Chamber Experiment

As the literature review shows a variety of environmental chambers have been used in previous studies of stone decay to simulate effects such as salt weathering (Mcgreevy and Smith, 1985; Warke et al., 2006), pollution (Ausset et al., 1996) and thermal weathering (2003; Prikryl et al., 2003; Smith et al., 2008a). To examine how changes in the climate may affect the weathering processes and the microorganisms present on Glasgow sandstones, a simulation experiment was set up in a Sayno Fitotron Plant Growth chamber located in the workshop of Historic Scotland, Edinburgh. The environmental

chamber replicates a preset range of temperatures, relative humidity and light settings.

This control over the set up of the chamber and the cycling of programmed conditions means that future climate conditions for Glasgow (as predicted by the UKCIP02) can be run within the chamber and on many samples simultaneously.

Six blond sandstones were used in this experiment: Bearl, Blaxter, Clashach, Cullalo, Dunhouse Buff and Scotch Buff (full mineralogical description of each stone is given in section 2.2.5). This sample set represents one commonly used replacement sandstone for each of the blond sandstone categories identified by Hyslop et al (2006). These sandstones were chosen as the majority of original quarries are now disused, leaving no present-day source for sampling of the stones. In addition, these are the stone types that are expected to be used for the majority of future constructions and repairs.

Each stone type was prepared by cutting it into three 9x9x9 cm cubes. During sawing of the blocks, oil was used as a lubricant, then washed with water. However, a few samples were left with small amounts of oil residues on the surfaces, which were later abraded off. In more extreme circumstances, where oil had penetrated into the sample, the top 3 mm of the affected surface was sawn off using only water as a lubricant. An unaffected face of the block was then used for the experiment.

After the blocks were cut, three stainless steel screws were drilled into the same surface of each block in a triangular pattern. Stainless steel screws were chosen as they would not corrode over time and thus could then be used as reference points for monitoring stone surface degradation. The screws should not interact with the block as plastic casings (raw plugs) were placed in first to restrict contact between the sandstone and the metal. Using a Konica Minolta Vivid 9i laser scanner, each block was scanned before being installed (02/08/2008) in the environmental chamber and rescanned at the end of the experiment on the 26/01/2010. The manufacturer’s specifications state that for the Konica Minolta Vivid 9i scanner it has a precision of 0.008 mm with an accuracy of 0.05 mm. Within the chamber, the blocks were divided into three sets, which each comprised of one block of each stone type. The three sets were comprised of an inoculated set, water only set and a chamber set (Figure 2-12). These sets were then arranged on one level within the chamber (Figure 2-13).

Figure 2-12: Plan view of environmental chamber set up.

1) Inoculated set, 2) water set, 3) chamber set.

Figure 2-13: Internal view of the environmental chamber.

The inoculated blocks involved using a variety of microbes, sampled from six different areas of typical weathering on blond sandstone surfaces from the West End of Glasgow.

These were collected from walls surrounding properties within the Dowanhill area of Glasgow. The microbes gathered were combined and thoroughly mixed before being equally divided up into seven 0.2 g samples. The microbe mixture was applied within one week of collection into the rock surface using droplets of water to help it bind, one

portion was retained for visual identification of the microbes. Visual identification was undertaken using a Zeiss Axioplan microscope, and three main species were identified.

The first has an elongated form with a green to brown coloured internal configuration, contained within a clear outer structure. This microbe is morphologically consistent with the algae Hyalotheca (Figure 2-14 A and B). The second main microbe has a morphology consistent with the fungi Rhizopus, which has previously been observed living within sandstone (Burford et al., 2003). Rhizopus has two distinct parts: the fibrous stolons and clusters of brown sporangium (Figure 2-14C and D). The third microbe has a plant-leaf-like structure (Figure 2-14E), but is yet to have been formally identified, although the

most likely option is for it to be a lichen or algae due to its size and form. Artificial rain water (composition in Table 2-6) was sprayed onto these inoculated blocks twice a week when in the chamber so that free water was available for the growth of microbes.

Figure 2-14: Comparison images of microbes seen and its morphological consistent image of suggested microbe.

A) typical Hyalotheca, (http://www.algalweb.net), B) microorganism seen in the mixture, C) a typical Rhizopus (http://www.doctorfungus.org), D) microbe seen in the mixture, E)

unidentified lichen.

The water-only set of blocks had no microbes present but required additional artificial rainwater sprayed onto their surface, in conjunction with the standard environment chamber set up, to imitate an increase in high magnitude events which are linked with heavy rainfall events, defined as 5 ml per minute (Svensson and Jakob, 2002). A spray bottle was used to distribute the artificial rainwater and tests were conducted to see how many sprays were required to deliver the right amount of water. Results showed that one spray equated to ~1.3 ml of water, therefore four sprays were used in each set of blocks (full detail of results are found on the electronic appendix).

The chamber set of blocks experienced only the internal conditions within the environmental climate chamber rather than being subjected to extra weathering processes, such as microbial action or wetting.

Artificial rainwater was used as the chamber could not run at the high humidity levels required, so this water helped to achieve the correct RH for the experiment. Artificial rainwater was preferred rather than collected rainfall so that its elemental composition

could be precisely controlled (shown in Table 2-6), using a formula modified from (Wakefield et al., 1996).

