Articles | Volume 13, issue 1
Biogeosciences, 13, 313–321, 2016
Biogeosciences, 13, 313–321, 2016

Research article 15 Jan 2016

Research article | 15 Jan 2016

Carbon storage in seagrass soils: long-term nutrient history exceeds the effects of near-term nutrient enrichment

A. R. Armitage1 and J. W. Fourqurean2 A. R. Armitage and J. W. Fourqurean
  • 1Department of Marine Biology, Texas A&M University at Galveston, Galveston, Texas, USA
  • 2Department of Biological Sciences and Southeast Environmental Research Center, Florida International University, Miami, Florida, USA

Abstract. The carbon sequestration potential in coastal soils is linked to aboveground and belowground plant productivity and biomass, which in turn, is directly and indirectly influenced by nutrient input. We evaluated the influence of long-term and near-term nutrient input on aboveground and belowground carbon accumulation in seagrass beds, using a nutrient enrichment (nitrogen and phosphorus) experiment embedded within a naturally occurring, long-term gradient of phosphorus availability within Florida Bay (USA). We measured organic carbon stocks in soils and above- and belowground seagrass biomass after 17 months of experimental nutrient addition. At the nutrient-limited sites, phosphorus addition increased the carbon stock in aboveground seagrass biomass by more than 300 %; belowground seagrass carbon stock increased by 50–100 %. Soil carbon content slightly decreased ( ∼  10 %) in response to phosphorus addition. There was a strong but non-linear relationship between soil carbon and Thalassia testudinum leaf nitrogen : phosphorus (N : P) or belowground seagrass carbon stock. When seagrass leaf N : P exceeded an approximate threshold of 75 : 1, or when belowground seagrass carbon stock was less than 100 g m−2, there was less than 3 % organic carbon in the sediment. Despite the marked difference in soil carbon between phosphorus-limited and phosphorus-replete areas of Florida Bay, all areas of the bay had relatively high soil carbon stocks near or above the global median of 1.8 % organic carbon. The relatively high carbon content in the soils indicates that seagrass beds have extremely high carbon storage potential, even in nutrient-limited areas with low biomass or productivity.

Short summary
The emerging field of blue carbon research seeks to quantify the carbon sequestration in coastal habitats. Seagrasses are highly productive, and have a particularly large carbon storage capacity, relative to area. This study evaluated the influence of nutrient input on seagrass carbon stocks in Florida Bay (USA). There was high carbon content in the soils, indicating that seagrass beds have extremely high carbon storage potential, even in nutrient-limited areas with low biomass or productivity.
Final-revised paper