Trace elements (Cu,Zn, and Hg) and δ<Superscript>13</Superscript>C/δ<Superscript>15</Superscript>N in seabird subfossils from three islands of the South China Sea and its implications

Seabird subfossils were collected on three islands of the Xisha Archipelago, South China Sea. Via elemental analysis, we identified that bird guano was a significant source for heavy metals Cu, Zn, and Hg. Cu and Zn levels in these guano samples are comparable to their levels in wildbird feces, but guano Hg was lower than previously reported. Trophic positions significantly impacted transfer efficiency of heavy metals by seabirds. Despite of a common source, trace elements, as well as stable isotopes (i.e., guano δ¹³C and collagen δ¹⁵N), showed island-specific characteristics. Bird subfossils on larger island had relatively greater metal concentrations and revealed higher trophic positions. Partition of element and isotope levels among the islands suggested that transfer efficacy of seabirds on different islands was different, and bird species were probably unevenly distributed among the islets. Island area is possibly a driving factor for distributions of seabird species.     

Trophic dynamics of U, Ni, Hg and other contaminants of potential concern on the Department of Energy’s Savannah River Site

The Department of Energy’s Savannah River Site is a former nuclear weapon material production and current research facility located in South Carolina, USA. Wastewater discharges from a fuel and nuclear reactor target manufacturing facility released depleted and natural U, as well as other metals into the Tims Branch-Steed Pond water system. We investigated the current dynamics of this system for the purposes of environmental monitoring and assessment by examining metal concentrations, bioavailability, and trophic transfer of contaminants in seven ponds. Biofilm, detritus, and Anuran and Anisopteran larvae were collected and analyzed for stable isotopes (δ ¹⁵N, δ ¹³C) and contaminants of potential concern (COPC) with a focus on Ni, U, and Hg, to examine metal mobility. Highest levels of Ni and U were found in biofilms U (147 and 332 mg kg^?1 DW, respectively), while highest Hg levels were found in tadpoles (1.1 mg kg^?1 DW). We found intraspecific biomagnification of COPCs as expressed through stable isotope analysis. Biofilms were the best indicators for contamination and Anuran larvae with the digestive tract removed were the best indicators of the specific bioavailability of the focal metals. Monitoring data showed that baseline δ ¹⁵N values differed between ponds, but within a pond, values were stable throughout tadpole Gosner stage, strengthening the case to use this species for monitoring purposes. It is likely that there still is risk to ecosystem integrity as COPC metals are being assimilated into lower trophic organisms and even low levels of this mixture has shown to produce deleterious effects to some wildlife species.     

Stable isotope fractionation to investigate natural transformation mechanisms of organic contaminants: principles, prospects and limitations

Gas chromatography-isotope ratio mass spectrometry (GC-IRMS) has made it possible to analyze natural stable isotope ratios (e.g., (13)C/(12)C, (15)N/(14)N, (2)H/(1)H) of individual organic contaminants in environmental samples. They may be used as fingerprints to infer contamination sources, and may demonstrate, and even quantify, the occurrence of natural contaminant transformation by the enrichment of heavy isotopes that arises from degradation-induced isotope fractionation. This review highlights an additional powerful feature of stable isotope fractionation: the study of environmental transformation mechanisms. Isotope effects reflect the energy difference of isotopologues (i.e., molecules carrying a light versus a heavy isotope in a particular molecular position) when moving from reactant to transition state. Measuring isotope fractionation, therefore, essentially allows a glimpse at transition states! It is shown how such position-specific isotope effects are "diluted out" in the compound average measured by GC-IRMS, and how a careful evaluation in mechanistic scenarios and by dual isotope plots can recover the underlying mechanistic information. The mathematical framework for multistep isotope fractionation in environmental transformations is reviewed. Case studies demonstrate how isotope fractionation changes in the presence of mass transfer, enzymatic commitment to catalysis, multiple chemical reaction steps or limited bioavailability, and how this gives information about the individual process steps. Finally, it is discussed how isotope ratios of individual products evolve in sequential or parallel transformations, and what mechanistic insight they contain. A concluding session gives an outlook on current developments, future research directions and the potential for bridging the gap between laboratory and real world systems.     

