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Environmental Science
Carl Mitchell

Freshwater Systems y Roughly 975 of earths water resides on the oceans and Is too salty to drink or to use to water crops o 25 is considered freshwaterwater that is relatively pure with few dissolved salts Some of which is tied up in glaciers icecaps and underground aquifers just over 1 part in 10000 of earths water is easily accessible for human use y Water is moving among reservoirs via the hydrological cycle o As it moves it redistributes heat erodes mountain ranges builds river deltas maintains organisms and ecosystems shapes civilizations and gives rise to political conflict Rivers and streams wind through landscapes y Water from rain snowmelt or springs runs downhill and converges where the land dips lowest forming streams creeks or brooks o Thesewatercourses merge into rivers which eventually lead to oceanA small river flowing into a larger one is a tributaryThe area of land drained by a river and all its tributaries is that rivers drainage basin or watershed y Rivers shape the landscape through which they runo The force of water gradually eats at the outer shore eroding soil from the bankMeanwhile sediment is deposited along the inside of the bend where water currents are weakerBecause of this river bends become exaggerated in shape y Eventually a bend may become such an extreme loop oxbow that water erodes a short cut from one end of the loop to the other creating a direct course oxbox lake y Areas nearest a rivers course that are flooded periodically are said to be within a rivers floodplain y Agriculture thrives in foodplains and riparian river side forests are productive and species rich Wetlands include marshes swamps and bogs y Wetlands are systems that combine elements of freshwater and dry land y in freshwater marshes shallow water allows plants to grow above the waters surface y Swamps also consist of shallow water rich in vegetation but they occur in forested areaso Also created when beavers build dams across streams with limbs from trees they have cut flooding wooden areas upstream y Bogs are ponds thoroughly covered with thick floating mats of vegetation and can represent a stage in aquatic succession y Wetland are extremely valuable as habitat for wildlifealso provide important ecosystem services by slowing runoff reducing flooding recharging aquifers and filtering pollutantsLakes and ponds are ecologically diverse systems y The region ringing the edge of a water body is named the littoral zone o Water is shallow enough here that aquatic plants grow from the mud and reach above waters surface o Has a lot of crayfish snails insect larvae for fish birds turtles and amphibians to feed off of y The benthic zone extends along the bottom of the entire water body o Many invertebrates live here feeding on detritus or preying on one another y Sunlight penetrates shallow waters of the limnetic zoneo Limnetic zone supports phytoplanktono Sunlight intensity decreases with depth clear water allows sunlight to penetrate deeply y Below the limnetic zone is the profundal zonethe volume of open water that sunlight does not reach o Lacks plant life and supports fewer animals y Oligotrophic lakes and ponds which have lownutrient and highoxygen conditions may slowly give way to the high nutrient lowoxygen conditions of eutrophic water bodies o Lakes or ponds change over time specie sof fish plants and invertebrates adapted to oligotrophic conditions may give way to those that thrive under eutrophic conditions y Lakes as big as the great lakes hold so much water that their biota is adapted to open water making them differ substantially in their characteristics from small lakes Groundwater plays key roles in the hydrologic cycle y Most precipitation percolates downward through the soil to become groundwater o Groundwater makes up 15 of earths freshwater supply o Is contained within aquifers porous formations of rock sand or gravel that hold waterAn aquifers upper layer zone of aeration contains pore spaces filled with airIn the lower layer zone of saturation the spaces are filled with water y The boundary between these two zones is the water table o Ex Picture a sponge resting partly in a tray of water top contains some water but bottom contains more y Any area where water infiltrates earths surface and reaches an aquifer below is known as an aquifer recharge zone y There are two broad categories of aquifers o A confined aquifer artesian aquifer exists when a water beating porous layer of rock sand or gravel is trapped between upper and lower layers of less permeable substrateoften clay In this situation the water is under great pressure o A unconfined aquifer has no such impermeable layer to confine it so its water is under less pressure and can be readily recharged by surface water y Groundwater becomes surface water through springs and wells o It flows until it reaches surface water bodies at discharge zones o Typical flow might be about 1 m per day so it can remain in an aquifer for a long time
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