Natural Discharge Research Articles

Assessing the relative impacts of land‐use change and river regulation on Burdekin River (Australia) floodplain wetlands

Abstract The Burdekin River floodplain wetlands are internationally important and act as a sink for sediments and nutrients that would otherwise enter the World Heritage‐listed Great Barrier Reef lagoon. The Burdekin River has the highest natural discharge of any Great Barrier Reef catchment and contributes the greatest mass of sediment to the reef. The river and its catchment have been substantially modified by land clearance, river regulation introduced in the 1960s, the construction of the Burdekin Falls Dam in 1987 and invasive aquatic plants. We hypothesised that the natural variability of Burdekin River discharge would render its wetland ecosystems resistant to human‐induced pressures. Diatoms were analysed from the sediments of two lower Burdekin River floodplain wetlands with contrasting regulation histories. Labatt Lagoon has a long history of flow alteration, whereas Swan's Lagoon has experienced limited regulation. Both wetlands experienced dramatic increases in sedimentation as a result of land clearance, yet the Swan's Lagoon diatom record indicates that the wetland's ecology remains within the range of natural variability. In contrast, Labatt Lagoon is markedly different from its pre‐settlement state. It is now permanent, having been ephemeral for more than 1000 years before European settlement. The conversion to artificial permanence facilitated aquatic plant invasion, resulting in more marked changes than widespread pastoralism. Modern diatom assemblages from 28 lower Burdekin River floodplain wetlands indicate that the contemporary flora of Swan's Lagoon is unusual. Most wetlands have similar assemblages to those in the Labatt Lagoon record in its present, altered state. It is possible, therefore, that the ecological shift registered in Labatt Lagoon is widespread. Diatom records highlight the striking impact that river regulation has had on the trajectory of the Burdekin floodplain wetlands. It is likely that wetland rehabilitation can be facilitated by the re‐introduction of a variable hydrological regime.

Riverine turtles select habitats maintained by natural discharge regimes in an unimpounded large river

AbstractTurtle populations are imperiled worldwide, but limited ecological information from unaltered systems hampers science‐based management and conservation of some species, especially riverine turtles such as the spiny softshell (Apalone spinifera). We therefore investigated movements and spatial habitat selection of 54 A. spinifera in 633 river kilometres (rkm) of the least‐altered river in the conterminous United States—the Yellowstone River in Montana—from 2005 to 2009. Movement rates and home ranges were smaller than in fragmented, altered river systems because nesting and overwintering habitats were common and in close proximity. Habitat selection also differed. A. spinifera in the Yellowstone River overwintered in unaltered bluff pools and summered in complex reaches with side channels, islands, and diverse habitats. However, those in the highly altered Missouri River used deep alluvial pools for overwintering and flooded, inundated, or backwatered tributary mouths in spring and summer. Importantly, selected habitats in both rivers were functionally similar, including complex river reaches (with multiple channels, islands, and diverse habitats) and natural pool types. Unfortunately, these are the very habitats that are limited in rivers affected by dams, bank stabilization, and channelization. Therefore, preservation of natural and diverse riverine habitats—and the fluvial dynamics that maintain them—may enhance conservation of A. spinifera in large rivers.

Two-dimensional velocity distribution modeling for natural river based on UHF radar surface current

Non-contact flow measurement method plays an increasingly important role in river discharge measurement. However, most channel cross-section velocity distribution models proposed by researchers have certain limitations in application, underwater velocities are always necessary when applied in narrow channels, which makes it challenging to calculate natural river discharge using water-surface velocities measured by remote sensing instruments. This letter takes water-surface velocities detected by UHF radar as boundary conditions and a new velocity distribution model is derived based on the Reynolds-Averaged Navier-Stokes (RANS) equations. UHF radar measures surface velocities of the cross-section, and velocities on the river bed of the cross-section are considered to be 0. The RANS equations are simplified to be a two-dimensional Poisson equation and the cross-section velocity distribution is solved by using the closed boundary conditions. Some field experiments were conducted in the Hanjiang River at Xiantao, Hubei, China in September 2017 and April–July 2018, the processing results of which show that the proposed model is superior to the power law and the log law models, especially near the side wall (narrow channel region). River discharges calculated by this method are highly consistent with those provided by Hubei Xiantao hydrologic station, which verifies the reliability of the model and the feasibility of using UHF radar to measure natural river discharge continuously and automatically.

