Global patterns of nitrate isotope composition in rivers and adjacent aquifers reveal reactive nitrogen cascading

Remediation of nitrate pollution of Earth’s rivers and aquifers is hampered by cumulative biogeochemical processes and nitrogen sources. Isotopes (δ15N, δ18O) help unravel spatiotemporal nitrogen(N)-cycling of aquatic nitrate (NO3−). We synthesized nitrate isotope data (n = ~5200) for global rivers and shallow aquifers for common patterns and processes. Rivers had lower median NO3− (0.3 ± 0.2 mg L−1, n = 2902) compared to aquifers (5.5 ± 5.1 mg L−1, n = 2291) and slightly lower δ15N values (+7.1 ± 3.8‰, n = 2902 vs +7.7 ± 4.5‰, n = 2291), but were indistinguishable in δ18O (+2.3 ± 6.2‰, n = 2790 vs +2.3 ± 5.4‰, n = 2235). The isotope composition of NO3− was correlated with water temperature revealing enhanced N-cascading in warmer climates. Seasonal analyses revealed higher δ15N and δ18O values in wintertime, suggesting waste-related N-source signals are better preserved in the cold seasons. Isotopic assays of nitrate biogeochemical transformations are key to understanding nitrate pollution and to inform beneficial agricultural and land management strategies

Chemical diagenesis of Siwalik sandstone: isotopic and mineralogical proxies from Surai Khola section, Nepal

Carbon and oxygen isotope values (δ13C and δ18O) of carbonate cement from the Siwalik sandstones were measured in the Surai Khola section (age: 13 Ma to 1 Ma) of western Nepal. The δ18O values of the cement show three evolutionary phases. From 12 Ma to ~6 Ma, the average δ18O (VPDB) values are - 13.6 ± 1.9‰ (n = 114) with a large spread from - 10‰ to - 18‰. This large spread probably indicates dissolution and re-precipitation of carbonate at various stages during burial. From 6 to 4 Ma, the δ18O values show a sharp increase with less scatter, with maximum δ18O value of ~ - 7‰. The average δ18O value for this period is - 10.7 ± 1.6‰ (n = 25). From 4 to 2 Ma, δ18O values remain fairly uniform with an average value of - 8.8 ± 1.2‰ (n = 17). The increase in δ18O values of carbonate cement in the sandstone occurs concurrently with that of pedogenic carbonate measured earlier by Quade et al. (1995), indicating a major role of meteoric water in controlling the δ18O value of diagenetic carbonate cement. The δ18O value of carbonate cement of sandstones, however, is lower than that of pedogenic carbonate in the 6 to 4 Ma time range due to precipitation of sandstone cement at a temperature higher than that of pedogenic carbonate. The δ13C (VPDB) value of calcite cement does not show any definite trend. The δ13C values during 12 to 7 Ma range from - 3.3‰ to - 9.9 ‰ with an average of - 7.1 ± 1.5‰ (n = 91). Higher δ13C values are more common in samples younger than 7 Ma; they vary from - 2.8‰ to - 9.2‰ with an average of - 5.7 ± 1.5‰ (n = 65) during 7 to 2 Ma. The increase in the post-7 Ma period is attributable to appearance of C4 plants, which have higher 13C / 12C, compared to C3 plants. The large spread in δ13C values of the cement probably indicates production of CO2 at various stages of diagenesis of the organic matter at different depths. Mineralogical composition also shows that diagenesis increases with depth. Clay minerals (< 2μ) separated from sandstone include smectite, illite, chlorite and kaolinite. Relative increase in the abundance of illite and decrease in the abundance of smectite indicate illitization of smectite with increase in burial depth. Presence of corroded features in K-feldspar suggests that dissolution of this mineral supplied potassium for illite formation

Effect of surfactants on bioherbicidal activity of Alternaria helianthi on multiple-seeded cocklebur

