Merge pull request #1120 from brian-eaton/ndep-ddep

cam6_4_024: Deposition fixes for aquaplanet and simple model configurations.
ESCOMP · Aug 28, 2024 · 265425a · 265425a
2 parents 6e32d03 + f7153a6
commit 265425a
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Showing 7 changed files with 294 additions and 44 deletions.
diff --git a/bld/build-namelist b/bld/build-namelist
@@ -509,6 +509,14 @@ if ($phys_mode_flags > 1) {
 my $simple_phys = 0;
 if ($adia_mode or $ideal_mode) { $simple_phys = 1; }
 
+# If running either a simple physics or an aquaplanet configuration, the nitrogen
+# deposition data is not used.  These files are set in buildnml and can't be overridden
+# via user_nl_cam.  So provide an override here.
+if ($simple_phys or $aqua_mode) {
+    $nl->set_variable_value('ndep_stream_nl', 'stream_ndep_data_filename', '" "');
+    $nl->set_variable_value('ndep_stream_nl', 'stream_ndep_mesh_filename', '" "');
+}
+
 # Single column mode
 my $scam = $cfg->get('scam');
 my $scam_iop = $cfg->get('scam_iop');
@@ -616,11 +624,17 @@ if ( ($chem ne 'none') or ( $prog_species ) ){
     }
 }
 if ($chem) {
-    # drydep_srf_file is only needed for prognostic MAM when the grid is unstructured.
-    # structured grids can do interpolation on the fly.
-    if ($chem =~ /_mam/ and ($dyn =~ /se|fv3|mpas/)) {
-        add_default($nl, 'drydep_srf_file');
+
+    # drydep_srf_file is not needed for simple physics or aquaplanet
+    if ( !($simple_phys or $aqua_mode) ) {
+
+        # drydep_srf_file is only needed for prognostic MAM when the grid is unstructured.
+        # structured grids can do interpolation on the fly.
+        if ($chem =~ /_mam/ and ($dyn =~ /se|fv3|mpas/)) {
+            add_default($nl, 'drydep_srf_file');
+        }
     }
+
     add_default($nl, 'dep_data_file');
 }
 

diff --git a/bld/namelist_files/namelist_definition.xml b/bld/namelist_files/namelist_definition.xml
@@ -9527,36 +9527,4 @@ If TRUE perform temp tendency scaling before send to fv3 dynamics
 Default: FALSE
 </entry>
 
-<!-- ndep stream forcing -->
-
-<!-- ========================================================================================  -->
-<!-- ndepdyn streams namelist                                                                  -->
-<!-- (only used when the ndep_list namelist variable (above) in drv_flds_in is not empty       -->
-<!-- ========================================================================================  -->
-
-<entry id="stream_datafile_ndep" type="char*256" category="ndep_stream"
-       group="ndep_stream_nml" valid_values="" input_pathname="abs" >
-Stream filename(s) for Nitrogen Deposition data
-</entry>
-
-<entry id="stream_meshfile_ndep" type="char*256" category="ndep_stream"
-       group="ndep_stream_nml" valid_values="" input_pathname="abs" >
-Stream meshfile for Nitrogen Deposition data
-</entry>
-
-<entry id="stream_year_first_ndep" type="integer" category="ndep_stream"
-       group="ndep_stream_nml" valid_values="" >
-First year to loop over for Nitrogen Deposition data
-</entry>
-
-<entry id="stream_year_last_ndep" type="integer" category="ndep_stream"
-       group="ndep_stream_nml" valid_values="" >
-Last year to loop over for Nitrogen Deposition data
-</entry>
-
-<entry id="model_year_align_ndep" type="integer" category="ndep_stream"
-       group="ndep_stream_nml" valid_values="" >
-Simulation year that aligns with stream_year_first_ndep value
-</entry>
-
 </namelist_definition>
diff --git a/doc/ChangeLog b/doc/ChangeLog
@@ -1,5 +1,219 @@
 ===============================================================
 
