Edith Cowan University, Research Online, Perth, Western Australia
Doi
Abstract
Coastal wetlands have long been identified as ecosystems that can ameliorate N inputs into the ocean. The processes associated with N uptake, transformation, and losses are relatively well understood for temperate wetlands; however, information on tropical wetlands is scarce. In this study, we conducted a whole ecosystem approach to measure N processes within tropical mangroves in the Moresby estuary in northeast Australia. We measured N stocks (trees and soils), inputs from sedimentation, fixation, and accumulation as woody biomass, and outputs through denitrification, anammox, and soil respiration (N2O emissions). Potential denitrification was detected along anammox (average, min-max) at 883 (485–1,450) gN ha−1 day−1, followed by sediment accumulation with 108 (0–375) gN ha−1 day−1, and tree uptake with 93 (13–153) gN ha−1 day−1. Lower rates were found for N fixation with 45 (0–260) gN ha−1 day−1 and soil respiration as N2O with uptakes of −0.36 (−2.7 – 0.40) gN ha−1 day−1. Overall, mangroves in the Moresby estuary are fixing some N in their standing litter while removing NO3 and NH4+ from the water column through denitrification and anammox, temporarily storing N as woody biomass, and accumulating particulate N in their sediments. These mangroves are also functioning as sinks of N2O. Thus, the protection and restoration of these mangroves provide water quality and climate benefits
