Search

Coastal lakes and estuaries are considered economic drivers for coastal communities by delivering invaluable economic and ecosystem services. The coastal ecosystems are facing recurrent hypoxia events (dissolved oxygen; DO < 2.0 mg L -1 ) and are emerging as a major threat to ecosystem structure and functioning. The Ashtamudi Lake, (area = 56 km 2 ), is one of the Ramsar sites in the State of Kerala and located on the SW coast of India. The waterways are extensively used for backwater tourism and for fishery activities. This paper discusses the spatio-temporal variation of water quality attributes with emphasis on hypoxia during non-monsoon and monsoon seasons. The extent of hypoxia on fishery diversity was discussed. The Southern Zone, adjacent to the urban area, shows the hypoxic condition with higher concentration of BOD, NO 3 -N, and NH 4 -N. The hypoxic condition is largely limited to the Southern Zone in both seasons. The occurrence of low DO in the lake is highly related to salinity and organic load in the lake system. The tracking of pollution sources in the lake system was also done through identification of pollution potential zones and found that catchments adjacent to Southern and Western Zones (urban regions) are the major source of pollution. The study suggests that hypoxia is chiefly attributed to anthropogenic interventions in the form of discharge of wastes into the lake causing overloading of nutrients and organic effluents, decrease in the freshwater supply, the absence of proper freshwater mixing or dilution, and effluent discharge from nearby urban centers., (© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Radon ( 222 Rn) is a colourless, odourless, inert, and radioactive noble gas (t 1/2  = 3.8 days) that emanates from rocks and soils as a result of the alpha decay of its parent, radium ( 226 Ra) in the decay series of uranium-238, is the focus of this study. Radon is produced in the crystal lattice of the minerals and emanates out through alpha recoil. It dissolves in water, and is also found in soil and air. Its distribution in water is more pertinent for scientific investigations. It can be measured by various methods. Certain properties of radon enable it to serve as an ideal tracer, viz., short-half life, inertness, high abundance in groundwater than surface water, preferential partitioning, sensitivity to sudden changes in subsurface conditions, non-invasiveness etc. This paper reviews the state-of-the-art techniques on the measurement of dissolved radon in water and its potential applications as a tracer and precursor in several hydrogeological and geological applications like understanding the surface water - groundwater interactions, hydrograph separation of streams, estimation of Submarine Groundwater Discharge (SGD), study of hydrodynamics and water balance of lakes, earthquake predictions, locating geological structures (faults/lineaments), geochemical explorations, NAPL contamination studies etc. Among the various applications presented, radon based approach is found to be more reliable in water resources domain than seismic precursory studies. The interpretations based on radon study in the above applications will pave the way for the improved understanding of the hydrological processes, and thus, help the planners and water managers for the sustainable development and management of water resources., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Studies on occurrence of radon in the environment are receiving growing attention worldwide due to its adverse impact on human health. Despite that, the dissolved radon in water is found to be a useful tracer in many hydrogeological studies. Although, several studies focused on the occurrence of high 222 Rn in groundwater, the processes responsible for its variation is still not well understood. Hence, an attempt has been made in the present study to elucidate the underlying factors influencing the abundance 222 Rn in hard rock (gneissic) aquifers of Karamana River Basin, southwest India. 222 Rn in groundwater was analyzed in 71 dug wells during the pre-monsoon period of 2017. A large variability in 222 Rn activities (170-68,350 Bq/m 3 ) was noticed in groundwater and high activities were mainly seen in the khondalite formation. No significant dependencies between 222 Rn activity and depth to water table, groundwater temperature and electrical conductivity were observed. However, majority of the presence of high 222 Rn activity in groundwater matches with the location of lineaments. Furthermore, radium content in the host rock, degree of weathering and fracturing and the emanation coefficient of the rock were found to have an important bearing on the occurrence of radon in groundwater. The underlying factors influencing the abundance of radon in hard rock aquifers were also conceptualized. Thus, the study highlights the usefulness of 222 Rn as a potential tool in delineating the macro-structural features like fractures/lineaments that are significant repositories of groundwater, which could be explored for groundwater development in hard rock terrains., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)