Sedimentation and sediment geochemistry in a tropical mangrove channel meander, Sungai Kerteh, Peninsular Malaysia

Hasrizal Shaari,Edward J Anthony,Abdul Hafidz Yusoff,Wan Mohd Afiq Wan Mohd Khalik,Riza Yuliratno Setiawan,Erick Naim,Che Abd Rahim Mohamed,Qatrunnada Mohd Nasir,Hui-Juan Pan

doi:10.1186/s40645-020-00362-y

Abstract

Tropical mangrove swamps are commonly characterized by dense networks of tidal channels that may show pronounced meandering and dendritic patterns. Channel meanders are sometimes accompanied by cut-offs, and, like classical fluvial meanders, record changes in hydrology and sedimentation over time. Channel meandering can, thus, be an important process that contributes to spatial and temporal variability in the preserved record of the sedimentology and geochemistry of mangrove sediments. The aim of this study is to highlight changes in channel meander sedimentation in response to a meander cut-off in a tropical mangrove swamp. Two short sediment cores were sampled, respectively from a point bar (core KR1, 122 cm) at the junction with the neck cut-off and inside the cut-off (core KR2, 98 cm) in the Sungai Kerteh mangroves of Peninsular Malaysia. The profile comparison was based on sediment characteristics, total organic carbon (TOC), and selected elements (Fe, Na, Mg, Mn, Ba, and Sr). A smaller standard deviation of mean grain size (MGS) was found at the point bar (4.37 ± 0.51 ϕ) than in the cut-off (4.43 ± 1.76 ϕ), indicating a difference in flow velocity between the two settings. In turn, these changes in grain size influence channel meander evolution via associated changes in TOC and heavy metals. In order to clarify these relationships, we used principal components analysis and factor analysis. An increased accumulation of selected elements and TOC at the cut-off site from a depth of ~ 60 cm to the core-top segment was probably associated with a slowing down of sediment settling. A higher TOC recorded in the cut-off (2.74 ± 1.42%) compared to the point bar (1.14 ± 0.46%) suggests a propensity for prolonged in situ accumulation of organic matter in the abandoned meander bend. This study provides grain size and sediment geochemical information that is consistent with patterns of active and inactive sedimentation in the meander bends of mangrove channels.

Highlights

Tidal channels in mangroves are important pathways for the transport of sediments, dissolved oxygen, nutrients, seedlings, and organic matter (Woodroffe 1992; Anthony 2009)
We know of no work, that has been undertaken to highlight the impact of channel meander evolution on mangrove sedimentation and on the sediment geochemistry
We document changes in mangrove channel meander sedimentation associated with a meander cutoff in a Malaysian mangrove system (Fig. 1) using grain-size and geochemical characteristics of core sediments in the vicinity of an abandoned meander

Summary

Introduction

Tidal channels in mangroves are important pathways for the transport of sediments, dissolved oxygen, nutrients, seedlings, and organic matter (Woodroffe 1992; Anthony 2009). In mangroves and saltmarshes, entrenched tidal channel networks are deemed to evolve very slowly through processes that include meander-bend erosion and sedimentation, with subsequently, very slow change of these inherited forms over multi-decadal to centennial timescales (Anthony 2009). Understanding these processes in mangrove forests can contribute to an understanding of changing present environments, under natural and human-induced processes that drive mangrove sedimentation, as well as of the paleo-environmental record (e.g., França et al 2015; Cohen et al 2016; Woodroffe et al 2016). We show that such sedimentological and geochemical characterization can be used in identifying change in mangrove environments

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