Articles | Volume 12, issue 16
Biogeosciences, 12, 4861–4874, 2015
Biogeosciences, 12, 4861–4874, 2015

Research article 17 Aug 2015

Research article | 17 Aug 2015

Soil carbon and nitrogen erosion in forested catchments: implications for erosion-induced terrestrial carbon sequestration

E. M. Stacy1, S. C. Hart2,3, C. T. Hunsaker4, D. W. Johnson5, and A. A. Berhe2,3 E. M. Stacy et al.
  • 1Sierra Nevada Research Institute, University of California, Merced, Merced, CA, USA
  • 2Environmental Systems Graduate Group, University of California, Merced, Merced, CA, USA
  • 3Life & Environmental Sciences and the Sierra Nevada Research Institute, University of California, Merced, Merced, CA, USA
  • 4Pacific Southwest Research Station, US Forest Service, Fresno, CA, USA
  • 5Department of Natural Resources and Environmental Science, University of Nevada, Reno, USA

Abstract. Lateral movement of organic matter (OM) due to erosion is now considered an important flux term in terrestrial carbon (C) and nitrogen (N) budgets, yet most published studies on the role of erosion focus on agricultural or grassland ecosystems. To date, little information is available on the rate and nature of OM eroded from forest ecosystems. We present annual sediment composition and yield, for water years 2005–2011, from eight catchments in the southern part of the Sierra Nevada, California. Sediment was compared to soil at three different landform positions from the source slopes to determine if there is selective transport of organic matter or different mineral particle size classes. Sediment export varied from 0.4 to 177 kg ha−1, while export of C in sediment was between 0.025 and 4.2 kg C ha−1 and export of N in sediment was between 0.001 and 0.04 kg N ha−1. Sediment yield and composition showed high interannual variation. In our study catchments, erosion laterally mobilized OM-rich litter material and topsoil, some of which enters streams owing to the catchment topography where steep slopes border stream channels. Annual lateral sediment export was positively and strongly correlated with stream discharge, while C and N concentrations were both negatively correlated with stream discharge; hence, C : N ratios were not strongly correlated to sediment yield. Our results suggest that stream discharge, more than sediment source, is a primary factor controlling the magnitude of C and N export from upland forest catchments. The OM-rich nature of eroded sediment raises important questions about the fate of the eroded OM. If a large fraction of the soil organic matter (SOM) eroded from forest ecosystems is lost during transport or after deposition, the contribution of forest ecosystems to the erosion-induced C sink is likely to be small (compared to croplands and grasslands).

Short summary
In the southern parts of the Sierra Nevada in California, we investigated erosion of carbon and nitrogen from low-order catchments. We found that eroded sediments were OM rich, with a potential for significant gaseous and dissolved loss of OM during transport or after depositional in downslope or downstream depositional landform positions.
Final-revised paper