Abstract: Multiple-seeded cocklebur (Xanthium strumarium L.) is a biotype which has different morphology and higher seedling production ability than common cocklebur. Greenhouse studies were conducted to investigate the bioherbicidal activity of Alternaria helianthi (Hansf.) Tubaki and Nishih. on multiple-seeded cocklebur as affected by various rates of Tenkoz COC® (crop oil concentrate), Activator 90® (non-ionic surfactant), BAS 9050 0 S® (methylated oil), Silwet L-77® (organosilicone surfactant) and Top film® (natural based surfactant). Taking X as the recommended rate for each surfactant, 0-X, ¼-X, ½-X, X and 2-X rates were used for each of the surfactants. Surfactants were added to the conidial suspension of A. helianthi. Each surfactant rate was also applied with sterile water without any A. helianthi spore. Treated plants were kept in the dew chamber for 6 h before transferring to the greenhouse. At the end of the experiment (two weeks after treatment), plant shoots were clipped at the soil surface and the fresh weights were determined. Alternaria helianthi resulted in significant reduction in fresh weight of multiple-seeded cocklebur as compared to the plants treated without the fungus. Among five surfactants, Activator 90® and Silwet L-77® had significant effects on the bioherbicidal activity of A. helianthi in reducing fresh weight of multiple-seeded cocklebur. Fresh weight decreased with increase in surfactant rates. Our data demonstrate that A. helianthi control multiple-seeded cocklebur more with higher rates of Activator 90® and Silwet L-77®

<SUP>13</SUP>C enrichment in the Palaeoproterozoic carbonate rocks of the Aravalli Supergroup, Northwest India: influence of depositional environment

The dolomitic carbonates from the Jhamarkotra Formation of the Palaeoproterozoic Aravalli Supergroup are characterized by widely variable carbon isotope ratios (&#948;13C) ranging from near zero to as high as + 12‰ V-PDB. The estimated maximum age (ca. 2150 Ma) of the Aravalli carbonates help bracketing these with the coeval carbonate bodies of the world that show high positive carbon isotope values. The intriguing existence of normal marine &#948;13C values in some pockets suggest influence of local scale depositional conditions prevailing in different sub-basins. Amongst these two sub-basins which showed high &#948;13C values, a hypersaline evaporative condition is considered responsible for the necessary enrichment in one, while methanogenesis (possibly in conjunction with sulphate reduction processes) might have caused such enrichment in the other. From the empirical association of the sub-basins with profuse stromatolitic phosphorite we infer that the depositional setting that favoured cyanobacterial growth (leading to formation of stromatolites) prevented growth of methanogenetic archaea in such anoxic environments. Our study therefore highlights the fact that the early Palaeoproterozoic 13C excursion in the Aravalli Supergroup is not essentially a time-specific event but is greatly dependent on the variation in the depositional palaeoenvironment prevailing in different sub-basins

Response of grassland ecosystem to monsoonal precipitation variability during the Mid-Late Holocene: Inferences based on molecular isotopic records from Banni grassland, western India.

Banni, located in the arid western India, is one of the largest tropical grasslands of the Asian continent. The net primary production in this grassland ecosystem is currently mediated by precipitation during the Indian summer monsoon (ISM). However, timing of the grassland expansion and its link to the intensity of monsoonal precipitation remains enigmatic due to the paucity of datasets. The major objective of this study is to understand the changes in monsoonal precipitation and vegetation for the last 4600 cal yr BP using hydrogen and carbon isotopic composition of n-alkanes (δDn-alkane and δ13Cn-alkane) measured from two core sediments (Chachi and Luna) in Banni region. The δ13CC29 and δ13CC31 values for Chachi core sediments vary from -30.9 ‰ to -27.2 ‰ and -34.4 ‰ to -25 ‰ respectively. The δ13Cn-alkane values from the core sediments are converted into %C4 plants based on a binary mixing model using the end-member δ13Cn-alkane values derived from the dominant modern vegetation in the Banni region. The prominent feature of the paleovegetation curve is the marked increase in the δ13Cn-alkane values after 2500 cal yr BP, which suggests proliferation of C4 grasses in this region. Similar changes after 2500 cal yr BP have also been observed in the δDn-alkane values. The δDC29 values are used to calculate δD value of paleoprecipitation that varied from 10 ‰ to -60.2 ‰. A significant increase in the δD values of paleoprecipitation (ca. 25 ‰) indicates a weakened ISM precipitation after ca. 2500 cal yr BP. The regional aridification and frequent fire events may have helped the expansion of C4 plant dominated grassland ecosystem in Banni region. Correlation between paleoclimatic records suggests that the southward migration of intertropical convergence zone and more frequent warm phases of El-Nino Southern Oscillation have triggered the weakening of monsoonal precipitation in the tropical region