+Tag name: cam6_4_024
+Originator(s): eaton
+Date: 27 Aug 2024
+One-line Summary: Deposition fixes for aquaplanet and simple model configurations.
+Github PR URL: https://github.com/ESCOMP/CAM/pull/1120
+
+Purpose of changes (include the issue number and title text for each relevant GitHub issue):
+
+Issue #866 - Aquaplanet cases should not require ndep
+PR #910 - No ndep in aquaplanet
+
+. Don't require the ndep stream for aquaplanet or simple models.  Also
+  remove the ndep datasets from the namelist when they aren't being used.
+  This prevents cime from downloading large unneeded files.
+  This doesn't change answers since the ndep fluxes are not used by these
+  configurations.
+
+. Don't require a drydep_srf_file for aquaplanet runs on unstructured
+  grids.  This does change answers since currently aquaplanet runs are
+  using the versions of this file which are meant for a CAM/CLM
+  configuration and are introducing an incorrect land surface signal into
+  the drydep calculations.
+
+resolves #866
+closes #910
+
+Describe any changes made to build system: none
+
+Describe any changes made to the namelist:
+
+. build-namelist is modified to remove the settings of
+  stream_ndep_data_filename and stream_ndep_mesh_filename when aquaplanet
+  or simple model configurations are used.
+
+List any changes to the defaults for the boundary datasets: none
+
+Describe any substantial timing or memory changes: none
+
+Code reviewed by: cacraig
+
+List all files eliminated: none
+
+List all files added and what they do: none
+
+List all existing files that have been modified, and describe the changes:
+
+bld/build-namelist
+. if simple model or aquaplanet remove the settings of
+  stream_ndep_data_filename and stream_ndep_mesh_filename 
+. modify logic so the add_default call for drydep_srf_file is not made for
+  simple models or aquaplanet 
+
+bld/namelist_files/namelist_definition.xml
+. remove the variables in the ndep_stream_nml group.  Not used.
+
+src/chemistry/mozart/chemistry.F90
+. chem_readnl
+  - add initializer for drydep_srf_file
+
+src/chemistry/mozart/mo_drydep.F90
+. get_landuse_and_soilw_from_file
+  - if drydep_srf_file not set, then set fraction_landuse to zero.
+
+src/cpl/nuopc/atm_import_export.F90
+. export_fields
+  - When ndep is not computed by WACCM, and the ndep stream isn't used,
+    then set Faxa_ndep to zero.
+
+src/cpl/nuopc/atm_stream_ndep.F90
+. add public module variable use_ndep_stream
+. stream_ndep_init
+  - if stream_ndep_data_filename not set, then set variable
+    use_ndep_stream=.false. (otherwise .true.)
+
+If there were any failures reported from running test_driver.sh on any test
+platform, and checkin with these failures has been OK'd by the gatekeeper,
+then copy the lines from the td.*.status files for the failed tests to the
