Sediment re-deposition in the mangrove environment of Can Gio, Saigon River estuary (Vietnam)

Schwarzer, Klaus; Thành, Nguyễn Công; Ricklefs, Klaus

doi:10.2112/si75-028.1

Cited by 26 publications

(17 citation statements)

References 21 publications

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“…For Avicennia leaves, t 50 reported in a Chinese mangrove was similar to the one we measured during the rainy season (<20 days) (Zhou et al, 2010), while in Pakistan, Shafique et al (2015) reported a t 50 close to 50 days, little bit higher than what we measured during the dry season. During the rainy season, the river level was really higher, as observed in other studies (Schwarzer et al, 2016), and thus the Avicennia stand, which develops at a lower elevation that the Rhizophora one, was subject to an increased frequency of tidal inundation that is probably responsible for the fast decay rates measured. Ashton et al (1999) reported that leaf litter immerged in seawater decomposed five times more quickly than one exposed to air.…”

Section: Mangrove Leaf Litter Decay Ratessupporting

confidence: 73%

“…The mean annual humidity is 86%, ranging from 80.8 to 91.4%. During the rainy season, representing ∼80% of the annual rainfall, the rivers bring much more silt, accreting the plain with an annual particles flux estimated at around 160 million tons (Milliman and Meade, 1983;Schwarzer et al, 2016). During the dry season, the fresh water flow is strongly reduced, and the coastal areas are severely affected by saline intrusion.…”

Section: Study Areamentioning

confidence: 99%

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Changes in Leaf Litter Quality During Its Decomposition in a Tropical Planted Mangrove Forest (Can Gio, Vietnam)

Vinh

Allenbach²,

Linh

et al. 2020

Front. Environ. Sci.

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Mangroves are highly productive ecosystems, being key components of trophic food chains along tropical coastlines. In Southern Vietnam, planted Rhizophora apiculata develops in the upper intertidal zone, while Avicennia alba naturally colonizes areas at lower elevation along tidal creeks. The main objective of this study was to quantify the seasonal variability of leaf litter decomposition rates considering that in previous studies we observed a strong influence of the monsoon on C and nutrients cycling within the mangrove and in adjacent creeks. We were also interested in changes in the quality of the leaf litter during its decomposition, focusing on nutrients, δ 13 C, and trace metals. To reach our goals, we used the litterbag technique. During the monsoon, leaf litter decay rates were increased in the Avicennia stand, most probably because of enhanced leaching resulting from a higher level of the river due to heavy rainfall. In addition, the enhanced decay rates measured in the Avicennia stand during the rainy season resulted in a strong 13 C depletion, while 13 C enrichment was measured in the other conditions. Elemental concentrations changes during decay were not clearly influenced by season, but depended on the element considered. K, Mg, Na, and Ca had t 50 values lower than the one of the bulk material. P and S contents also rapidly decreased during the first decomposition stages, but these elements had longer t 50 values than the bulk leaves. Conversely, an enrichment in most trace metals was observed during leaf litter decomposition whatever the season. We suggest that these metals were either trapped from the water column and the forest floor by organic molecules composing the litter, or subjected to litter decomposers uptake. Consequently, this study shows that the release or the uptake of elements during mangrove leaf litter decomposition varied with different parameters, which may have ecological implications on the nature of the elements exported toward adjacent ecosystems, and on their primary productivity.

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Section: Mangrove Leaf Litter Decay Ratessupporting

confidence: 73%

Section: Study Areamentioning

confidence: 99%

Changes in Leaf Litter Quality During Its Decomposition in a Tropical Planted Mangrove Forest (Can Gio, Vietnam)

Vinh

Allenbach²,

Linh

et al. 2020

Front. Environ. Sci.

