Water

San Marcos Springs

I. Water Resources and the Hydrologic Cycle

A. Two thirds of the earth is covered in water, but of that, only 3% is freshwater, and 1% is easily accessible fresh water.

B. Water is essential for biochemical reactions and is involved in nearly every environmental system – in fact, the hydrologic cycle influences all other nutrient cycles.

I’m the most important of all the

biogeochemical cycles. Take that nitrogen!

I. Water Resources and the Hydrologic Cycle

C. US water use by category:46% Industry, 41% agriculture, 13% domestic

Worldwide Water Use

70% Agriculture, 20% industry, 10% domestic

I. Water Resources and the Hydrologic Cycle

D. When precipitation occurs, several things can happen:

1) Water soaks into the soil, in a process called infiltration. The water may stay in the soil to be used by organisms, or percolate further down into an aquifer, and recharge the aquifer.

I. Water Resources and the Hydrologic Cycle

2) Water not absorbed into the soil flows across the land and into rivers, lakes, streams, and eventually to the oceans. Runoff waters can originate from precipitation or stem from melting snow or ice.

a) An expanse of land where the surface runoff and groundwater drains into a common point – usually a stream, lake, or river – is called a watershed, which can range in size from a few acres to many square miles.

Major US watersheds include the Mississippi, Rio Grande, Colorado, and Colombia.

I. Water Resources and the Hydrologic Cycle

b) And, unlike water filtered by the soil, runoff water can serve as a collector of nutrients, sediment, or other pollutants on the land that can affect the quality of water throughout a watershed.

I. Water Resources and the Hydrologic Cycle

3) Most water, however, returns to the air in the form of water vapor; the bulk of this evaporation occurring by means of the oceans. Roughly half of land-based evaporation occurs on the surface area of plants, called transpiration. These together are sometimes referred to as evapotranspiration.

Transpiration Mini Demo

Sketch the relative amounts of transpiration in the three plants.

The hydrologic cycle

II. Understanding Aquifers

A. Aquifers provide drinking water for over half the world’s population.

B. Aquifers are in theory renewable resources, but pollution can contaminate aquifers and people frequently pull more water out than is being recharged back in.

C. Karst is a landscape formed from the dissolution of soluble rocks including limestone, dolomite and gypsum. It is characterized by sinkholes, caves, and underground drainage systems

II. Understanding Aquifers

D. Porosity is the percentage of open space in a rock or surface material. Permeability is a measure of a material's ability to transmit fluids. If the pores are very small or if they are not connected to form a channel, the material will have a low primary permeability. If the material is fractured (broken) the permeability will be increased.

II. Understanding Aquifers

E. A sandstone aquifer, for instance, acts like a sponge, and water slowly seeps between the grains of sand at a rate of inches per day. A karst aquifer, on the other hand, stores water in fractures, conduits, and cavities and can transport water up to miles per day!

II. Understanding Aquifers

F. Aquifers, to hold water, must have an impermeable bottom and top. When this happens, it is called a confined aquifer or the artesian zone. Water can escape through small holes (springs) or man-made wells.

II. Understanding Aquifers

II. Understanding Aquifers

G. Water recharges back into the aquifer in the recharge zone, an area with an unconfined upper layer, or through cracks, holes, fissures, or sink holes.

It’s Where We Live• These springs led to the development of major towns along the aquifer:

Salado, Georgetown, Austin, San Marcos, New Braunfels, San Antonio, Uvalde, Brackettville, and Del Rio. All of these towns are sited where major springs discharge from the Edwards aquifer.

SaladoSalado

AustinAustin

San MarcosSan Marcos

Del RioDel Rio New New BraunfelsBraunfels

UvaldeUvaldeBrackettvilleBrackettville

GeorgetownGeorgetown

San AntonioSan Antonio

III. Issues with Water

A. Main ways to get more drinking water: 1) Extract more groundwater2) Build more dams3) Transfer water from one place to another4) Convert salty seawater to fresh water5) Use water more sustainably

IV. Extract more groundwater

A. Advantages and DisadvantagesAdvantages Disadvantages

Available year-round Aquifer depletion from over pumping

Exists almost everywhere Sinking of land (subsidence)

Some aquifers renewable if not over pumped or contaminated

Aquifers polluted for decades or centuries

No evaporation losses Saltwater intrusion into drinking water supplies in costal areas

Cheaper to extract than most surface waters

B. When water is pumped from underground aquifers, sand and rock aquifers can collapse, causing subsidence. This leads to large sinkholes. In the US, Phoenix, Baton Rouge, the San Joaquin Valley, and Houston have major problems with subsidence. Mexico City has one of the worst problems in the world, with some areas of the city subsiding as much as 33 feet.

C. Water tables are falling through many areas of the world because the rate of pumping exceeds the rate of natural recharge from precipitation.

