An intricate network of soil microorganisms From: Commonwealth Scientific and Industrial Research Organisation (CISRO).

The study, performed by scientists from the University of New Hampshire, the University of California-Davis and the Marine Biological Laboratory, examined how microorganisms in the soil respond to temperature changes.  By learning more about that process, scientists could then improve the prediction of how much carbon dioxide is released from the soil.

Microorganisms in the soil release carbon dioxide as a byproduct of how they utilize their food source.  There are two types of food sources: glucose, a simple food source that is release from plant roots, and phenol, a complex food source that comes from decomposing organic matter such as wood and leaves.  Under normal conditions, they release at least 10 times the amount of carbon dioxide that human activities do in a year through the breakdown of these two food sources.  For a perspective on what this amount means, take a look at the graph below, taken from a study from 2010.

Time series of global carbon emissions from fossil fuels. Image from EPA.

This dramatic amount of carbon dioxide is usually absorbed through the root uptake of trees.  But if the soil warms too much, then these microorganisms are not as efficient at breaking down their food, and thus release more carbon dioxide as they expend the energy.  They are then over-producing, and the trees and plants will not take up as much.  In the short term, it may lead to a positive feedback cycle – where more carbon dioxide is emitted contributing to the rising amount of carbon dioxide in the atmosphere.

However, this same research showed that these microorganisms may have the once again become efficient with their food breakdown after many years of warmer soil temperatures.  After approximately 18 years, the community once again became efficient in their ability to break down food.  This may be due to one of the following things: a change in the community of microorganisms (i.e. the type of microorganism changes), a change in the available nutrients,  and/or species adaptation.

While GLOBE doesn’t have protocols to look directly at microorganisms in the soil, it does have protocols to examine soil temperature.  This is just as important, because soil temperature directly affects many things, such as the timing of Budburst, Green Up and Green Down.  The timing of the phenological processes is important because it informs farmers when to plant crops.   For these reasons, it is very valuable to collect soil temperature data and monitor its changes through the seasons and years.

Suggested activity: Have you collecting soil temperature data?  Did you participate in December’s Surface Temperature Field Campaign?  Have you seen any changes?  We’d love to hear about your experience!  Leave a comment, share with us on our Facebook page, or send us an email.  And make sure you enter the data you’re collecting into the GLOBE database!

-Jessica Mackaro

In May, we took a look at Qatar and Saudi Arabia, also part of the GLOBE Near East North Africa region, who are facing similar concerns, with water scarcity being the major worry. Vegetation in the region has adapted to the dry climate; however, as the climate continues to change, agricultural success is expected to fluctuate more wildly.  While this is also a concern in Oman, water scarcity is tied to soil salinity – a problem the country is facing more frequently.

Salinity is the amount of saltiness or dissolved salt content (sodium chloride, magnesium and calcium sulfates, and bicarbonates) in a body of water or in soil.  As the amount of rainfall decreases while temperatures increase, more salt is able to accumulate in the soil due to increased evaporation rates.  Since 1990, the balance between use of lower salinity water, a.k.a. freshwater, and the annual freshwater recharge has been disturbed so much that crops have been yielding less and fields are abandoned.

Why do crops yields suffer from higher salinity?  Higher soil salinity results in plants not being able to draw as much water from the soil.  And in locations such as Oman that require irrigation, more salt is added to the soil than is removed.  Additionally, Oman’s coastal locations are favorable for sea salt spray to accumulate in the soil.  It is possible to use two GLOBE investigations, soils and hydrology, to monitor soil and water properties to determine the current salinity and any rate of change.  Sultan Qaboos University has been looking into ways to mitigate soil and water salination, especially since the country has been facing water shortages.

The Batinah region of Oman, an area greatly affected by high soil salinity, photo from tourismoman.com.au

Hope isn’t completely lost, as there are means to correct salt-affected soils.  This includes improving drainage or reducing evaporation by using mulches.  With these mitigation efforts, it is anticipated that soil salinity can drop and crops can flourish again.

