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This study aimed to compare the properties of the constructions made by Microcerotermes pakistanicus, a wood-feeding termite species building carton nests, to those made by the fungus-growing termite Odontotermes obesus in a secondary forest in the Western Ghats region of Kerala. X-ray computed tomography (X-ray CT) showed that the pinnacle of O. obesus termitaria was very thick and compact with a central cavity and numerous unconnected galleries in its inner part. Conversely, the construction of M. pakistanicus appeared as a very porous media made of abundant and connected galleries following a radial trajectory, and the galleries were separated from the others by a thin wall. Despite significant differences in terms of soil chemical properties, Odontotermes obesus termitaria and sheetings had similar properties to those of the surrounding topsoil. Conversely, M. pakistanicus nest had unique chemical properties distinct from those of O. obesus or the surrounding soil. Moreover, although M. pakistanicus builds carton nests from its faeces, minerals were also measured within its termitaria. In conclusion, this study shows the very different properties of O. obesus and M. pakistanicus constructs. It also suggests the need for soil ecologists to consider carton-nests as a third group of soil-nest type, in addition to those built by soil or litter feeders and fungus-growers which edify termitaria from soil and different amount of organic matter. Further studies are also needed to determine their functional impacts on soil and nutrient dynamics.

The present study aimed to assess the role of homegarden (HG) in safeguarding the tree diversity and carbon (C) density or storage in the Thodupuza urban region of Idukki district in Kerala, India. A stratified random approach was used for selecting the four homegardens (HGs) with a size of 1hectare (ha). The study mainly focused on species richness, diversity, above ground biomass, carbon, correlation and distribution of carbon with various variables, species and group wise carbon storage of the system. A total of 992 trees from 66 species belonging to 31 families were enumerated with representation of 4 endemic, 1 vulnerable, 1 endangered and 23 exotics. The diversity indices obtained were closer to those of the forest ecosystem. Above ground biomass and carbon density were estimated to be 67.06 t/ha (tonne/hectare) and 31.85 6 t/ha respectively. Species Tectona grandis showed dominancy in carbon and Important Value Index. Correlation analysis among species revealed that carbon exhibited a strong positive trend with basal area and tree density, but in the case of plot (HG)-wise examination only basal area had a strong positive relationship. The diametric class analysis showed skewed type of distribution for carbon and tree density while diversity had reverse j-shaped curve. Among the two plant groups, cultivated species had an edge over native in storing carbon. Overall, this assessment shows the potential of using homegardens as a socio-ecological systems for sustainable development particularly in terms of land availability and climate mitigation options in the face of rapid urbanization.

An eco-friendly method of silver nanoparticle (SNPs) synthesis is presented by utilizing a terrestrial weed, Mucuna bracteata DC. This plant based nanoparticles are effectively reducing anionic dye, Reactive Red 120 by adsorption—an effective method of dye removal from effluents. The method enables the rapid synthesis of SNPs at ambient conditions without any use of hazardous chemicals. The characterization of nanoparticles with UV-visible spectrophotometer indicated the absorption peak at 299 of blue shift; SEM and TEM analysis has revealed the presence of particles with spherical morphology of about 30–80 nm in size; The X-ray diffraction and EDAX studies confirmed the presence of silver atoms; The FT-IR spectra indicated the role of hydroxyl functional groups and amino group of the phyto extract, are responsible for the reduction and stabilizing silver ions in to SNPs. The dye removal results showed that the adsorption process increases when the concentration of nanoparticles increases. The adsorption process obeys Langmuir isotherm (R2 value were 0.994 and RL value lies between 0 and 1) and pseudo second order kinetics (R2 value were 0.998) more effectively. The isotherm and kinetic model confirmed that Mucuna bracteata based SNPs can be used as a suitable adsorbent for the removal of dyes from effluents.

Trace metal contamination in aquatic ecosystems is of significant concern in countries like India having a recent industrial history. The present study mainly focuses on the spatial and temporal distribution, occurrence and toxicity of five trace metals (Hg, Cd, Zn, Cu and Pb) in water and sediment matrix of Vembanad Lake system (VLS), India. Mercury analysis was done by using Cold Vapor Atomic Fluorescence Spectrometer, and the other metals were analysed using Volta metric-Trace metal analyser. The spatial distribution of trace metals in the study area showed the following trends, Zn > Pb > Cu > Cd > Hg, Zn > Pb > Cu > Hg > Cd for surface water and bottom water respectively. Health risk assessment on human population associated with trace metals was also calculated to predict their health impacts on human through non-dietary exposure. The trace metals contamination in water and sediments of VLS are potential to cause cancer on human population associated with the system. Ecological risk indices showed that the northern portion of VLS is more contaminated with trace metal than the other part of the system.

Progressive fragmentation of larger plastic debris due to the mechanical action of wind/waves, prolonged exposure to ultraviolet radiation, or biological degradation has led to the formation of microplastics or MPs (5 mm). MPs are pervasive in nature and hence, ubiquitous in distribution across the global marine systems. The Arctic Ocean, despite its remoteness, has been reported to contain a high concentration of MPs. However, studies on the presence of MPs in the sediment compartments of the Arctic Ocean are relatively lesser than that of the water column, surface water and Arctic fauna. Similarly, MP pollution of the Arctic fjords remains understudied. Here, we present the occurrence of MPs in the sediments of Kongsfjorden, an Arctic fjord in the Svalbard archipelago. Sediment samples from eight locations in Kongsfjorden, when analyzed, reveal the presence of MPs in three sites, with values ranging from 4 to 24 MPs/kg (dry weight) sediment. The highest number of MPs was observed at site K5 (24 particles/kg). On an average, 2.87 MPs/kg were recorded and their size ranged from 55 μm to 381 μm. Stereomicroscopic observation of MPs indicated fragment and fibers as the morphotypes of MPs. Polymer profile analysis with micro-Raman spectroscope confirmed high-density polyethylene (HDPE), low-density polyethylene (LDPE) and polyamide (PA) as the polymer components of the MPs found in the sediment samples. Of these, HDPE was the predominant polymer. Further detailed studies are needed to understand the source and the mechanisms involved in transporting MPs to the sediment and their impact on Arctic fjords.

