The size distribution of organic carbon in headwater streams in the Amazon basin

Despite the strong representativeness of streams in the Amazon basin, their role in the accumulation of coarse particulate organic carbon (CPOC), fine particulate organic carbon (FPOC), and dissolved organic carbon (DOC) in transport, an important energy source in these environments, is poorly known. It is known that the arboreal vegetation in the Amazon basin is influenced by soil fertility and rainfall gradients, but would these gradients promote local differences in organic matter in headwater streams? To answer this question, 14 low-order streams were selected within these gradients along the Amazon basin, with extensions that varied between 4 and 8 km. The efficiency of the transformation of particulate into dissolved carbon fractions was assessed for each stream. The mean monthly benthic organic matter storage ranged between 1.58 and 9.40 t ha^?1 month^?1. In all locations, CPOC was the most abundant fraction in biomass, followed by FPOC and DOC. Rainfall and soil fertility influenced the distribution of the C fraction (p?=?0.01), showing differentiated particulate organic carbon (POC) storage and DOC transportation along the basin. Furthermore, the results revealed that carbon quantification at the basin level could be underestimated, ultimately influencing the global carbon calculations for the region. This is especially due to the fact that the majority of studies consider only fine particulate organic matter and dissolved organic matter, which represent less than 50 % of the stored and transported carbon in streambeds.     

Mine water geochemistry and metal flux in a major historic Pb-Zn-F orefield, the Yorkshire Pennines, UK

Recent studies have shown up to 6 % of rivers in England and Wales to be impacted by discharges from abandoned metal mines. Despite the large extent of impacts, there are still many areas where mine water impact assessments are limited by data availability. This study provides an overview of water quality, trace element composition and flux arising from one such area; the Yorkshire Pennine Orefield in the UK. Mine drainage waters across the orefield are characterised by Ca–HCO₃–SO₄-type waters, with moderate mineralization (specific electrical conductance: 160–525 μS cm^?1) and enrichment of dissolved Zn (≤2003 μg?L^?1), Ba (≤971 μg?L^?1), Pb (≤183 μg?L^?1) and Cd (≤12 μg?L^?1). The major ion composition of the waters reflects the Carboniferous gritstone and limestone-dominated country rock, the latter of which is heavily karstified in parts of the orefield, while sulphate and trace element enrichment is a product of the oxidation of galena, sphalerite and barite mineralization. Contaminant flux measurements at discharge sites highlight the disproportionate importance of large drainage levels across the region, which generally discharge into first-order headwater streams. Synoptic metal loading surveys undertaken in the Hebden Beck sub-catchment of the river Wharfe highlight the importance of major drainage levels to instream baseflow contamination, with diffuse sources from identifiable expanses of waste rock becoming increasingly prominent as river flows increase.     

Silver behaviour along the salinity gradient of the Gironde Estuary

Dissolved and particulate Ag concentrations (Ag_D and Ag_P, respectively) were measured in surface water and suspended particulate matter (SPM) along the salinity gradient of the Gironde Estuary, South West France, during three cruises (2008–2009) covering contrasting hydrological conditions, i.e. two cruises during intermediate and one during high freshwater discharge (~740 and ~2,300 m³/s). Silver distribution reflected non-conservative behaviour with 60–70 % of Ag_P in freshwater particles being desorbed by chlorocomplexation. The amount of Ag_P desorbed was similar to the so-called reactive, potentially bioavailable Ag_P fraction (60?±?4 %) extracted from river SPM by 1 M HCl. Both Ag_P (0.22?±?0.05 mg/kg) and Ag_P/Th_P (0.025–0.028) in the residual fraction of fluvial and estuarine SPM were similar to those in SPM from the estuary mouth and in coastal sediments from the shelf off the Gironde Estuary, indicating that chlorocomplexation desorbs the reactive Ag_P. The data show that desorption of reactive Ag_P mainly occurs inside the estuary during low and intermediate discharge, whereas expulsion of partially Ag_P-depleted SPM (Ag_P/Th_P ~0.040) during the flood implies ongoing desorption in the coastal ocean, e.g. in the nearby oyster production areas (Marennes-Oléron Bay). The highest Ag_D levels (6–8 ng/L) occurred in the mid-salinity range (15–20) of the Gironde Estuary and were decoupled from freshwater discharge. In the maximum turbidity zone, Ag_D were at minimum, showing that high SPM concentrations (a) induce Ag_D adsorption in estuarine freshwater and (b) counterbalance Ag_P desorption in the low salinity range (1–3). Accordingly, Ag behaviour in turbid estuaries appears to be controlled by the balance between salinity and SPM levels. The first estimates of daily Ag_D net fluxes for the Gironde Estuary (Boyle’s method) showed relatively stable theoretical Ag_D at zero salinity (Ag _D ⁰ = 25–30 ng/L) for the contrasting hydrological situations. Accordingly, Ag_D net fluxes were very similar for the situations with intermediate discharge (1.7 and 1.6 g/day) and clearly higher during the flood (5.0 g/day) despite incomplete desorption. Applying Ag _D ⁰ to the annual freshwater inputs provided an annual net Ag_D flux (0.64–0.89 t/year in 2008 and 0.56–0.77 t/year in 2009) that was 12–50 times greater than the Ag_D gross flux. This estimate was consistent with net Ag_D flux estimates obtained from gross Ag_P flux considering 60 % desorption in the estuarine salinity gradient.     

