Effect of litterbags on rate of organic substrate decomposition along soil depth and geomorphic gradients

Purpose

The effect of litterbags on rate of organic substrate decomposition and how the magnitude of this effect varies depending on different soil and environmental variables remains poorly quantified. In this work, I determine the effect of mesh litterbags on decomposition of organic substrate at different landform positions and soil depths in a small, naturally eroding watershed.

Materials and methods

Results presented here are derived from an 18-month field decomposition experiment using a common substrate, wood. I monitored the rate of mass loss of wood as is and the same type of wood enclosed in litterbags constructed from nylon mesh material with 1-mm wide openings. The study was carried out in three to four depths each at four geomorphologically distinct landform positions along an undisturbed hillslope in Northern California.

Results and discussion

Enclosure of wood inside mesh litterbags significantly changed its rate of decomposition overall and the percent C and C/N ratio of the decomposing substrate, at an inconsistent rate at the different depths and landform positions. The highest change in mass loss due to bagging was observed on the surface of the soil, on the summit part of the hillslope where there was up to 80-times more difference in decay rate of bagged vs. not-bagged substrate. At depth, the effect of bagging on rate of mass loss reached a maximum of 10 times at 50 cm depth in the alluvial/colluvial plain at the base of the study hillslope.

Conclusions

Results from this study underscore the need to exercise caution when inferring rates of organic substrate decomposition in dynamic hillslope environments from litterbag decomposition experiments conducted on the surface of soil or flat landscapes.