Estimating the fractional distribution of sediment-bound heavy metals is highly significant for its ecological risk assessment in contaminated aquatic systems, since environmental factors enhance the mobility of heavy metals and its accumulation in different ecological matrices. In this study, the fractional distribution of Zn, Cd, Pb and Cu in the sediments of the Cochin estuary, along the south-west coast of India, was estimated along with its accumulation in four edible crustaceans. The high mobility of heavy metals in the Cochin estuary was evident from the distribution in fractions other than residual fraction. The exchangeable fractions of Zn and Cd were high in the Cochin estuary, indicating its high bioavailability. Even though the exchangeable fraction is negligible, Pb poses the risk of bioaccumulation due to the presence of oxidisable and reducible fractions. The level of heavy metals varies in different species of edible prawns, and high accumulation of all metals was observed in Metapenaeus dobsoni. Various risk assessment indices show that Cd and Pb pose significant ecological and human health risks in the Cochin estuary.

Estimating the fractional distribution of sediment-bound heavy metals is highly significant for its ecological risk assessment in contaminated aquatic systems, since environmental factors enhance the mobility of heavy metals and its accumulation in different ecological matrices. In this study, the fractional distribution of Zn, Cd, Pb and Cu in the sediments of the Cochin estuary, along the south-west coast of India, was estimated along with its accumulation in four edible crustaceans. The high mobility of heavy metals in the Cochin estuary was evident from the distribution in fractions other than residual fraction. The exchangeable fractions of Zn and Cd were high in the Cochin estuary, indicating its high bioavailability. Even though the exchangeable fraction is negligible, Pb poses the risk of bioaccumulation due to the presence of oxidisable and reducible fractions. The level of heavy metals varies in different species of edible prawns, and high accumulation of all metals was observed in Metapenaeus dobsoni. Various risk assessment indices show that Cd and Pb pose significant ecological and human health risks in the Cochin estuary.

United Nations Framework Convention on Climate Change highlights the significance of carbon storage and emission in forests towards climate change mitigation. The aim of this study was to quantify the tree biomass and carbon density (carbon storage) in the tropical dry forest of the Chinnar Wildlife Sanctuary of Kerala located in the Southern Western Ghats, India. We investigated the species-wise contribution of carbon (C) storage, as well as the species-wise and plot-wise correlation between carbon and other dendrometric variables. We also analysed the girth (diameter) wise distribution of carbon and tree density in the study region. The study was conducted in eight selected sample plots of the region, each with an area of 0.1 hectare. Species-specific volume and specific gravity relationship coupled with suitable regression equation were used to estimate biomass. Tree carbon was assumed to be 47% of the biomass. The results showed that the average biomass and carbon density of the vegetation were 64.13 t ha-1 and 30.46 t-C ha-1, respectively. Among the 32 species identified, Tamarindus indica L. (17%), Hardwickia binata Roxb. (14%), Terminalia arjuna (Roxb. ex DC.) Wight & Arn (10%) and Pleiospermium alatum (Wight & Arn.) Swingle (10%) were dominant as for carbon storage. The correlation analysis showed that basal area is a good predictor of tree biomass and carbon, while the role of tree density and tree diversity remain uncertain in determining carbon storage. With respect to diametric class distribution, tree density showed a reverse J-shaped pattern indicating the sustainable regeneration of the analysed forest, where the small- (diameter at breast height 3-9 cm) to medium-sized trees (diameter at breast height 10-69 cm) were found to contribute to more than 50% of biomass and carbon in the forest. The study provides useful information for carbon mitigation strategies in a tropical dry forest in the Southern Western Ghats.

The existence of Organochlorine pesticides (OCP's) and trace metals in tropical aquatic environments may cause a severe threat on account of their ubiquitous nature and long persistence. Monitoring of such contaminants has assumed immense significance in recent times. The present study assessed the OCP's and trace metal contamination in the surface sediments of the Vembanad wetland system in India. Various pollution indices were calculated to determine the sediment quality of the system and were also compared with uncontaminated sediments. Geo-accumulation index for Mercury varied from moderately to extremely polluted. The mean concentration of pesticide residues and trace metals in the sediments of Vembanad is found to be higher than in other aquatic systems in India. The situation demands further studies which focus on the potential bioaccumulation of OCPs and metals in the benthic food chain, succeeding biota and their impact on human consumption as the system supports a huge population for their livelihood. The Present study provides a baseline information on the spatial distribution of priority pollutants along with ecological risk status of Vembanad estuarine system (VES).

Phytoremediation is a promising option for the treatment of municipal solid waste leachate. Combining the leachate pollution index with the phytotoxicity data will be useful in predicting the suitable concentration of leachate for the phytoremediation applications. Understanding the tolerant mechanisms of plants to leachate stress will further help to select the appropriate dose. The aim of the study was to investigate the effect of different concentrations of leachate on germination, growth, chlorophyll content and antioxidant enzyme activities in the plant Vigna unguiculata. The crude leachate has an LPI value of 31.99 with high concentration of organic matter, ammonia and dissolved solids. The results of the phytotoxicity study suggest that at lower concentrations the leachate enhanced the germination and promoted plant growth. Up to 5% concentration (v/v) of the leachate which had a LPI value of 11.84 the growth promotion was observed in V. unguiculata. This was made possible by the controlled modulation of reactive oxygen species through the enhanced antioxidant enzyme activities. However at higher concentration, the pollutants in leachate disrupt the enzyme activities and leads to the peroxidation of membrane lipids and significantly affected the plant growth. The study suggest that phytotoxic effects in plants are directly related to the LPI value and leachate with LPI values less than 10 are likely to promote plant growth and LPI values greater than 10 are likely to exert detrimental effect on the plant.