Tracing lead pollution sources in abandoned mine areas using stable Pb isotope ratios

This study focused on Pb isotope ratios of sediments in areas around an abandoned mine to determine if the ratios can be used as a source tracer. For pretreatment, sediment samples were dissolved with mixed acids, and a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS, Nu plasma II) was used to investigate the Pb isotopic composition of the samples. The measured isotope ratios were then corrected for instrumental mass fractionation by measuring the ²⁰³Tl/²⁰⁵Tl ratio. Repeated measurements with the NIST SRM 981 reference material showed that the precision of all ratios was below 104 ppm (±2σ) for 50 ng/g. The isotope ratios (²⁰⁷Pb/²⁰⁶Pb) found were 0.85073?±?0.0004~0.85373?±?0.0003 for the main stream, while they were 0.83736?±?0.0010 for the tributary and 0.84393?±?0.0002 for the confluence. A binary mixing equation for isotope ratios showed that the contributions of mine lead to neighboring areas were up to 60 %. Therefore, Pb isotope ratios can be a good source tracer for areas around abandoned mines.     

Hydropower production and river rehabilitation: A case study on an alpine river

Despite the numerous benefits of hydropower production, this renewable energy source can have serious negative consequences on the environment. For example, dams act as barriers for the longitudinal migration of organisms and transport of particulate matter. Accelerated siltation processes in the receiving river reduce the vertical connectivity between river and groundwater. Hydropeaks, caused by short-term changes in hydropower operation, result in a negative impact on both habitat and organisms, especially during winter months when natural discharge is low and almost constant. In this study, we report the current deficits present in the River Rhone from two different scientific perspectives – fish ecology and hydrology. Potential rehabilitation solutions in synergy with flood protection measures are discussed. We focus on the effects of hydropeaking in relation to longitudinal and vertical dimensions and discuss local river widening as a potential rehabilitation tool. The fish fauna in the Rhone is characterized by a highly unnatural structure (low diversity, impaired age distribution). A high correlation between fish biomass and monotonous morphology (poor cover availability) was established. Tracer hydrology provided further details about the reduced permeability of the riverbank, revealing a high degree of siltation with K values of about 4.7 × 10^?6 m s^?1. Improving the hydrologic situation is therefore essential for the successful rehabilitation of the Rhone River. To this end, hydropeaks in the river reaches must be attenuated. This can be realized by a combination of different hard technical and soft operational measures such as retention reservoirs or slower up and down ramping of turbines.     

Groundwater quality assessment in semi-arid regions using integrated approaches: the case of Grombalia aquifer (NE Tunisia)

As many arid and semi-arid regions in the Mediterranean Basin, the Grombalia coastal aquifer (NE Tunisia) is affected by severe groundwater exploitation and contamination. Therefore, quality assessments are becoming increasingly important as the long-term protection of water resources is at stake. Multidisciplinary investigations, like the one presented in this paper, are particularly effective in identifying the different origins of mineralization within an aquifer and investigating the impact of anthropogenic activities on groundwater quality. An integrated assessment, focused on the combined use of geostatistical, geochemical and isotopic (δ¹⁸O, δ²H and ³H) tools, was performed in the Grombalia aquifer between February and March 2014. The overall goal was to study the main processes controlling aquifer salinization, with special focus to nitrate contamination. Results indicate a persisting deterioration of water quality over the whole basin except the south-eastern zone juxtaposing the recharge area of the aquifer. Nitrate contents exceed the drinking water standard (50 mg/l) in 70% of groundwater samples, mainly due to the excessive use of fertilizers and urban activities. Stable isotope measurements showed the contribution of modern rainwater to aquifer recharge and proved the presence of evaporation contributing to the salinity increase. Tritium values of groundwater samples suggested two hypotheses: the existence of mixture between old and recent water or/and the existence of two recharge periods of the aquifer, pre- and post-nuclear weapons test. Principal component analysis confirmed the geochemical interpretation, highlighting that water-rock interaction evaporation effect and intensive anthropogenic activities constitute the main processes controlling the regional groundwater mineralization.     

