Drivers of erosion and suspended sediment transport in three headwater catchments of the Mexican Central Highlands

Quantifying suspended sediment exports from catchments and understanding suspended sediment dynamics within river networks is important, especially in areas draining erodible material that contributes to the siltation of downstream reservoirs and to the degradation of water quality. A one-year continuous monitoring study of water and sediment fluxes was conducted in three upland subcatchments (3.0, 9.3, and 12.0 km2) located within the Cointzio basin, in the central volcanic highlands of Mexico (Michoacán state). Two subcatchments generated high sediment exports (i.e., Huertitas, 900–1500 t km− 2 y− 1 and Potrerillos, 600–800 t km− 2 y− 1), whereas the third subcatchment was characterized by a much lower sediment yield (i.e., La Cortina, 30 t km− 2 y− 1). Such disparities in subcatchment behaviours were associated with the presence of severely gullied areas in Huertitas and Potrerillos rather than with rainfall erosivity indices. An adapted classification of hysteretic patterns between suspended sediment concentration (SSC) and discharge was proposed because 42% of flood events contributing to 70% of sediment export were not discriminated by the classical clockwise/anticlockwise typology. This new classification allowed the identification of relationships in the hydrosedimentary responses of successive floods. A stream transport capacity limit was also detected during hydrograph recession phases. Overall, hydrosedimentary processes proved to be seasonally dependent: sediment export was repeatedly limited by the stream transport capacity during the first part of the rainy season, whereas a channel minimum erosivity threshold was frequently reached at the end of the season.