1. Water Exchange Required to Maintain Nitrate Concentrations in Recirculating Marine Systems Brantley Miller

2. Nitrogen Essential to all living organisms Found in protein structure Used for tissue growth Excess N released in waste Inorganic compounds are production limiting Used by bacteria and plants Key for food chain

3. Nitrogen Cycle Complex biochemical cycle Different levels of ecosystem Sinks and sources Interconnected with other element cycles Balance is key Inputs & outputs Circulation Figure 1: Diagram of nitrogen cycle and its interconnectivity to other marine cycles such as carbon, phosphorus and oxygen. (Gruber, 2008)

4. Nitrification Multiple processes Bacteria metabolism Oxidation reactions Poisonous intermediate compounds Nitrate Oxygen & algae Water transport Figure 2: Nitrogen cycle plotted against oxidation state. Processes in grey indicate taking place in regions of low oxygen (anoxic). (Gruber, 2008)

5. Modeling Recirculating System Bird, Stewart 2007 http://www.aquariumdesigngroup.com/ Well circulated High Reynolds number Inertial dominate Quasi-closed Limited exchange Inputs & outputs Multicomponent Well established ecosystem Bacteria rxn Bio load

6. Modeling Recirculating System (Rate of increase of NO₃⁻) = (Net rate of addition of NO₃⁻) + (Rate of production of NO₃⁻) Rate of addition Water entering Pollution Rate of removal Water leaving System concentration Rate of production Fish waste Other biological processes

7. Estimating Production of Nitrates due to Feeding Ammonia-N Production = 0.289 (Feed Fed) Nitrite-N Production = 0.024 (Feed Fed) Phosphate-P Production = 0.0162 (Feed Fed) Suspended Solids = 0.52 (Feed Fed) Biochemical Oxygen Demand = 0.60 (Feed Fed) Chemical Oxygen Demand = 1.89 (Feed Fed) (Wheaton) Function of amount fed 2-4% of fish mass Ammonia to nitrite Nitrite to nitrate Oxygen demand (Ward, 2008)

8. Describing Nitrates leaving the System Water leaving Concentration Flow rate Removal of algae

9. Putting it Together Flow required is a function of desired NO₃⁻ concentration and local fish mass Maintain concentration of nitrate (<1ppm) Fixed bio load NO₃⁻ production based on fish mass / feed Conservation of mass Assumptions and BCs Make modeling situationally dependent