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Erratic EC response of Hydros 21 sensors

Home › Forums › Monitor My Watershed › Erratic EC response of Hydros 21 sensors

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    • 2023-05-15 at 1:10 PM #17815
      Jim Moore
      Participant

        I have a Mayfly sensor station on a small perennial trib to Marsh Creek.  I was noticing step changes in the EC of over 100µS in the 5 minute sampling interval.  Suspecting that this was a defective sensor so I co-located another sensor and got a similar result and the two EC readings were uncorrelated. Therefor I put both sensors in a filled bucket and observed no erratic behavior.  I was told by a tech at Meter Group that moving water can cause that large a step change in the EC reading.  I have looked at a number of stations in some of the local streams and have not seen such large step changes in EC.  I attached some photos for reference.

        I wonder if any one else is observing step changes of EC of this magnitude?

      • 2023-05-15 at 1:15 PM #17816
        Jim Moore
        Participant

          smaller file sent

          Attachments:

          1. IMG_9250.heic

        • 2023-05-16 at 9:30 AM #17820
          dan@wachusett
          Participant

            Jim,

            I have seen similar fluctuations in some of the streams where I have Hydros21 sensors. Typically, step changes > 100 µS in 5 or 15 minutes only occur during runoff/snowmelt events. In the winter, after a snow event with road salt application and subsequent melt I have seen > 2,000 µS fluctuations in 15 minutes as the salt pulses work their way down the streams. In the non-snow season a rain event can quickly dilute the streams that have base flows with high conductivity, dropping very quickly in 15 minutes.

            If there is no active runoff/snowmelt I tend to see more stable conditions without such rapid fluctuations.

            -Dan

             

          • 2023-05-16 at 9:58 AM #17821
            Jim Moore
            Participant

              Thanks for the input, Dan@wachusett.  I think I figured out my problem – it was the bubbles in the stream as you can see in the attached photo when I was co-locating two sensors! I moved the sensor probe about a foot to calmer waters and now the results look normal.

              Attachments:

              1. IMG_9251.heic

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