Ecosystems

Ecosystem:  All the organisms in a community plus abiotic factors  ecosystems are transformers of energy& processors of matter.  Ecosystems are self-sustaining  what is needed?  energy  producers  cycling of nutrients

Energy budget of ecosystems  Production by autotrophs sets energy budget for an ecosystem  Marine  light, temperature & nutrients  depth  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 O 2 production Or…. “N.P.P.”Net Primary Productivity- (GPP – respiration) Limiting factors:Sunlight Precipitation Nitrogen & Phosphorus Obviously varies greatly by biome……

Primary production Where is productivity highest per meter?Total on Earth?

Regional annual net primary productivity Mapping chlorophyll density by satellite

Too much of a good thing? Eutrophication High Phosphorus  Algae “over-produce”  (P is limiting nutrient) Lots of Algae die  Decomposers 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” _ __ 10000

But speaking of CYCLES….

abiotic reservoir:  CO 2 in atmosphere enter food chain:  photosynthesis = carbon fixation in Calvin cycle recycle:  decaying organic material return to abiotic:  respiration  combustion abiotic reservoir:  CO 2 in atmosphere enter food chain:  photosynthesis = carbon fixation in Calvin cycle recycle:  decaying organic material return to abiotic:  respiration  combustion

abiotic reservoir:  surface & atmospheric water enter food chain:  precipitation & plant uptake recycle:  transpiration return to abiotic:  evaporation & runoff abiotic reservoir:  surface & atmospheric water enter food chain:  precipitation & plant uptake recycle:  transpiration return to abiotic:  evaporation & runoff

abiotic reservoir:  rocks, minerals, soil enter food chain:  erosion releases soluble phosphate  uptake by plants recycle:  decomposing bacteria & fungi return to abiotic:  loss to ocean sediment abiotic reservoir:  rocks, minerals, soil enter food chain:  erosion releases soluble phosphate  uptake by plants recycle:  decomposing bacteria & fungi return to abiotic:  loss to ocean sediment

Even though the atmosphere is over 70% Nitrogen Can 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!! abiotic reservoir:  N in atmosphere enter food chain:  nitrogen fixation by soil & aquatic bacteria recycle:  decomposing & nitrifying bacteria return to abiotic:  denitrifying bacteria abiotic reservoir:  N in atmosphere enter food chain:  nitrogen fixation by soil & aquatic bacteria recycle:  decomposing & nitrifying bacteria return to abiotic:  denitrifying 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 N 2 + O > 2 NO (nitric oxide) The nitrous oxide formed combines with oxygen to form nitrogen dioxide. 2 NO + O > 2NO 2 Nitrogen dioxide readily dissolves in water to product nitric and nitrous acids; 2 NO 2 + H 2 O > HNO 3 + HNO 2 Keep in mind that less than 5% of the atmospheric nitrogen gets fixed in this way…

Biomagnifications Toxins become more concentrated as they move through food webs Toxins cannot be broken down, but there are less and less organisms at each trophic level.

BioMagnification  PCBs  GE power plant on Hudson River  PCBs in sediment  striped bass nesting areas