7.2 Coastal processes and estuarine environments
4 min read•august 7, 2024
Coastal processes shape our shorelines, creating diverse landforms and ecosystems. From to , these dynamic environments are constantly changing due to waves, tides, and . Understanding these processes is crucial for managing coastal areas and protecting them from erosion and .
Coastal ecosystems are incredibly productive, supporting rich biodiversity and providing valuable services to humans. Estuaries, salt marshes, and mangroves act as nurseries for marine life, filter pollutants, and protect shorelines from storms. However, these ecosystems face threats from human activities and climate change, making conservation efforts essential.
Coastal Processes
Sediment Transport and Erosion
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- moves sediment along the coast parallel to the shoreline due to waves approaching at an angle, resulting in the gradual migration of sediment and reshaping of coastlines over time
- Wave action erodes and transports sediment, particularly during storm events, leading to changes in beach profiles and coastal morphology (formation of cliffs, sea stacks, and sea arches)
- Beach erosion occurs when the rate of sediment removal exceeds the rate of sediment deposition, often exacerbated by human activities such as coastal development, dam construction, and sea-level rise
- brings cold, nutrient-rich water from deeper ocean layers to the surface near the coast, driven by wind patterns and Ekman transport, supporting highly productive marine ecosystems (Peruvian upwelling system)
Tidal Influences
- Tides are the regular rise and fall of sea level caused by the gravitational pull of the moon and sun, with two high tides and two low tides occurring approximately every 24 hours and 50 minutes
- , the difference between high and low tide, varies depending on the location and the alignment of the moon and sun (spring tides during full and new moons, neap tides during quarter moons)
- Tidal currents transport sediment and nutrients, influencing coastal geomorphology and the distribution of marine organisms (intertidal zones)
- Tidal forces also affect the mixing and circulation patterns in estuaries and coastal waters, impacting salinity gradients, nutrient dynamics, and the distribution of marine life (tidal marshes, mangrove forests)
Coastal Landforms
Barrier Islands and Spits
- Barrier islands are elongated, narrow landforms that run parallel to the coast, separated from the mainland by a lagoon or bay, formed by the accumulation of sediment through longshore drift and wave action (Outer Banks of North Carolina)
- Barrier islands protect the mainland coast from storm surges and wave energy, providing a buffer against and flooding
- are similar to barrier islands but are attached to the mainland at one end, formed by longshore drift and the deposition of sediment in the direction of the prevailing current (Farewell Spit, New Zealand)
- Both barrier islands and spits are dynamic landforms that can migrate, erode, or accrete over time in response to changes in sea level, sediment supply, and storm events
Estuaries and Coastal Wetlands
- Estuaries are partially enclosed coastal bodies of water where freshwater from rivers and streams mixes with saltwater from the ocean, creating unique brackish water environments (Chesapeake Bay, San Francisco Bay)
- Estuaries are highly productive ecosystems, serving as nursery grounds for many marine species and supporting diverse plant and animal communities adapted to the varying salinity and tidal conditions
- Salt marshes are coastal wetlands that develop in the intertidal zones of estuaries and bays, characterized by salt-tolerant vegetation (cordgrass, pickleweed) that traps sediment and provides habitat for numerous species (birds, fish, crustaceans)
- Mangroves are tropical and subtropical coastal wetlands dominated by salt-tolerant trees and shrubs with complex root systems that stabilize sediment, protect shorelines from erosion, and provide critical habitat for marine life (Caribbean, Southeast Asia)
Coastal Ecosystems
Productivity and Nutrient Dynamics
- Coastal ecosystems, including estuaries, salt marshes, and mangroves, are among the most productive ecosystems on Earth due to the abundant supply of nutrients from both terrestrial and marine sources
- Nutrient inputs from rivers, coastal upwelling, and tidal mixing support high primary productivity by phytoplankton and aquatic vegetation, forming the base of complex food webs that sustain diverse marine life
- , the excessive enrichment of coastal waters with nutrients (nitrogen and phosphorus) from human activities such as agricultural runoff and sewage discharge, can lead to algal blooms, oxygen depletion, and the degradation of coastal habitats (Gulf of Mexico dead zone)
- Coastal wetlands, particularly salt marshes and mangroves, play a crucial role in , acting as natural filters that trap and process excess nutrients, sediments, and pollutants, thereby improving water quality and protecting adjacent marine ecosystems
Ecosystem Services and Conservation
