This lecture will help you understand:

1. This lecture will help you understand: • Water and the hydrologic cycle • Water’s distribution on Earth • Freshwater ecosystems • Use and alteration of freshwater systems • The marine environment

2. Freshwater systems • Water may seem abundant, but drinkable water is rare • Freshwater = relatively pure, with few dissolved salts • Only 2.5% of Earth’s water is fresh • Most freshwater is tied up in glaciers and ice caps

3. Water storage • Water Reservoir – a place in the atmosphere, ocean or underground where water is stored for a period of time

4. Rivers & streams wind through landscapes • Water from rain, snowmelt, or springs forms streams, creeks or brooks • These merge into rivers, and eventually reaches the ocean • Tributary = a smaller river flowing into a larger one • Watershed = the area of land drained by a river and its tributaries

5. Rivers & streams wind through landscapes • Hydrology – the study of the occurrence, distribution and movement of water on, in & above the Earth

6. A river may shift course • Floodplain = areas nearest to the river’s course that are flooded periodically • Frequent deposition of silt makes floodplain soils fertile • Riparian = riverside areas that are productive and species-rich • Water of rivers and streams hosts diverse ecological communities

7. Wetlands include marshes, swamps, and bogs • Wetlands = systems that combine elements of freshwater and dry land • Freshwater marshes = shallow water allows plants to grow above the water’s surface • Swamps = shallow water that occurs in forested areas • Can be created by beavers • Bogs = ponds covered in thick floating mats of vegetation • A stage in aquatic succession

8. Wetlands are valuable • Wetlands are extremely valuable for wildlife • They slow runoff • Reduce flooding • Recharge aquifers • Filter pollutants • People have drained wetlands, mostly for agriculture • Southern Canada and the U.S. have lost more than half of their wetlands

9. Lakes and ponds are ecologically diverse • Lakes and ponds are bodies of open, standing water • Littoral zone = region ringing the edge of a water body • Benthic zone = extends along the entire bottom of the water body • Home to many invertebrates • Limnetic zone = open portions of the lake or pond where the sunlight penetrates the shallow waters • Profundal zone = water that sunlight does not reach • Supports fewer animals because there is less oxygen

10. A typical lake

11. Lakes vary in their nutrients and oxygen • Oligotrophic lakes and ponds = have low nutrient and high oxygen conditions • Eutrophic lakes and ponds = have high nutrient and low oxygen conditions • Eventually, water bodies fill completely in through the process of succession • Inland seas = large lakes that hold so much water, their biota is adapted to open water

12. Lake Baikal

13. Groundwater plays a key role • Groundwater = any precipitation that does not evaporate, flow into waterways, or get taken up by organisms • Groundwater makes up one fifth of the Earth’s freshwater supply • Aquifers = Porous sponge-like formations of rock, sand, or gravel that hold groundwater • Zone of aeration = pore spaces are partially filled with water • Zone of saturation = spaces are completely filled with water • Water table = boundary between the two zones • Aquifer recharge zone = any area where water infiltrates Earth’s surface and reaches aquifers

15. A typical aquifer

16. There are two categories of aquifers • Confined or artesian = water-bearing, porous rocks are trapped between layers of less permeable substrate (i.e., clay) • Is under a lot of pressure • Unconfined aquifer = no upper layer to confine it • Readily recharged by surface water • Groundwater becomes surface water through springs or human-drilled wells • Groundwater may be ancient: the average age is 1,400 years

17. The Ogallala Aquifer • The world’s largest known aquifer • Underlies the Great Plains of the U.S. • Its water has allowed farmers to create the most bountiful grain-producing region in the world

18. Water is unequally distributed across Earth’s surface • Different regions possess vastly different amounts of groundwater, surface water, and precipitation • Many areas with high population density are water- poor and face serious water shortages

19. Water is distributed unevenly in time, too • Monsoon seasons bring concentrated storms • Half a region’s annual rain may fall in a few hours • People erect dams to store water

