How does rising atmospheric CO2 affect marine organisms?

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Center Experiment #2: Setup Directions


Setup Directions

Real-Time Results

Final Results

Setup Directions

The basic unit, or biosphere, of this experiment is constructed from two 3-liter soda pop bottles.  After purchasing sufficient for your needs (two per unit plus six others for each 3-unit set), you should thoroughly rinse them out after removing their contents.  Then peel off the paper labels that are glued to the bottles and remove the glue that sticks to the bottles with a commercial solvent (we use De-Solv-It).  At this point, we also wash the outsides of the bottles with soapy water to remove any traces of the solvent.

When the outsides of the bottles are totally clean, we use the sharp point of a pen to puncture each bottle near its top.  Through these holes we insert the tip of one of the blades of a scissors and commence cutting in a spiraling pattern down to the level where the top of the bottle stops flaring outward, i.e., to the point where the greatest diameter of the bottle is first encountered, whereupon we make a complete cut around the bottle and remove its top, leaving that portion which resembles a cylinder, until it slopes inward to produce stubby "legs" at its base.

At this point we typically once again wash the bottles, inside and out, with soapy water, carefully rinsing and drying them.  Each bottle that is to serve as the top half of a unit then has two holes punched in it -- on opposite sides and about 4 cm above its recently cut edge -- with the sharp point of a pen.  These holes should provide a snug fit for pieces of silicone air tubing that will eventually be threaded through them.

We next fill each bottle to be used as the base of one of our experimental units to a depth of 7 cm with clean (rinsed) natural aquarium gravel.  Then we place within the biosphere, on top of this layer of gravel, two 0.5-liter water bottles that have been similarly cleansed and "decapitated."  At this point we cut an 18- x 15.5-cm piece of black felt material and place it within the 3-liter pop bottle, pressing it against the side of the bottle so that one of its 18-cm edges rests upon the top of the gravel in the bottom of the bottle and its two 15.5-cm sides just reach to the points where the two water bottles touch the inside of the pop bottle.

Figure 1Figure 1 shows how a typical base unit should look at this state of construction, when viewed from the side that does not have the black felt pressed against it.  Now, fill the two water bottles with tap water and begin carefully filling the remainder of the pop bottle with more clean aquarium gravel.  Figure 2 When finished with this step, your biosphere base should look like the one depicted in Figure 2, when viewed from the side, or as shown in Figure 3, when viewed from the front.

Now is the time to introduce the experimental plant material into the biosphere base.  One pothos leaf, prepared as described in the setup directions for Experiment 1,Figure 3 should be placed in the center of the gravel between the two water bottles and the side of the pop bottle that does not have the black felt next to it; while a second leaf should be placed between the black felt and the front side of the pop bottle, again analogously to the way in which the pothos leaves of Experiment 1 were placed between the black felt and the front glass panels of the 10-gallon biospheres of that study.

With this step completed, water should be added to the aquarium gravel to totally saturate it and cover its top to a depth of about 1 cm.  Then, lay two pencils across the top of the biosphere base so as to support one of the upper-unit pop bottles in an inverted position over the top of the bottle containing the two pothos leaves.  While an assistant holds the two bottles in this position - separated from each other by the thickness of the pencils and aligned so that the two puncture holes in the upper bottle are located over the two water bottles in the lower pop bottle - remove about a 9-cm length of the 2-inch-wide clear cellophane tape from its roll and apply it so as to run parallel to the cut edges of the two pop bottles, linking them together over about a fourth of their circumferences.  Then do likewise directly across from where this first piece of tape was applied, and repeat the procedure twice more to link the two bottles over essentially all of their common circumference.

Figure 4The pencils between the two halves of this truly inexpensive beggar's biosphere may now be removed and the remaining gaps between them covered with tape.  When this step is completed, thread a two-foot length of silicone air tubing through each of the two puncture holes in the top unit and direct the tubes into the two water bottles, as shown in Figure 4.  These tubes will serve as the siphons through which water for CO2 tests will be withdrawn (and replenished) during the experiment.  Figure 5 Finally, label each unit thus constructed and, if possible, set them in groups of three where they can receive some natural light through a window, as shown in Figure 5.

In this experiment, we have two 3-unit sets of beggar's biospheres sitting in front of the left and right panels of a double window in one of our offices.  Two of our individual units will start out totally sealed, while the others will have progressively more and larger holes cut in the cellophane tape that links their upper and lower halves (all of these holes are very small).  Figure 6 When these initial perforations have been made, two other pop bottles - with both their tops and bottoms removed - should be positioned at each end and slightly in front of each 3-unit set of biospheres.  These two bottles are to be used as supports for a 30-inch strip-light, containing a 20-watt fluorescent light bulb, which should be set on its edge so as to continuously illuminate the front side of the plants, as shown in Figure 6.

At this stage, the experiment has essentially begun; and biospheric airspace CO2 concentration measurements should be made every Monday, Wednesday and Friday, as described in our CO2 Measurement Technique section.

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