass in either the controlled or dry chambers. This shows that the soda lime absorbed more CO2 in the presence of wet soil.

Discussion

The use of the soda-lime method has been used repeatedly as a way to measure the

respiration output soil CO2 fluxes ( Grogan 1998, Montieth 1964, Keith and Wong 2006, Sohi

and Cross 2011). Limitations with the soda-lime method have been noted to occur through

inaccuracies as the rate at which soda-lime adsorbs CO2, is ‘ not in balance with the efflux

rates being measured’ ( Grogan 1998). This has lead to suggestions that the method of soda

lime is able to over estimate flux rates of CO2 ( Grogan 1998) thus the recommendation of

the use of a calibration curve is required in order to compensate for this measurement error (

Figure 4, Grogan 1998). Given that the mass of soda-lime were inaccurately recorded in this

report, the disproportionate values of change in soda lime mass ( due to holding excess

water) recorded within chambers 3 and 4 ( Figure 3 and 4) ( wet soil) was to be expected.

To amend this result chamber 4 was air dried and reweighed to produce a mass increase in

soda lime of 0.149g. In hindsight, the correction factor of ( 1.69) should have been multiplied

Figure 3

by this result in order to compensate for the underestimation of CO2 absorption, and

measure the mass difference to calculate the true mass of CO2 absorbed ( Grogan 1998).

Comparison of the relative change (%) in mass of soda lime of chamber 4 ( AD) 9 (1.99%),

to the values obtained from chambers 5 and 6 ( Dry soil) ( -1.37, -1.98%) ( Figure 4)

suggests that within this investigation, the soda lime within the wet chamber, adsorbed more

CO2, and therefore the wet soil sequestered more carbon dioxide at a faster rate than the

change in recorded within the dry chambers. The low levels of carbon dioxide release of the

dry soil is congruent with findings from ( Lal 2008, Farage 2003) who note that drylands soils

contain considerably less carbon, predominantly due to lack of plant productivity. Although it

has been recognised that the storage time of carbon with drier soils its longer than that in

wet soils, thus enabling soils to have a greater carbon sequestration potential (Farage 2003).

Given the closed system in which this investigation was conducted, the moisture variable

would have influenced the rate of change noticed in chamber 4 ; the rate of reaction of

decomposition of carbon dioxide, by the soda lime, could have been enhanced by microbial

activity in the presence of water molecules, in comparison to a chemical reaction of the drier

substrate.

Within the closed system of this investigation, soil moisture plays a role in the ability for soil

to sequester carbon, however this design does not factor for external climate factors such as

the advance of atmospheric temperature, which has been found to influence the rate at

which carbon is released from the terrestrial sinks ( Serrezze 2010, Brocker 2012). Studies

have observed recent trends of atmospheric warming, especially within the Northern

Hemisphere ( Serrezze et al 2006, IPPC 2013), which coincide with increased levels of

terrestrial carbon flux due to the subsequent release of CO2 from the thawing permafrost

tundra( Schuur,et al 2009). This produces a positive feedback on the climate system,

whereby the decomposition of organic matter, subsequently releases greenhouse gases into

the atmosphere ( Biskaborn 2019) and reinforces . As permafrost soils within the Northern

Hemisphere hold double the amount of carbon as the atmosphere ( Schuur et al 2009)

current climate scenarios predict their ability to amplify the escalating trends of global

warming and air temperature (Melillo, J. 2002) resulting in continued losses of soil carbon,

attributable to moisture changes and permafrost warming ( Schuur et al 2009)

Furthermore, enhanced atmospheric warming trends in the Northern Hemisphere have been

also found to impact soils ability to not only capture but retain CO2 (Gabbattiss, J. 2019) due

to enhanced decomposition resulting from altered soil moisture and thermal regimes

( Waddinton et al 2014). Peatlands are a significant store of terrestrial global carbon

