Stabilization Mechanisms and Decomposition Potential of Eroded Soil Organic Matter Pools in Temperate Forests of the Sierra Nevada, California

Abstract

The lateral destination and potential decomposition of soil organic matter mobilized by soil erosion depends on factors such as the amount and type of precipitation, topography, the nature of mobilized organic matter (OM), potential mixing with mineral particles, and the stabilization mechanisms of the soil OM. This study examined how the relative distribution of carbon (C) and nitrogen (N) in different OM fractions varied in soils from eroding slopes and in eroded sediments in a series of low‐order forested catchments in the western Sierra Nevada, California. We found that precipitation amount played a major role in mobilizing OM. More than 40% of the OM exported from these forested catchments was free particulate OM, or OM physically protected inside relatively less stable macroaggregates, compared to OM inside microaggregates or chemically associated with soil minerals. Years with high amounts of precipitation generally transported more mineral‐associated OM, with lower C and N concentrations, while sediment transported in drier years was more enriched in unprotected, coarse particulate OM derived from surficial soils. When incubated under the same conditions, sediment C (from material captured in settling basins) produced 72–97% more CO2 during decomposition than soil C did. Our results suggest that without stabilization through burial or reconfigured organomineral associations, this sediment OM is prone to decomposition, which may contribute to little to no terrestrial CO2 sink induced from erosion in these Mediterranean montane forest ecosystems.

Divergent changes in particulate and mineral-associated organic carbon upon permafrost thaw

“…Apart from their distinct protection statuses, the density differences between POC and MAOC could also lead to a larger loss of POC through lateral transport. Given that POC has a lower density than MAOC 18 , it is more vulnerable to leaching than MAOC because of the preferential transport of light organic particles 49 , 50 . Nevertheless, although MAOC is more stable than POC, over long-term scales (i.e., decadal or centennial timescales), it would also be decomposed and laterally transferred 50 , 51 .…”

“…Given that POC has a lower density than MAOC 18 , it is more vulnerable to leaching than MAOC because of the preferential transport of light organic particles 49 , 50 . Nevertheless, although MAOC is more stable than POC, over long-term scales (i.e., decadal or centennial timescales), it would also be decomposed and laterally transferred 50 , 51 . However, this part of the MAOC loss might be offset by increased microbial residual C (an important source of MAOC) 18 , 39 , 52 either along the thaw sequence or at most of the regional thermokarst-impacted sites (Supplementary Fig.…”

Effect of recreation on the spatial variation of soil physical properties

“…The organic horizon also contributes to a good water regime by increasing the absorption capacity of the soil, reducing runoff and increasing moisture retention [18]. Organic horizon is a source of nutrients needed for plant growth and can effectively buffer the underlying mineral soil horizons, which are more vulnerable to compaction [19] and erosion by rainfall [20]. Organic horizons are generally less susceptible to erosion than mineral soil, but if organic matter is crushed by trampling, it can also be eroded, exposing the mineral soil beneath it [21][22][23].…”

Impacts of climate and forest management on suspended sediment source and transport in montane headwater catchments

“…Sediment yields in headwater catchments have often been reported because of their importance to water quality, ecosystem nutrient balances and downstream habitats (Kjelland et al, 2015;Olson & Hawkins, 2017;Stacy et al, 2015Stacy et al, , 2019Yang et al, 2022). Studies of sediment yield alone, however, provide limited information on the source and transport of suspended sediment useful for managing erosion and sediment delivery.…”

“…In montane headwater basins, suspended sediment is derived from multiple sources, including: channel bed and bank erosion; raindrop splash, sheetwash, rill and gully erosion on hillslopes; erosion from unpaved roads and other disturbed areas; mass movement; and resuspension of in‐channel sediment that was previously deposited (Arismendi et al, 2017; Bryan, 2000; Gomi et al, 2005; Leonard et al, 1979). Sediment yields in headwater catchments have often been reported because of their importance to water quality, ecosystem nutrient balances and downstream habitats (Kjelland et al, 2015; Olson & Hawkins, 2017; Stacy et al, 2015, 2019; Yang et al, 2022). Studies of sediment yield alone, however, provide limited information on the source and transport of suspended sediment useful for managing erosion and sediment delivery.…”