Historical reconstruction of sediment accumulation rates as an indicator of global change impacts in a tropical crater lake

Lakes are effective sentinels of global change owing to their sensitivity to land-use changes and climate variability in their catchment. Santa María del Oro Lake (SAMO, NW Mexico) is of interest both for global change studies and as a natural resource to sustain the economy of local communities. Four sediment cores were used to evaluate the temporal variations of sediment accumulation, under the hypothesis that changes in sediment input are mostly driven by anthropic activities developed in the lake surroundings. Radiocarbon (¹⁴C) dating of SAMO sediments was precluded by a large and variable reservoir effect, inducing an age offset of ~ 4000 years. Well-constrained chronologies over the past century were obtained by ²¹⁰Pb dating, corroborated by the stratigraphic markers ¹³⁷Cs, ^239+240Pu, and ¹⁴C-fraction modern. Geochemical, magnetic susceptibility, and meteorological data were used to elucidate the main controls of sedimentation processes in the lake. Mass accumulation rates were high, likely because of the natural vulnerability of catchment soils to hydric and aeolian erosion. The highest values, observed towards the lakeshore, were attributed to the influence of seasonal runoff from the surrounding steep hills, and the proximity of human settlements and agricultural fields. Mean mass accumulation rates increased with time (from 0.03 ± 0.01 g cm⁻² year⁻¹ between 1900 and 1950, to 0.14 ± 0.10 g cm⁻² year⁻¹ after the 1950s), although the most recent values were comparable to the mean values during the pre-1950 period. Accumulation maxima across the lake, occurring mostly since the 1980s, concurred with precipitation minima and were related to terrigenous pulses associated with soil erosion, likely favored by lower soil humidity and the occurrence of wildfires during dryer years. Controls on the development of human settlement and agriculture practices should be included in the long-term environmental management plans for the conservation of the lake resources.