BIO 366 1st Edition Lecture 6Chapter 33.1- Water Cycles between Earth and the AtmosphereWater- 75-95% of weight of all living cells 75% of planets surfaceWater Cycle or hydrologic cycle- process by which water travels in a sequence from the air to Earth and returns to the atmosphere-Marine and freshwater are linked directly and indirectly as components in water cycle-Driving force- solar radiation which heats Earth’s atmosphere and provides energy for the evaporation of waterPrecipitation- sets water cycle in motion with water vapor eventually falling into some form of precipitation circling the atmosphereInterception- process when water is intercepted by vegetation (dead organic matter on the ground) and urban structures and streets-various amounts of water never infiltrate the ground but evaporates directly back into the atmosphereInfiltration- Water moving down into the soil-rate depends on type of soil, slope, vegetation, and intensity of precipitationSurface runoff- also known as overland flow-excess water flowing across the surface of the ground during heavy rain when soil is saturated-runoff can be as much as 85% because of low infiltrationGroundwater- water that seeps down and collects in the layers of clay or rockTranspiration- process when plants roots take in water from the soil and lose it through their leaves and other organs-the evaporation of water from internal surfaces of leaves, stems, and other livingpartsEvapotranspiration- the total amount of evaporating water from the surfaces of the ground and vegetation3.2- Water has Important Physical PropertiesHydrogen bonding- where hydrogen atoms act as connecting links between water moleculesSpecific heat- the number of calories necessary to raise the temperature of 1 gram of water 1 degree CelsiusCohesion- water molecules sticking firmly to one another and resisting external forces that would break their bondsSurface tension- molecules drawn downwards on surfaces resulting in a surface that is taut like an inflated balloon-important to the lives of aquatic organismsViscosity- property of a material that measures the force necessary to separate the molecules and allow and object to pass through the liquid-the source of frictional resistance to objects moving through water3.3- Light varies with Depth in Aquatic EnvironmentsTwo processes for the amount of light entering the water surface:Alive and dead suspended particles intercept the light and either absorb or scatter it Water absorbs light itself and absorbs some wavelengths more than others 3.4- Temperature Varies with Water DepthThermocline- region of vertical depth profile where the temperature declines most rapidly -density change at the thermocline acts as a physical barrier that prevents mixing of the upper and lower layersEpilimnion- upper layer of warm, lighter (less dense) water where thermocline is locatedHypolimnion- deeper layer of cold, denser water3.5- Water Functions as a SolventSolution- liquid that is a homogeneous mixture of two or more substancesSolvent- the dissolving agent of a solutionSolute- substance that is dissolvedPractical Salinity Units(psu)- how salinity is expressed-represented as % and measured as grams of chlorine per kilogram of water3.6- Oxygen Diffuses from the Atmosphere to the Surface WatersDiffusion- general tendency of molecules to move from region of high concentration to low3.7- Acidity Has a Widespread Influence on Aquatic EnvironmentsAcidity- measure of abundance of hydrogen ions in a solution -the greater number of H+ ions the more acidityAlkaline- solutions that have a large number of OH- and few H+ ionspH- the measure of acidity and alkalinity3.8- Water Movements Shape Freshwater and Marine EnvironmentsUpwelling- process where warm surface currents of the tropical waters that move northward and southward bring up deep, cold, oxygenated waters from below-A pattern of coastal upwelling is created when water moves upward from the deep replacing the surface water3.9- Tides Dominate the Marine Coastal EnvironmentSprungen- the brimming fullness and active movement of waterIntertidal zone- an environment of extremes-Area lying between the water lines of high and low tide3.10- The Transition Zone between Freshwater and Saltwater EnvironmentsPresents Unique ConstraintsEstuary- place where freshwater mixes with saltwater -temperatures fluctuate considerablyTidal overmixing- mixing of freshwater and seawater when a tidal wedge of seawater moves upstream in a tidal river faster than freshwater moves seaward -seawater on the surfaces tends to risk as lighter freshwater rises to the