SEDIMENT CONNECTIVITY AT NATURAL AND PERTURBATED MOUNTAIN GORGE SLOPES AT IZTA-POPO NATIONAL PARK (CENTRAL MEXICO) USING OSL AND SFM HRDEMS

Assessing sediment connectivity in a river basin is important to understand the mechanism of sediment transfer and the erosion and its depositional processes. Here we study sediment connectivity at the headwaters of two mountain gorges known as Altzomoni and Amalacaxco. They are located at Izta-Popo National Park (I-PNP), at ~4,000 m asl, in the alpine grassland where high-mountain processes predominate (i.e. gravitational processes). Altzomoni headwater gorge remains in natural state while Amalacaxco headwater gorge is perturbated by man-made actions implemented at I-PNP and based in afforestation and the constructions of trenches and ditches to prevent soil erosion. We evaluated sediment connectivity along two transversal profiles to the channel using methodology base on (1) a multitemporal (one year) study of optically stimulated luminescence (OSL) signals using a portable OSL (POSL) reader and (2) on high-resolution DEMs obtained by means of a terrestrial laser scanner and SFM. We correlated the resulting POSL signals with topographical properties calculated on the HRDEMs. Main results indicated that POSL signals tend to decrease downslope in the natural Altzomoni headwater and, by contrast, POSL values tend to increase in the perturbed Amalacaxco headwater. This behavior has also been observed in two other headwaters at I-PNP, one of them selected for being perturbed (known as Apatlaco) and the other for remaining in natural state (known as Nexpayantla), obtaining same results. This suggest that man-made actions in the park are modifying the natural connectivity of superficial sediment prevailing on the high-mountain headwaters and opens a debate about the side effects of changing the transfer of sediment and nutrients in a highly sensitive mountain ecosystem. We conclude that using POSL values whit topographical analysis is a promising to study sediment connectivity in high mountain areas and to identify erosion in fluvial systems due to man-made actions.