Nutrient Cycles Eutrophication Nitrogen –Chemical Forms in the Aquatic Environment –Chemical...

Nutrient Cycles• Eutrophication

• Nitrogen– Chemical Forms in the Aquatic Environment– Chemical Transformations– Cycle

• f-ratio

• Carbon

Nutrient Cycles and Eutrophication

• Light penetration with depth

• Mixing and stratification

• Phytoplankton nutrient use

• Ocean circulation

Eutrophic

• Refers to areas that contain high nutrient concentrations and support high biological productivity

Eastern Boundary Currents

Upwelling

Eutrophication

• An increase of nutrients in a system (N or P) which promotes excessive plant growth (and decay) and is likely to cause severe reductions in water quality

Increase in nutrient loading

Experimental Lakes Area

Point and Nonpoint sources of chemical inputs

Algal Bloom in Lake

Before After

Adverse effects of eutrophication on lakes,

reservoirs, rivers and coastal marine waters • Increased biomass of phytoplankton • Toxic or inedible phytoplankton species • Increases in blooms of gelatinous zooplankton • Increased biomass of benthic and epiphytic algae • Changes in macrophyte species composition and

biomass • Decreases in water transparency • Taste, odor, and water treatment problems • Dissolved oxygen depletion • Increased incidences of fish kills • Loss of desirable fish species • Reductions in harvestable fish and shellfish • Decreases in perceived aesthetic value of the water

body

New species invasion

• Eutrophication may cause competitive release - nutrient normally limiting ↑↑.

• ↑ nitrogen might allow new, competitive species to invade and outcompete original inhabitant species

The changes in nutrient levels and biology can directly affect humans:

•    The water can be injurious to health•    The amenity value of the water may decline•    Increased vegetation may impede water flow and

navigation•    Commercially important species of fish may disappear•    Treatment of drinking water may be difficult and supply

can have an unacceptable taste or odor

Prevention of eutrophication

The main effects caused by eutrophication:

1.     Species diversity decreases and the dominant biota changes

2.     Plant and animal biomass increase

3.     Turbidity increases

4.     Rate of sedimentation increases, shortening the lifespan of the lake

5.     Anoxic conditions may develop

Gulf of Mexico

Caspian Sea

Algal Bloom

Oligotrophic Lake Eutrophic Lake

Oligotrophic Lake Eutrophic Lake

Chemical Forms – Nitrogen

Chemical Forms – N

• NO32- (Nitrate)

• NO2- (Nitrite)

• NH4+ (Ammonium)

• CO(NH2) 2 (Organic, Urea)

• N2 (Dissolved gas)

• N2O (Nitrous Oxide)

Annual Surface Nitrate Concentration

The Marine Nitrogen Cycle

The Marine Nitrogen Cycle

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The Marine Nitrogen Cycle

**

The Marine Nitrogen Cycle

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Denitrification

Nitrification

NO32- (Nitrate) → NO2

- (Nitrite) → NH4+ (Ammonia)

Heterotrophic microbes (anerobic)

NH4+ (Ammonia) → NO2- (Nitrite) → NO32- (Nitrate) Heterotrophic microbes (aerobic)

Nitrate Uptake into the Cell

Reduction steps: Reduced forms of nitrogen are ‘preferred’

NO3 NO3 NO2 NH4

Reduction steps

Diffusional Gradient

Proteins

Phytoplankton other Autotrophs - Assimilatory N Reduction

NitratePhytoplankton

Up

wel

lin

gM

ixin

g

Ver

tica

lF

lux

N2 FixationRiversDeposition

PONDIN

Euphotic Zone

f-ratio

Upwelling Zone 0.8Gyre 0.1Global Average < 0.5

New Production

New + Regenerated Production

Sediment traps

to catch

sinking particles

Sustainable yields

NitratePhytoplankton

Up

wel

lin

gM

ixin

g

Ver

tica

lF

lux

N2 FixationRiversDeposition

PONDIN

Euphotic Zone

Fishing

New Production

Oligotrophic gyres

Upwelling regions