Bed Load Sediment Transport and Morphological Evolution in a Degrading Uniform Sediment Channel Under Unsteady Flow Hydrographs

AbstractFlume experiments are conducted to investigate the intrinsic links between time‐varying bed load transport properties for uniform sediments and bed surface morphology under unsteady hydrograph flows, in the absence of upstream sediment supply. These conditions are representative of regulated river reaches (e.g., downstream of a dam) that are subject to natural flood discharges or managed water releases, resulting in net degradation of the river bed. The results demonstrate that the hydrograph magnitude and unsteadiness have significant impacts on sediment transport rates and yields, as well as hysteresis patterns and yield ratios generated during the rising and falling limbs. A new hydrograph descriptor combining the influence of total water work and unsteadiness on bed load transport is shown to delineate these hysteresis patterns and yield ratios while correlating strongly with overall sediment yields. This provides an important parametric link between unsteady hydrograph flow conditions, bed load transport, and bed surface degradation under imposed zero sediment feed conditions. As such, maximum bed erosion depths and the longitudinal bed degradation profiles along the flume are strongly dependent on the magnitude of this new hydrograph descriptor. Similarly, nonequilibrium bedforms generated along the flume indicate that formative conditions for alternate bars, mixed bar/dunes, or dunes are defined reasonably well by an existing morphological model and the new hydrograph descriptor. These findings provide a new framework for improved predictive capabilities for sediment transport and morphodynamic response in regulated rivers to natural or imposed unsteady flows, while their wider application to graded sediments is also considered.

Integration of physical abuse clinical decision support at 2 general emergency departments.

The study sought to develop and evaluate an electronic health record-based child abuse clinical decision support system in 2 general emergency departments. A combination of a child abuse screen, natural language processing, physician orders, and discharge diagnoses were used to identify children <2 years of age with injuries suspicious for physical abuse. Providers received an alert and were referred to a physical abuse order set whenever a child triggered the system. Physician compliance with clinical guidelines was compared before and during the intervention. A total of 242 children triggered the system, 86 during the preintervention and 156 during the intervention. The number of children identified with suspicious injuries increased 4-fold during the intervention (P < .001). Compliance was 70% (7 of 10) in the preintervention period vs 50% (22 of 44) in the intervention, a change that was not statistically different (P = .55). Fifty-two percent of providers said that receiving the alert changed their clinical decision making. There was no relationship between compliance and provider or patient demographics. A multifaceted child abuse clinical decision support system resulted in a marked increase in the number of young children identified as having injuries suspicious for physical abuse in 2 general emergency departments. Compliance with published guidelines did not change; we hypothesize that this is related to the increased number of children identified with suspicious, but less serious injuries. These injuries were likely missed preintervention. Tracking compliance with guidelines over time will be important to assess whether compliance increases as physician comfort with evaluation of suspected physical abuse in young children improves.

Dynamics of Wastewater Effluent Contributions in Streams and Impacts on Drinking Water Supply via Riverbank Filtration in Germany-A National Reconnaissance.

The discharge of wastewater effluents to a stream that is subsequently used for drinking water abstraction has been previously referred to as de facto water reuse. Where the abstraction of surface water for drinking water production occurs via induced bank filtration or aquifer recharge, additional site-specific factors should be considered to assess the impact of wastewater effluents on bank-filtered water. This study represents the first national reconnaissance to quantify wastewater effluent contributions in streams across Germany and consequences for indirect drinking water abstraction from these streams. An automated assessment using ArcGIS was conducted for river basins considering minimum and mean average discharge conditions of streams as well as discharge from more than 7500 wastewater facilities. In urban areas, where the natural base discharge is low, wastewater effluent contributions greater than 30-50% were determined under mean minimum discharge conditions, which commonly prevail from May to September. A conceptual model was proposed to estimate critical bank filtrate shares resulting in exceedances of monitoring trigger levels for health-relevant chemicals as a universal qualitative assessment regarding the relevance of de facto reuse conditions in surface waters used for drinking water abstraction. This approach was validated using chemical monitoring data for three case study locations.

