Changes to Optional Gypsum Block Soil Moisture Protocol

Introduction/Offer

This message is about a very important change to the optional gypsum block soil moisture protocol and an offer to get new sensors for free.

From time-to-time, scientists must update and improve their measurement protocols and equipment to meet data quality standards, scientific objectives and to take advantage of new technologies. Despite your earnest participation in this investigation, I feel that the gypsum block sensors are not a sensitive to soil water content as was expected or is required. The good news is that an alternative exists which can be directly substituted into this protocol.

Gypsum block replacement effort

I propose that all schools replace their gypsum block sensors with Watermark sensors over the next six months so that by Sept. 1, 1999 (an the sooner the better), only data collected using Watermark sensors will be accepted into the GLOBE data archive. To promote this change, I will provide, free of charge, four new watermark sensors to any school that has reported this type of data at any time during the past 12 months.

What I need from you:

email jwash@hwr.arizona.edu to confirm your willingness to make this change and continue to report this type of data. Please send me the address where I should mail the new sensors (by 4/23/99) and indicate if you need wire lead lengths longer than 6 feet (1.8 m),
Over the next 12 months, I expect you to recalibrate the new sensors by making a series of gravimetric measurements throughout a full drying cycle. As was the case with the gypsum block, you can start to report raw daily readings about one week after installation.
Please report both gypsum block and Watermark readings for at least one month, if you are able to place the new sensors adjacent to the old ones. On Sept. 1, 1999, we will expect all sites to report only data collected using Watermark sensors.

About the Watermark sensors

Watermark sensors operate on the same principle as gypsum block sensors - they both contain two electrodes between which an AC resistivity measurement is made with the Delmhorst meter. This resistance can be related to soil water content after calibration against gravimetric samples. Watermark sensors have a gypsum core AND a tough silica and stainless steel outer shell that make them much less suseptible to in situ degradation. You will need to follow the same installation instructions as given for gypsum blocks, making particular care to soak the Watermark sensors for at least an hour before installation.

UA/GLOBE Home; Last updated: 4/7/99, Comments: jwash@hwr.arizona.edu