Spatio-temporal variability in macroinvertebrate community structure and ecological health status of a tropical dynamic river-estuarine system, India: An integrated approach of multivariate analysis.

River-estuarine ecosystems are under severe anthropogenic threat due to resource exploitation, transportation, sewage/industrial discharges, and pollutants from surrounding areas. Monitoring the water quality and biological communities is essential for assessing ecosystem health and sustainability. Present study integrated the ecological community data along with water quality analysis to understand the impact of anthropogenic pressures on benthic macroinvertebrates. Samples were collected from 10 locations (comprising of both rural and urban areas) for Benthic macroinvertebrates, physico-chemical and microbiological parameters along the lower stretch of the Bhagirathi-Hooghly river-estuarine (BHE) system during the post-monsoon seasons of 2020, 2021, and 2022. During the entire study period, a total of 5730 individuals from 54 families in 19 orders of 3 phylum of macroinvertebrate were recorded. Among them Thiaridae (27.1%) and Chironomidae (22.8%) were found to be the most abundant families. Based on the water quality data Cluster analysis and nMDS indicated two distinct groups of locations: Group-I with rural settings and Group-II with urban settings. Alpha diversity metrics showed higher diversity (2.817) and evenness (0.744) in rural locations (Group-I) compared to urban locations (Group-II). The overall saprobic score of the macroinvebrate data revealed Group-I (5.09) to be in good condition, while Group-II (4.95) showed moderately polluted conditions. Redundancy analysis (RDA) highlighted the correlation of pollution-tolerant species (Chironomidae, Culicidae) with high organic loads i.e., biochemical oxygen demand (BOD), chemical oxygen demand (COD) in Group-II. In contrast, Group-I locations exhibited positive correlations with Dissolved Oxygen (DO) and supported less pollution-tolerant organisms (Coenagrionidae, Dytiscidae). The study emphasizes the importance of integrated analysis of ecological community data and water quality parameters to assess the health status of river-estuarine ecosystems.

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.

Imprints of COVID-19 lockdowns on total petroleum hydrocarbon levels in Asia's largest brackish water lagoon.

India successfully executed one of the strictest lockdowns in the world during the height of the COVID-19 pandemic in early 2020, which provided unique opportunities to analyze the second-largest populous country's anthropogenic footprint on its natural systems. India's first Ramsar site and the world's second-largest brackish water system Chilika lagoon experienced a substantial decline (64%) in the total petroleum hydrocarbon (TPHC) level in water, which was attributed to the massive declines or, at times, an abrupt complete halt of motorized boat operations for fishing and tourism. Using the TPHC values during the lockdown period, our study recommends a TPHC baseline threshold of 2.02 µg L-1 and 0.91 µg g-1 for Chilika waters and sediment, respectively. These baseline values can be used to quantify oil pollution and to formulate policy and management action plans for Chilika lagoon as well as for other similar ecosystems by local environmental agencies.

Structural variation of coloured dissolved organic matter during summer and winter seasons in a tropical estuary: A case study.

The diurnal variations in water quality and optical properties of organic matter were studied in the Gautami-Godavari estuary during two contrasting seasons. Dissolved inorganic nitrogen (DIN) and silicate showed similar patterns with the tide during summer, whereas in winter contrasting trends were noticed. Three-folds higher N to P ratio was recorded in winter than in summer. The spectral slope ratio (SR) and specific ultra violet absorption coefficient (SUVA) peaked during summer (1.28 ±â€¯0.09 and 3.95 ±â€¯0.2) followed by winter (1.10 ±â€¯0.18 and 1.91 ±â€¯0.35). The parallel factor (PARAFAC) analysis of excitation emission matrix (EEM) fluorescence spectra was extracted three humic (C1, C2, C3) and one protein-like (tryptophan (C4)) fluorophore components. Humic like fluorophores inversely correlated with the tide in both the seasons, due to influence of seawater. In summer, the Chlorophyll a (Chl a) and dissolved organic carbon (DOC) showed positive correlations with humic like and C4 fluorophores, suggesting the insitu organic matter production.

Bioavailable dissolved organic matter and its spatio-temporal variation in a river dominated tropical brackish water Lagoon, India.

Bioavailable dissolved organic carbon (BDOC), nitrogen (BDON) and their degradation rate constants were measured for the Chilika Lagoon, India. Long-term laboratory incubation experiments (90 days) were conducted at a constant temperature (25 °C) to quantify the bioavailable dissolved organic matter (DOM) and the possible degradation rate coefficients. The results showed that 41 ±â€¯12% of dissolved organic carbon (DOC) and 47 ±â€¯17% of dissolved organic nitrogen (DON) were BDOC and BDON respectively, with their stoichiometry found to be higher than the Redfield ratio. A first order exponential non-linear fitting routine was used to estimate pool sizes. The degradation rate constant (k) for the BDOC varied from 0.127-0.329 d-1 and BDON from 0.043-0.306 d-1 during the study period. Half-lives of the BDOC and BDON ranged from 2.1-5.4 and 2.2-15.9 days, respectively. Overall, the results showed that a fraction of the labile DON was transported from the lagoon to the adjacent coastal sea.

Loricate ciliates as an indicator of eutrophication status in the estuarine and coastal waters.

Owing to the environmental sensitivity of ciliate species, the monitoring and assessment of these communities can indicate the health of the aquatic environment. Sampling for loricate ciliates was carried out during different seasons at three different locations in the estuarine and coastal waters of Kochi, Southwest coast of India. The loricate ciliate community comprising of 27 species belonging to 10 genera revealed significant differences among the three sampling locations. The maximum numerical abundance and less species diversity of loricate ciliates were recorded at the estuarine locations whereas the minimum abundance and more species diversity were encountered in the coastal waters. Multivariate statistical analyses revealed that Tintinnopsis beroidea and Tintinnopsis uruguayensis were correlated positively with nutrients in the estuarine environment, which receives large amount of anthropogenic inputs. Thus, we propose that these two loricate ciliates may be considered as a potential bioindicator of eutrophication status in marine ecosystems.

Scales and drivers of seasonal pCO2 dynamics and net ecosystem exchange along the coastal waters of southeastern Arabian Sea.

The impact of seasonal coastal upwelling on the dynamics of dissolved inorganic carbon (DIC) and sea-air fluxes of CO2 along the coastal waters of Kochi was investigated during 2015, as a part of Ecosystem Modelling Project. The surface water pCO2 varied from 396 to 630µatm during the study period. Significant inter-seasonal variations were found in the distribution of physico-chemical variables and surface pCO2. An increase of 102.1µatm of pCO2 was noticed over a two-decade period with a rate of 5.3µatmy-1. There was an agreement between the fluxes of CO2 and net ecosystem production (NEP) with respect to the trophic status while NEP was higher than CO2 fluxes by a factor of 3.9. The annual net ecosystem exchange (NEE) was estimated to be 15.02mmolCm-2d-1 indicating that the coastal waters of Kochi are highly heterotrophic in nature.