Rajesh Kumar Ranjan

Assessment of metal enrichments in tsunamigenic sediments of Pichavaram mangroves, southeast coast of India

The 26 December 2004-Tsunami has deposited sediments in the Pichavaram mangrove ecosystem, east coast of India. Ten surface and three core sediment samples were collected within thirty days of the event. High concentrations of Cd, Cu, Cr, Pb, and Ni were observed in the tsunamigenic sediments. With respect to Fe, Zn, and Mn, there was little variation as compared to pre-tsunami values. The geo-accumulation index was calculated in order to assess the contamination of heavy metals in the sediments. The sediments were extremely contaminated with respect to Cd and they showed moderate to strong contamination with respect to Cr, Pb and Ni. The study highlighted the future risk of enhanced metal pollution in near future in this mangrove ecosystem.

Metal speciation studies in the aquifer sediments of Semria Ojhapatti, Bhojpur District, Bihar

The pollution of aquifer sediments by heavy metals has assumed serious concern due to their toxicity and accumulative behavior. Changes in environmental conditions can strongly influence the behavior of both essential and toxic elements by altering the forms in which they occur and therefore quantification of the different forms of metal is more meaningful than total metal concentrations. In this study, fractionation of metal ions in aquifer sediments of Semria Ojhapatti area, Bhojpur district, Bihar has been studied to determine the ecotoxic potential of metal ions. The investigations suggest that iron, copper, and arsenic have a tendency to remain associated in the following order residual > reducible > acid-soluble > oxidizable; manganese and zinc have tendency to be associated as residual > acid-soluble > reducible > oxidizable. The risk assessment code reveals that manganese and zinc occur in significant concentration in acid-soluble fraction and therefore comes under the high risk category and can easily enter the food chain. Most of the iron, copper, and arsenic occur as immobile fraction (i.e. residual) followed by its presence in reducible fraction and would pose threat to the water quality due to changing redox conditions. The metal enrichment factor in the study area shows moderate to significant metal enrichment in the aquifer sediments which may pose a real threat in near future. The geo-accumulation index of metals also shows that the metals lie in the range of strongly contaminated (for iron at shallow depths) to moderately contaminated to uncontaminated values.

Phosphorus dynamics in shallow eutrophic lakes: an example from Zeekoevlei, South Africa

Zeekoevlei is the largest freshwater lake in South Africa and has been suffering from hyper-eutrophic conditions since last few decades. We have used total P (TP), dissolved phosphate (PO43−), organic P (OP), calcium (Ca) and iron (Fe) bound P fractions to investigate the relevant physical, chemical and biological processes responsible for sedimentation and retention of P and to study phosphorus (P) dynamics in this shallow lake. In addition, redox proxies (V/Cr and Th/U ratios) are used to study the prevailing redox conditions in sediments. Adsorption by CaCO3 and planktonic assimilation of P are found to control P sedimentation in Zeekoevlei. Low concentration of the labile OP fraction in surface sediments restricts the release of P by bacterial remineralisation. Low molar Ca/P and Fe/P ratios indicate low P retention capacity of sediments, and P is most likely released by desorption from wind-induced resuspended sediments and mixing of pore water with the overlying water column.

Geochemical modeling to evaluate the mangrove forest water

The knowledge about genetic origin of the chemical elements is important for the evaluation of hydro-geochemistry of aquatic ecosystem. In the present study, pre- and post-monsoon samples were collected to identify the role of rain and seawater in the hydro-geochemical processes. Geochemical model and multivariate statistical methods of data analysis were jointly used to define the variations and the genetic origin of chemical parameters of water in mangrove ecosystem. The geochemical model, WATEQ4F, was executed to compute the saturation indices of the minerals with respect to surface water. The interpretation of the saturation indices for minerals shows that the majority of samples fall in the category of under saturation state except for fluorite. An increase in the concentration of various nutrients, namely, nitrate and phosphate, was observed. Suitability of water was checked on the basis of chemical categorisation by Aquachem software. Grouping of waters on the Piper diagram suggested a common composition and origins. Further results showed that pre- and post-monsoon samples mainly consist of Na–Cl and Ca–Cl water type indicating a significant contribution of cations and anions from terrestrial and marine inputs in the mangrove ecosystem.

Trace metal fractionation in the Pichavaram mangrove–estuarine sediments in southeast India after the tsunami of 2004

The geochemistry of coastal sediments of southern India was altered after the tsunami in 2004. A five-step sequential extraction procedure was applied to assess the effects of tsunami on mobility and redistribution of selected elements (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn). Ten surface sediments and three cores were analyzed for different metal fractions (exchangeable, carbonate, reduced, oxidized, and residual). Total metal concentrations increased in mangrove sediments after the tsunami, but their spatial distribution did not show significant variation (except Mn). The sediments were mixed by the tsunami, and there was lack of variation in metal concentrations in different fractions with depth (except Pb and Mn). High concentrations of Pb and Zn occurred in the oxide fractions, whereas Cu, Cr, Cd, and Ni were high in the organic and sulfide-rich fractions. Metals in the residual fraction (lattice bound) had the highest concentration suggesting their non-availability and limited biological uptake in the system. Most of the metals (except Mn) do not constitute a risk based on the different geochemical indices.

Dissolved Metal Distribution in Indian Mangrove Ecosystem: Case Studies from East Coast of India

Mangroves represent highly dynamic and fragile ecosystem, which occupy a large fraction of the tropical and subtropical coastline, dominating the intertidal zone of diverse environmental settings. The potential role of mangrove ecosystems as sinks for anthropogenic contaminants in tropical and subtropical areas has been widely recognized. Sediments are important carriers of trace metals in the hydrological cycle and because metals are partitioned with the surrounding waters, they reflect the quality of an aquatic system (Szefer et al., 1995). Heavy metals are natural constituents of the marine environment and some of them, such as Cu, Fe, Zn, and Mn, are biologically essential for normal growth and development (Astorga Espana et al., 2004). Metals such as Cd and Hg have no known use in physiological processes (Darmono and Denton, 1990), but when present in excess have ecological significance due to their toxicity and cumulative behaviour and constitute a potential hazard for environment.

Hydrogeochemistry and Arsenic Distribution in the Gorakhpur District in the Middle Gangetic Plain, India

About one-third of the earth’s land surface is facing challenge of water scarcity in both quantitative and qualitative terms (Postel SL, Last oasis: facing water scarcity, 2nd edn. W.W. Norton, New York, 1997). In the last few decades, the global finding of the presence of elevated concentrations of various toxic solutes from natural and anthropogenic sources has limited the available volume of safe drinking water. Understanding the aquifer hydraulic properties and hydrochemical characteristics of water is crucial for proper planning, management and sustainable utilization of groundwater. Generally, the motion of groundwater along its flow paths below the ground surface increases the concentration of the chemical species; hence the groundwater chemistry could reveal important information on the geological history of the aquifers and the suitability of groundwater for domestic, industrial and agricultural purposes (Kortatsi BK, Aquat Geochem 13(1):41–74, 2007).