The effects and the toxicity increases caused by bicarbonate,chloride, and other water components during the UV/TiO<Subscript>2</Subscript> degradation of oxazaphosphorine drugs

The influences of HCO₃ ^?, Cl^?, and other components on the UV/TiO₂ degradation of the antineoplastic agents ifosfamide (IFO) and cyclophosphamide (CP) were studied in this work. The results indicated that the presence of HCO₃ ^?, Cl^?, NO₃ ^?, and SO₄ ^2? in water bodies resulted in lower degradation efficiencies. The half-lives of IFO and CP were 1.2 and 1.1 min and increased 2.3–7.3 and 3.2–6.3 times, respectively, in the presence of the four anions (initial compound concentration = 100 μg/L, TiO₂ loading =100 mg/L, anion concentration = 1000 mg/L, and pH = 8). Although the presence of HCO₃ ^? in the UV/TiO₂/HCO₃ ^? system resulted in a lower degradation rate and less byproduct formation for IFO and CP, two newly identified byproducts, P11 (M.W. = 197) and P12 (M.W. = 101), were formed and detected, suggesting that additional pathways occurred during the reaction of ?CO₃ ^? in the system. The results also showed that ?CO₃ ^? likely induces a preferred ketonization pathway. Besides the inorganic anions HCO₃ ^?, Cl^?, NO₃ ^?, and SO₄ ^2?, the existence of dissolved organic matter in the water has a significant effect and inhibits CP degradation. Toxicity tests showed that higher toxicity occurred in the presence of HCO₃ ^? or Cl^? during UV/TiO₂ treatment and within 6 h of reaction time, implying that the effects of these two anions should not be ignored when photocatalytic treatment is applied to treat real wastewater.     

Response surface modeling for optimization heterocatalytic Fenton oxidation of persistence organic pollution in high total dissolved solid containing wastewater

The rice-husk-based mesoporous activated carbon (MAC) used in this study was precarbonized and activated using phosphoric acid. N₂ adsorption/desorption isotherm, X-ray powder diffraction, electron spin resonance, X-ray photoelectron spectroscopy and scanning electron microscopy, transmission electron microscopy, ²⁹Si-NMR spectroscopy, and diffuse reflectance spectroscopy were used to characterize the MAC. The tannery wastewater carrying high total dissolved solids (TDS) discharged from leather industry lacks biodegradability despite the presence of dissolved protein. This paper demonstrates the application of free electron-rich MAC as heterogeneous catalyst along with Fenton reagent for the oxidation of persistence organic compounds in high TDS wastewater. The heterogeneous Fenton oxidation of the pretreated wastewater at optimum pH (3.5), H₂O₂ (4 mmol/L), FeSO₄?7H₂O (0.2 mmol/L), and time (4 h) removed chemical oxygen demand, biochemical oxygen demand, total organic carbon and dissolved protein by 86, 91, 83, and 90 %, respectively.     

