Megacities are not only important drivers for socio-economic development but also sources of environmental challenges. Many megacities and large urban agglomerations are located in the coastal zone where land, atmosphere, and ocean meet, posing multiple environmental challenges which we consider here. The atmospheric flow around megacities is complicated by urban heat island effects and topographic flows and sea breezes and influences air pollution and human health. The outflow of polluted air over the ocean perturbs biogeochemical processes. Contaminant inputs can damage downstream coastal zone ecosystem function and resources including fisheries, induce harmful algal blooms and feedback to the atmosphere via marine emissions. The scale of influence of megacities in the coastal zone is hundreds to thousands of kilometers in the atmosphere and tens to hundreds of kilometers in the ocean. We list research needs to further our understanding of coastal megacities with the ultimate aim to improve their environmental management.

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Rare earth elements (REEs) are considered as useful tracers of various surface geological processes in the river system. REEs and heavy metals (V, Pb, Cr, Co, Ag, Zn, Cd, Ni) were analyzed from the suspended sediments of Ganges and surficial sediments of Yamuna, Brahmaputra, Jamuna, Padma and Meghna, using VG Thermal Ionization Mass Spectrometer. Physical weathering process seems to be a major controlling factor for the distribution of REE and trace metals in the sediments of the Himalayan rivers. Weathering of the surface crustal area in the drainage basin shows significant variations due to changes in lithology and influence of tributaries. The distribution of REE shows an almost uniform pattern due to factors such as river transportation processes and high level of terrigenous mixing in the bed sediments. The results show that finer grain size and high content of clay mineral (illite) in these sediments are possible traps for the accumulation of metals. Anthropogenic activities seem to have very little influence in controlling the elemental distribution in the Himalayan rivers.

Microbial degradation has long been recognized as the key rescue mechanism in shaping the oil polluted marine environments and the role of indigenous populations or their functional genomics have never been explored from Indian marine environments, post an oil spill event. In the current study, high throughput metagenomic analysis, PLFA profiling and mass spectrophotometric analysis was performed in combination with metabolomics to capture signature variations among the microbial communities in sediment, water and laboratory enrichments. Contrary to the previous reports, the bloom of Pseudomonadales (specifically genus Acinetobacter) in oiled sediment and Methylococcales in oiled water outnumbered the relative abundance of Alcanivorax in response to hydrocarbon contamination. Overall enhancement of xenobiotic degradation was suggested by metabolomic analysis in sediment and water post the spill event and varying quantitative assemblage of enzymes were found to be involved in hydrocarbon utilization. Laboratory enrichments revealed the competitive advantage of sediment communities over the water communities although unique taxa belonging to the later were also found to be enriched under in vitro conditions. Simultaneous analysis of sediment and water in the study provided explicit evidences on existence of differential microbial community dynamics, offering insight into possibilities of formulating nature identical solutions for hydrocarbon pollution.