Multiparameter daily time-series analysis to groundwater recharge assessment in a caldera aquifer: Roccamonfina Volcano, Italy

The definition of hydrogeological conceptual models sometimes suffers on uncertainties depending on the available dataset. The availability and the elaboration of long-term hydrogeological dataset allow ensuring a better definition of the aquifer dynamics and features. One of the main features, which can benefice on long-term datasets, is the recharge quantification. According to the literature, several methods exist to calculate the recharge and to get a deeper insight in recharge mode assessment. Most of them allow the quantification of infiltrating water by means of meteo-climatic data and land use information. In this research, a combined approach on hydrogeological time-series is proposed. The Cross-Correlation among the rainfall and the piezometric levels was applied to point out the response time of each aquifer layer. In addition, the Water Table Fluctuation method was used to indirectly quantify the recharge.The study area is the Roccamonfina Volcano caldera (Italy), where lateral inflows are absent, and the almost total natural groundwater discharge occurs in the Savone delle Ferriere stream. Here, a monitoring scheme of the major hydrogeological features was implemented. The local rainfall, the groundwater levels in 2 wells tapping the different aquifer layers, and the river stage of the Savone delle Ferriere stream were measured daily during the 2016–2017 period. The analyses defined different recharge modes for each aquifer layer. The aquifer recharge rates, calculated with different approaches, are comparable to each other and in line with the mean groundwater discharge through the Savone delle Ferriere streambed springs.

A deep groundwater origin for recurring slope lineae on Mars.

The recurring slope lineae on Mars have been hypothesized to originate from snow melting, deliquescence, dry flow or shallow groundwater. Except for the dry flow origin, these hypotheses imply the presence of surficial or near-surface volatiles, placing the exploration and characterization of potential habitable environments within the reach of existing technology. Here we present observations from the High Resolution Imaging Science Experiment, heat-flow modelling and terrestrial analogues, which indicate that the source of recurring slope lineae could be natural discharge along geological structures from briny aquifers within the cryosphere, at depths of approximately 750 m. Spatial correlation between recurring slope lineae source regions and multi-scale fractures (such as joints and faults) in the southern mid-latitudes and in Valles Marineris suggests that recurring slope lineae preferably emanate from tectonic and impact-related fractures. We suggest that deep groundwater occasionally surfaces on Mars in present-day conditions. Observations and heat-flow modelling suggest that briny groundwater surfacing from fractures forms recurring slope lineae on Mars.

Evaluation of basin storage–discharge sensitivity in Taiwan using low‐flow recession analysis

AbstractSensitivity analysis of the hydrological behaviour of basins has mainly focused on the correlation between streamflow and climate, ignoring the uncertainty of future climate and not utilizing complex hydrological models. However, groundwater storage is affected by climatic change and human activities. The streamflow of many basins is primarily sourced from the natural discharge of aquifers in upstream regions. The correlation between streamflow and groundwater storage has not been thoroughly discussed. In this study, the storage–discharge sensitivity of 22 basins in Taiwan was investigated by means of daily streamflow and rainfall data obtained over more than 30 years. The relationship between storage and discharge variance was evaluated using low‐flow recession analysis and a water balance equation that ignores the influence of rainfall and evapotranspiration. Based on the obtained storage–discharge sensitivity, this study explored whether the water storage and discharge behaviour of the studied basins is susceptible to climate change or human activities and discusses the regional differences in storage–discharge sensitivity. The results showed that the average storage–discharge sensitivities were 0.056 and 0.162 mm−1 in the northern and southern regions of Taiwan, respectively. In the central and eastern regions, the values were both 0.020 mm−1. The storage–discharge sensitivity was very high in the southern region. The regional differences in storage–discharge sensitivity with similar climate conditions are primarily due to differences in aquifer properties. Based on the recession curve, other factors responsible for these differences include land utilization, land coverage, and rainfall patterns during dry and wet seasons. These factors lead to differences in groundwater recharge and thus to regional differences in storage–discharge sensitivity.

