Excess nitrogen is converted into urea in the liver. Return to the soil Decomposers break down the protein of dead organisms into amino acids. Some of these are used for their own growth and the rest is converted into ammonia. This process requires oxygen. Denitrifying bacteria obtain energy by reducing NO3- to N2 and thrive in anaerobic conditions.
Eutrophication means enrichment.
Recently man has greatly increased this process. Algal bloom as minerals usually limiting. Usually vigorous less palatable species with a reduction in diversity. The conflicting pressures on the Broads. Taking core samples from the mud at the bottom of the lake to examine past use and the impact of boating.