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UT ENS 112 - Chapter 12

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Environmental Science 112FALL SEMESTER 2018INSTRUCTOR: DR. Adrienne [email protected] 12Freshwater Systems● Majority (97.5%) of Earth’s Water is in the oceans and is too salty to drink or use for irrigation○ Only 2.5% is considered fresh water, water that is relatively pure and free from salts■ 79% trapped in ice caps and glaciers■ 20% trapped in groundwater ■ 1% is surface water, fresh water that is easily available to us● Figure 12.3● Surface water is located atop Earth’s surface, such as in a river or lake● Groundwater is water beneath the surface that resides within pores in soil or rock○ Any water that does not evaporate, flow into waterways, or get taken up by organisms will infiltrate into groundwater○ Groundwater can remain underground for thousands of years at a timeGroundwater plays key roles in the hydrologic cycle● Groundwater is contained within aquifers…● …● Areas where water can infiltrate through the surface and reach the aquifer = recharge zone● Confined aquifers are trapped between impermeable clay, while unconfined aquifers are notSurface Water converges in river and stream ecosystems1● Surface water becomes groundwater by infiltration● Groundwater becomes surface water through springs● Water that falls from the sky or melts from snow or a glacier that flows over a land surface is called runof○ Runof converges in low-lying areas, forming streams, which can merge into rivers, which eventually reach a lake or oceans● The are of land drained by a river system and all of its tributaries makes up that river’s drainage basin or watershed● Areas near a river's course that are flooded periodically are within the rivers floodplain○ Frequent flooding and deposition of soil makes floodplain soils especially fertile○ Agriculture thrives in flood plains, and riparian forests near riversides are especially rich in speciesLakes and ponds are ecologically diverse systems● Different Zones○ Littoral: outer edge/coast, aquatic plants○ Limnetic: top, sun, photosynthesis, phytoplankton○ Profundal: middle, no sun, no photosynthesis○ Benthic: bottom, no sun, no photosynthesis● Ponds and lakes can change over time as rivers and streams bring them nutrients● Oligotrophic lakes and ponds are low in nutrients and high in oxygen● Over time, the addition of nutrients can transition the lake or pond to eutrophic -- high-nutrient, low oxygen -- conditionsFreshwater wetlands include marshes, swamps, bogs, and vernal ponds● Wetlands are systems where the soil is saturated with water●Freshwater marshes consist of plants that grow above the water's surface●Swamps also contain standing water but are in forested areas2●Bogs are ponds covered in thick floating mats of vegetation● Wetlands can be seasonal, such as vernal pools that form in the snowmelt of early springs and dry up later in the summer● Wetlands provide many water-related ecosystem services including slowing runoff, reducing flooding, recharging aquifers, and filtering pollutants● Wetlands have been heavily impacted by human activities, including draining and filling for agriculture, withdrawing water for irrigation, and construction of damsThe Oceans● The world’s five oceans are all connected, making a single body of water that covers 71% of Earth’s surfaceThe physical makeup of the ocean is complex● Ocean water contains ~ 96.5% water by mass, with the rest consisting of ions from dissolved salts○ The salts arise from runoff that carries salts and sediments from continents into the oceans● Sunlight does not penetrate ocean water deeply, so temperatures tend to decrease with depth● Vast, river like flows of water called currents are driven by differences in density, heating, cooling, gravity, and wind● Water movement○ Horizontal■ Currents○ Vertical ■ Pulling● Brings nutrients up the the surface ↑■ Downwelling3● Moving water from the surface down to the depths ↓● Can bring oxygen down to the depths and takes carbon dioxide down to the depths, and out of the atmosphere● Surface winds and heating also create vertical currents in seawater● Upwelling pulls cold,deep, nutrient-rich water to the surface● Surface currents that converge create downwellings, which transport warm surfacewater to deeper waters, providing and influx of dissolved oxygen and “burying” carbon dioxide from the atmosphere● Many parts of the ocean floor are rugged and complex○ Underwater volcanoes can build islands above sea level○ The Mid-Atlantic Ridge is an underwater mountain range that runs the lengthof the Atlantic OceanOcean Currents afect Earth’s climate● The thermohaline circulation is a worldwide current system in which warmer, lower-salinity water moves along the surface and colder, saltier (denser) water moves horizontally below the surface○ This moves warm water in the Gulf Stream to the Atlantic Ocean near Europe, where heat is released and the cooler water sinks● The region of downwelling near western Europe is called the North Atlantic Deep Water (NADW)○ Scientists are concerned that an influx in freshwater from melting glaciers in Greenland could disrupt this flow■ Water loses heat to cold air and sinks■ Sunlight warms water on ocean's surface in tropics■ This whole process takes about 1000 yearsOcean currents afect Earth’s climate● The El Nino-Southern Oscillation (ENSO) is a systematic shift in atmospheric pressure, sea surface temperature, and ocean circulation in the tropical Pacific 4Ocean● Under normal conditions, prevailing winds blow from east to west along the equator, forming a large convective loop in the atmosphere○ This causes a “pile-up” of warm water to form near Indonesia, fueling storms in that region● El Nino conditions are triggered when air pressure decreases in the eastern pacific and increases in the western Pacific○ This can create storm activity in normally arid regions like california and drierconditions in Indonesia● La Nina events are the opposite of El Nino events; unusually cold waters rise to the surface and extends westward, causing winds blowing to the west to strengthen● ENSO cycles occur every 2-8 years○ Scientists are studying whether changes in air and sea temperatures are increasing the frequency and strength of these cyclesMarine and Coastal Ecosystems● Regions of ocean water differ greatly, with certain zones supporting more life


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