Late Holocene mangrove dynamics of the Doce River delta, southeastern Brazil: Implications for the understanding of mangrove resilience to sea-level changes and channel dynamics

Abstract

This work aims to understand mangrove resilience to changes in a wave-influenced delta in southeastern Brazil during the late Holocene using an integrated analysis of palynology, sedimentology, and geochemistry (δ13C, δ15N, C:N and C:S ratio), and radiocarbon dating on two sediment cores. The data indicated three mangrove succession phases: 1) an estuarine point bar/tidal flat occupied by a mixture of mangrove species (~2660 - ~ 2050 cal yr BP); 2) a tidal flat dominated by Laguncularia mangroves (~2050 - ~ 900 cal yr BP); and 3) tidal flats with Laguncularia mangroves upstream and establishment of Rhizophora/Avicennia mangrove at the river mouth (~900 cal yr BP until present). The geochemical results suggest a dominance of C3 terrestrial plants with a mixture of C4 plants and organic matter of marine/estuarine origin throughout the late Holocene. Laguncularia and Rhizophora trees were established since ~ 2660 cal yr BP as pioneers, followed thereafter by Avicennia. Currently, tidal flats upstream are occupied by mangroves mainly represented by Laguncularia. Rhizophora/Avicennia mangroves occur at the mouth of the river. The relative sea-level fall during the late Holocene, as well as the channel dynamics, caused the development of tidal flats and mangrove succession inland. The succession of Rhizophora, Laguncularia, and Avicennia, followed by the permanence of only Laguncularia, is likely related to the resilience of each mangrove genus to habitat disturbance (e.g., salinity and sediment grain size fractions) caused by sea-level changes and channel dynamics. Our results show that mangroves may be resilient to the effects of Atlantic sea-level fluctuations, but the floristic structure in the past is different from that of today.