DECOMPOSABILITY OF ORGANIC MATTER IN SEDIMENTS ERODED FROM EIGHT LOW-ORDER CATCHMENTS, SIERRA NEVADA, CALIFORNIA

Erosion laterally distributes soil organic matter across a landscape and may result in a net C sink if eroded OM is relatively more protected from decomposition after deposition in lower-lying depositional landform positions through organomineral associations or burial. Conversely, erosion can disrupt aggregates and expose previously protected material. To determine the net impact of erosion on the C balance, we need to know the magnitude of material transported, as well as its composition and potential to decompose. Predictive erosion models incorporate meteorological variation into estimates of sediment detachment and transport. However, little is known about how these drivers impact the composition of sediment, which could drastically alter its potential to decompose. In conjunction with a study on the magnitude of annual sediment transport, we assessed the decomposability of soil and eroded sediment from eight low-order watersheds in the southern Sierra Nevada to evaluate differences in composition over time and space. Decomposability was approached from two directions: (1) carbon dioxide evolution and changes in inorganic nitrogen during a soil incubation (43 days) at field capacity, and (2) a suite of extracellular enzyme assays, including potentials for C-, N-, and P-rich compounds. The ultimate fate of the OM will depend on when and where it is deposited, but the combination of total transport with decomposability estimates what can potentially decompose in a short period of time, when the direct feedback of land management decisions to the ecosystem can be monitored and adjusted.