Research Updates

 

This research incorporates iron-loaded crosslinked chitosan (CS) polymeric structure into the interlayer lattice space of Montmorillonite clay (MT) to enhance the phosphate adsorption capacity of MT. The synthesized Fe-loaded crosslinked chitosan montmorillonite composite (Fe-CS-MT) is evaluated effectively for phosphate removal from aqueous media. Batch adsorption experiments optimized the influence of adsorption parameters, i.e., contact time (50 min), solution pH (3), and adsorbent dosage (2 g L−1) for phosphate removal. The experimental results of equilibrium and kinetic studies indicated that phosphate adsorption on Fe-CS-MT follows Pseudo-second-order kinetic and Freundlich isotherm models with a high degree of accuracy. A series of analytical tools used to profile the investigated material's surface features involves CHNS Analyser, SEM-EDX, FTIR, XRD, XRF, UV-Visible Spectrophotometer, TGA, DSC, and surface analysis. The calculations of the thermodynamic study confirmed the endothermic and spontaneous nature of the phosphate adsorption process. This study presents an eco-friendly adsorbent tested in natural conditions to assess the feasibility of removing phosphate from an aqueous phase.

Bibliographic Info: Sandhya Sudhakaran, Elezabeth, V. A., Harsha Mahadevan, Anoop Krishnan, K. [2021]. Crosslinked chitosan-montmorillonite biocomposite with Fe intercalation: Enhancing surface chemistry for improved phosphate adsorption. Surfaces and Interfaces, Vol. 27, Art. 101468. https://doi.org/10.1016/j.surfin.2021.101468

 

 

Grazing The Netravathi estuary is a micro- to mesotidal, tropical, shallow estuary with an abundant density of phytoplankton. The impact of the zooplankton grazing rate and the selected environmental variables on the phytoplankton community structure was studied seasonally from 2017 to 2019. Microplanktons of centric diatoms such as Skeletonema costatum and Cosinodiscus radiatus dominated during monsoon seasons, whereas dinoflagellates such as Peridinium sp. and Ceratium furca were observed in high numbers at the estuary during non-monsoon seasons. Water temperature showed a strong association with grazing rates of microzooplankton (r = 0.910). Canonical correspondence analysis studies established an intensification in grazing rate during non-monsoon seasons by calanoid copepods which in turn occasioned the reduction of microplanktons belonging to diatoms. Moreover, during monsoon seasons, diminution in grazing rates of calanoid copepods coupled with the presence of micro larvae as a secondary consumer of zooplankton resulted in the proliferation of centric diatoms. The grazing behaviour of microzooplankton affected the phytoplankton species diversity of the estuary in a negative manner (D = 0.29 in 2017 Pre-M, D = 0.76 in 2019 Pre-M). Selective grazing behaviour of calanoid copepods concerning temperature alteration exerted a strong influence in determining the phytoplankton community structure of the estuary to a great extent.

Bibliographic Info: Ratheesh Kumar, M., Anoop Krishnan, K. [2021]. Grazing behaviour of tropical calanoid copepods and its effect on phytoplankton community structure. Environmental Monitoring and Assessment, Vol. 193 (8), Art. 495. https://doi.org/10.1007/s10661-021-09306-5

 

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Reconst Recurrent sea-level changes are reflected in the formation of coastal landforms; estuary, lakes, lagoons and barrier beaches during the late Quaternary period along the Kerala coast, SW India. The sediment core from these landforms was addressed for sediment lithofacies, geochemical parameters and associated foraminiferal assemblages to reconstruct the late Quaternary environment. The textural characteristics of the sediment indicate a shallow marine to lagoon and swampy/marsh environment. A layer of coarse sandy sediment (7–9 m thickness) is overlying the late Pleistocene (40 Kyrs BP) sediment sequence. The sediment was deposited under violent to the calm environment attributing its deposition in diverse energy regimes. This is also corroborated with the micro-textures of quartz grains. The geochemical elemental relationship (Rb vs K2O, Ni vs TiO2, K2O/Na2O vs SiO2/Al2O3, discriminant function) is established with paleoweathering, provenance and tectonic setting. An abundant population of Ammonia beccarii, A. tepida, E. discoidale, N. scaphum. A. beccarii in the sediments reveals their high tolerance and adaptability to the changing environment. The multiproxy studies on sediments, support a stronger monsoon in the early Holocene leading to the incursion of high-water levels, increased flow discharge and bottom scouring but, weak monsoon and arid climate prevailed during the Last Glacial Maximum (LGM). A conceptual model is proposed to depict the shoreline evolution and its climate.

