251 Exam 3: Hydrologic Cycle, Water Use, Watersheds

Dr. Herrman

How much of the Earth’s surface is water?

71%

How much of the Earth’s water is Saltwater?

97.5% (96.5% is ocean water)

How much of the Earth’s water is freshwater?

2.5%

What are the threats that face our oceans?

Overharvesting, climate change, sea level rise from glacial melt and thermal expansion, acidification from CO2, and coastal eutrophication

Groundwater

Location in the soil profile where 100% of the pore space is filled with water

How much of the water available on Earth is available as drinking water?

0.01%

Where is the majority of the Earth’s glaciers? (90%)

Antarctica

Lubrication

Losing ice off of the top of the ice sheet due to temperatures and warm water from below which melts the undersides of the ice

What part of Antarctica has the thickest and most ice?

The Eastern Half

Where are the other 9% of glaciers found?

Greenland

Where is the most ice loss happening around Greenland?

the perimeter

Where are the rest of the glaciers found on Earth? (1%)

Mountain ranges, Iceland and Alaska

How much freshwater does groundwater provide?

30%

Water table

the fluctuating line that marks the difference between the unsaturated and saturated zones in the soil

Aquifer

a body of groundwater that can be extracted by a well

What is groundwater used for?

drinking water and irrigation

What provides cleaner water: groundwater or surface water?

groundwater supplies

Where does the United States get its drinking water from?

60% gets it from lakes and rivers, 40% from groundwater

How much of the US population relies on wells?

10-15%

Condensation

the process that converts water vapor into a liquid

What is the temperature / vapor relationship for condensation?

warm air holds more water vapor than cold air, so anytime that warm air cools quickly, it will create excess water vapor resulting in more condensation

What happens to air as it rises in altitude?

It cools down due to lower pressure and less molecular friction, creating clouds since cold air cannot hold moisture

How do clouds form?

When warm air rises and then cools due to increased altitude, it cannot hold moisture so they form

Convection

Heating air causes it to become less dense and rise in elevation and altitude

When does convection occur?

at the end of very hot summer days

Frontal Systems (fronts colliding)

Cold front is dense and hugs the grounds surface —> warm front blows in and collides with cold front which acts like a wedge, forcing the warm air higher in altitude

What do fronts colliding lead to?

condensation, precipitation, thunderstorms, etc.

Orographic Lifting

warm air hits the side of a range and wind forces it over the mountain, causing condensation and precipitation

What happens on the western side of a mountain range with orographic lifting?

this side is very wet

What happens on the eastern side of the mountain range with orographic lifting?

this side if very dry and often faces drought

Advective Fog

Warm, moist air comes in contact with a colder parcel of land by horizontal air movement

What is advective fog associated with?

wind movement

Radiative Fog (Dew)

Cold, cool, calm nights follow warm and humid afternoons create fog on the surface in low-lying areas

Evaporation Fog

When a cold front advances onto a lake after a warm day

Surface Condensation

Cold surface quickly comes into contact with warm, moist air and the surfaces cannot hold the moisture

What surfaces commonly have surface condensation?

plants

Net Precipitation

SF + TF - I

Stemflow (SF)

Channels precipitation directly toward root structure

Throughfall (TF)

Passes through the leaf layer before reaching the soil

Interception (I)

Caught by the vegetative surface of the tree and evaporated back into the atmosphere

What ecosystem has the highest Interception percentage?

Coniferous forests due to snowfall

Infiltration

where surface water seeps into the groundwater

What factors influence infiltration?

Permeability, slope, land use, vegetative cover, soil structure, organic matter content and precipitation intensity

Precipitation that is lost to the atmosphere via evaporation from the leaves of plants is called what?

Interception

What will happen to infiltration if slope is decreased?

It will increase

Which of the following will have the lowest infiltration rate?

A loam textured soil with high organic matter content

What soil texture allows for higher infiltration?

coarse soil textures with large pores (sandy soils)

Slope impacting infiltration rate negatively

high slope causes more runoff

Slope impacting infiltration rate positvely

a flat slope will have more opportunity to infiltrate down into the soil

Land use / vegetative cover infiltration rate negatives

bare soil is not good at promoting infiltration

Land use / vegetative cover infiltration rate positives

the more root and stem structure there is, the harder it is going to be to work its way across the landscape which creates more infiltration

What will have more stems per square meter – grasses or forests?

