Biomonitoring of petroleum hydrocarbon residues in commercially important fish and shrimp species from a tropical coastal ecosystem Chilika, India: Associated human health risk assessment.

Petroleum hydrocarbons (PHCs) residues in commercially important fish and shrimp species from Asia's largest brackish water lagoon, Chilika and their dietary risk factors like Bioaccumulation factor (BAF), Estimated dietary intake (EDI) and Exposure risk index (ERI) were investigated. The PHCs in water samples were found within the range of 2.21 to 9.41 µg/l; while in organisms, PHCs varied from 0.74 to 3.16 µg/g (wet weight). The lowest and highest PHCs concentration was observed in Etroplus suratensis (0.74 ± 0.12; crude fat 0.57 %) and Nematalosa nasus (3.16 ± 0.12; crude fat 6.43 %) respectively. From human health risk view point, the calculated BAF, EDI, ERI were within the prescribed safe limits. Our finding suggests that Nematalosa nasus can be used as biomonitor species for petroleum hydrocarbon contamination status for this ecosystem and also continuous pollution monitoring programs must be conducted by the concerned authorities to safeguard this important aquatic ecosystem.

Ecosystem-scale insights into the dynamics of dissolved organic matter in an Asia's largest brackish water lagoon: Sources, fluxes, and biogeochemical significance.

A twenty-four month long observational study conducted in an Asia's largest brackish water ecosystem, Chilika Lagoon, India, aimed to unravel dissolved organic matter (DOM) dynamics in this tropical brackish water ecosystem. The study assessed the interplay between allochthonous and autochthonous DOM sources during lean and active flow periods based on regional rainfall. Dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) fluxes were analyzed, considering catchment runoff, phytoplankton production, benthic-pelagic interactions, and sea-lagoon exchanges as contributors. Contrary to conventional thinking, the study found autochthonous processes to be more significant than conservative mixing in shaping DOM dynamics. It introduced a novel conceptual model illustrating the multifaceted origins of DOM, encompassing catchment runoff, phytoplankton, benthic-pelagic interactions, bacterial activity, and sea-lagoon exchanges. These findings underscore the importance of holistic management strategies for Chilika Lagoon to preserve its ecological health, given its vital role in global carbon cycling, fisheries, and aquaculture.

Impact of extreme events on the transformation of hydrological characteristics of Asia's largest brackish water system, Chilika Lake.

The earth is experiencing the impact of climate change due to global warming. Lake ecosystems are no exception and are expected to cope with the consequences of extreme climatic events (hereafter ECE), such as storms, floods, and droughts. These events have significant potential to alter the hydrological characteristics (HC) influencing the physical, chemical, and biological behavior of lake ecosystems. Considering such ecosystem's high-value services and benefits, it is the need of the hour to monitor and evaluate the impact of ECE on lake ecosystems. The second-largest brackish water system in the world, Chilika Lake, situated at the shore of the Bay of Bengal (BoB), has encountered a total of 1306 tropical cyclonic storms in the last 131 years. Since most tropical cyclones lead to heavy floods, this could be devastating for the ecosystem and its services. Hence, in order to bridge the knowledge gap, the present study was carried out to understand its impact, based on the available field data of more than two decades (1999 to 2020) and historical records of ECE and HC since 1840 and 1915 respectively from the literature. The study revealed that the ECE attributed to short-term changes in HC which were reflected through an immediate change in trophic state index (TSI, indicator of lake health) and trophic switchover (net autotrophic to heterotrophic) between net sink and source of carbon dioxide (CO2) in specific regions. This study showed that both the ECE as well as a human intervention (opening of the new mouth) had an integrated role in the maintenance of HC within the lake as indicated by the variability of salinity level which is the lifeblood of the Chilika. Major ECE factors which controlled the salinity in Chilika were freshwater input through cyclone-induced flash flooding and seawater exchange through varying mouth conditions, i.e., opening of the new mouth, shifting, and widening of existing mouths due to cyclone impacts. The impact of the cyclone-induced flash flood was sustained for a couple of months to years depending on the magnitudes. As evidenced from the historical data available for ECEs, respective mouth variability, and salinity regime, ECE was found to maintain the salinity regime of the lake in the long run. Since the hydrological characteristics are found to be maintained through ECE as well as human intervention, the Chilika Lake recorded a substantial increase in fishery, seagrasses, Irrawaddy dolphins, migratory birds, and reduction in weed infestation. This study highlights the importance of historical data collection through a continuous systematic lake monitoring program which would enable understanding the ecosystem functioning and behavior with ECE-induced changing environmental conditions which is also a key component for formulating a sustainable management action plan for lake ecosystems around the globe.