Fluctuations in the phosphorus cycle in aquatic ecosystems
a. can lead to changes in the growth rates of aquatic populations
b. are never caused by human impact on the environment
c. lead to a decrease in the amount of phosphorus found in sediment
d. never occur naturally

c

explanation:

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.