Unveiling two millennia of ecosystem changes in the Azores through elementome trajectory analysis.

The elemental composition of ecosystems responds to environmental perturbations such as land-use change, offering valuable insights into the impacts of global change. This study applies trajectory analysis to two millennia of elemental composition (elementome), including carbon (C), nitrogen (N), and other geochemical elements records from five lakes in the Azores archipelago. By integrating multivariate elemental data, we aim to reconstruct past environmental shifts and understand long-term ecosystem dynamics in response to anthropogenic and non-anthropogenic impacts. We quantified elementome trajectory analysis metrics, such as elemental turnover, trajectory directionality, and trajectory speed, as ecological indicators to quantify the magnitude and graduality of island ecosystem disturbances. We also tracked elemental shifts over time using CONISS analysis and compared these shifts with previously published environmental reconstructions from the same lakes. Additionally, we analyzed and compared trajectory shapes across the lakes to identify patterns and differences. Our results indicate that the elementome trajectories primarily reflected changes in erosion rates, in-lake biological activity, and catchment dynamics, characterized by distinct patterns of climate variability, wildfires, and agropastoral activities. Trajectory shapes revealed different patterns across shallow and deeper lakes. Our findings demonstrate the utility of Elementome Trajectory Analysis for disentangling the complex interplay between natural and anthropogenic drivers of ecosystem change in island environments, providing a powerful new tool for paleoecological reconstructions and for monitoring changes at a catchment level.