ResumenLas turberas alto andinas, llamadas también bofedales, presentan altas tasas de acumulación de carbono y sensibilidad a los cambios climáticos, motivo por el cual son consideradas como excelentes registros para estudios ambientales de alta resolución. El presente estudio reconstruye, a través del análisis del testigo APA01 ubicado en la cabecera de cuenca del río Cachi en Ayacucho, la historia paleoambiental de los últimos 2 500 años. Las dataciones del testigo se determinaron por radiocarbono usando un Espectrómetro de Masas con Acelerador de Partículas (AMS), la estimación del carbono orgánico se realizó a través de un analizador elemental PDZ Europa ANCA-GSL. Los resultados evidencian cambios en las tasas de acumulación de carbono y en el clima local durante el Holoceno Tardío; específicamente durante los últimos 2 500 años antes del presente. Durante el periodo denominado Anomalía Climática Medieval (ACM), alrededor de 1040 Después de Cristo (DC) a 1300 DC, el clima más seco provocó una desaceleración en la acumulación de carbono debido a una reducción del nivel freático que induce a una reducción en la producción de materia orgánica con un pico negativo en la concentración de carbono. Al final de la Pequeña Edad de Hielo (PEH), entre 1600 DC y 1890 DC, la acumulación de carbono presentó alta variabilidad. Posteriormente, el ambiente de turba se caracteriza principalmente por un aumento considerable de las tasas de acumulación de carbono debido al aumento de la tasa de sedimentación que posiblemente esté relacionado con el retroceso de los glaciares en los Andes centrales. El reciente aumento drástico en la tasa de sedimentación y la reducción de las concentraciones de carbono advierten de una posible disminución futura de estos ecosistemas.

Abstract. Climate change has altered precipitation and temperature patterns in the tropical Andes. As a result, tropical glaciers have retreated significantly over the past 50 years and have even disappeared in some areas. Andean peatlands, one of the most important Andean carbon reservoirs, also seem to be affected by these climate changes, since glaciers have been recognized as one of their vital water sources. Here, we point out the important role of Andean peatlands on carbon accumulation rates (CAR), one of the highest in the world, and the impact of climate on carbon storage over the last 65 years, using four peat cores. The peat cores were radiocarbon-dated and ages were post-bomb calibrated and chronological models indicated basal ages (30 cm depth) ranging from 1957 to 1972 CE, where accumulation rates reached up 1.7 cm yr−1. For both peatlands, carbon accumulation rates are high (mean of 470 and 220 g C m−2 yr−1 at APA 1 and APA 2 sites, respectively) and can reach up to 1010 g C m−2 yr−1. Distichia muscoides is the dominant species in the Peruvian Central Andes peatlands and the high CAR, among other factors, is a characteristic of this species. Our results point out that a marked decrease of CAR after the early 1980s at both peatlands is likely related to an increase in annual temperature, which is responsible for the retreat of glaciers. We use a new high-resolution proxy (Skrzypek et al., 2011) based on the δ13C of Distichia along the cores to evaluate the temperature variability at the site. We observed a general trend of increase in the reconstructed temperature from both studied peatlands from 1.9 to 2 ºC for the period 1970–2015 CE. Comparison with air temperature data from the NCEP-NCAR reanalysis for the higher resolution cores shows a good relationship and an increase of 2.15 °C for the same period. Temperature increase may directly affect CAR by an increase in organic matter degradation rates. The decrease in CAR during the period of study may also be due to a decrease in melt water inflow generated by the retreat of glaciers that have almost disappeared today in the catchments as a consequence of regional warming. Our findings emphasize that marked changes in carbon accumulation rates demonstrate the high ecological sensitivity of tropical high-Andean peatlands, endangering their outstanding role in the regional (and even global) C cycle as large C sinks that contribute to the mitigation of global climate change.

This study presents an empirical method for identifying and monitoring acidic lakes impacted by acid rock drainage (ARD) processes in the Cordillera Blanca, Peru, using Landsat 8 images. ARD poses a threat to water security for downstream populations and has been associated with glacier retreat in various river catchments in the region. Previous research has linked water source acidification to the progressive exposure of the sulphide-rich Chicama Formation (Js-Chic), previously covered by perennial ice. However, traditional identification methods rely on labor-intensive ground-based field campaigns, limiting the scope of studies and hindering future predictions. Upon correlating the Landsat 8-derived pH proxies with the Js-Chic map, a higher Js-Chic exposure was observed near highly acidic lakes. Notably, Js-Chic exposure areas exceeding 60 hectares coincided with highly acidic lakes (pH < 4). We also analyzed glacial retreat in the study basins through a time series of the Normalized Difference Snow Index (NDSI) from 1986 to 2019, finding greater glacial retreat in basins with acidic lakes. We also compared vegetation quality in these basins over the same period using the average Normalized Difference Vegetation Index (NDVI) and observed higher vegetation quality in acidic-lake basins. We then developed a methodology to assess lake acidity based on the spectral signatures of 28 lakes in the Cordillera Blanca. These results suggest that a greater Js-Chic exposure area near a lake may indicate acidity. We applied this methodology on 267 lakes in the Cordillera Blanca and found 60 lakes to be highly acidic with a pH < 4 (22.5%), and 207 lakes (77.5%) with a pH > 4. However, these findings should be supplemented with more complex analyses, as there is currently limited in situ monitoring data on lake pH.

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