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Limnology: An Overview of Inland Water Ecosystems, Exams of Water Resources Planning and Management

Western Governors University (WGU)Water Resources Planning and Management

A concise overview of limnology, the study of inland waters. It covers essential topics such as lake habitat zones (trophogenic, tropholytic, littoral, limnetic, profundal, benthic), trophic states (oligotrophic, mesotrophic, eutrophic), and the limiting nutrient concept. It also details various organisms found in these ecosystems, including cyanobacteria, eubacteria, algae, macrophytes, protozoa, and various invertebrate and vertebrate species. The document highlights the importance of studying inland water systems for water resources, recreation, food, agriculture, and sustaining biological life. It also touches on the properties of water and plankton communities, offering a comprehensive introduction to limnology. Useful for students and researchers interested in aquatic ecology and environmental science, providing a solid foundation for further study and research.

Typology: Exams

2025/2026

Available from 12/10/2025

Prof-Cornel
Prof-Cornel šŸ‡ŗšŸ‡ø

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Limne
Pool, marsh or lake
Liminology
The science of inland waters, concerned with all the factors that influence living
populations within those waters
- Includes running and standing waters
- Large lakes to small ponds
- Fresh waters to extremely pools and lakes
Limnology as an Interdisciplinary Science
Geology, physics, mathematics, computer science, chemistry, biology
Lake Habitat Zones
Trophogenic zone, tropholytic zone, littoral zone, limnetic zone, sublittoral zone,
profundal zone, benthic zone
Littoral Zone
- Intercepts nutrients
- Refuge from Predators
- Nursery for Fish
- Species diversity
- Trophogenic zone
Profundal Zone
- Found in lakes deep enough for summer stratification
- Deep, cold region with low current
- Light reduced or absent
- Oxygen may be scarce or depleted
- Characterized by decay
- Decomposition of aerobic organisms
Limnetic/Pelagic Zone
- Plankton and Zooplankton are free floating and drifting
- Trophogenic zone
Submerged Aquatic Vegetation (SAV)
- Found in Limnetic Zone
- Nutrient uptake
- Sediment stabilization
- Habitat
- Oxygen production
- Trophogenic zone
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Limne Pool, marsh or lake Liminology The science of inland waters, concerned with all the factors that influence living populations within those waters

  • Includes running and standing waters
  • Large lakes to small ponds
  • Fresh waters to extremely pools and lakes Limnology as an Interdisciplinary Science Geology, physics, mathematics, computer science, chemistry, biology Lake Habitat Zones Trophogenic zone, tropholytic zone, littoral zone, limnetic zone, sublittoral zone, profundal zone, benthic zone Littoral Zone
  • Intercepts nutrients
  • Refuge from Predators
  • Nursery for Fish
  • Species diversity
  • Trophogenic zone Profundal Zone
  • Found in lakes deep enough for summer stratification
  • Deep, cold region with low current
  • Light reduced or absent
  • Oxygen may be scarce or depleted
  • Characterized by decay
  • Decomposition of aerobic organisms Limnetic/Pelagic Zone
  • Plankton and Zooplankton are free floating and drifting
  • Trophogenic zone Submerged Aquatic Vegetation (SAV)
  • Found in Limnetic Zone
  • Nutrient uptake
  • Sediment stabilization
  • Habitat
  • Oxygen production
  • Trophogenic zone