( Waddington et al 2014) Covering 3% of the earths surface, they hold up to a 5th of the

carbon ( Swindles et al 2019 ) and therefore and have the ability to exhibit positive or

negative feedbacks to the climate system. Within European Peatlands, increasing

temperatures and disturbances from poor land management means that the currently

waterlogged conditions, which stores vast amount of carbon in anaerobic conditions, are

being exposed to oxygen ( Natural England 2010). This exposure not only comes from

surface disturbance, but also through patterns of changing vegetation within the ecosystems

resulting a shift from peat mosses to shrubs ( Gabbattiss, 2019). A similar vegetation shift

has occurred within the Arctic Tundra ( Schuur et al 2009) as a result of the changing

climates. This relays the significance of the interaction between biogeochemical responses

to changing climates, and the sequential impact that can have on the soils ability to retain

and emit carbon ( Swindles 2019, Nichols 2019)

The vast size of the carbon terrestrial sink does provide an opportunity to sequester carbon

dioxide emissions that are being produced as a results of anthropogenic activity ( IPPC

2013). Amendments to the soil to enhance its capacity for carbon uptake include crop

management practices such as nitrogen fertilization ( Deem 2017), the use of biochar ( Sohi

and Cross 2011) However the capacity of the terrestrial carbon sink makes predictions of

carbon flux unpredictable to measure accurately ( Nicohols 2019). Therefore the

understanding of the factors that can influence this natural cycle are imperative as the future

capacity of the earths carbon sink are sensitive to changes within the moisture content of the

soil and also the prevailing interactions between the land and the atmosphere ( Green 2019).

As shown in the figures 5 and 6, the influence of soil moisture variability, is just one aspect

that can alter the sequestration potential of soils. Future trends within the variability of soil

moisture suggest this could cause a reduction in the present capacity of the land as a carbon

sink. Parallel to these changes, increasing temperatures, accelerating levels of CO2, and

disruptive activity through land use change and poor agricultural management, could also

significantly alter the rate at which terrestrial soils are able to sequester carbon within the

future. If an equilibrium is not achieved within the dynamic land- atmosphere relationship this

could lead to an acceleration of the atmospheric growth of CO2 (Green 2019)

Appendix/ Figures

Figure 5 : A graph to illustrate the global changes in soil moisture variability and associated terrestrial respiratory potential ( 1971-2000) and future predictions of soil moisture variability ( 2056-2085)( Green 2019)

Figure 4 : A graph to illustrate the relationship between CO2 efflux rates with the correction factor of 1.69 and edited by (Grogan 1998)

References

Amundson, R. and Biardeau, L. (2018). Opinion: Soil carbon sequestration is an elusive climate mitigation tool. Proceedings of the National Academy of Sciences, 115(46), pp.11652-11656.

Ballantyne, A. P., Alden, C. B., Miller, J. B., Tans, P. P., & White, J. W. C. (2012). Increase in observed net carbon dioxide uptake by land and oceans during the past 50 years. Nature, 488(7409), 70–72. doi:10.1038/nature11299 

Biskaborn, B. K., Smith, S. L., Noetzli, J., Matthes, H., Vieira, G., Streletskiy, D. A., … Lantuit, H. (2019). Permafrost is warming at a global scale. Nature Communications, 10(1).

Broecker, W. (2012)The carbon cycle and climate change: Memoirs of my 60 years science. Geochemical Perspectives 1(2), 221-340.

Conway, P.P. Tans, L.S. Waterman, K.W. Thoning, D.R. Kitzis, K.A. Masarie, and N. Zhang, (1994), Evidence of interannual variability of the carbon cycle from the NOAA/CMDL global air sampling network, J. Geophys. Research, vol. 99, 22831-22855

Deem, L. M., & Crow, S. E. (2017). Biochar. Reference Module in Earth Systems and Environmental Sciences. doi:10.1016/b978-0-12-409548-9.10524-x 

Dineshkumar, N., Mugundhan, K., Srinivasan, P.S.S., Visagavel, K. and Sakthivel, D., 2016. Analysis of workplace safety and health hazards in soda recovery plant. Advances in Natural and Applied Sciences, 10(9 SE), pp.81-86.

Farage, P., Pretty, J. and Ball, A., 2003. Biophysical aspects of carbon sequestration in

drylands. University of Essex.

Figure 6 : A graph to illustrate the global changes in temperature change and correlating changes in soil moisture ( a & c 1971-2000) ( b & d 2056-2085)(Green 2019)

Freeman, B. (2016). Absorption of Carbon Dioxide | Anesthesiology Core Review: Part One Basic Exam | AccessAnesthesiology | McGraw-Hill Medical. [online] Accessanesthesiology.mhmedical.com. Available at: https://accessanesthesiology.mhmedical.com/content.aspx?bookid=974&sectionid=61586921 [Accessed 28 Novermber. 2019].

