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Earth Science
Table of Contents
Unit 9 Overview: Earth's Ecosystems and Biomes
9.1 Biogeochemical Cycles
9.2 Terrestrial Biomes and Ecosystems
9.3 Aquatic Ecosystems and Wetlands
9.4 Biodiversity and Conservation
9.5 Human Impacts on Ecosystems

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9.3 Aquatic Ecosystems and Wetlands

Citation:

Aquatic ecosystems are diverse underwater worlds teeming with life. From oceans to lakes, these environments support unique organisms adapted to life in water. This section explores the types, characteristics, and importance of aquatic ecosystems, including marine, freshwater, and wetland habitats.

Human activities significantly impact aquatic ecosystems through pollution, overfishing, and habitat destruction. Climate change further threatens these delicate environments. Understanding these ecosystems is crucial for conservation efforts and maintaining the vital services they provide to both nature and humans.

Aquatic Ecosystem Types and Characteristics

Marine and Freshwater Ecosystems

  • Aquatic ecosystems are divided into two main categories: marine ecosystems (oceans, coral reefs, estuaries) and freshwater ecosystems (lakes, rivers, streams, wetlands)
  • Marine ecosystems have high salinity (salt content), while freshwater ecosystems have low salinity
  • Marine ecosystems cover about 71% of the Earth's surface and are home to a vast array of plant and animal life adapted to the saltwater environment
  • Freshwater ecosystems, although smaller in total area, support a significant portion of the Earth's biodiversity and provide critical ecosystem services

Ocean Zones and Coral Reefs

  • Oceans are the largest marine ecosystems and are divided into zones based on depth and light penetration (pelagic, benthic, abyssal)
    • Pelagic zone is the open water column, divided into sunlit epipelagic and darker mesopelagic and bathypelagic zones
    • Benthic zone is the ocean bottom, including the seafloor and sediments
    • Abyssal zone is the deepest part of the ocean, characterized by complete darkness, high pressure, and cold temperatures
  • Coral reefs are diverse marine ecosystems found in warm, shallow waters and are built by coral polyps that secrete calcium carbonate skeletons
    • Coral reefs support an estimated 25% of all marine species and provide critical habitat, food, and shelter
    • Coral reefs are highly sensitive to changes in water temperature, acidity, and pollution, making them vulnerable to human impacts

Estuaries, Lakes, and Rivers

  • Estuaries are partially enclosed coastal bodies of water where freshwater from rivers and streams meets and mixes with salt water from the ocean, creating unique brackish water habitats
    • Estuaries support high biodiversity and serve as nurseries for many marine species
    • Estuaries are influenced by tides and experience variations in salinity and water level
  • Lakes are large, inland bodies of standing freshwater that can be classified based on their nutrient content (oligotrophic, mesotrophic, eutrophic) and thermal stratification
    • Oligotrophic lakes have low nutrient levels and clear water, while eutrophic lakes have high nutrient levels and may experience algal blooms
    • Thermal stratification occurs in deeper lakes during summer, with warm, less dense water on top and cold, denser water at the bottom
  • Rivers and streams are flowing freshwater ecosystems that transport water, nutrients, and sediments from land to larger water bodies, shaping the landscape through erosion and deposition
    • Rivers and streams have a longitudinal gradient of physical and chemical conditions from headwaters to mouth
    • The flow regime and substrate type influence the distribution and diversity of aquatic organisms in rivers and streams

Importance of Wetlands

Wetland Characteristics and Biodiversity

  • Wetlands are transitional areas between land and water, characterized by waterlogged soils, hydrophytic vegetation, and various periods of flooding
  • Wetlands provide critical habitats for a wide range of plant and animal species, supporting high levels of biodiversity
    • Many endangered and threatened species depend on wetlands for survival (whooping cranes, swamp pink orchids)
    • Wetlands serve as breeding grounds and nurseries for numerous fish, amphibians, and invertebrates
  • Wetland types include marshes, swamps, bogs, and fens, each with distinct hydrological and ecological characteristics

