The$Water$Cycle$and$its$ Importance$biol336-bowen.wikispaces.umb.edu/file/view/water_lecture_ECO...
Transcript of The$Water$Cycle$and$its$ Importance$biol336-bowen.wikispaces.umb.edu/file/view/water_lecture_ECO...
The Water Cycle and its Importance
Ecosystems Ecology
Water Proper8es • Water is unique in that it is the only natural substance that is
found in all three physical states—liquid, solid, and gas—at the temperatures normally found on Earth.
• Bonds to itself through rela8vely weak hydrogen bonds • Water is unusual in that the solid form, ice, is less dense than
the liquid form, which is why ice floats. • Water is called the "universal solvent" because it dissolves
more substances than any other liquid. • Water molecules are cohesive (s8ck to each other) and
adhesive (s8ck to surfaces) • Water has a high specific heat index—it absorbs a lot of heat
before it begins to get hot.
Capillary Ac8on
• Cri8cal for Plants, humans, groundwater movement, and more
Rainfall
• The amount of precipita8on that falls around the world may range from less than 0.1 inch per year in some deserts to more than 900 inches per year in the tropics
• For cloud forma8on/rainfall to occur (condensa8on), water vapor in the air must be cooled to the dew point, the temperature at which net condensa8on occurs
Evapotranspira8on • Studies have shown that the oceans, seas, lakes, and rivers
provide nearly 90 percent of the moisture in the atmosphere via evapora8on, with the remaining 10 percent being contributed by plant transpira8on.
• With transpira8on, plants u8lize ~10% of water from roots for biochemical processes. ~90% is transpired away
• Over land: evapora8on < Precipita8on • Over ocean: evapora8on > Precipita8on • Plants transpire to:
– Remain cool – Take up nutrients – Maintain turgor pressure of structures and stomata
Factors Affec8ng Runoff • The rate of rainfall -‐ A lot of rain in a short period tends to run off the land
into streams rather than soak into the ground. • The topography of the land -‐ Topography is the lay of the land -‐-‐ the hills,
valleys, mountains, and canyons. Water falling on uneven land drains downhill un8l it becomes part of a stream, finds a hollow place to accumulate, like a lake, or soaks into the ground.
• Soil condi6ons -‐ Small par8cles (like clays) have lower infiltra8on rates, larger par8cles (sandy soils) have higher infiltra8on rates
• Density of vegeta6on -‐ It has long been known that plant growth helps decrease erosion caused by flowing water by slowing water flow
• Amount of urbaniza6on -‐ Roads, pavement, and parking lots create impervious surfaces where water can no longer seep into the ground. Rather, water is funneled into creeks and streams that were never meant by nature to handle so much runoff. This can cause problems in urban areas.
Water is cri8cal for ecosystems, so how do we explain rainfall
distribu8on?
8/29/11 Chapin et al., 2011 Fig. 2.23b
8/29/11 Chapin et al., 2011 Fig. 2.8
ITCZ: Inter-‐Tropical Convergence Zone
Coriolis Effect: • Wind deflects to the
right in N hemisphere • Wind deflects to the
leb in S hemisphere
Note: Wind flows from High to Low pressure
Hadley Cell Circula8on (KNOW THIS!)
Ocean Currents: A regional control on precipita8on
8/29/11 Chapin et al., 2011
• Solid lines: warm
• Dashed lines: cool
• In general: – Warm currents interac8ng with land: more rainfall
– Cold currents interac8ng with land: less rainfall
Fig. 2.11
• Seasonal insola8on and differen8al hea8ng between land and sea cause large High and Low Pressure systems, which shib around and influence rainfall paherns
8/29/11 Chapin et al., 2011 Fig. 2.9b
• In general: Low pressure systems are associated with rising air (which can lead to rain)
• High pressure systems associated with stable weather
Major Air Masses
• Major air masses can shib slightly depending on factors like seasonality, but in general the moisture content of the air masses is a factor for regional rainfall
Orographic Libing
• Higher eleva8ons tend to receive more rainfall
• Mountain chains can influence regional rainfall paherns drama8cally
Washington State: Precipita8on/Rain shadow effect
Land-‐Sea Hea8ng: Large and Small Scale Effects
8/29/11 Chapin et al., 2011 Fig. 2.13
4 Main Ways to Uplib Air (necessary for Clouds/Rainfall)
Summary: What factors affect rainfall distribu8on?
