Impacts of oil pollution on mangroves

Pollution such as oil pollution can kill mangroves by heavy or viscous oil that covers the trees’ breathing pores thereby asphyxiating the subsurface roots which depend on the pores for oxygen. In addition, the toxicity of substances in the oil, having lower molecular weight aromatic compounds, can damage cell membranes in the subsurface roots. This in turn impairs the normal salt exclusion process and the resulting influx of salt is a source of stress to the plants. Furthermore, organisms living among and on the mangrove trees can be affected.  Heavy mortalities of organisms may occur as a direct result of the oil. For example, oil may penetrate burrows in the sediments, killing crabs and worms, or coat molluscs on the sediment surface and aerial roots. Oil pollution can suffocate the trees and kill tress leading to loss of habitat for organisms living in the branches and canopy of the trees, and in the aerial root systems.

Experiments conducted found that seedlings and saplings are susceptible to oil exposure. For example, in field studies with Avicennia marina, it was found that greater than 96% of seedlings exposed to a weathered crude oil died, compared to no deaths among the unoiled controls. Stressed man­groves due to oil pollution could show differences in growth rates or alter reproductive timing or strategy. In addition to tree mortality due to oil pollution; leaf defoliation, deformation, and stunting; seedling deformation and mortality; lenticel expansion; adventitious growth of pneumatophores; and changes in the density and distribution of plants and animals were also reported as a consequence of the effects of oil pollution on mangrove forests

Reference

Biological impacts of oil pollution: Mangroves. 1993. http://www.ipieca.org/publication/biological-impacts-oil-pollution-mangroves

Oil spills in mangroves. 2010. http://www.eoearth.org/view/article/159877/

Charles D. Getter, Geoffrey I. Scott, t and Jacqueline Michel. 1981. THE EFFECTS OF OIL SPILLS ON MANGROVE FORESTS: A COMPARISON OF FIVE OIL SPILL SITES IN THE GULF OF MEXICO AND THE CARIBBEANS.http://ioscproceedings.org/doi/pdf/10.7901/2169-3358-1981-1-535

Sediments have a great capacity to accumulate pollutants in aquatic systems, even when these compounds present low concentrations in the waters, and therefore are regarded as one of the most representative environmental indicators of contamination and can be used to map, trace and monitor anthropogenic sources of contamination and/or anomalies caused by geochemical natural processes. Many scientists have studied mercury contamination in surface sediments of sheltered environments, like estuaries, lagoons and bays. In their studies mercury contamination due to anthropogenic activities was observed. Two of these identified sources were: chloro-alkali factories, in which mercury cathodes were used for chlorine production and factories which processed imported ore containing traces of mercury.

It is known that the concentration of a contaminant in sediment tends to increase when particle sizes decrease because of enlargement of the surface area per unit. Therefore, an estimation of contaminant immobilization requires information about the grain size distribution and relationship between particle size, mineralogical differences and concentration of the contaminant in the sediment. Normalization is a common approach to compensate for anomalous metal concentrations in sediments and soils caused by grain size and mineralogical differences. In aquatic ecosystems, inorganic mercury enters a complex cycle in which it can be methylated in water and/or in sediments producing methylmercury, the most toxic form of Hg. Methylmercury level in sediments is controlled by competing and simultaneous methylation and demethylation reactions.

This depends on the pollutant and the concentrations.

There was interesting article recently by Wang et al in Aquatic Biology 2014 Vol. 20 119-127 on the inhibitory effect sewage on the mangrove microrhizal associated fungi which I imagine would have a big impact

Also have look at the final report from the PUMPSEA project that actually looked at this in detail http://cordis.europa.eu/publication/rcn/12994_en.html

And if you enter effluent and mangrove in any search engine you will be bombarded with numerous scientific articles on the matter -especially with reference to aquaculture effluent - low levels of effluent have been shown to enhance growth especially in mangrove that are nutrient limited.

Sediments have a great capacity to accumulate pollutants in aquatic systems, even when these compounds present low concentrations in the waters, and therefore are regarded as one of the most representative environmental indicators of contamination and can be used to map, trace and monitor anthropogenic sources of contamination and/or anomalies caused by geochemical natural processes. Many scientists have studied mercury contamination in surface sediments of sheltered environments, like estuaries, lagoons and bays. In their studies mercury contamination due to anthropogenic activities was observed. Two of these identified sources were: chloro-alkali factories, in which mercury cathodes were used for chlorine production and factories which processed imported ore containing traces of mercury.