We present the first study of microplastics in the sediments of Vembanad Lake, a Ramsar site in India. Microplastics are emerging pollutants of increasing environmental concern with a particle size of5 mm, which originate from successive degradation of larger plastic debris or are manufactured as small granules and used in many applications. The impact of microplastics pollution on the environment and biota is not well known. Vast data exist in the literature on marine microplastics while reports on freshwater ecosystems are scarce. In this context, to examine the occurrence of microplastic particles (MPs) in the Vembanad Lake, samples were collected from ten sites and processed for microplastic extraction through density separation. Identification of the polymer components of MPs was done using micro Raman spectroscopy. MPs were recovered from all sediment samples, indicating their extensive distribution in the lake. The abundance of MPs recorded from the sediment samples is in the range of 96-496 particles m

Mercury (Hg) contamination in aquatic systems is a universal concern because of its persistence, bioaccumulation, toxicity, and trans-boundary nature. The current study focuses on monitoring the fate and transport of Hg in aquatic matrices such as water, interstitial water, sediment and fish in a tropical coastal ecosystem. The cold vapour atomic fluorescence spectrometer was used for the Hg analysis. The study assessed the fractionation of Hg and its methylation potential in sediments. The high Hg concentration in fish tissues showed the ineffectiveness of biogeochemical control over the methyl Hg mobility and bioavailability through the food web. Research results indicate that the accumulation potential of Hg subsequently increases along the food chain. The conducive physico-chemical environment at the sediment–water interface supports chemical transformations/transport of Hg from one matrix to the next. The fate of Hg in the lake has also been discussed based on the data generated.

Sustainability is considered as a remedy for the environmental issues arising due to overconsumption of natural resources. In this context, the general household consumption pattern in India and—one of its states—Kerala has been studied for a period of 50 years. Generally Monthly Per capita Consumer Expenditure (MPCE) is linked with consumption, disparities in consumption pattern among different sectors of the society and sustainability at large. This study is based on the data from National Sample Survey Organization, Government of India. The findings of this study indicate that the MPCE has gone up for India and Kerala during the study period. The state of Kerala has an increased MPCE than the country; the rate of increase is twofold for its rural sector and 1.5 fold for the urban sector. Increased consumption consequent to urbanisation has been found to be the cause for the change in consumption pattern of Kerala.

Natural fibres have recently become attractive to scientific community as an alternative reinforcement for fibre reinforced polymer (FRP) composites. As compared to conventional fibres, such as glass and carbon FRPs have low cost, fairly good mechanical properties, ecofriendly and bio-degradability characteristics. In the present work, bio based nanocomposites were successfully developed using cellulose nano whisker as filler in natural rubber latex by water evaporation method. The cellulose nano whisker were prepared from “Moringa oleifera” (Drum Stick vegetable Fibre) by acid hydrolysis. The morphology of cellulose whiskers/NR nanocomposites was investigated by Scanning Electron Microscope. The presence of nano cellulose whiskers (CW) in the NR matrix was observed by using Fourier transfer-infra red (FTIR) spectroscopy. The tensile properties such as tensile strength, tensile modules and elongation at break were measured by Universal Testing Machine. Thermal degradation of the nanocomposites were also analyzed using thermal gravimetric analysis (TGA). The result of the study shows that CW in the nanocomposites prepared during this study are randomly oriented and distributed homogeneously throughout the matrix. The FTIR analysis provided clear evidence of the presence of nano CW in the NR matrix that can be observed by the absorption peaks at 1033 and 1057 cm−1 assigned to C–O stretching of cellulose and TGA analysis showed the thermal stability of the nanocomposites increased with increasing CW, tensile strength and modulus values were also increased with CW addition. Hence the present study shows that the cellulose nano whiskers from Moringa oleifera has improved the properties of natural rubber based composite and can be considered as a good natural reinforcing material for future applications.

The scarcity of freshwater has emerged as one of the most pressing problems of the 21st century. This problem could be addressed partially by collection, treatment and reuse of greywater. In this context, constructed wetlands (CWs) become attractive due to their simple mode of operation, effectiveness in treatment and applicability at small/single household levels as well as in community levels. Hence the present study investigates the treatment of greywater in a laboratory scale horizontal sub-surface flow constructed wetland planted with Axonopus compressus (Sw.) P. Beauv. – a common landscape plant. The experiment was conducted for a period of 50 days with change in wastewater every 10 days (1 run). During each run the wastewater was circulated using a peristaltic pump at an HRT of 7.8 h. The results show that CWs planted with A. compressus performed well in the treatment of greywater than the unplanted control with an average removal of 93% turbidity, 95% COD, 98% NO 3 − –N, 67% PO 4 3− –P, and 95% of anionic surfactants. The plant also survived well with increase in biomass and number during the experiment and proved to be an efficient bioagent suitable for the treatment of greywater in CWs. The study further suggests that the use of commercially valuable ornamental plants in the CWs as bioagents will improve the aesthetic beauty, public acceptance and help to generate revenue apart from the major benefit of wastewater treatment.

Contamination of estuarine system due to heavy metals is a severe issue in tropical countries, especially in India. For the evaluation of the risk due to heavy metals, the current study assessed spatial and temporal variation of acid-volatile sulfide (AVS), simultaneously extracted metal (SEM), and total metal concentration as toxicity indicator of aquatic sediments in Vembanad Lake System (VLS), India. Surface sediment samples collected from 12 locations from the northern portion of VLS for 4 years during different seasons. The results suggest, in post-monsoon season, 91% of the sampling locations possessed high bioavailability of metals and results in toxicity to aquatic biota. The average seasonal distribution of SEM during the period of observations was in the order post-monsoon > pre-monsoon > monsoon (1.76 ± 2.00 > 1.35 ± 0.60 > 0.80 ± 0.54 μmol/g). The concentration of individual metals on ∑SEM are in the order SEM Zn > SEM Cu> SEM Cd ≈ SEM Pb > SEM Hg. Considering annual ΣSEM/AVS ratio, 83% of the sites cross the critical value of ‘One,’ reveals that active sulfide phase of the sediment for fixing the metals is saturated. The molar ratio (differences between SEM and AVS) and its normalized organic carbon ratio reveals that in the post-monsoon season, about 42% of the sites are in the category of adverse effects are possible. The study suggests the toxicity and mobility of the metals largely depend on the available AVS, and the current situation may pose harm to benthic organisms.

