# Ticket #1283 (new assessed)

## BA input is incorrectly ignored in calculating Ecosim rates

Reported by: | Carlw | Owned by: | joeb |
---|---|---|---|

Priority: | normal | Milestone: | NOT SET |

Component: | Ecosim | Version: | 6.4.0 BETA |

Severity: | major | Keywords: | |

Cc: |

### Description

Ecosim assumes that each detritus pool is at equilibrium (dB/dt=0) at the Ecopath base. Its basic model for detritus biomass dynamics is dB/dt=Inputs-kB, where in most cases k represents decomposition rates due to microorganisms. So for dB/dt to equal 0 at the initial state, k has to satisfy dB/dt=0=inputs-kB, and from this we can calculate the decomposition (or export or whatever causes detritus loss) rate parameter k as k=inputs/B where B is the ecopath base detritus biomass. Note here that inputs is the sum of all flows to detritus from within the system, plus import rate.

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CarlW: To fix this bug, we would have to solve the more general condition dB/dt=inputs-kB for k, with dB/dt set to the ecopath input biomass accumulation rate BA. That is, we would solve BA=inputs-kB for k, to give the decomposition rate k=(Inputs-BA)/B. This would allow you to model the possibility (in a world without decomposers) of BA=inputs, ie k=0, and detritus would accumulate.

In terms of EwE development, what you have uncovered is that we need to either change one ecosim subroutine to include BA in the calculation of the k’s, or else change the ecopath interface to not allow users to specify Bas for detritus. Probably best we fix the ecosim k calculation.

VILLY AND JOE: this is weird, because we are in fact already subtracting BA(i) in the calculation of DetritusOut?(i) (the k parameter above) near the end of SimDetritusMT. When I try setting BA>0 for a detritus group, the value of m_EPData.BA(i) reaching simdetritus has been set to 0.