Check In HW and Set Up 5 Yeast Dilutions

Sentinel Species?

Warwick E. Kerr

Sentinels of Global Warming?

Biogeochemical Cycles

How do biogeochemical cycles reflect the 1st law of thermodynamics?

Nutrient Cycles

• Materials necessary to build tissues and carry out essential life functions

• Examples: Carbon, Phosphorus, Nitrogen

HYDROLOGIC CYCLE

• Evaporation• Condensation

• Powered by solar radiation

Primary Productivity v. Rainfall

Carbon Cycle

• Appx. 49,000 metric gigatons of carbon on Earth and in atmosphere

• 71% in ocean• 22% fossilized• 3% in dead matter• 2% in live matter• 1% in atmosphere

Mutualism & The Carbon Cycle

• Photosynthesis “fixes” gaseous carbon (in form of CO2) into a more stable form (glucose/C6H12O6)

• Cellular Respiration releases carbon in form of CO2

A Precarious Balance

• CO2 is only a small fragment of the atmosphere (0.04%)

• Less than 2% of the world’s CO2 comes from burning fossil fuels

• YET, the carbon cycle is rapidly becoming unbalanced in its ability to absorb the increases in CO2

NITROGEN CYCLE

• 78% of atmosphere is DIATOMIC NITROGEN (N2)

• N2 is essentially useless to living organisms as the triple covalent bonds between nitrogen atoms make it chemically inert

• To “liberate” nitrogen it must be chemically reacted with other atoms

ABIOTIC NITROGEN FIXATION

• High energy reactions like lightning and vulcanism can break the triple bonds of N2

• Liberated nitrogen reacts with oxygen to create Nitrate (NO3) and Nitrite (NO2)

BIOTIC NITROGEN FIXATION

• Rhizobium bacteria use the enzyme nitrogenase to break apart N2 in the absence of oxygen

• To isolate themselves from oxygen, Rhizobium live in nodules on legumes

Phosphorus & Algal Blooms

• Excess phosphorus in aquatic ecosystems allows for algal populations to increase drastically by raising the carrying capacity

• However, biological oxygen demand becomes too high and system crashes