Mercury contamination in the water bodies of developing countries is a serious concern due to its toxicity, persistence, and bioaccumulation. Vembanad, a tropical backwater lake situated at the southwest coast of India, is the largest Ramsar site in southern India. The lake supports thousands of people directly and indirectly through its resources and ecosystem services. It is highly polluted with toxic pollutants such as heavy metals, as it receives effluent discharges from Kerala's major industrial zone. In the present study, water, pore water, sediment, and fish samples collected from Vembanad Lake were analysed for total mercury (THg) and methyl mercury (MHg) contents. The maximum concentrations of THg and MHg in surface water samples were31.8 and 0.21 ng/L, respectively, and those in bottom water samples were 206 and 1.22 ng/L, respectively. Maximum concentration of THg in surface sediment was observed during monsoon season (2850 ng/g) followed by that in the pre-monsoon season (2730 ng/g) and the post-monsoon season (2140 ng/g). The highest sediment concentration of MHg (202.02 ng/g) was obtained during monsoon season. The spatial variation in the mercury contamination clearly indicates that the industrial discharge into the Periyar River is a major reason for pollution in the lake. The mercury pollution was found to be much higher in Vembanad Lake than in other wetlands in India. The bioaccumulation was high in carnivorous fishes, followed by benthic carnivores. The THg limit in fish for human consumption (0.5 mg/kg dry wt.) was exceeded for all fish species, except for Glossogobius guiris and Synaptura orientalis. The concentration of THg was five times higher in Megalops cyprinoides and four times higher in Gazza minuta. Significant variation was observed among species with different habits and habitats. Overall, risk assessment factors showed that the mercury levels in the edible fishes of Vembanad Lake can pose serious health impacts to the human population.

Heavy metal contamination of water bodies and groundwater is a major concern of the modern world. Rhizofiltration--the use of plant root system to remove/extract pollutants from wastewater--has proven advantages over conventional methods of treatment. However, commercialization of this in situ remediation technology requires a better understanding of plant-metal interactions especially on the ability of different plant species to accumulate metals at different parts of the plant system which is critical for the successful remediation of contaminated medium. Many aquatic and terrestrial plants have been reported to accumulate heavy metals when grown hydroponically. Therefore, a batch experiment with different concentrations of lead and a nutrient film technique (NFT) experiment with recycling of wastewater were employed in this study in order to investigate the rhizofiltration of lead-containing wastewater using Plectranthus amboinicus, an aromatic medicinal plant. Results show that P. amboinicus is tolerant to a wide range of lead concentrations and nutrient deficiency. The plant accumulates considerable amount of lead, particularly in the roots, and translocation to the stem and leaf was limited, indicating that the use of leaves/above-ground parts of the plant for medicinal purposes is not hindered by its ability to remove lead from the soil or water. The study also suggests that the plant can be considered for the clean-up of lead-contaminated wastewater in combination with safe biomass disposal alternatives.

The sedimentary record of trace metals in Cochin Estuary (Southwest coast of India) during the past few decades have evaluated by analyzing core sediment and examined their ecological risk. The collected cores were examined for the depositional trends, metal enrichment, and distribution of organic carbon. Sedimentation rate was determined using the 210Po/210Pb isotope method. Chronological study reveals that Core I has aged between 1940’s to the present and Core II has been formed since 1880’s. For Core I, the average sedimentation rate obtained is 1.27 ± 0.52 cm/year, and for the Core II, it is 1.19 ± 0.23 cm/year. Both the core samples have shown similar down core distribution pattern of metals and are in the order of Zn > Cu > Pb > Cd. Metal concentration of the core samples displays an increasing trend from the bottom layer to successive upper layers. A notable variation was observed on both the core sample from 30 cm depth to the surface. The results of this study assume that the metal contamination issue of the lake system has been mounting after the industrialization of 1940's. The increase in elemental concentration after 1990's demonstrates the progressive increment and recent addition of metallic contaminants. Present study suggests regional specific preindustrial background concentration of Zn, Pb, Cu, and Cd, which can be utilized for monitoring sediment quality of the estuarine systems in India.

The presence and distribution of a few organochlorine pesticides (OCPs) in the paddy fields of the Kuttanad agroecosystem (KAE) was examined in the present study. Kuttanad forms a part of the Vembanad wetland system which is a Ramsar site of international importance in the state of Kerala. This study, to the best of our knowledge, is the first report on the occurrence of OCP residues in KAE. Pesticide residue analysis was done with gas chromatograph (GC-ECD). Twenty-one soil samples were collected for the multiresidual analysis of OCPs. Sixteen OCP residues with a notable concentration were observed from the study area. α-BHC; β-BHC; γ-BHC; δ-BHC; α-chlordane; γ-chlordane; heptachlor; 4,4-DDT; 4,4-DDE; 4,4-DDD; α-endosulfan; β-endosulfan; aldrin; dieldrin; endrin aldehyde; and endrin ketone were the residues observed. The percentage-wise occurrence of OCP residues in the soil samples analysed (total of 63 samples from 21 sites, three samples per site) exhibits the following order: Σ BHC˃ Σ chlordane ˃ Σ dieldrin ˃ Σ aldrin ˃ Σ endrin˃ Σ heptachlor = endosulfan˃ Σ DDT. All pesticides detected from KAE are in the list of priority pollutants of US Environmental Protection Agency (USEPA). The distribution pattern of OCPs in the KAE soils revealed their origin as both historical and recent application of pesticides. Health risk assessment of OCP residues on human population was also conducted. The findings indicated that the concentrations of OCPs were within the permissible limits of USEPA, thus, the human population in the study area was safe.

