Organic carbon dynamics in mangrove ecosystems : a review

TLDR: Knowing on mangrove carbon dynamics has improved considerably in recent years, but there are still significant gaps and shortcomings, and relevant research directions are suggested.

About: This article is published in Aquatic Botany.The article was published on 2008-08-01 and is currently open access. It has received 1018 citations till now. The article focuses on the topics: Blue carbon & Organic matter.

Figures

Table 2 Total carbon oxidation (tot C-ox) measured as benthic CO2 release and partitioning of electron acceptors in mangrove sediments

Fig. 5. Relationship between the proportion of iron respiration (FeR) to total anaerobic carbon oxidation in mangrove sediments and the corresponding concentration of reactive Fe(III). Data are from Thailand (Kristensen et al., 2000); Australia (Kristensen and Alongi, 2006) and Tanzania (Kristensen, unpublished). Full line shows the best fit with a constant a = 0.044 to the equation %FeR = 100 (1 exp( a Fe(III))).

Fig. 8. Mixing diagrams of DOC concentrations on the mangrove-fringed North Brazilian shelf (October–November 2001; Dittmar et al., 2006) and a mangrove tidal creek in Tanzania (Ras Dege; September 2005; Bouillon et al., 2007b).

Fig. 9. Comparison between the area-normalized organic carbon runoff from mangrove forests (DOC: Dittmar et al., 2006) and major world rivers (Spitzy and Leenheer, 1991) from all climate zones draining a variety of continental biomes. POC export rates from mangrove forests assume that more than 50% of the reported litter export (Jennerjahn and Ittekkot, 2002) is rapidly lost to the DOC pool and/or assimilated and not exported as suspended or floating matter off the inner-coastal zone (see text for details).

Fig. 4. Decay constants of a variety of mangrove litter (bold) and submerged macrophytes from temperate areas (light) as a function of the initial POC:TN ratio of the material. Least squares linear regression lines and correlation coefficients are shown for comparison (Twilley et al., 1986; Robertson, 1988; Twilley et al., 1997; Wafar et al., 1997; Tam et al., 1998; Mfilinge et al., 2002).

Fig. 6. An example of a 24-h time-series of DOC and water level in a tidal creek that drains about 2.2 km2 of a well-developed mangrove forest in tropical Brazil (Bragança) during the rainy season (29–30 May, 1997; Dittmar and Lara, 2001a). Source assignment of DOC was made with a molecular lignin approach (Dittmar et al., 2001). Annual average values (n = 17) are shown for low and high tide.

Frequently asked questions

Q1. What is the mechanism for tannin removal from leaves?

which induces an increase in polymerization of condensed tannin, is an important mechanism for tannin removal from leaves. 

Q2. What contributions have the authors mentioned in the paper "Organic carbon dynamics in mangrove ecosystems: a review" ?

Alongi et al. this paper reviewed and discussed the current knowledge on production, composition, transport, pathways and transformations of organic carbon in tropical mangrove environments. 

Q3. How does the efficiency of carbon burial in mangrove sediments increase with stand age?

As primary production increases with stand age, the efficiency of carbon burial in sediments increases, from 16% for a 5-year-old forest to 27% for an 85-year-old stand (Alongi et al., 2004). 

Q4. What is the role of the leaf-removing crab in the mangrove forest of Bragança?

In the mangrove forest of Bragança (northern Brazil), the leaf-removing crab Ucides cordatus has a key-role for leaf-litter turnover, significantly impacting litter export and decomposition (Schories et al., 2003). 

Q5. What is the organic content of suspended matter?

The organic content of suspended matter is low, typically in the 2–4% range (Bouillon et al., 2003), which is comparable to or lower than that of mangrove sediments. 

Q6. Why is lignin considered as a tracer of terrestrial plant remains?

Because of the exclusive association with higher plants, lignin is usually considered as a specific tracer of terrestrial plant remains. 

Q7. What is the effect of the ageing process on the palatability of brown leaves?

The higher palatability of brown leaves compared with green and, in particular, yellow leaves probably results from improved nutritional value and removal of inhibitory compounds by the ageing process (Poovachiranon and Tantichodok, 1991). 

Q8. What are the main characteristics of the carbohydrates in mangrove sediments?

neutral carbohydrates show selective degradation patterns in mangrove sediments, which can provide specific details on their sources, despite their overall low concentrations. 

Q9. How much DOC is refractory in mangrove porewater?

Photodegradation and bio-incubation experiments indicate that a substantial fraction ( 50%) of the DOC in mangrove porewater is refractory on a time-scale of weeks to years. 

Q10. What is the effect of the feeding activity of sesarmid crabs on the availability of organic?

Sesarmid crabs ingest twice as much material than they actually assimilate (Thongtham and Kristensen, 2005), which means that half of the ingested litter subsequently becomes available as faeces for decomposer or detritus food webs. 

Q11. What is the impact of the consumption of mangroves on the overall organic carbon dynamics?

Considering their overall abundance and high secondary productivity, consumers may have a profound impact on the overall organic carbon dynamics in mangrove systems. 

Q12. What are the effects of grazing by epifauna on microalgal standing?

Exclusion experiments have shown that grazing by epifauna significantly reduces microalgal standing stocks (Branch and Branch, 1980; Webb and Eyre, 2004; Kristensen and Alongi, 2006), which in combination with the physical modifications and disturbance of the sediment surface, may have a number of indirect effects on microbial and meiofaunal communities (Dye and Lasiak, 1986; Schrijvers et al., 1998). 

Q13. How many studies have described their composition in mangrove tissues?

Amino acids can represent up to 9% of mangrove leaf biomass (Hernes et al., 2001), but very few studies have described their composition in mangrove tissues. 

Q14. What is the effect of the feeding activity of sesarmid crabs on the availability of leaf?

The feeding activity of sesarmid crabs not only affects the availability of leaf litter on the forest floor and its subsequent export, but many of these crabs typically take the leaves down in their burrow for storage, where they continue to decompose (Skov and Hartnoll, 2002). 

Q15. What is the relative importance of phytoplankton to the total mangrove ecosystem primary productivity?

The relative importance of phytoplankton to the total mangrove ecosystem primary productivity is expected to vary with geomorphology, water currents, turbidity and nutrient levels, e.g., 20% for the Fly River delta, Papua New Guinea (Robertson et al., 1992), 50% in Terminos Lagoon, Mexico (Day et al., 1987), and far exceeding mangrove inputs in other ecosystems (e.g. Wafar et al., 1997; Li and Lee, 1998). 

Q16. What is the average global carbon content of the mangrove sites?

Looking into the datasets used by Duarte et al. (2005), the sediment carbon content of the mangrove sites considered was 8.5%, whereas a more exhaustive data compilation indicates that a representative global estimate of carbon content is likely to be close to 2.2% (Fig. 2), suggesting that the data used in this bottom-up approach is biased towards organicrich systems and hence overestimates the global carbon accumulation in mangroves. 

Q17. Why was the DOC export rate not accounted for in past studies?

The reason behind this discrepancy is probably that the gradual release of DOC from floating and suspended detritus in the water column was not accounted for in past studies.