Groundwater dynamics in fossil fractured carbonate aquifers in Eastern Arabian Peninsula: A preliminary investigation

Eastern Arabian Peninsula represents the main natural groundwater discharge area of the Arabian platform fossil aquifer system. In such settings, connections between aquifers could strongly affect the flow dynamics, water quality and availability as well as karst formation and landscape evolution. Geological structures such as folds and faults are central to aquifer connectivity, yet their role on groundwater flow is poorly understood. Herein, we perform mapping of exposed and buried structural features in the Qatar Peninsula using Landsat, Sentinel-2 and ALOS-PalSAR scenes, correlated with field, GPR and isotopic data to assess their role in aquifer connections and groundwater dynamics. Our results suggest that ENE-WSW oriented fold-related faults act as vertical conduits along which artesian upward leakages from the deep Aruma aquifer take place into the shallower main aquifer unit (i.e. Umm er Radhuma and Rus) in southern Qatar Peninsula. On the other hand, downward leakage from the freshwater lens in the Dammam aquifer take place in northern Qatar Peninsula. The deep, brackish, and gaseous-rich waters ascending along faults in south Qatar Peninsula, in addition to degrading the water quality in the main aquifer unit, enhance dissolution of carbonates and evaporites leading to strong karstification that produces abundant collapse features. Our findings suggest that structure controls can add significant complexity to recharge mechanisms and groundwater dynamics in fossil aquifers. Future large-scale radar subsurface mapping will be essential to resolve the variability of the water heads in such areas and its correlation to structural discontinuities.

Complexity of Saharan paleoclimate reconstruction and implications for modern human migration

Chronological and geochemical data from scarp and scarp-foot depression sediments (SSDS) have been used for deciphering Saharan paleoclimates and patterns of migration of anatomically modern humans (AMH). U–Th dating of thick accumulations of SSDS indicates prevalent deposition during long-lasting cool glacial periods (marine isotope stage [MIS] 6, 8, 10, and 12) and limited deposition during warm interglacial periods (MIS 5, 7 and 13). In contrast, Quaternary sediments associated with short residence, hydrologic systems in Sinai yielded MIS 2 OSL ages of 27.7 to 10.2 ka. The lack of SSDS of MIS 2 ages and the wide range of warm and cool stages in Eastern Sahara is attributed to: (1) lengthy travel times of groundwater prior to discharge and deposition of SSDS from deep groundwater originating from distant sources, and (2) sampling and dating of SSDS from depressions where natural discharge has been apparently continuous through wet and dry periods. Given that the previously dated depression SSDS could have been deposited during dry periods, and that the ages of SSDS reflect the timing of groundwater discharge rather than the ages of the wet periods during which recharge occurred, we suggest that earlier interpretations of Saharan paleoclimate and AMH migrations that heavily relied on dating of SSDS should be revisited.

Long-Term Drinking Water Quality Assessment Using Index and Multivariate Statistical Analysis for Three Water Treatment Plants of Erbil City, Iraq

Safe source of drinking water is always considered as an essential factor in water supply for cities and urban areas. As a part of this issue, drinking water quality is monitored via a useful scheme: developing drinking water quality index DWQI. DWQI is preferably used as it summarizes the whole physicochemical and bacteriological properties of a drinking water sample into a single and simple term. In this study, an evaluation was made for three drinking water treatment plants DWTPs named: Efraz 1, Efraz 2 and Efraz 3 that supply drinking water to Erbil City. The assessment was made by testing thirteen physicochemical and two bacteriological parameters during a long period of (2003 – 2017). It has been found that turbidity, electrical conductivity EC, total alkalinity, total hardness, total coliform and fecal coliform have more influence on drinking water quality. DWQI results showed that the quality of drinking water supplied by the three DWTPs in Erbil City fallen within good level. Except various occasional periods where the quality was varying from good to fair. The quality of the drinking water supply never reached the level of marginal or poor over the time investigated. The applied hierarchical clustering analysis HCA classifies the drinking water dataset into three major clusters, reflecting diverse sources of the physicochemical and bacteriological parameter: natural, agriculture and urban discharges.