Variability of Indian monsoonal rainfall over the past 100 ka and its implication for C<SUB>3</SUB>-C<SUB>4</SUB> vegetational change

Oxygen and carbon isotope ratios of soil carbonate and carbon isotope ratios of soil organic matter (SOM) separated from three cores, Kalpi, IITK and Firozpur, of the Ganga Plain, India are used to reconstruct past rainfall variations and their effect on ambient vegetation. The &#948;<SUP>18</SUP>O values of soil carbonate (&#948;<SUP>18</SUP>O<SUB>SC</SUB>) analyzed from the cores range from -8.2 to -4.1&#8240;. Using these variations in &#948;<SUP>18</SUP>O<SUB>SC</SUB> values we are able, for the first time, to show periodic change in rainfall amount between 100 and 18 ka with three peaks of higher monsoon at about 100, 40 and 25 ka. The estimation of rainfall variations using &#948;<SUP>18</SUP>O value of rainwater-amount effect suggests maximum decrease in rainfall intensity (~ 20%) during the last glacial maximum. The &#948;<SUP>13</SUP>C values of soil carbonate (&#948;<SUP>13</SUP>C<SUB>SC</SUB>) and SOM (&#948;<SUP>13</SUP>C<SUB>SOM</SUB>) range from &#8722; 6.3 to + 1.6&#8240; and &#8722; 28.9 to &#8722; 19.4&#8240;, respectively, implying varying proportions of C<SUB>3</SUB> and C<SUB>4</SUB> vegetations over the Ganga Plain during the last 100 ka. The comparison between monsoonal rainfall and atmospheric CO<SUB>2</SUB> with vegetation for the time period 84 to 18 ka indicate that relative abundances of C<SUB>3</SUB> and C<SUB>4</SUB> vegetations were mainly driven by variations in monsoonal rainfall

Isotope and faunal abundance and TOC data from eastern Arabian sea during last 25 kiloyear by Majumder et al., 2023

We present multiproxy data spanning between ~25000 and 3500 calibrated years before the present (cal yr BP) from the eastern Arabian sea (EAS). This is possibly the first record of stable isotope record in pteropods from the EAS. Based on this dataset, we found that the Indian summer monsoon (ISM) was weak during the Last Glacial Maximum (LGM). Moreover, upwelling intensity was high during the early Holocene, which was followed by a significant weakening of ISM during the 4.2 ka event

Origin of graphite, and temperature of metamorphism in Precambrian Eastern Ghats Mobile Belt, Orissa, India: a carbon isotope approach