Oligotrophic

  • Low nutrients
  • Low primary producers
  • Low grazers and insects
  • Low fish production
  • Clear water
  • Sandy/low organic matter on bottom Mesotrophic
  • Moderate nutrients
  • Increased primary productivity
  • More grazers and insects
  • More fish production
  • Moderate water clarity
  • More aquatic plants
  • Some organic sediment accumulation Eutrophic
  • High nutrients
  • High primary productivity
  • Large number of grazers and insects
  • Moderate fish production
  • Low water clarity, or
  • Clear with aquatic plants
  • High organic sediment accumulation Trophic State Change
  • Nutrients & Productivity
  • Sediment & Accumulation
  • Species Shifts
  • Species Richness Limiting Nutrient Concept Plants need nutrients to grow.
  • Nitrogen and Phosphorus are the main nutrients
  • For every unit of N, you need so many units of P (Redfield Ratio 106 carbon : 16 nitrogen : 1 phosphorus)
  • If one nutrient is not in sufficient supply, it will limit the total production potential For algae:
  • N:P > 17 Phosphorus Limited
  • N:P < 10 Nitrogen Limited
  • Play an important role in food web
  • Contain species of human health concern Types of Algae
  • Chlorophyta: Green algae
  • Pyrrophyta: Dinoflagellates
  • Golden brown algae: Cryptophyta and Chrysophyceae Macrophytes
  • Large, vascular plants
  • Nearly all terrestrial plants that have adapted to aquatic growth
  • Less gas dissolved in water
  • Reduced light in water
  • Lack of wind or insect pollination
  • Damage from water movements Protozoa
  • Unicellular
  • Ubiquitous
  • Consumes bacteria, cyanobacteria, algae, other protozoans
  • Prey for oligochaetes, chironomids, rotifers
  • Do not tolerate anoxic conditions Porifera
  • 32 species of freshwater sponges
  • Restricted to waters containing silica Cnidaria
  • Hydrozoa only Platyhelminthes
  • Turbellaria
  • Benthic scavengers Rotifera
  • "wheel animals"
  • free living herbivores and predators
  • have Corona Mollusca
  • Gastropoda: snails and limpets - highly mobile
  • Bivalvia: clams and muscles - not as mobile Annelida
  • Oligochaeta: have setae
  • Hirudinea: leeches, have suckers Arthropoda
  • Chelicerata: parasitic insects, aquatic
  • Hexapoda: aquatic Crustacea
  • Subphylum in Arthropoda
  • Malacostraca: crayfish and shrimps, isopods
  • Ostracoda: seed shrimps
  • Brachiopoda: fairy shrimps, tadpole shrimps, cladocerans
  • Copepoda: zooplanktons Hemiptera
  • "true bugs"
  • piercing-sucking mouth parts Diptera
  • flies, gnats and mosquitoes
  • complete metamorphosis
  • important disease vectors Odonata
  • dragonflies and damselflies
  • aquatic nymphs Ephemeroptera
  • have three caudal filaments
  • many species are indicators of clean water
  • emerge in autumn in large numbers Trichoptera
  • caddis flies
  • nymphs construct nets and cases
  • cool lotic waters Plecoptera
  • stone flies
  • inhabitants of clean, cool waters
  • good bioindicators Megaloptera
  • dobson flies
  • predaceous larvae Isopoda
  • pill bugs, sow bugs
  • aquatic and terrestrial forms Pisces
  • fishes
  • true freshwater fish have no recent marine background or ancestry: minnows (cyprinidae), sunfishes (centrarchidae), perches (percidae), pikes (esocidae)
  • Mictic females develop, produce haploid eggs via meiosis
  • Unfertilized eggs develop into males, who then mate with mictic females to produce thick-walled resting eggs --> resistant to adverse environmental conditions
  • Eggs remain in diapause until favorable conditions return
  • Hatch into amictic females Rotifers: Population Dynamics
  • Different species exhibit different population peaks
  • Some in early summer, others in winter/early spring Rotifers: Cyclomorphosis
  • Seasonal polymorphism
  • Elongation, enlargement or reduction, production of spines, which prevent ingestion from other organisms
  • Reduces sinking rate, copes with larger prey, better resist predation
  • Formation of spines induced by kairomone produced by predator Rotifers: Use by Fish
  • Too small to be important as food for most fish
  • May be important in diets of some larval fish
  • Potential prey for predatory copepods
  • Vertical migration upward at midday to avoid copepods Cladocera: Characteristics & Feeding
