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Groundwater resources in tropical regions are largely dependent on recharge by rainwater infiltration through soil layers with variable time. However, the rainwater infiltration through soil is a serious concern in urban tropics where it interacts with landfills at the dumpsites, potentially contaminating adjoining groundwater. In this study, the stable isotopic compositions of oxygen and hydrogen (δ18O and δ2H, respectively) in groundwater and leachates, adjoining municipal dumpsites in urban tropics (Bangalore, Kolkata and Durgapur located in diverse rainfall zonation of India), were analyzed to investigate their recharge sources and trace the possible mixing of leachate contaminants under three diverse climatology. The measured values of δ18O and δ2H suggested that the groundwater in these sites reflects higher recharge by rainwater. However, the d-excess values indicated secondary effects suggesting the groundwater has experienced significant modifications. The end member analysis using δ18O-d-excess relation pinpointed an additional leachate contribution from adjoining dumpsites. The critical fraction of leachate infiltration to groundwater quantified using two component mixing model ranged between (i) 1 and 33% in Bangalore, (ii) 5 and 13% in Kolkata and (iii) 18 and 76% in Durgapur, with its variability dependent on seasonality and aquifer connectivity. This information is crucial for groundwater management to secure water quality and to quantify potential hydrological contaminants particularly in drier seasons and drier regions, when and where the demand for groundwater is high, respectively.

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Huge amount of waste is generated by the pineapple processing industries which raises concerns regarding its safe disposal into the environment. This ever-increasing problem of waste management can be solved by the valorization of pineapple by-products to high-value compounds. The extraction of proteolytic enzyme, bromelain from pineapple rind using green techniques can help to overcome the drawbacks associated with conventional methods. In the present study, the extraction of bromelain from pineapple rind using microwave assisted technique resulted in considerable amount of proteolytic activity (127.8 U/mL) and protein content (2.55 mg/mL). The optimized extraction conditions were found as 200 W microwave power, 1:5 solid/ liquid ratio and after treatment time of 10 min. Highest specific activity (512 U/mg) of bromelain was obtained after using gel filtration chromatography. FTIR result confirmed the presence of functional groups in bromelain, whereas, XRD analysis indicated the semi-crystalline nature of bromelain. The results indicated MAE as an effective green technique for the extraction of bromelain from pineapple rind. The proteolytic action of the extracted bromelain makes it a suitable functional ingredient for its applications in bakery, dairy, and seafood processing industries.

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Nitrogen fertilizers result in high crop productivity but also enhance the emission of N2O, an environmentally harmful greenhouse gas. Only approximately a half of the applied nitrogen is utilized by crops and the rest is either vaporized, leached, or lost as NO, N2O and N2 via soil microbial activity. Thus, improving the nitrogen use efficiency of cropping systems has become a global concern. Factors such as types and rates of fertilizer application, soil texture, moisture level, pH, and microbial activity/diversity play important roles in N2O production. Here, we report the results of N2O production from a set of chamber experiments on an acidic sandy-loam agricultural soil under varying levels of an inorganic N-fertilizer, urea. Stable isotope technique was employed to determine the effect of increasing N-fertilizer levels on N2O emissions and identify the microbial processes involved in fertilizer N-transformation that give rise to N2O. We monitored the isotopic changes in both substrate (ammonium and nitrate) and the product N2O during the entire course of the incubation experiments. Peak N2O emissions of 122 ± 98 µg N2O-N m-2 h-1, 338 ± 49 µg N2O-N m-2 h-1 and 739 ± 296 µg N2O-N m-2 h-1 were observed for urea application rate of 40, 80, and 120 µg N g-1. The duration of emissions also increased with urea levels. The concentration and isotopic compositions of the substrates and product showed time-bound variation. Combining the observations of isotopic effects in δ15N, δ18O, and 15N site preference, we inferred co-occurrence of several microbial N2O production pathways with nitrification and/or fungal denitrification as the dominant processes responsible for N2O emissions. Besides this, dominant signatures of bacterial denitrification were observed in a second N2O emission pulse in intermediate urea-N levels. Signature of N2O consumption by reduction could be traced during declining emissions in treatment with high urea level.

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Feitsui Reservoir, a freshwater body in Taiwan with minimal anthropogenic stress, meets the water demand for the population of more than five million living in Taipei city. In view of the biogeochemical processes controlling the long-term trophic status of this socio-economically and ecologically important aquatic system, probing the nitrogen cycle and its dynamics is essential. Here, we monitored the concentration and stable isotopic compositions (δ15N, δ18O, and Δ17O) of nitrate in the Feitsui Reservoir and in the atmospheric wet deposition at intervals of 1-2 weeks for a year, along with measurements of environmental data such as chlorophyll a, dissolved oxygen, and community respiration. Emphasis was laid on Δ17O (= δ17O - 0.52 × Î´18O) because of the mass-conservative behavior of Δ17O during partial assimilation and denitrification. The present approach offered an effective method to quantify the gross nitrification and removal/uptake rates of nitrate in the reservoir. The atmospheric nitrate exhibited elevated Δ17O values ranging from 12.6‰ to 30.1‰ (23.3 ± 5.0‰), compared to the lower Δ17O values of ~0 to 4.6‰ (1.1 ± 0.7‰) recorded in the reservoir nitrate. Utilizing Δ17O for dissolved nitrates, we observed a seasonal trend of higher nitrification and removal rates during the summer than in the winter. Our estimates showed annually-averaged nitrification rate of 55 ± 11 mmol m-2 d-1 and removal/uptake rate of 57 ± 11 mmol m-2 d-1 (or a nitrate turnover time of ~2.5 months), representing the active nature of nitrogen cycling in this preserved subtropical reservoir.

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The oxygen isotopic composition (δ18O) of plant organic matter (OM) is primarily governed by the δ18O of source water (δ18OSW) and climatic factor of relative humidity (RH). Among the cereals, the growth of rice plants is critically dependent on the water availability in the growth-environment. In the present study, we investigated the sensitivity of δ18O in the bulk organic matter of rice grains to RH of their growth-environment. Our experimental setup consisted of both glasshouse and field experiments, where eight genotypes were grown at RH levels ranging from 67% to 87%. The δ18O measured in bulk grain OM and source water was used to calculate the net oxygen isotopic enrichment (Δ18OOM). Regression analysis of Δ18OOM with RH demonstrated a significant relationship (r2 = 0.96; p < 0.0001), thereby implying that the isotopic signature of evaporative conditions gets recorded in the rice grain OM. In addition, our study involved a separate experiment that monitored the degree of oxygen isotope enrichment in water samples extracted from different parts of the rice plant. For this purpose, we sampled four of the above eight genotypes along with three other rice genotypes that were grown in both open cultivation fields and glasshouse. Water present in the culms, leaves, and grains were extracted quantitatively. Isotopic analyses revealed progressive 18O enrichment of the water in the culms and leaves and intermediate enrichment values of that in the grains. Based on the isotope data, we validated mechanistic models for prediction of δ18O of the leaf water and that of the plant carbohydrates. The model predictions were in close agreement with the experimental observations. The study provides insights into the rice plant's oxygen isotope systematics that build the foundation for future applications of the stable isotope technique to study the interactions between rice and environment.

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