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## Carbon and Nitrogen Conservation

When subgrid areas change, it is important to properly adjust the carbon and nitrogen state variables, which occur on both the patch (vegetation) and column (soil) levels. This is done through a three-step process:

1. Patch-level state variables are adjusted for changes in patch areas, with any lost mass being distributed to various pools.
2. Column-level state variables are updated based on fluxes from the patch-level adjustments, to conserve mass.
3. Column-level state variables are then adjusted for changes in column areas, with mass lost from shrinking columns being redistributed to growing columns.

Some key assumptions include only tracking net area changes, and assuming growing columns proportionally expand into shrinking columns. Non-vegetated land units contribute zero carbon/nitrogen when shrinking, but store any pre-existing soil carbon/nitrogen when growing.

In contrast to water and energy, no special treatment is needed for new columns, as their state is derived from a weighted average of shrinking column states.