Examples1. India and China – Widespread drilling of

inexpensive tube wells by farmers has caused the water table to drop in many area, sometimes by meters a year. The drop in the water table leads to deeper well drilling.

2. Saudi Arabia – Gets 30% of it’s water from deep fossil aquifers. Hydrologists estimate that that because of aquifer depletion, irrigated agriculture will disappear in 10 – 20 years.

3. United States – Groundwater is being withdrawn four times faster than it is recharging. The Ogallala, the world’s largest known aquifer, supplies one third of the groundwater used in the US. The Ogallala has a very slow rate of recharge (a pseudo-fossil aquifer) and is being pumped at 10 -40 times the recharge rate in TX and OK.

a. In some areas of Texas, this over pumping has lowered the water table by over 100 feet, making pumping too expensive to irrigate crops in some areas.

V. Build more dams

A. A dam is a structure built across a river to control the river’s flow. After a dam is built an artificial lake or reservoir is created behind the dam.

B. The main purpose of a dam is to capture and store run off to release or use from the reservoir as needed.

C. There are about 800,000 dams worldwide, 45,000 of them larger than 50 feet high.

V. Build more dams

Advantages Disadvantages

Supply reliable water Can only be placed on a river

Generates electricity Many suitable areas already dammed

Recreational activities People displaced when built

Can reduce downstream flooding Silting occurs and renders dams useless after 50-150 years

High water loss due to evaporation

Species endangerment (20% world’s freshwater fish and plants endangered/extinct due to dams)

D. Examples – Colorado River Basin (US) – 14 major dams on Colorado River. Supplies water to LA, Las Vegas, San Diego, and Imperial Valley in CA.

1. Problems: Colorado river fed by snow pack in Rockies, area in rain shadow of Rockies, legal pacts allocate more water withdrawal than river actually provides, water does not reach all the way to the Gulf of California.

VI. Transfer water from one place to another

A. Some places are water-rich and some are water-poor. Transferring water from one area to another via tunnels, aqueducts, and underground pipes can sometimes help.

B. It is relatively expensive and inefficient to transfer water.

C. Example 1: California water project1. One of the world’s largest water transfer

projects. Water is transported from northern to southern California. Causes huge conflicts in California. Agriculture uses up 75% of the water, often growing water-thirsty crops such as alfalfa and rice in desert-like conditions. Because water prices are so low, investing in improved irrigation is not economical.

2. Aral Sea disaster – In Former Soviet Union, massive water diversion project for irrigation of crops. Over 90% of original water is gone. Sea bed salts blow onto fields, polluting the soil and killing crops. Fishing industry destroyed, half the local bird and mammal species gone, loss of thermal moderation by sea.

VII. Desalination

A. Desalination involves removing salt from ocean water or brackish (slightly salty) aquifer water.

B. Distillation (boiling water and collecting the steam) or reverse osmosis (forcing water through filters with very small holes the salts can’t pass through) are the two main methods.

C. Saudi Arabia has the world’s largest number of desalination plants, and the US has the world’s second highest capacity. Israel gets 50% of it’s water from desalination and China’s costal cities get 16-25% of their water from desalination.

D. As Australia struggles with record drought, they are also building more desalination plants. They plan to get 30% of their water this way.

D. Desalination is very expensive, takes lots of energy to do, and produces large quantities of briny wastewater which is challenging to dispose of.

E. Currently, desalination is practical for water-short, wealthy countries.

VIII. Use water more sustainablyA. Agriculture – There are four types of

irrigation, ranging from least to most efficient.

1. Furrow irrigation – Unlined trenches in fields are dug and water is released into the trenches. Results in a loss of about 35% of water (65% efficiency).

2. Flood irrigation – Flooding a whole field with water. It is about 70% efficient – about 30% of water does not reach target crops. Slightly more efficient than furrow irrigation because water seeps evenly over the crops and does not just stay in the furrows.

3. Spray irrigation – Using pipes and nozzles to spray water on a field. Center pivot is one of the most common.

4. Drip or Microirrigation

• About 95% efficient• Very effective in arid areas or with perennial

crops (fruit trees, etc)

C. Saving Water in City/Industry

1. Fix leaking pipe infrastructure in the city (40-60% of the water supplied to major cities in developing nations is lost through leakage of water mains, pipes, pumps

2. Homeowners

a. Change irrigation systems in lawns, switch to water-conserving landscaping – approximately 50% of water bill is lawn sprinkler systems (use TONS of water!)

b. Update appliances and fixtures

D. How Can Government Help with Conservation?

1. Carrot: Provide rebates for water-conserving fixtures and appliances, rainwater harvesting barrel rebates, price breaks for using less water (currently you get price breaks for using more).

2. Sticks: Mandatory water restrictions, price increases