+appropriate machine below.  All failed tests must be justified.
+
+derecho/intel/aux_cam:
+
+ERP_Ln9.f09_f09_mg17.FCSD_HCO.derecho_intel.cam-outfrq9s (Overall: PEND)
+- pre-existing failure due to HEMCO not having reproducible results issues #1018 and #856
+
+SMS_D_Ln9_P1280x1.ne0ARCTICne30x4_ne0ARCTICne30x4_mt12.FHIST.derecho_intel.cam-outfrq9s (Overall: PEND)
+SMS_D_Ln9_P1280x1.ne0CONUSne30x8_ne0CONUSne30x8_mt12.FCHIST.derecho_intel.cam-outfrq9s (Overall: PEND)
+- pre-existing pend/failures -- need fix in CLM external
+
+ERC_D_Ln9.f19_f19_mg17.QPC6.derecho_intel.cam-outfrq3s_cosp (Overall: DIFF)
+ERC_D_Ln9.f19_f19_mg17.QPMOZ.derecho_intel.cam-outfrq3s (Overall: DIFF)
+ERC_D_Ln9.f19_f19_mg17.QPX2000.derecho_intel.cam-outfrq3s (Overall: DIFF)
+ERI_D_Ln18.f45_f45_mg37.QPC41850.derecho_intel.cam-co2rmp_usecase (Overall: DIFF)
+ERP_D_Ln9.f19_f19_mg17.QPC6.derecho_intel.cam-outfrq9s (Overall: DIFF)
+ERP_D_Ln9_P64x2.f09_f09_mg17.QSC6.derecho_intel.cam-outfrq9s (Overall: DIFF)
+ERP_Ln9_P24x3.f45_f45_mg37.QPWmaC6.derecho_intel.cam-outfrq9s_mee_fluxes (Overall: DIFF)
+SCT_D_Ln7.T42_T42_mg17.QPC5.derecho_intel.cam-scm_prep (Overall: DIFF)
+SMS_D_Ld2.f19_f19_mg17.QPC5HIST.derecho_intel.cam-volc_usecase (Overall: DIFF)
+SMS_D_Ln9.f19_f19_mg17.QPC5M7.derecho_intel.cam-outfrq9s (Overall: DIFF)
+SMS_D_Ln9.ne16_ne16_mg17.QPX2000.derecho_intel.cam-outfrq9s (Overall: DIFF)
+- expected namelist diffs due to ndep data
+- expected diffs in cpl.hi file (atmImp_Faxa_ndep1, atmImp_Faxa_ndep2)
+
+ERC_D_Ln9.ne16_ne16_mg17.FADIAB.derecho_intel.cam-terminator (Overall: NLFAIL)
+ERC_D_Ln9.T42_T42_mg17.FDABIP04.derecho_intel.cam-outfrq3s_usecase (Overall: NLFAIL)
+ERC_D_Ln9.T42_T42_mg17.FHS94.derecho_intel.cam-outfrq3s_usecase (Overall: NLFAIL)
+ERS_Ln9.ne0TESTONLYne5x4_ne0TESTONLYne5x4_mg37.FADIAB.derecho_intel.cam-outfrq3s_refined (Overall: NLFAIL)
+SMS_D_Ln9.f19_f19_mg17.QPC2000climo.derecho_intel.cam-outfrq3s_usecase (Overall: NLFAIL) details:
+- expected namelist diffs due to ndep data
+
+ERC_D_Ln9.ne16_ne16_mg17.QPC5HIST.derecho_intel.cam-outfrq3s_usecase (Overall: DIFF)
+ERC_D_Ln9_P144x1.ne16pg3_ne16pg3_mg17.QPC6HIST.derecho_intel.cam-outfrq3s_ttrac_usecase (Overall: DIFF)
+SCT_D_Ln7.ne3_ne3_mg37.QPC5.derecho_intel.cam-scm_prep (Overall: DIFF)
+- expected namelist diffs due to ndep data
+- expected diffs in cpl.hi file (atmImp_Faxa_ndep1, atmImp_Faxa_ndep2)
+- expected diffs in cam output due to fixing drydep land surface file
+
+derecho/nvhpc/aux_cam: PASS
+
+izumi/nag/aux_cam:
+
+DAE.f45_f45_mg37.FHS94.izumi_nag.cam-dae (Overall: FAIL)
+- pre-existing failure - issue #670
+
+ERC_D_Ln9.f10_f10_mg37.QPC5.izumi_nag.cam-carma_sea_salt (Overall: DIFF)
+ERC_D_Ln9.f10_f10_mg37.QPC5.izumi_nag.cam-outfrq3s_cosp (Overall: DIFF)
+ERC_D_Ln9.f10_f10_mg37.QPC5.izumi_nag.cam-outfrq3s_subcol (Overall: DIFF)
+ERC_D_Ln9.f10_f10_mg37.QPC6.izumi_nag.cam-outfrq3s_am (Overall: DIFF)