Historical trend of nitrogen and phosphorus loads from the upper Yangtze River basin and their responses to the Three Gorges Dam

Excessive inputs of nitrogen and phosphorus (N and P) degrade surface water quality worldwide. Impoundment of reservoirs alters the N and P balance of a basin. In this study, riverine nutrient loads from the upper Yangtze River basin (YRB) at the Yichang station were estimated using Load Estimator (LOADEST). Long-term load trends and monthly variabilities during three sub-periods based on the construction phases of the Three Gorges Dam (TGD) were analyzed statistically. The dissolved inorganic nitrogen (DIN) loads from the upper YRB for the period from 1990 to 2009 ranged from 30.47?×?10⁴ to 78.14?×?10⁴ t, while the total phosphorus (TP) loads ranged from 2.54?×?10⁴ to 7.85?×?10⁴ t. DIN increased rapidly from 1995 to 2002 mainly as a result of increased fertilizer use. Statistics of fertilizer use in the upper YRB agreed on this point. However, the trend of the TP loads reflected the combined effect of removal by sedimentation in reservoirs and increased anthropogenic inputs. After the TGD impoundment in 2003, decreasing trends in both DIN and TP loads were found. The reduction in DIN was mainly caused by ammonium consumption and transference. From an analysis of monthly loads, it was found that DIN had a high correlation to discharges. For TP loads, an average decrease of 4.91 % in October was found when the TGD impoundment occurred, but an increase of 4.23 % also occurred in July, corresponding to the washout from sediment deposited in the reservoir before July. Results of this study revealed the TGD had affected nutrient loads in the basin, and it had played a role in nutrient reduction after its operation.     

Interannual variability of transboundary sulphur flux

A study was conducted by the Atmospheric Environment Service (AES) to compute the transboundary sulphur flux between eastern Canada and the eastern United States on a monthly and annual basis for the years 1980–1983.The S fluxes were calculated using the AES Lagrangian model. SO₂ and SO₄ concentrations were computed at 16 line segment mid-points along the Canada-U.S. border from western Ontario through Quebec to the Maritimes. Sulphur fluxes were determined at 6-h intervals and summed temporally and spatially to obtain the total transboundary S flux. By using only the Canadian and only the U.S. emissions, the total S flux contributions from each country could be determined.Canadian and U.S. emissions declined from 1980 to 1983 by 20% and 11%, respectively, then increased slightly in 1983. The total annual S flux from the U.S. to Canada ranged from 1.86 Mt S (1980) to 1.61 Mt S (1983) while the flux from Canada to the U.S. ranged from 0.75 Mt S (1980) to 0.52 Mt S (1982). Fluxes between both countries were highest (lowest) in the winter (summer) because of the stronger (lighter) winds and higher (lower) SO₂ concentrations. However, SO₄ mass flux peaked in summer and early fall because of higher chemical conversion rates.Annual transboundary fluxes were observed to change by up to 20% in response to emissions changes and meteorological variability and these two influences should be considered together when assessing flux changes.     

Comparative performance of flat sheet and spiral wound modules in the nanofiltration of reactive dye solution

Background and purpose

Besides the opportunities for reuse, stringent regulations and growing public awareness demand an enhanced quality of effluent from dye industries. Treatment of an aqueous solution of dye (reactive red 198) was carried out in a nanofiltration unit using both flat sheet and spiral wound modules to obtain a comparative performance evaluation in terms of permeate flux and quality.

Methods

Hydrophilized polyamide membrane with molecular weight cutoff of 150 was used for the experiments. Effects of trans-membrane pressure (TMP), feed concentration and addition of salt on permeate flux were investigated. Percent reduction of color, chemical oxygen demand (COD), total dissolved solid (TDS), and conductivity were determined to assess performance of the membrane.

Results

The maximum flux decline was 16.1% of its initial value at 490 kPa TMP with 50 ppm feed concentration in spiral wound module, whereas the same in flat sheet under same conditions was 7.2%. The effect of TMP showed a quasi-linear increase in flux with increasing pressure. Increased permeate concentration led to the reduction in observed retention of dye in the membrane. The average reduction in color, COD, and TDS were 96.88%, 97.38%, and 89.24%, respectively. The decline in permeate flux was more in case of spiral wound module compared to flat sheet. However, spiral wound module performed better in terms of color removal, COD reduction, and TDS removal.

