LIMNOLOGYDR. SANJAY SINGHDEPTT. OF BOTANY
CMP DEGREE COLLEGE, ALLAHABAD
“the oceanography of lakes”
Study of the functional relationships and productivity of freshwater communities, as they are regulated by the dynamics of their physical, chemical, and biotic environments
Gradually grew to encompass all inland waters
Today includes standing water (lentic habitats) as well as running water (lotic habitats)
INTRODUCTION
Properties of waterUnique characteristics of
water regulate the chemical, physical, and metabolic activities in freshwater systems1) non-linear relationship between temperature and density2) high specific heat3) viscosity-density relationship4) high surface tension5) 3 atoms arranged into non-linear molecule6) 104.5° angle
Structure of Water Molecule
Each water molecule can have hydrogen bonds with as many as 4 other water moleculesStructure most obvious in iceCreates tetrahedral patternLots of space between moleculesLow density - it floats
Temperature-Density
Non-linearMaximum density at 4°CLower density at higher and lower temperaturesHydrogen bonding and molecular movement
Specific HeatOr heat capacity - high for waterAmount of heat energy required to raise unit mass 1°CBecause of hydrogen bondingTemperature changes occur more gradually in lakes than in terrestrial environsLakes can buffer climate of nearby land masses
Warmer in winter, cooler in summer
Viscosity-Density RelationViscosity - resistance to flowViscosity of water increases as density increasesIt doubles as temp decreases from 25°C to 0°CChange not apparent to human eyeProfound effect on movements of microscopic plants and animals, and sinking of particles in lakes
High Surface TensionHydrogen bonding interrupted at air-water interface“molecules exert an inward adhesion to the liquid phase”Molecules at surface resist being pulled apartAllows objects that would normally sink in water to be supported on the surfaceMercury is the only liquid with a higher surface tensionIncreases slightly with increased salinity, decreases with increased temperature, addition of organic compounds
Limnology(lentic = lakes and ponds; lotic = streams and rivers)
Lake Zones
Limnology: light
Limnology: lightWATER CLARITYCauses and significance
Causes•Turbidity (Suspended solids)•Plankton blooms•Pollutants
Significance•Reduces light penetration•Reduces Photosynthesis•Reduses feeding efficiency of fishes
Heating and coolingSources of heat:
1.Direct solar radiation (most important)2.Groundwater and springs 3.Ground (minor)
Losses of heat:
1.Thermal radiation (primary)2.Conduction3.Evaporation4.Outflow
Temperature Cycles & Lake StratificationMost lakes mix during some seasons and become stratified during other seasons.These terms refer to the vertical circulation of water: Mixing = circulation, Stratification = lack of mixing (development of layers)The mixing pattern has a large effect on lake chemistry and the biotaLakes have traditionally been classified according to their annual mixing pattern or mixing regime (amictic, monomictic, dimictic, etc.)
Temperate zone Dimictic Lake
Stratified
Stratified
Mixing
Mixing
Thermal zones in a stratifed lake
Metalimnion
Mixing and Stratification
ESSENTIALS 0F A THERMAL PROFILE: WHAT DOES IT MEAN?
Thermal stratification-Effects vertical circulation of water and reduces mixing of deep and surface water
• Prevents up welling of nutrients• Concentrates pollution
Unstratified lake-Allow nutrients to react shallow water-Nutrients and light allowed for photosynthesis
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