55 5 end of ch 55 Human Impacts on Ecosystems Humans add nutrients fertilizers to soil which allows more crops to grow increasing productivity Creating dead zones Most of the middle US is used for agriculture and agriculture fields don t hold nutrients well because they are constantly plowed so lots of extra nutrients are added to increase productivity Most of the water and therefore the added nutrients in the US are drained out through the Mississippi River Nutrient rich fresh water sits on top of the salt water in the gulf and cut off the salt water from contact with oxygen The nitrogen and phosphorous from fertilizers cause huge increase in algae growth When the algae die they sink to the bottom salt water and decompose using up oxygen in the deeper water This area becomes a DEAD ZONE because there isn t enough oxygen so fish and all other organisms either die or avoid the area Winter brings relief but spring runoffs restart the cycle Biological magnification use Mercury as an example When mercury enters an aquatic ecosystem it is consumed by algae Then plankton eats the algae and fish eat the plankton HOWEVER in order to grow 1g a fish must consume 10g of plankton THEREFORE the new fish tissue will have 10 times the amount of mercury than the plankton had A bird would have 1000 times more mercury than the plankton The higher up the trophic level the more toxin they have in their system Climate and green house gases By burning fossil fuels CO2 in an inactive form we are increasing the rate at which CO2 is put back into the atmosphere and slowing down the rate at which heat is lost resulting in temperatures being raised Green house gases gases that absorb heat When humans modify the ecosystems they are helping humans survive over other species and effectively ALTERING THE CARRYING CAPACITY K so our growth continues to be exponential PROBLEM we are damaging ecosystems by doing this which decreases our productivity so we then depend on the fossil fuels and fertilizers which are the original causes for dead zones and global warming
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