Ecosystems

Ecosystem:All the organisms in a community plus abiotic factorsecosystems are transformers of energy& processors of matter.

Ecosystems are self-sustaining

what is needed?

energy

producers

cycling of nutrients

Energy budget of ecosystemsProduction by autotrophs sets energy budget for an ecosystem

Marine

light, temperature & nutrientsdepth

Terrestrial

light, moisture, temperature

latitude & climate

nutrients

Nutrient Cycling

Decomposition connects all trophic levels

Energy transfer

Nutrients

Recycled by…

loss of energy as heat

<20% efficiency

OK- Time for some definitions here…..

Primary Productivity-“the amount of light energy converted to chemical energy.”

Defined in terms of either:

“G.P.P.”Gross Primary Productivity- Determined by O2 productionOr….

“N.P.P.”Net Primary Productivity-

(GPP – respiration)Determined by Biomass of dry wt. added

g/m2/yr

Limiting factors: •Sunlight•Precipitation•Nitrogen & Phosphorus

Obviously varies greatly by biome……

Primary productionWhere is productivity highest per square meter?

Total on Earth?

Regional annual net primary productivity

Mapping chlorophyll density by satellite

Too much of a good thing?

Eutrophication

High PhosphorusAlgae “over-produce” (P is limiting nutrient)

Lots of Algae dieDecomposers consume all the oxygen.

Secondary Productivity“rate that CONSUMERS convert chemical energy into

their own biomass.

Energy flow THROUGH an ecosystem, it does NOT cycle!!

Efficiency: Remember the 10% rule“only about 10% of energy is transferred from one trophic level to the next”

1

1 10

1_ 100

1 1000

1__ 10000

But speaking of CYCLES….

Even though the atmosphere is over 70% NitrogenCan NOT be assimilated in its elemental form!

This bacteria is called“Rhizobium”

Note that this is a different pathway that uses a different set of bacteria.

In fact, 3 completely different classes of bacteria!!

Another way in which molecular nitrogen is modified is via the discharge of lightning.

The tremendous energy released by the electrical discharges breaks the strong bonds between nitrogen atoms, causing them to react with oxygen.

lightning N2 + O2 --------------> 2 NO (nitric oxide)

The nitrous oxide formed combines with oxygen to form nitrogen dioxide. 2 NO + O2 ---------------> 2NO2

Nitrogen dioxide readily dissolves in water to product nitric and nitrous acids;2 NO2 + H2O -------> HNO3 + HNO2

Keep in mind that less than 5% of the atmospheric nitrogen gets fixed in this way…

Biomagnifications

BioMagnification

PCBs GE power plant on Hudson RiverPCBs in sediment

striped bass nesting areas