6.4 Lakes, wetlands, and their ecological importance
6 min read•august 7, 2024
and are crucial components of freshwater systems, supporting diverse ecosystems and providing essential services. These water bodies form through various geological processes, developing unique characteristics that influence their ecology and function within the hydrologic cycle.
From regulating water quality to supporting biodiversity, lakes and wetlands play vital roles in Earth's ecosystems. They offer habitat for countless species, help control floods, and provide recreational opportunities, making their conservation critical for both environmental and human well-being.
Lake Characteristics and Processes
Lake Formation and Structure
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- Lakes form in depressions on Earth's surface that fill with water from precipitation, runoff, groundwater seepage, or melting glaciers
- Can be created by various geological processes such as glaciation (Great Lakes), tectonic activity (rift lakes like Lake Baikal), volcanic activity (crater lakes), or fluvial processes (oxbow lakes)
- Lake basins are typically divided into littoral zone (shallow, near-shore area), limnetic zone (open water area), and profundal zone (deep, bottom waters)
- Littoral zone supports rooted aquatic plants, diverse invertebrate communities, and fish spawning areas due to ample light penetration
- Limnetic zone is the main area of by phytoplankton, supporting zooplankton and fish populations
- Profundal zone is typically cold, dark, and nutrient-rich, supporting decomposers and bottom-dwelling organisms
Lake Stratification and Mixing
- Many lakes develop thermal stratification during summer months, with warm, less dense water (epilimnion) overlying cooler, denser water (hypolimnion), separated by a thermocline
- Stratification affects the distribution of dissolved oxygen, nutrients, and organisms throughout the water column
- In fall, surface waters cool and become denser, causing the lake to mix (turnover) and redistribute nutrients and oxygen
- In winter, some lakes develop inverse stratification, with colder, less dense water near the surface and warmer, denser water at the bottom
- Dimictic lakes mix twice per year (spring and fall), while monomictic lakes mix once (usually in winter), and polymictic lakes mix frequently throughout the year
- Meromictic lakes have a permanently stratified bottom layer (monimolimnion) that does not mix with the upper layers
Eutrophication and Water Quality
- is the process of nutrient enrichment in a lake, leading to increased primary production and potentially harmful algal blooms
- Can occur naturally over long time scales or be accelerated by human activities such as agricultural runoff, sewage discharge, or urban development
- Excess nutrients, particularly phosphorus and nitrogen, stimulate the growth of phytoplankton and aquatic plants
- As organic matter from algal blooms decomposes, it consumes dissolved oxygen, leading to hypoxic or anoxic conditions in the bottom waters
- Anoxia can cause fish kills, release of nutrients and toxins from sediments, and shifts in species composition towards more tolerant organisms
- Cultural eutrophication is a major threat to water quality and ecosystem health in many lakes worldwide (Lake Erie, Lake Taihu)
Wetland Ecology
Wetland Types and Characteristics
- Wetlands are transitional ecosystems between terrestrial and aquatic environments, characterized by waterlogged soils, hydrophytic vegetation, and hydric soils
- Can be classified based on hydrology, vegetation, and substrate into categories such as , , , and fens
- Marshes are dominated by herbaceous plants like cattails and rushes, with standing water for much of the growing season (Everglades)
- Swamps are forested wetlands with trees adapted to periodic flooding, such as cypress and mangroves (Okefenokee Swamp)
- Bogs are acidic, nutrient-poor wetlands dominated by sphagnum moss and shrubs, with little groundwater input (peatlands of Canada and Siberia)
- Fens are similar to bogs but receive groundwater inputs, resulting in less acidic conditions and greater plant diversity (prairie potholes)
Hydrophytic Vegetation and Adaptations
- Hydrophytes are plants adapted to growing in water or waterlogged soils, with specialized structures and physiological adaptations
- Many hydrophytes have aerenchyma tissue, which contains air spaces that allow oxygen transport to roots in anoxic soils
- Some plants have adventitious roots that grow from stems or leaves to access oxygen above the water surface (mangroves, bald cypress)
- Floating plants like water lilies and duckweed have leaves with large air spaces for buoyancy and gas exchange
- Submerged plants like pondweeds and coontail have thin, dissected leaves to reduce drag and increase surface area for nutrient uptake
- Emergent plants like cattails and bulrushes have tall, rigid stems to withstand water currents and wind
Biogeochemical Cycling in Wetlands
- Wetlands play a critical role in the cycling of nutrients, carbon, and other elements between the atmosphere, land, and water
- Anaerobic conditions in wetland soils promote slow decomposition and accumulation of organic matter, making them important carbon sinks
