Nitrate reduction coupled with microbial oxidation of sulfide in river sediment

Purpose

Nitrate (NO ₃ ^? ) is often considered to be removed mainly through microbial respiratory denitrification coupled with carbon oxidation. Alternatively, NO ₃ ^? may be reduced by chemolithoautotrophic bacteria using sulfide as an electron donor. The aim of this study was to quantify the NO ₃ ^? reduction process with sulfide oxidation under different NO ₃ ^? input concentrations in river sediment.

Materials and methods

Under NO ₃ ^? input concentrations of 0.2 to 30?mM, flow-through reactors filled with river sediment from the Pearl River, China, were used to measure the processes of potential NO ₃ ^? reduction and sulfate (SO ₄ ^2? ) production. Molecular biology analyses were conducted to study the microbial mechanisms involved.

Results and discussion

Simultaneous NO₃ ^? removal and SO₄ ^2? production were observed with the different NO ₃ ^? concentrations in the sediment samples collected at different depths. Potentially, NO ₃ ^? removal reached 72 to 91?% and SO ₄ ^2? production rates ranged from 0.196 to 0.903?mM?h^?1. The potential NO ₃ ^? removal rates were linearly correlated to the NO ₃ ^? input concentrations. While the SO ₄ ^2? production process became stable, the NO ₃ ^? reduction process was still a first-order reaction within the range of NO ₃ ^? input concentrations. With low NO ₃ ^? input concentrations, the NO ₃ ^? removal was mainly through the pathway of dissimilatory NO ₃ ^? reduction to NH ₄ ⁺ , while with higher NO ₃ ^? concentrations the NO ₃ ^? removal was through the denitrification pathway.

Conclusions

While most of NO ₃ ^? in the sediment was reduced by denitrifying heterotrophs, sulfide-driven NO ₃ ^? reduction accounted for up to 26?% of the total NO ₃ ^? removal under lower NO ₃ ^? concentrations. The vertical distributions of NO ₃ ^? reduction and SO ₄ ^2? production processes were different because of the variable bacterial communities with depth.     

Biotic and abiotic processes controlling water chemistry during snowmelt at rabbit ears pass,Rocky Mountains,Colorado, U.S.A.

The chemical composition of snowmelt, groundwater, and streamwater was monitored during the spring of 1991 and 1992 in a 200-ha subalpine catchment on the western flank of the Rocky Mountains near Steamboat Springs, Colorado. Most of the snowmelt occurred during a one-month period annually that began in mid-May 1991 and mid-April 1992. The average water quality characteristics of individual sampling sites (meltwater, streamwater, and groundwater) were similar in 1991 and 1992. The major ions in meltwater were differentially eluted from the snowpack, and meltwater was dominated by Ca²⁺, SO ₄ ^2? , and NO ₃ ^? . Groundwater and streamwater were dominated by weathering products, including Ca²⁺, HCO ₃ ^? (measured as alkalinity), and SiO₂, and their concentrations decreased as snowmelt progressed. One well had extremely high NO ₃ ^? . concentrations, which were balanced by Ca²⁺ concentrations. For this well, hydrogen ion was hypothesized to be generated from nitrification in overlying soils, and subsequently exchanged with other cations, particularly Ca²⁺. Solute concentrations in streamwater also decreased as snowmelt progressed. Variations in groundwater levels and solute concentrations indicate that most of the meltwater traveled through the surficial materials. A mass balance for 1992 indicated that the watershed retained H⁺, NH ₄ ⁺ , NO ₃ ^? , SO ₄ ^2? and Cl^? and was the primary source of base cations and other weathering products. Proportionally more SO ₄ ^2? was deposited with the unusually high summer rainfall in 1992 compared to that released from snowmelt, whereas NO ₃ ^? was higher in snowmelt and Cl^? was the same. The sum of snowmelt and rainfall could account for greater than 90% of the H⁺ and NH ₄ ⁺ retained by the watershed and greater than 50% of the NO ₃ ^? .     

Mid-term trends in acid precipitation,streamwater chemistry and element budgets in the strengbach catchment (Vosges Mountains,France)

In the Vosges Mountains (NE of France), integrated plot-catchment studies have been carried out since 1985 in the Strengbach basin to study the influence of acid atmospheric inputs on surface water quality and element budgets. In this paper, available mid-term time series (1985–1991) have been considered to detect obvious trends, if any, in surface water chemistry and element budgets. Air quality data showed a slight decline for SO₂, whereas NO₂ slightly increased over the period, but these trends are not very significant. This is in agreement with increased N concentration (mainly as NH ₄ ⁺ ) and with the stability of SO ₄ ^2? in open field precipitation. Because of a significant decrease in rainfall amount over the period, only inputs of NH ₄ ⁺ increased significantly whereas H⁺ and SO ₄ ²⁺ inputs declined. In spring and streamwaters, pH and dissolved Si concentration increased mainly as a result of a reduced flow. Na⁺, K⁺, Cl^? and HCO-3~^? concentrations remained stable whereas Ca²⁺, Mg²⁺ and SO ₄ ²⁺ concentrations declined significantly. Only NO ₃ ^? concentration increased significantly in springwaters. The catchment budgets revealed significant losses of base cations, Si and SO ₄ ^2? . These losses decreased over the period. Nitrogen was retained in the ecosystem. However, a longer record is needed to determine whether or not changes in surface water chemistry have resulted from short-term flow reductions or long-term changes in input-output ion budgets. This is specially true with N because the decline in SO ₄ ^2? output was accompanied by N accumulation.     

