title: Limits on carbon sequestration in arid blue carbon ecosystems.
abstract: Coastal ecosystems produce and sequester significant amounts of carbon ("blue carbon"), which has been well documented in humid and semi-humid regions of temperate and tropical climates but less so in arid regions where mangroves, marshes, and seagrasses exist near the limit of their tolerance for extreme temperature and salinity. To better understand these unique systems, we measured whole-ecosystem carbon stocks in 58 sites across the United Arab Emirates (UAE) in natural and planted mangroves, salt marshes, seagrass beds, microbial mats, and coastal sabkha (inter- and supratidal unvegetated salt flats). Natural mangroves held significantly more carbon in above- and belowground biomass than other vegetated ecosystems. Planted mangrove carbon stocks increased with age, but there were large differences for sites of similar age. Soil carbon varied widely across sites (2-367 Mg C/ha), with ecosystem averages that ranged from 49 to 156 Mg C/ha. For the first time, microbial mats were documented to contain soil carbon pools comparable to vascular plant-dominated ecosystems, and could arguably be recognized as a unique blue carbon ecosystem. Total ecosystem carbon stocks ranged widely from 2 to 515 Mg C/ha (seagrass bed and mangrove, respectively). Seagrass beds had the lowest carbon stock per unit area, but the largest stock per total area due to their large spatial coverage. Compared to similar ecosystems globally, mangroves and marshes in the UAE have lower plant and soil carbon stocks; however, the difference in soil stocks is far larger than with plant stocks. This incongruent difference between stocks is likely due to poor carbon preservation under conditions of weakly reduced soils (200-350 mV), coarse-grained sediments, and active shoreline migration. This work represents the first attempt to produce a country-wide coastal ecosystem carbon accounting using a uniform sampling protocol, and was motivated by specific policy goals identified by the Abu Dhabi Global Environmental Data Initiative. These carbon stock data supported two objectives: to quantify carbon stocks and infer sequestration capacity in arid blue carbon ecosystems, and to explore the potential to incorporate blue carbon science into national reporting and planning documents.
authors.affiliation: Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, Maryland, 21037, USA.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Schile
authors.affiliation: Department of Fisheries and Wildlife, Oregon State University, 104 Nash Hall, Corvallis, Oregon, 97331, USA.
authors.forename: J Boone
authors.initials: JB
authors.lastname: Kauffman
authors.affiliation: Silvestrum Climate Associates, LLC, 150 Seminary Drive 1E, Mill Valley, California, 94941, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Crooks
authors.affiliation: Department of Biological Sciences and Marine Education and Research Center, Institute for Water and Environment, Florida International University, 11200 SW 8th Street, Miami, Florida, 33199, USA.
authors.forename: James W
authors.initials: JW
authors.lastname: Fourqurean
authors.affiliation: Abu Dhabi Global Environmental Data Initiative (AGEDI), PO Box 45553, Abu Dhabi, UAE.
authors.forename: Jane
authors.initials: J
authors.lastname: Glavan
authors.affiliation: Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, Maryland, 21037, USA.
authors.forename: J Patrick
authors.initials: JP
authors.lastname: Megonigal
mesh_terms: D035961:Alismatales / Q000502:physiology*; D057965:Carbon Sequestration; D017753:Ecosystem; D014479:United Arab Emirates; D053833:Wetlands
keywords: 
  Arthrocnemum macrostachyum
  ; 
  Avicennia marina
  ; 
  Halodule uninervis
  ; 
  Halophila ovalis
  ; 
  Halophila stipulacea
  ; Abu Dhabi; United Arab Emirates; blue carbon; carbon pools; carbon stocks