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