Calibration and Validation of Far Field Dilution Models for Outfall at Worli, Mumbai

The city of Mumbai, India with a population of 15 million discharges about 2225 MLD of domestic wastewater after partial treatment to adjoining marine water body. Under the Mumbai Sewage Disposal Project Scheme, sewage is being disposed to the west coast at Worli and Bandra through 3.4 kms long submarine outfalls. A field study was conducted at recently commissioned outfall diffuser location at Worli, at the onset of neap flood tide to study the dispersion patterns and measure the far field dilutions using radio and dye tracers. Estimated dilutions using different tracers were compared with outputs from an empirical model (Brooks) and a 2D numerical model (DIVAST). Validation using parameters such as BOD and FC, indicated a good match for BOD in near field compared to FC. The radiotracer ⁸²Br and Rhodamine WT generally gave good correlation with Brooks' and DIVAST models for nearfield, however at further distances predictions were not accurate.     

南极大气气溶胶中铅同位素比值的研究

通过对电感耦合等离子体质谱(ICP-MS)的工作条件和参数进行优化,建立了ICP-MS测定铅同位素比值的精确方法,测量了2007—2009年南极中山站采集到的气溶胶样品中208Pb/206Pb、207Pb/206Pb和206Pb/207Pb的比值。结果表明,南极大气气溶胶中铅同位素比值在逐年缓慢地发生线性变化,线性相关系数为0.996 2;气溶胶铅同位素示踪揭示南极附近国家(除南非)释放的铅可能成为南极大气中铅的重要来源。     

Application of SMR to Modeling Watersheds in the Catskill Mountains

Very few hydrological models commonly used in watershed management are appropriate for simulating the saturation excess runoff. The Soil Moisture Routing model (SMR) was developed specifically to predict saturation excess runoff from variable source areas, especially for areas where shallow interflow controls saturation. A recent version of SMR was applied to two rural catchments in the Catskill Mountains to evaluate its ability to simulate the hydrology of these systems. Only readily available meteorological, topographical, and landuse information from published literature and governmental agencies was used. Measured and predicted streamflows showed relatively good agreement; the average Nash–Sutcliffe efficiency for the two watersheds were R ²=72% and R ²=63%. Distributed soil moisture contents and the locations of hydrologically sensitive areas were also predicted well.     

Enrichment of <Superscript>15</Superscript>N/<Superscript>14</Superscript>N in wastewater-derived effluent varies with operational performance of treatment systems: implications for isotope monitoring in receiving environments

Stable nitrogen isotope ratios are routinely used to trace the dispersion and assimilation of wastewater-derived N in receiving environments, but few isotope studies have investigated wastewater treatment plants and ponds themselves. An improved understanding of N isotope compositions in effluent will help assess treatment plant processes and performance and will help trace sources of excess nutrients in receiving environments. Here, we assess N budgets and treatment processes in seven wastewater treatment plants and wastewater stabilisation ponds in northern Australia based on concentrations and isotope ratios of N in effluent. We show that δ¹⁵N values in effluent are linked to treatment type, effectiveness of conversion of ammonia and levels of gaseous N emissions. These relationships suggest that N isotope monitoring of wastewater treatment plants and ponds can provide an integrated assessment of treatment performance and gaseous N emissions on a pond- or plant-wide scale that is not readily available through other methods. Our findings further imply that monitoring N isotope ratios in receiving environments cannot be assumed to be universally effective as their sensitivity to uptake of wastewater-derived N will vary with the characteristics of individual treatment systems. Paradoxically, N isotope monitoring is less effective where treatment systems are functioning poorly and where monitoring needs are the greatest.     

An assessment of the potential adverse properties of fluorescent tracer dyes used for groundwater tracing

The potential ecotoxicity of fluorescent dyes used in tracing, and their possible effects on human health, were evaluated by reviewing available toxicological information for 12 dyes — fluorescein, Lissamine Flavine FF, Rhodamine WT, Rhodamine B, Sulpho Rhodamine G, Sulpho Rhodamine B, eosin, pyranine, Phorwite BBH Pure, Tinopal 5BM GX, Tinopal CBS-X, and Diphenyl Brilliant Flavine 7GFF — and a dye-intermediate, amino G acid. This evaluation used available toxicological information, test data on analogous substances, and mathematical expressions for biological activity. Based on set criteria for human health and acute ecotoxicity, the evaluation indicated that these tracers have low to moderate levels of concern. The use of these tracers for the study of groundwater flow is appropriate if consideration is given to the overall human health and environmental effects. Their use in the environment requires tracer concentrations not exceeding 1–2 mg 1^–1 persisting for a period in excess of 24 h in the groundwater at the point of groundwater withdrawal or discharge. A simple calculated potential dose was used in a comparison of the estimated acute toxicity of Rhodamine WT in rats to the known acute oral toxic dose in humans for several known acutely toxic chemicals. This comparison showed that none of the fluorescent dyes evaluated would present an acutely toxic threat at or substantially above the recommended 2 mg 1^–1 concentration.The U.S. Governments right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged. Disclaimer: The views of this paper are solely those of the authors and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency.     

