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Chapter 3 notes for the aquatic environment.
Typology: Lecture notes
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Chapter 3 – The Aquatic Environment Water is the essential substance of life Water Cycles Between Earth + the Atmosphere Water cycle (hydrologic cycle) – process by which water travels in a sequence from the air to the Earth + returns to the atmosphere o Solar radiation is the driving force behind the water cycle because it provides the energy for the evaporation of water Water vapor eventually falls in some sort of precipitation Interception – occurs when precipitation falls onto vegetation, dead organic matter, + urban structures or streets. This water evaporates directly back to the atmosphere Infiltration – precipitation that reaches the soil + moves into the ground o Surface runoff – occurs when soils is saturated o Water that seeps down to an impervious layer of rock collects as ground water
Evapotranspiration – total amount of evaporating water o Superficial water in terrestrial + aquatic environments returns to the atmosphere by evaporation o Transpiration – evaporation of water from the internal surfaces of plants Stomata open to in take CO2, lose water from opening up Ecological Issues: Groundwater Resources Irrigation of agricultural fields provides a steady supply of water o Generally supplied by groundwater
The High Plains – Ogalla aquifer supplies about 30% of irrigation water used in the US o Aquifer – a layer of water – bearing rock, sand, or gravel water is deep underground o NOT a limitless resource o This aquifer is being withdrawn faster than it is being recharged Decreased water levels have increased costs for pumping water Some water no longer meets EPA standards for human consumption Water’s Important Physical Properties H2O atoms are asymmetrically bonded to one another H atoms share an e- w/ O2 through a covalent bond o H2O is polar Aquatic organisms must cope w/ frictional resistance of water + overcome viscosity o High viscosity due to greater density Light Varies w/ Depth in Aquatic Environments Some light that strikes surface of water is reflected; amount of light is related to angle of light o Light does not penetrate uniformly to depths Longer light wavelengths (red light) are absorbed first. Blue wavelengths alone penetrate the depths
Seasonal changes in the input of solar radiation give rise to changes in the vertical depth profile o Position of thermocline is permanent in tropical waters Temperature profile of a flowing body of water is highly variable Oxygen Diffuses from Atmosphere to the Surface Waters Oxygen diffuses from atmosphere into surface waters of aquatic environments
o ★ Rate of diffusion is dependent on solubility of O2 (greater in cold water) + the diffusion gradient ★ O2 diffuses from the surface to the waters below O2 may become stratified in lakes + ponds during summer o Warm water holds less O o Both atmosphere + aquatic plants are O2 sources o O2 demand by organisms decreases w/ depth Many lakes undergo semiannual mixing of water (turnover) O2 is not uniformly distributed within the depths of the ocean o Max O2 levels are in the upper 10 – 20 m o O2 content of flowing water is high due to greater contact of water w/ atmosphere Even at saturated levels, O2 supply in aquatic environments is meager when compared w/ supply in atmosphere o O2 is a great limiting factor: water can’t hold much O Water Movements Shape Freshwater + Marine Environments Currents + waves determine the nature of aquatic environments o Current velocity forms character + structure of a stream Surface waves are generated by wind
Organisms that live in sand + mud do not experience the same fluctuations as those living on rocky shores Transition Zone Between Freshwater + Saltwater Environments Presents Unique Constraints Estuary – place where freshwater joins + mixes w/ saltwater o Strongly influenced by tides + experiences wide fluctuations in temperature as tidal water advances + recedes Inflowing freshwater + tidal saltwater influence the salinity of the estuary o Variation in salinity Estuaries are areas of low organism diversity but high productivity o Low diversity but lots of them