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ePaper created 2013-03-20, 16:12:44 | version 1.25.4
8 Water at last! NH+ 4 NH3 NO- 2 NO- 3 What is the “biological equilibrium”? When speaking colloquially about the biolog- ical equilibrium, this in most cases refers to the so-called nitrogen cycle. Once it has es- tablished in a pond, pond keepers may lean back and let natural self purification powers do the work. The nitrogen cycle is schemati- cally shown here: 1 Too much food, fish waste and dead plant parts pollute the waterpollute the water 2 Purification bacteria first convert pollutants into NH4 + /NH3 (ammonium, ammonia)(ammonium, ammonia) 3 Purification bacteria convert NH4 + /NH3 into NO2 – (nitrite) 4 Purification bacteria convert NO2 – into NO3 – (nitrate) = plant nutrient 1 2 3 4 Breakdown of the pollutants ammonia (NH3), nitrite (NO2) and nitrate (NO3)