Are you a GLOBE school using hydrology and/or soil protocols to look at salinity?  Have you noticed any changes in your data?  We’d love to hear from you!  Leave us a comment or send us an email at science@globe.gov.

-Jessica Mackaro

The GLOBE Inquiry Model is a simple way to describe how scientists investigate questions. It’s easier to deal with the inquiry process in the classroom if the steps are described. In reality, the way scientists “do” inquiry is much messier, and different scientists have different ways of doing their research. But, in the end, they have to do all the same things that will be described here. Often, scientists return to each step a number of times while they are learning about the question they are investigating. This was illustrated a little bit in the puddle blog.

To summarize, here are the steps

1. Observe natural phenomenon
2. Explore, extend, and refine observations
3. Develop investigation plan
4. Conduct investigation
5. Analyze data
6. Summarize findings and conclusions
7. Share findings and conclusions
8. Identify new research questions

This is but one summary. There are many other ways of summarizing the inquiry process. For example, “Form a hypothesis” is often a listed step (in fact, is an option under “Explore, extend, and refine observations.”) Also, “Conduct Investigation” includes making observations, but they are now more systematic.

Note that not all scientific investigations start with a hypothesis. In some investigations, a question is narrowed down until an answer seems possible given the time and resources available for the investigation. For example, it is quite legitimate to ask “Has snowfall decreased in my hometown in the last 50 years?” Sometimes scientists start investigations with a question and develop a hypothesis in the course of the study. Other times, scientists alter their hypotheses as they discover new things.

Okay, let’s get started.

1. Observe the natural phenomenon
The way I work is that I look for surprises – something I can’t easily explain. Maybe if I don’t understand it, other people don’t either.
In this case, I saw a puddle that remained large (and possibly even grew) even though it had not rained or snowed for several days. Also, the puddle remained liquid, which seemed surprising given subfreezing temperatures for several days. This didn’t make sense to me. So I started to watch the puddle.

2. Explore, extend, and refine questions
In February, I walked to the puddle several times in a few days, to see what was happening to it. The fact that it was still there intrigued me. Also, I discovered a line of fire hydrants on the same side of the road as the puddle, which meant that there was an underwater pipe. (Was the pipe broken?) Finally, I noticed salt crystals on the road one morning; with newly fallen snow melting around the salt crystals. (Could the salt be keeping the water from freezing?)

3. Develop investigation plan
Given the observations I had made – no rain, possible broken underground pipe, very cold weather, I had two hypotheses regarding the origin of the puddle, namely:

1. The puddle was the result of a break in the pipe connecting the fire hydrants.
2. The puddle was fed by water running downhill beneath the surface (it was frozen at the surface).

I also had two hypotheses why the puddle was liquid.

1. The puddle was supplied by underground water that was warm enough to be liquid
2. The puddle didn’t freeze because of the salt on the road.

To see whether a leaky pipe caused the puddle:

1. In February, I decided to interview people who knew about the road.
2. In March, I decided to check to see if the puddle was there after several warm and dry days. If there was a leaky pipe, I would have expected to see a puddle.

To see whether the puddle came from water below the frozen ground:

1. In February, I decided to look for data showing it was possible for the soil (and water) below the surface to be warmer than freezing during short (week-long) periods with air below freezing. (It would have been ideal to take measurements near the puddle, but I did not have the proper equipment).
2. In February, I also decided it was important to check to see whether there was water on the surface, even thought it was quite cold.
3. In March, I decided to check to find how underground water could flow onto the street.

Notice that this was not all done at once. I went back and refined my investigation plan, when I found out I had the opportunity to check further.

4. Conduct Investigation

To investigate whether the puddle was supplied by underground water:

1. I continued to observe the puddle to see whether it was changing in size (February).
2. I obtained wintertime data from Smileyberg, Kansas, and Bondville, Illinois, to see how soil temperature behaved during ~week-long periods when temperatures were much colder than normal (and also below freezing). I plotted the air temperature and soil temperature during the cold periods, to confirm that the soil temperature could be above freezing (February).
3. I looked for openings in the street and curb for underground water to flow through to supply the puddle.