Gabbattiss, J. (2019). Europe’s carbon-rich peatlands show ‘widespread’ and ‘concerning’ drying trends. [online] Carbon Brief. Available at: https://www.carbonbrief.org/europes-carbon-rich-peatlands-show-widespread-and-concerning-drying-trends [Accessed 4 Nov. 2019].

Green, J.K., Seneviratne, S.I., Berg, A.M. et al ( 2019). Large influence of soil moisture on long-term terrestrial carbon uptake. Nature 565, 476–479

Grogan, P. (1998). CO2 flux measurement using soda lime: correction for water formed during co2adsorption. Ecology, 79(4), pp.1467-1468.

IPPC (2013): Collins, M et al 2013: Long-term Climate Change: Projections, Commitments and Irreversibility. PAGE 1079 -1085 In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Keith, H. and S.C. Wong (2006) Measurement of soil CO2 efflux using soda lime absorption: both quantitative and reliable. Soil Biology and Biochemistry 38:1121-113

Keenan, T. and Williams, C. (2018). The Terrestrial Carbon Sink. Annual Review of Environment and Resources, 43(1), pp.219-243.

Lal,R (2004) ‘Soil Carbon Sequestration Impacts on Global Climate Change and Food

Security’, Science, 304(5677), pp. 1623,1627.

Limpens, J., Berendse, F., Blodau, C., Canadell, J. G., Freeman, C., Holden, J., Roulet, N., Rydin, H., and Schaepman-Strub, G, ( 2008) Peatlands and the carbon cycle: from local processes to global implications – a synthesis, Biogeosciences, 5, 1475–1491

Melillo, J. (2002). Soil Warming and Carbon-Cycle Feedbacks to the Climate System. Science, 298(5601), pp.2173-2176.

Monteith, J. L., G. Steicz, and K. Yabuki. 1964. Crop photosynthesis and the flux of carbon dioxide below the canopy. Journal of Applied Ecology 1:321–337

Montello, D. R. and Sutton, P. C. (2013) An introduction to scientific research methods in geography & environmental studies. 2nd edn. London: SAGE.p22-32

Natural England (2010) England's peatlands: carbon storage and greenhouse gases (NE257) [Online] http://publications.naturalengland.org.uk/publication/30021

Nichols, J.E. and Peteet, D.M. (2019) Rapid expansion of northern peatlands and doubled estimate of carbon storage, Nature Geoscience, 

Ojanen, P., Minkkinen, K., Alm, J., & Penttilä, T. (2010). Soil-atmosphere CO2, CH4 and N2O fluxes in boreal forestry-drained peatlands. Forest Ecology and Management, 260(3), 411-421

Pleijel et al. (1998) Nitrous oxide emissions from a wheat field in response to elevated carbon dioxide concentration and open-top chamber enclosure. Environmental pollution 102 (s1), 167-171.

Schuur, E., Vogel, J., Crummer, K. (2009) The effect of permafrost thaw on old carbon release and net carbon exchange from tundra. Nature 459, 556–559

Serreze, m.c. & francis, j.a. climatic change (2006) observational evidence of recent change in the northern high-latitude environment76: 241. Https://doi.org/10.1007/s10584-005-9017-y

Smith, T., Cramer, W., Dixon, R., Leemans, R., Neilson, R. and Solomon, A. (1993). The global terrestrial carbon cycle. Water, Air, & Soil Pollution, 70(1-4), pp.19-37.

Sohi S & Cross A (2011) The priming potential of biochar products in relation to labile carbon contents and soil organic matter status. Soil Biology & Biochemistry 43, 21272134

Swindles, G.T., Morris, P.J., Mullan, D.J. (2019) Widespread drying of European peatlands in recent centuries. Nat. Geosci. 12, 922–928 doi:10.1038/s41561-019-0462-z

Waddington, J., Morris, P., Kettridge, N., Granath, G., Thompson, D. and Moore, P. (2014). Hydrological feedbacks in northern peatlands. Ecohydrology, 8(1), pp.113-127.