The Application of Biofortification in Natural Rubber Processing Wastewater Treatment

According to the water quality of natural rubber processing wastewater and related sewage discharge standards, a combination process of anaerobic and two-stage biological contact oxidation (A/O1/O2 biofilm) was used to treat natural rubber processing wastewater. Biofortification was considered as the core technology in this case that Bacterial agents were directly added and biological fillers were adopted to fix the microorganisms, and therefore strengthen the operation of the biological treatment system. After the commissioning of this process, it was officially put into operation, and related sewage discharge indicators (including pH, SS, NH3-N, COD and BOD5 ) had shown to meet all the first-level standard of “Integrated wastewater Discharge Standard”(GB8978-2002).

Trend Analysis Variations and Relation Between Discharge and Rainfall: a Study on Kushiyara River

Water resources and rivers play a very important role in economy and agriculture. But due to climate change and improper management, water resources are losing the natural discharge capacity from upper stream. This study was under taken to find out the trends and variability of rainfall and discharge at two stations of the Kushiyara River. Rainfall and discharge data Daily time series data of stream flow or discharge at Sheola (1976 to 2007) and Sherpur (1982 to 2007) and observed discharge data in certain interval from 2008 to 2016 have been analyzed in this study. For trend analysis, Mann-Kendall Test (MK) and Sen’s Slope Estimator method were used as non-parametric test and relationship assessment was done by undertaking Pearson’s Coefficient of Correlation. Annual discharge at Sheola and Sherpur station showed downward trend and maximum discharge was found downward trend at both stations. In Mannkendall test and Sen’s Slope Estimator method showed downward trend in most cases. Climate change and improper land management may have influenced the present condition.J. Environ. Sci. &amp; Natural Resources, 10(2): 121-132 2017

Hydrogeochemical characterization and evolution of a regional karst aquifer in the Cuatrociénegas area, Mexico

The Cuatrocienegas area is useful for the investigation of the effect of groundwater extraction in the Chihuahuan freshwater xeric ecoregion. It has been investigated at this time using a selection of geochemical indicators (major, minor and trace elements) and δ34S data, to characterize the origin of groundwater, the main geochemical processes and the mineral/groundwater interactions controlling the baseline geochemistry. The area is composed of limestones of Mesozoic age, with a composite thickness of about 500 m, overlaid by basin fill (poorly consolidated young sediments). Substantial water extraction and modification of natural discharges from the area along the last century have produced a detrimental impact on ecosystem structure and function. Water–rock interactions, mixing and evaporative processes dominate the baseline groundwater quality. Natural recharge is HCO3–Ca type in equilibrium with calcite, low salinity (TDS < 500 mg/L), Cl− lower than 11 mg/L and average Li+ concentration of 0.005 mg/L. Along the groundwater flow systems, δ34S evidence and mass transfer calculations indicate that Cretaceous gypsum dissolution and dedolomitization reactions adjust water composition to the SO4–Ca type. The increase of water–rock interaction is reflected by Cl− values increase (average 68 mg/L), TDS up to about 1500 mg/L and an average Li+ concentration of 0.063 mg/L. Calculations with chemical geothermometers indicate that temperature at depth could be at maximum of 15–20 °C higher than field-measured temperature for pozas. After groundwater is discharged to the surface, chemical evolution continues; water evaporation, CO2 degassing and precipitation of minerals such as gypsum, calcite and kaolinite represent the final processes and reactions controlling water chemical composition.

