Hydroclimate and Aquatic Biomes: Nutrient Dynamics and Productivity, Summaries of Geography

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Introduction to the Aquatic Biomes

Lecture 15

Hydroclimate

-^ Aquatic systems are very different from terrestrial ones,

but :

-^ A soils analogy^ –

Think of the surface of lakes and oceans as very watery soils – Nutrients incorporated into particles sink 1-10 m/day – Aquatic “soils” weather hyper-rapidly^ •^

A nutrient rich body of water can be stripped of its nutrients in a single season

-^ Aquatic systems will be plant growth deserts unless nutrients are supplied tosurface waters regularly • A Tundra Biome/forest understory analogy –^ Recall that dim light can limit plant growth in some situations when everythingelse is favorable –^ Aquatic systems are lighted enough for photosynthesis only near the surface • Hydroclimates suitable for rapid plant growth are the relatively raresituations where light and nutrients are both present. • Most hydroclimates are more or less severely light or nutrient limited

Classifying the aquatic biomes.

This is a standard terminology for the oceans. The important

dimensions are water column (pelagic) versus bottom (benthic), and water depth (continental shelf, continentalslope, abyssal). Note also the terms “planktonic” for plants and animals of the pelagic (more generally anyplants or animals that live suspendeded in the water column), “Benthic” for plants and animals that live on therocks or muds of the bottom, and “littoral” for the subset of benthic animals that live at shallow enough depthsfor photosynthesis to be important.

Oceanic Biomes according to A.R. Longhurst.

Ocean current system.

Note how the Oceanic Biomes are relate to the currents. Each ocean basin

north and south of the equator is dominated by a subtropical gyre, home of the Central Biome. The SubpolarBiome is poleward of the northern and southern currents of the subtropical gyre. The Transitional Biomeoccupies the poleward currents of the central gyres extending equatorward with the cold currents of thegyres. The Tropical Biome is situated on the equatorial currents of the subtropical gyres, extending polewardon the west side of the ocean basins with warm currents like the Gulf Stream

Chesapeake Estuary

Estuaries.

Estuaries are bodies of water where salt and freshwater mix. Apart from having considerable scientificinterest because of their unusual properties, they are veryimportant to humans. Estuaries frequently make good ports.They tend to be very productive and have large fish andshellfish yields. They are also useful for transporting wastes.“Reclaiming estuary salt marshes and mud flats for agriculture.Municipal, and industrial purposes is often cheap and easy.Human settlement around and impact on estuaries is unusuallyheavy.

Properties of Water

Water is relatively dense (compared to air) In particular, since plant and animal tissue is mostly water, plants and animals are generally only a little denser than water. This makes planktonic and nektonic life possible. Octopus can walk and penguins fly with tiny wings.

Tiny phytoplankton live suspended inthe water column Zooplankton can migrate up and down the watercolumn with little expenditure of energy because theyare only a little heavier than water

Each flap a penguin’s wingmoves against a dense fluiddriving the heavy-bodiedbird swiftly with a tiny wingare compared to a flyingbird Because an octopus’ body isalmost the same density as water,it can stand up and walk without askeleton

Water has high heat capacity

Water is a polar molecule. Oxygenis such a strong attractor of electronscompared to hydrogen that the Oside of the molecule has a strongnegative and the H side a strongpositive charge.

Liquid water has strongish H-O bonds between adjacentmolecules. As heat is added to water they act like rubberbands, holding the molecules together. To get a givenamount of vibration in a given molecule (which is what wemeasure as temperature) heat energy has to work againstthese rubber band bonds. Water’s bond between moleculesus unusually strong, allowing it to absorb a lot of energy perdegree rise in temperature.

Phase changes occur at earth temperatures

and pressures

All three phases of water occur onearth. Changes from the solid to liquidand liquid to gas phase require largeamounts of energy, the latent heat offusion and the latent heat ofvaporization to tear down solidcrystals and especially to tear apartthe O-H bonds between watermolecules. We have alreadydiscussed the latent heat ofvaporization in connection with heattransport by water vapor and therelease of latent heat of vaporizationin he powering of storms.

Ice floats. Most solids sink to the bottom oftheir liquids. Think how much different theearth would be if ice sank! At least at thepresent time, the oceans would be almost allice with a little melt-water at the surface,thicker at tropical latitudes and thinner at thepoles.

Water is a strong solvent for many

substances

Highly polar water molecule tends to surround negatively and positively charged atoms ormolecules with one end of the water molecule or the other. As the other atom or moleculeacquires a thick coat of water, its bonds with other charged atoms or molecules becomeweak, and the substance like NaCl dissolves.