- Wetland plants and microbes facilitate the removal of excess nutrients like nitrogen and phosphorus from water through uptake and transformation
- Denitrification by anaerobic bacteria converts nitrate to atmospheric nitrogen gas, helping to reduce nitrogen loads in downstream waters
- Sulfate reduction in salt marshes produces hydrogen sulfide, which can bind with heavy metals and reduce their toxicity
- Methane production by methanogenic archaea in wetland soils is a significant source of atmospheric greenhouse gases
- Wetland soils also act as sinks for pollutants like heavy metals, pesticides, and hydrocarbons, helping to improve water quality
Habitat Diversity and Ecosystem Interactions
- Wetlands support a wide range of plant and animal species adapted to the unique hydrologic and soil conditions
- Provide critical habitat for many threatened and endangered species, such as the whooping crane, wood stork, and bog turtle
- Serve as important breeding, nesting, and feeding grounds for migratory birds, fish, and invertebrates (Chesapeake Bay, Prairie Pothole Region)
- Contribute to the productivity of adjacent ecosystems by exporting organic matter, nutrients, and organisms
- Act as nursery areas for commercially important fish and shellfish species, supporting coastal fisheries and economies
- Provide connectivity between aquatic and terrestrial habitats, facilitating the movement of species and gene flow
- Influence local and regional climate through evapotranspiration, , and temperature moderation
Ecosystem Services of Lakes and Wetlands
Regulating and Supporting Services
- Lakes and wetlands provide numerous ecosystem services that benefit human well-being and support ecological processes
- is a key service, as wetlands filter pollutants, sediments, and excess nutrients from surface water and groundwater
- Flood control is another important service, as lakes and wetlands store and slowly release water, reducing the intensity of downstream flooding
- Shoreline stabilization by wetland vegetation helps to reduce erosion and protect against storm surges and sea-level rise
- Climate regulation through carbon sequestration in lake sediments and wetland soils helps to mitigate greenhouse gas emissions
- and transformation in lakes and wetlands supports primary production and maintains ecosystem productivity
- Groundwater recharge is facilitated by some lakes and wetlands, helping to maintain water supplies for human use and ecosystem needs
Provisioning and Cultural Services
- Lakes and wetlands provide valuable provisioning services such as fresh water for drinking, irrigation, and industrial use
- Many communities rely on lakes and wetlands for food production, including fish, shellfish, waterfowl, and aquatic plants (rice, cranberries)
- Wetland plants like reeds, sedges, and willows are used for construction materials, handicrafts, and biofuels
- Peat from bogs is harvested for use as a fuel source and horticultural substrate in some regions (Ireland, Russia)
- Lakes and wetlands also offer important cultural services, such as recreation, tourism, and aesthetic appreciation
- Activities like fishing, boating, birdwatching, and hunting generate significant economic benefits for local communities (Finger Lakes, Okavango Delta)
- Many lakes and wetlands have cultural and spiritual significance for indigenous peoples, serving as sacred sites and traditional use areas
- Provide opportunities for scientific research, environmental education, and nature-based learning experiences
Key Terms to Review (21)
Bogs: Bogs are a type of wetland characterized by spongy peat deposits, acidic waters, and a unique ecosystem that supports specific plant and animal species. These ecosystems play a crucial role in carbon storage, water filtration, and providing habitat for various organisms, making them ecologically significant components of the landscape.
Carbon Sequestration: Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide (CO2) to mitigate climate change and its associated effects. This process can occur naturally through biological systems, such as forests and oceans, or through technological methods aimed at reducing CO2 levels in the atmosphere.
Climate resilience: Climate resilience refers to the ability of a system, community, or ecosystem to anticipate, prepare for, respond to, and recover from climate-related stresses and shocks. This concept is crucial for understanding how lakes and wetlands can adapt to changing climate conditions while maintaining their ecological integrity and functions. The resilience of these ecosystems helps ensure they continue to provide essential services such as water filtration, flood control, and habitat for diverse species even amidst climate variability and extreme weather events.
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.
Flood mitigation: Flood mitigation refers to the strategies and measures taken to reduce the impact of flooding on communities and ecosystems. These efforts can include a range of approaches, from engineering solutions like levees and floodwalls to natural methods such as restoring wetlands and managing land use. Effective flood mitigation not only protects human lives and property but also preserves vital ecological functions of lakes and wetlands, which play crucial roles in water absorption and habitat maintenance.
