Nutrient Pollution

Eutrophication From the Greek: “eutrophos,” meaning “well-nourished” “Cultural eutrophication” means that we caused it

The Nitrogen Cycle All life requires nitrogen compounds – e.g. to make amino acids, which build proteins. Nitrogen gas, N 2, makes up 79% of the atmosphere, but is it inert. Nitrate and ammonia can be used by plants, but it requires a great deal of energy to break apart N 2 molecules. /BiologyPages/N/NitrogenCycle.html

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.

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:

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

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.

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

The Nitrogen Cycle Other bacteria, particularly ones living in anaerobic conditions, use nitrate as a substitute for oxygen in their metabolism. They produce N 2 gas as a by-product.

Human Population Causes of lower rates: Economic stringencies Availability of birth control Emergence of women’s rights Delayed first reproduction Demand for more education Lower infant mortality Social security Source: Valiela, Data from Pop. Ref. Bureau and UN Note that the rate of population growth did NOT decrease because of pollution.

Data from Pop. Ref. Bureau and UN By 2050, ~30% more people By 2030, ~60% of world population will be living in urban areas

From Valiela (2005). Global Coastal Change, Blackwell Science Publ. Data from Van Breemen et al. (2002), and Dow and Dewalle (2000). Land use on watersheds is changing fast Tendency for urbanization to increase

From Nicholls and Small (2002), and Valiela et al. (1992) Population is Coastal

European watersheds Waquoit Bay watersheds Data of Garnier et al. (2002). From Valiela et al. (2000). Nutrient export (kg km -2 y -1 )

Changes in land use on the watershed of Waquoit Bay on Cape Cod Massachusetts, From Valiela and Bowen (2002)

N inputs (10 3 kg N yr -1 ) From Bowen and Valiela (2001)

N and P enrichment experiments. N and P enrichment experiments. Example results from a trial in Jobos Bay, PR, Teichberg et al.

ControlNitrate

Phosphate Control Venice, Italy Photo by M. Teichberg

Increases in primary production —owing to increased nitrogen supply—are associated with increases in secondary production (fish, in this case). From Nixon and Buckley (2002)

Final thoughts… Nitrogen, once added to a marine ecosystem, can be cycled through many times, potentially contributing to hypoxia each time (see next week’s lecture).