Leachate Characterization and Assessment of Groundwater Pollution Near Municipal Solid Waste Landfill Site

Leachate and groundwater samples were collected from Gazipur landfill-site and its adjacent area to study the possible impact of leachate percolation on groundwater quality. Concentration of various physico-chemical parameters including heavy metal (Cd, Cr, Cu, Fe, Ni, Pb and Zn) and microbiological parameters (total coliform (TC) and faecal coliform (FC)) were determined in groundwater and leachate samples. The moderately high concentrations of Cl⁻, NO⁻ ₃, SO²⁻ ₄, NH⁺ ₄, Phenol, Fe, Zn and COD in groundwater, likely indicate that groundwater quality is being significantly affected by leachate percolation. Further they proved to be as tracers for groundwater contamination. The effect of depth and distance of the well from the pollution source was also investigated. The presence of TC and FC in groundwater warns for the groundwater quality and thus renders the associated aquifer unreliable for domestic water supply and other uses. Although some remedial measures are suggested to reduce further groundwater contamination via leachate percolation, the present study demand for the proper management of waste in Delhi.     

Annual Growth of Four Pleurocarpous Moss Species and Their Applicability for Biomonitoring Heavy Metals

Data on the annual production per area of mosses used as biomonitors is of major importance in the calculation of heavy metal deposition rates derived from concentration values. Therefore, annual biomass production per area was determined for Hylocomium splendens (127 ± 61 gm^-2 yr^-1), Pleurozium schreberi (161 ± 56 gm^-2 yr^-1), Hypnum cupressiforme (188 ± 62 gm^-2 yr^-1) and Abientinella abietina (144 ± 45 gm^-2 yr^-1) at 54 sites in Austria. Annual increments were detected by morphological criteria. Central European populations of mosses produce on average 10% (H. splendens) and 39% (P. schreberi) more biomass per area than populations from Northern Europe or Canada.Due to great differences in biomass production at various sites it is suggested calculating heavy metal deposition rates by using mean values only for larger areas and to take only data from accurate measurements of annual growth rates for the calculations of the depositions at single sites.A comparison between heavy metal concentrations (As, Cd, Co, Cr, Cu, Fe, Hg, Mo, Ni, Pb, V, Zn) in H. cupressiforme and A. abietina showed comparable uptake efficiences for both mosses with somewhat higher values (quotient > 1) in H. cupressiforme. These results correspond with those obtained from other monitoring species (e.g. H. splendens).     

Suitability of selected bioindicators of atmospheric pollution in the industrialised region of Ostrava,Upper Silesia,Czech Republic

This study is a continuation of our preceding research identifying suitable environmental samples for the tracing of atmospheric pollution in industrial areas. Three additional types of environmental samples were used to characterise contamination sources in the industrial area of Ostrava city, Czech Republic. The region is known for its extensive metallurgical and mining activities. Fingerprinting of stable Pb isotopes was applied to distinguish individual sources of anthropogenic Pb. A wide range of ²⁰⁶Pb/²⁰⁷Pb ratios was observed in the investigated samples: ²⁰⁶Pb/²⁰⁷Pb = 1.168–1.198 in mosses; ²⁰⁶Pb/²⁰⁷Pb = 1.167–1.215 in soils and ²⁰⁶Pb/²⁰⁷Pb = 1.158–1.184 in tree cores. Black and brown coal combustion, as well as metallurgical activities, is the two main sources of pollution in the area. Fossil fuel burning in industry and households seems to be a stronger source of Pb emissions than from the metallurgical industry. Concentration analyses of tree rings showed that a significant increase in As concentrations occurred between 1999 and 2016 (from 0.38 mg kg^?1 to 13.8 mg kg^?1). This shift corresponds to the use of brown coal from Bílina, Czech Republic, with an increased As concentration. The burning of low-quality fuels in households remains a problem in the area, as small ground sources have a greater influence on the air quality than do industrial sources.     

