Ecosystem Ecology I. IntroductionII. Energy FlowIII. Biogeochemical Cycles

III. BIOGEOCHEMICAL CYCLESA. Overview

“Turns fast”

“Turns slow”Large reservoir

Small reservoir

FLUX

B. The Water Cycle

  Atmosphere (13)

OVER OCEAN OVER LAND  Rain Evaporation Rain Evaporation(385) (425) (111) (71)  

Oceans - 97% Runoff and Groundwater (40)(1,380,000) Lakes and Rivers (100)

Water content in sedimentary

rock near surface

(210,000) 

B. The Water Cycle

Biosphere (1)

All values in teratons (x 1018 g)

B. The Water Cycle

B. The Water Cycle

- Effects of Life1. Plant biomass pumps water out of the soil into the atmosphere, increasing evaporation rates.

2. Volatiles act as nuclei on which raindrops can form ("Smoky Mountains"), increasing local precipitation. Large forests stimulate the rainfall they depend on.

-Effects of Life:

1)Cut forest – reduce evapotranspiration, increase runoff and river discharge2)Eventually, reduce precipitation, and reduce river discharge.

B. The Water Cycle

- Effects of Humans

B. The Water Cycle

-Effects of Humans

1. Control 50% of surface runoff of planet - 70% agriculture

- 20% industry - 10% personal use

Most population growth is in tropical/arid areas where more water is needed to grow the same amount of crop, because

PET > Precipitation

98% of water ‘footprint’ for animals is for their feed.30% of all water used for animals is for beef cattleAnother 20% for dairy cattle

B. The Water Cycle

-Effects of Humans

1. Control 50% of surface runoff of planet - 70% agriculture

- 20% industry - 10% personal use

2. Dams

2. Dams – Three Gorges, Yangtze River

Ship locks

2. Dams – Three Gorges, Yangtzee River

1.5 miles wide, 600 feet high

Largest dam in the world – largest engineering project in the world.

1.5 miles wide, 600 feet high

Reservoir 570 feet deep and nearly 400 miles long.

100

Energy = 18 nuke plants. At full power, reduces coal consumption by 31 million tonnes per year, avoiding 100 million tonnes of greenhouse gas emissions

Regulate a deadly, flood-prone river:

The 1998 flood (before the dam): 3,704 dead, 15 million homeless and $26 billion in economic loss. A staggering 25 million acres (~Kentucky) were evacuated, 13.3 million houses were damaged or destroyed.

Displaced 1.2 million people

Cover 1300 important archeological sites

2. Dams – Problems:

- Flood upstream habitats

- release toxins into water

- cause eutrophication

- reduce oxygen content of water

- sediment buildup decreases “head” and power generation

- sediment trap starves downstream of sediment and nutrients – erosion of river delta and loss of productive estuary - reduce fisheries productivity

“The construction of dams is increasingly regarded as the biggest conservation threat to aquatic and riparian biodiversity in many river basins throughout the world.”

J. Wu, J. Huang, and X. Han. 2003. Science 302:11-49-1150.

B. The Water Cycle

-Effects of Humans

1. Control 50% of surface runoff of planet - 70% agriculture

- 20% industry - 10% personal use

2. Dams

3. Overtapped RiversMajor rivers like the Colorado, Nile, Ganges, Yellowdon’t reach the ocean for months at a time – all thewater is drawn off by humans upstream.

Hoover – 726 ft tall

Glen Canyon – 710 ft

Cohen, et al (2001). A preliminary water balance for the Colorado River Delta, 1992-1998. J. Arid Environments 49:35-48.

Hoover Dam

Glen Canyon Dam

Yellow River (China):

Days Dry at Mouth:

1995: 122

1996: 133

1997: 226

(7 months!)

3. Overtapped Rivers

3. Overtapped Rivers

The Aral Sea, Kazakhstan:

once the 4th largest inland sea in world

Has lost 60% of its water, drawn off for agricultural purposes.

- Salinization increased, killing the productive fisheries industry

- Agriculture – salt increased 6X by 1994 the productivity had dropped by 20-50%.

3. Overtapped Rivers

The Aral Sea, Kazakhstan:

- salt and dust in air became a significant health problem

April 2003

3. Overtapped Rivers

The Ganges and Indus:

Water is diverted for agriculture.

-Salt water intrudes mangrove estuaries

-Kills mangroves

-Nursery areas for fish

-Storm breaks and flood regulators.

3. Overtapped Rivers

Other Problems of "overtapping" rivers...

1. Reduced water availability

2. Salinized soils (20% worldwide)

3. Regional Conflicts

- “water rights” issues cross state and

national boundaries

3. Regional Conflicts

- Egypt: gets 97% of its water from outside its borders… water treaties with the Sudan are the oldest on record.

- Ethiopia, with headwaters of the Blue Nile, wants to construct dams for hydroelectric power. Egypt and Sudan have battled them for decades.

“The only matter that could take Egypt to war again is water” –

Anwar Sadat, 1979

3. Regional Conflicts

- The Jordan River (Jordan and Israel)

- The Indus (India and Pakistan)

- The Ganges (India and Bangladesh)

- The Colorado: Colorado, Utah, Arizona, Nevada, California

1. Control 50% of surface water

2. Dams

3. Overtapped Rivers

4. Overtapped groundwater

- In Punjab (Indus Valley):

Wealthy can dig deeper wells, lowering water table, making it

inaccessible for shallow wells.

1. Control 50% of surface water

2. Dams

3. Overtapped Rivers

4. Overtapped groundwater

- In Punjab (Indus Valley):

pumping from wells exceeds recharge by 27%. Water table

falling 0.7 m/yr

Wealthy can dig deeper wells, lowering water table, making it inaccessible for shallow wells.

- The Ogallala Aquifer:

Under 174,000 square miles and 8 agricultural states.

95% of pumped water is for irrigation

PUMPING:

1949: 4 million acre-feet/yr

1980: 18 million acre-ft/yr

2000: 3-4 mill. a-ft/yr

- The Ogallala Aquifer:

Under 225,000 square miles and 8 agricultural states.

95% of pumped water is for irrigation

WATER LEVEL:

1950: dropped 5 ft/yr

1990’s: 1.35 ft/yr

Decline in well yields correlates with 20-50% decline in productivity in Texas High Plains (dry)

- The Ogallala Aquifer:

Lubbock, Texas:

18 inches of rain

80 inches of evaporative potential

Irrigation has to make up that difference AND water the plants!!

- The Ogallala Aquifer:

What’s left?

3.27 billion acre-feet (WOW!) It is 1000 feet deep in some areas of Nebraska

(U.S. – 2.3 billion acres)

Is it inexhaustible?

- The Ogallala Aquifer:

Is it inexhaustible?

That depends on where you are… when saturation depth drops to 30 feet, can’t sustain high volume pumping for agriculture (1000 gallons/min)

Dropping 1 ft/yr…

Landsat image, North Texas, 2010

So, to produce food we spread the water in rivers over our agricultural land. This produces food, but also increases evaporation of that water.

We are also ‘mining’ water from the ground, increasing it’s transfer.

So humans are increasing flux rates… and eventually, through these exchanges, the water ends up in the ocean where it resides for a long time.