Geomorphology of Wetlands

• Geomorphology of Wetlands

Introduction

• Environmental change is a pressing global issue.
• Climate patterns, landforms, and landscapes must be studied.
• Geomorphology studies the origin and evolution of landforms such as mountains, valleys, rivers, wetlands, and estuaries.
• Wetlands provide ecosystem services that benefit human wellbeing.
• Understanding wetlands' structure, function, and potential changes is essential for environmental management.

Definition of Geomorphology

• Geomorphology is derived from the Greek words 'ge' (earth), 'morphe' (form), and 'logos' (discourse).

What Are Wetlands?

• Wetlands are transitional zones between terrestrial and aquatic environments.
• The ground is saturated or shallowly flooded, leading to oxygen-depleted soils.
• Wetland plants possess adaptations for oxygen transport to their roots.
• Wetlands are biologically diverse and productive ('ecological hotspots').
• Plant tissue in wetlands has low nutrients and palatability with the exception of mangrove environments.
• Variations in soil wetness lead to distinct vegetation zones.
• Wetlands store sediment and soils, both inorganic and organic.

Defining Wetlands

• Wetlands are areas inundated or saturated, supporting plants adapted to wet conditions.
• The Ramsar Convention provides a global framework for wetland conservation.
• This convention defines wetlands including lakes, rivers, aquifers, swamps, marshes, grasslands, peatlands, oases, estuaries, deltas, coastal areas, coral reefs and human-made sites.
• Other definitions of wetlands are narrower, and exclude underground features, offshore coastal features, open water bodies (rivers, lakes) and many human-made sites.

Geomorphology and Wetlands

• Understanding wetland formation and development is crucial for effective management.
• Hydrology is a key factor in wetland formation, affecting soil and vegetation.
• Geomorphological processes influence landscape characteristics and wetness.
• Focus should be on longer-term changes to account for regional and local hydrology.
• Geomorphology is important to consider because wetland structure and function, infrastructure stability and human activities will be affected or even threatened.

Importance of Geomorphology

• Geomorphology's contributions to wetland studies have been historically limited.
• Hydrologists and ecologists have focused on local, short-term processes.
• Geomorphologists have neglected wetlands due to classification difficulties.

Booklet Overview

• Booklet focuses on wetlands in a near-natural state.
• It provides insight into wetlands impacted by human activities.
• The booklet provides sources of additional information.

Key Point 1: Wetlands Shaped by Mass Movements

• Wetlands are shaped by geomorphological processes involving mass movements.
• These processes include tectonic activity, weathering, erosion, and deposition.
• Mass movement is primarily downwards (higher to lower), but can be upwards due to tectonic uplift.
• Wetlands form where water flow is concentrated or drainage is impeded.
• Tectonic subsidence can create depressions for major wetlands.
• Wetlands may form in depressions via bedrock scouring, landslides, tributary fans, and wind activity.
• Wetlands are considered in their wider landscape context.
• Landforms are classified as depositional or erosional.
• Most wetlands accumulate mass over time, forming thick sediment piles.

Key Point 2: Range of Landscape and Climate Settings

• Wetlands form in humid and dryland regions.
• Humid regions have abundant surface water (high precipitation, low evapotranspiration).
• Dryland regions have overall surface water deficits (low precipitation, high evapotranspiration).
• In drylands such as the Okavango, large wetlands exist due to river inflows and local factors.
• Factors include tectonic subsidence and ponding.
• Wetlands in drylands can be seasonal or ephemeral and expand and contract through the year.
• A universally-accepted wetland classification is lacking.
• Classifications are based on geomorphological and hydrological characteristics.
• Compared to humid region wetlands, dryland wetlands typically feature longer desiccation periods, channels that decrease in size downstream, higher chemical sedimentation, more frequent fires, and longer developmental timescales.