Use of Stable Nitrogen Isotopes and Permeable Membrane Devices to Study what Factors Influence Freshwater Mollusk Survival in the Conasauaga River

Recent biological inventory data shows severe declines in freshwater mussel abundance and biodiversity in the Conasauga River Basin in Northwest Georgia, USA. Based on assessments of habitat conditions, mussel populations should be sustainable. We conducted a study of sediment and water quality to evaluate the impact of anthropogenic contamination on mussel populations. Permeable membrane devices (PMD), polar organic chemical integrative samplers (POCIS™), conventional water and sediment quality analyses, and stable nitrogen isotope ratio analyses (δ¹⁵N) of snails and sediments were used to assess sediment and water quality at target sites throughout the basin. Ambient concentrations of organic contaminants in water were well below any aquatic life criteria; concentrations of some nutrients were detected above aquatic life criteria levels. Most mussel species in the river are endangered or threatened; therefore, snails were collected for δ¹⁵N analyses. Mean δ¹⁵N values for snails collected at forested upper watershed sites (national forest areas) were significantly lower than δ¹⁵N values from snails in agricultural areas. δ¹⁵N values for raw cow manure and manure-treated soil were similar to δ¹⁵N values for snails collected in agricultural areas. Dissolved nitrate from water samples had elevated δ¹⁵N values similar to the upper range of δ¹⁵N values for snails in agricultural areas. Data, particularly stable nitrogen isotope data, indicates that a land use change from national forest land to agriculture alters nitrogen sources to the basin and snails. Implications of nutrient release on freshwater molluscan reproduction, growth, and survival are discussed.     

Nitrogen isotope ratios in pine bark as an indicator of N emissions from anthropogenic sources

The article describes the use of Scots pine bark to identifynitrogen sources in eastern Germany, as well as background areas in Russia and Bulgaria, by using natural isotope ratios of total nitrogen (N_t) and individual N compoundssuch as ammonium (NH₄ ⁺), nitrate (NO₃ ^-)and amid nitrogen (amide-N). The samples collected were analysed using an elemental analyser in connection with a gas isotope mass spectrometer (EA-IRMS). Natural ¹⁵N abundances in pine bark from impact areas suggest that the ammonium accumulated on the surface of the bark is releasedfrom livestock management. Bark of Scots pines growing near agricultural land had highly depleted ¹⁵N_t values (between –8 and –12), while bark from background areas (unpolluted areas) displayed slightly negative ¹⁵N_t values (mean ¹⁵N_t = –3.8). It is assumed that part of the N adsorbed on the bark surface is mainly derived from ammonia(mean ¹⁵N_t = –40.3) escaping from livestock housing and during the application of manure. This assumption is confirmed by experiments under controlled conditions in which manure samples were spread on soil. In addition, temporal and spatial variations of ¹⁵N_t abundances in pine bark from various locations in eastern Germany as wellas pine stands in Nature Park Dübener Heath are discussed.     

Monitoring and validating the temporal dynamics of interday streamflow from two upland head micro-watersheds with different vegetative conditions during dry periods of the growing season in the Bohemian Massif,Czech Republic

At present, dynamic land use, climate change, and growing needs for fresh water are increasing the demand on the ecosystem effects of forest vegetation. Mountainous areas are at the forefront of scientific interest in European forest ecology and forest hydrology. Although uplands cover a significant area of the Czech Republic and other countries and are often covered with forest formations, they do not receive an appropriate amount of attention. Therefore, two experimental upland head micro-watersheds in the Bohemian Massif were selected for study because they display similar natural conditions, but different vegetative conditions (forest versus meadow). During the 2011 growing season, short-term streamflow measurements were carried out at the discharge profiles of both catchments and were evaluated in relation to climatic data (rainfall and temperature). The basic premise was that the streamflow in a forested catchment must exhibit different temporal dynamics compared to that in treeless areas and that these differences can be attributed to the effects of woody vegetation. These conclusions were drawn from measurements performed during dry periods lasting several days. A decreasing streamflow trend during the day part of the day (0900–1900 hours) was observed in both localities. The decrease reached approx. 44 % of the initial morning streamflow (0.24 dm³ s^?1 day^?1) in the treeless catchment and approx. 20 % (0.19 dm³ s^?1 day^?1) in the forested catchment. At night (1900–0900 hours), the streamflow in the forested catchment increased back to its initial level, whereas the streamflow in the treeless catchment stagnated or slowly decreased. We attribute these differences to the ecosystem effects of woody vegetation and its capacity to control water loss during the day. This type of vegetation can also function as a water source for the hydrographic network during the night.     

