The Final Post

April 29 - I’m going to miss my Winogradsky columns. This is my last blog entry and as I was taking photos of my columns for this posting it suddenly hit me that I wouldn’t be able to see what happens next, what new colors (or smells) would emerge from the layering of water and mud/soil. I got a bit sad… One of these days, when I’m living somewhere with enough room to keep a couple of columns for a much more extended period of time, I’ll have to make some more columns and see what happens over the course of a couple of … maybe years. I mean, seeing the incredible changes in my columns after only a few months has been very exciting. I wonder if a column of a few years would constantly change, or would it reach a growth/development plateau at some point and then stop changing. Well, something to find out in the future!

On to my final observations and conclusions for these columns.

Over the course of the two+ months that my Winogradsky columns have been sitting, I’ve observed a lot of changes in all four columns (fig. 1). As a reminder, I had set up three experimental columns and one control, with my objective being to see what would grow in columns filled with Thames mud and/or water. Column A (Potting Soil + Tap Water) was my control. My experimental columns were Column B (Potting Soil + Thames Water), Column C (Thames Mud + Tap Water) and Column D (Thames Mud + Tap Water).

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Fig. 1 My four Winogradsky Columns: from left, Column A, B, C and D. (a) What all four columns looked like at the very beginning of the experiment (after a day of settling). (b) What all four columns looked like at the end of the experiment.

The columns that were the most productive were Columns C and D, though during the last couple of weeks I started to see changes in the columns with potting soil (more on that later!). There were many similarities in the microbial growth in Columns C and D (fig. 2). Both had extensive growth throughout the mud layer, with first orange and then green patches of microbes. The growth started in the sides of the column facing the sunlight, and then spread out from there, which suggests (especially with the green growth) that those were phototrophs. At the end of the experiment, there was a portion of the columns that still did not exhibit microbial growth in the mud section (fig. 3).

Fig. 2 Columns C and D at the end of the experiment. As you can see by just looking at them, the changes that took place are pretty similar between the two, though growth occurred at faster and greater rate in Column C.

Fig 3 A closer look at Column C, where you can really see where there is growth in the mud layer and where there is none. (Sorry about the glare, though if you enlarge the photo the difference is very striking). The area where there is no visible growth was facing away from the sunlight.

The water in both turned a light green color, and there was a lot of growth on the walls of the column in the aqueous part (fig. 4), both green and brown colored. As there was more green then brown, it looks like the brown was growth that came later.

Fig. 4 Closeup of the water layers in Columns C and D. You can see the separate brown splotches more clearly in Column D (on the right) as they have merged together more in Column C. Also, note the difference in the transition zones between the mud and the water in both columns. In Column C, the difference is less distinct than in Column D, likely due to the buildup of growth.

There was noticeable biofilm development in both columns (though Column D never reached the amount that was seen by the end of the first month in Column C), and when the cling film was removed from the columns, they had a similar earthy smell, though Column C’s might have been just a bit sharper.

While there were many similarities between Columns C and D, there were also several differences, mainly in the sheer amount of growth. Column C had much larger patches throughout the mud, and there were more green particles and brown patches on the sides of the bottle throughout the water column. Also, at the transition point between the mud and the water, there was considerable growth in Column C, where as in Column D the transition was very distinct. Though Column D ended the experiment with larger amounts of biofilm on the water’s surface (fig. 5), had Column C not experienced its tragic accident I am confident that the biofilm on the surface would have been quite thick indeed. It makes me wonder how porous the cling film I used to wrap the top of the columns was, and if the microorganisms that made up the biofilm were aerobes or not. If the cling film was thick enough, eventually the atmosphere in the columns would have become anaerobic as the oxygen was used up. Would the microbes on the surface have died then? Or would the (potential) photoautotrophs have produced enough oxygen to sustain the biofilm? I guess had I left the columns grow for longer, that is something I would have been able to better discover!

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Fig. 5 (a) The biofilm on the surface of Column C, post-accident. Note the bubbles indicating gas production. (b) The biofilm on the surface of Column D. Seems to be better established than what is seen in Column C.