It is known that the concentration of a contaminant in sediment tends to increase when particle sizes decrease because of enlargement of the surface area per unit. Therefore, an estimation of contaminant immobilization requires information about the grain size distribution and relationship between particle size, mineralogical differences and concentration of the contaminant in the sediment. Normalization is a common approach to compensate for anomalous metal concentrations in sediments and soils caused by grain size and mineralogical differences. In aquatic ecosystems, inorganic mercury enters a complex cycle in which it can be methylated in water and/or in sediments producing methylmercury, the most toxic form of Hg. Methylmercury level in sediments is controlled by competing and simultaneous methylation and demethylation reactions.

The mangrove is at the same time a complex and a fragile system that should be protected for the sake of biodiversity among others. When facing urbanization stress, these mangroves, depending on their size, could be shifted. This is one solution to preserve small sized mangrove. This ecosystem has the particularity to stand on the interface of salty and non-salty water, hence this ecosystem is specific and much more study is needed to better understand how the plants in such ecosystem face the organic pollution such as wastewater for instance. In my point of view, the enforcement of regulation could definitely help the preservation of such kind of fragile systems.

As you can see in the excellent answers here published, your question deals with a very complex and varying issue. Effects on mangroves vary according to the pollutants involved, their concentrations, their persistence, etc. Also depend on the mangrove condition, intensity of water flushing by currents (degree of confinement) or dilution potnetial of pollutants, etc. It is my simple answer for a very open and complex question.  More specific questions are needed to provide better targeted answers.

Thank you all for the answers. Mercury is one of the most toxic metal and it may also hamper normal metabolic pathway in mangroves. Please mention your thoughts and findings on this issue.

Apart from all the facts the development activities also play a vital roll. Mainly desalination of lagoons and marshy land reclamation in the name of productivity enchantment also kill the mangrove population

I have uploaded two presentation and one of my question related this development has been answered condusivelly those may be useful for this discyssion

In recent years, a number of industries and aquaculture farms have been developed around the estuaries of delta near its mouth. The effluents from these industries and aquaculture are discharged into estuary at the deltaic confluence point of river with ocean or sea;  which enters into the estuary and poses threat to the mangrove ecosystem.

The above tests on water needs to be within permissible limits for human consumption.

Mercury impacts on living organisms @Shankhadeep Chakraborty 

Mercury reaches coastal habitats/mangroves through river discharge into estuaries. From there, a number of abiotic processes influence mercury cycling in tropical coastal waters. Mercury (Hg) is an environmental pollutant that accumulates in aquatic ecosystems, generating health concerns for consumers of contaminated organisms (e.g. seafood). The most common organic form of Hg, methylmercury (MeHg), is of particular concern because it is a potent neurotoxin and bio- magnifies in aquatic food webs

The accumulation of trace/heavy metals (such as mercury) in mangrove sediments may decrease growth and respiration rates of mangroves, and will also negatively impact associated animals including fish, and crabs.

Concentrations of mercury and other metals are toxic to invertebrate and fish larvae (note : mercury is most toxic to aquatic organisms compared to other metals), and metals can cause physiological stress and affecting crab reproduction.

Though inorganic mercury has low toxicity to aquatic organisms however the organic mercury complexes (e.g. methyl mercury) are more toxic and tend to bio-accumulate (note: organo mercury compounds are 4 to 31 times more toxic than inorganic mercury).

Mercury compounds can damage vital tissues and organs including gill, liver, kidney, brain and skin of fish and may reduce reproductive success. In fish, the pre-hatch stage is most susceptible to intoxication. The notable ‘Minamata disease’ is a classic example of bio-accumulation and bio-magnification of mercury in seafood which resulted 21 deaths in Japan.

Mercury (methyl-mercury) is reported to accumulate in fish tissues at higher concentrations, which may be related with high bio-concentration factors of methyl-mercury for fish

References

Costa et al.  2012. Mercury in tropical and subtropical coastal environments Environmental Research 119:  88. 100.http://www.sciencedirect.com/science/article/pii/S0013935112002046

https://www.researchgate.net/publication/261216635_Climate_Change_and_Chemicals_Environmental_and_Biological_Aspects

Book Book: Chemicals and Climate Change: Environmental and Biolog...

Thanks guys for suporting shankhadeep. keep it up.

In terms of heavy metals, we do not have much reliable experimental evidence on polluting effects of metals in “the real world”. We know that metals can be toxic to most organisms (see results from studies in laboratories). What we do not know, however, is whether the same effects will inevitably occur in natural environments. In general, few studies have been done with metals under natural conditions and even fewer had manipulative experiments or other frameworks of evidence that would allow conclusive answers (i.e. a cause–effect relationship due to the contamination by metals). Most studies have, however, reported smaller diversity and abundances of taxa in areas contaminated by metals. Under natural conditions, metals are less likely to be harmful than suggested by many laboratory studies. This may be due to several reasons, such as the interaction of the metals with other variables (biotic and abiotic) and the concentrations used. In the field, many variables and their interactions are occurring, such as dilution of the metals, decreasing the actual concentration encountered by the organisms. Very few field experiments have demonstrated important ecological effects of metals on organisms. Many experiments found no effects. Usually, these effects varied so much in time and space that it has been difficult to estimate a definitive effect of metals. For more information see the following paper:

Mayer-Pinto, M., A. J. Underwood, T. Tolhurst & R. A. Coleman, 2010. Effects of metals on aquatic assemblages: What do we really know? Journal of Experimental Marine Biology and Ecology 391: 1-9.

