Post on 26-Dec-2015
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