added TP loading and GPP dependent on TP
nearly complete version, but still need submodels that are dependent on met data, etc.: ET, Evap, temp. profile, k
reorganized version that includes TP, but still need submodels that are dependent on met data, etc.: ET, Evap, temp. profile, k; also has issues of TP going negative due to too much sedimentation, driven by too high of POC concentrations by an order of magnitude
switched from problematic TP modeling to SRP