- Coastal ecosystems provide numerous valuable services to human society, including shoreline protection, carbon sequestration, water purification, and recreational opportunities (fishing, birdwatching, ecotourism)
- Salt marshes and mangroves act as natural buffers against coastal erosion, storm surges, and sea-level rise, dissipating wave energy and stabilizing shorelines, thus reducing the vulnerability of coastal communities to natural hazards
- These ecosystems also serve as important carbon sinks, sequestering atmospheric carbon dioxide through high rates of primary productivity and the accumulation of organic matter in sediments (blue carbon)
- However, coastal ecosystems face numerous threats, including habitat destruction, , overfishing, and climate change-induced stressors such as sea-level rise, ocean acidification, and increased storm intensity
- Conservation and restoration efforts, such as the creation of marine protected areas, the rehabilitation of degraded wetlands, and the implementation of sustainable coastal management practices, are crucial for maintaining the health and resilience of coastal ecosystems and the services they provide
Key Terms to Review (22)
Barrier islands: Barrier islands are long, narrow landforms that run parallel to the mainland coast, primarily composed of sand and sediment. They serve as natural shields, protecting the coastline from the impact of waves, storm surges, and tidal forces, while also providing unique habitats for various species and recreational areas for human use.
Coastal erosion: Coastal erosion is the process where coastlines are eroded or worn away by the forces of waves, currents, tides, and human activities. This natural phenomenon can lead to significant changes in coastal landscapes, impacting ecosystems, human settlements, and infrastructure. Understanding coastal erosion is crucial because it can be exacerbated by events like tsunamis and is influenced by various coastal processes and the dynamics of estuarine environments.
Coastal upwelling: Coastal upwelling is the process where deep, cold, nutrient-rich water rises to the surface along coastlines, typically driven by wind patterns and ocean currents. This phenomenon plays a crucial role in enhancing productivity in marine ecosystems, particularly in areas where it occurs regularly, such as along the western coasts of continents. The influx of nutrients from the depths supports a rich diversity of marine life and has significant implications for fisheries and coastal economies.
Deltas: Deltas are landforms created at the mouth of a river where it meets a body of water, such as an ocean or a lake. They are formed through the deposition of sediment carried by the river as the flow velocity decreases upon entering the standing water, allowing materials to settle. Deltas are characterized by their unique triangular or fan-shaped structure and play a crucial role in coastal processes and estuarine environments.
Estuaries: Estuaries are coastal bodies of water where freshwater from rivers and streams meets and mixes with saltwater from the ocean. These unique environments are characterized by their rich biodiversity and serve as crucial habitats for various species, playing an important role in coastal processes and nutrient cycling.
Eutrophication: Eutrophication is the process by which a body of water becomes overly enriched with nutrients, often leading to excessive growth of algae and other aquatic plants. This phenomenon can result in decreased oxygen levels in the water, harming aquatic life and disrupting ecosystems. It connects to several environmental aspects, including nutrient cycling, water quality management, and ecosystem health.
Habitat loss: Habitat loss refers to the process by which natural habitats are rendered unusable for the organisms that live there, often due to human activities. This phenomenon significantly impacts biodiversity, as it leads to decreased population sizes and species extinction. The causes of habitat loss can vary, including urban development, agricultural expansion, pollution, and climate change, all of which threaten ecosystems and the services they provide.
Integrated Coastal Zone Management: Integrated coastal zone management (ICZM) is a process that promotes a sustainable and coordinated approach to managing coastal resources, balancing environmental, economic, and social objectives. It aims to address the complex interactions between coastal ecosystems and human activities while considering the needs of various stakeholders. By integrating scientific research, policy-making, and community involvement, ICZM strives to protect coastal environments and ensure sustainable development.
Longshore drift: Longshore drift is the process by which sediment is transported along a coastline parallel to the shore, primarily due to the action of waves hitting the beach at an angle. This movement is influenced by the prevailing wind direction and wave patterns, resulting in a gradual shift of sand and other materials along the shoreline. This phenomenon plays a crucial role in shaping coastal landscapes and affecting sediment deposition in estuarine environments.
