1.4 Coastal lake formation
9 min read•august 20, 2024
Coastal lakes form at the intersection of land and sea through various geological processes. Understanding their origins is crucial for predicting their characteristics and behavior. Factors like glacial activity, sea level changes, and coastal geomorphology play key roles in shaping these unique water bodies.
These lakes can be classified based on their geomorphology, hydrology, and connection to the sea. From lagoons and fjords to estuarine lakes, each type has distinct features and ecological communities. Studying these differences helps inform management and conservation efforts for these vital ecosystems.
Coastal lake origins
- Coastal lakes form through various geological processes at the interface between land and sea
- Understanding the origins of coastal lakes is crucial for predicting their hydrological and ecological characteristics
- The formation of coastal lakes is influenced by factors such as glacial activity, sea level fluctuations, and coastal geomorphology
Glacial processes in formation
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- Glacial scouring during ice ages carved out depressions in the landscape that later filled with water to form lakes
- Melting glaciers deposited sediments (moraines) that can dam water and create lakes
- Isostatic rebound after glacial retreat caused land uplift and isolation of water bodies from the sea
- Examples of glacial lakes include the Great Lakes in North America and lakes in Scandinavia
Sea level changes and isolation
- Rising sea levels during interglacial periods can flood low-lying coastal areas and create shallow lakes
- Conversely, falling sea levels can isolate water bodies from the ocean, forming brackish or freshwater lakes
- Isolation can occur through the formation of sand bars or spits that separate the lake from the sea
- The Baltic Sea and the Black Sea are examples of large water bodies that have undergone isolation due to sea level changes
Coastal erosion and deposition
- Waves, currents, and tides can erode coastlines and transport sediments, reshaping the coastal landscape
- Longshore drift can deposit sediments and form barrier islands or spits that enclose water bodies, creating lagoons or coastal lakes
- Coastal dunes can also block the flow of water and create lakes in the space between the dunes and the shoreline
- Examples include the coastal lakes of the Gulf Coast of the United States and the lakes along the Baltic Sea coast
Types of coastal lakes
- Coastal lakes can be classified based on their geomorphology, hydrological characteristics, and connection to the sea
- Different types of coastal lakes have distinct features and ecological communities
- Understanding the types of coastal lakes is important for their management and conservation
Lagoons and barrier island lakes
- Lagoons are shallow, elongated water bodies separated from the ocean by barrier islands or sand spits
- They have limited exchange with the sea through narrow inlets or channels
- Barrier island lakes form when sand deposits completely isolate a water body from the ocean
- These lakes are characterized by low and high variability in water levels
- Examples include the Laguna Madre in Texas and the Vistula Lagoon between Poland and Russia
Fjords and fjord-type lakes
- Fjords are deep, narrow, and elongated coastal inlets carved by glacial
- They have a distinct sill at the mouth that restricts water exchange with the ocean
- Fjord-type lakes are former fjords that have been isolated from the sea due to land uplift or
- These lakes often have deep basins, steep sides, and a layer of freshwater overlying saltwater
- Examples include the fjords of Norway and Chile, and the fjord-type lakes of New Zealand and Canada
Estuarine lakes and tidal basins
- Estuarine lakes are coastal water bodies that have a significant input of freshwater from rivers and a connection to the sea
- They experience tidal influences and have a gradient of salinity from freshwater to seawater
- Tidal basins are shallow, enclosed water bodies that are regularly flooded by tides
- These lakes support unique estuarine habitats and species adapted to varying salinity and water levels
- Examples include Lake Pontchartrain in Louisiana and the Wadden Sea along the North Sea coast
Hydrological characteristics
- The hydrological characteristics of coastal lakes are influenced by their water sources, exchange with the sea, and climate
- Understanding the hydrology of coastal lakes is crucial for managing water resources and predicting ecosystem responses
- Coastal lakes exhibit a wide range of hydrological conditions, from freshwater to hypersaline
Freshwater vs brackish water
- Coastal lakes can be classified as freshwater or brackish depending on their salinity levels
- Freshwater coastal lakes have low salinity (<0.5 ppt) and are mainly fed by precipitation, groundwater, and surface runoff
- Brackish coastal lakes have higher salinity (0.5-30 ppt) due to a greater influence of seawater input
- The salinity of coastal lakes can vary seasonally and spatially, creating distinct habitats for aquatic organisms
- Examples of freshwater coastal lakes include Lake Mývatn in Iceland and Lake Skadar in Albania and Montenegro
Water balance and exchange
- The water balance of coastal lakes is determined by the inputs (precipitation, surface , groundwater) and outputs (evaporation, surface outflow, groundwater seepage)