Conclusion

Substantial removal of color was achieved in the nanofiltration experiments with a marked reduction in COD and TDS. The process allowed the production of permeate stream with great reutilization possibilities.     

Monitoring the Multi-Year Carbon Balance of a Subarctic Palsa Mire with Micrometeorological Techniques

This article reports a dataset on 8 years of monitoring carbon fluxes in a subarctic palsa mire based on micrometeorological eddy covariance measurements. The mire is a complex with wet minerotrophic areas and elevated dry palsa as well as intermediate sub-ecosystems. The measurements document primarily the emission originating from the wet parts of the mire dominated by a rather homogenous cover of Eriophorum angustifolium. The CO₂/CH₄ flux measurements performed during the years 2001–2008 showed that the areas represented in the measurements were a relatively stable sink of carbon with an average annual rate of uptake amounting to on average ?46 g C m^?2 y^?1 including an equally stable loss through CH₄ emissions (18–22 g CH₄–C m^?2 y^?1). This consistent carbon sink combined with substantial CH₄ emissions is most likely what is to be expected as the permafrost under palsa mires degrades in response to climate warming.     

Sources and mass fluxes of the main contaminants in a heavily polluted and modified river of the North China Plain

Many rivers in China and other newly industrialized countries have suffered from severe degradation of water quality in the context of rapid economic growth. An accounting method was developed to investigate the source and mass fluxes of the main contaminants in the Ziya River, a severely polluted and heavily modified river in a semiarid area of the North China Plain, where chemical oxygen demand (COD) and ammonia nitrogen (NH₄-N) were the most important indicators of pollution. The results showed that the urban sewage with high concentration of COD and NH₄-N dominated the streams, contributing to 80.7 % of the streamflow, 92.2 % of COD, and 94.5 % of NH₄-N. The concentrations of COD and NH₄-N in streams varied from 24.0–195.0 to 5.8–43.8 mg/L, respectively. Mass fluxes of COD and NH₄-N of all pathways were quantified. Much of the polluted water was diverted to irrigation, and some eventually flowed into the Bohai Sea. Installation of adequate wastewater treatment facilities and making strict discharge standards can help improve the water quality. Our findings imply that a simple accounting method provides an extremely well-documented example for load estimation and can be useful for intervention strategies in heavily polluted and modified rivers in newly industrialized countries.     

The distribution and sea–air transfer of volatile mercury in waste post-desulfurization seawater discharged from a coal-fired power plant

The waste seawater discharged in coastal areas from coal-fired power plants equipped with a seawater desulfurization system might carry pollutants such as mercury from the flue gas into the adjacent seas. However, only very limited impact studies have been carried out. Taking a typical plant in Xiamen as an example, the present study targeted the distribution and sea–air transfer flux of volatile mercury in seawater, in order to trace the fate of the discharged mercury other than into the sediments. Samples from 28 sampling sites were collected in the sea area around two discharge outlets of the plant, daily and seasonally. Total mercury, dissolved gaseous mercury and dissolved total mercury in the seawater, as well as gaseous elemental mercury above the sea surface, were investigated. Mean concentrations of dissolved gaseous mercury and gaseous elemental mercury in the area were 183 and 4.48 ng m^?3 in summer and 116 and 3.92 ng m^?3 in winter, which were significantly higher than those at a reference site. Based on the flux calculation, the transfer of volatile mercury was from the sea surface into the atmosphere, and more than 4.4 kg mercury, accounting for at least 2.2 % of the total discharge amount of the coal-fired power plant in the sampling area (1 km²), was emitted to the air annually. This study strongly suggested that besides being deposited into the sediment and diluted with seawater, emission into the atmosphere was an important fate for the mercury from the waste seawater from coal-fired power plants.     