Species diversity of earthworms in tropics is less studied compared to those of the temperate regions. Despite the fact that there have been numerous studies on earthworm diversity in the Western Ghats of India, there still exists scope for more earthworm species which are yet to be described. The present work involves a survey of earthworms in the Nilgiri biosphere reserve (NBR)—a part of a biodiversity hot spot of Western Ghats. Despite being a part of the biodiversity hot spot, studies on earthworm diversity at NBR are very limited. Unless an authentic record of earthworm species is made available, the consequence of human interference, habitat alteration or climate change on the species diversity cannot be assessed. An attempt has been made in this study to conduct a survey of earthworm species available in the selected forest ecosystems of the NBR. The findings of this study have shown that 84.67 % of the earthworm species identified is native, while the rest are exotic. On the basis of total number of earthworms collected, exotics accounted for 1.55 %, indicating the predominance of native species in the study area and indicating that this habitat is less disturbed. Among the species identified from Mukurthi, Priodochaeta pellucida is listed as vulnerable and has never been encountered since its discovery about 100 years ago. Shannon–Weiner indices showed that evergreen forests of Silent Valley have a high species diversity as do shola/grasslands of Mukurthi and moist deciduous forests of Muthanga.

Transformations among different mercury species associated with sediments can have a major effect on the metal's mobility and potential for methylation and hence bioaccumulation. In the present study, various fractions of mercury in the sediments of Vembanad wetland system analysed. Total mercury (THg) concentration in the surface sediment varied from 16.3 to 4,230 ng/g. The results of sequential extraction showed that the major portion of mercury in these sediments existed as elemental form followed by organo-chelated form. The least portion observed was the residual fraction (mercury of natural origin). Even though the percentage of mercury observed in the easily available fractions is relatively small, absolute values of these mobile Hg fractions are quite high due to the very high total mercury values. The fractionation of mercury in the sediment was controlled by the organic matter, sulphur complexes and concentration of THg. The results showed that the bioavailability of mercury is high as the amount of mercury found in the initial three fractions is high, which can also enhance the methylation potential of the Vembanad wetland sediments. The fractionation pattern of mercury also revealed the presence of anthropogenic mercury content in the Vembanad wetland sediments.

Cochin estuary is one of the highly polluted aquatic systems of the southwest coast of India. The present study focuses on the assessment of heavy metals (Zn, Cd, Pb, and Cu) present in the sediments of Cochin estuary and the adjoining Periyar River. The sediments were analyzed for total metal content and various chemically bound fractions such as exchangeable, carbonate bound, easily reducible, organic, and residual. Total metal content of sediment was found higher than the average values reported from other Indian rivers. The mean concentration of Zn, Cd, Pb, and Cu in the sediments was 1,249.44, 9.5, 221.37, and 166.14 μg/g, respectively. The results of sequential extraction showed that the concentration of Cd was high in the first two weakly bound fractions (exchangeable and carbonate bound) than the other metals, which are high in residual and organic bound fractions. Risk-assessment code analysis and environmental indices (enrichment factor and pollution load index) suggest that the sediments are highly polluted with metals, especially Cd.

Mercury, a global pollutant, has become a real threat to the developing countries like India and China, where high usage of mercury is reported. Mercury and other heavy metals deposited in to the aquatic system can cause health risk to the biota. The common edible fishes such as Mugil cephalus, Arius arius, Lutjanus ehrenbergii, Etroplus suratensis were collected from Cochin backwaters, Southwest India and analysed for mercury and other heavy metals (zinc, cadmium, lead and copper) in various body parts. Kidney and liver showed highest concentration of metals in most fishes. The omnivore and bottom feeder (E. suratensis) showed high concentration of mercury (14.71 mg/kg dry weight) and other metals (1.74 mg/g—total metal concentration). The average mercury concentration obtained in muscle was 1.6 mg/kg dry weight (0.352 mg/kg wet weight), which is higher than the prescribed limits (0.3 mg/kg wet weight). The concentration of other heavy metals in the muscles of fishes were found in a decreasing order Zn>Cu>Cd>Pb and are well below WHO permissible limits that were safe for human consumption. Metal selectivity index (MSI) obtained for all the metals except mercury showed that both carnivores and omnivores have almost same kind of affinity towards the metals especially Zn and Cd, irrespective of their feeding habit. The MSI values also indicate that the fishes have the potential to accumulate metals. High tissue selectivity index (TSI) values were reported for kidney, muscle and brain for all metals suggests that the metal concentration in these tissues can serve as an indication of metal polluted environment. Even if the daily intakes of Zn, Cd, Pb and Cu from these fishes are within the provisional maximum daily intake recommended by WHO/FAO, the quality is questionable due to the high hazard index obtained for mercury (>1). Fishes like E. suratensis being a favourite food of people in this region, the high consumption of it can lead to chronic disorders as this fish has high concentration of metals.

The structure, function, and ecosystem services of tropical forest depend on its species richness, diversity, dominance, and the patterns of changes in the assemblages of tree populations over time. Long-term data from permanent vegetation plots have yielded a wealth of data on the species diversity and dynamics of tree populations, but such studies have only rarely been undertaken in tropical forest landscapes that support large human populations. Thus, anthropogenic drivers and their impacts on species diversity and community structure of tropical forests are not well understood. Here we present data on species diversity, community composition, and regeneration status of tropical forests in a human-dominated landscape in the Western Ghats of southern India. Enumeration of 40 plots (50 m × 20 m) results a total of 106 species of trees, 76 species of saplings and 79 species of seedlings. Detrended Correspondence Analysis ordination of the tree populations yielded five dominant groups, along disturbance and altitudinal gradients on the first and second axes respectively. Abundant species of the area such as Albizia amara , Nothopegia racemosa and Pleiospermum alatum had relatively few individuals in recruiting size classes. Our data indicate probable replacement of rare, localized, and old-growth ‘specialists’ by disturbance-adapted generalists, if the degradation is continuing at the present scale.

