Sediment carbon storage increases in tropical, oligotrophic, high mountain lakes

Abstract

• El Sol and La Luna are valuable sentinels of global change by displaying detectable signs of anthropic disturbances from 1950 onwards. • The higher mass accumulation rates and organic carbon burial rates from 1950 onwards are result of human activities and atmospheric dust deposition. • Sharing the same climatic conditions, climate change unlikely caused the recent higher organic carbon burial observed in both lakes. High mountain lakes are valuable sentinels of global change because they are sensitive to environmental stress and integrate changes in the atmosphere and their catchment areas. This study tested the hypothesis that local and regional anthropogenic stressors have affected productivity, sedimentation, and organic carbon burial in two tropical high mountain lakes in central Mexico. We studied changes in the water column (Secchi disc depth, total suspended solids (TSS), and chlorophyll- a concentrations) and surface sediments (chlorophyll- a and organic carbon concentrations) in El Sol Lake and La Luna Lake during the period 2000–2018, and organic carbon burial rates in sediment cores (∼1884–2014) dated with lead-210 ( 210 Pb). We observed increasing water turbidity, TSS, and organic carbon in surface sediments in El Sol Lake. Different responses of the two lakes were caused by lower pH in La Luna Lake and a threefold residence time of TSS in El Sol Lake compared to La Luna Lake, mostly attributable to their different surface/volume ratios. Organic carbon burial rates were slightly higher at La Luna Lake until 2000, when they became higher at El Sol Lake due to increasing sediment accumulation and organic carbon concentrations. In both lakes, results show significantly higher organic carbon burial rates since the 1950s, likely resulting from the deposition of human-induced wind-blown particles derived from activities at the volcano slopes and long-distance transport from highly urbanized areas. Anthropogenic impacts rather than climate change, therefore, caused the recent higher organic carbon burial rates observed in both lakes. Methods and findings from this study provide a valuable basis for comparing changes in other high mountain lakes worldwide.