Grasses (grasslands)

How does organic matter impact infiltration?

Higher organic matter holds onto moisture so it will cause a soil to not infiltrate well

How does precipitation intensity impact infiltration?

depending on how quickly it happens, it can overwhelm a soils ability to infiltrate which can create more runoff

Horton Overland Flow

when rainfall intensity exceeds the soil's infiltration capacity, leading to surface runoff (95% of what we see on the landscape)

Saturated-excess Overland FLow

Precipitation raises the water table to the soil surface and runoff is generated

Where does Saturated-Excess Overland Flow commonly occur?

next to a waterbody

A rain event that lasts several days but is not very intense is occurring. Adjacent to a river overland runoff can be observed. Which mechanism of runoff does this describe?

Saturated-Excess Overland Flow

Why are we worried about surface runoff and overland flow?

High potential for creating water quantity and quality concerns due to flooding, erosion, nutrients and hydrocarbons

Evaporation

Liquid water is converted into vapor from water surface, bare soil, or snow cover

How much of liquid water is returned to the atmosphere by evaporation?

90%

Transpiration

when the stoma of a plant opens and releases water vapor and allows in carbon dioxide

Evapotranspiration

the total amount of water that evaporates from surfaces like soil, water bodies, and vegetation, plus the water transpired by plants

Where is Evapotranspiration most common?

Wetlands

What are the primary drivers of Evapotranspiration?

Climate, Plants and Environmental Factors such as soil

How does climate impact ET?

Need hot temperatures, sunlight, humidity and wind speed

What plant factors impact ET?

morphology and photosynthetic pathway

What environmental factors (soil) impact ET?

soil fertility, soil water holding capacity, cover crops and pests

How many inches of rainfall does Wisconsin get per year?

32-33 inches

How much ET does Wisconsin have per year?

25 inches

Potential ET (PET)

the measure of water loss for a short green grass with the assumption that there is not water loss

What is the drawback with PET?

it is an overestimate and a rough approximation

When is PET higher?

summer months due to higher temps and sunlight

ET - Actual

the measure of water loss for a specific plant community that is exposed to changing weather patterns

How accurate are Actual ET measurements?

95%

When is Actual ET higher?

summer and spring months due to increased water availability

How do we measure PET?

Pan evaporation method

How do we measure Actual ET?

Lysimeter and Eddy Covariance Towers

Sublimation

The process that converts ice and snow directly into a vapor

When does sublimation occur?

with strong, dry winds —> warm wind comes into contact with snow

La Nina Forcing Factor

cold water and strong trade winds forces strong pacific ocean upwelling and inland precipitation

El Nino Forcing Factor

warm water and weak winds forces pacific ocean blockages and offshore precipitation

Moderate Forcing Factor

moderate cold water in pacific ocean creates moderate upwelling with normal inland precipitation

How is North America impacted by La Nina?

warm and dry conditions in the South, cold and wet conditions in the North

How is North America impacted by El Nino?

wet and cool conditions in the south, warm and dry conditions in the north

During a La Nina event what happens off the western coast of South America?

The oceanic upwelling is enhanced

Why have we observed sea level rise?

Rises ocean temperatures and melting glaciers

Watershed

A plot of land that all drains to a common outlet point

What is the most important landscape characteristic when delineating a watershed boundary?

Topography

What watershed ecosystem typically is the smallest?

Lakes (with the exception of the great lakes)

Ephemeral Stream

a stream that dries up during part of the year

Primary headwaters

where the stream starts, a 1st order stream

What is the highest order stream?

12th order

What is the only 12th order stream?

the Amazon River at the outlet point

What is the highest order stream in the US?

The Mississippi River (10th order)

What is the Wisconsin River's stream order?

6th order

What happens if bedrock is close to the surface?

water cannot infiltrate into groundwater so runoff is more likely

Discharge (Q)

volume of water per unit time

Hydrograph

Discharge of a stream transect over time

Peak discharge

Max discharge achieved after a precipitation event