The carbon isotope composition of graphite and carbon and oxygen isotope composition of associated calcite from different locations of the Eastern Ghats Mobile Belt (EGMB) of Orissa have been measured in order to understand the origin of graphite. The &#948;<SUP>13</SUP>C values of graphite range from -2.4&#8240; to -26.6&#8240;. Forty-four of sixty-one samples have &#948;<SUP>13</SUP>C values less than -20&#8240;. Most of these low &#948;<SUP>13</SUP>C values graphite corresponds to schists and disseminations in khondalite and calc-silicate granulites, thus indicating graphitization of organic matter. The remaining light-carbon-graphite occurs as veins which is the result of graphitization of transported organic matter. The graphite with intermediate &#948;<SUP>13</SUP>C value (-13&#8240; to -19&#8240;) indicates carbon contributions from both organic and carbonates sources and/or mantle sources. The higher &#948;<SUP>13</SUP>C values graphite (-2.4&#8240; to -8.8&#8240;) represent mantle carbon and/or carbonate sources without significant contribution from organic carbon. The temperatures of metamorphism have been estimated using carbon isotope ratios of graphite and associated calcite of calc-silicate granulites, where typical cation exchange thermometer assemblages are lacking and significant mineral reaction textures used to calculate pressure-temperature of metamorphic events are absent. Metamorphic temperatures obtained 945&#176;C are close to the ultrahigh-temperature reported from the EGMB. The minimum temperature estimated using the graphite-carbonate carbon isotope ratio is 90&#176;C. The lower estimates of temperatures probably indicate changes in the carbon isotope ratio of calcite by decarbonation reaction or armoring of carbonaceous matter in silicates during metamorphism preventing continuous exchange with calcite

New Late Cretaceous titanosaur sauropod dinosaur egg clutches from lower Narmada valley, India: Palaeobiology and taphonomy

The Upper Cretaceous (Maastrichtian) Lameta Formation is well-known for its osteological and oological remains of sauropods from the eastern and western parts of the Narmada Valley, central India. The newly documented ninety-two titanosaur clutches from Dhar District (Madhya Pradesh State, central India) add further to this extensive data. Previously parataxonomy of these titanosaur clutches was carried out with a few brief reports on palaeobiological and taphonomic aspects. The quantitative data collected from the new clutches (this study) opens avenues to additionally understand more about titanosaur palaeobiology and to qualitatively understand preservation and taphonomical aspects of their egg clutches. Herein, we document 256 eggs and three clutch patterns (viz. circular, combination, linear) that are assignable to six oospecies. The high oospecies diversity points to a possible high diversity in titanosaur taxa in the Indian sub-continent though it is not reflected in titanosaurid body fossils. All the macro- and micro-structures helped in understanding egg deformation and preservation from a taphonomic point of view. Additionally, a pathologic egg documented from the study area helped in understanding the reproductive biology of titanosaurs, such as the possibility of segmented oviduct and sequential laying of eggs by titanosaurs. In addition, we made an attempt to infer aspects such as egg burial, absence of parental care, colonial nesting behavior. All the egg clutches were observed within sandy limestone and calcareous sandstone lithologies that occur in scattered outcrops with rocks showing floating siliciclastic grains in a micritic groundmass. Further, the presence of ferruginous sandstone in the Jamniapura and Padlya regions (Dhar District, central India) is indicative of a possible alluvial/fluvial setting. The presence of grainy intraclastic fabric, alveolar-septal fabrics, brecciation and shrinkage cracks observed in the clutch-bearing rocks are indicative of a low energy-low gradient palustrine depositional condition in a fluvial/alluvial setting. Finally, we envisage that a few egg clutches of this area were laid close to lake/pond margins while most were laid away from the lake/pond margins, and thus, were hatched

Field photographs showing sedimentary features in the clutch-bearing outcrops.

(A) The outcrop from Dholiya Raipuriya shows a characteristic brecciated nodular structure. Some nodules show autobrecciation represented as brecciated fragments with a gap in between them which indicates that the nodules fitted with each other before the disruption. The autobrecciation indicates the non-transported character of the nodules. The areas where zig-saw fit does not exist between nodules indicate their rotation and translocation after shrinkage and collapse (after Dhiman et al. [15]). (B) Intraclast collapse breccias from Dholiya Raipuriya showing variably spaced sub-angular, sub-rounded, and elliptical shaped coarse-grained brecciated clasts in a carbonate matrix. (C) In outcrops at Padlya, the chert exists in association with brecciated nodular limestone where the light grey zones show shrinkage characteristics while the dark grey zones are matrix-rich areas. The brecciated nodules also show zig-saw fit at some places while at other areas the zig-saw fit has collapsed.</p