Phytoplankton Productionacross different systems

g C m-2 d-1 (net)

From Mann (2000) Ecology of Coastal Waters, 2nd Ed., Blackwell Science, MA, 406 pp.

The Nitrogen

Cycle

“Nitrogen Fixation”

We can make ammonia in factories, using atmospheric nitrogen and hydrogen (usually from natural gas or petroleum).

Requires great pressure, and temperatures of 600 degrees C!

Lightening can do the same thing (makes about 5-8% of the total nitrogen fixed.

We have become the dominant source of nitrogen fixation on the Earth – partly by making

fertilizerand partly by growing legumes

Dissolved Oxygen and Hypoxia

• ~8 mg/L = saturation (note that warmer water can hold less dissolved gas)

• <5 mg/L is a violation of water quality laws (depends on the classification of the body of water)

• <4 mg/L some species will avoid a place• 2 to 0 mg/L = hypoxia to anoxia: 50%

mortality in 1-4 days

Effects of Hypoxia

• Under hypoxic/anoxic conditions organisms will– First increase their breathing rate– Then they decrease their activity or

leave– Then die– Some use anaerobic metabolic

pathways (oysters)

Factors influencing Hypoxia

• Severity• Duration• Suddenness of Onset (e.g. wind

sloshing and the “Crab Jubilee” in the Chesapeake)

• Species type (shellfish, finfish, eggs, etc.)

• Temperature (warm is worse)

Chesapeake Bay Annual Cycle of

Stratification and Anoxia

Source: Tyler & Seliger

Chesapeake Bay

Long Island Sound

EXTRAS

Change of community structure

• Eutrophication can cause greater plankton and “nuisance algae” growth

• Increased phytoplankton growth causes greater shade on the bottom

• This can kill off important species of “Submerged Aquatic Vegetation” such as Eel Grass

Loss of cover of seagrass meadows in Waquoit Bay through the end of the 20th century (Modified from

Valiela et al. 1992).

Altered structure of estuarine producers under increased nitrogen loads, for estuaries with different residence times.

From Valiela et al. (2001)

Nitrogen Sources

Ammonia factory

• “National Public Radio reports that low cost Anhydrous Ammonia is the single greatest technical development of the last 200 years.  At least 2 times more land in the US would need to be in production to feed only our citizens if low cost Anhydrous Ammonia was not available.”

Source: http://www.exactrix.com/dewi.htm

The Nitrogen

Cycle

Certain bacteria have also figured out how to fix nitrogen.

Requires a huge expenditure of ATP.

Nitrogen-fixing bacteria usually live in a symbiotic relationship with legumes.

Cyanobacteria can also do this in aquatic systems.

The Nitrogen

Cycle

Other bacteria, particularly ones living in anaerobic conditions, use nitrate as a substitute for oxygen in their metabolism.

They produce N2 gas as a by-product.

Denitrification in Sewage Treatment:Budd Inlet, South Puget Sound

Hypoxia

Chesapeake Bay and N-loading