Low Carbon sink capacity of Red Sea mangroves

Abstract

Mangroves forests of Avicennia marina occupy about 135 km² in the Red Sea and represent one of the most important vegetated communities in this otherwise arid and oligotrophic region. We assessed the soil organic carbon (C_org) stocks, soil accretion rates (SAR; mm y^-1) and soil C_org sequestration rates (g C_org m^-2 yr^-1) in 10 mangrove sites within four locations along the Saudi coast of the Central Red Sea. Soil C_org density and stock in Red Sea mangroves were among the lowest reported globally, with an average of 4 ± 0.3 mg C_org cm^-3 and 43 ± 5 Mg C_org ha^-1 (in 1 m-thick soils), respectively. Sequestration rates of C_org, estimated at 3 ± 1 and 15 ± 1 g C_org m^-2 yr^-1 for the long (millennia) and short (last century) temporal scales, respectively, were also relatively low compared to mangrove habitats from more humid bioregions. In contrast, the accretion rates of Central Red Sea mangroves soils were within the range reported for global mangrove forests. The relatively low C_org sink capacity of Red Sea mangroves could be due to the extreme environmental conditions such as low rainfall, nutrient limitation and high temperature, reducing the growth rates of the mangroves and increasing soil respiration rates.

Figure 1

Vertical profiles of (A) % organic carbon (C_org), (B) C_org density (g C_org cm⁻³), and (C,D) δ¹³C and δ¹⁵N (‰) in mangrove soils in central Red Sea. It was not possible to plot average values for the replicate cores against decompressed depths because replicate cores experienced different degrees of compaction during coring.

Figure 2

The sources of soil organic carbon (C_org) in mangrove forests obtained using IsoSource from potential organic matter sources and soil δ¹⁵N and δ¹³C values.

Figure 3

(A) Total and (B) excess concentration profiles of ²¹⁰Pb in dated mangrove soil cores of Central Red Sea. It was not possible to plot average values for the replicate cores against decompressed depths because replicate cores experienced different degrees of compaction during coring.

Figure 4

Location of the Central Red Sea mangrove forests sampled. The map was produced with ArcMap Version 10.2. Background map credits: the World Administrative Divisions layer provided by Esri Data and Maps, and DeLorme Publishing Company. Redistribution rights are granted http://www.esri.com/~/media/Files/Pdfs/legal/pdfs/redist_rights_103.pdf?la=en.