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Life in Water

Chapter 3

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The Hydrologic Cycle

• Over 71% of the earth’s surface is covered by water: Oceans contain 97%. Polar ice caps and glaciers contain 2%. Freshwater in lakes, streams, and ground

water make up less than 1%.

• Solar heating and gravity are major forces.

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The Hydrologic Cycle (interactive)

Net Movement and Processes:

* Evaporation from oceans

* Atmospheric transport to land and condensation.

* Precipitation onto land.

* Gravity flow back to Ocean.

- Run off to surface waters (lake & streams)

- Infiltration to groundwater

Transpiration and evaporation on land takes place but on average it is less than precipitation, so water enter streams and groundwater.

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The Hydrologic Cycle

• Turnover time (residence time) is the time required for the entire volume of a reservoir to be renewed (replaced). Atmosphere 9 days Rivers systems 12-20 days Groundwater 300 years Oceans 3,100 years Glaciars & ice-caps 16,000 years

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Aquatic Biomes

• Marine Oceans and seas Coral reefs and kelp

forests Intertidal shores:

rocky or soft bottom. Estuaries, salt

marshes and mangrove forests

• Inland Waters Ponds and lakes Streams and rivers Wetlands Groundwater

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Properties to consider

• Water Movement• Temperature• Light• Salinity• Nutrients• Oxygen• Human influence

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Oceans and SeasGeography of Ocean Basins

• Major Ocean Basins: Pacific is oldest & largest (180 million km2) Indian is smallest (75 million km2) Atlantic is in between (106 million km2)

• Depth: Average about 4000 m Deepest trench is > 10,000 m deep

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Oceanic Circulation

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Deep Blue Sea – Structure

• Littoral Zone (intertidal zone): Shallow shoreline.

• Neritic Zone: Coast to continental shelf break.• Oceanic Zone: Beyond continental shelf.

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Deep Blue Sea - Structure

• Benthic: Habitat on bottom of ocean.

• Pelagic: Habitat off the bottom of the ocean.

http://www.oceansalive.org/

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Deep Blue Sea - Physical Conditions

• Light Approximately 80% of solar energy striking the

ocean is absorbed in first 10 m. None below 600 m, yet oceans are ≈4000 m on average.

• Temperature Sunlight increases velocity of water.

Rapid motion decreases density, thus warm water floats on top of cooler water.

Thermocline: Layer of water through which temperature changes rapidly with depth.

Creates thermal stratification.

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http://www.ccpo.odu.edu/~arnoldo/ocean405/globalcolor.gif

Ocean Phytoplankton Biomass as Chlorophyll

13http://topex-www.jpl.nasa.gov/aviso/text/general/discover/images/arrow.gif

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Deep Blue Sea - Chemical Conditions

• Salinity In the open ocean, salinity varies from

about 34 ppt to 36.5 ppt. Lowest salinity occurs near equator

where precipitation exceeds evaporation.

Highest salinity occurs in subtropics where evaporation exceeds precipitation.

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Deep Blue Sea - Chemical Conditions

• Oxygen A liter of air contains about 200 ml of

oxygen at sea level, while a liter of seawater contains a maximum of 9 ml of oxygen.

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Deep Blue Sea - Biology

• Photosynthetic organisms are limited to upper epipelagic zone (euphotic zone). Phytoplankton and zooplankton. Due to size, oceans contribute 1/2 of total

photosynthesis in the bioshpere.• Chemosynthesis occurs near undersea:

hot springs cold seeps

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http://www.njscuba.net/biology/img/zooplankton.gifhttp://www.njscuba.net/biology/img/phytoplankton.gif

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Deep Blue Sea - Human Influences

• For most of human history, vastness of oceans has acted as a buffer against human intrusion.

• New human-induced threats: Overharvesting Dumping Sediment and Nutrients

19http://www.whalersdiveclub.org/webpages/whalers_photo_gallery.htm

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Coral Reefs and Kelp Forests

• Reefs and kelp beds both grow in surface waters with sufficient light for photosynthesis. Both limited by temperature.

• Currents deliver oxygen and nutrients, and remove waste products. Biological productivity may depend on

flushing action.• Reefs and kelp beds among most productive

and diverse ecosystems.

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Marine Shores

• Inhabitants of intertidal zone are adapted to amphibious existence. Differential tolerances to periodicity of air

exposure leads to zonation of species.• Due to increased accessibility, intertidal

zones are experiencing increasing human exploitation.

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Intertidal Zonation

24http://www.clarku.edu/departments/biology/biol201/jlagliva/Nahant,%2520Intertidal%2520zonation.jpg

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Estuaries, Salt Marshes, and Mangrove Forests

• Estuaries are found where rivers meet the sea.

http://ccmaserver.nos.noaa.gov/images/estuary.jpg

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Estuaries, Salt Marshes, and Mangrove Forests

• Salt Marshes and Mangrove Forests are concentrated along low-lying coasts. Transistion between land and sea All driven by ocean tides and river flow.

Transport organisms, nutrients, oxygen, and remove wastes.

Extremely vulnerable to human intrusion.

27http://www.edc.uri.edu/restoration/html/gallery/saltmarsh.htm

28http://www.stevesbasement.com/mangroveforestA2.jpg

Mangrove

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Salt Marshes and Mangrove Forests