Answer:
utrophication - "Increase in the rate of supply of organic nutrients in an ecosystem"
Highly concentrated nutrients including phosphates and nitrates can be introduced to a body of water from runoff. A majority of this runoff can be traced to agricultural projects, urban factories, and septic or waste management systems. The increase of toxic wastes and nitrogen allows for algae to grow abundantly, through biomagnification this becomes problematic as highly toxified algae infects the entire food chain. Additionally, algal blooms can obstruct sunlight, deplete water-oxygen levels, and even harbor new invasive species. All of these effects reduce healthy biodiversity within an ecosystem.
Biomagnification- "the accumulation of persistent chemicals in the living tissues of consumers in food chains."
For example, a pesticide would be sprayed in a marsh to kill mosquitos. The pesticide will accumulate in the microscopic organisms, like plankton, in the marsh. Then organisms who consume the plankton absorb the harmful pesticide as well. As this process goes further up the food chain the amount of the pesticide grows so that higher level consumers build up dangerous amounts of the harmful chemicals.