Development and evaluation of the Maxey-Eakin recharge method

The Maxey-Eakin method affords a convenient means to estimate natural groundwater recharge and has been widely applied to desert basins in the Southwestern United States. The method relies simply on recharge percentages applied to volumes of precipitation within a basin, with recharge percentage increasing with precipitation. It has been presumed that the method was developed for closed desert basins, where recharge equals natural discharge. The recharge coefficients were derived through a trial-and-error process using an annual precipitation map of Nevada dated 1936, applied to natural discharge by phreatophytes in 13 valleys in Nevada. Details of the derivation have not been published and have not been reproduced by anyone. The identity of the valleys used in the derivation cannot be confirmed. The 1936 precipitation data likely underestimated the mean annual precipitation, and field measurements indicate that the estimates of natural discharge by phreatophytes were also underestimated. Nevertheless, the method has been extensively utilized, even outside Nevada, apparently with good results. The wide applicability of the recharge coefficients may be attributed more to the excellent professional judgment of the developers than to the trial-and-error process that relied on phreatophyte uptake and the 1936 precipitation map of Nevada.

Study on Smoke Behavior in Under-viaduct Stations by using Scale Reduced Model.

In the event of fire at concourse of rail stations under elevated platforms, smoke may emit through stairways leading from the concourse to platforms as well as standard natural smoke discharge outlets decreed by the Building Standards Law. However there is little knowledge about smoke discharge from the concourse via the stairway. In this study, Experiments regarding smoke flow in the case of fire in concourse of rail stations below elevated platforms were carried out compare volume of smoke emitted through stairway opening with that emitted through standard natural smoke discharge outlets as decreed by the Building Standards Law, with a simple scale reduced model which stairway was placed at right angle to the concourse. As a result, in these experiments, relationship of smoke discharge between stair openings and standard natural smoke discharge outlet was found.

Climate-induced discharge variations of the Nile during the Holocene: Evidence from the sediment provenance of Faiyum Basin, north Egypt

Abstract The Faiyum Basin of northern Egypt occupies a key location on the source-to-sink pathway of the Nile. High-resolution grain size, organic carbon and carbonates, as well as geochemical and magnetic analyses, were conducted on a sediment core retrieved from the basin to infer changes in sediment provenance in association with climate-induced variations in Nile River discharge during the Holocene. A high Si/Al ratio in the coarse sediment with weak magnetic properties prior to ca. 9.7 cal ka BP indicated prevalent aeolian activities in the lake basin, revealing no Nile discharge inputs and thus a dry Nile. Initial high values of the mobile elements (CaO, MgO and Sr) after ca. 9.7 cal ka BP with well-sorted finer sediment marked the establishment of a flow connection between the basin and the Nile since then. This establishment was followed by a durative hydrological connection to the Nile until ca. 5.0 cal ka BP inferred from high organic matter and stable magnetic and geochemical properties of the finer sediment, implying a humid climate phase of the Nile between ca. 9.7–5.0 cal ka BP. Afterwards, an increasing Ti/Al ratio and magnetism of the sediment indicated a brief change in sediment provenance, as material from the volcanic Ethiopian Uplands carried by the Blue Nile and the Atbara became dominant. A drying climate prevailed in the Nile Basin after ca. 5.0 cal ka BP. Although the Ti/Al ratio and sediment magnetic properties still showed a prominent sediment contribution from the volcanic Ethiopian Uplands, the natural discharge from the river Nile to the Faiyum Basin was weakened, especially when increasing water extraction by humans occurred after ca. 4.0 cal ka BP. The sediment provenance pattern of the Faiyum Basin was substantially influenced by climate-induced variations of the Nile discharge in response to the advance/retreat of the African Summer Monsoon (ASM) driven by the northward/southward migration of the Inter-Tropical Convergence Zone (ITCZ).