The toxicity and bioaccumulation of two heavy metals—lead (Pb) and cadmium (Cd)—in a semi-aquatic plant, Colocasia esculenta (L. Schott), from a synthetic heavy metal solution were studied. Young plants of equal size were grown hydroponically in shallow raceways containing Hoagland medium amended with 20, 40, and 60 mg l−1 of Pb and 2, 4, and 6 mg l−1 of Cd. The medium containing heavy metals was allowed to flow through the raceways with a change in influent heavy metal solution on every 5th day. The experiment was continued for 20 days. A set of control raceways—one comprised of nutrient medium with heavy metal supplements, devoid of plants, and another with the plants and nutrient medium having no metal supplement—was also simultaneously run. Chlorosis in the leaves was the prominent toxicity symptom observed due to Pb and Cd on the test plants. A significant decrease in the relative growth, biomass productivity, and total chlorophyll content were noticed in the plants with an increase in concentration of metal supplement in the solution and exposure time. Both metals accumulated to higher concentrations in the roots than in shoots, suggesting that the metals were bound to the root cells and their translocation to the leaves was limited. The results of the 20-day-long experiments indicate that from a phytoremediation perspective, C. esculenta is a promising plant species for remediation of wastewater polluted with lower concentrations of Pb and Cd.

Changes in tree and understory plant diversity and community composition in two sites at different disturbance levels were studied on the Anaikatty hills, Western Ghats. Systematic sampling using small scale permanent quadrates (50 x 20 m for trees, 5 x 5 m for shrubs/saplings, 1 x 1 m for herbs/seedlings) enumerated 3,376 individuals of trees (106 species), 8,599 of individuals shrubs (122 species) and 16,659 individuals of herbs (145 species). Among the two sites, species richness and diversity were highest for low disturbed stand (98 and 3.9, respectively) compared to high disturbed site (45 and 2.71, respectively). Result of cluster analysis showed that two distinct clusters were formed on the basis of disturbance of the area in concordance with our field observation. A total of 37 species were common to both sites, sixty one species exclusively found in low disturbed site and eight species were pertained to highly disturbed site. Mann-Whitney test based on Monte Carlo approximation at 95% confidence levels indicated that both populations were not entirely different. The clear difference was only observed for average basal area of trees, density of seedlings, number of species, density and diversity for shrubs and number of species and diversity for herb. The species composition were different in two stand i.e., Nothopegia racemosa-Albizia amara-Maba neilghrrensis in low disturbed stand and Albizia amara-Pleiospermium alatum-Bauhinia racemosa in high disturbed stand. The major disturbance factors identification using spearman rank correlation indicated that the disturbance in low disturbed habitats were mostly from past logging followed by cutting and illicit felling and grazing, while in high disturbed habitats, it was human presence, past logging and lopping and fuel wood collection.

An aquatic macrophyte-based wastewater treatment study was carried out to investigate the nutrient removal efficiency of Colocasia esculenta, a common semi-aquatic macrophyte. Domestic sewage was used as the wastewater in this study. Apart from the removal of nutrients, the stabilisation of the organic matter present in the wastewater was also assessed in terms of COD removal. The plants were cultured in shallow raceways supported by a gravel bed substratum and the wastewater was allowed to flow through the raceways continuously in subsurface flow (SSF) mode. This experiment was conducted for 20 days with a change of wastewater every 20th day initially and every 5th day at a later stage of the experiment. Control raceways without plants were also operated. The results of the study revealed that the subsurface flow systems planted with C. esculenta could decrease the nitrate and phosphate content of the wastewater, besides organic matter. The quality of treated water from the raceways with plants was better than those without plants. Also C. esculenta was found to resist COD concentration as high as 1650 mg l−1.

Studies are presented on new types of anaerobic digesters in which chopped or dry crushed Ipomoea carnea was fed without any other pretreatment, in an attempt to develop commercially viable means of utilizing the otherwise very harmful plant. Two types of solid-feed anaerobic digesters (SFADs) were studied. The first type had a single vessel in which the bottom 35% portion was separated from the top portion by a perforated PVC disk. The weed was charged from the top and inoculated with anaerobically digested cowdung-water slurry. The fermentation of the weed in the reactor led to the formation of volatile fatty acids (VFAs) plus some biogas. The leachate, rich in the VFAs, was passed through the perforated PVC sheet and collected in the lower portion of the vessel. The other type of reactors had two vessels, the first one was fully charged with the weed and the second received the VFA leachate. With both types were attached upflow anaerobic filters (UAFs) which converted the leachate into combustible biogas consisting of approximately 70% methane. All SFADs developed very consistent performance in terms of biogas yield within 17 weeks of start. The two-compartment reactors yielded significantly more biogas than the single-compartment reactors of corresponding total volume, and the reactors with which anaerobic filters (AF) were attached yielded more biogas than the ones without AF. The best performing units generated 2.41m(3) of biogas per m(3) of digester volume, as compared to 0.1-0.2m(3) of biogas, m(-3)d(-1), obtainable with conventional digesters. This indicates the viability of this technology. The spent weed can be vermicomposted directly to obtain good soil-conditioner cum fertilizer; earthworm Eudrilus eugeniae produced 540mg vermicast per animal every day, achieving near total conversion of feed to vermicast in 20 days. The proposed systems, thus, makes it possible to accomplish total utilization of ipomoea.

