Climatic, anthropogenic and sea level influences on the vegetation landscape of a lagoonal system, over the last 3350 years

Abstract

This study explores the influence of dry and wet weather events, sea-level fluctuations, and anthropogenic activities on vegetation dynamics over the past 3,350 cal years BP. Sedimentological and palynological analyses were supported by radiocarbon (¹⁴C) and lead-210 (²¹⁰Pb) dating of a 110 cm sediment core (GAR 1) extracted from the northwest sector of the Garzón Lagoon, Uruguay. Lagoon is an intermittently closed system, periodically opening to the sea, with a maximum depth of 5 m. Two different time windows are presented: part of the late Holocene and the last 150 years. Between 3,350 and 2,345 cal years BP, sea levels were high, and the lagoon maintained a broad connection to the sea, favoring halophytic vegetation, including Amaranthaceae and Poaceae, indicative of a salt marsh environment. After 2,345 cal yr BP, an increase in freshwater algae Botryococcus spp., resulting from a brief eutrophication episode, and a pronounced rise in arboreal taxa, particularly the Moraceae/Urticaceae group, signaled a shift towards a more freshwater-influenced system. The contemporary period (1841–2021 CE) is marked by pronounced climatic variability, alternating wet and dry episodes, and intensified anthropogenic activities, including Pinus spp. afforestation and expanded agricultural practices. These human interventions significantly impacted sedimentation rates and influenced the Garzón lagoon's ecological dynamics.