Nitrogen Cycling and Mass Balance in the World’s Mangrove Forests

Abstract

Nitrogen (N) cycling in mangroves is complex, with rapid turnover of low dissolved N concentrations, but slow turnover of particulate N. Most N is stored in soils. The largest sources of N are nearly equal amounts of mangrove and benthic microalgal primary production. Dissolved N fluxes between the forests and tidal waters show net uptake, indicating N conservation. N2-fixation is underestimated as rapid rates measured on tree stems, aboveground roots and cyanobacterial mats cannot currently be accounted for at the whole-forest scale due to their extreme patchiness and the inability to extrapolate beyond a localized area. Net immobilization of NH4+ is the largest ecosystem flux, indicating N retention. Denitrification is the largest loss of N, equating to 35% of total N input. Burial equates to about 29% of total inputs and is the second largest loss of N. Total inputs slightly exceed total outputs, currently suggesting net N balance in mangroves. Mangrove PON export equates to ≈95% of PON export from the world’s tropical rivers, but only 1.5% of the entire world’s river discharge. Mangrove N2O emissions, denitrification, and burial contribute 0.4%, 0.5–2.0% and 6%, respectively, to the global coastal ocean, which are disproportionate to their small worldwide area.

Mangrove crab intestine and habitat sediment microbiomes cooperatively work on carbon and nitrogen cycling

“…To date, N 2 -fixation in mangrove ecosystems has been detected mainly in sediments [5,46,[49][50][51][52][53]. Similarly, we also detected nitrogenase activity in the upper, burrow, and root regions of the mound (Fig 6D).…”

“…Recent studies using stable isotope analysis suggest that the dominant nitrogen sources for crabs are animal tissues and microphytobenthos (MPB) [11,41,45]. However, information on nitrogen metabolism in mangrove crabs is more limited than that on carbon metabolism [46][47][48]. Nitrogen fixation is a key reaction for the nitrogen cycle in ecosystems because it requires high energy because of the cleavage of the triple bond in N 2 .…”

Fate of Dissolved Nitrogen in a Horizontal Levee: Seasonal Fluctuations in Nitrate Removal Processes

“…To better characterize the processes responsible for nitrogen removal in the horizontal levee, we performed mass balances on nitrogen and a suite of redox-active elements (e.g., sulfur and iron) and collected seasonal measurements of redox-active aqueous species. Mass balance approaches have often been used to quantify nitrogen cycle processes in constructed wetlands. − These methods are advantageous because they (1) can be applied easily at a field scale, (2) do not require specialized instrumentation, and (3) do not involve manipulations that have the potential to bias results . However, mass balances must be paired with additional methods (e.g., 15 N pool dilution studies) to directly quantify nitrogen cycle process rates. , In our study, mass balance results were supported with measurements of microbial gene abundances and assessments of mineral formation using synchrotron-based X-ray fluorescence spectromicroscopy.…”

Evaluation of the quality of mangrove ecosystems using macrozoobenthos as bioindicators in the Southern Coast of East Java, Indonesia

“…High nitrate levels have negative impacts on the environment such as eutrophication, increasing the growth of harmful algal blooms (HABs), decreasing water oxygen levels, and worsening the balance of the N biogeochemical cycle (Roberts et al 2012;Li et al 2014;Wei et al 2020), although mangrove vegetation can denitrify nitrate in the waters and sediment (Alongi 2020;Hao et al 2022). High nitrate levels will significantly disrupt mangrove growth and cause death because mangroves have reached a certain tolerance range (Hao et al 2022).…”