When is used to explain a set of observations, there is always a chance that an alternative explanation may be more accurate. In the practice of science, this type of reasoning is used to develop explanations.

answer; ////increased water pollution; ///////////////////////

the answer is:

carbon dioxide

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.