Hydrological controls on carbon accumulation in sedimentary environments of a Peruvian high-Andean lacustrine system

Lacustrine systems of the tropical Andes are recognized as important carbon sinks, although the sensitivity of their carbon cycle remains poorly understood. This study assessed organic matter sources and controls on carbon accumulation in the high-altitude Conococha lacustrine system of the central Peruvian Andes using elemental and isotopic proxies. Two 30-cm sediment cores were analyzed for total organic carbon (TOC), total nitrogen (TN), and stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N). Sediment chronology was established using excess ²¹⁰Pb activity and the Constant Flux-Constant Sedimentation (CFCS) model to calculate sediment accumulation rates (SAR) and carbon burial rates. The mean SAR was 0.36 cm yr⁻¹, covering approximately 1940–2020 AD. Average TOC accumulation rates ranged from 128.3 to 146.6 g m⁻² yr⁻¹, with the highest values recorded in the nearshore core. A marked increase in carbon accumulation began around 2000 AD, coinciding with the construction of a water-retention dam in 2001. Relative to pre-dam conditions, TOC fluxes increased by 1.34 times offshore and 1.52 times nearshore, indicating that hydrological regulation enhanced carbon burial efficiency through reduced flow velocity, longer water residence time, and greater retention of sediments and organic matter. Stable isotopes and TOC:TN ratios revealed spatial differences in organic matter sources: nearshore sediments recorded a mixed organic matter source, whereas offshore sediments reflected mainly algae-derived material linked to eutrophic conditions. This study illustrates how this lacustrine system acts as a hydrologically sensitive site of carbon accumulation, highlighting the influence of human-driven hydrological modifications on long-term biogeochemical dynamics in this high-Andean lacustrine system.