Abstract
Mangroves and salt marshes are among the most productive ecosystems in the global coastal ocean. Mangroves store more carbon (739 Mg CORG ha−1) than salt marshes (334 Mg CORG ha−1), but the latter sequester proportionally more (24%) net primary production (NPP) than mangroves (12%). Mangroves exhibit greater rates of gross primary production (GPP), aboveground net primary production (AGNPP) and plant respiration (RC), with higher PGPP/RC ratios, but salt marshes exhibit greater rates of below-ground NPP (BGNPP). Mangroves have greater rates of subsurface DIC production and, unlike salt marshes, exhibit active microbial decomposition to a soil depth of 1 m. Salt marshes release more CH4 from soil and creek waters and export more dissolved CH4, but mangroves release more CO2 from tidal waters and export greater amounts of particulate organic carbon (POC), dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC), to adjacent waters. Both ecosystems contribute only a small proportion of GPP, RE (ecosystem respiration) and NEP (net ecosystem production) to the global coastal ocean due to their small global area, but contribute 72% of air–sea CO2 exchange of the world’s wetlands and estuaries and contribute 34% of DIC export and 17% of DOC + POC export to the world’s coastal ocean. Thus, both wetland ecosystems contribute disproportionately to carbon flow of the global coastal ocean.
Highlights
Salt marshes and mangrove forests are intertidal ecosystems comparable sensu lato in that they both occupy the coastal land–sea interface; the former mostly in sheltered temperate and high- latitude coastlines, the latter along quiescent subtropical and tropical shores [1]
PGPP/RC ratios are significantly greater in mangrove forests than in salt marshes and are equivalent to those estimated for tropical terrestrial forests [52]
In mangrove soils, respired carbon as dissolved inorganic carbon (DIC) (and dissolved organic carbon (DOC) and CH4) is produced to a depth of at least 1 m [94] and perhaps to greater depths considering that there is no indication of a clear decline in production rates measured over surface−100 cm profiles [94]
Summary
Salt marshes and mangrove forests are intertidal ecosystems comparable sensu lato in that they both occupy the coastal land–sea interface; the former mostly in sheltered temperate and high- latitude coastlines, the latter along quiescent subtropical and tropical shores [1] Both ecosystems are characterized by a rich mixture of terrestrial and marine organisms, forming unique estuarine food webs, and play an important role in linking food webs, inorganic and organic materials, and biogeochemical cycles between the coast and adjacent coastal zone. Tides and waves (to a much lesser extent) are an auxiliary energy subsidy that allows both ecosystems to store and transport newly fixed carbon, sediments, food and nutrients, and to do the work of exporting wastes, heat, gases and solutes to the atmosphere and adjacent coastal zone This subsidized energy is used indirectly by organisms to shunt more of their own energy into growth and reproduction, making tidal power one of the main drivers regulating these intertidal systems [1]. Pglianngktionnsiczoemfmroumnitvieisruinseasdtjaocreenpt tiles, such carseeakllsigaantdorwsaatnerdwcaryoscaordeilperso.ductive and abundant, and well-adapted to complex hydrology and Swaaltemr cahresmheisstrayn. dThmesaenogpraoqvueeftoidreasl tws aatreerscharobstoonr-graicnhismecsorsaynsgteinmgsinthsaizteafrreompevricreuisveesdtotoreppltailyesa, role in clismuachteasreaglluiglaattoiorsna,nbdiocrgoecoocdhileems. ical cycling, and in capturing and preserving large amounts of carbon thSaatltcmouanrstheersbaanladnmceanagnrtohvreofpooregsetsnaicreCcOar2boenm-riiscshioecnossy[4st–e6m].s tIhtaitsaurenpcelercaerivteodwtohpaltayexateronlte both ecosyisntecmlims actoenrsetgituultaetiaons,igbnioigfiecoacnhtecmaircbaol ncyscilninkgi,natnhde ignlocbapatlucroinagstaanl docperaens,earvnidngwlharegtehearmroeustnotrsinofg and replancatirnbgonnethwatmcoaursnhteersbaanladncme aanngthrorovpeosgwenililcaCssOis[2] teimniassmioenliso[r4a–t6in].gItcliismuanteclecahrantogew. hTaht uesx,teannt ibmopthroved undeerrecspotaslaynnsdttieinnmggs oncofenwcsatrimtbuaotrensahaeslsilgonacinaftdicioamnntaacnnagrdrboobvnaelssainnwkcieilnlwtahisetshigsiltnobitnahleacsomeaeseltciaoolrsoayctiesnatgenm, calsnimdisawutehrgectehhnaetrnlgyreesn.teoTerhidnuegsd,a.naIdnn this synthiemspisr,ovsiemd iulanrditeiresstaannddindg iffoferceanrbcoens ianllocacartbioonn acnydclibnaglainncebowtihtheincotshyessteemecsosayrseteimdes nitsifiuergdetnotlybetter undenrseteadnedd. hIonwthtihs esyynftuhnescitsi,onsi,meislapreitcieiasllayndwidtihfferreegnacreds tino tcharebironroclyecilningcairnbobnothcyeccloinsygstienmtsheargelobal coastaidleoncteifaiend. to better understand how they function, especially with regard to their role in carbon cycling in the global coastal ocean
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