💧Limnology Unit 7 – Aquatic Plants and Littoral Zone Ecology

Key Concepts and Definitions

• Limnology studies inland aquatic ecosystems, including their biological, chemical, and physical characteristics
• Aquatic plants are photosynthetic organisms adapted to live partially or fully submerged in water
• Littoral zone refers to the nearshore area where sunlight penetrates to the bottom, allowing aquatic plants to grow
• Macrophytes are aquatic plants visible to the naked eye and include emergent, submergent, and floating plants
• Phytoplankton are microscopic algae suspended in the water column and contribute to primary production
  • Include groups such as diatoms, dinoflagellates, and cyanobacteria
• Benthic algae grow attached to substrates like rocks, sediments, or other aquatic plants
• Photosynthesis is the process by which aquatic plants convert sunlight into chemical energy, releasing oxygen as a byproduct
• Eutrophication is the excessive growth of aquatic plants and algae due to nutrient enrichment, often leading to oxygen depletion and water quality issues

Aquatic Plant Types and Adaptations

• Emergent plants are rooted in the sediment with leaves and stems extending above the water surface (cattails, rushes)
  • Adaptations include hollow stems for gas exchange and support tissues to maintain upright growth
• Submergent plants grow entirely underwater and are either rooted or free-floating (pondweeds, coontail)
  • Adaptations include thin, flexible leaves to reduce drag and increase surface area for nutrient uptake
  • Some species have specialized leaves or stems to absorb nutrients directly from the water
• Floating plants have leaves that float on the water surface and can be either rooted or free-floating (water lilies, duckweed)
  • Adaptations include waxy leaf coatings to repel water and air-filled tissues for buoyancy
• Amphibious plants can grow in both aquatic and terrestrial environments, adapting to changing water levels (smartweeds, some sedges)
• Many aquatic plants have reduced or absent root systems, as they absorb nutrients directly from the water
• Some aquatic plants have specialized reproductive strategies, such as fragmentation or production of turions (overwintering buds)

Littoral Zone Characteristics

• Littoral zone extends from the shoreline to the depth where sufficient light penetrates for plant growth
  • Depth of the littoral zone varies depending on water clarity and light availability
• Substrate in the littoral zone can range from rocky to sandy or silty, influencing plant community composition
• Wave action and water level fluctuations create diverse microhabitats within the littoral zone
• Littoral zone is a highly productive area, supporting a wide range of aquatic organisms
  • Provides spawning and nursery habitats for fish and other aquatic animals
• Littoral zone plays a crucial role in nutrient cycling, as aquatic plants take up nutrients from the sediment and water
• Seasonal changes in water temperature and light availability affect littoral zone dynamics and plant growth

Ecological Roles of Aquatic Plants

• Aquatic plants are primary producers, converting sunlight into biomass and supporting aquatic food webs
• Provide habitat and shelter for various aquatic organisms, including fish, invertebrates, and waterfowl
  • Submergent plants create complex underwater structures, while emergent plants offer above-water refugia
• Stabilize sediments and reduce shoreline erosion through their root systems and by dampening wave action
• Improve water quality by absorbing excess nutrients, filtering suspended particles, and releasing oxygen through photosynthesis
• Aquatic plants can influence water chemistry, such as pH and dissolved oxygen levels, through their metabolic processes
• Some aquatic plants have allelopathic properties, releasing compounds that inhibit the growth of other plants or algae
• Aquatic plants serve as a food source for various herbivores, including waterfowl, turtles, and aquatic mammals
• Decomposition of aquatic plant material contributes to the detrital pool, supporting detritivores and nutrient recycling