- Water exchange with the sea can occur through tidal inlets, subsurface seepage, or occasional breaching of barrier islands
- The degree of water exchange affects the residence time, salinity, and nutrient dynamics of coastal lakes
- Coastal lakes with limited water exchange are more susceptible to eutrophication and hypoxia
- Examples of coastal lakes with different water exchange patterns include Lake Ichkeul in Tunisia and Lake Chilika in India
Stratification and mixing patterns
- Coastal lakes can develop vertical stratification due to differences in temperature, salinity, or density
- Stratification can be seasonal (thermocline) or persistent (halocline) depending on the lake's characteristics and climate
- Mixing patterns in coastal lakes are influenced by wind, tides, and freshwater inflow
- Complete mixing (polymictic) occurs in shallow lakes, while partial mixing (meromictic) is common in deep, saline lakes
- Stratification and mixing affect the distribution of nutrients, oxygen, and organisms in the water column
- Examples of stratified coastal lakes include Lake Mogilnoe in Russia and Lake Faro in Italy
Ecological features
- Coastal lakes support diverse and productive ecosystems due to their unique hydrological and geomorphological characteristics
- The ecological features of coastal lakes are influenced by factors such as salinity, , and nutrient availability
- Understanding the ecology of coastal lakes is essential for their conservation and management
Productivity and trophic status
- Coastal lakes can be highly productive due to the input of nutrients from both terrestrial and marine sources
- The trophic status of coastal lakes ranges from oligotrophic (low productivity) to eutrophic (high productivity)
- Eutrophic coastal lakes are characterized by high nutrient levels, algal blooms, and low water transparency
- Primary productivity in coastal lakes is driven by phytoplankton, benthic algae, and aquatic macrophytes
- The productivity of coastal lakes supports diverse food webs and fisheries
- Examples of productive coastal lakes include Lake Nakaumi in Japan and Lake Vistonis in Greece
Aquatic vegetation and habitats
- Coastal lakes support a variety of aquatic vegetation, including submerged, floating, and emergent plants
- The distribution and composition of aquatic vegetation are influenced by salinity, water depth, and substrate type
- Submerged aquatic vegetation (seagrasses) provides important habitats for fish and invertebrates
- Emergent vegetation (reeds, rushes) stabilizes shorelines and provides nesting sites for waterbirds
- Coastal lakes also have unique habitats such as salt marshes, mudflats, and sandy beaches
- Examples of coastal lakes with diverse aquatic vegetation include Lake Albufera in Spain and Lake Sibayi in South Africa
Fish and invertebrate communities
- Coastal lakes support diverse fish and invertebrate communities adapted to varying salinity and hydrological conditions
- Fish species in coastal lakes include both freshwater and marine species, as well as estuarine specialists
- Invertebrate communities in coastal lakes include mollusks, crustaceans, and aquatic insects
- The composition and abundance of fish and invertebrates are influenced by factors such as salinity, water temperature, and dissolved oxygen
- Coastal lakes serve as important nursery and feeding grounds for commercially important fish species
- Examples of coastal lakes with notable fish and invertebrate communities include Lake Nokoué in Benin and Lake Timsah in Egypt
Human impacts on coastal lakes
- Coastal lakes are increasingly threatened by human activities and global environmental changes
- Understanding the human impacts on coastal lakes is crucial for developing effective management and conservation strategies
- The main human impacts on coastal lakes include eutrophication, pollution, shoreline development, and climate change
Eutrophication and pollution
- Coastal lakes are susceptible to eutrophication due to excessive input of nutrients from agricultural runoff, sewage discharge, and atmospheric deposition
- Eutrophication leads to algal blooms, oxygen depletion, and loss of biodiversity
- Pollution from industrial effluents, pesticides, and heavy metals can accumulate in coastal lake sediments and biota
- Microplastic pollution is an emerging threat to coastal lake ecosystems and food webs
- Examples of coastal lakes affected by eutrophication and pollution include Lake Mariout in Egypt and Lake Taihu in China
Shoreline development and modification
- Coastal lakes are often subject to intense shoreline development for urbanization, tourism, and recreational activities
- Shoreline modifications such as dredging, filling, and hardening can alter the hydrological and sedimentary processes of coastal lakes
- Loss of natural shoreline habitats (wetlands, beaches) can impact the biodiversity and ecological functions of coastal lakes
- Coastal infrastructure can also impede the migration and spawning of fish and other aquatic organisms
- Examples of coastal lakes affected by shoreline development include Lake Qarun in Egypt and Lake Illawarra in Australia
Climate change effects on hydrology
- Climate change can have significant impacts on the hydrology and ecology of coastal lakes
- Rising sea levels can increase the salinity and inundation of coastal lakes, altering their water balance and biotic communities
- Changes in precipitation patterns can affect the freshwater input and water level fluctuations of coastal lakes
