Hydrology Update, January 4, 1997
Analysis of All Reported GLOBE Dissolved Oxygen Data

Dear GLOBE colleagues,

GLOBE schools have made many observations of dissolved oxygen levels at their hydrology study sites. All reported data from the period October to December 1996 are shown in the graph below. 15 schools are reporting data, and 10 of these have made at least two measurements as of the end of December, 1996.

Here is a quick assessment of what has been reported so far, by school:

• Belton Junior High School, Belton, Texas reported two data points at a level of 9 mg/L. This amount of dissolved oxygen suggests a healthy water source for fish and plants to live in. We encourage Belton to continue making dissolved oxygen measurements, to see how their levels change in the winter and spring.
• Tabor Academy, Marion, Massachusetts is measuring a water source where the dissolved oxygen levels are around 10 - 11 mg/L. This range of oxygen levels is supersaturated for a temperature range above 11 deg C at 0 m. elevation. At the same time that Tabor recorded these DO measurements, they recorded temperatures in a range of 6-8 degrees Celsius. What could cause D.O. levels to get so high?
• Simsbury High School, Simsbury, CT is of particular interest to at least one member of the hydrology research group because Chris Gutmann, a hydrology assistant at the University of Arizona, grew up in Connecticut. Simsbury High School reports that their water showed levels of dissolved oxygen at 11 during October and a sharp rise to a level of 14 in mid-November. The dissolved oxygen measurements are very consistent until the last entry. We would very much like to know why the last entry is higher. Temperatures measured by Simsbury HS ranged from 1-9 degrees Celsius during this time. On a cautioning note, the recorded temperature when Simsbury HS measured 14 mg/L dissolved oxygen, was 3 degrees C. This D.O. measurement is supersaturated for this temperature. This suggests that the calibration of Simsbury's dissolved oxygen kit may be off.
• Okemos High School, Okemos, MI displays a surprising jump from 4 to 12 in their D.O. measurements. After a gentle reminder about the importance of careful calibration of equipment used for taking measurements, we propose that if this trend is correct, it might reflect a combination of a drop in water temperature and a drop in the level of biological oxygen demand during the winter.
• Mastricola Middle School, Merrimack, NH shows a drop in D.O. from 9 to 7 over a month period of time, Nov - Dec. This drop may represent something interesting in this watershed and we think it is important for the school to think about what may be causing this drop. The range of 7-9 mg/L dissolved oxygen is a very healthy one for fish and plants.
• Happy Valley High School, Elizabethton, TN measures in their water dissolved oxygen levels that range from 10 to 12 over a period of about a month. This may be the result of a decrease in water temperature or it may reflect something else. It will be interesting to compare water temperature records with these measurements.
• Goethe-Schule, Wetzlar, Germany reports two entries that indicate that their water site possesses fairly high levels of dissolved oxygen (13 mg/L). It is interesting to note that 13 mg/L D.O. at the temperature recorded, 3.8 degrees C, is very near to saturated. This water source is probably actively mixed with the surrounding air.
• Vinalhaven High School, Vinalhaven Island, ME initially measured D.O. levels as high as 10 mg/L but then note a downward trend in their D.O. over the course of the next month and a half, when they measured it at 7 mg/L. What might cause this kind of drop in oxygen levels? Perhaps certain types of algae that produce oxygen during earlier times of the year begin to die off about this time, and cease to produce oxygen. Another possibility is that the D.O. level is coming back down from some episode that substantially increased the oxygen level.
• Crescent Elk School, Crescent City, CA measures their data on a very regular basis and shows the changes that take place in their site on a bi-weekly basis. Their oxygen levels gradually go up and down over a range of about 5 to 10 mg/L. It is interesting to note what appears to be an overall decline in dissolved oxygen levels during the 3 month time span shown. This would lead an observer to speculate that the D.O. levels are decreasing as water temperatures decrease. But does this make sense? Not really, since we'd expect D.O. levels to increase with a decrease in water temperature. What might account for this trend? As scientists, we would like to know information about what plant activity has been like over this time period, and about how water discharge levels have changed over this period of time.
• Chemisches Institut Dr. Flad, Stuttgart, Germany shows the most frequent and consistant series of measurements of the GLOBE schools. They show that dissolved oxygen levels in their area fluctuate over a range of about 10 to 18 mg/L. While trying to figure out what might have produced such high D.O. measurements, the hydrology team realized that the Chemisches Institut does not always record temperature measurements with their dissolved oxygen entries. Since D.O. is so temperature dependent, we strongly recommend that schools report water temperature if they measure dissolved oxygen.

  Other schools reporting one dissolved oxygen entry include:

  • Enka High School, Enka, North Carolina, USA
  • Naples High School, Naples, Florida, USA
  • Jarrow Montessori, Boulder, Colorado, USA
  • Northeast High School, Arma, Kansas, USA
  • Clark County R-1 High School, Kahoka, Missouri, USA

I hope that this brief report has stimulated some questions. Feel free to send email to me (roger@hwr.arizona.edu) or to my assistant, Chris Gutmann (cgutmann@hwr.arizona.edu).

Sincerely,

Roger Bales
Professor of Hydrology & Water Resources
University of Arizona