Surface runoff and nitrogen (N) loss in a bamboo (Phyllostachys pubescens) forest under different fertilization regimes

Nitrogen (N) losses from agricultural fields have been extensively studied. In contrast, surface runoff and N losses have rarely been considered for bamboo forests that are widespread in regions such as southern China. The thriving of bamboo industries has led to increasing fertilizer use in bamboo forests. In this study, we evaluated surface runoff and N losses in runoff following different fertilization treatments under field conditions in a bamboo (Phyllostachys pubescens) forest in the catchment of Lake Taihu in Jiangsu, China. Under three different fertilization regimes, i.e., control, site-specific nutrient management (SSNM), and farmer's fertilization practice (FFP), the water runoff rate amounted to 356, 361, and 342 m³?ha^?1 and accounted for 1.91, 1.98, and 1.85 % of the water input, respectively, from June 2009 to May 2010. The total N losses via surface runoff ranged from 1.2 to 1.8 kg?ha^?1. Compared with FFP, the SSNM treatment reduced total nitrogen (TN) and dissolved nitrogen (DN) losses by 31 and 34 %, respectively. The results also showed that variations in N losses depended mainly on runoff fluxes, not N concentrations. Runoff samples collected from all treatments throughout the year showed TN concentrations greater than 0.35 mg?L^?1, with the mean TN concentration in the runoff from the FFP treatment reaching 8.97 mg?L^?1. The loss of NO₃ ^?–N was greater than the loss of NH₄ ⁺–N. The total loss of dissolved organic nitrogen (DON) reached 23–41 % of the corresponding DN. Therefore, DON is likely the main N species in runoff from bamboo forests and should be emphasized in the assessment and management of N losses in bamboo forest.     

Spatial and temporal variations of nitrous oxide flux between coastal marsh and the atmosphere in the Yellow River estuary of China

To investigate the spatial and seasonal variations of nitrous oxide (N₂O) fluxes and understand the key controlling factors, we explored N₂O fluxes and environmental variables in high marsh (HM), middle marsh (MM), low marsh (LM), and mudflat (MF) in the Yellow River estuary throughout a year. Fluxes of N₂O differed significantly between sampling periods as well as between sampling positions. During all times of day and the seasons measured, N₂O fluxes ranged from ?0.0051 to 0.0805 mg N₂O m^?2 h^?1, and high N₂O emissions occurred during spring (0.0278 mg N₂O m^?2 h^?1) and winter (0.0139 mg N₂O m^?2 h^?1) while low fluxes were observed during summer (0.0065 mg N₂O m^?2 h^?1) and autumn (0.0060 mg N₂O m^?2 h^?1). The annual average N₂O flux from the intertidal zone was 0.0117 mg N₂O m^?2 h^?1, and the cumulative N₂O emission throughout a year was 113.03 mg N₂O m^?2, indicating that coastal marsh acted as N₂O source. Over all seasons, N₂O fluxes from the four marshes were significantly different (p?<?0.05), in the order of HM (0.0256?±?0.0040 mg N₂O m^?2 h^?1)?>?MF (0.0107?±?0.0027 mg N₂O m^?2 h^?1)?>?LM (0.0073?±?0.0020 mg N₂O m^?2 h^?1)?>?MM (0.0026?±?0.0011 mg N₂O m^?2 h^?1). Temporal variations of N₂O emissions were related to the vegetations (Suaeda salsa, Phragmites australis, and Tamarix chinensis) and the limited C and mineral N in soils during summer and autumn and the frequent freeze/thaw cycles in soils during spring and winter, while spatial variations were mainly affected by tidal fluctuation and plant composition at spatial scale. This study indicated the importance of seasonal N₂O contributions (particularly during non-growing season) to the estimation of local N₂O inventory, and highlighted both the large spatial variation of N₂O fluxes across the coastal marsh (CV?=?158.31 %) and the potential effect of exogenous nitrogen loading to the Yellow River estuary on N₂O emission should be considered before the annual or local N₂O inventory was evaluated accurately.     

Effects of an invasive polychaete on benthic phosphorus cycling at sea basin scale: An ecosystem disservice

