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Palaeogeography and dynamics of the deltaic wetland of Save River, Mozambique
Stockholm University, Faculty of Science, Department of Physical Geography. Universidade Eduardo Mondlane, Moçambique.ORCID iD: 0000-0001-5649-6998
Stockholm University, Faculty of Science, Department of Physical Geography.
Stockholm University, Faculty of Science, Department of Physical Geography.
Stockholm University, Faculty of Science, Department of Physical Geography.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Many mangrove wetland systems in deltaic environments are negatively affected by massive sedimentation from river inflows. In this paper we use the example of the Save River delta to assess the palaeogeographic distribution of mangrove wetlands and to analyze their dynamics. To track past occurrences of mangrove wetlands in the study area we have integrated sedimentological data with siliceous microfossil analysis combined with AMS radiocarbon and OSL dating. The results show a fine-grained deposit with an approximate thickness of 2 m, present at different sampling sites. In the upper deltaic plain, the deposit is interbedded between sand layers, while in the lower deltaic plain the deposit occupies the uppermost stratigraphic position. In most of the sampling sites the deposit shows a succession with brackish-marine diatoms in the bottom while the upper part shows only scattered occurrences Based on sedimentological and microfossil characteristics we have interpreted the layer to represent a mangrove wetland deposit. The development of the deposit in the study area is suggested to have been initiated around 3100 cal. yrs BP, induced by sea-level rise. Thereafter, the development followed the combined effect of a sea-level fall and delta progradation processes. In some areas, particularly in the proximal part of the delta, the mangrove deposit has developed progressively on top of the delta-front. From around 1300 years ago (OSL) onwards, massive alluvial sedimentation impacted the mangrove ecosystem. However, the retreat of mangrove wetland coincided with a regional fall of sea-level. At the edges of the alluvial deposit, the current mangrove ecosystem has reclaimed the habitat in some sectors where gully erosion has exposed the once extinct mangrove habitat.

Keyword [en]
Delta progradation, mangrove wetland, mangrove degradation, Save River delta, biogeomophology, palaeoenvironmental reconstruction
National Category
Earth and Related Environmental Sciences
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-126061OAI: oai:DiVA.org:su-126061DiVA: diva2:897083
Funder
Sida - Swedish International Development Cooperation Agency, 2011-002102
Available from: 2016-01-24 Created: 2016-01-24 Last updated: 2016-01-28Bibliographically approved
In thesis
1. Geomorphology and environmental dynamics in Save River delta, Mozambique: A cross-timescale perspective
Open this publication in new window or tab >>Geomorphology and environmental dynamics in Save River delta, Mozambique: A cross-timescale perspective
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Long-term perspectives on the evolution of river deltas have provided useful knowledge capable of responding to pending questions related to the ongoing climate and environmental changes. Increasing utilization pressure on delta environments has necessitated increased attention to protect the socio-economic and ecological values. As a result, multiple local initiatives have been designed, aimed at mitigating environmental deterioration and implementing adaptive measures, but many such initiatives have shown limited success. This thesis uses a case study of Save River delta in Mozambique to explore the relation between geomorphological evolution and socio-ecological system dynamics in delta environments. In addition, key environmental variables that concern the society today are highlighted and discussed in a management perspective. The results of the study show the development of Save River delta from the mid-Holocene to the present. The geomorphological settings of the delta suggest a faulted coastline over which subsequent deposition of fluvial sediments has formed a protruding delta front. Between c. 3000 and 1300 years ago, fine-grained sediments accumulated on top of the delta-front in the proximal part of the delta. This type of material was deposited under intertidal conditions and supported the formation of mangrove habitat. The geographical distribution of the mangrove deposit was driven by successive stages of back-barrier swamp formation and sea-level change as the delta evolved. From c. 1300 years ago, the river delta started to receive fluvial sediments from pulses of floods forming an alluvial floodplain. These sediments have accumulated mainly on the fine-grained mangrove wetland deposit. All the geomorphological features have evolved in a shoreward-shifting pattern over time. Centennial to decadal changes observed in the delta have followed a predictable geomorphological pattern, which is also part of the millennial evolution. The mangrove system, the base for the socio-economic system, is consequently strongly affected by the geomorphological development of the area. An increasing sensitivity of socio-ecological systems to environmental stressors, e.g. floods, cyclones and erosion, has motivated multiple initiatives to work towards a sustainable management of delta environments. This thesis highlights the need for interplay between geomorphology and ecology, considering both long- and short-term dynamics of delta environments. Hitherto, management initiatives have been concentrated on fragmented interventions of controlling water flow, which have disrupted the natural dynamics by obstructing the sedimentation-erosion cycle. To change this trend, coastal planners need to consider the significance of natural processes, e.g. cyclones, floods, erosion and accretion, for the long-term ecological and social sustainability of delta environments.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography, Stockholm University, 2016. 35 p.
Series
Dissertations from the Department of Physical Geography, ISSN 1653-7211 ; 53
Series
, Dissertations from the Department of Physical Geography, ISSN 1653-7211 ; No 53
Keyword
Save River delta, deltaic wetlands, biogeomorphology, climate change, landscape evolution, coastal management, socio-ecological systems
National Category
Physical Geography Geology
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-126064 (URN)978-91-7649-311-3 (ISBN)
Public defence
2016-03-11, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Sida - Swedish International Development Cooperation Agency, Decision No. 2011-002102
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2. Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2016-02-17 Created: 2016-01-24 Last updated: 2016-02-08Bibliographically approved

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Massuanganhe, ElidioBerntsson, AnnikaRisberg, JanWesterberg, Lars-OvePreusser, FrankBjursäter, Stefan
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