Kinetics of D/H isotope fractionation between molecular hydrogen and water

At equilibrium, the D/H isotope fractionation factor between H2 and H2O (αH2O-H2(eq)) is a sensitive indicator of temperature, and has been used as a geothermometer for natural springs and gas discharges. However, δDH2 measured in spring waters may underestimate subsurface temperatures of origin due to partial isotopic re-equilibration during ascent and cooling. We present new experimental data on the kinetics of D–H exchange for H2 dissolved in liquid water at temperatures below 100 °C. Comparing these results with published exchange rates obtained from gas phase experiments (100–400 °C), we derive a consistent activation energy of 52 kJ/mol, and the following rate expressions;lnk=9.186-6298/Tandk1=9764.61[H2O]e-6298/Twhere T is absolute temperature (K), k is the universal rate constant ([L/mol]/hr), and k1 is a pseudo-first-order constant (hr−1) applicable to water-dominated terrestrial systems by constraining [H2O] as the density of H2O (in mol/L) at the P-T of interest. The density-dependent rate constant accounts for the kinetic disparity of D–H exchange with H2 when dissolved in liquid H2O relative to a gas/steam phase, exemplifed by 1/k1 at 100 °C of ∼2 days in liquid, versus ∼7 yrs in saturated steam. This difference may explain the high variability of δDH2 observed in fumarolic gases. Fluids convecting in the crust frequently reach T > 225 °C, where isotopic equilibrium is rapidly attained (<1 hr). We compare fractionation factors measured in natural fluids (αOBS) with values expected for equilibrium at the T of acquisition. Where these values differ, we use kinetic models to estimate cooling rates during upward advection that account for the observed disequilibrium. Models fit to fluids from Yellowstone Park and the Lost City (deep-sea) vent field, both recovered at ∼90 °C, require respective transit times of ∼7 hrs and ∼11 days between higher temperature reaction zones and the surface. Using estimates of subsurface depths of origin, however, suggests similar mean fluid flow rates (10 s of meters/hr). Additional complications must be considered when interpreting the δDH2 of lower-temperature effluent. When applied to data from deep-sea hydrothermal systems, our kinetic models indicate microbial catalysis accelerates D–H exchange once fluids cool below ∼60 °C. The H2 measured in both continental alkaline springs and fracture fluids from Precambrian shield rock is likely produced at T < 100 °C, through processes such as serpentinization. In these settings, δDH2 values appear closer to equilibrium with H2O than those from geothermal systems. Considering kinetic isotope effects may yield H2 that is out of equilibrium when generated at lower temperatures, we calculate maximum (isothermal) times to apparent isotopic equilibrium of 1.3 yrs at 50 °C, 9 yrs at 25 °C, and 35 yrs at 10 °C. A similar calculation applied to Antarctic brines (−13 °C), where measured δDH2 is far from equilibrium, yields ∼350 yrs. This time is shorter than the fluids have been isolated (2.8 ka), suggesting kinetic isotope effects associated with H2 destruction or loss via diffusion may also be possible.

Spatio-temporal variability and source identification for metal contamination in the river sediment of Indian Sundarbans, a world heritage site

Metal pollution is a subject of growing concern as it affects the whole food chain of an ecosystem by bioaccumulation. Growing industrialization and anthropogenic intervention have put tremendous pressure on self-sustaining ecosystems worldwide. Sundarbans mangrove estuary, being a UNESCO World Heritage site, suffers severely from anthropogenic stress, urbanization, ecotourism, overexploitation of natural resources and discharges of industrial as well as municipal waste products. Our study unfolds the extent of metal pollution in the sediment of this estuarine mangrove ecosystem and also investigates the source and distribution of these metals. Extensive samplings were performed during three major seasons, namely pre-monsoon, monsoon, and post-monsoon for two consecutive years at ten sampling stations along the major river networks of the mangrove estuary. Seasonal variations of these metals, physicochemical properties, and soil texture studies were performed to explore the sediment quality of the study area. Positive correlation was observed between the pollutants and siltation. Several environmental indices were investigated to explore the degree of metal pollution which revealed contamination of Cd, Cr, and Pb to cross the permitted safe index in the study area. Pollution load index indicates the spatial as well as seasonal variation of eco toxic metal load along the course of the rivers. Statistical analyses such as principal component analysis and correlation matrix identified different sources for metal contamination. Almost 700 tannery industries are located in the upstream region of the rivers, and several small- and large-scale battery industries seem to be the main possible source for Cd, Cr, and Pb pollution. Analysis of the results indicates the alarming condition of this heritage site. The metal concentrationsbeyond toxicity thresholds are responsible for gradual deterioration of this estuarine mangrove which may only be protected by developing sustainable management planning.