We present studies on solid-feed anaerobic digesters (SOFADs) in which chopped Colocasia esculenta was fed without any other pretreatment, in an attempt to develop an efficient means of utilizing the semi-aquatic weed that is otherwise an environmental nuisance. Two types of SOFADs were studied. The first type had a single vessel with two compartments. The lower portion of the digester, 25% of the total volume, was separated from the upper by a perforated PVC disk. The weed was charged from the top and inoculated with anaerobically digested cow dung–water slurry. The fermentation of the weed in the digester led to the formation of volatile fatty acids (VFAs) plus some biogas. The bioleachate, rich in the VFAs, passed through the perforated PVC disk and was collected in the lower compartment of the digester. The other type of digesters, referred to as anaerobic multi-phase high-solids digesters (AMHDs), had the same type of compartmentalized digester unit as the first type and an additional methaniser unit. Up-flow anaerobic filters (UAFs) were used as methaniser units, which converted the bioleachate into combustible biogas consisting of ∼60% methane. All SOFADs developed a consistent performance in terms of biogas yield within 20 weeks from the start. Among the two types of digesters studied, the AMHDs were found to perform better with a twofold increase in biogas yield compared to the first type of digesters.

Microbial fuel cells (MFCs) are an emerging type of biological wastewater treatment units with simultaneous power generation. The present study demonstrates an effective treatment of greywater and generation of electricity in a double-chambered MFC. This MFC was fabricated using cost-effective and easily available materials replacing expensive materials like Nafion membranes, graphite electrodes, etc. Experimental results showed a maximum open circuit voltage of 0.64 ± 0.04 V and 114 ± 1.41 mA current during the study period. The results further indicate a maximum power generation of 24.50 mW along with 307.69 mW/m² of power density; 34.62 mA/m² of current density, 1.33 W/m³ of volumetric power density, 0.15 A/m³ of volumetric current density and a power yield of 0.40 mW /kg of COD removal. The chemical oxygen demand (COD) removal efficiency was 77.6 %. The use of low-cost and easily available raw materials has brought down the total manufacturing cost of MFCs used in this study to less than USD 4.0. However, the performance of the MFCs used in the current study is comparable with other sophisticated MFCs built with expensive raw materials reported in the literature. This cost-effective MFC used in the present study might be an effective replacement of expensive MFCs for wastewater treatment at scaled-up levels. DOI: http://dx.doi.org/10.5755/j01.erem.71.3.11482

A procedure has been developed for extracting volatile fatty acids (VFAs) from water hyacinth (WH) using simple and inexpensive equipment of the type commonly available in the rural households of the third world countries. The VFAs thus extracted were used as feed supplement in cow dung-fed floating-dome biogas digesters. As tens of thousands of such digesters are in operation across the third world, the aim of these studies has been to provide for such digesters feed derived from phytomass, especially for use whenever animal dung is in short supply or is unavailable. The VFA extraction was based on aerobic/facultative degradation of water hyacinth and significant quantities were extracted from each WH charge daily for upto 6 days. When cow-dung slurry was fortified with the VFAs and fed to a conventional biogas digester, it yielded about 22% higher quantity of biogas per unit feed than was obtained from equivalent mass (dry weight basis) of the unfortified cow-dung slurry. The technique developed by us enables phytomass to be utilized as feed supplement in biogas digesters without causing the problems of solids accumulation, frothing and clogging known to be associated with phytomass feed. After VFAs have been extracted from it, the ‘spent’ water hyacinth was vermicomposted and used as soil conditioner-cum-fertilizer.

Litter of the mango (Mangifera indica) tree leaves was composted and then converted into vermicast by the action of the earthworm Eudrilus eugeniae Kinberg. After over nine months of continuous operation the vermireactors with 62.5 animals l(-1) generated approximately 13.6g vermicast per litre of reactor volume (l) per day (d) whereas the reactors with 75 animals l(-1) produced approximately 14.9 g vermicast l(-1) d(-1). This difference in performance of the reactors operating in duplicate at the two different earthworm densities was statistically significant (or = 90% confidence level) for most of the nine-month span. The animals grew well in all reactors, increasing their zoomass by approximately 103% and producing approximately 157 offspring. Not a single of the 1100 animals died during the first four months. In the subsequent five months a total of 122 worms died, representing a loss of approximately 2% per month. We attribute this to the normal process of ageing. The ability of the earthworms to survive, grow and breed in the vermireactors fed with composted mango tree leaves, and a rising trend in vermicast output inspite of the death of a few worms after four months of reactor operation, indicate the sustainability of this type of vermireactors. The studies also indicate that even better vermireactor efficiency may be possible by modifying the reactor geometry. Studies on changes in C:N ratio during composting and vermicomposting revealed that whereas composting helped in lowering the ratio due to loss of carbon in bacterial metabolism, vermicomposting had no such effect on the ratio.

The viability of vermireactors fed with different proportions of water hyacinth (WH) and cowdung (CD) was assessed over six-month trials. All reactors performed sustainably with a steadily rising vermicast output, worm zoomass, and number of offspring. There was no mortality in any of the reactors. A change in the WH:CD ratios from 4:1 to 6:1 had no discernable impact on the reactor performances. Attempts were also made to improve the efficiency of the reactors in terms of vermicast production per unit time and per unit digester volume. These attempts led to the 'high-rate' vermireactor in which 5.6 times greater vermicast was produced per litre of digester volume per day than in the 'low-rate' reactors. The high-rate vermireactors also performed sustainably, with steady vermicast output, animal growth, and reproduction.

Paper waste, spiked with varying proportions of cowdung, was vermicomposted in `low-rate' and `high-rate' reactors. The former type of reactors had earthworm populations and feed loading rates similar to ones recommended by previous workers. The `high-rate' reactors were operated with 12.5 times higher earthworm densities and feed loading rates. All the reactors were studied for six months to assess the vermicast output, survivability, growth and reproduction of the earthworms – hence the sustainability of the reactors – for long-term, continuous operation. The studies revealed the viability of the high-rate vermireactor concept. The high-rate reactors consistently produced over 6.5 times more castings per unit digester volume with no adverse effect on the earthworm population, as reflected by (a) absence of mortality, (b) consistent growth in worm zoomass, and (c) normal rate of reproduction. The studies also revealed that an increase in the cowdung fraction in the feed from 14.3% to 20% (4:1 paper:cowdung blends to 6:1 blends) had little positive impact on the vermicast output or earthworm health. This indicated that spiking of paper feed with ∼14% cowdung, or perhaps an even smaller fraction, might be adequate to support earthworms in the paper-fed vermireactors.

