Mangroves are woody plants that grow at the interface between land and sea in tropical and sub-tropical latitudes where they exist in conditions of high salinity, extreme tides, strong winds, high temperatures and muddy, anaerobic soils. There may be no other group of plants with such highly developed morphological and physiological adaptations to extreme conditions.

Because of their environment, mangroves are necessarily tolerant of high salt levels and have mechanisms to take up water despite strong osmotic potentials. Some also take up salts, but excrete them through specialized glands in the leaves. Others transfer salts into senescent leaves or store them in the bark or the wood. Still others simply become increasingly conservative in their water use as water salinity increases Morphological specializations include profuse lateral roots that anchor the trees in the loose sediments, exposed aerial roots for gas exchange and viviparous waterdispersed propagules.

Mangroves create unique ecological environments that host rich assemblages of species. The muddy or sandy sediments of the mangal are home to a variety of epibenthic, infaunal, and meiofaunal invertebrates Channels within the mangal support communities of phytoplankton, zooplankton and fish. The mangal may play a special role as nursery habitat for juveniles of fish whose adults occupy other habitats (e.g. coral reefs and seagrass beds).

Because they are surrounded by loose sediments, the submerged mangroves' roots, trunks and branches are islands of habitat that may attract rich epifaunal communities including bacteria, fungi, macroalgae and invertebrates. The aerial roots, trunks, leaves and branches host other groups of organisms. A number of crab species live among the roots, on the trunks or even forage in the canopy. Insects, reptiles, amphibians, birds and mammals thrive in the habitat and contribute to its unique character.

Living at the interface between land and sea, mangroves are well adapted to deal with natural stressors (e.g. temperature, salinity, anoxia, UV). However, because they live close to their tolerance limits, they may be particularly sensitive to disturbances like those created by human activities. Because of their proximity to population centers, mangals have historically been favored sites for sewage disposal. Industrial effluents have contributed to heavy metal contamination in the sediments. Oil from spills and from petroleum production has flowed into many mangals. These insults have had significant negative effects on the mangroves.

Habitat destruction through human encroachment has been the primary cause of mangrove loss. Diversion of freshwater for irrigation and land reclamation has destroyed extensive mangrove forests. In the past several decades, numerous tracts of mangrove have been converted for aquaculture, fundamentally altering the nature of the habitat. Measurements reveal alarming levels of mangrove destruction. Some estimates put global loss rates at one million ha y−1, with mangroves in some regions in danger of complete collapse. Heavy historical exploitation of mangroves has left many remaining habitats severely damaged.

These impacts are likely to continue, and worsen, as human populations expand further into the mangals. In regions where mangrove removal has produced significant environmental problems, efforts are underway to launch mangrove agroforestry and agriculture projects. Mangrove systems require intensive care to save threatened areas. So far, conservation and management efforts lag behind the destruction; there is still much to learn about proper management and sustainable harvesting of mangrove forests.

Mangroves have enormous ecological value. They protect and stabilize coastlines, enrich coastal waters, yield commercial forest products and support coastal fisheries. Mangrove forests are among the world's most productive ecosystems, producing organic carbon well in excess of the ecosystem requirements and contributing significantly to the global carbon cycle. Extracts from mangroves and mangrove-dependent species have proven activity against human, animal and plant pathogens. Mangroves may be further developed as sources of high-value commercial products and fishery resources and as sites for a burgeoning ecotourism industry. Their unique features also make them ideal sites for experimental studies of biodiversity and ecosystem function. Where degraded areas are being revegetated, continued monitoring and thorough assessment must be done to help understand the recovery process. This knowledge will help develop strategies to promote better rehabilitation of degraded mangrove habitats the world over and ensure that these unique ecosystems survive and flourish.

Biology of mangroves and mangrove Ecosystems

Geochemistry of Recent oxic and anoxic marine sediments: Implications for the geological record

The flow of homogeneous fluids through porous media: analogies with other physical problems

https://homepages.uc.edu/~algeot/Algeo-Maynard-ChemGeol-2004.pdf

Trace-element behavior and redox facies in core shales of Upper Pennsylvanian Kansas-type cyclothems

