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Geomorphology and environmental dynamics in Save River delta, Mozambique: A cross-timescale perspective
Stockholm University, Faculty of Science, Department of Physical Geography. Universidade Eduardo Mondlane. (Geomorphology and Gaciology)ORCID iD: 0000-0001-5649-6998
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 [en]
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: urn:nbn:se:su:diva-126064ISBN: 978-91-7649-311-3 (print)OAI: oai:DiVA.org:su-126064DiVA: diva2:897089
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: 2017-02-23Bibliographically approved
List of papers
1. Geomorphology and landscape evolution of Save River delta, South-central Mozambique
Open this publication in new window or tab >>Geomorphology and landscape evolution of Save River delta, South-central Mozambique
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(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

The Save River delta has well-preserved geomorphological and sedimentological features with potential to reveal its evolution as well as past regional environmental changes, which are anticipated to integrate into other data at a global scale. In this study we mapped and integrated these features to understand the environmental processes that drove the late evolution of the delta. The results suggest that the present configuration of the delta was primarily dominated by a delta-front protruding into the sea, in a faulted coast section that may have favoured the formation of the depocenter. The development of the delta-front was initiated prior to c. 3100 cal. yrs BP, and around this age, fine-grained sediments started to accumulate on it forming a mangrove wetland deposit that expanded from the proximal sector of the delta to the current position shown in a geomorphological map. The results show successive dune ridges in the southern sector of the delta which indicate a series of consecutive shorelines over time as the delta prograded towards the current position. These dunes have created favourable conditions for accumulation of fine-grained sediments in the back-barrier sectors, contributing to the development of the mangrove wetland. An alluvial floodplain developed during the last millennium, probably a result of high precipitation the catchment area.

Keyword
Delta evolution, Save River delta, mangrove wetland, delta progradation, Mozambique coast, coastal dunes
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-126049 (URN)
Available from: 2016-01-24 Created: 2016-01-24 Last updated: 2016-01-28Bibliographically approved
2. Palaeogeography and dynamics of the deltaic wetland of Save River, Mozambique
Open this publication in new window or tab >>Palaeogeography and dynamics of the deltaic wetland of Save River, Mozambique
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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
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:nbn:se:su:diva-126061 (URN)
Funder
Sida - Swedish International Development Cooperation Agency, 2011-002102
Available from: 2016-01-24 Created: 2016-01-24 Last updated: 2016-01-28Bibliographically approved
3. Morphodynamics of deltaic wetlands and implications for coastal ecosystems: A case study of Save River Delta, Mozambique
Open this publication in new window or tab >>Morphodynamics of deltaic wetlands and implications for coastal ecosystems: A case study of Save River Delta, Mozambique
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Deltaic wetlands experience changes over time with substantial impacts on the coastal ecosystems. These changes, either they are natural or human induced, are caused by multiple factors through complex links and interdependences, and constitute challenges for coastal management aiming to set up practical adaptation measures. In this study, we apply a case study of Save River Delta to interpret the typical morphodynamic pattern on the deltaic plain over an interdecadal timescale and the implications for the coastal ecosystems, with emphasis on mangrove. Our results indicate a pattern of the geomorphological changes on the deltaic wetland in river and back-barrier sectors. In both sectors, erosion and accretion are reflexive processes resulting in geomorphological settings characterized by a distinctive interaction with the ecosystem; on the one hand, mangrove trees colonize new favorable settings; on the other hand, the existing mangrove trees undergo degradation related to the morphodynamic processes. Notwithstanding current episodic events that affect the deltaic wetlands (e.g. cyclones and floods), the changes observed in the study area are part of interdecadal timescale morphodynamics. These changes were consistent for the 50 years’ time period analyzed. If on the one hand some of the episodic and high magnitude weather events such as floods undermine the status of the deltaic ecosystem, on the other hand these events contribute to develop the same ecosystem in a wider timescale.

Keyword
Coastal wetlands, biogeomorphology, delta plain, Save River delta, climate change, mangrove, succession, Mozambique
National Category
Earth and Related Environmental Sciences
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-126052 (URN)
Funder
Sida - Swedish International Development Cooperation Agency, 2011-002102
Available from: 2016-01-24 Created: 2016-01-24 Last updated: 2016-01-28Bibliographically approved
4. Mangrove’s response to cyclone Eline (2000): what’s happening 14 years late
Open this publication in new window or tab >>Mangrove’s response to cyclone Eline (2000): what’s happening 14 years late
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(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-126053 (URN)
Available from: 2016-01-24 Created: 2016-01-24 Last updated: 2016-01-28Bibliographically approved
5. Deltaic coasts under climate-related catastrophic events - Insights from the Save River delta, Mozambique
Open this publication in new window or tab >>Deltaic coasts under climate-related catastrophic events - Insights from the Save River delta, Mozambique
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2015 (English)In: Ocean and Coastal Management, ISSN 0964-5691, E-ISSN 1873-524X, Vol. 116, 331-340 p.Article in journal (Refereed) Published
Abstract [en]

The deltaic coast of the Save River is characterized by mangrove wetland, one of the most important coastal ecosystems in Mozambique. This ecosystem provides direct services to the neighbouring communities and contributes to the productivity of the marine ecosystem. This region has, however, been hit by recurrent catastrophic events that have caused negative impacts on the ecosystem and in people's lives, posing challenges for its management. In this article we use this area as a case study to structure and propose an interactive and integrated approach for coastal zone management under recurrent climate-related catastrophic events. Our results show a need for systematic interaction between the decision makers (at the different levels) and the communities to set up adaptive measures for climate-related events. Also, we noticed that the presence of the neighbouring communities is a factor to capitalize on the adaptation activities by maximizing their participation as active actors in the process. Therefore, we conclude that a continuous process of adaptation and preparedness to climate-related catastrophic events (focused on both social and ecological systems) constitutes a leverage variable to be used for sustainable management of the coastal zones.

Keyword
Climate change, Adaptation, Coastal management, Cyclones, Sustainability
National Category
Earth and Related Environmental Sciences
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-123779 (URN)10.1016/j.ocecoaman.2015.08.008 (DOI)000364436700033 ()
Available from: 2015-12-23 Created: 2015-12-07 Last updated: 2017-12-01Bibliographically approved

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