Question about the phosphorus parameter in efdc

In model version 8.4, simulations for parameters such as algae and total active metals are turned off. All settling parameters, atmospheric deposition of all phosphorus pollutants, release of phosphates from sediment, and all phosphorus transformation parameters (particle hydrolysis and dissolved mineralization parameters) are disabled. The initial values include only one type of phosphorus component, namely RPOP or LPOP or DOP or PO4. It can be assumed that only one phosphorus component is being simulated.

When only simulating RPOP and setting a non-zero value for the “RPOP minimum hydrolysis rate parameter,” it is observed that the total phosphorus in the lake remains in equilibrium. However, it is found that RPOP is directly converted into PO4 instead of DOP, which is confusing. According to the theoretical manual, RPOP hydrolysis should produce DOP, and only the mineralization of DOP can generate PO4. But the minimum mineralization rate for DOP is set to 0.

When only simulating DOP and setting a non-zero value for the "DOP minimum mineralization rate parameter, it is observed that the total phosphorus in the lake is not in equilibrium. The DOP concentration decreases by approximately 77 tons, and the total phosphorus stock also decreases by the same amount. However, the PO4 concentration in the lake does not increase and remains at 0, while LPOP and RPOP are also 0. This indicates that DOP seems to disappear directly from the model, contrary to the theoretical expectations.

Furthermore, attempts were made to enable algae simulation, settling parameters, and other normal model settings. It was found that changing the “DOP minimum mineralization rate” parameter did not affect the PO4 concentration. Similar observations were made when using models created by other people where the PO4 concentration remained unchanged after modifying the “DOP minimum mineralization rate” parameter.