  • Small crustaceans, with head and body covered by bivalve carapace
  • Swim by using large second antennae
  • Phytoplankton, detritus for food
  • Selective filtering and can alter phytoplankton succession Cladocera: Reproduction
  • Parthenogenesis by diploid females throughout most of the growing season
  • Continues until interrupted by: temp reductions, drying, crowding, decrease in food size
  • Some eggs develop into diploid males
  • Females produce haploid eggs
  • Mate with males
  • Fertilized eggs overwinter in thickened brood pouch ephippium - which can withstand severe conditions
  • Can be transported by birds to other waters
  • Hatch under favourable conditions into parthenogenetic females Cladocera: Population Dynamics
  • Overwinter as adults, others as resting eggs Cladocera: Diurnal Vertical Migrations
  • Twice a day
  • Most migrate to surface at dusk, downward at dawn (light intensity the stimulus)
  • Reasons: avoid visual feeding fish by feeding on phytoplankton after dark and improve food utilization Cladocera: Cyclomorphosis
  • Extension of head to form helmet
  • Increase of caudal spine length
  • Advantage of allowing for continued growth of transparent peripheral structures without enlarging central portion of body
  • Reduces predation Cladocera: Use by Fish
  • Large species favoured by many fish
  • Eliminates large forms, small ones flourish (big forms often predatory) Copepods: Characteristics
  • Microcrustaceans in same size range as cladocerans
  • Several different groups based on differences in body structure
  • 2 major groups: cyclopoids and calanoids Cyclopoids
  • Short 1st antennae
  • Littoral, but few are open-water planktonic forms
  • Seize food particles and bring them to mouth - raptorial
  • Most are predators, some are herbivores
  • Move by swimming with legs Calanoids
  • Long 1st antennae
  • Almost strictly open-water planktonic
  • Filter feeders on algae, detritus
  • Have filtering appendages near mouth - maxillae Copepods: Reproduction
  • No parthenogenesis (females cannot produce copies of themselves)
  • Both males, females present
  • Sexual reproduction always present
  • Fertilized eggs carried attached to female's abdomen
  • Eggs hatch into nauplius larvae - 3 pairs of legs
  • Grow and molt several times to become copepodite, grow and molt more before becoming adult
  • Longer period time from egg to adult than in rotifers, cladocerans
  • May have resting eggs (overwinter), or diapause in egg or copepodite stage Copepod: Community Dynamics
  • Limited by few general characteristics
  • Food availability
  • Type of substrate (what is on the bottom of lakes) Littoral vs. Profundal
  • Benthic animals living in littoral region varied than those in profundal region
  • Reflection of abundance of microhabitats
  • Less stressful living conditions Littoral Benthos
  • Protozoans, sponges, rotifers, cladocerans, copepods
  • Seldom food limited
  • Proximity to phytoplankton, macrophytes Microbethos
  • Very tiny
  • Outnumber macrobenthos, and may contribute up to 50% of benthic production Sublittoral Benthos
  • Boundary between littoral & profundal
  • Species diversity drops off sharply
  • Mussels, ostracods, copepods, cladocerans Profundal Benthos
  • Very poor diversity
  • Oxygen limited
  • Profundal Benthos in Eutrophic lakes resemble those of grossly polluted systems
  • Low diversity --> monotony: great number of individuals, but only 1 or 2 species represented Profundal Benthos: Typical Profundal Assemblage Chironomus Midge Larvae: hemoglobin picks up limited oxygen Oligochaete worms: Tubifex and Limnodrilus, which bury heads in organic sediments, wave tails with gills Fingernail clams: Pisidium- become dormant during anaerobic periods Phantom midge larvae: spend day on sediments, migrate into water column at night to prey on zooplankton Profundal Benthos: Less Productive Lakes
  • Profundal benthos more diverse in less productive (oligotrophic) lakes
  • More species of midge larvae, oligochaetes, mayflies, hexagenia
  • More crustaceans
  • Make vertical migrations up to metalimnion at night General Benthos Pattern
  • Diverse group in heterogenous, oxygenated littoral zone
