Uncoupled surface and below-ground soil respiration in mangroves: implications for estimates of dissolved inorganic carbon export

Abstract

Potential disparities between rates of surface and below-ground respiration were examined in seven mangrove forests of different topographic height in Timor Leste. Differences in surface respiration between air-exposed and inundated soils were inconsistent, but surface respiration rates increased, with tidal elevation. Net primary production (NPP) on air-exposed soils declined with increasing forest cover indicating light limitation beneath the canopy. NPP and respiration were linearly related under both air-exposed and inundated conditions. Rates of DIC release from the soil surface varied among forests, correlating only with soil carbon (TOC) and nitrogen (TN) and their stoichiometric ratios. Sulfate reduction was detected to maximum depth of unconsolidated soil, correlating only with TOC and TN content at discrete depth intervals. DIC concentrations in drainage channels were equivalent to porewater concentrations. The rate of carbon mineralized by sulfate reducers (SRC) was equivalent to rates of total carbon oxidation (TCO) measured at the soil surface in forests at tidal heights B0.5 m above mean sea-level (MSL). However, SRC was increasingly greater than TCO in forests residing from 1.0 up to 2.5 m above MSL. Most carbon mineralized in subsurface deposits appears to seep out of the forest via groundwater. Rates of surface respiration therefore underestimate rates of total benthic carbon mineralization in forests at topographic heights C0.5 m above MSL, suggesting that the amount of respiratory carbon exported from many mangrove forests has also been underestimated. AbbreviationsNPP Net primary production DIC Dissolved inorganic carbon TOC Total organic carbon TN Total nitrogen SRC Carbon oxidation via sulfate reduction TCO Total carbon oxidation MSL Mean sea-level DBH Diameter-at-breast height ABG Above-ground biomass LAI Leaf area index TP Total phosphorus AVS Acid-volatile sulphide CRS Chromium-reducible sulphur SRR Sulfate reduction OW Overlying tidal water PW Porewater

Groundwater‐derived dissolved inorganic and organic carbon exports from a mangrove tidal creek: The missing mangrove carbon sink?

“…A similar global mangrove ''missing carbon'' value of , 2.7 g C m 22 d 21 was found by Alongi (2009). Previous mangrove carbon budgets have neglected the exchange of DIC, which may lead to significant underestimation of both ecosystem gross primary production and respiration.…”

“…However, studies suggest that significant transformations of the organic matter pool occur during transport (Peterson et al 1994;Maher and Eyre 2010), and that there is a substantial, yet poorly constrained, flow of terrestrial carbon through subsurface pathways (Cai et al 2003;Santos et al 2009). In addition, our understanding of the transport and transformation of carbon as it transits from terrestrial to oceanic biomes suffers from a lack of data from a variety of ecosystems and latitudes, including mangroves (Bouillon et al 2008;Kristensen et al 2008a;Alongi 2009).…”

“…Further, mangrove forests are among the most carbon-rich tropical forests, with a majority of the carbon belowground (Donato et al 2011). In spite of the clear importance of these ecosystems in terms of the global carbon cycle, more than half of the carbon fixed by mangroves (112-160 Tg C yr 21 ) is unaccounted for by estimates of the various carbon sinks (Bouillon et al 2008;Alongi 2009). This may represent a large global flux of carbon equivalent to , 12-17% of the ''missing anthropogenic carbon sink.'…”

Are mangroves drivers or buffers of coastal acidification? Insights from alkalinity and dissolved inorganic carbon export estimates across a latitudinal transect

“…Sulfate reduction results in the generation of alkalinity, assuming that a portion of the sulfide produced is not reoxidized [ Ovalle et al ., ; Alongi et al ., ; Burdige , ]. Tidal pumping drives pore waters, enriched in p CO 2 , alkalinity, and DIC, to surrounding waters where these solutes are laterally exported to the coastal ocean or outgassed to the atmosphere as CO 2 [ Borges et al ., ; Bouillon et al ., ; Bouillon et al ., ; Koné and Borges , ; Alongi et al ., ; Maher et al ., ; Call et al ., ].…”

Carbon Budgets for Caribbean Mangrove Forests of Varying Structure and with Phosphorus Enrichment

“…The C sources and nutrients supporting microbial respiration in the scrub forests are derived from litter and the microbial mats [37,38] but may also be from the mangrove peat. High rates of CO2 emissions were observed following clearing of mangroves at Twin Cays [18] suggesting that the peat may be decomposed under some conditions [66] and also that living tree roots may suppress decomposition of soil organic matter [67]. Although anoxia due to tidal flooding contributes to slow rates of decomposition of soil C in mangroves, other factors, potentially associated with productivity of trees, e.g., competition for limiting P, may also play important roles in suppressing microbial metabolism and thus decomposition of soil organic matter [67].…”