Macrofaunal activities in sediments modify nutrient fluxes in different ways including the expression of species-specific functional traits and density-dependent population processes. The invasive polychaete genus Marenzelleria was first observed in the Baltic Sea in the 1980s. It has caused changes in benthic processes and affected the functioning of ecosystem services such as nutrient regulation. The large-scale effects of these changes are not known. We estimated the current Marenzelleria spp. wet weight biomass in the Baltic Sea to be 60–87 kton (95% confidence interval). We assessed the potential impact of Marenzelleria spp. on phosphorus cycling using a spatially explicit model, comparing estimates of expected sediment to water phosphorus fluxes from a biophysical model to ecologically relevant experimental measurements of benthic phosphorus flux. The estimated yearly net increases (95% CI) in phosphorous flux due to Marenzelleria spp. were 4.2–6.1 kton based on the biophysical model and 6.3–9.1 kton based on experimental data. The current biomass densities of Marenzelleria spp. in the Baltic Sea enhance the phosphorus fluxes from sediment to water on a sea basin scale. Although high densities of Marenzelleria spp. can increase phosphorus retention locally, such biomass densities are uncommon. Thus, the major effect of Marenzelleria seems to be a large-scale net decrease in the self-cleaning capacity of the Baltic Sea that counteracts human efforts to mitigate eutrophication in the region.     

Analyzing sediment dissolved oxygen based on microprofile modeling

Sediment plays a key role in controlling the oxygen demand of aquatic systems. The reaction rate, penetration depth, and flux across the sediment–water interface (SWI) are important factors in sediment oxygen consumption. However, there were few methods to collect these data until recently. In this study, methods were developed to simulate the oxygen microprofile and calculate the sediment oxygen consumption rate, oxygen penetration depth, and oxygen flux across the SWI. We constructed a sediment oxygen measuring system using an oxygen microelectrode and a control device. The simulation equations were derived from both zero and first-order kinetic models, while the penetration depth and the oxygen flux were calculated from the simulation results. The method was tested on four prepared sediment samples. Decreases in dissolved oxygen in surface sediment were clearly detected by the microelectrode. The modeled data were a good fit for the observed data (R ²?>?0.95), and zero-order kinetics were more suitable than first-order kinetics. The values for penetration depth (1.3–3.9 mm) and oxygen fluxes (0.061–0.114 mg/cm²/day) calculated by our methods are comparable with those from other studies.     

Coastal hydrogeological system of Mar Piccolo (Taranto,Italy)

The Mar Piccolo basin is an internal sea basin located along the Ionian coast (Southern Italy), and it is surrounded primarily by fractured carbonate karstic environment. Because of the karstic features, the main continental water inflow is from groundwater discharge. The Mar Piccolo basin represents a peculiar and sensitive environment and a social emergency because of sea water and sediment pollution. This pollution appears to be caused by the overlapping effects of dangerous anthropogenic activities, including heavy industries and commercial and navy dockyards. The paper aims to define the contribution of subaerial and submarine coastal springs to the hydrological dynamic equilibrium of this internal sea basin. A general approach was defined, including a hydrogeological basin border assessment to detect inflowing springs, detailed geological and hydrogeological conceptualisation, in situ submarine and subaerial spring measurements, and flow numerical modelling. Multiple sources of data were obtained to define a relevant geodatabase, and it contained information on approximately 2000 wells, located in the study area (1600 km²). The conceptualisation of the hydrogeological basin, which is 978 km² wide, was supported by a 3D geological model that interpolated 716 stratigraphic logs. The variability in hydraulic conductivity was determined using hundreds of pumping tests. Five surveys were performed to acquire hydro-geochemical data and spring flow-yield measurements; the isotope groundwater age was assessed and used for model validation. The mean annual volume exchanged by the hydrogeological basin was assessed equal to 106.93 10⁶ m³. The numerical modelling permitted an assessment of the mean monthly yield of each spring outflow (surveyed or not), travel time, and main path flow.     

Recharge and Flow in the Medicine Lake Volcano–Fall River Springs Groundwater Basin,California

Isotopic measurements of the 34 m³/s discharge from the Fall River Springs of northern California indicate recharge from 50 km upgradient in high elevation regions of Medicine Lake Volcano. Age determinations suggest less than 20-year travel time. Data demonstrate Klamath Basin further north cannot be a recharge source. Mass balance calculations support that annual precipitation on the volcano supplies observed spring discharge, requiring 50%–75% recharge rates. Radiocarbon and δ¹³C of dissolved inorganic carbon indicate 30%–40% is derived from magmatic CO₂. Measured excess ³He is also consistent with the presence of magmatic gas derived from the Quaternary Age Medicine Lake Volcano.     

Local deposition of mercury in topsoils around coal-fired power plants: is it always true?

