The diagram illustrates the sources and concentration levels of nitrogen in the groundwater of a coastal city, along with the natural processes involved in the nitrogen cycle.
Nitrogen enters the groundwater system from several sources. On the land surface, nitrogen is introduced through coastal vegetation, domestic and market gardens, industrial activities, and waste disposal. Fertilizers used in gardening and agriculture contribute significantly to nitrogen runoff, while household waste and industrial discharge, including wastewater ponds, release nitrogen-rich substances into the soil. These sources lead to varying nitrogen concentrations in the groundwater, which are visually represented in darker shades in the diagram.
Once nitrogen reaches the soil, it undergoes a series of chemical and biological transformations. Ammonia and ammonium are produced and may either be adsorbed by soil particles or converted through nitrification. Some nitrogen is also removed via denitrification, a process that releases it back into the atmosphere. Ultimately, nitrogen flows with groundwater towards the ocean, where it is discharged.
The diagram highlights the complexity of nitrogen movement in groundwater and emphasizes the impact of human activities on its concentration levels.