Four specices of detritivorous (humus-former) earthworms were tested for their ability to vermicompost paper waste blended with cowdung in 6:1 (w/w) ratio. The anecic Lampito mauritii, Kinberg and the epigeic Eudrilus eugeniae, Kinberg were the most effective of the four species employed; 20 animals of each of these species generated castings amounting to about 52% of the feed mass (75 g) per fortnight. The performance of these two species was followed by the anecic Drawida willsi, Michaelsen and the epigeic Perionyx excavatus, Perrier; they achieved approximately 46% vermiconversion in comparable settings. The vermireactors were sustainable as the animals have remained consistently healthy and reproductive over a period of six months, and are continuing to remain so, turning in a steadily rising vermicast output. During this period E. eugeniae have grown to 2.3 times their original weight while the other three species have more than trebled their weights. The studies establish the feasibility of vermicomposting as a viable process for the gainful utilization of paper waste in an environmentally clean manner. They also indicate that all the four species of the worms screened by us are suitable for the process, with L. mauritii and E. eugeniae a shade more efficient than the other two species.

Anaerobic digestion is one of the major steps involved in the treatment of dairy industry waste-waters and many CSTRs (continuously-stirred tank reactors) are functioning for this purpose all over the world. In this paper, the authors describe their attempts to upgrade a CSTR's performance by incorporating a biofilm support system (BSS) within the existing reactor. The focus of the work was to find an inexpensive and easy to install BSS which could significantly enhance the rates of waste treatment and methane recovery. Rolls of nylon mesh (with ∼1 mm openings), of 5 cm height and 2 cm dia, when incorporated in the CSTR at the biofilm surface (with a digester volume ratio 0.3 cm2/cm3), enabled the CSTR to perform better with > 20% improvement in the methane yield. Such simple BSS devices can significantly improve the performance of a CSTR anaerobic digester treating dairy wastes. The enhancement is due to the development of active biofilms which not only enhance the microorganism-waste contact but also reduce the microbial washout. Such devices are inexpensive and very easy to incorporate — the gains are thus achieved with very little cost and effort.

Anaerobic digestion of municipal solid waste (MSW) was studied in ‘high solids digesters’ (HSDs) for generating energy (as methane). Three kinds of HSDs were employed in which the waste along with inoculum (consisting of pre-digested cow dung slurry) were subjected to anaerobic digestion. The first type (HSD-I) was provided with two chambers; the upper chamber served as a solid phase in which only the solid portions of vegetable waste were subjected to digestion, while the lower chamber served as liquid phase where the leachates were allowed to ferment. The second type (HSD-II) was similar to HSD-I but had no partition. The third type (HSD-III) had two distinct units, one for solid phase and the other for the liquid phase; the units were connected by a tap with a flow regulator valve. The reactor performance was assessed in terms of biogas yield. The results of the study indicate that the performance efficiency (in terms of biogas yield) of the HSDs increased with the increase in the degree of phase separ...

Mercury, a global pollutant, is popping up in places where it was never expected before and it burdens in sediments and other non-biological materials. It is estimated to have increased up to five times the pre-human level due to anthropogenic activities. Vembanad backwaters, one of the largest Ramsar site in India, which have extraordinary importance for its hydrological function, are now considered as one of the mercury hot spots in India. In this study, surface sediment samples of Vembanad Lake and nearshore areas have been seasonally analysed for total mercury and methyl mercury concentrations while the core sediment samples were analysed for total mercury. The results showed that the northern part of the lake was more contaminated with mercury than the southern part. The mercury concentration was relatively high in the subsurface sediment samples, indicating the possibility of historic industrial mercury deposition. A decreasing trend in the mercury level towards the surface in the core sediment was also observed. The geochemical parameters were also analysed to understand the sediment mercury chemistry. Anoxic conditions, pH and organic carbon, sulphur and Fe determined the presence of various species of mercury in the sediments of Vembanad Lake. The prevailing physical and geochemical conditions in Vembanad Lake have indicated the chances of chemical transformation of mercury and the potential hazard if the deposited mercury fractions are remobilised.

The concentration of heavy metals in the environment is increasing at an alarming rate due to the high rate of industrialisation and intensive agricultural practices over the past few decades. Since most of the heavy metals are persistent and toxic in nature, they significantly reduce agricultural productivity and pose severe threat to human beings through food chain contamination. In recent years, phytoremediation has gained considerable attention as a solar driven green technology for the removal of heavy metals. In the present study we examined the Cadmium (Cd) removal potential of Macaranga peltata - one of the woody species emerging in early successions ‐ found very common in Kerala. The experiment was conducted in batch mode for a period of 20 days in three different concentrations of Cd (0.5, 1.5, and 2.5 mg/L) in two different mediums (distilled water and 10% Hoagland nutrient solution). The percentage removals of Cd by M. peltata from three treatments in distilled water were 98, 93 and 89% respectively, where as in the case of Hoagland nutrient medium it was 90, 89 and 82% respectively. The results show higher removal efficiency in distilled water as compared to Hoagland nutrient medium. The analysis of the plants revealed that most of the Cd was accumulated in the roots followed by stem and leaf. Cd accumulation also affected the chlorophyll content of the plant at higher concentrations. The study shows that M. peltata is a promising plant for the phytoremediation of Cd. Since most of the earlier studies on phytoremediation were carried out using smaller plants with less biomass production and growth rate, the use of M. peltata -one of the fastest growing tree species in the present study receives special attention.