Erodibility of soil and organic matter: independence of organic matter resistance to interrill erosion

Abstract

The enrichment of organic matter in interrill sediment is well documented; however, the respective roles of soil organic matter (SOM) and interrill erosion processes for the enrichment are unclear. In this study, organic matter content of sediment generated on two silts with almost identical textures, but different organic matter contents and aggregations, was tested. Artificial rainfall was applied to the soils in wet, dry and crusted initial conditions to determine the effects of soil moisture and rainfall and drying history on organic matter enrichment in interrill sediment. While erosional response of the soils varied significantly, organic matter enrichment of sediment was not sensitive to initial soil conditions. However, enrichment was higher on the silt with a lower organic matter content and lower interrill erodibility. The results show that enrichment of organic matter in interrill sediment is not directly related to either SOM content or soil interrill erodibility, but is dominated by interrill erosion processes. As a consequence of the complex interaction between soil, organic matter and interrill erosion processes, erodibility of organic matter should be treated as a separate variable in erosion models. Further research on aggregate breakdown, in particular the content and fate of the organic matter in the soil fragments, is required. densities has to be developed as well. Based on a principal understanding of the interaction between soil, interrill processes and SedOM, an applicable model for interrill erodibility of organic matter has to be developed.On a larger scale, the enrichment of organic matter in sediment generated by interrill processes requires research on the on-site fate of the organic matter. Off-site effects of eroded sediment are well documented, and sinks within a watershed can be identified through spatially distributed runoff models (Polyakov and Lal, 2004; Quinton et al., 2006). However, on a field scale, deposition and exposure of sediment enriched in organic matter to the atmosphere potentially enhances mineralization. Therefore, erosion, transport and deposition of interrill sediment enriched in organic matter have to be studied in detail on a within-field scale. Quality and stability of the eroded organic matter also require special attention to assess the role of interrill processes for soil-atmosphere interaction in the global carbon cycle. 802 N. J. Kuhn

Exploring particle size distribution and organic carbon pools mobilized by different erosion processes at the catchment scale

“…Haregeweyn et al 2008;Boix-Fayos et al 2009), suggesting that mineralization of OC during the erosion processes at the catchment scale is enhanced compared to other spatial scales as suggested in previous works (e.g. Kuhn 2007;Nadeu et al 2010). The mean sediment ER TOC (0.40±0.24) was very low compared to that of other field studies of similar spatial scale under natural conditions, where the ER TOC ranged between 0.8 and 5.6 (e.g.…”

Soil erosion in New Zealand is a net sink of CO2

“…The most important systematic error is the assumption that the carbon concentration of sediment is the same as the soil at the source of erosion. Kuhn (2007) reported that sediment from surfi cial erosion can have a carbon enrichment of up to 50%. Although enrichments of this magnitude are unlikely for massmovement erosion, we take a conservative approach and assign a systematic error of +50% and −25% to represent this uncertainty; as well as that associated with change in carbon content of sediment during transport in rivers (this should be small as travel times in New Zealand's steep and generally short rivers are rarely more than several days).…”

Hillslope and catchment scale soil organic carbon concentration: An assessment of the role of geomorphology and soil erosion in an undisturbed environment

“…Investigations of non-tilled agricultural areas or undisturbed hillslopes are few (Yoo et al, 2006) or incomplete (Ritchie et al, 2004). Field experiments and flume studies also provide the capacity for solid insights under controlled conditions and demonstrate how much more work is needed to understand field processes (Kuhn, 2007;Schiettecatte et al, 2008).…”