Managed retreat: Managed retreat is a strategy used to address the impacts of coastal erosion and sea level rise by intentionally relocating human structures and communities away from vulnerable coastal areas. This approach is designed to reduce risk while allowing natural processes to restore coastal ecosystems, balancing human needs with environmental resilience. It involves careful planning and collaboration among stakeholders to ensure that the relocation process is sustainable and equitable.
Mangrove swamp: A mangrove swamp is a coastal ecosystem characterized by the presence of salt-tolerant trees known as mangroves, which thrive in intertidal zones where saltwater and freshwater mix. These unique ecosystems provide critical habitat for various species, stabilize coastlines, and play a vital role in nutrient cycling within coastal environments.
Nutrient Cycling: Nutrient cycling refers to the continuous movement and exchange of essential nutrients through various components of the ecosystem, including soil, water, air, and living organisms. This process is vital for maintaining ecosystem health, supporting plant growth, and ensuring the sustainability of food webs.
Paul S. F. G. L. de Boer: Paul S. F. G. L. de Boer is a notable researcher and academic known for his contributions to the understanding of coastal processes and estuarine environments. His work emphasizes the interaction between physical processes, biological responses, and human activities in coastal areas, providing insights that are crucial for managing and protecting these delicate ecosystems.
Pollution: Pollution is the introduction of harmful substances or products into the environment, leading to detrimental effects on ecosystems and human health. It can manifest in various forms, including chemical, physical, and biological contaminants, disrupting natural processes and causing imbalances in both coastal and freshwater environments. Understanding pollution is crucial for recognizing its impact on biodiversity, water quality, and the overall health of ecosystems.
Robert McLachlan: Robert McLachlan is a prominent figure in the field of coastal processes and estuarine environments, particularly known for his contributions to the understanding of sediment transport dynamics and hydrodynamics in these areas. His research has helped illuminate how physical processes in coastal regions impact ecosystems, human activities, and the management of these vital environments. McLachlan's work often emphasizes the interplay between natural phenomena and anthropogenic influences, making his insights invaluable for coastal science and environmental policy.
Salinity Gradient: A salinity gradient is the variation in salt concentration in water, typically observed in coastal and estuarine environments where freshwater from rivers meets saltwater from the ocean. This gradient plays a crucial role in determining the physical and biological characteristics of these environments, influencing factors like water density, circulation patterns, and habitat distribution for various aquatic species.
Salt marsh: A salt marsh is a coastal ecosystem characterized by the presence of salt-tolerant grasses, herbaceous plants, and various aquatic organisms. These unique habitats are typically found in the intertidal zones of estuaries, where freshwater from rivers mixes with saltwater from the ocean. Salt marshes play a critical role in coastal protection, water filtration, and providing habitat for diverse wildlife.
Sea-level rise: Sea-level rise refers to the increase in the average level of the Earth's oceans due to various factors, including climate change, melting ice sheets, and thermal expansion of seawater. This phenomenon is closely linked to coastal processes and estuarine environments as it influences coastal erosion, habitat loss, and the salinity of estuaries, ultimately affecting the ecosystems and human activities that depend on these regions.
Sediment Transport: Sediment transport refers to the movement of solid particles, such as sand, silt, and clay, from one location to another by the action of wind, water, or ice. This process is vital in shaping landscapes and ecosystems, as it affects soil composition and landform development. Through mechanisms like erosion, deposition, and resuspension, sediment transport plays a key role in the dynamics of coastal environments and river systems.
Spits: A spit is a coastal landform that consists of a narrow stretch of sand or gravel that extends from the shore into the water, often forming a hook-like shape at the end. Spits are formed by the process of longshore drift, where sediment is transported along the coastline by wave action and currents. They serve as important features in coastal processes, influencing sediment deposition and habitat creation in estuarine environments.
Tidal range: Tidal range is the vertical difference in water level between high tide and low tide at a specific location. This phenomenon is influenced by various factors, including the alignment of the Earth, moon, and sun, as well as the shape of the coastline and the presence of coastal features. Understanding tidal range is essential as it affects coastal processes, sediment transport, and estuarine environments, which are vital for ecosystem health and human activities.
Urbanization: Urbanization is the process by which an increasing percentage of a population comes to live in urban areas, resulting in the growth and expansion of cities. This phenomenon is often driven by factors such as economic opportunities, migration, and population growth, significantly impacting various environmental and social systems.