Factors Affecting Aquatic Plant Growth

• Light availability is a primary factor, as aquatic plants require sufficient light for photosynthesis
  • Water clarity, depth, and shading from riparian vegetation can influence light penetration
• Nutrient availability, particularly nitrogen and phosphorus, can limit or promote aquatic plant growth
  • Excess nutrients from anthropogenic sources can lead to eutrophication and algal blooms
• Water temperature affects metabolic rates and growth, with optimal ranges varying among species
• Substrate type and stability influence root anchoring and nutrient availability for aquatic plants
  • Some species prefer specific substrates, such as sandy or organic-rich sediments
• Water level fluctuations and wave action can impact plant establishment, distribution, and survival
• Competition among aquatic plant species and with algae for resources like light and nutrients shapes community composition
• Herbivory by aquatic animals can control aquatic plant populations and influence species dominance
• Water chemistry variables, such as pH, salinity, and dissolved oxygen, can affect aquatic plant physiology and distribution

Sampling and Identification Techniques

• Aquatic plant surveys involve mapping the distribution and abundance of species within a waterbody
  • Surveys can be conducted using transects, quadrats, or remote sensing methods
• Rake tosses or grab samples are used to collect submergent and floating-leaved plants for identification
• Emergent plants can be identified and quantified using visual observations or plot sampling techniques
• Underwater cameras or divers may be employed to assess submergent plant communities in deeper waters
• Aquatic plant identification relies on morphological characteristics such as leaf shape, arrangement, and flowers or fruits
  • Dichotomous keys and field guides aid in species identification
• Voucher specimens are often collected and pressed for later verification and reference
• Biomass estimation techniques, such as dry weight or volume displacement, provide quantitative data on aquatic plant abundance
• Remote sensing methods, including aerial photography and satellite imagery, can map aquatic plant distributions over large areas
  • Spectral signatures of different plant species can be used for classification

Human Impacts and Management

• Eutrophication from nutrient pollution is a major threat to aquatic plant communities, leading to algal blooms and reduced water clarity
  • Management strategies include nutrient load reductions from point and non-point sources
• Invasive aquatic plant species can outcompete native plants, alter ecosystem functions, and impede recreational activities
  • Control methods include physical removal, herbicide application, and biological control agents
• Shoreline development and habitat modification can degrade littoral zone habitats and reduce aquatic plant diversity
  • Restoration efforts focus on revegetating shorelines and creating buffer zones to minimize human impacts
• Herbicide use for aquatic plant control can have unintended consequences on non-target species and water quality
  • Integrated pest management approaches prioritize non-chemical control methods and targeted herbicide application
• Water level management in reservoirs and lakes can affect aquatic plant communities, with drawdowns used to control certain species
• Mechanical harvesting of aquatic plants is used to improve recreational access and remove excess biomass
  • Harvested material can be used for composting or bioenergy production
• Public education and outreach are crucial for promoting sustainable aquatic plant management and preventing the spread of invasive species

Case Studies and Real-World Applications

• Lake Okeechobee, Florida: Nutrient pollution from agricultural runoff has led to extensive cyanobacterial blooms and impacts on aquatic plant communities
  • Restoration efforts include implementing best management practices in the watershed and constructing treatment wetlands
• Chesapeake Bay, USA: Submergent aquatic vegetation (SAV) has declined due to eutrophication and water clarity issues
  • SAV restoration targets have been set, and efforts include nutrient load reductions and seagrass planting
• Lake Victoria, East Africa: Water hyacinth, an invasive floating plant, has proliferated due to nutrient enrichment and poses challenges for transportation and fisheries
  • Control strategies include manual removal, herbicide application, and the introduction of biological control agents like weevils
• Kissimmee River, Florida: Channelization of the river in the 1960s led to the loss of floodplain habitats and aquatic plant diversity
  • River restoration project aimed to restore natural meandering and reconnect the floodplain, enhancing aquatic plant communities
• Laurentian Great Lakes, North America: Invasive Eurasian watermilfoil has spread rapidly, outcompeting native plants and impacting recreational activities
  • Management approaches include mechanical harvesting, herbicide treatments, and the use of native insect biological control agents
• Lake Biwa, Japan: Long-term monitoring of aquatic plant communities has provided insights into the impacts of eutrophication and climate change
  • Research findings have informed management strategies, such as nutrient reduction targets and shoreline restoration efforts