Ecosystem Services and Functions

  • Wetlands act as natural water filters, removing pollutants, excess nutrients, and sediments from water before it reaches other water bodies, thus improving water quality
    • Wetland plants and microorganisms absorb and break down contaminants (nitrogen, phosphorus, heavy metals)
    • Wetlands trap sediments and prevent them from clogging downstream water bodies
  • Wetlands help regulate water flow by absorbing and slowly releasing water during periods of heavy rainfall or snowmelt, reducing the risk of flooding downstream
    • Wetlands act as natural sponges, storing water and releasing it gradually
    • Floodplain wetlands dissipate the energy of floodwaters and protect adjacent uplands
  • Wetlands serve as important carbon sinks, storing large amounts of organic carbon in their soils and vegetation, which helps mitigate climate change
    • Wetlands, particularly peatlands, store more carbon per unit area than any other terrestrial ecosystem
    • When wetlands are drained or destroyed, stored carbon is released into the atmosphere, contributing to global warming
  • Wetlands provide various other ecosystem services, such as groundwater recharge, shoreline stabilization, and recreational opportunities (birdwatching, fishing, hunting)
    • Wetlands help maintain groundwater levels by allowing water to percolate into aquifers
    • Coastal wetlands, such as mangroves and salt marshes, buffer shorelines from erosion and storm surges

Adaptations in Aquatic Environments

Adaptations for Living in Water

  • Aquatic organisms have evolved various adaptations to cope with the physical and chemical challenges of living in water, such as buoyancy, locomotion, gas exchange, and osmoregulation
  • Fish have streamlined bodies, fins for locomotion, and gills for efficient gas exchange in water. Some fish have swim bladders to regulate buoyancy
    • Streamlined body shapes reduce drag and improve swimming efficiency
    • Fins provide propulsion and steering, with different types of fins serving specific functions (caudal, pectoral, pelvic, dorsal, anal)
    • Gills extract dissolved oxygen from water and expel carbon dioxide and nitrogenous wastes
    • Swim bladders allow fish to adjust their buoyancy by filling or emptying the bladder with gas
  • Aquatic mammals (whales, dolphins, seals) have adaptations such as blubber for insulation, flippers for locomotion, and specialized respiratory and circulatory systems for diving
    • Blubber is a thick layer of fat that provides insulation and energy storage
    • Flippers are modified limbs that provide efficient propulsion and steering in water
    • Aquatic mammals have large lungs, high oxygen-carrying capacity in their blood, and the ability to store oxygen in their muscles for extended dives
  • Aquatic plants have adaptations such as flexible stems, reduced cuticles, and aerenchyma tissue to facilitate gas exchange and buoyancy in water
    • Flexible stems allow plants to move with water currents and avoid damage
    • Reduced cuticles minimize the barrier to gas exchange and nutrient uptake
    • Aerenchyma tissue is a spongy tissue with air spaces that allows for gas exchange and provides buoyancy

Trophic Interactions and Community Structure

  • Aquatic ecosystems exhibit complex trophic interactions, with energy and nutrients flowing through food chains and food webs from primary producers to consumers and decomposers
    • Primary producers (phytoplankton, algae, aquatic plants) convert sunlight into chemical energy through photosynthesis
    • Primary consumers (zooplankton, herbivorous fish) feed on primary producers
    • Secondary consumers (carnivorous fish, aquatic insects) feed on primary consumers
    • Tertiary consumers (top predators) feed on secondary consumers
    • Decomposers (bacteria, fungi) break down dead organic matter and recycle nutrients back into the ecosystem
  • Competition, predation, and symbiosis are important biotic interactions that shape the structure and function of aquatic communities
    • Competition occurs when organisms vie for limited resources (food, space, mates), leading to niche differentiation and resource partitioning
    • Predation is the consumption of one organism (prey) by another (predator), influencing population dynamics and trophic cascades
    • Symbiosis involves close associations between different species, such as mutualism (both species benefit, like clownfish and sea anemones), commensalism (one species benefits without harming the other), and parasitism (one species benefits at the expense of the other)

Human Impacts on Aquatic Ecosystems

Pollution and Overfishing

  • Pollution from agricultural runoff, industrial waste, and sewage discharge can lead to eutrophication, causing algal blooms, oxygen depletion, and fish kills in aquatic ecosystems
    • Excess nutrients (nitrogen and phosphorus) from fertilizers and sewage stimulate the growth of algae and aquatic plants
    • Algal blooms can block sunlight, reduce water clarity, and produce toxins harmful to aquatic life and humans
    • When algae die and decompose, oxygen is consumed, leading to hypoxic or anoxic conditions that stress or kill aquatic organisms
  • Overfishing disrupts marine food webs, causing declines in fish populations and shifts in species composition, which can have cascading effects on the entire ecosystem
    • Overfishing occurs when fish are harvested faster than they can reproduce, leading to population collapses
    • The removal of top predators can cause trophic cascades, altering the abundance and distribution of lower trophic levels
    • Bycatch, the unintended capture of non-target species, can further impact marine biodiversity and ecosystem functioning