- Warming water temperatures can lead to shifts in species distributions, phenology, and ecosystem metabolism
- Ocean acidification can impact the calcifying organisms and food webs of coastal lakes
- Examples of coastal lakes vulnerable to climate change effects include Lake Ichkeul in Tunisia and the Coorong in Australia
Management and conservation
- Effective management and conservation of coastal lakes require a holistic approach that addresses the multiple stressors and stakeholders involved
- Monitoring and assessment of water quality, biodiversity, and ecosystem health are essential for informed decision-making
- Restoration and protection strategies aim to mitigate human impacts and enhance the resilience of coastal lake ecosystems
Water quality monitoring and assessment
- Regular monitoring of water quality parameters (nutrients, salinity, dissolved oxygen) is crucial for detecting and managing eutrophication and pollution
- Assessment of sediment quality can provide insights into the long-term impacts of human activities on coastal lakes
- Biological indicators (phytoplankton, macroinvertebrates, fish) can be used to assess the ecological status of coastal lakes
- Remote sensing and modeling tools can help monitor and predict changes in coastal lake water quality and hydrology
- Examples of coastal lake monitoring programs include the Laguna Lake Development Authority in the Philippines and the Coastal Lakes Monitoring Program in Australia
Restoration and protection strategies
- Restoration of coastal lakes may involve measures such as nutrient load reduction, sediment remediation, and shoreline rehabilitation
- Establishment of protected areas and buffer zones can help preserve the natural habitats and biodiversity of coastal lakes
- Sustainable land use practices in the catchment area can reduce the input of nutrients and pollutants into coastal lakes
- Engaging local communities and stakeholders in the management and conservation of coastal lakes can promote stewardship and sustainable use
- Examples of coastal lake restoration projects include the Chilika Lake Restoration Project in India and the Lake Manzala Engineered Wetlands in Egypt
Balancing human use and ecosystem health
- Coastal lakes provide important ecosystem services such as water supply, fisheries, and recreation, but these uses must be balanced with the maintenance of ecosystem health
- Integrated coastal zone management (ICZM) can help coordinate the multiple uses and stakeholders of coastal lakes
- Sustainable fisheries management, including catch limits and gear restrictions, can help maintain the productivity and diversity of coastal lake fisheries
- Ecotourism and environmental education can promote public awareness and support for coastal lake conservation
- Adaptive management approaches can help coastal lake managers respond to changing environmental and social conditions
- Examples of coastal lakes where human use and ecosystem health are being balanced include Lake Chilwa in Malawi and Lake Gippsland in Australia
Key Terms to Review (18)
A. J. McMahon: A. J. McMahon is known for his significant contributions to the understanding of coastal lake formation, particularly through his research on how environmental factors and geological processes shape these unique ecosystems. His work emphasizes the interplay between freshwater and marine environments, and how this interaction influences the biological diversity and water chemistry of coastal lakes. McMahon’s studies have helped establish foundational concepts that inform current limnological research.
Bar-built lakes: Bar-built lakes are coastal lakes that form when a barrier, usually a sandbar or barrier island, separates a body of water from the ocean or another larger water body. These lakes often develop in areas where sediment deposition occurs, creating a natural dam that traps water and leads to the formation of a lake behind it. Their unique characteristics are shaped by their proximity to coastal processes, making them significant for understanding coastal ecosystems and hydrology.
Brackish Water: Brackish water is a type of water that has a higher salinity than freshwater but lower salinity than seawater. It typically forms in areas where freshwater from rivers and streams mixes with saltwater from oceans or seas, leading to unique ecological characteristics. This transitional water environment supports diverse biological communities and plays a crucial role in coastal ecosystems, particularly in the formation of coastal lakes.
Drowned River Valleys: Drowned river valleys are coastal landforms that occur when rising sea levels inundate river valleys, causing the land to be submerged and creating estuarine environments. This process typically occurs as a result of glacial melting or tectonic activity, leading to a rise in sea levels that fills the valleys with seawater. These unique environments often host a mix of freshwater and saltwater, contributing to rich biodiversity and complex ecosystems.
Erosion: Erosion is the process of wearing away and removing soil and rock material from one location and transporting it to another. This natural process can be influenced by various factors such as water flow, wind, ice, and human activities. Erosion plays a significant role in shaping landscapes, affecting sediment transport and deposition, and influencing the formation of coastal lakes, as well as impacting the analysis of sediments through coring techniques and geochemical indicators.
