What percentage of the solar energy that reaches the marsh is incorporated into gross primary production?

5.8 % of solar energy will be incorporated into gross primary production.

Explanation:

Ecological efficiency is defined as the amount of energy transfer from one trophic level to the next trophic level.  In a ecosystem autotrphic organisms produce the organic energy from solar energy. According to the thermodynamics, there is no 100 % energy producer and consumer. That means some amount of energy is missing from one trophic level to the other.

In the ecosystem only 10% of energy is transferred from one trophic level to the next and production ratio is varying in different ecosystems. for example, grassland has higher gross production that an aquatic system.