What is the impact on cycle
Too much fertilizer can cause many plants to die do to all the green yuck that goes on top. That yuck causes the plants to not reach the sun and it cuts out oxygen level which makes many plants to die to the lack of sun and oxygen.
Back ground information
Most plants get the nitrogen they need from soil. Many farmers use fertilizers to add nitrogen to the soil to help plants grow larger and faster. Both nitrogen fertilizers and forest fires add huge amounts of nitrogen into the soil and nearby lakes and rivers. Water full of nitrogen causes plants and algae to grow very fast and then die all at once when there are too many for the environment to support. https://eo.ucar.edu/kids/green/cycles7.htm
How the cycle works
Five main processes cycle nitrogen through the biosphere, atmosphere, and geosphere: nitrogen fixation, nitrogen uptake through organismal growth, nitrogen mineralizationthrough decay, nitrification, and denitrification. Microorganisms, particularly bacteria, play major roles in all of the principal nitrogen transformations.