• General Global distribu8on: – La8tudinal atmospheric circula8on
• Regional Distribu8on factors: – Major air masses – Ocean currents – Proximity to ocean/large water bodies – Orographic libing (mountains)
• Local rainfall: – Localized uplib (see previous slide)
How Does Water Impact Ecosystems?
8/29/11 Chapin et al., 2011 Fig. 2.22
8/29/11 Chapin et al., 2011 Fig. 2.24
8/29/11 Chapin et al., 2011 Fig. 2.37a
8/29/11 Chapin et al., 2011 Fig. 2.23b
Human Impacts to the Water Cycle
• Average American Water use: ~2000 gal/day (twice global average)
• -‐ Everything requires water. When factoring in the average goods consumed, our individual daily use is 1,400 litres/person in Asia and 4,000 litres/person in Europe and North America, according to the FAO.
Groundwater Deple8on
Dams: Pros/Cons?
• Can provide large amounts of energy (1/5 of electricity worldwide)
• Can create reservoirs for water consump8on
• About 25% of the en8re world’s sediment flow gets trapped behind dams
• Can have drama8c nega8ve ecological impacts
• In certain cases: can be a large emiher of methane (a powerful greenhouse gas)
Deforesta8on: Major impacts to Water cycle
8/29/11 Chapin et al., 2011
Fig. 2.14
Case Study: The Loess Plateau aka “China’s Sorrow”
• Known as the cradle of Chinese civiliza8on • Was originally fer8le croplands, but over 8me
deforesta8on and over-‐grazing has lead to the highest soil erosion rates in the world
• Consequence: soil inputs to the Yellow River have caused massive floods – 1931 Flood: 1-‐4 million people killed – 1887 Flood: 1-‐2 million people killed
Impervious Surfaces: Increase runoff and decrease infiltra8on
Note: Urbaniza8on is a rapidly growing process. Currently about 48% of the popula8on lives In ci8es. By 2030 it is predicted to be 60%
Storm water management
Tradi8onal design: Remove stormwater though engineering:
• curbed streets • catchbasins • pipes to receiving waters (or deten8on ponds).
A solu6on: Low Impact Development (LID)
Types of Water Pollutants • Micro-‐organisms (human/animal waste) – Giardia, E. Coli, viruses
• Disinfec8on-‐byproduct – Bromate, Chlorite, haloace8c acids
• Disinfectants (control microbes) – Chloramines, chlorine
• Inorganic chemicals – Arsenic, cadmium, lead
• Organic chemicals – Atrazine, dioxins, PCBs,
pH/Acid Rain • The pH of water determines the solubility (amount
that can be dissolved in the water) and biological availability (amount that can be u8lized by aqua8c life) of nutrients (phosphorus, nitrogen, and carbon) and heavy metals (lead, copper, cadmium, etc.).
“FRACKING” (Research it)
Future of Water Resources
Water Vapor in the atmosphere: Posi8ve Feedback Loop
• Water vapor has the largest warming effect of any greenhouse gas • Models predict that the hydrologic cycle will intensify as the globe
warms (more precipita8on over land, more evapora8on over oceans) – These shibs will vary spa8ally and seasonally
• Weather paherns and extreme events are predicted to intensify and become more frequent
Glacial Retreat
Reduced Snowpack/Early Snowmelt
• Will significantly impact freshwater supplies for
• Will nega8vely impact: – Groundwater recharge – Fish migra8on/spawns – Pollu8on levels – Hydropower
Urban Farming?