Soil Monitoring

Stacked array of soil sensors at depths of 15, 30, 50, and 100 cm.

Pepperwood maintains one of the most comprehensive real-time soil monitoring networks in Northern California. Understanding our soils is essential for effectively managing and conserving natural resources. Furthermore, tracking water stored in soils is vital for sustainable water use. Soils serve as a physical link between abiotic and biotic factors, integrating flora into a dynamic network of particles, nutrients, and hydrology that shapes our ecosystem. In addition to providing the physical rooting medium, soils provide the water storage and nutrient accessibility our ecosystem needs to grow and thrive.

Moreover, soils help us assess our vulnerability to natural disasters like wildfires and floods. Soil moisture is a driver of live fuel moisture. As such, this monitoring supports proactive fire prevention and management measures, ultimately safeguarding communities and natural habitats. Additionally, understanding soil moisture conditions allows us to forecast potential flooding, enabling timely evacuations and emergency responses. Finally, by exploring the interactions within water and carbon cycles, soil monitoring enhances our understanding of landscape dynamics and climate change impacts.

Project Details

Timeline

2012 - Present

Funding

Generous Donors

Pepperwood’s Soil Monitoring Networks

a soil core extracted for volumetric water content calibration and bulk density during a sensor install with our partners at the USGS.

A soil core was extracted for volumetric water content calibration and bulk density during a sensor installation with our partners at the USGS.

Throughout the preserve, there are nearly 180 soil sensors arranged in strategic, stacked arrays at depths of 15, 30, 50, and 100cm. These arrays facilitate the visualization of processes such as infiltration, saturation, and root zone utilization, enabling us to quantify water stored in the soil and assess the overall water balance. The data is recorded in real-time and transmitted to a central database via telemetry networks.

Additionally, we monitor 17 neutron probe access wells monthly to track changes in soil moisture storage below the dominant root zone, extending well beyond the typical installation depths of standard soil moisture sensors. Researchers highly value neutron probes for their ability to provide reliable, repeatable measurements of soil moisture below the root zone without destructive sampling.

Measuring water recharge is particularly challenging due to its underground nature and variations in space and time. However, neutron probes offer a viable solution. First, the neutrons emitted interact with the hydrogen in water molecules. Then, we measure the resulting density of the neutron cloud around the source, which is correlated with water content. Through a series of robust calibrations, we convert these data into volumetric water content.

Soil moisture data are crucial for validating remote sensing efforts and serve as important covariates in other ecological monitoring studies, as they influence forest growth and plant species distribution. Moreover, it is a critical component in understanding the water balance. By monitoring the movement of water through the land, we can analyze how stewardship practices—such as prescribed burning and grazing—along with natural events like drought, affect water resources and the biological components of the ecosystem.