Bibliographic Info: Varghese T. I., Prakash, T N., Sheela Nair, L., Sreenivasulu, G., Nagendra, R. [2021]. Reconstruction of the paleoenvironment of the late Quaternary sediments of the Kerala coast, SW India. Journal of Asian Earth Sciences, Vol. 222, Art. 104952. https://doi.org/10.1016/j.jseaes.2021.104952

 

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Tropical Tropical urbanized coastal regions are hotspots for the discharge of nutrient-enriched groundwater, which can affect sensitive coastal ecosystems. Here, we investigated how a beach modifies groundwater nutrient loads in southern India (Varkala Beach), using flux measurements and stable isotopes. Fresh groundwater was highly enriched in NO3 from sewage or manure. Submarine groundwater discharge and nearshore groundwater discharge were equally important contributors to coastal NO3 fluxes with 303 mmol NO3 m–1 day–1 in submarine and 334 mmol NO3 m–1 day–1 in nearshore groundwater discharge. However, N/P ratios in nearshore groundwater discharge were up to 3 orders of magnitude greater than that in submarine groundwater, which can promote harmful algae blooms. As groundwater flowed through the beach, N/P ratios decreased toward Redfield ratios due to the removal of 30–50% of NO3 due to denitrification and production of PO4 due to mineralization of organic matter. Overall, tropical beaches can be important natural biogeochemical reactors that attenuate nitrogen pollution and modify N/P ratios in submarine groundwater discharge.

Bibliographic Info: Oehler, T., Murugan, R., Mintu E. George, Suresh Babu, D. S., Dähnke, K., Ankele, M., Böttcher, M. E., Santos, I. R., Moosdorf, N. [2021]. Tropical beaches attenuate groundwater nitrogen pollution flowing to the ocean. Environmental Science and Technology, Vol. 55 (12), pp. 8432-8438. https://doi.org/10.1021/acs.est.1c00759

 

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Signatures Macrophysical and microphysical features of clouds and precipitation at coastal [20 m above Mean Sea Level (MSL)] and high-altitude cloud physics observatory (HACPO; 1820 m above MSL) sites on the windward side of Western Ghats are examined using ground (Ceilometer and Disdrometer) and satellite-based observations for the years 2017 and 2018 during the pre- and post-monsoon seasons. Low- and high-level clouds dominate over the coastal site, whereas at HACPO, middle-level clouds dominate with a prominent diurnal cycle. Stratiform and convective raindrop size distributions (RSDs) show that nearly 80% of total precipitation was convective in both the seasons at the coastal site. The relative increase in mass-weighted mean diameter (Dm), lower value of normalized intercept parameter (Nw) and higher mean cloud effective radius of ice and liquid phase imply deeper cloud formation in the site. But at HACPO, 54.85% of precipitation is evolved from the convective core and 45.15% from the stratiform core. Lower specific humidity, less liquid water content and weak convective available potential energy signify a dry environment which delimits vertical growth of orographic clouds in coherence with RSD variations having low Dm and high Nw with low rainwater content. Enhanced collision-coalescence in the deep convective clouds sustained by strong updraft results in precipitation with high concentration of mid and large size drops at coastal site, whereas in HACPO, middle-level clouds persist for longer periods favoring warm rain processes by shallow convection that cause smaller drops at the surface.

Fig. 1: The topography of the study area showing locations of the coastal and high-altitude cloud physics observatory (HACPO) sites.

Bibliographic Info: Sumesh, R. K., Resmi, E. A., Unnikrishnan. C. K., Dharmadas Jash, Ramachandran, K. K. [2021]. Signatures of shallow and deep clouds inferred from precipitation microphysics over windward side of Western Ghats. Journal of Geophysical Research: Atmospheres, Vol. 126 (10), Art. e2020JD034312. https://doi.org/10.1029/2020JD034312