BEAUFORT WATERSHED STEWARDS – DECEMBER 2024
Everyone loves a good mystery. Book store and library shelves are stacked with murder mysteries. Police procedurals are a staple of television. True crime podcasts are a hot trend. If you explore the history of science, you will find that it is one mystery after another. A current scientific mystery has to do with the mass of the neutrino. Two different methods for measuring this quantity produce differing results. Physicists are excited about this conflict because its resolution will produce new insights into how the universe is put together.
The Beaufort Watershed Stewards (BWS) will not be working on the neutrino mass problem any time soon. We have our own mystery to resolve. We commissioned the firm, Ecoscape, to perform a trend analysis on the data from three of our creeks, Cowie, Mud Bay, and Wilfred. These are the creeks we started sampling first and are the only ones for which we have five years’ worth of data. (Trend analysis isn’t credible for data sets of less than five years.) This is a milestone for BWS. When we first started sampling local creeks, we dreamed of the day when we would have five years’ worth of data. That day has finally arrived!
Trend analysis, for all the non-statisticians in the audience, is simply looking for patterns of change. The parameters we measure when we sample our creeks are, Dissolved Oxygen, Specific Conductivity, Turbidity, Temperature, and pH. These parameters all change with the seasons as temperatures go up and down and rainfall ebbs and flows. Over a five-year period, however, some of the highs might get higher or some of the lows might get lower. This is important for tracking the health of our water supply. (For those of you in the audience who ARE statisticians, Ecoscape used the Mann-Kendall or Seasonal Mann-Kendall test, as appropriate.)
And now for the mystery. None of the parameters showed a significant trend except for one, Dissolved Oxygen (DO), a basic measure of stream health. On all three creeks, DO showed a downward trend. There is an inverse relationship between water temperature and dissolved oxygen; when temperature goes up, DO goes down and vice versa. We see this consistently in our data. DO goes down during the warmer months and comes back up during the colder months. But the trend of ever lowering DO was NOT matched by a trend of warming water. How could that be? Aha! A mystery!
There may be a simple explanation, in which case we will have broadened our understanding of stream health. Or the explanation may not be simple, in which case we may get to do some scientific sleuthing. There is probably no chance that this problem will be the basis for a best-selling mystery novel but it’s a fun little puzzle, nonetheless.