Habitat Alteration and Invasive Species

  • Habitat destruction, such as draining wetlands for development or converting them to agricultural land, leads to the loss of biodiversity and impaired ecosystem functions
    • Wetland loss reduces water storage capacity, filtration, and carbon sequestration
    • The destruction of riparian habitats along rivers and streams increases erosion, sedimentation, and water temperature
    • Coastal development (seawalls, jetties) disrupts natural shoreline processes, leading to erosion and the loss of important habitats (beaches, dunes)
  • Invasive species introduced by human activities can outcompete native species, alter habitat structure, and disrupt ecosystem balance
    • Invasive aquatic plants (water hyacinth, Eurasian watermilfoil) can form dense mats that block sunlight, reduce oxygen levels, and impede navigation
    • Invasive fish (Asian carp, lionfish) can outcompete native species for food and habitat, leading to population declines and changes in community structure
    • Invasive invertebrates (zebra mussels, Asian clams) can alter water chemistry, clog water intake pipes, and foul boat hulls and other submerged structures

Climate Change and Water Management

  • Climate change, driven by human activities, can lead to rising sea levels, ocean acidification, and changes in water temperature and chemistry, affecting the distribution and survival of aquatic organisms
    • Rising sea levels can inundate coastal wetlands, alter salinity gradients, and displace coastal communities
    • Ocean acidification, caused by the absorption of atmospheric carbon dioxide, can impair the growth and survival of calcifying organisms (corals, mollusks)
    • Changes in water temperature can alter the metabolic rates, reproductive cycles, and geographic ranges of aquatic species, leading to shifts in community composition and ecosystem functioning
  • Dams and water diversions for irrigation, hydropower, or flood control can alter the natural flow regimes of rivers and streams, affecting aquatic habitats and the species that depend on them
    • Dams can block the migration routes of fish (salmon, eels), prevent sediment transport, and alter downstream flow patterns and water temperatures
    • Water diversions can reduce instream flows, degrade water quality, and fragment aquatic habitats
    • Altered flow regimes can impact the timing and magnitude of floods and droughts, affecting the life cycles and survival of aquatic organisms

Key Terms to Review (19)

