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It is imperative to understand the carbon (C) and nitrogen (N) pools in tropical mangrove systems considering the diminished C storage potential and increasing nutrient loading in a global context due to rising anthropogenic disturbances. Here, we report that the Mangalavanam Coastal Wetland (MCW), a tropical mangrove stand, is a C‐rich environment, with high sediment total organic carbon (70.35 ± 23.84 mg/g) and the δ13C (−26.56 ± 0.65‰) signatures indicate that the major source of carbon in the study area is from mangrove litter. The total nitrogen concentration in the sediment (3.78 ± 0.18 mg/g) was high despite the low N environment of mangrove ecosystems where the mangrove leaf litter was a major contributor to C. The sediment δ15 N (7.70 ± 0.23‰) signatures indicated that the influence of anthropogenic N discharges and the contribution of marine algae were the primary cause of N enrichment. The mean δ13C and δ15N signatures of the mature mangrove leaves of the MCW were −28.66 ± 1.04‰ and 5.93 ± 0.65‰, respectively. The mangrove dweller crab Parasesarma plicatum was observed to have enriched δ13C (−23.78 ± 0.33‰) and δ15N (6.54 ± 0.35‰) signatures, indicative of a mixed dietary source. This study provides the impetus for ongoing conservation efforts to limit the loss of carbon storage and protect against the impact of anthropogenic nitrogen loadings on lowering the carbon and nitrogen emission potential for this system, which can have implications for other tropical mangrove systems as well. [ABSTRACT FROM AUTHOR]

Abstract: Marine pollutants in relation to planktonic and benthic organisms were examined at two locations along Karnataka coast, one at Kulai (74°47.74′′E and 12°55.16′′N) receiving huge amount of industrial effluents from fertilizer, petroleum and chemical plants along with the sewage discharges. The other site Padubidri (74°45′′E and 13°10′′N) is located 20km away, which is a typically agricultural and fishing village having no stress of industrial discharges. Although the concentrations of dissolved oxygen (DO), nutrients and trace metals in water and sediment showed marginal differences at these two locations, the concentration of petroleum hydrocarbon (PHC) remained exceptionally high with a maximum of 1523μg/l at Kulai which is 10 times higher than that at Padubidri (144μg/l). Biomass and population of phytoplankton and zooplankton showed that the seasonal differences were more conspicuous rather than the regional changes. Macro and meiobenthic population remained high at both the locations during the two seasons. Phytoplankton species indicated that centric diatoms such as Rhizosolenia, Leptocylindricus, Chaetoceros, Thalassiosira and Coscinodiscus contributed to >90% of population in May and >70% in January at Kulai. While mixed population of centric, pennate, cyanophycean and dinoflagellates prevailed at Padubidri in January. Lower species diversity and richness accompanied with dominance of fast growing centric diatoms over pennates observed at Kulai act as an index for detection of organic pollution and nutrient enrichment. Similarly, proliferation of benthic bivalves >54% at Kulai relative to Padubidri suggests that these organisms could sustain organic and industrial pollutants. The results suggest that although Kulai receives large quantities of industrial and sewage effluents responsible for alteration of the ecosystem structure, the excellent wind-driven mixing and tidal flushing keep the waters well aerated thus reducing the severe pollution stress by dispersing the organic and other pollutants. Direct relationship of PHC with Cd and Pb as contaminants, NO3 and PO4 as oxidants of excess PHC and species diversity as promoters of phytoplankton (centric diatoms) and benthic bivalves shown by multiple regression analysis further suggest that these biological parameters could serve as indicators for detecting moderately high environmental stress at Kulai, compared to Padubidri. [Copyright &y& Elsevier]