+ERC_D_Ln9.f10_f10_mg37.QPC6.izumi_nag.cam-outfrq3s_cospsathist (Overall: DIFF)
+ERC_D_Ln9.f10_f10_mg37.QPC6.izumi_nag.cam-outfrq3s (Overall: DIFF)
+ERC_D_Ln9.f10_f10_mg37.QPWmaC6.izumi_nag.cam-outfrq3s (Overall: DIFF)
+ERC_D_Ln9.f10_f10_mg37.QSPCAMS.izumi_nag.cam-outfrq3s (Overall: DIFF)
+ERC_D_Ln9.ne16_ne16_mg17.QPC4.izumi_nag.cam-outfrq3s_usecase (Overall: DIFF)
+ERC_D_Ln9.ne16pg3_ne16pg3_mg17.QPC4.izumi_nag.cam-outfrq3s_usecase (Overall: DIFF)
+ERC_D_Ln9.T5_T5_mg37.QPC4.izumi_nag.cam-outfrq3s_usecase (Overall: DIFF)
+ERI_D_Ln18.f10_f10_mg37.QPC5.izumi_nag.cam-outfrq3s_eoyttrac (Overall: DIFF)
+ERI_D_Ln18.f19_f19_mg17.QPC6.izumi_nag.cam-ghgrmp_e8 (Overall: DIFF)
+PLB_D_Ln9.f10_f10_mg37.QPC5.izumi_nag.cam-ttrac_loadbal0 (Overall: DIFF)
+PLB_D_Ln9.f10_f10_mg37.QPC5.izumi_nag.cam-ttrac_loadbal1 (Overall: DIFF)
+PLB_D_Ln9.f10_f10_mg37.QPC5.izumi_nag.cam-ttrac_loadbal3 (Overall: DIFF)
+SMS_D_Ln3.ne5pg3_ne5pg3_mg37.QPX2000.izumi_nag.cam-outfrq3s (Overall: DIFF)
+SMS_D_Ln6.ne5_ne5_mg37.QPWmaC4.izumi_nag.cam-outfrq3s_physgrid_tem (Overall: DIFF)
+SMS_D_Ln7.T42_T42_mg17.QPSCAMC5.izumi_nag.cam-scmarm (Overall: DIFF)
+SMS_D_Ln9.f10_f10_mg37.QPC5.izumi_nag.cam-rad_diag_mam (Overall: DIFF)
+SMS_D_Ln9.f10_f10_mg37.QPC6.izumi_nag.cam-outfrq3s_ba (Overall: DIFF)
+SMS_P48x1_D_Ln3.f09_f09_mg17.QPC6HIST.izumi_nag.cam-outfrq3s_co2cycle_usecase (Overall: DIFF)
+SUB_D_Ln9.f10_f10_mg37.QPC5.izumi_nag.cam-outfrq3s (Overall: DIFF)
+- expected namelist diffs due to ndep data
+- expected diffs in cpl.hi file (atmImp_Faxa_ndep1, atmImp_Faxa_ndep2)
+
+ERC_D_Ln9.mpasa480z32_mpasa480.FHS94.izumi_nag.cam-outfrq3s_usecase (Overall: NLFAIL)
+ERI_D_Ln18.ne5_ne5_mg37.FADIAB.izumi_nag.cam-outfrq3s_bwic (Overall: NLFAIL)
+ERI_D_Ln18.ne5pg3_ne5pg3_mg37.FADIAB.izumi_nag.cam-outfrq3s_bwic (Overall: NLFAIL)
+ERS_Ln27.ne5pg3_ne5pg3_mg37.FKESSLER.izumi_nag.cam-outfrq9s (Overall: NLFAIL)
+ERS_Ln9.ne5_ne5_mg37.FADIAB.izumi_nag.cam-outfrq9s (Overall: NLFAIL)
+PEM_D_Ln9.ne5_ne5_mg37.FADIAB.izumi_nag.cam-outfrq3s (Overall: NLFAIL)
+SMS_D_Ln9_P1x1.ne5_ne5_mg37.FADIAB.izumi_nag.cam-outfrq3s (Overall: NLFAIL)
+TMC_D.f10_f10_mg37.QPC5.izumi_nag.cam-outfrq3s_eoyttrac (Overall: NLFAIL)
+TMC_D.T5_T5_mg37.QPC5.izumi_nag.cam-ghgrmp_e8 (Overall: NLFAIL)
+- expected namelist diffs due to ndep data
+
+ERC_D_Ln9.ne5_ne5_mg37.QPC5.izumi_nag.cam-outfrq3s_ttrac (Overall: DIFF)
+ERP_Ln9.ne5pg3_ne5pg3_mg37.QPC6.izumi_nag.cam-outfrq9s_clubbmf (Overall: DIFF)
+PLB_D_Ln9.ne5_ne5_mg37.QPC5.izumi_nag.cam-ttrac_loadbal0 (Overall: DIFF)
+PLB_D_Ln9.ne5_ne5_mg37.QPC5.izumi_nag.cam-ttrac_loadbal1 (Overall: DIFF)
+PLB_D_Ln9.ne5_ne5_mg37.QPC5.izumi_nag.cam-ttrac_loadbal3 (Overall: DIFF)
+- expected namelist diffs due to ndep data
+- expected diffs in cpl.hi file (atmImp_Faxa_ndep1, atmImp_Faxa_ndep2)
+- expected diffs in cam output due to fixing drydep land surface file