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“…We explain the low concentrations observed by the strong tidal influence, which hinders the accumulation of sediments in the Saigon River channel, and the runoff on urban surfaces during the monsoon. This contamination transfer pattern raises concerns about potential impacts further downstream in depositional areas such as the Can Gio mangrove (Schwarzer et al, 2016), an ecosystem providing important services, in particular fisheries (Vo and Kuenzer, 2013).…”

Section: Resultsmentioning

confidence: 99%

Where has the pollution gone? A survey of organic contaminants in Ho Chi Minh city / Saigon River (Vietnam) bed sediments

et al. 2019

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A wide range of persistent organic chemicals, including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), some insecticides, as well as polybrominated diphenyl ethers (PBDEs) and some perfluoroalkyl substances (PFASs) were analyzed in 17 bed sediments collected along the Saigon River and at adjacent canal mouths from upstream to downstream in Ho Chi Minh City (Vietnam). Concentrations were rather low for PAHs, as well as for legacy PCBs and dichloro-diphenyl-trichlorethane and metabolites (DDTs), or below detection limits for several PFASs and all PBDEs measured. Several insecticides (chlorpyrifos-ethyl, and the pyrethroids cypermethrin and λ-cyhalothrin) displayed rather high concentrations at a few sites within the city. There was no distinct upstreamdownstream trend for PAHs, (DDTs) or PCBs. Although adjacent canal sediments tended to be more contaminated than Saigon River sediments, the differences were not significant. Emissions are almost certainly substantial for PAHs, and probably also for other contaminants such as PBDEs and some PFASs. During the dry season, contaminants are presumably stored in the city, either in canals or on urban surfaces. Heavy rainfall during the monsoon period carries away contaminated particle flows into the canals and then the Saigon River. The strong tidal influence in the river channel hinders the accumulation of contaminated particles. Contaminated deposits should accordingly be investigated further downstream in depositional environments, such as the mangrove.

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“…The flood plain vegetation can diminish local velocity by 20 to 44% compared to the main channel, which leads to reduced erosion and enhanced sediment retention (Struve et al 2003, Liu et al 2013. Specifically, both numerical simulations (Gelfenbaum et al 2007, Willemsen et al 2016) and field observations (Schwarzer et al 2016) have shown enhanced sedimentation within a mangrove forest, relative to regions without forest.…”

Section: Introductionmentioning

confidence: 98%

Comparison of drag and velocity in model mangrove forests with random and in-line tree distributions

Shan

Liu

Nepf

2019

Journal of Hydrology

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This study examined the role of tree arrangement (random versus aligned) on the drag forces and velocity inside a 1/12 th-scale model mangrove forest over a range of tree density (trees m-2). Each model tree included an aerial root system geometrically similar to Rhizophora, with maximum root height HR max and water depth H > HR max. The non-dimensional root density was defined as a r HR max , with root zone frontal area per volume, a r. For both random and aligned low-density forests, a r HR max < 0.1, the vertical profile of velocity followed a boundary layer shape. Within both random and aligned high-density forests, a r HR max > 0.1, the velocity was diminished in the root zone (z < HR max) and enhanced above the root zone, relative to the boundary layer profile. For all forest arrangements, the force on the roots dominated the force on the entire tree, even in cases with diminished velocity within the root zone. Compared with a tree at the leading edge, a tree inside a randomly distributed forest could experience either a greater or lesser force, and the variation in drag force increased with tree density. In contrast, for an aligned distribution of trees the force on an individual tree within the forest was always diminished relative to a tree at the leading edge. A drag coefficient was defined using a quadratic drag law. The forest-average drag coefficient, defined using the channel-average velocity, was up to 30 percent higher for random tree arrangements, compared to in-line tree arrangements.

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Sediment re-deposition in the mangrove environment of Can Gio, Saigon River estuary (Vietnam)

Cited by 26 publications

References 21 publications

Changes in Leaf Litter Quality During Its Decomposition in a Tropical Planted Mangrove Forest (Can Gio, Vietnam)

Changes in Leaf Litter Quality During Its Decomposition in a Tropical Planted Mangrove Forest (Can Gio, Vietnam)

Where has the pollution gone? A survey of organic contaminants in Ho Chi Minh city / Saigon River (Vietnam) bed sediments

Comparison of drag and velocity in model mangrove forests with random and in-line tree distributions

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