PAGE 1: AQUATIC ECOLOGY & PHYSICAL PROPERTIES
I. PROPERTIES OF THE WATER MOLECULE
● Polarity: Water has a positive and negative end, making it the Universal Solvent .
● Hydrogen Bonding: Causes Cohesion (water sticks to water) and Surface Tension .
● Density: Max density is at 4 celcius . Ice is less dense than liquid water, allowing it to float and insulate life
below.
● Specific Heat: Water resists temperature changes, stabilizing aquatic climates.
II. THE HYDROLOGIC CYCLE
● Infiltration/Percolation: Water soaking into soil/aquifers.
● Evapotranspiration: Water leaving plants and soil into the air.
● Runoff: Water flowing over land into bodies of water; carries pollutants.
III. STREAM & RIVER SYSTEMS (LOTIC)
● Stream Order: Smallest headwaters = 1st Order . Two 1sts make a 2nd ; two 2nds make a 3rd .
● River Continuum Concept (RCC):
○ Headwaters (1-3): Shaded, cold, dominated by Shredders (eat leaves/detritus).
○ Mid-reach (4-6): Open canopy, more sun/algae, dominated by Scrapers/Grazers .
○ Large Rivers (7+): Turbid (cloudy), deep, dominated by Collectors (eat fine floating bits).
● Riffle vs. Pool: Riffles (shallow/fast/oxygenated) vs. Pools (deep/slow/sediment).
IV. LAKE SYSTEMS (LENTIC)
● Zonation:
○ Littoral: Shallow shore, rooted plants (high biodiversity).
○ Limnetic: Open surface water, light reaches (phytoplankton).
○ Profundal/Aphotic: Deep, dark, cold.
○ Benthic: The very bottom sediment (decomposers).
● Thermal Stratification (Summer):
○ Epilimnion: Warm, low-density top layer.
○ Metalimnion (Thermocline): Rapid temperature drop.
○ Hypolimnion: Cold, dense bottom layer (often low oxygen).
● Turnover: Occurs in Spring/Fall . Surface water hits 4c (max density), sinks, and mixes the lake, bringing
oxygen to the bottom and nutrients to the top.
PAGE 2: NUTRIENT CYCLES & HUMAN IMPACT
I. THE NITROGEN CYCLE
● Nitrogen Fixation: $N_2$ gas -> Ammonia ($NH_3$). Done by specialized bacteria.
● Nitrification: Ammonia $\rightarrow$ Nitrite ($NO_2^-$)->$ Nitrate ($NO_3^-$) . Nitrates are the primary
nutrient plants use.
● Assimilation: Plants take up nitrates to build proteins.
● Denitrification: Bacteria convert nitrates back into $N_2$ gas in oxygen-poor (anaerobic) conditions.
II. PHOSPHORUS & OTHER MACRONUTRIENTS
● Limiting Factor: Phosphorus is usually the scarcest nutrient in freshwater; its presence controls algal
growth.
● Carbon Cycle: Involves $CO_2$ for photosynthesis and carbonic acid/bicarbonate for pH buffering.
III. CULTURAL EUTROPHICATION
● Step 1: Nutrient influx (Nitrogen/Phosphorus from fertilizer/sewage).
● Step 2: Algal Bloom (rapid growth of algae).
● Step 3: Algae die and sink to the bottom.
● Step 4: Decomposition. Aerobic bacteria eat the dead algae.
● Step 5: Hypoxia. Bacteria use up all Dissolved Oxygen (DO) .
● Step 6: Fish and other oxygen-dependent life suffocate and die.
IV. POLLUTION TYPES
● Point Source: Identifiable "end-of-pipe" discharge (factories, sewage plants).
● Non-Point Source: Diffuse runoff (pesticides from 1,000 lawns, road salt, acid rain).
● Thermal Pollution: Hot water discharge from power plants (reduces DO solubility).
● Acid Rain: Lowers pH; caused by Sulfur/Nitrogen oxides from burning fossil fuels.
PAGE 3: MACROINVERTEBRATES & INVASIVE SPECIES
I. THE BIOTIC INDEX (HBI)
● Organisms are indicators because they cannot swim away from pollution.
● Formula: HBI =summation (n_i times a_i)}/(N) where n = # of individuals, a = tolerance value, N = total # of
individuals.
● Lower HBI = Better Water Quality.
II. IDENTIFICATION BY TOLERANCE
● Class 1 (Pollution Sensitive - High Quality):
○ Mayfly: 3 tails, abdominal gills.
○ Stonefly: 2 tails, thoracic ("armpit") gills.
