A. N. Balchand

Metal concentrations in recently deposited sediments of Cochin backwaters, India

Abstract The concentrations of a number of metals (Cd, Cu, Co, Cr, Fe, Mn, Ni, Pb and Zn) were determined in recently deposited sediments before, during and after flood conditions in the lower reaches of two large tropical rivers and in their adjoining estuarine beds of the Cochin backwater system, southwest India. Markedly elevated concentrations (ppm) of some metals, Cd (0.6–1.8), Cr (20–35), Ni (20–45) and Pb (12–18), were observed near the discharge outlets of industrial units. The results show enrichment of metals during post-flood periods in selected regions of the estuary, indicative of accumulation in sedimentary material. There were pronounced seasonal variations in the distribution of trace metals in the sediments which coincided with the flushing of bottom bed material to nearshore coastal plains. This study reveals that the transport of trace metals associated with bottom sediments occurs predominantly during the monsoonal months (flood conditions). Analyses of dissolved and particulate metals in overlying waters revealed that Cu and Cd concentrations consistently covaried, while Zn, Ni and Pb covaried on a seasonal basis with sediment-associated metals. There was no correlation between trace metal concentrations and organic carbon content of the sediments.

Heavy metal speciation in sediments of cochin estuary determined using chemical extraction techniques

Abstract Sequential extraction was used to characterise the various forms of cadmium, copper, lead and zinc in the sediments of Cochin estuary, southwest India, a typical positive tropical estuary. The forms determined were exchangeable cations, carbonate bound, easily reducible (combined with FeMn oxides), organic/sulphide phases and residual fractions. The concentrations determined indicated selective accumulation of the various metals in the different phases of the sediments, with spatial variability. The speciation pattern varies widely for different metals in the freshwater zone, through the estuarine reaches, before being preferentially accumulated in esoteric fractions at the seaward end. The influence of natural estuarine processes in modifying the anthropogenic inputs and in the selective enrichment of quasi-stable metal species is highlighted. The paper also discusses interspecies relationships in the sediments of this coastal region and compares the metal levels with those from other regions.

Trace metal speciation in a tropical estuary — Significance of environmental factors

Abstract Speciation studies on the metals Cd, Cu and Zn were carried out in the Periyar and the Muvattupuzha Rivers and the adjoining estuary, a typical tropical waterway in southwest India. Metal species were classified as: (i) dissolved (0.45 μm) (AAS); (ii) Chelex-100 labile (ASV); (iii) metal released upon UV irradiation (AAS) and Chelex-100 labile metal released upon UV irradiation (ASV); (iv) exchangeable particulate-associated metal; and (v) total particulate-associated metal. Samples of particulate matter were treated with HOAc to obtain the exchangeable metal fraction, while strong acid digestion yielded the acid-leachable fraction. The results indicate the presence of varying proportions of metal species and their affinity to bind with solid phases. The particulate fractions of metals determined reveal the role of sorption processes in regulating trace metal levels. This study highlights the influence of numerous environmental factors, such as (a) the influx of riverine input of metals regulated by dams/reservoirs; (b) introduction of industrial effluents and sewage; (c) modifications arising from anthropogenic activities; and (d) hydrographic changes related to complexity of water use.

Speciation of trace metals in sediments of a tropical estuary

Axial surveys were performed in the two river tributaries of the Cochin estuary, SW India during November 1988. Surficial sediments were subjected to sequential chemical extractions to delineate five metal fractions, namely, exchangeable, carbonate bound, easily reducible, organic/sulfide bound, and residual. The results indicated selective accumulation of Mn and Ni in carbonate bound and organic/sulfide forms, along with marginal amounts of Co in the exchangeable fraction. Large portions of Fe and Cr occurred in the residual fraction, whereas composite fractionation of Zn species was noticed. The exchangeable fractions of Fe and Cr as well as of easily reducible cobalt were below detection limits. The levels of Cr and Zn indicate anthropogenic inputs in this estuary, whereas Co and Ni show regional contamination exceeding natural levels. The analytical speciation procedure helps to deduce the sedimental diagenetic processes in the estuarine environment.

Fractionation of phosphorus in the sediments of a tropical estuary

Fractionation of phosphorus in the sediments of the Cochin estuary situated along the southwest coast of India was studied by applying sequential chemical extraction. The different forms of phosphorus were estimated seasonally (premonsoon, monsoon, and postmonsoon) under eight different schemes. The major forms of phosphorus analyzed were exchangeable P, anion exchangeable P, carbonate-bound P, labile and resistant organic P, Fe and Al P, calcium-bound P, and hydrolyzable surplus P. Quantitatively, the above fractions in isolation or in combination vary in content due to chemoestuarine variability and seasonal fluctuations. Changes in speciation have been noted in association with salinity variations in the waterway, especially following enhanced river runoff during the monsoon. The chemical forms of the sediment-bound phosphorus in the northern parts of this estuary have been shown to be modified by nonpoint sources. Sediment P fractionation defines the role of chemical speciation of phosphates (as nutrients) and is indicative of the processes controlling the pathways of P into the coastal waters. The changes in the exchangeable P, together with marked regional variations in calcium-bound P, exemplify the complex estuarine variability of phosphorus. Enhanced amounts of exchangeable P mark its appearence in high saline waters, signifying the presence of biologically available nutrient phosphorus. The calcium-bound P and hydrolyzable surplus P show significant relation with sediment organic carbon and Fe whereas other forms do not exhibit any marked covariation. The Ca and Na NTA extraction scheme is very specific in its selectivity.