Estuarine Dynamics: Estuarine dynamics refers to the complex physical, chemical, and biological interactions occurring in estuaries, where freshwater from rivers meets and mixes with saltwater from the ocean. These interactions play a crucial role in shaping the estuarine ecosystem, influencing nutrient cycling, sediment transport, and habitat availability for various species. The dynamics are heavily influenced by factors such as tides, river flow, and seasonal changes, which can alter salinity gradients and water movement within these unique environments.
Eutrophication Control: Eutrophication control refers to the management practices aimed at reducing nutrient pollution, particularly nitrogen and phosphorus, that leads to excessive growth of algae in aquatic systems. Effective eutrophication control is crucial for maintaining water quality and ensuring the health of coastal ecosystems, which can be disrupted by algal blooms, hypoxia, and loss of biodiversity. By addressing the sources of nutrient loading, eutrophication control helps protect coastal lakes from degradation and promotes the sustainability of these vital freshwater resources.
H. J. H. D. Blumberg: H. J. H. D. Blumberg is a prominent figure in limnology, known for his contributions to understanding coastal lake formation and the ecological dynamics of these environments. His work often emphasizes the interplay between geological processes and biological communities, highlighting how coastal lakes serve as unique ecosystems that reflect both freshwater and marine influences.
Habitat Diversity: Habitat diversity refers to the variety of different environments in a given area that support a wide range of species and ecological processes. High habitat diversity leads to increased biodiversity, as different species are adapted to thrive in specific conditions, while also providing various ecosystem services essential for the health of ecosystems. This concept is crucial for understanding how different habitats, particularly coastal areas, can influence the distribution and abundance of aquatic life.
Inflow: Inflow refers to the movement of water into a body of water, such as lakes, rivers, or coastal systems. This process plays a crucial role in determining the water balance, influencing nutrient dynamics, and affecting the ecological health of these aquatic environments. Understanding inflow is essential for assessing how freshwater inputs can shape the characteristics and functioning of both coastal lakes and the overall flushing rates in various water bodies.
Littoral zone: The littoral zone is the nearshore area of a lake or coastal body of water that is shallow enough to support aquatic plant life and is often characterized by its rich biodiversity. This zone extends from the high water mark, which is rarely inundated, to the edge of the water where light penetration allows for photosynthesis, making it vital for many aquatic organisms. Understanding this zone is important because it plays a crucial role in lake zonation, influences coastal lake formation, and possesses a unique structural complexity.
Morphology: Morphology is the study of the form and structure of organisms, including their shapes, sizes, and arrangements. In the context of coastal lake formation, understanding morphology is essential as it helps in analyzing how the physical characteristics of a lake can influence its hydrology, ecology, and overall function. The morphology of coastal lakes is shaped by various factors such as sediment deposition, erosion, and the interactions with surrounding landforms and water bodies.
Nutrient Cycling: Nutrient cycling refers to the movement and exchange of organic and inorganic matter back into the production of living matter. It is a fundamental ecological process that ensures the availability of essential nutrients for organisms, maintaining ecosystem productivity and health.
Outflow Dynamics: Outflow dynamics refers to the processes and factors that influence the movement of water from a water body, such as a coastal lake, to adjacent environments, such as rivers, wetlands, or the ocean. These dynamics can affect water quality, sediment transport, and ecological interactions within and around the lake. Understanding outflow dynamics is crucial for managing coastal lake ecosystems and their responses to environmental changes.
Salinity: Salinity refers to the concentration of salts in water, typically expressed in parts per thousand (ppt) or practical salinity units (PSU). It is a crucial factor influencing the physical and chemical properties of aquatic systems, affecting everything from water density and circulation patterns to biological processes such as nutrient availability and organism distribution.
Sedimentation: Sedimentation is the process through which particles settle out of a fluid, forming layers of sediment over time. This natural phenomenon plays a crucial role in shaping landscapes and ecosystems, influencing water quality and nutrient cycles in aquatic environments, as well as contributing to coastal lake formation and the movement of nutrients like phosphorus.
Water Level Fluctuations: Water level fluctuations refer to the changes in the height of water in lakes, rivers, and coastal areas over time. These changes can be caused by a variety of factors including precipitation, evaporation, wind, and human activities like dam operations. Understanding these fluctuations is crucial for managing ecosystems and maintaining the health of coastal lakes, as they can significantly influence salinity levels, habitat availability, and overall water quality.
Wetland Restoration: Wetland restoration is the process of returning a degraded or altered wetland to its natural state, enhancing its ecological functions and biodiversity. This practice is crucial for improving water quality, providing habitat for wildlife, and mitigating flooding. It connects deeply with coastal lake formation, where wetlands can stabilize shorelines and influence water quality; restoration ecology, which focuses on repairing ecosystems; and the littoral zone structure, where wetlands contribute to the overall health of aquatic ecosystems.