Habitat diversity: Habitat diversity refers to the variety of different habitats within a specific area or ecosystem, encompassing the range of environments that support various forms of life. This diversity plays a crucial role in maintaining ecological balance, as each habitat supports unique species and interactions that contribute to the overall health of ecosystems. A rich tapestry of habitats, such as lakes and wetlands, fosters biodiversity and resilience against environmental changes.
Invasive species: Invasive species are organisms that are non-native to a particular ecosystem and whose introduction causes or is likely to cause harm to the environment, economy, or human health. They disrupt local ecosystems by outcompeting native species for resources, altering habitats, and affecting biodiversity. This disruption can have cascading effects, impacting ecosystem services and leading to biodiversity loss.
J. David Allan: J. David Allan is a prominent ecologist and researcher known for his contributions to the study of freshwater ecosystems, particularly lakes and wetlands. His work focuses on understanding the ecological dynamics and the significance of these water bodies in maintaining biodiversity, ecosystem services, and environmental health.
Lakes: Lakes are large, inland bodies of standing water that can be freshwater or saltwater, surrounded by land. They play a crucial role in the Earth's ecosystems, providing habitat for various species, regulating local climates, and serving as vital water sources for both humans and wildlife.
Marshes: Marshes are wetland ecosystems characterized by the presence of herbaceous plants and waterlogged soil, often found in low-lying areas or adjacent to lakes and rivers. They play a critical role in the environment by providing habitat for wildlife, improving water quality, and acting as natural flood control systems. Marshes are typically dominated by grasses, sedges, and reeds, and they can be freshwater or saltwater, influencing the biodiversity and ecological dynamics of the surrounding areas.
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.
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.
Primary production: Primary production is the process by which autotrophs, like plants and phytoplankton, convert sunlight or chemical energy into organic matter through photosynthesis or chemosynthesis. This process is foundational in ecosystems, as it provides the energy necessary for all other trophic levels, making it essential for the ecological dynamics of lakes and wetlands.
Restoration ecology: Restoration ecology is a scientific discipline focused on the recovery and restoration of ecosystems that have been degraded, damaged, or destroyed. It emphasizes the importance of understanding ecological processes and interactions to effectively restore biodiversity and ecosystem functionality. This field plays a crucial role in mitigating biodiversity loss and enhancing the health of various habitats, such as wetlands and lakes, while also informing conservation strategies and the management of protected areas.
Robert Wetzel: Robert Wetzel was an influential limnologist known for his extensive research on freshwater ecosystems, particularly lakes and wetlands. His work significantly advanced the understanding of nutrient cycling, primary productivity, and the ecological roles of these water bodies, shedding light on their importance in biodiversity and ecosystem services.
Species richness: Species richness refers to the number of different species represented in a given ecological community, ecosystem, or habitat. It is an important measure of biodiversity that reflects the variety of life forms within a specific area, contributing to ecosystem stability and resilience. The higher the species richness, the more diverse and potentially stable the ecosystem, which is crucial for processes such as nutrient cycling and habitat provision.
Sustainable management: Sustainable management is the practice of utilizing resources in a way that meets current needs without compromising the ability of future generations to meet their own needs. This concept emphasizes balancing economic growth, environmental health, and social equity. By integrating ecological principles into resource management, it promotes long-term resilience and biodiversity, ensuring that ecosystems and resources remain viable for years to come.
Swamps: Swamps are wetland ecosystems characterized by the presence of waterlogged soil and a variety of vegetation, including trees and shrubs. These ecosystems play a crucial role in maintaining biodiversity, regulating water quality, and providing essential habitats for numerous species. Swamps can be freshwater or saltwater, and they often serve as transition zones between terrestrial and aquatic environments.
Turbidity: Turbidity refers to the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye. This characteristic is essential in understanding the quality of lakes and wetlands, as high turbidity can significantly impact the ecological balance by affecting light penetration, photosynthesis in aquatic plants, and the overall health of aquatic ecosystems.
Water Purification: Water purification is the process of removing contaminants and impurities from water to make it safe for human consumption and other uses. This process is vital for maintaining healthy ecosystems, particularly in lakes and wetlands, which serve as natural filters for pollutants and provide clean water for various organisms. Effective water purification techniques help sustain biodiversity and ensure the ecological balance of these critical habitats.
Wetlands: Wetlands are unique ecosystems where water is either present at or near the surface, either permanently or seasonally, and they support a rich variety of plant and animal life. These areas include swamps, marshes, and bogs, and they play a crucial role in the environment by providing habitat, improving water quality, and acting as buffers against flooding. Wetlands are integral to maintaining ecological balance and supporting biodiversity.