Key point 3: Wetland processes result from interactions to the earth system

• Wetland processes involve interactions between the atmosphere, hydrosphere, geosphere, and biosphere.
• Geomorphological and climatic factors provide the framework for these interactions.
• In the Okavango Delta, interactions result in tree-fringed islands with saline interiors.
• Islands concentrate salt compounds locally, act as stores for carbonates in inorganic forms.
• complex, subtle interactions characterise wetlands globally.
• In the northern hemisphere, beaver, growth of vegetation activities promote the formation of shallow lakes.
• These lakes regulate water flows, concentrate sediment, nutrients and organic matter.
• Overall, wetlands have strong influences on hydrological, sedimentary and biogeochemical cycles.

Key Point 4: Dynamic Nature of Wetlands

• Wetlands are naturally dynamic, changing in response to external conditions such as tectonic, geological, climatic, and sea-level changes.
• Extreme events cause changes to erosional and depositional patterns, impacting water distribution.
• Climate change drives changes over decades to millennia.
• Old channels, in places as Macquarie Marshes, Australia and Okavango Delta, Botswana are much larger than current channels.
• It demonstrates the climate-related changes in river inflows.
• Climate and sea-level changes can expand/contract wetland landscapes.
• Progressive river erosion or tectonic activity also drives wetland changes by processes such as subsidence, land uplift promoting and impeding their formation.

Key Point 5: Wetland Dynamics

• Wetlands are subject to changing ecological conditions or geomorphological adjustments.
• Vegetation succession and channel creation transform open water into woodlands.
• Sedimentation creates alluvial ridges, diverting water and leading to channel switching.
• Channel switching alters patterns in the Okavango Delta regarding fluctuations in flow.
• This flow is regulated by bank composition
• Flow diversions are also increased by hippo trails.

Key Point 6: Wetlands Are Archives of Past Change

• Wetlands contain histories of their development through landforms, sediments, and biological remains.
• Preserved river channels and wind-blown dunes provide insights into past climates.
• Biological matter provides details on past conditions.
• Geochronological techniques establish sediment deposition ages.
• Limited studies show long histories for Southern African dryland wetlands.

Key Point 7: Response to environmental change

• Environmental change includes increased coastal erosion, desiccation and gully development
• Changing Ecological conditions and geomorphological adjustments have some impact on wetlands
• Types of wetlands may be particularly vulnerable to dramatic and irreversible changes include those located in landscape positions that are particularly sensitive to sea level rise or located in marginal climatic settings where even small variations in rainfall or river inflow may lead to large wetland changes such as many wetlands in drylands or mountains.
• The physical structurer of some wetlands may function close to thresholds where changes in wetland slope may impact other wetland parameters

Key Point 8: Impact of human activities

• Loss due to land conversion. Includes: Agriculture, Grazing, Forestry and Urban Developments
• Drainage Modifications - Flow diversion, Channelization and Groundwater Abstraction activities also cause problems.
• The situation became even more intense through European Colonization in the “New World" and with development.
• Regulations - Various forms of legislation provide framework for environmental governance. (Ramsar Convention)

Key Point 9: Vulnerability and Buffering

• Increased magnitude/frequency of geohazards caused by climate change and human activity.
• Geohazards = flash floods, coastal storm surges, droughts/wildfires.
• Coastal wetlands provide key role in absorbing the action of storm surges, and inland wetlands can help in attenuating flood peaks through the downstream transfer of sediment.
• Wetland management is therefore important as a way to protect broader areas that are prone to extremes.

Key Point 10: Sustainable Use and Geomorphology

• Geomorphology helps enable the conservation, restoration, and construction/enhancement of wetlands to protect wetland delivery of ecosystem services.
• Ecosystem Services - contribute to human wellbeing. (Provisioning, Regulating, Supporting and Cutural Services)
• Active "Wise Management" as the method ensure preservation for future uses, by identifying between different ecosystem services.
• Geomorphological understanding is necessary for successful management.
• Integrated rural land management should be based on allowing natural geomorphological processes to operate where this is applicable.