Accumulation of Carbonates Contributes to Coastal Vegetated Ecosystems Keeping Pace With Sea Level Rise in an Arid Region (Arabian Peninsula)

Abstract

Anthropogenic sea level rise (SLR) presents one of the greatest risks to human lives and infrastructures. Coastal vegetated ecosystems, that is, tidal marshes, seagrass meadows, and mangrove forests, elevate the seabed through soil accretion, providing a natural coastline protection against SLR. The soil accretion of these ecosystems has never been assessed in hot desert climate regions, where water runoff is negligible. However, tropical marine ecosystems are areas of intense calcification that may constitute an important source of sediment supporting seabed elevation, compensating for the lack of terrestrial inputs. We estimated the long‐term (14C‐centennial) and short‐term (210Pb‐20th century) soil accretion rates (SARs) and inorganic carbon (Cinorg) burial in coastal vegetated ecosystems of the Saudi coasts of the central Red Sea and the Arabian Gulf. Short‐term SARs (±SE) in mangroves of the Red Sea (0.27 ± 0.22 cm/year) were twofold the SLR for that region since 1925 (0.13 cm/year). In the Arabian Gulf, only mangrove forest SAR is equivalent to local SLR estimates for the period 1979–2007 (0.21 ± 0.09 compared to 0.22 ± 0.05 cm/year, respectively). Long‐term SARs are comparable or higher than the global estimates of SLR for the late Holocene (0.01 cm/year). In all habitats of the Red Sea and Arabian Gulf, SARs are supported by high carbonate accretion rates, comprising 40% to 60% of the soil volume. Further studies on the role of carbonates in coastal vegetated ecosystems are required to understand their role in adaptation to SLR.

Toward a mechanistic understanding of “peat collapse” and its potential contribution to coastal wetland loss

“…, Saderne et al. ). Carbonic acid formed during microbial respiration and root excretions, and nitric or sulfuric acids formed during nitrogen and sulfur cycling could drive the pH low enough to dissolve carbonate substrates, as observed in seagrass beds of Biscayne Bay, FL (Zieman ).…”

“…The compaction of fine-grained sediments is considered a major contributor to coastal wetland submergence, particularly in deltas, but is typically documented as a deep, gradual process of subsidence (Coleman et al 1998, Meckel et al 2007). Dissolution of mineral matter may be significant in carbonate coastal ecosystems (e.g., Florida Everglades [USA], Yucatan Peninsula, Australia, and the Arabian Peninsula) where carbonates contribute substantially to coastal wetland soil volume (Breithaupt et al 2017, Saderne et al 2018. Carbonic acid formed during microbial respiration and root excretions, and nitric or sulfuric acids formed during nitrogen and sulfur cycling could drive the pH low enough to dissolve carbonate substrates, as observed in seagrass beds of Biscayne Bay, FL (Zieman 1972).…”

Role of vegetated coastal ecosystems as nitrogen and phosphorous filters and sinks in the coasts of Saudi Arabia

“…The Arabian Gulf, on the other hand, receives water from the Shatt al Arab River in the north, which itself is a result of the confluence of the Tigris and Euphrates Rivers. The sediments of the Red Sea and Arabian Gulf originate mainly from carbonate deposits from seawater and deposited airborne sediment of terrestrial origin, which is reported to comprise up to one-third of Gulf sediments (Sugden 1963, Saderne et al 2018. Dust deposition from frequent dust storms originating in the Sahara and the Arabian Peninsula is believed to be one of the primary sources of nutrients to the Red Sea and the Gulf (Acosta et al 2013, Engelbrecht et al 2017).…”

“…The Red Sea is oligotrophic, with P and N sea surface concentrations estimated, in its central part, at 0.05-0.1 μmol kg −1 and 0.03-0.2 μmol kg −1 , respectively (Weikert 1987, Wafar et al 2016. Saderne et al (2018) measured surface water concentrations of P and N, in a seagrass (Khor Almasena'a) and mangrove area, from the same study zone, and reported annual mean (±SD) records of 0.8±0.4 μmol P kg −1 and 1.3±0.5 μmol N kg −1 , and 2.3±0.5 μmol P kg −1 and 0.9±0.2 μmol N kg −1 , respectively. The chemical oceanography of the Arabian Gulf has been largely understudied, with only five sampling expeditions since 1965 (although substantial gray literature exists) (Al-Yamani and Naqvi 2019).…”

“…Here, we assess N and P stocks and accumulation rates in the sediments of seagrass meadows and mangroves along the Saudi coast in the Red Sea, as well as in those of seagrasses, mangroves and saltmarshes along the Saudi coast in the Gulf. We measured the N and P stocks in 0.2 m sediment cores, and, calculated the short-and long-term accumulation rates using the 210 Pb and 14 C sediment accretion rates reported for the same cores by Cusack et al (2018) and Saderne et al (2018). We use the changes in accumulation rates to hypothesize on changes in ecosystem functioning in the coastal ecosystems over the past millennia to centuries.…”