Contrasting natural and anthropic historical changes in two estuarine systems on the Brazilian coast: Benthic foraminiferal-based Paleo-Ecological Quality Status

This study uses a multiproxy approach to investigate two estuarine ecosystems located along the Brazilian Atlantic coast and their historical changes. In the last century, the Santos-São Vicente-Bertioga Estuary (Santos) has been subjected to anthropogenic influences such as heavy industrialization and the construction of the Santos Port. The Caravelas-Nova Viçosa Estuary (Caravelas) has preserved most of its pristine condition but has been mainly affected by naturally driven changes after the opening of a new inlet around the 1960s. We use sedimentological, geochemical, and benthic foraminiferal indices to investigate the distinct drivers of environmental changes throughout the history of these two estuaries. Different biotic indices were tested to assess the Paleo-Ecological Quality Status (Paleo-EcoQS): the diversity index exp(H'_bc), the Ecological Quality Ratio (EQR) computed based on local reference conditions, the Tolerant Species Index (TSI) and the Enhanced Benthic Foraminifera Oxygen Index (EBFOI). The Principal Component Analysis (PCA) highlights the systems' responses to different causes of impact, either anthropogenic or natural. In Santos, the PCA indicates a strong association between sediment composition, heavy metal enrichment, and the prevalence of stress-tolerant species, reflecting a decline in the Paleo-EcoQS linked to industrial and urban pressures. Caravelas exhibits a dynamic response to natural processes, with positive PCA scores correlated with organic matter inputs and sediment dynamics, suggesting resilience despite fluctuating environmental conditions. This work shows the importance of sedimentary records in distinguishing between natural and human-induced impacts, having great scientific and social relevance both for biomonitoring and informing conservation strategies.