To investigate the broken-pipe hypothesis:

1. I asked my nephew about whether the pipe could be broken. He thought it unlikely because the pipes were very new.
2. I checked the puddle location a month later, when warm weather dried the ground. There was no puddle, which made me think that the pipe was probably o.k.
3. Also, I knew from my family and the appearance of the ground that the pipe had not been repaired.

To investigate the salt hypothesis:

1. I looked for evidence of salt on the road (salt crystals, melting around the crystals, and white stain on the road where salty water had dried up).
2. I interviewed a colleague who had been involved in studying arctic ice.

5. Analysis of the data

1. I compared the puddle sizes (from memory and photographs).
2. I plotted the air temperature and soil temperature at several levels to confirm that the soil could remain above freezing even when the air got quite cold.
3. I compiled evidence of salt (the crystals, the stain the road where the puddle had been, Even the slushy appearance of the water was associated with it being cold and salty).
4. I compiled evidence that the pipes were not leaking (the pipes were new, the contractor had a good reputation, there was no puddle after a dry spell, and it was obvious no one had repaired the pipe between my visits to the site).

6 and 7. Summarizing findings and conclusion and sharing findings

By doing my blog, I was working on this part even before I had finished the investigation. Were I to write this as a report, I would summarize the hypothesis, methods, and results as if they were done in an orderly manner. The timing of a result – be it before or after I was working on hypotheses, doesn’t really matter in the final report.

Were I not doing a blog, I would have recorded similar information in my laboratory notebook, so that I could be reminded of the details when I wrote the final report. (Here is a sample final report.)

8. Identify new research questions

It is rare that someone finishes up a research project without thinking of more questions. I was thinking of them the entire time. I was so excited about the possibility of underground water causing a liquid puddle when the air temperature was well below freezing, I didn’t think of the effects of salt. That is, until the next day when I saw the snow melting around the salt crystals. Now, I’m wondering if the cars disturbing the puddle kept it from freezing as well. And tomorrow I might think of other ideas.

It is not easy to decide when to finish a study. If you are a student, you have a due date that forces you to stop. If you are scientist, and are being paid to finish a project by a deadline, you also have to stop – at least until you can find someone to pay you to answer your next question.

In fact, scientists I know usually find that their investigations often lead to more questions than answers.

In the same way, thinking about the evidence kept giving me new ideas for what to look for. So, instead of a few tasks done one by one, I was sometimes doing several at once.

Figure 8. Me enjoying the relatively cool temperatures in a hole. The shade helped, too! Photo by Lorrie McWhinny.

Figure 9 shows how the temperature varied beneath a winter wheat field in south-central Kansas during the late spring-early summer of 2002. The temperature 7.5 centimeters below the surface (blue curve) reaches a maximum in the early afternoon, with the peaks slightly later as you go to lower levels. Note that the daytime temperature at 7.5 centimeters below the surface is warmer than that at 15 centimeters, and so on, with the coolest temperatures at 80 centimeters below the surface.

Figure 9. Soil temperature as a function of day of year for a winter-wheat site in south-central Kansas. The distances in cm (centimeters) indicate how far below the ground surface the measurement is being taken. Day 138 is 18 May, Day 150 is 30 May, Day 180 is 29 June. All data for 2002. Date collected and processed by Professor Richard Cuenca, Oregon State University. The maxima in the blue curve occur in the early afternoon.

These data, which are fairly typical, are consistent with our impression that the soil is usually cooler than the surface for most of the day during summertime. (The cooler surface temperatures on some days appear to be related to rainfall.)

The surface temperature for the same site appears in figure 10. Notice how the surface temperature peaks during the day about five degrees higher than at 7.5 centimeters during the first part of the data record, and then 10-15 degrees higher than the temperature at 7.5 centimeters late in the record. The change is related to cooling of the winter wheat (the sensor is measuring the temperature of the winter wheat) due to evapotranspiration during the first part of the record. Once the winter wheat stops growing and becomes golden, transpiration is no longer happening and the dry wheat and then the wheat stubble and ground surface are strongly heated by the sun.

