Topographic controls of soil organic carbon in semi-mantled landscapes

Authors: PATTON, NICHOLAS - IDAHO STATE UNIVERSITY; LOHSE, KATHLEEN - IDAHO STATE UNIVERSITY; Seyfried, Mark; GODSEY, SARAH - IDAHO STATE UNIVERSITY; PARSONS, SUE - IDAHO STATE UNIVERSITY

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2019
Publication Date: 4/23/2019
Citation: Patton, N.R., Lohse, K.A., Seyfried, M.S., Godsey, S.E., Parsons, S.B. 2019. Topographic controls of soil organic carbon in semi-mantled landscapes. Scientific Reports. 9:6390. https://doi.org/10.1038/s41598-019-42556-5.
DOI: https://doi.org/10.1038/s41598-019-42556-5

Interpretive Summary: Since 1960, roughly one quarter of the carbon dioxide released to the atmosphere by human activities has ended up on the land, probably in soils. At present, we have a poor knowledge of where that carbon dioxide is stored or how long it may be retained in the soil. Carbon storage in semiarid rangelands is often overlooked because the amount stored tends to be low on a per acre basis. However, such rangeland occupy abo0ut 40% of the land surface, so they may be critical. In this study we set out to determine how soil carbon amounts vary with different kinds of topogarphy. The intent is to be able to estimate carbon storage over large areas based on topographic position. We found that carbon storage is strongly affected by topographic position and that we could use simple formulas to make accurate calculations of carbon storage. In particular, we found that north-facing slopes store much more carbon that south-facing slopes (about 3 times). We also found that soil carbon estimate could be greatly improved by considering soil depth, for which used used previously developed equations to determine. Our primary finding is that we can calculate soil carbon storage in a landscape with complex terrain with much greater accuracy than previously due to equations we developed in this study.

Technical Abstract: Mountainous terrain defines many dryland regions and results in pronounced variation in soil thickness and soil organic carbon (SOC) stocks that is not currently captured by carbon and global climate models. Here we quantify how total profile SOC to the mobile regolith varies with topographic morphometry, aspect and curvature, to estimate SOC storage within a 1.8 km2 granite-dominated catchment in Idaho, U.S.A. We show that total profile SOC varies significantly with aspect (p<0.0002) and topographic microtopography as measured by hillslope curvature (p<0.0001); the north-facing aspect sites have 3.0 times more total SOC per area than the south-facing aspect sites, and convergent areas have 6.4 times more total SOC per area compared to divergent areas. SOC below 0.3 and 1 m depth is > 80 and 30 % of the catchment total SOC. We conclude that the distribution of SOC is strongly controlled by aspect and surface terrain elements governing soil thickness within a semiarid catchment and suggest that more information is likely contained in the topographic metric of curvature when the entire vertical dimension of soil is determined.