Carbon sequestration: Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide (CO2) to mitigate or reverse climate change. This can occur naturally through biological processes, such as photosynthesis in plants, or through technological methods that capture CO2 emissions from industrial processes. The effectiveness of carbon sequestration is crucial in addressing rising greenhouse gas levels and enhancing the health of aquatic ecosystems.
Ramsar Convention: The Ramsar Convention is an international treaty established in 1971 aimed at the conservation and sustainable use of wetlands worldwide. It emphasizes the importance of wetland ecosystems, recognizing their critical roles in biodiversity, water purification, and flood control. By promoting the designation of Wetlands of International Importance, the convention seeks to enhance global awareness and commitment to wetland preservation.
Sustainable management: Sustainable management refers to the practice of using resources in a way that meets current needs without compromising the ability of future generations to meet their own needs. This approach balances ecological, social, and economic factors to ensure that ecosystems remain healthy and can continue to provide essential services over time.
Restoration ecology: Restoration ecology is the scientific study and practice of restoring ecosystems that have been degraded, damaged, or destroyed. This field focuses on bringing back biodiversity and ecosystem functions through various techniques, including reforestation, wetland restoration, and the removal of invasive species. By understanding the natural processes of ecosystems, restoration ecology aims to rehabilitate environments to a state where they can sustain native species and provide essential ecological services.
Clean Water Act: The Clean Water Act is a foundational piece of environmental legislation in the United States, enacted in 1972 to regulate the discharge of pollutants into the nation's waters and to restore and maintain the integrity of the country's waters. This act aims to protect aquatic ecosystems and wetland environments by establishing water quality standards and permitting processes for industrial discharges, while also addressing the importance of ensuring clean water access for both human use and wildlife habitats.
Habitat loss: Habitat loss refers to the process by which natural habitats become unable to support the species that live there, resulting in a decline or extinction of local flora and fauna. This phenomenon often occurs due to human activities such as urban development, agriculture, deforestation, and pollution, leading to significant changes in ecosystems and biodiversity. It poses a serious threat to wildlife and contributes to the global biodiversity crisis.
Benthic organisms: Benthic organisms are species that live on or in the bottom sediments of aquatic environments, including oceans, rivers, and lakes. These organisms play a crucial role in the aquatic ecosystem, contributing to nutrient cycling and serving as a food source for various predators. Benthic organisms include a wide variety of life forms, from microscopic bacteria to large invertebrates and fish, each adapted to their unique habitat within the sediment.
Water filtration: Water filtration is the process of removing impurities and contaminants from water to make it safe for consumption and use. This process is essential for maintaining the health of aquatic ecosystems and wetlands, as it helps to preserve water quality by eliminating pollutants, excess nutrients, and harmful microorganisms. Effective water filtration plays a critical role in supporting biodiversity, protecting habitats, and ensuring clean water resources for both humans and wildlife.
Bogs: Bogs are a type of wetland characterized by waterlogged, acidic conditions and the accumulation of peat, a partially decayed organic material. They typically develop in cooler climates and are known for their unique plant life, including sphagnum mosses and various shrubs. Bogs play an essential role in carbon storage and provide habitat for specialized wildlife, making them an important component of aquatic ecosystems and wetlands.
Plankton: Plankton refers to the diverse group of microscopic organisms that drift freely in aquatic environments, unable to swim against currents. These organisms play a crucial role in aquatic ecosystems, serving as the foundational food source for many marine and freshwater species. Plankton includes both phytoplankton, which are plant-like organisms that perform photosynthesis, and zooplankton, which are small animals that feed on phytoplankton or other zooplankton.
Marshes: Marshes are wetland areas that are characterized by the presence of herbaceous plants and are often found at the edges of lakes, rivers, and coastal regions. These ecosystems are crucial for biodiversity, serving as habitat for numerous species of plants, animals, and microorganisms, while also providing essential ecosystem services such as water filtration and flood protection.
Swamps: Swamps are a type of wetland characterized by the presence of water, either permanently or seasonally, and are dominated by herbaceous plants and trees. These ecosystems play a vital role in water filtration, flood control, and providing habitat for diverse wildlife. They often serve as transitional zones between land and water, showcasing unique biodiversity and ecological functions.
Freshwater ecosystems: Freshwater ecosystems are vital habitats that include rivers, lakes, ponds, wetlands, and streams, characterized by low salt concentration and a diverse array of life forms. These ecosystems are crucial for supporting biodiversity, regulating water cycles, and providing essential resources for humans and wildlife. They play a significant role in the global environment by serving as sources of drinking water, agricultural irrigation, and recreational areas.
Marine ecosystems: Marine ecosystems are vast and complex environments located in oceans and seas, supporting a diverse array of organisms and interactions. These ecosystems include various habitats such as coral reefs, estuaries, and the deep sea, playing crucial roles in global climate regulation, nutrient cycling, and supporting biodiversity. The intricate relationships among marine species contribute to the overall health and balance of the oceanic environment.
Trophic levels: Trophic levels are the hierarchical layers in an ecosystem that categorize organisms based on their feeding relationships and energy transfer. These levels typically include producers at the base, followed by primary consumers, secondary consumers, and tertiary consumers, with each level representing a step in the food chain. Understanding trophic levels is essential for grasping energy flow, nutrient cycling, and the interactions between various species within an ecosystem.
Biodiversity: Biodiversity refers to the variety of life forms on Earth, including the different species of plants, animals, fungi, and microorganisms, as well as the ecosystems they form and the genetic diversity within those species. This concept is crucial for maintaining ecosystem stability and resilience, influencing how organisms interact with each other and their environments. A rich biodiversity supports essential ecological processes, such as nutrient cycling, pollination, and climate regulation, which are interconnected with biogeochemical cycles, terrestrial biomes, and aquatic ecosystems.
Eutrophication: Eutrophication is the process by which a body of water becomes overly enriched with nutrients, leading to excessive growth of algae and other aquatic plants. This phenomenon can cause significant ecological impacts, including oxygen depletion and disruption of aquatic ecosystems. As nutrient inputs from sources like fertilizers, sewage, and runoff increase, they stimulate algal blooms that can harm water quality and marine life.
Phosphorus cycle: The phosphorus cycle is the biogeochemical process through which phosphorus moves through the environment, including soil, water, and living organisms. Unlike other biogeochemical cycles, phosphorus does not have a significant gaseous phase and primarily cycles through geological and biological processes. This cycle plays a crucial role in ecosystems, influencing plant growth and the health of aquatic ecosystems.
Nitrogen cycle: The nitrogen cycle is the series of processes by which nitrogen and its compounds are interconverted in the environment and in living organisms. This cycle is crucial for life, as nitrogen is a key component of amino acids, proteins, and nucleic acids, linking it to the overall health of ecosystems, including both terrestrial and aquatic environments. Through various transformations, such as nitrogen fixation, nitrification, denitrification, and ammonification, nitrogen moves between the atmosphere, soil, and living organisms, maintaining ecosystem balance.