20. Climate change will cause water shortages • Climate change will cause • Altered precipitation patterns • Melting glaciers • Early season runoff • Intensified droughts • Flooding • Increasing probability that there will be still less water for more people

21. How we use water • We have achieved impressive engineering accomplishments to harness freshwater sources • 60 % of the world’s largest 227 rivers have been strongly or moderately affected • Dams, canals and diversions • Consumption of water in most of the world is unsustainable • We are depleting many sources of surface water and groundwater • Water is becoming non-renewable resource

22. Water supplies houses, agriculture, and industry • Proportions of these three types of use vary dramatically among nations • Arid countries use water for agriculture • Developed countries use water for industry

23. Different types of water use • Consumptive use = water is removed from an aquifer or surface water body, and is not returned • Non-consumptive use = does not remove, or only temporarily removes, water from an aquifer or surface water • Electricity generation at hydroelectric dams

24. Areas where water use exceeds supply

25. US WATER USAGE

26. We are depleting groundwater • Groundwater is easily depleted • Aquifers recharge slowly • 1/3 of world population relies on groundwater • As aquifers become depleted • Water tables drop • Salt water intrudes in coastal areas • Sinkholes = areas where ground gives way unexpectedly • Some cities (Venice, Mexico City) are slowly sinking • Wetlands dry up

27. Will we see a future of water wars? • Freshwater depletion leads to shortages, which can lead to conflict • 261 major rivers cross national borders • Water is a key element in hostilities among Israel, Palestinians, and neighboring countries • Many nations have cooperated with neighbors to resolve disputes

28. Oceans cover most of the Earth’s surface • The oceans influence global climate, team with biodiversity, facilitate transportation and commerce and provide resources • They cover 71% of Earth’s surface and contain 97% of Earth’s surface water • Oceans influence the atmosphere, lithosphere and biosphere

29. The oceans contain more than water • Ocean water is 96.5% water • Plus ions of dissolved salts • Evaporation removes pure water & leaves a higher concentration of salt • Nutrients (nitrogen & phosphorus) • Dissolved gas • Nitrogen - diffusion • Carbon Dioxide - diffusion • Oxygen is added by plants, bacteria & atmospheric diffusion • Salinity – the amount of dissolved inorganic solids in water • Freshwater < 0.5 ppt • Brackish 0.5 – 17 ppt • Ocean 35 ppt (3.5 %)

30. Ocean water is vertically structured • Temperature declines with depth • Heavier (colder saltier) water sinks • Light (warmer and less salty) water remains near the surface • Temperatures are more stable than land temperatures • Water’s high heat capacity • It takes much more heat to warm water than air • Oceans regulate the earth’s climate • They absorb and release heat • Ocean’s surface circulation

31. The ocean has several layers • Surface zone • Warmed by sunlight and stirred by wind • Consistent water density • Pycnocline = below the surface zone • Density increases rapidly with depth • Deep Zone = below the pycnocline • Dense, sluggish water • Unaffected by winds, storms, sunlight, and temperature

32. Ocean water flows horizontally in currents • Currents = the ocean is composed of vast riverlike flows • Driven by density differences, heating and cooling, gravity, and wind • Influence global climate and El Niño and La Niña • Transport heat, nutrients, pollution, and the larvae of many marine species • Some currents such as the Gulf Stream are rapid and powerful • The warm water moderates Europe’s climate

33. The upper waters of the oceans flow in currents

34. Surface winds and heating create vertical currents • Upwelling = the vertical flow of cold, deep water towards the surface • High primary productivity and lucrative fisheries • Also occurs where strong winds blow away from, or parallel to, coastlines • Downwellings = oxygen-rich water sinks where surface currents come together

35. Seafloor topography can be rugged and complex • The seafloor consists of… • Underwater volcanoes • Steep canyons • Mountain range • The planet’s longest range is under water • Mounds of debris • Trenches • Some flat areas

36. A stylized bathymetric profile of the ocean