A review of bioturbation and sediment organic geochemistry in mangroves

Abstract

Mangroves, which are a group of salt tolerant plant community growing in the transition zones of fresh and marine water systems, play an important role as sediment trap. In mangrove ecosystems, litterfall accumulates as organic carbon and nutrients over the sediment surface, where bioturbation profoundly affects the sediment biogeochemistry.Here, we provide a brief overview of the bioturbating organisms in mangroves and discuss their roles in controlling the sediments organic biogeochemistry. The mangrove soils formed on marine alluvium is transported as sediment and deposited by the river and sea. This type of soil is typically saline, anoxic, acidic and periodically waterlogged and composed of different combinations of sand, silt, clay and mud. The decapod crustaceans, specifically, crabs are the main bioturbating organisms in mangroves ecosystem. Moreover, amphipod, callianassid, penaeid shrimp, alpheid shrimp, thalassinid lobster, sipunculid worm, bivalves and bony (teleostei) and shark-like (elasmobranchii) fishes contribute to the biogenic dispersal of sediment particles. Bioturbation processes by these organisms are reported to control nutrients and carbon cycling across the sediments. Activities such as feeding, burrowing and ventilation also influence the decomposition rate of sediment organic matter and nutrient exchange. However, anthropogenic pollution from power plant effluent (hot-water outflows), heavy metals, pesticides, polychlorinated biphenyls (PCBs), industrial pollutants, eutrophication (fertilizers and sewage) and oil spills are major concerns impacting the mangrove sediments and ecosystems.

Evaluating watershed health in Costa Rican national parks and protected areas

“…Bormann and Likens (1994) explain that land-clearing causes an oversupply of nitrate in the upper soil layers; nitrates that were once stored were then able to be added to the Río Grande de Térraba from surface water runoff. Excess nitrates are of concern, as nutrient enrichment is a major threat to marine ecosystems as it limits the ability for mangroves to grow (Sarker et al 2019;Reel et al 2010).…”

Heavy Metal Contamination and Ecological Risk Assessments in Urban Mangrove Sediments in Zhanjiang Bay, South China

“…1 However, rapid urbanization, industrialization, and industrial and agricultural production activities in coastal areas in recent decades have generated a large number of heavy metal pollutants, which flow into the ocean along with surface runoff and directly discharge nearshore, causing serious destruction to mangroves. 2 − 4 The mangrove wetland ecosystem has a strong interception, adsorption, and fixation effects on heavy metals due to its unique habitat characteristics, and thus, it often becomes a pollution sink for heavy metal pollutants. 5 − 7 Heavy metal pollutants have been a hot topic in research since the heavy metals have diverse sources, strong resistance to decomposition, long residual time, high toxicity, etc., and may even cause great harm to biological and human health through the food chain or other migration pathways.…”

Contrasting organic matter composition in pristine and eutrophicated mangroves revealed by fatty acids and stable isotopes (Rio de Janeiro, Brazil)

“…Bioturbating organisms (e.g. crabs) and the presence of roots contribute to increased sediment oxidation and subsequent remineralization of SOM (Kristensen & Alongi, 2006;Zhu et al, 2018;Sarker et al, 2021). Indeed, mangrove sediments emit to the atmosphere at low tide and export with tidal pumping, significant amounts of CO2 and CH4 coming from the mineralisation of SOM (Kristensen et al, 2008b;Poungparn et al, 2009;Nóbrega et al, 2016).…”