Definition: The area of land where all of the water drains.
Think of a watershed like a Bathtub. the hills surrounding an area are the sides of the bathtub, the water runs down to the lowest elevation, and drains into the Ocean.
The boundary of a watershed is known as the Divide.
Understanding watersheds can go a long way towards understanding what is in your water, where water pollution is coming from, and what is the best way to resolve any water pollution issues.
#1 User is Agriculture for Irrigation
70% of all freshwater is used globally by agriculture for irrigation purposes.
41% of all U.S. freshwater is used by agriculture for irrigation.
20% of all Freshwater is used by Industry. Most of this is used for Power Generation.
38% of Freshwater in the U.S. is used for Power Plant Cooling. 11% is used by industry.
The East Coast of the U.S. is unique because it uses most of its water for Power Generation. The rest of the U.S. follows the rest of the world with irrigation as the main water consumer.
There are two types of aquatic biomes:
- Freshwater- includes Lakes, Rivers, Streams, Ponds and Inland Wetland areas.
- Marine- includes Estuaries, Coral Reefs, Coastal Wetlands, the Oceanic Zone, and Polar Ecosystems
What type of life can be found in these biomes? (Both Freshwater and Marine)
- Plant like plankton are called Phytoplankton and are capable of photosynthesis. Picture on top left.
- Zooplankton are the animal like plankton. Picture on top right
- Nekton are organisms that are capable of swimming against the current. Picture on bottom left.
- Benthic organisms or benthos are organisms that live on the bottom layers of the aquatic biome. Picture on bottom right.
- Decomposers can be found throughout both as well.
Freshwater biomes must have a salinity of less than 1 part per million. there are two types of biomes:
- Lentic systems are lakes, ponds, and inland wetlands that are standing still. I think about the word siLent to help remember the difference.
- Lotic systems are the moving streams and rivers. Think about locomotive to help remember.
Layers of a Lake
- Littoral Zone is the coastal areas of a lake or pond. Lots of aquatic plants and macro-invertebrates can be found here.
- The open area in the middle of the lake is called the Limnetic Zone. (Both the Littoral and the Limnetic Zone get the most light: a mnemonic device could be using the fact that both start with Li for light.) This area is where the Phytoplankton (plant like) and Zooplankton (animal like) are found. Phytoplankton can use photosynthesis to create their own food, so they need the well lit area to stay algae free.
- The middle layer under the Limnetic Zone is called the Profundal Zone. This is a dimly lit layer where most of the nekton are found. Nekton are organisms that can move against the current or swim.
- The bottom layer of the lake, pond, or stream is called the Benthic Zone. This is where the bottom dwelling organisms or benthos live.
In the summer the top layer is warm and the bottom layers are progressively cooler. In the winter, the top layer is coldest and the layers get progressively warmer as you go down. During the Fall and Spring, the water temps are the same throughout, so you have a mixing of the waters occur. This mixing of oxygen and nutrients is vital to an aquatic biome and is known as Overturn.
Layers of the Ocean
- The Coastal Zone of the ocean is only 10% of the surface area, but contains 90% of all of the life found in the ocean.
- The open sea is called the Euphotic Zone. This is the well lit area of the sea where the plankton are located which make up the base of the food pyramid in the ocean.
- The dimly lit layer of the ocean is called the Bathyal Zone. Many nekton can be found here.
- The bottom layer of the ocean is called the Abyssal Zone. Bottom feeders, Deposit feeders, and chemosynthetic bacteria can be found here.
Coral Reefs are the most diverse ecosystems on the planet. They are made of massive colonies of polyps, which are soft bodied organisms related to jellyfish and sea anenomes.
- These polyps live in secreted skeletons of Calcium Carbonate CaCO3. Just about every shell you find on the beach or in the ocean is made from this. (mineral is called calcite, and a bunch of calcite together form the rock limestone.)
- Most reefs live in mutualistic symbiosis with a single-celled algae called Zooxanthellae (zo-zan-THELL-ee) which give the reefs their color and are photosynthetic.
- Reefs typically only grow about a half a centimeter per year, but they are among the oldest and most productive ecosystems in the world.
When corals are placed under stress, they expel the zooxanthellae and lose their coloring. This gives them a "bleached" look. The most common reasons for this are:
- Sediment runoff and deposition eroding from freshwater rivers and streams.
- Climate change
- Increased UV radiation
- Runoff of pesticides, fertilizers, and industrial chemicals.
This is the largest aquifer in the world. Some areas of the aquifer are so depleted that the water table is more than 600ft below ground.
Water mining is a huge issue with the ogallala aquifer, with irrigation accounting for 94% of its use. The aquifer is extremely overdrafted, with little to no recharge occurring. The aquifer could be depleted in a few decades. If it goes dry, over $20 billion worth of food and fiber will vanish from the world's markets.
The Ogallala aquifer supplies all of the water for the breadbasket of the U.S.
The Three Gorges Dam in China
The Three Gorges Dam is the largest dam in the world. It displaced more than 1.5 million people with the flooding of the Yangtze River behind the dam.
The dam is designed to produce approx. 18,000 MegaWatts of energy, which is 20X the power of the Hoover Dam. This should provide China with over 10 percent of its energy needs.
The Aral Sea
The Aral sea in Uzbekistan was once the 4th largest freshwater lake. (Lake Baikal in Russia is the largest.)
Since 1960, enormous amounts of irrigation water have been diverted from the inland Sea and its two feeder rivers (Amu Darya and the Syr Darya), resulting in a large-scale water transfer project for irrigation of cotton and rice cropland (two water intensive crops).
This large-scale water diversion project, coupled with droughts and high evaporation rates in this area's hot and dry climate, has caused a ecological, economic, and health disaster.