One thing that really surprised me from what I observed in Columns C and D, was that the column with tap water was much more productive than the column with Thames water. I had expected that the river water would create an environment that mimicked natural conditions and would therefore be more productive. I wonder if the slightly brackish nature of the river water inhibited growth? Looking at Columns A and B there seemed to be greater productivity in Column A, (Tap Water), over Column B (Thames Water), which supports the observation that the tap water was more supportive of growth than the Thames water.

Speaking of Columns A and B, over the course of the experiment there was much less growth in these two than in Columns C and D, and I despaired of seeing development at all. (Well, for Column A that would have been a good thing, as it was my control column!) However, by the end of the trial I was happily surprised (please see entry "Action in Columns A and B!!!"). As well, what I observed was fairly different from what I saw in the other two columns, which made things even more interesting. First of all, the water in both columns was a foggy, light brown color (fig. 6) likely due to color leaching out from the potting soil. If there had been any photosynthetic bacteria, I was not able to identify it by color.

Fig. 6 Changes in Columns A and B! Note the foggy, light brown color of the water, as well as the indeterminate transition zones between the potting soil and the water. If you enlarge the photo, you'll be able to see the bubble layer on top pretty well.

Also, as the material from the surface had eventually (finally!) settled to the bottom, I was able to see activity on the surface, in the form of lots of bubbles in (fig. 7) and a little bit of green growth around the circumference of the water’s surface in Column A (fig. 8)!

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Fig. 7 The bubbles at the surface of (a) Column A and (b) Column B.

Fig. 8 Green growth around the circumference of the water's surface! (Also visible in fig. 7a)

Column B had a hazy funnel of material in the middle of the water column, (fig. 9) and both columns had a very indefinite transition between the potting soil and the water (see back to fig. 6 again). Also interesting to note, there seemed to have been a lot more evaporation in Columns A and B, than in Columns C and D. They did start out with lower water levels (please see entry “Get Ready, Get Set Up”), however at the end there was far less than at the beginning.

Fig. 9 I found this funnel of material in the center of Column B to be very interesting as none of the others had this.

The most impressive development I saw in those columns was in Column A (fig. 10). Along the part of the column that faced the sun, there was a large swath of grayish growth that led up from the soil layer all the way to the top of the water layer. It looked like there were little bits of green; perhaps it was the precursor to more photosynthetic organisms. I’m curious though as to why there was much evidence of it in the water portion, but no growth in the soil portion. Perhaps, when compared with the gray-colored Thames mud, the potting soil was too dark to be able to provide a good look at what may or may not have been growing there. Also, there was a difference in the smell between Columns A and B. Column B’s smell was very similar to that of Columns C and D, earthy. Column A, however not only had an earthy smell, but also smelled strikingly of rotten eggs. Sulfur production???

Fig. 10 Please excuse the camera angle, but it was the best way to show the swath of gray running from the top of the mud layer to the top of the bubbles on the surface of the water. This was the side that received the most sunlight.

One thing I do wish I had had access to throughout this experiment would have been a microscope and slides. I think it would have been very interesting to see what was growing close up, though I did have fun just watching colors and patterns appear on a macro scale. I found it very interesting the range of changes I saw, especially considering that I did not add anything to the columns to promote growth. I wonder if whatever was in the Thames river water served to inhibit growth? Also, I wonder if potting soil columns are normally that slow to develop and if they really do not have that much in the way of microbes living in it. I would have thought that even though it was a commercially packaged soil, there would still be ample nutrients to encourage growth, as it is supposed to be a good medium for plant life (hmmmm, maybe that’s why my plants aren’t doing so well…). Even though Column A was supposed to be my control, and perhaps I wasn’t supposed to see any growth in it, maybe it showed what baseline columns are supposed to be like. Maybe next time I’ll try this experiment with a variety of potting soils and see how they all compare.

As I said, I’ll miss my columns, but I had a lot of fun watching them grow! Thank you for the opportunity!