Spectroscopic Assessment of Soil Organic Matter in Wetlands from the High Andes

Abstract

Wetlands are valuable for their function as C sinks, water conservation and filtering, flood control, and as a recreational landscape. In the Central and Southern Andes, peatlands (a.k.a., bofedales) are also a source of good quality pastures for wild and domestic South American camelids (Vicugna pacos, Lama glama, and Vicugna vicugna). In the present study, whole soil samples from seasonally and permanently flooded bofedales were analyzed using laser‐induced fluorescence spectroscopy (LIFS) and electron paramagnetic resonance (EPR) to assess soil organic matter (SOM) stability. The results obtained by both techniques were comparable (R2 = 0.88) and proven to be reliable indicators of increased or reduced SOM stability and thus suitable methods for assessing its humification index. The humification values determined in the permanently flooded bofedal were lower than for the seasonally flooded one. Deeper in the soil profiles of both bofedal types, the humification process of SOM attains more advanced stages, with a relative increase of more recalcitrant organic compounds. An important factor is the presence of water in permanently flooded bofedales, which slows down organic matter decomposition due to anaerobiosis. Results from a portable LIFS system also showed significant correlations when compared with both the bench LIFS system (R2 = 0.88) and the EPR (R2 = 0.62). The portable system constitutes an affordable option for the in situ characterization of SOM. This assessment is of outmost importance in agroecosystems acting as green house gases sink or sources under variable climatic conditions.