Comprehensive Study Guide for University Limnology

Introduction to Ecology and Environments

• Ecology Defined: The study of interrelations between organisms and their environments. Occasionally termed natural history, hexiology, bionomics, or ethology.

• Environmental Divisions:

  • Lithosphere: Land masses.

  • Hydrosphere: Oceans, lakes, streams, and subterranean waters.

• Hydrography Subdivisions:

  • Oceanography: Study of large salt-water masses.

  • Limnology: Study of inland waters (usually fresh).

• Limnology Definition: The branch of science dealing with the biological productivity of inland waters and all causal influences (physical, chemical, biological, meteorological) determining it.

• Ecosystem Dynamics:

  • Lotic Series (Running-water): Brook > creek > river. Characterized by continuous movement in a definite direction.

  • Lentic Series (Standing-water): Lake > pond > swamp. Characterized by lack of continuous flow in a definite direction.

History of Limnology and Oceanography

• Early Oceanography: Traced back to ancient seagoers and expeditions (e.g., Cook's voyages, the Challenger expedition under Wyville Thomson).

• Beginnings of Limnology: Existed as a distinct field for less than 60 years. Rooted in observations by Aristotle ($384-322$ B.C.).

• Invention of the Microscope: Late 16th century. Anton van Leeuwenhoek ($1632-1723$) first described minute water organisms.

• Discovery of Plankton: Term proposed by Hensen in 1887. Johannes Müller and Peter Erasmus Müller identified microscopic life in the North Sea and Swiss lakes.

• F. A. Forel ($1841-1912$): Known as the founder of modern limnology. Published Le Léman ($1892-1904$) and Handbuch der Seenkunde ($1901$).

• American Limnology: Early work by Louis Agassiz ($1850$) on Lake Superior. Development led by Birge and Juday (Wisconsin lakes), Reighard, and Ward.

Physical Features of Inland Waters

• Morphometry: Measurement of lake basin size and form (shoreline, area, depth, slope, volume).

• Pressure: Density of pure water is $62.4$ lb/cu ft at $4$ C. Hydrostatic pressure at depth is the weight of the water column plus atmospheric pressure.

• Density-Temperature Relationship: Water reaches maximum density at $4$ C ($1.000000$ g/cm³). It becomes less dense as it cools toward $0$ C or warms above $4$ C ($0.999870$ at $0$ C; $0.998230$ at $20$ C).

• Viscosity: Internal friction that decreases as temperature rises. Water is more mobile at summer temperatures than near freezing.

• Thermal Stratification:

  • Epilimnion: Upper, warm, circulating layer.

  • Thermocline (Metalimnion): Region of rapid temperature drop (at least $1$ C per meter of depth).

  • Hypolimnion: Lower, cold, stagnant layer.

• Seasonal Cycle:

  • Spring Overturn: Lake becomes homothermous at $4$ C; wind circulates water from top to bottom.

  • Summer Stagnation: Stratification prevents mixing between layers.

  • Fall Overturn: Surface cools to match bottom temperature; total circulation occurs.

  • Winter Stagnation: Inverse stratification under ice (colder water on top).

• Light Penetration: Measured via Secchi’s Disk or Pyrlimnometer. Transmission is affected by absorption (water itself), stain (color/organic matter), and turbidity (suspended particles).

• Water Color: True color (colloids/solutes) vs. apparent color (suspended matter/sky reflection). Often measured on the platinum-cobalt scale.

Chemical Conditions and Dissolved Gases

• Dissolved Oxygen ($O_2$): Vital for respiration. Enters via atmosphere/agitation and photosynthesis. Consumed by respiration, decomposition, and reduction by other gases. Saturation at $0$ C is $10.2$ cc/l; at $25$ C is $5.8$ cc/l.

• Carbon Dioxide ($CO<em>2$): Derived from air, ground water, respiration, and decomposition. Occurs as free $CO</em>2$, bound (monocarbonates), and half-bound (bicarbonates).

• Hardness Classification:

  • Soft-water: Bound $CO_2 < 5$ cc/l.

  • Medium-class: Bound $CO_2$ is $5-22$ cc/l.

  • Hard-water: Bound $CO_2 > 22$ cc/l.

• Hydrogen-ion Concentration ($pH$): Measure of acid intensity. $pH = 7$ is neutral. Natural waters range from $3.2$ to $10.5$.

• Dissolved Solids: Inorganic (Nitrogen, Silicon, Phosphorus) and Organic (Carbon, Nitrogen, Fats). Total dissolved organic matter in Wisconsin lakes averaged $12.8$ mg/l.

• Phosphorus ($P$): Often a limiting factor for productivity. Occurs as soluble phosphate or organic phosphorus.

Lake Basin Dynamics and Evolution

• Origin of Basins: Glacial action, landslides, solution (limestone sinks), volcanic craters, and river activities.

• Shore Dynamics:

  • Shore Cutting: Erosion by wave action.

  • Shore Building: Formation of beach ridges, bars, and sand spits.

• Extinction of Lakes: Primarily via filling with sediments (wind-blown materials, stream silts, organic plant remains) or drainage by outlets.

• Bottom Deposits: Classified as inorganic (boulders, sand, clay, marl) or organic (detritus, peat, muck). Stratification of mud (varves) reveals historical chronologies.

• Basin Seal: Fine sediments clog bottom interstices, preventing outseepage.