Table 2-6: Chemical composition of artificial rain water.

Chemical Moles g per l

NaCl 0.28 16.4

MgSO4 0.016 1.9

KNO3 8x10^-3 0.8

CaSO4 8m10^-3 1.1

Used in environmental chamber experiments.

Once the blocks were placed in the chamber, conditions were set to mimic summer and winter seasons. The chamber was set to simulate two weeks of summer and then two weeks of winter.

Summer and winter cycles were chosen as the predicted changes to these seasons are better constrained within the UKCIP02 report as changes to spring and autumn are often stated to be within “natural” variability. Therefore, using these seasons, allowed us to clearly observe the changes in the decay process due to seasonal conditions. Also, summer and winter were used so that the extremes of weathering within Glasgow could be identified.

Summer months were defined as June, July and August within the UKCIP02 report whilst winter months were defined as December, January and February. These will be the standard throughout this study.

The summer set up is shown in Table 2-7 and is repeated 14 times in each cycle. The winter set up again is run 14 times in each cycle and is shown in Table 2-8. The temperature reduction after six hours in both cycles was to compensate for the heat produced by the fluorescent tubes and incandescent lamps within the environmental chamber. The amount of light produced also varied by 25% from the centre (605.9 μmol m²s^-1) to the back right corner (455.8 μmol m²s^-1) of the chamber, which was measured using a hand held Macam Q203 Quantum Radiometer pyronometer.

Table 2-7: Environmental chamber set up for summer cycle.

Time Temperature (°C) Relative Humidity

(%)

Light Setting

6 Hours 18.2 78.6 On

6 Hours 16.2 78.6 On

12 Hours 18.2 78.6 Off

Table 2-8: Environmental chamber set up for winter cycle.

Time Temperature (°C) Relative Humidity

(%)

Light Setting

6 Hours 8 87.8 On

6 Hours 6 87.8 On

12 Hours 8 87.8 Off

Due to a breakdown of the environmental chamber from September 2008 to January 2009, the blocks were transferred to the University of Glasgow’s Gregory building where they were placed in a laboratory on the 4^th floor and faced a southerly directed window.

This was to allow them to receive natural light whilst in a controlled environment. While being located at the University of Glasgow regular artificial rain continued to be sprayed on. Once returned to the chamber, to compensate for the reduction of time within the chamber, the cycles were shortened to ten days of summer and winter, to help maximise the amount of “years” the blocks experienced. The full cycle experienced by the

sandstone blocks over the two year period are schematically represented in Figure 2-15.

To monitor the actual temperature and RH that the blocks experienced throughout the whole experiment, an IButton datalogger (detailed latter in section 2.1.8) was kept with the blocks at all times to record these parameters on an hourly basis. A sample of the results from the IButton is shown in (Figure 2-16). A large range was seen in the recorded temperature and RH as the environmental chamber tries to regulate the conditions and establish an average.

Figure 2-15: Sketch graph of cycles experienced by chamber blocks.

Blue) winter cycle, red) summer cycle, green) time out of chamber. Solid lines = two week cycles, dotted lines = 10 day cycle.

Figure 2-16: Data from environmental chamber showing the programmed conditions against data recorded by the IButton.

Graph shows a 10 day cycle of both summer and winter, Y-axis in °C for temperature and % for RH.

2.1.7.1 Prediction of Future Climate Conditions

The temperature and RH settings used in the climate chamber experiment were

determined using the average present day values for summer and winter seasons. These data were derived from the archive data collected by the University of Glasgow weather station over the summer months of 2003-2007 and winter months of 2004-2007 to estimate the conditions experienced in the Glasgow area. Then, using the United Kingdom Climate Impacts Program 2002 (UKCIP02) report (Hulme et al., 2002) which outlined various emission paths and indicated how these scenarios may affect the climate. The outlined scenarios are: low (525 ppm CO2 by 2080s), low to medium (562

ppm CO2 by 2080s), medium to high (715 ppm CO2 by 2080s) and high (810 ppm CO2 by 2080s) (Table 2-9). More up-to-date predictions (UKCIP09 report) have been published but were not available when experiments for this study were designed. The UKCIP09 report is on a 25 Km grid plot, whereas the model from the UKCIP02 report is of

comparatively poorer spatial resolution, (plotted on a 50 Km grid) but still sufficient for the needs of this study. The UKCIP02 calculations are reported on a map of the UK in a colour code fashion. The area used to represent Glasgow and the surrounding area is shown in Figure 2-17. Calculations presented later are based on the “medium to high”

scenario, as this is believed to be the most likely (Anderson and Bows, 2008).

Figure 2-17: A replica of the UK maps used in the UKCIP02 report.

The grey square represents the area used to predict the Glasgow changes.

These average values for present day conditions were then extrapolated out using the data for the 2080 conditions in order to predict the climate of the Glasgow region in a medium-to-high scenario (Table 2-9). The year 2080 was used as this is the model limit that the UKCIP02 report covers.

Table 2-9: UKCIP02 report figures for the four climate change scenarios.

Scenario 2020s CO2 (ppm) 2050s CO2 (ppm) 2080s CO2 (ppm)

Low Emissions 422 489 525

Medium-Low Emissions 422 489 562

Medium-High Emissions 435 551 715

High Emissions 437 593 810

Data retrieved from Hulme et al. (2002).