💧Limnology Unit 12 – Freshwater Ecosystem Management

Key Concepts and Definitions

• Limnology studies inland aquatic ecosystems (lakes, rivers, wetlands, groundwater)
• Freshwater ecosystems contain water with low concentrations of dissolved salts and other total dissolved solids
  • Salinity is typically less than 1 part per thousand (ppt) or 1,000 parts per million (ppm)
• Lentic ecosystems refer to still or standing water habitats (lakes, ponds, wetlands)
• Lotic ecosystems encompass flowing water habitats (rivers, streams, springs)
• Wetlands are areas where water covers the soil or is present at or near the surface for a significant part of the year (marshes, swamps, bogs)
• Watershed represents the area of land that drains water, sediment, and dissolved materials to a common outlet (river, lake, ocean)
• Eutrophication is the excessive enrichment of a water body with nutrients, leading to algal blooms and oxygen depletion
  • Can be natural or accelerated by human activities (agricultural runoff, sewage discharge)

Freshwater Ecosystem Types

• Lakes are large, inland bodies of standing water formed by various processes (glacial, tectonic, volcanic)
  • Classified based on nutrient levels (oligotrophic, mesotrophic, eutrophic)
• Ponds are smaller, shallower water bodies that may be permanent or seasonal
• Rivers are natural, flowing watercourses that transport water, sediment, and dissolved materials from source to mouth
  • Divided into upper, middle, and lower reaches with distinct characteristics
• Streams are smaller, tributary watercourses that feed into rivers
• Wetlands include marshes, swamps, bogs, and fens, each with unique hydrological and ecological features
  • Provide critical habitat, water filtration, and flood control services
• Groundwater refers to water stored in aquifers beneath the Earth's surface
  • Interacts with surface water through recharge and discharge processes

Physical and Chemical Properties

• Temperature influences water density, stratification, and biological activity
  • Thermal stratification occurs in lakes during summer (epilimnion, metalimnion, hypolimnion)
• Light penetration depends on water clarity and depth, affecting photosynthesis and primary production
• Dissolved oxygen is essential for aquatic life and varies with temperature, depth, and biological processes
  • Hypoxia (low oxygen) can result from eutrophication or stratification
• pH measures the acidity or alkalinity of water, influencing chemical reactions and biological communities
• Nutrients (nitrogen, phosphorus) are essential for plant growth but can cause eutrophication in excess
• Dissolved organic matter (DOM) includes compounds from decomposing plant and animal material, affecting water color and chemistry
• Turbidity refers to water clarity, influenced by suspended sediment, algae, and other particles

Biological Components and Interactions

• Primary producers (algae, aquatic plants) form the base of the food web, converting sunlight into organic matter through photosynthesis
• Zooplankton are small, drifting animals that graze on algae and serve as food for larger organisms
  • Include rotifers, copepods, and cladocerans (Daphnia)
• Macroinvertebrates are larger, bottom-dwelling organisms that play key roles in nutrient cycling and energy transfer (insects, crustaceans, mollusks)
• Fish occupy various trophic levels, from herbivores to top predators
  • Influenced by water temperature, oxygen levels, and habitat structure
• Amphibians (frogs, salamanders) and reptiles (turtles, snakes) rely on both aquatic and terrestrial habitats
• Waterfowl (ducks, geese) and mammals (beavers, otters) also depend on freshwater ecosystems
• Microbial communities (bacteria, fungi) drive decomposition and nutrient cycling processes

Human Impacts and Pollution

• Eutrophication from nutrient loading (agricultural runoff, sewage discharge) leads to algal blooms, oxygen depletion, and fish kills
• Habitat degradation results from land-use changes, channelization, and dam construction
  • Alters flow regimes, sediment transport, and connectivity
• Invasive species introduced by human activities can disrupt native communities and ecosystem functions (zebra mussels, Asian carp)
• Chemical pollution from industrial effluents, pesticides, and pharmaceuticals can have toxic effects on aquatic life
  • Bioaccumulation occurs when pollutants concentrate up the food chain
• Microplastics are small plastic particles that can be ingested by organisms and transfer through the food web
• Climate change impacts include altered precipitation patterns, warming temperatures, and shifts in species distributions
• Overexploitation of fisheries and other aquatic resources can lead to population declines and ecosystem imbalances

Management Strategies and Conservation

• Watershed management involves protecting and restoring the entire drainage basin to improve water quality and ecosystem health
  • Best management practices (BMPs) reduce nonpoint source pollution from agriculture and urban areas
• Riparian buffer zones are vegetated areas along waterways that filter pollutants, stabilize banks, and provide habitat
• Water quality monitoring programs track physical, chemical, and biological parameters to assess ecosystem status and trends
  • Biotic indices based on macroinvertebrate communities indicate long-term conditions
• Habitat restoration projects aim to improve degraded ecosystems through actions like channel reconfiguration, wetland creation, and fish passage structures
• Invasive species control efforts seek to prevent, eradicate, or manage non-native populations through various methods (physical removal, biocontrol, public education)
• Protected areas (national parks, wildlife refuges) conserve representative freshwater ecosystems and their associated biodiversity
• Environmental flow regulations ensure adequate water quantity and timing to support ecological functions downstream of dams and diversions

Case Studies and Real-World Applications

• Laurentian Great Lakes represent the largest surface freshwater system on Earth, facing challenges like invasive species (sea lamprey), eutrophication (Lake Erie), and legacy contaminants (PCBs)
  • Binational management efforts have led to improved water quality and fisheries
• Everglades restoration in Florida aims to restore natural hydrology and ecosystem functions in a highly modified wetland landscape
  • Includes projects to increase freshwater flows, reduce nutrient inputs, and enhance habitat connectivity
• Mekong River Basin in Southeast Asia supports high biodiversity and human livelihoods but is threatened by hydropower development, overfishing, and climate change
  • Transboundary cooperation is essential for sustainable management
• Urban stream syndrome describes the ecological degradation of streams in cities due to altered hydrology, increased pollution, and decreased biodiversity
  • Green infrastructure (rain gardens, permeable pavement) can mitigate stormwater impacts

Current Research and Future Challenges

• Advancing understanding of freshwater biodiversity patterns, drivers, and threats
  • Applying environmental DNA (eDNA) techniques for species monitoring and early detection of invasives
• Quantifying the role of freshwater ecosystems in global carbon cycling and climate regulation
  • Methane emissions from lakes and reservoirs may be significant
• Developing ecological indicators and thresholds for assessing ecosystem health and guiding management decisions
  • Integrating multiple lines of evidence (water quality, habitat, biological communities)
• Evaluating the effectiveness of conservation and restoration strategies through adaptive management frameworks
  • Incorporating stakeholder input and socioeconomic considerations
• Predicting and mitigating the impacts of climate change on freshwater ecosystems and their services
  • Shifts in hydrologic regimes, water temperatures, and species ranges
• Enhancing public awareness, engagement, and stewardship of freshwater resources
  • Citizen science programs, outreach campaigns, and experiential learning opportunities