In the diagram below you have an aquatic system with low dedritus content and an
ID: 111151 • Letter: I
Question
In the diagram below you have an aquatic system with low dedritus content and another with high detitrus content. Please explain:
a. What factors and which mechanism during the nitrogen cycle in the water are responsible for the increase for the increase of nitrogen released as N2 into the atomosphere.
b. What is the difference between NO3 production vs partiulate Nproduction in the diagrams presented below
c. How do rivers and ponds effect the cycling of nitrogen in a given ecosystem
Rivers Are Important Modifiers of Nitrogen Exports The amount of nitrogen a river delivers to the ocean is much less than the amount that enters that river (A)1,600 1,400 E 1,200 1,000 800 600 North Sea Nw European coast . NE US. Baltic SW European coast 200 . Canada 1,000 2,000 3000 4,000 5,006/00 7000 80 00 N input from human activities (kg/km /y Denitrification and biological uptake are both enhanced by increases in organic detritus in rivers and streams Denitrfica undwater NH DON Particulate N Low detritus content High detritus content ECOLOGY 2e, Figure 21.16Explanation / Answer
a. Nitrogen in gaseous form is unusable and has to be converted into usable forms through a process known as fixation. The bacteria plays an important role for the fixation of the nitrogen. The bacteria which are either free living or form symbiotic associations with other organisms like protozoa or plants convert N2 into ammonia. Some bacteria convert ammonia into nitrate and nitrate to N2 or other gases. While other bacteria and fungi degrade organic matter and releases the fixed nitrogen to be used by other organisms. All these procesess include the nitrogen cycle in aquatic ecosystem which are responsible for release of increased nitrogen into the atmosphere.
b. Both particulate N and N2 increase when there is high detritus content in the ocean. This is due the fact that the process of denitrification accelerates which is responsible for production of N2 as well as the biological uptake increases which in turn increases the concentration of particulate N.
c. The presence of large amount of gravels in the pond and the rivers helps in colonization of useful bacteria responsible for denitrification process which in turn convert ammonia into less toxic and useful forms of nitrite and nitrate. This nitrate is then absorbed by aquatic plants or undergoes process of denitrification in anaerobic conditions which convert the nitrogen back to nitrogen gas. Also nitrate can also be removed by high fluctuation in water level in the rivers. Nitrogen can also be fixed in these water bodies during the atmospheric fixation by lightning. Organic debris like leaves, dead fishes decompose and break down to ammonia as a by product which restarts the cycle of denitrification. The oxygen present in these water bodies are also responsible for denitrification. Thus ponds and rivers affect the process of nitrogen cycle significantly.