Mangrove forests in tropical and subtropical regions are among the most productive and diverse ecosystems around the globe despite the usually limited nitrogen (N) availability. However, many waterways have experienced eutrophication as a result of intensive anthropogenic activities and it is unclear how the increased nutrient loads may affect nutrient status and nitrogen cycles in mangroves.
Analysis of the δ¹³C and δ¹⁵N isotope composition, coupled with the contents and stoichiometries of total organic carbon (TC), total nitrogen (TN), total phosphorus (TP), were performed on the water, sediments and plant leaves from the Qi’ao island mangrove reserve in order to assess the nutrient status. The overlying water of Qi’ao island was eutrophic, while low soil C:N ratios indicated high soil fertility and fast C and N mineralization rates. However, the low foliar N:P values appeared to be related to N limitation, though the high plant-soil discrimination in δ¹⁵N reflected high N use efficiency in Qi’ao mangrove ecosystem. Those preliminary findings suggested the poor nutrient status in a suburb mangrove ecosystem that is subject to intense human activities such as sewage discharge and fish farming.
 

Mangrove, Stoichiometry, Stable isotopes, Nutrient limitation, Nitrogen cycle