Figure 10. For same site as Figure 4, except for surface temperature. Note that the wheat becomes golden (senescent, stops growing, is almost ready to harvest) around Day 150 (30 May).

The same happens to the bare ground at other sites – the surface is much warmer than the temperature 7.5 cm below the surface.
Have you been in a cave in the summertime? Caves, being farther from the surface, are even cooler. At the Devil’s Icebox, a cave not far from where I am writing this blog in Columbia, Missouri, the temperature stays at about 56°F (13°C) all year, even though the average summertime high temperature in Columbia is in the upper eighties (around 30° Celsius) and the average wintertime low temperature here is in the mid-teens (around -8° C).

So in the summer, the ground gets cooler as you dig down, — at least through the upper few meters. In the winter, the ground gets warmer farther down. And in caves, the temperature doesn’t change much at all. In fact, I once read that a cave temperature is a good first guess of the average above-ground air temperature at the cave’s location.

Similarly, people in many countries take advantage of the cool below-ground temperatures too store food during the hot summer. Also, some people take advantage of the temperature several feet below the surface to heat their homes in the winter and cool their homes in the summer.

Kristina has studied Arctic ice and the effects of salt in the sea water on freezing. So she suggested that another factor be considered: salt on the roads. This would be a modification of the spring-water hypothesis, to allow for the effect of salt.

In the United States, road crews often apply sodium chloride or magnesium chloride to roads because these two compounds can melt snow or ice on the roads, making them safer to drive on. This happens because these two compounds dissolve in water. Salty water has a lower freezing temperature than pure water.

On my trip out from my brother and sister-in-law’s house to take a picture of the puddle, the road was solid white. But coming back, I noticed something interesting: The ice and snow was starting to melt in little spots.

Figure 6. Ice and snow melting in spots on road.

When I looked more closely, I discovered a salt crystal at the center of each spot, surrounded by melting snow and ice. You can see a few of the crystals and their impact on the surrounding ice in Figure 7, below.

Figure 7. Salt crystal at the center of widening circles of melting ice and snow. The salt crystal is dissolving in the water, lowering its melting point.

If they spread salt crystals on the road the morning I took most of the puddle pictures (the fire hydrant picture was taken later in the day), I am guessing that salt was used on the road earlier in the winter as well.

So the puddle that I think was spring-fed may have been able to remain liquid thanks to salt on the road. And, since the puddle was in a low part of the road, salt may have washed down to this part of the road during the rains of the previous week.

So – it is likely that the puddle formed from underground water seeping into the road (built with cracks to allow the concrete to expand and contract), and the puddle stayed liquid because of a supply of warmer water, and a little salt. There are of course many more things I could do to confirm this hypothesis, but it seems reasonable given the facts I have available.

Suppose the puddle had been there from the previous week’s rains, and I simply missed it. Then the salt in the road might be sufficient to keep the puddle from freezing entirely.

Recall from last time that I mentioned that the water feeding the puddle would be coming to the surface from under the ground – either a broken pipe or water flowing horizontally through the soil

In my recent 27 February blog about the air temperature and the surface temperature , I wrote about the “energy budget” of air about 1.5 meters above the surface (to explain why the maximum temperature was in the late afternoon), and I also wrote about the surface temperature, which reaches a maximum in the early afternoon.

To understand why the water feeding the puddle (and the surrounding soil) wasn’t frozen, we need to learn something about how temperature varies with depth beneath the surface.

The heating and cooling below ground is mostly by conduction. During the winter, the surface vegetation protects the soil from cooling, and upper soil layers protect the soil layers farther down.

For example, Figure 3 compares the air temperature and the temperature just 2 cm below the surface on a corn/soybean farm near Champaign, Illinois, USA (near Chicago). While the air temperature fluctuates quite a bit, the temperature at 2 centimeters below the surface changes much less. Particularly interesting is the cold weather between about 25 February and 5 March, when the soil temperature stayed warm in spite of the cold night-time temperatures. Figure 4 focuses more closely on that time period.