On the determination and distribution of hydroxylated aromatic compounds in estuarine waters

Abstract A modified methodology to determine the hydroxylated aromatic compounds in aquatic waters and sediments has been developed. Interference in seawater samples were overcome by addition of citrate solution permitting the blue colour development on reduction of tungsto‐ and molybdo‐ phosphoric acids by the aromatic hydroxylated groups present in lignins and tannins. The above procedure was adopted to study the fate of tannin and lignin like substances (TALLS) in tropical estuarine and coastal waters and sediments receiving pulp‐paper effluents.

Phosphate fractionation in mud bank sediments from the southwest coast of India

Mud banks are unique, occurring along the southwest coast of India. They are known as ‘Zones of Bio-rhythm’, providing shelter to abundant aquatic life. The cyclic variation of nutrients in this region provides a clue to the continued and enriched presence of a variety of fish.This study reports on the different forms of phosphate in the resuspended sediments collected during the seasons with and without mud banks from the above mentioned coastal zones. Applying sequential and parallel chemical extractions using eight different schemes, the major forms of phosphate namely exchangeable P, anion exchangeable P, carbonate bound P, labile and resistant organic P, Fe-, Al- and Ca bound P and hydrolysable P have been determined.Quantitatively, these fractions vary and exhibit seasonal fluctuations. The concentration of potentially available anion exchange P, together with resistant organic and hydrolysable surplus P, provide an explanation to the existing organic food web supporting the aquatic life. Sediment phosphate fractionation reflects the role of chemical speciation of nutrients in the propagation of mud banks and is indicative of the biogenic processes controlling the pathways of phosphate in these coastal waters.

Speciation and estuarine modification of zinc during transport in a tropical fluvial environment

The estuarine modifications of zinc during its transport through the tropical Cochin estuary was evaluated by speciation studies. The fractions of zinc reported include Chelex‐100 labile and organically bound metal in the aqueous phase and exchangeable and total metal in the particulate phase. The behaviour of each of the above fraction in relation to the environmental factors such as salinity, suspended solids load and DOC is presented. The behavioural profile indicates the removal of all the fractions in the saline region of this tropical estuary. The mass balance indicated accumulation of zinc in the estuarine regions.

A survey of the protein content in estuarine waters

A survey of the protein content in a tropical estuary and its nearshore regions are reported for two seasons—postmonsoon (November 1987) and monsoon (June 1988)—using a modified dye binding method. The content of protein varied from 0.05 to 8.0μgl‐1 in the fresh and estuarine waters with little variability between surface and bottom values. The enhanced biological production during postmonsoon months causes a higher level of protein in the lower estuary compared to low values in the freshwater, riverine end. Increased terrestrial runoff and discharge of industrial waste mainly from seafood processing units are linked to the higher concentrations of protein in monsoon, more than double the content during postmonsoon. Auxiliary data on chlorophylla, organic NO3 ‐—N, PO3 4—P, urea and dissolved organic carbon support the above contention. Interparametric relationships suggest seasonally varying correlation between protein and chlorophylla, urea and DOC, signifying the role of biological control.

Environmental studies on impacts of dredging

The coastal zone acts as a major interface between the ocean and continents. Harbours located in this zone face grave problems from sedimentation, which is a global issue for most of the harbours of the world. Dredging which counter acts sedimentation, brings about innumerable environmental impacts — both positive and negative. As a case study, this paper reports the impacts of dredging conducted at Cochin harbour which is the second largest port along the west coast of India; this port is a nodal center in trade and commerce connecting south east Asia to European sector. The harbour operation mainly depends on maintenance form of dredging bringing about impacts which have both direct and indirect effects in the long term. The important parameters selected for this study are salinity, current, extinction coefficient, turbidity, nutrients, chlorophyll and bottom fauna. An assessment is made on both positive and negative impacts which indicate rise in turbidity, changes in nutrient content and biota. The current practice on dredging is conducive to harbour operations, regulating the material made available to the near shore areas and highlights the possible venues for utilization of spoil for reclamation of land and wetland development. A flow chart identifies the areas vulnerable to impacts arising out of dredging and its consequential environmental issues.