  • Less diversity in more homogenous profundal zone Maxima of Abundance As systems become more productive, zone of maximum production shifts from littoral to profundal, then declines in profundal It shifts as you add more nutrients Seasonal Abundance Patterns
  • Lowest in summer
  • Emergence of adults, high predation
  • Maximum densities and growth typically in autumn and winter in temperate zone Predation by Fish
  • Predation can drastically reduce invertebrate standing crop --> may be >50% of populations in some littoral areas
  • Predation losses in profundal areas generally much lower
  • Despite intense predation pressure, benthos dynamics and production mostly controlled by food supply (eg, how much energy they have) Ecosystem Ecology
  • Organisms absorb, transform and eventually release chemicals and energy in multiple forms
  • Not a closed system, but as system receives sunlight, exchanges gases with atmosphere, and receives runoff from terrestrial habitats Food Chains
  • Trophic levels (producers, consumers, detrital community)
  • Within each level, species with a variety of niches
  • Ectomorphs: organisms occupying similar niches in different environment (having similar physical characteristics) Energy Flow
  • All ecosystems rely on an energy input to operate
  • First two laws of thermodynamics: laws mean that only a small fraction of energy is utilized in limiting productivity and length of food chain How do organisms avoid decay and postpone death?
  • We feed continuously on negative entropy
  • Take in orderliness from organic compounds
  • Most important source: primary producers
  • 8 - 10% light energy converted to biomass
  • 20% spent on cells, metabolism Only expend about 15-25% of the energy that they fix Secondary Production P = (N1 - N2) x (w1 + w2 )/ 2 N1 = number of animals per unit area at beginning of year N2 = number of animals per unit area at end of year w1,w2 = mean weight of individuals at beginning and end of year
  • Difficult to measure in comparison with primary production
  • Allows a calculation of yield, a rough approximation of net production
  • Mortality and reproduction not taken into account using this method Secondary Production: Introduction of fish
  • Introducing fish at beginning of season, harvest later to measure how much weight they gained
  • Allows a calculation of yield or net production
  • Mortality and reproduction not taken into account Allen Curve Method
  • Study cohort through the year, usually offspring born that year
  • Sampling gives estimates of number of individuals per m2 and weight of each individual (sample & weigh several times)
  • Area under curve represents annual production Trophic cascades
  • Idea that predators can control populations in trophic levels below them
  • Top-down control by predators, or bottom-up control (primary production) Limits on primary production Redfield ratio is often the starting point to consider nutrient limitation N:P > 17 phosphorus limitation N:P < 10 = nitrogen limitation 10<N:P<17 = co-limitation Our predictions based on these ratios don't always match reality Limits on primary production: 21 lakes and ponds in Wapusk National Park
  • Collected water containing algae from these waterbodies and tested the effecting of adding nitrogen and phosphorus
  • 38% of lakes not limited by either nutrient
  • 26% P-limited, 13% N-limited

Limits on primary production: 30 small lakes

  • In cumbria, Wales, Scotland and Ireland
  • Collected water with algae and added N,P or N+P to determine limiting nutrients
  • 24% of lakes limited by P
  • 13% by N
  • 63% both N and P Limits on primary production: Limitations of Phosphorus, Nitrogen and both Limits on primary production: Relationship between phosphorus and cholorphyll a
  • Believed if add more phosphorus, chlorophyll a increases
  • However, it takes into account the different lakes, eg. Tropical and arctic
  • Our part of the world exhibits the belief, but the tropical and arctic do not Limits on primary production: Other variables
  • If line is perfectly flat, then the variable doesn't influence TP- chlorophyll relationship
  • Slope up or down, indicate or influence relationship
  • mean depth, max depth, secchi depth, total nitrogen, elevation