Geomorphic regulation of floodplain soil organic carbon concentration in watersheds of the Rocky and Cascade Mountains, USA

Daniel N. Scott,Ellen E. Wohl

doi:10.5194/esurf-6-1101-2018

Abstract

Abstract. Mountain rivers have the potential to retain OC-rich soil and store large quantities of organic carbon (OC) in floodplain soils. We characterize valley bottom morphology, floodplain soil, and vegetation in two disparate mountain river basins: the Middle Fork Snoqualmie in the Cascade Mountains and the Big Sandy in the Wind River Range of the Rocky Mountains. We use this dataset to examine variability in OC concentration between these basins as well as within them at multiple spatial scales. We find that although there are some differences between basins, much of the variability in OC concentration is due to local factors, such as soil moisture and valley bottom geometry. From this, we conclude that local factors likely play a dominant role in regulating OC concentration in valley bottoms and that interbasin differences in climate or vegetation characteristics may not translate directly into differences in OC storage. We also use an analysis of OC concentration and soil texture by depth to infer that OC is input to floodplain soils mainly by decaying vegetation, not overbank deposition of fine, OC-bearing sediment. Geomorphology and hydrology play strong roles in determining the spatial distribution of soil OC in mountain river corridors.

Highlights

Terrestrial carbon storage plays an important role in regulating the global carbon cycle and the distribution of carbon between oceans, the atmosphere, long-term (105–109 years) storage in rock, and short- to moderate-term storage in the biosphere (101–104 years, including vegetation and soil) (Aufdenkampe et al, 2011; Battin et al, 2009)
Of cores with more than a single sample, 32 % (7/22) of cores stratified by slope in the wet basin, 32 % (8/25) of cores stratified by floodplain type in the wet basin, and 6 % (2/31) of cores in the semiarid basin exhibit organic carbon (OC) concentration peaks at depth
We present floodplain soil OC concentration data from two disparate watersheds to compare how interbasin variability between the two watersheds compares with intra-basin variability in geomorphic and hydrologic characteristics in determining OC concentration

Summary

Introduction

Terrestrial carbon storage plays an important role in regulating the global carbon cycle and the distribution of carbon between oceans, the atmosphere, long-term (105–109 years) storage in rock, and short- to moderate-term storage in the biosphere (101–104 years, including vegetation and soil) (Aufdenkampe et al, 2011; Battin et al, 2009). It is essential to quantify the spatial variability of OC stored in the biosphere to constrain the effects of climate change on feedbacks between biospheric and atmospheric carbon storage (Ballantyne et al, 2012). In the context of the carbon cycle, floodplains can act as a major component of the biospheric carbon pool (Aufdenkampe et al, 2011; Battin et al, 2009).

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