Figures 3 For February and March 2002, air temperature and soil temperature (Ts) at 2 cm below the surface, a corn/soybean farm near Champaign, Illinois (Latitude 40.00621, Longitude -88.29041). Day 30 = 30 January; Day 60 – 1 March, Day 90 – 31 March). Data available on the Web at http://cdiac.ornl.gov/ftp/ameriflux/data/Level1/Sites_ByName/Bondville/FLUX-2002/.

Figure 4. For the 25 Feburary-6 March time period on Figure 5, Air temperature, surface temperature, and soil temperatures down to 64 cm below the ground.

Notice that the soil temperature gets warmer as you go down, illustrating the “insulation” effect of the higher layers of soil. From Figure 5, we see a similar pattern at Smileyberg, Kansas. On average, the soil temperature at Smileyberg was 1.9 degrees Celsius warmer than the air temperature in January, and 1.1 degrees warmer than the air temperature in February. Notice how the ground stayed warm between Days 24 and 32 (24 January and 1 February), in spite of the cold temperatures. This is just like the behavior we saw at the Bondville site.

Figure 5. For grassland site near Smileyberg in Southeast Kansas, the Air temperature (about 2 m) and soil temperature (average 0-5 cm). Data from Argonne National Laboratory, courtesy R.E. Coulter, Argonne National Laboratory.

Thus it is quite believable that there could be liquid water close to the surface, particularly since the air was much warmer the week before I got to Missouri. (Since I saw no frozen water on the surface uphill of the road, the water could have come up through cracks in the road.)

The temperature for the last few days has been below -5°C (about 20°F). The wind on my daily walks is cold but invigorating.

So, I was surprised yesterday when we drove over a puddle and water splashed on our windshield. It froze instantly. Given the air temperature, this is not surprising. The car thermometer read 17°F (-8°C).

How could there be water in a puddle after three days of subfreezing temperatures?

I decided to investigate on this morning’s walk, and found out a few interesting facts. Figures 1 and 2 show the puddle up close and from a distance. My footprints and the tire tracks in Figure 1 indicate that the puddle was “slushy.” It was easy to make footprints in it. So it is not surprising that passing cars were getting splashed when they drove over the puddle. The second picture shows the puddle with a fire hydrant on the north side of the road (and to the east of the puddle). A line of fire hydrants lies to the north of this road; so I conclude there is a pipe connecting them.

Figure 1. Slushy puddle with footprints (left) and tire track (right). At the time of the picture, the air temperature at this location had been below freezing for several days.

Figure 2. Picture of puddle taken later in the day, after more frozen precipitation (ice pellets) covered the rest of the road with white. Note the red fire hydrant. The puddle is at a low point in the road, and the ground slopes downward toward the puddle from the north.

So, I came away with two hypotheses.

First hypothesis. The puddle is being fed from extremely wet soil. There has been a lot of precipitation around here recently. I knew this because I had been monitoring the weather the week before I got here. I am guessing that the soil is saturated and the water table is quite high.

So, the water could just be flowing downhill, perhaps atop the bedrock, which comes quite close to the surface. Or, the puddle could be fed by an underground spring. There are many springs in this part of the country. The bedrock, close to the surface, is Burlington limestone, which has multiple cracks and caves – paths for the water to follow.

Second hypothesis. The pipe connecting the fire hydrants just happened to have been broken here.

These two hypotheses are based on my impression that the puddle wasn’t there before 20 February. In either case, as we shall see, salt added on the road could have kept the water from freezing once it reached the surface.

I talked to my nephew, who was around when the road was built, and he supported the first hypothesis, because they found a lot of springs when they built the road. The springs are fairly active: my sister-in-law said that swimmers in a lake to the south of the road frequently noticed cool spots, where the cool spring water was feeding the lake. The springs also suggest that the water table is normally high. So, after an unusually wet period, it would be plausible that the water is running down the hillside beneath the surface.

Next time: Why wouldn’t the water running down the hillside beneath the surface be frozen?