+
+izumi/gnu/aux_cam:
+
+ERC_D_Ln9.f10_f10_mg37.FADIAB.izumi_gnu.cam-terminator (Overall: NLFAIL) details:
+ERC_D_Ln9.ne5pg2_ne5pg2_mg37.FADIAB.izumi_gnu.cam-outfrq3s (Overall: NLFAIL) details:
+ERC_D_Ln9.ne5pg3_ne5pg3_mg37.FADIAB.izumi_gnu.cam-outfrq3s (Overall: NLFAIL) details:
+ERP_Ln9.ne5_ne5_mg37.FHS94.izumi_gnu.cam-outfrq9s (Overall: NLFAIL) details:
+PEM_D_Ln9.ne5pg3_ne5pg3_mg37.FADIAB.izumi_gnu.cam-outfrq3s (Overall: NLFAIL) details:
+- expected namelist diffs due to ndep data
+
+ERC_D_Ln9.f10_f10_mg37.QPC4.izumi_gnu.cam-outfrq3s_diags (Overall: DIFF) details:
+ERC_D_Ln9.f10_f10_mg37.QPC5.izumi_gnu.cam-outfrq3s_unicon (Overall: DIFF) details:
+ERC_D_Ln9.f10_f10_mg37.QPC5.izumi_gnu.cam-rad_diag (Overall: DIFF) details:
+ERC_D_Ln9.f10_f10_mg37.QPSPCAMM.izumi_gnu.cam-outfrq3s (Overall: DIFF) details:
+ERC_D_Ln9.ne5_ne5_mg37.QPC4.izumi_gnu.cam-outfrq3s_nudging_ne5_L26 (Overall: DIFF) details:
+ERC_D_Ln9.ne5_ne5_mg37.QPC5.izumi_gnu.cam-outfrq3s_ba (Overall: DIFF) details:
+ERI_D_Ln18.T5_T5_mg37.QPC4.izumi_gnu.cam-co2rmp (Overall: DIFF) details:
+SCT_D_Ln7.T42_T42_mg17.QPC4.izumi_gnu.cam-scm_prep (Overall: DIFF) details:
+SCT_D_Ln7.T42_T42_mg17.QPC6.izumi_gnu.cam-scm_prep_c6 (Overall: DIFF) details:
+SMS_D_Ln3.f10_f10_mg37.QPMOZ.izumi_gnu.cam-outfrq3s_chemproc (Overall: DIFF) details:
+SMS_D_Ln9.f10_f10_mg37.QPWmaC4.izumi_gnu.cam-outfrq9s_apmee (Overall: DIFF) details:
+- expected namelist diffs due to ndep data
+- expected diffs in cpl.hi file (atmImp_Faxa_ndep1, atmImp_Faxa_ndep2)
+
+ERP_D_Ln9.C48_C48_mg17.QPC6.izumi_gnu.cam-outfrq9s (Overall: DIFF) details:
+ERP_D_Ln9.ne3pg3_ne3pg3_mg37.QPC6.izumi_gnu.cam-outfrq9s_rrtmgp (Overall: DIFF) details:
+ERP_Ln9.ne5_ne5_mg37.QPC5.izumi_gnu.cam-outfrq9s (Overall: DIFF) details:
+PLB_D_Ln9.ne5pg3_ne5pg3_mg37.QPC5.izumi_gnu.cam-ttrac_loadbal0 (Overall: DIFF) details:
+PLB_D_Ln9.ne5pg3_ne5pg3_mg37.QPC5.izumi_gnu.cam-ttrac_loadbal1 (Overall: DIFF) details:
+PLB_D_Ln9.ne5pg3_ne5pg3_mg37.QPC5.izumi_gnu.cam-ttrac_loadbal3 (Overall: DIFF) details:
+SCT_D_Ln7.ne3_ne3_mg37.QPC6.izumi_gnu.cam-scm_prep_c6 (Overall: DIFF) details:
+SMS_D_Ln9.ne5pg3_ne5pg3_mg37.QPC5.izumi_gnu.cam-outfrq3s_ttrac (Overall: DIFF) details:
+- expected namelist diffs due to ndep data
+- expected diffs in cpl.hi file (atmImp_Faxa_ndep1, atmImp_Faxa_ndep2)
+- expected diffs in cam output due to fixing drydep land surface file
+
+CAM tag used for the baseline comparison tests if different than previous
+tag:
+
+Summarize any changes to answers: BFB except CAM5/6 aquaplanet runs on
+  unstructured grids have answer changes due to fixing the land surface
+  types used by dry deposition calculations
+
+===============================================================
+===============================================================
+
 Tag name: cam6_4_023
 Originator(s): jet
 Date: Aug 26, 2024

