Soil pits were excavated in 2023 across contrasting hillslopes in Watershed 10 at the H.J. Andrews Experimental Forest (LTER), Oregon, USA, to investigate how differences in subsurface water-storage capacity influence plant-accessible water, hydraulic redistribution, and associated soil physical, chemical, and biological properties in a second-growth Douglas-fir (Pseudotsuga menziesii)–dominated forest (~500 m elevation). The watershed receives >2000 mm annual precipitation, primarily as winter rainfall. Soil pits were hand-dug to ~100 cm, and bulk soil was sampled by horizon for physical and chemical analyses; intact cores were collected for soil water retention measurements. Pit-face photographs were used to quantify rooting distributions with depth. Each pit was instrumented with zero-tension lysimeters at two depths for bulk soil-water chemistry and with in situ sensors measuring volumetric water content, temperature, and electrical conductivity (multiple depths), soil CO2 (two depths), and soil water potential (one depth).
Pamela L. Sullivan, Xander Takver
This study was established to better understand how differences in subsurface water storage capacity influence plant-accessible water, hydraulic redistribution, and associated soil physical, chemical, and biological properties. Previous work has established that hillslopes in this watershed have distinct differences in subsurface water storage capacity. The SE facing hillslope has a relatively shallow soil layer that rapidly transitions to unconsolidated and consolidated bedrock which limits deep water storage and is therefore referred to as Low Storage or LS. The NW facing hillslope is underlain by a thick layer of highly weathered bedrock (saprolite) which has a high porosity and is relatively easy for roots to penetrate and subsequently has a high capacity to store plant-accessible water throughout the growing season. This slope is referred to as High Storage or HS. This study aims to understand how these differences facilitate plant-mediated hydraulic redistribution and near-surface soil water dynamics. Furthermore, we aim to understand how these near surface water dynamics affect soil physical, chemical, and biological properties.