I am a bit puzzled by the answer given by Tolhurst. Taking this 100%, it would imply that we don't have problems at all, and no ecotox effects will be found in nature. Mind you, some areas are so polluted, that nobody will want to touch the sediments there. That is not without reason.

One thing to remember is that the estuarine, or mangrove ecosystems have species that are used to large stresses. These environments are not easy to live in, and heavy metal pollution is just one of the things to take care of by organisms. This might hamper the statistical proof that pollutants cause effects.

Another important factor is bioavailability. In land soils, this is pretty well described. In mangrove/estuarine systems, things are much more complex, and many metals are either non bound or completely bound. If the pollutant is there, but you don't get in contact with it, you will not see an effect. In many cases, the additional pollution coming from smaller sized particles, less food availability etc is much larger than what the direct effects of the heavy metals will be.

For the original question: this is a very wide question, it might be easier to answer if you break down the subject first into more manageable bits.

Thank you all.

To clarify: I'm not saying there is no effect, just that many studies could not find a significant effect. This is due to there being many other interacting variables, which potentially mask impacts. What is required are better designed experiments with proper controls to determine what the impacts are of different levels of contamination.

Sediments are the key catalysts of environmental food cycles and the dynamics of water quality. Sediments in rivers, lakes, and oceans have been contaminated by pollutants. Mangrove forests and adjacent mudflats are increasingly affected by sediments.

The impact of urbanization on tropical mangroves (Fortaleza, Brazil): Evidence

from PAH distribution in sediments.

http://www.inct-tmcocean.com.br/pdfs/produtos/32_cavalcanteetal.pdf

I am late to this discussion because of other responsibilities. I did wish to point out the following references to add for oil pollution in mangroves.  They note the multi-year fate and effects of spilled oil in this mangrove ecosystem. Best wishes, John

J. B. C. Jackson, J. D. Cubit, B. D. Keller, V. Batista,

K. Burns, H. M. Caffey, R. L. Caldwell, S. D. Garrity, C.

D. Getter, C. Gonzalez, H. M. Guzman, K. W. Kaufmann,

A. H. Kanp, S. C. Levings, M. J. Marshall, R. Steger, R. C.

Thompson, and E. Weil, “Ecological Effects of a Major

Oil Spill on Panamanian Coastal Marine Communities,”

Science 243 (1989): 37–44.

 S. D. Garrity, S. C. Levings, and K. A. Burns, “The

Galeta Oil Spill. I. Long Term Effects on the Physical

Structure of the Mangrove Fringe,” Estuarine, Coastal and

Shelf Science 38 (1994): 327–48.

K. A. Burns, S. D. Garrity, D. Jorissen, J.

MacPherson, M. Stoelting, J. Tierney, and L. Yelle-

Simmons, “The Gaketa Oil Spill. II. Unexpected

Persistence of Oil Trapped in Mangrove Sediments,”

Estuarine, Coastal and Shelf Science 38 (1994): 349–64;

S.C. Levings, S. D. Garrity, and K. A. Burns, “The Galeta

Oil Spill. III. Chronic Reoiling, Log-Term Toxicity of

Hydrocarbon Residues and Effects on Epibiota in the

Mangrove Fringe,” Estuarine, Coastal and Shelf Science 38

(1994): 365–95;

K. A. Burns, and L. Yelle-Simmons, “The

Galeta Oil Spill. IV. Relationship Between Sediment and

Organism Hydrocarbon Loads,” Estuarine, Coastal and

Shelf Science 38 (1994): 397–412.

K. A. Burns, S. D. Garrity, and C. Levins. “How

Many Years Until Mangrove Ecosystems Recover From

Catastrophic Oil Spills?,” Marine Pollution Bulletin 26

(1993): 239–45.

The vast majority of the nutrient pool of mangrove forests is stored in the soil and not in the trees. Mangrove soils are typically saline, anoxic, acidic and frequently waterlogged. The delivery of nutrients in sediments and water during tidal inundation and sporadically in floodwaters associated with cyclones and hurricanes provides significant sources of nutrients for mangroves

http://treephys.oxfordjournals.org/content/30/9/1148.full

Mangroves have great capacity to recover from oil contamination. Avicennia marina that I am working on could stand 10% oil contaminated soil.