fixed big bug with horizontal diff (#88)

* fixed big bug with horizontal diff

Author: kthyng

docs/whats_new.md

@@ -1,5 +1,9 @@
 # What's New
 
+## Unreleased
+
+* Fixed bug so that horizontal diffusivity is now properly applied to model output.
+
 ## 2.5.0 (March 9, 2026)
 
 * Change to NWGOA config to fix issue with wet/dry sims not running with NWGOA.

particle_tracking_manager/models/opendrift/config_opendrift.py

@@ -144,7 +144,11 @@ class OpenDriftConfig(TheManagerConfig):
     # add od_mapping to what should otherwise be in TheManagerConfig
     horizontal_diffusivity: float | None = FieldInfo.merge_field_infos(
         TheManagerConfig.model_fields["horizontal_diffusivity"],
-        Field(json_schema_extra=dict(od_mapping="drift:horizontal_diffusivity")),
+        Field(
+            json_schema_extra=dict(
+                od_mapping="environment:constant:horizontal_diffusivity"
+            )
+        ),
     )
     stokes_drift: bool = FieldInfo.merge_field_infos(
         TheManagerConfig.model_fields["stokes_drift"],