R. Mohanraj

Heavy metal partitioning in sediments and bioaccumulation in commercial fish species of three major reservoirs of river Cauvery delta region, India

Chemical partitioning of heavy metals (Fe, Mn, Cu, Cr, Pb, Zn, Ni) were determined in surface sediments of three reservoirs at the Delta region of Cauvery River, India. The abundance of metals in sediments varied in the following descending order: Fe, Mn, Cr, Zn, Cu, Ni, and Pb. Higher concentrations of Zn, Pb, Fe, Mn and Cu in exchangeable and carbonate fraction indicated toxicity risk to the biota. Therefore, to understand the extent of bioaccumulation, six commercial fish species were collected from the same sites and analyzed for heavy metals distribution in different organs. Among the metals found in fish samples, iron was observed in the highest concentration, followed by Zn, Pb, Cr, Mn, Cu, and Ni. Concentrations of Pb, Cr and Zn in many fish samples exceeded the permissible limits of Food and Agriculture Organization. The concentrations of Pb (17.7-31.7%), Cr (6.2-15.1%), Cu (15.2-30.5%) and Zn (30-40%) associated with exchangeable and carbonate fractions had significant positive correlation with the respective metal concentrations in fish. Among the fish species, Catla catla and Etroplus suratensis showed the highest accumulation of metals suggesting risk for human consumption.

GIS-Based Modified SINTACS Model for Assessing Groundwater Vulnerability to Pollution in Vellore District (Part of Palar River Basin), Tamil Nadu, India

Though traditionally considered to be less vulnerable to pollution than surface water, the groundwater resources face multiple sources of contamination during the recent times. In this paper, we employed modified SINTACS (Normal and Severe) model over a region known for thick clusters of leather processing industries, and dependence of domestic and industrial water supply on groundwater resources. Several parameters including, depth to groundwater, effective infiltration, unsaturated zone attenuation capacity, soil attenuation capacity, hydrogeological characteristics of the aquifer, hydraulic conductivity and topographical slope were spatially evaluated and subjected to overlay analysis after assigning appropriate ratings and weights to identify the different vulnerability levels in the study area. The results show that, the groundwater vulnerability to pollution is very high on the eastern part of the study area, under the influences of gentle slope, alluvial soil and higher permeability. In addition, scattered occurrences of vulnerable zones aligned along the river course are also identified.

Toxicity of Neonicotinoid Pesticide Imidacloprid and Impediment of Ecosystem Services

In agro-ecosystems, pollinators perform a variety of ecological services. The ecological role of pollinators and their ecosystem services are critical to the health of many ecosystems. Pollination by birds and bees are recognized as an important ecosystem function maintaining the dynamics of agro-ecosystems. As agriculture covers a significant portion of the globe, it necessitates the evaluation of their ecosystem services. There are overwhelming evidence that pollinators are experiencing tremendous population decline. Global agricultural encroachment, agriculture intensification, changes in cropped pasture, urban development and extensive use of pesticides are the major threats to farmland birds. Despite ecological importance and global awareness, farmland birds and bees are often considered as species of low conservation value. The worldwide use of neonicotinoid insecticides has raised concern over the decline of pollinators in the farmlands globally. Neonicotinoids are neurotoxins, applied to variety of agricultural crops to control sucking and biting pests and are readily incorporated into plant cells, inclusive of pollen and nectar. Among neonicotinoids, imidacloprid is found to have startling effects, disrupting several ecosystem services, inhibiting pollination and threatening global food security. The study focuses on imidacloprid and its wider risk to the environment with effects on non-target pollinators especially birds and bees. Some of the effects on bees include disrupting social behavior, foraging and altered navigation and in birds reduced reproduction and offspring immunity. Though the scientific community is intently examining the potential effects of imidacloprid on pollinators, the research warrants further investigations with field-realistic concentrations and at relevant exposure levels. This would facilitate the functioning of pollinators and promote sustainable agriculture by reducing the impact of neonicotinoids. This review summarizes the potential lethal and sublethal effects of neonicotinoid pesticide imidacloprid on pollinators and other invertebrate groups and also helps us to better understand the extent of their toxicity.

Species Diversity and Functional Assemblages of Bird Fauna along the Riverine Habitats of Tiruchirappalli, India

Riverine ecosystems have complex relationship with human since time immemorial and play an integral role in the socio-economy of a region. However, many riverine habitats, particularly within urban centers in the developing countries are subjected to overexploitation that affects the natural ecological processes and functions of rivers. Such perturbations in riverine habitats are often linked to biodiversity loss. Birds discharge crucial ecosystem services and are closely associated to wetlands and rivers for their survival. This study attempts to document the bird diversity and their community assemblages along the riverine habitats in relation to urban effects, vegetative attributes, seasonal parameters and other anthropogenic pressures. The study finds that bird diversity and species richness were higher in the rural landscape and gradually decreased towards the urban region. A total of 120 bird species consisting of two ‘Near Threatened’ were recorded along the riverine habitats of the River Cauvery. Few species (Egretta garzetta and Phalacrocorax niger), were found to be densely populated and adapted to the urban environment while few others declined. Salient features of the results include: seasonality did not affect the variability of the riverine species and the difference in composition of birds during the wet and dry seasons were insignificant. While the factors namely, tree cover, tree height, and number of trees were found to be positively correlated, the anthropogenic factors namely, extent of built up land, noise levels and vehicular traffic contributed negatively towards bird diversity. Among the various riverine stretches/study sites, the Kallanni region recorded highest species richness and diversity. The most important conservation measure would be to declare Kallanai an important bird reserve and the agricultural farmlands on either sides of river Cauvery at Kallanai be declared as ‘High Nature Value’ (HNV) wetlands/farmlands to protect the overall biodiversity.

Phosphorous Fractionation in Surface Sediments of the Cauvery Delta Region, Southeast India

Phosphorus is both a nutrient and a key factor responsible for eutrophication of freshwater ecosystem. Knowledge on geochemical forms of phosphorous is one among the proxies to monitor the quality of an aquatic ecosystem. Channel-bed sediment samples were collected from the Cauvery River in delta region, fractionated into five namely, exchangeable P, Fe-P, Al-P, Ca-P and Residual-P and were studied. Total phosphorous concentration of ranged between 360 and 1,070 mg/kg. The mean values of P fractions are: HCl-P (68 %), NaOH-P (12 %) and NH4Cl-P (8 %). Among the phosphorous fractions studied, HCl extractable P recorded as a dominating chemical form. It implies P had a preferential association with Ca. The pH of the river sediments varied from 7.37 to 8.69 implying alkaline nature. Total Organic Carbon (TOC) and Organic Matter (OM) of the sediments showed ranges of 0.04–1.0 % and 0.14–3.45 %, respectively. Total Nitrogen (TN) of the sediment samples was in the range between 0.08 and 0.20 %. The C/P and N/P ratios ranged 1.65–78.67 and 1.33–6.69, respectively.