Phosphorus Budget of the Sundarban Mangrove Ecosystem: Box Model Approach R. Ray1,2 & N. Majumder1 & C. Chowdhury1 & S. Das1 & T. K. Jana1, Estuaries and Coasts (2018) 41:1036–1049 https://doi.org/10.1007/s12237-017-0332-0, Received: 26 March 2017 /Revised: 3 October 2017 /Accepted: 4 October 2017 # Coastal and Estuarine Research Federation 2017 Abstract: Phosphorus (P) cycling in mangroves plays an important role in productivity but the magnitude of atmospheric input in the mangrove P budget is still uncertain. This study applied a box model approach to assess P budget in the Indian Sundarban, the world’s largest mangrove ecosystem for conceptual understanding of P cycling and for better representation of transport and transformation of P within the mangrove ecosystem. The P content in the sediment (0.19–0.67 μg g−1) was found much below its maximum retention capacity (322 μg g−1) and was lower than the mean marine sediment (669 μg g−1). The C:N and C:P ratios were correlated (r2 = 0.66, P < 0.01) and the major fraction of available P was recycled within the organic structure of mangrove ecosystem, thus maintaining productivity through conservation strategies. Atmospheric input accounted for 56.7% of total P input (16.06 Gg year−1) and 50% of total P output (14.7 Gg year−1) was attributed to plant uptake. Budget closing or unaccounted P (1.36 Gg) was only 8.5% of the total input. Two feedback pathways, i.e., input of P from dust fallout and biochemical mineralization of organic matter, significantly affected P availability. The findings of the study suggest that atmospheric deposition is of major importance as a natural and/or anthropogenic forcing function in the Sundarban mangrove system. Keywords P budget . Biomass . Litter fall . Box model . Mangrove . Sundarban