Allogenic and autogenic effects on mangrove dynamics from the Ceará Mirim River, north‐eastern Brazil, during the middle and late Holocene

Abstract

It is possible that climate changes and sea level fluctuations (allogenic processes) are and will cause major changes in mangrove dynamics. However, other driving forces may be significantly affecting this system. Distinguishing allogenic and autogenic influence on mangroves is a challenging question, because mechanisms related to the natural dynamics of depositional environments (autogenic processes) have strong influences on the establishment and degradation of mangroves. Thus, impacts on mangroves caused by autogenic processes may be erroneously attributed to allogenic mechanisms. Therefore, it is imperative to identify the ‘fingerprint’ of global changes in modern mangrove dynamics. In order to characterize the influence of these forces on mangroves, this work has used geomorphology and vegetation maps integrated with sedimentological and palynological data, radiocarbon dating, as well as δ13C, δ15N and C/N from sedimentary organic matter. The inter‐proxy analyses reveal an estuarine influence with mangrove development along the Ceará Mirim River, north‐eastern Brazil, since ~6920 cal yr bp, after the post‐glacial sea level rise. Relative sea level (RSL) has been stable during the middle and late Holocene. Mangrove establishment along this fluvial valley begins at about 6920 cal yr bp, caused by the sea‐level stabilization, an allogenic influence. However, after its establishment, wetland dynamics were mainly controlled by autogenic factors, related to channel migrations, instead of allogenic process. Some influence of sea‐level and climate changes on mangrove dynamics in this estuarine channel have been weakened by more intense tidal channels activities. Therefore, the expansion and contraction of mangrove areas along the estuary of the Ceará Mirim River since 6920 cal yr bp has been mainly influenced by channel dynamics that regulate the accretion and erosion of mangrove substrates. Copyright © 2018 John Wiley & Sons, Ltd.

Effects of the middle Holocene high sea‐level stand and climate on Amazonian mangroves

“…By contrast, autogenic disturbances on mangroves occur on small time scales (annual to interannual, 0.5–10 years) and with local impacts on the ecosystem (Pickett and White, 2005) such as strong winds (Jeltsch, 1992), fires (Ratz, 1995) and insect attacks (Coley and Barone, 1996; Menezes and Mehlig, 2005). The tidal channel dynamics related to erosion and sediment deposition on tidal flats can also affect the spatial distribution of mangroves locally with some effect on the pollen signal down‐core (Moraes et al ., 2017; Ribeiro et al ., 2018). These processes are inherent to the depositional system and vegetation dynamics (Beebower, 1964; Cohen et al ., 2020a).…”

“…In the present study, a geodesic landmark and the upper tidal flats, occupied by modern Bragança mangroves (2.1 ± 0.1 m amsl), were used as a reference to record RSL changes in the studied cores. Isotopic (δ 13 C and δ 15 N) and C/N analyses of sedimentary organic matter associated with mangrove pollen grains along topographically referenced cores have been used to identify trends of RSL changes (Cohen et al, 2005b(Cohen et al, , 2012(Cohen et al, , 2014a(Cohen et al, , 2015(Cohen et al, , 2020aLamb et al, 2006;Fontes et al, 2017;Ribeiro et al, 2018). The relationship between δ 13 C and C/N, as well as δ 15 N, allows for the identification of the source of sedimentary organic matter, mainly between end-members: terrestrial-and aquatic-derived organic matter (Deines, 1980;Schidlowski et al, 1983;Meyers, 1994;Tyson, 1995).…”

“…RSL on the Rio Grande do Norte coast in north‐east Brazil (Fig. 1) reached the current level at ~7000 cal a bp (Ribeiro et al ., 2018), while the highstand (~1.3 m) was reached at ~5900 cal a bp (Boski et al ., 2015). RSL decreased continually along the southern and north‐eastern coasts of Brazil during the late Holocene (Angulo et al ., 2006).…”

Impacts of Holocene and modern sea‐level changes on estuarine mangroves from northeastern Brazil

“…response to eustasy), Middle and Late Holocene mangrove dynamics were mainly controlled by autogenic factors, such as channel migrations, since RSL has been relatively stable during the Middle and Late Holocene in this sector of the Brazilian coast (Ribeiro et al, 2018). For instance, the northern Brazilian Amazon littoral zone, mainly characterized by low topographic gradients, extensive tidal flats and strong fluvial influences, exhibited a continuous mangrove belt during the Middle Holocene, likely caused by the post-glacial sealevel rise associated with a period of relatively low fluvial discharge.…”

“…While this mangrove establishment can be regarded an allogenic-forced process (i.e. response to eustasy), Middle and Late Holocene mangrove dynamics were mainly controlled by autogenic factors, such as channel migrations, since RSL has been relatively stable during the Middle and Late Holocene in this sector of the Brazilian coast (Ribeiro et al, 2018). In contrast, coastline sectors in southeastern Brazil, such as the Espírito Santo littoral zone, suggest a mangrove-coastal evolution with a stronger sea-level allogenic controlled relationship.…”