Antimony in the environment: a review focused on natural waters: I. Occurrence

Published information, both theoretical and experimental, on As chemical behavior in soils is reviewed. Because of many emission sources, As is ubiquitous. Thermodynamic calculations revealed that As(V) species (HAsO
 4
 2-
 >H2AsO
 4
 -
 at pH 7) are more abundant in soil solutions that are oxidized more than pe+pH>9. Arsenic is expected to be in As(III) form (HAsO
 2
 0
 =H3AsO
 3
 0
 >AsO
 2
 -
 =H2AsO
 3
 -
 at pH 7) in relatively anoxic soil solutions with pe+pH<7. Adsorption on soil colloids is an important As scavenging mechanism. The adsorption capacity and behavior of these colloids (clay, oxides or hydroxides surfaces of Al, Fe and Mn, calcium carbonates, and/or organic matter) are dependent on ever-changing factors, such as hydration, soil pH, specific adsorption, changes in cation coordination, isomorphous replacement, crystallinity, etc. Because of the altering tendencies of soil colloids properties, adsorption of As has become a complex, empirical, ambiguous, and often a self contradicting process in soils. In general, Fe oxides/hydroxides are the most commonly involved in the adsorption of As in both acidic and alkaline soils. The surfaces of Al oxides/hydroxides and clay may play a role in As adsorption, but only in acidic soils. The carbonate minerals are expected to adsorb As in calcareous soils. The role of Mn oxides and biogenic particles in the As adsorption in soils appears to be limited to acidic soils. Kinetically, As adsorption may reach over 90% completion in terms of hours. Precipitation of a solid phase is another mechanism of As removal from soil solutions. Thermodynamic calculations showed that in the acidic oxic and suboxic soils, Fe-arsenate (Fe3(AsO4)4)2) may control As solubility, whereas in the anoxic soils, sulfides of As(III) may control the concentrations of the dissolved As in soil solutions. In alkaline acidic oxic and suboxic soils, precipitation of both Fe- and Ca-arsenate may limit As concentrations in soil solutions. Field observations suggest that direct precipitation of discrete As solid phases may not occur, except in contaminated soils. Chemisorption of As oxyanions on soil colloid surfaces, especially those of Fe oxide/hydroxides and carbonates, is believed to a common mechanisms for As solid phase formation in soils. It is suggested that As oxyanions gradually concentrate on colloid surfaces to a level high enough to precipitate a discrete or mixed As solid phase. Arsenic volatilization is another As scavenging mechanism operating in soils. Many soil organisms are capable of converting arsenate and arsenite to several reduced forms, largely methylated arsines which are volatile. These organisms may generate different or similar biochemical products. Methylation and volatilization of As can be affected by several biotic (such as type of organisms, ability of organism for methylation, etc.) and abiotic factors (soil pH, temperature, redox conditions, methyl donor, presence of other ions, etc.) factors. Information on the rate of As biotransformations in soils is limited. In comparison to the biologically assisted volatilization, the chemical volatilization of As in soils is negligible.

Arsenic Chemistry in Soils: An Overview of Thermodynamic Predictions and Field Observations

Thermodynamics data of As species were used to develop the solubility isotherms of As minerals and solution species. The effect of redox on the stability of As minerals and the distribution of As solution species was also simulated. In oxygenated and alkaline systems, Ca3(AsO4)2 was the most stable As mineral followed by Mn3(AsO4)2. It was postulated that in such environments Ca3(AsO4)2 and Mn3(AsO4)2 might precipitate. Arsenic(V) oxide was too soluble to become an important solid phase in the aqueous environment. Under reduced and acidic concitions (pe + pH 8), arsenate species were important whereas in reduced systems (pe + pH < 8), As(III) species were in abundance. Arsine gas can only form if the system was very reduced and acidic. Below pH 2.2, H3AsO4° was in abundance. As pH increased, H2AsO4− species was important, followed by AsO43− above pH 12. The results of thermodynamic stability and solubility models have been discussed in reference to soil environment.

Environmental behavior of arsenic in soils: Theoretical

The particular inquiry is made to envision the characteristics of magneto-hydrodynamic oscillatory oblique stagnation point flow of micropolar nanofluid. The applied magnetic field is assumed parallel towards isolating streamline. A relative investigation is executed for copper and alumina nanoparticles while seeing water type base fluid. To be more specific, in the presence of both weak and strong concentration, the physical situation of micropolar fluid is mathematically modeled in terms of differential equations. The transformed mixed system is finally elucidated by midpoint method with the Richardson extrapolation development and shooting mechanism with fifth order R–K Fehlberg technique. The impact of governing parameters are shown and explored graphically. The obtained results are compared with existing published literature. Moreover, it is found that the magnetic susceptibility of nanofluids shows provoking nature towards copper as compared to Alumina. Also it is perceived that Cu–water shows higher wall shear stress and heat transfer rate than Al2O3–water. Additional, the thickness of momentum boundary layer is thin for weak concentration as related to strong concentration.

/pdf/numerical-simulation-of-oscillatory-oblique-stagnation-point-3dae2ryr58.pdf

Numerical simulation of oscillatory oblique stagnation point flow of a magneto micropolar nanofluid

The invasion and occupation of Kuwait by the Iraqi forces and the resulting Gulf War in 1991 led to unprecedented environmental contamination, the effects of which will be felt for years to come. The air was polluted by emissions from hundreds of burning oil wells, the sea fouled by the largest oil spill in history, and the land scarred by massive bombardment and troop movement. Information regarding this environmental legacy of the Gulf War has hitherto been scattered throughout the popular and scientific press. This is the first book that brings together what is currently known about the environmental aftermath of this tragic war.

Muhammad Sadiq

Papers

Arsenic Chemistry in Soils: An Overview of Thermodynamic Predictions and Field Observations

Environmental behavior of arsenic in soils: Theoretical

Numerical simulation of oscillatory oblique stagnation point flow of a magneto micropolar nanofluid

The Gulf War Aftermath: An Environmental Tragedy

Sediment composition and metal concentrations in mangrove leaves from the Saudi coast of the Arabian Gulf