diff --git a/src/chemistry/mozart/chemistry.F90 b/src/chemistry/mozart/chemistry.F90
@@ -422,6 +422,8 @@ subroutine chem_readnl(nlfile)
          tracer_srcs_fixed_ymd_out = tracer_srcs_fixed_ymd, &
          tracer_srcs_fixed_tod_out = tracer_srcs_fixed_tod  )
 
+    drydep_srf_file = ' '
+
     if (masterproc) then
        unitn = getunit()
        open( unitn, file=trim(nlfile), status='old' )

diff --git a/src/chemistry/mozart/mo_drydep.F90 b/src/chemistry/mozart/mo_drydep.F90
@@ -519,6 +519,16 @@ subroutine get_landuse_and_soilw_from_file()
     character(len=shr_kind_cl) :: locfn
     logical :: lexist
 
+    if (len_trim(drydep_srf_file) == 0) then
+       write(iulog,*)'**************************************'
+       write(iulog,*)' get_landuse_and_soilw_from_file: INFO:'
+       write(iulog,*)' drydep_srf_file not set:'
+       write(iulog,*)' setting fraction_landuse to zero'
+       write(iulog,*)'**************************************'
+       fraction_landuse = 0._r8
+       return
+    end if
+
     call getfil (drydep_srf_file, locfn, 1, lexist)
     if(lexist) then
        call cam_pio_openfile(piofile, locfn, PIO_NOWRITE)

diff --git a/src/cpl/nuopc/atm_import_export.F90 b/src/cpl/nuopc/atm_import_export.F90
@@ -25,7 +25,7 @@ module atm_import_export
   use srf_field_check   , only : set_active_Faxa_nhx
   use srf_field_check   , only : set_active_Faxa_noy
   use srf_field_check   , only : active_Faxa_nhx, active_Faxa_noy
-  use atm_stream_ndep   , only : stream_ndep_init, stream_ndep_interp, stream_ndep_is_initialized
+  use atm_stream_ndep   , only : stream_ndep_init, stream_ndep_interp, stream_ndep_is_initialized, use_ndep_stream
 
   implicit none
   private ! except
@@ -199,7 +199,8 @@ subroutine advertise_fields(gcomp, flds_scalar_name, rc)
        call set_active_Faxa_nhx(.true.)
        call set_active_Faxa_noy(.true.)
     else
-       ! The following is used for reading in stream data
+       ! The following is used for reading in stream data, or for aquaplanet or simple model
+       ! cases where the ndep fluxes are not used.
        call set_active_Faxa_nhx(.false.)
        call set_active_Faxa_noy(.false.)
     end if
@@ -1118,25 +1119,51 @@ subroutine export_fields( gcomp, model_mesh, model_clock, cam_out, rc)
        end do
     end if
 
-    ! If ndep fields are not computed in cam and must be obtained from the ndep input stream
     call state_getfldptr(exportState, 'Faxa_ndep', fldptr2d=fldptr_ndep, rc=rc)
     if (ChkErr(rc,__LINE__,u_FILE_u)) return
     if (.not. active_Faxa_nhx .and. .not. active_Faxa_noy) then
+
+       ! ndep fields not active (i.e., not computed by WACCM).  Either they are not needed,
+       ! or they are obtained from the ndep input stream.
+
+       ! The ndep_stream_nl namelist group is read in stream_ndep_init.  This sets whether
+       ! or not the stream will be used.
        if (.not. stream_ndep_is_initialized) then
           call stream_ndep_init(model_mesh, model_clock, rc)
           if (ChkErr(rc,__LINE__,u_FILE_u)) return
           stream_ndep_is_initialized = .true.
        end if
-       call stream_ndep_interp(cam_out, rc)
-       if (ChkErr(rc,__LINE__,u_FILE_u)) return
-       ! NDEP read from forcing is expected to be in units of gN/m2/sec - but the mediator
-       ! expects units of kgN/m2/sec
-       scale_ndep = .001_r8
+
+       if (use_ndep_stream) then
+
+         ! get ndep fluxes from the stream
+         call stream_ndep_interp(cam_out, rc)
+         if (ChkErr(rc,__LINE__,u_FILE_u)) return
+         ! NDEP read from forcing is expected to be in units of gN/m2/sec - but the mediator
+         ! expects units of kgN/m2/sec
+         scale_ndep = .001_r8
+
+      else
+
+          ! ndep fluxes not used.  Set to zero.
+          do c = begchunk,endchunk
+             do i = 1,get_ncols_p(c)
+                cam_out(c)%nhx_nitrogen_flx(i) = 0._r8
+                cam_out(c)%noy_nitrogen_flx(i) = 0._r8
+             end do
+          end do
+          scale_ndep = 1._r8
+
+      end if
+
     else
+
        ! If waccm computes ndep, then its in units of kgN/m2/s - and the mediator expects
        ! units of kgN/m2/sec, so the following conversion needs to happen
        scale_ndep = 1._r8
+
     end if
+
     g = 1
     do c = begchunk,endchunk
        do i = 1,get_ncols_p(c)