Soil Moisture Data

Measurements of soil moisture were made by utilizing the Echo-20 probes manufactured by Decagon. The Echo probes measure the dielectric constant of the soil via capacitance methods which can then be converted into volumetric water content values. Echo probes generally do not require any site specific calibration provided unless there is a significant solute presence. We chose to measure the soil moisture states at four separate locations along a hillslope transect running from ridge to stream as shown by numbers 1-4 on the Gamboa Site Map. At each of theses locations a soil pit was dug as deep as possible until weathered bedrock was reached. The weathered bedrock, at which point further digging was essentially impossible, was reached on average at 1.2 - 1.5 m depth. At total of four probes were inserted at varying depths and the soil pit was then backfilled with care to approximate the natural soil density. Unfortunately, it was impossible in practice to place the sensors at equal depths across all soil pits. At depths of 30-80 cm numerous tree roots or rocks would often prohibit sensor placement at the desired depth. In most cases sensor placement below 75 cm was impossible due to weathered bedrock.

Fig 1 Soil moisture pit number two before being backfilled, a typical soil profile transitions from highly organic layer to clay and finally weathered in place bedrock. Weathered bedrock can be seen in this picture as the splotches of white material and make sensor placement and further digging nearly impossible.