Mercury (Hg) is a toxic element that is emitted to the atmosphere through human activities, mainly fossil fuel combustion. Hg accumulations in soil are associated with atmospheric deposition, while coal-burning power plants remain the most important source of anthropogenic mercury emissions. In this study, we analyzed the Hg concentration in the topsoil of the Kozani–Ptolemais basin where four coal-fired power plants (4,065 MW) run to provide 50 % of electricity in Greece. The study aimed to investigate the extent of soil contamination by Hg using geostatistical techniques to evaluate the presumed Hg enrichment around the four power plants. Hg variability in agricultural soils was evaluated using 276 soil samples from 92 locations covering an area of 1,000 km². We were surprised to find a low Hg content in soil (range 1–59 μg kg^?1) and 50 % of samples with a concentration lower than 6 μg kg^?1. The influence of mercury emissions from the four coal-fired power plants on soil was poor or virtually nil. We associate this effect with low Hg contents in the coal (1.5–24.5 μg kg^?1) used in the combustion of these power plants (one of the most Hg-poor in the world). Despite anthropic activity in the area, we conclude that Hg content in the agricultural soils of the Kozani–Ptolemais basin is present in low concentrations.     

Integrated chemical species analysis with source-receptor modeling results to characterize the effects of terrain and monsoon on ambient aerosols in a basin

This study integrated estimated oxidation ratio of sulfur (SOR) and oxidation ratio of nitrogen (NOR) with source-receptor modeling results to identify the effects of terrain and monsoons on ambient aerosols in an urban area (north basin) and a rural area (south basin) of the Taichung Basin. The estimated results indicate that the conversion of sulfur mainly occurs in fine particles (PM_2.5), whereas the conversion of nitrogen occurs in approximately equal quantities of PM_2.5 and coarse particles (PM_2.5–10). The results show a direct relationship for PM_2.5 between the modeling results with SOR and NOR. The high PM_2.5 SOR, NOR, and secondary aerosol values all occurred in the upwind area during both monsoons; this shows that the photochemical reaction and the terrain effect on the pollutant transmission were significant in the basin. Additionally, the urban heat island effect on the urban area and the valley effect on the rural area were significant. The results show that secondary aerosol in PM_2.5–10 contributed approximately 10 % during both monsoons, and the difference in the contribution from secondary aerosol between both areas was small. Vehicle exhaust emissions and wind-borne dust were two crucial PM_2.5–10 contributors during both monsoons; their average contributions in both areas were higher than 34 and 32 %, respectively.     

Geochemical behaviour of dissolved trace elements in a monsoon-dominated tropical river basin,Southwestern India

The study presents a 3-year time series data on dissolved trace elements and rare earth elements (REEs) in a monsoon-dominated river basin, the Nethravati River in tropical Southwestern India. The river basin lies on the metamorphic transition boundary which separates the Peninsular Gneiss and Southern Granulitic province belonging to Archean and Tertiary–Quaternary period (Western Dharwar Craton). The basin lithology is mainly composed of granite gneiss, charnockite and metasediment. This study highlights the importance of time series data for better estimation of metal fluxes and to understand the geochemical behaviour of metals in a river basin. The dissolved trace elements show seasonality in the river water metal concentrations forming two distinct groups of metals. First group is composed of heavy metals and minor elements that show higher concentrations during dry season and lesser concentrations during the monsoon season. Second group is composed of metals belonging to lanthanides and actinides with higher concentration in the monsoon and lower concentrations during the dry season. Although the metal concentration of both the groups appears to be controlled by the discharge, there are important biogeochemical processes affecting their concentration. This includes redox reactions (for Fe, Mn, As, Mo, Ba and Ce) and pH-mediated adsorption/desorption reactions (for Ni, Co, Cr, Cu and REEs). The abundance of Fe and Mn oxyhydroxides as a result of redox processes could be driving the geochemical redistribution of metals in the river water. There is a Ce anomaly (Ce/Ce*) at different time periods, both negative and positive, in case of dissolved phase, whereas there is positive anomaly in the particulate and bed sediments. The Ce anomaly correlates with the variations in the dissolved oxygen indicating the redistribution of Ce between particulate and dissolved phase under acidic to neutral pH and lower concentrations of dissolved organic carbon. Unlike other tropical and major world rivers, the effect of organic complexation on metal variability is negligible in the Nethravati River water.