The Nitrogen Cycle in the Coral Reef
Monday, 23 October 2023
Oh no, not another 'nitrogen crisis'! Some coral reefs in the wild are severely affected by pollution. For example, due to the discharge of sewage water near the reef. In this case, the result could be a high amount of nitrogen in the water causing algae to grow rapidly, ultimately overgrowing and suffocating the corals. Burgers' Ocean is home to one of the largest coral reef basins in aquaria worldwide. The nitrogen levels in this aquarium are closely monitored. When the fish are fed, they subsequently excrete waste, often in the form of nitrogen compounds. For the Ocean team, it's crucial to understand what happens to this nitrogen, whether it's too much or too little. Several students from Wageningen University have tackled this issue. The result is a computer model that calculates the entire nitrogen cycle. Assembling this model was a puzzle, with each student contributing to solving a piece of it. Sophie Cooijmans was the last student to work on this project.
In and out
In essence, you can consider the coral reef aquarium as a 'black box.' You pour something in, take something out, and various processes occur within the box. What goes in includes fish food, approximately 5 kg per week. After analysing all the types of food, it turns out that there are 95 grams of nitrogen in the weekly food ration. Different filters remove nitrogen compounds from the water. However, a significant portion of the nitrogen is converted, consumed, and recycled within the reef itself. The symbiotic tiny algae within the corals and algae on the stones absorb a portion. Bacteria also play a role. Some specific types of bacteria convert the nitrogen compound ammonium into nitrate. Other bacteria transform nitrate into nitrogen gas.
A gas bubble
Sophie used specialised equipment from Wageningen University to collect gases above the aquarium and analyse them. Every animal emits carbon dioxide (CO2), so you can directly measure the 'excess' CO2 just above the aquarium. Additionally, the nitrogen gas produced by bacteria escapes at the surface. By capturing the nitrogen gas, you can calculate how much nitrogen leaves the aquarium this way. Another piece of the puzzle has been solved! The computer model closely approximates the processes taking place in the aquarium, which helps the team understand what's happening and prevents Burgers' Ocean's coral reef from entering a nitrogen crisis!