Assessing the ecological effects of human impacts on coral reefs in Bocas del Toro,Panama

Environmental and biological reef monitoring was conducted in Almirante Bay (Bahía Almirante) in Bocas del Toro, Panama, to assess impacts from anthropogenic developments. An integrated monitoring investigated how seasonal temperature stress, turbidity, eutrophication and physical impacts threatened reef health and biodiversity throughout the region. Environmental parameters such as total suspended solids [TSS], carbon isotopes (δ¹³C), C/N ratios, chlorophyll a, irradiance, secchi depth, size fractions of the sediments and isotope composition of dissolved inorganic carbon [DIC] of the water were measured throughout the years 2010 and 2011 and were analysed in order to identify different impact sources. Compared to data from Collin et al. (Smithsonian Contributions to the Marine Sciences 38:324–334, 2009) chlorophyll a has doubled at sites close to the city and the port Almirante (from 0.46–0.49 to 0.78–0.97 μg l^?1) and suspension load increased, visible by a decrease in secchi depth values. Visibility decreased from 9-13 m down to 4 m at the bay inlet Boca del Drago, which is strongly exposed to river run off and dredging for the shipping traffic. Eutrophication and turbidity levels seemed to be the determining factor for the loss of hard coral diversity, most significant at chlorophyll a levels higher than 0.5 μg l^?1 and TSS levels higher than 4.7 mg l^?1. Hard coral cover within the bay has also declined, at some sites down to <10 % with extremely low diversities (7 hard coral species). The hard coral species Porites furcata dominated the reefs in highly impacted areas and showed a strong recovery after bleaching and a higher tolerance to turbidity and eutrophication compared to other hard coral species in the bay. Serious overfishing was detected in the region by a lack of adult and carnivorous fish species, such as grunts, snappers and groupers. Study sites less impacted by anthropogenic activities and/or those with local protection showed a higher hard coral cover and fish abundance; however, an overall loss of hard coral diversity was observed.     

Mussel isotope signature as indicator of nutrient pollution in a freshwater eutrophic lake: species, spatial, and seasonal variability

Stable nitrogen isotope ratios of five mussel species from littoral and pelagic areas were investigated with different trophic states in the eutrophic Lake Taihu, the third largest lake in China. Interpopulation variability for these mussels was relatively small in foot tissues because of the slow turnover time. Seasonal and spatial variations among the δ ¹⁵N values of mussels might be due in part to the natural variation in δ ¹⁵N values of potential food sources and the variation in the amount of human pollutions discharged into various locations of the lake. Although the increase of mussel δ ¹⁵N values was accompanied by the increase of nutrient concentrations in most situations in this study, statistically significant correlations were only 22% of the total correlations in this survey, which might be attributed to the different time-scale variations in nutrient concentrations and isotope signatures and the unknown details of the trophic pathways and metabolism for incorporation of these nutrients.     

Variations in some environmental characteristics including C and N stable isotopic composition of suspended organic matter in the Mandovi estuary

Chemical and isotopic (??¹³C and ??¹⁵N) investigation of the Mandovi estuary along the Indian west coast affected strongly by the seasonal monsoon cycle was carried out. The Mandovi estuary is a major waterway for Goa and extensively used for transportation of iron and manganese ore. In addition, with large population centers as well as agricultural fields located on its shores, the estuary is assumed to have been influenced by human activities. Measurements of chemical and isotopic parameters made in the lower part of the estuary during the southwest (SW) monsoon and post-monsoon seasons reveal distinct changes, and it is observed that despite considerable enrichment of macronutrients during the SW monsoon, productivity of the estuary (phytoplankton biomass), as inferred from the chlorophyll-a content, is not as high as expected. This is due to occurrences of high turbidity and cloud cover that limits photosynthetic productivity. The isotopic characterization (C and N isotopes) of suspended organic matter produced/transported during the monsoon and post-monsoon seasons of year 2007 provides a baseline dataset for future isotopic studies in such type of tropical estuaries.