Monitoring and Modeling Nitrate Persistence in a Shallow Aquifer

A modeling study on fertilizer by-products fate and transport was performed in an unconfined shallow aquifer equipped with a grid of 13 piezometers. The field site was located in a former agricultural field overlying a river paleochannel near Ferrara (Northern Italy), cultivated with cereals rotation until 2004 and then converted to park. Piezometers were installed in June 2007 and were monitored until June 2009 via pressure transducer data loggers to evaluate the temporal and spatial variation of groundwater heads, while an onsite meteorological station provided data for recharge rate calculations via unsaturated zone modeling. The groundwater composition in June 2007 exhibited elevated nitrate (NO ₃ ^? ) and chloride (Cl^?) concentrations due to fertilizer leaching from the top soil. The spatial distribution of NO ₃ ^? and Cl^? was heterogeneous and the concentration decreased during the monitoring period, with NO ₃ ^? attenuation (below 10?mg/l) after 650?days. A transient groundwater flow and contaminant transport model was calibrated versus observed heads and NO ₃ ^? and Cl^? concentrations. Cl^? was used as environmental tracer to quantify groundwater flow velocity and it was simulated as a conservative species. NO ₃ ^? was treated as a reactive species and denitrification was simulated with a first order degradation rate constant. Model calibration gave a low denitrification rate (2.5e^?3 mg-NO ₃ ^? /l/d) likely because of prevailing oxic conditions and low concentration of dissolved organic carbon. Scenario modeling was implemented with steady state and variable flow time discretization to identify the mechanism of NO ₃ ^? attenuation. It was shown that transient piezometric conditions did not exert a strong control on NO ₃ ^? clean up time, while transient recharge rate did, because it is the main source of unpolluted water in the domain.     

Effects of Land Use on Hydrochemistry and Contamination of Karst Groundwater from Nandong Underground River System, China

The Nandong Underground River System (NURS) is located in Southeast Yunnan Province, China. Groundwater in NURS plays a critical role in socio-economical development of the region. However, with the rapid increase of population in recent years, groundwater quality has degraded greatly. In this study, the analysis of 36 groundwater samples collected from springs in both rain and dry seasons shows significant spatial disparities and slight seasonal variations of major element concentrations in the groundwater. In addition, results from factor analysis indicate that NO ₃ ^? , Cl^?, SO ₄ ^2? , Na⁺, K⁺, and EC in the groundwater are mainly from the sources related to human activities while Ca²⁺, Mg²⁺, HCO ₃ ^? , and pH are primarily controlled by water–rock interactions in karst system with Ca²⁺ and HCO ₃ ^? somewhat from anthropogenic inputs. With the increased anthropogenic contaminations, the groundwater chemistry changes widely from Ca-HCO₃ or Ca (Mg)-HCO₃ type to Ca-Cl (+NO₃) or Ca (Mg)-Cl (+NO₃), and Ca-Cl (+NO₃+SO₄) or Ca (Mg)-Cl (+NO₃+SO₄) type. Concentrations of NO ₃ ^? , Cl^?, SO ₄ ^2? , Na⁺, and K⁺ generally show an indistinct grouping with respect to land use types, with very high concentrations observed in the groundwater from residential and agricultural areas. This suggests that those ions are mainly derived from sewage effluents and fertilizers. No specific land use control on the Mg²⁺ ion distribution is observed, suggesting Mg²⁺ is originated from natural dissolution of carbonate rocks. The distribution of Ca²⁺ and HCO ₃ ^? does not show any distinct land use control either, except for the samples from residential zones, suggesting the Ca²⁺ and HCO ₃ ^- mainly come from both natural dissolution of carbonate rocks and sewage effluents.     

Deposition of air pollutants in a wind-exposed forest edge

The atmospheric deposition of air pollutants at a forest edge was studied by means of monitoring canopy throughfall at the edge and at five different parallel lines in the forest behind the edge. The investigation was carried out at a pine forest on the Swedish west coast. Throughfall and bulk deposition samples were analyzed for volume, SO ₄ ^2? , NO ₃ ^? , Cl^?, NH ₄ ⁺ , Na⁺, K⁺, Mg²⁺, Ca²⁺, and for pH. The results show that the throughfall flow at the edge was increased substantially for most ions. The ratios in throughfall flows between the edge and the line 50 m into the forest were for SO ₄ ^2? , 1.5, NO ₃ ^? 2.9, NH ₄ ⁺ 2.7, and Na⁺ 3.1. Since this effect is not only valid for forest edges but also for hillsides, hilltops, and edges between stands of different age, etc., there might be substantial areas which get much larger total deposition than the normally considered closed forest.     

Examination of the Dissolved Inorganic Nitrogen Budget in Three Experimental Microbasins with Contrasting Land Cover—A Mass Balance Approach

A long-term hydrological and water chemistry research was conducted in three experimental microbasins differing in land cover: (1) a purely agricultural fertilized microbasin, (2) a forested microbasin dominated by Carpinus betulus (European hornbeam), and (3) a forested microbasin dominated by Picea abies (L.) (Norway spruce). The dissolved inorganic nitrogen (DIN: NH ₄ ⁺ , NO ₂ ^? , NO ₃ ^? ) budget was examined for a period of 3 years (1991–1993). Mean annual loads of DIN along with sulfate SO ₄ ^2? and base cations Ca²⁺, Mg²⁺, Na⁺, K⁺, and HCO ₃ ^? were calculated from ion concentrations measured in stream water, open-area rainfall, throughfall (under tree canopy), and streamwater at the outlets from the microbasins. Comparison of the net imported/exported loads showed that the amount of NO ₃ ^? leached from the agricultural microbasin is ～3.7 times higher (43.57 kg ha^?1?a^?1) than that from the spruce dominated microbasin (11.86 kg ha^?1?a^?1), which is a markedly higher export of NO ₃ ^? compared to the hornbeam dominated site. Our analyses showed that land cover (tree species) and land use practices (fertilization in agriculture) may actively affect the retention and export of nutrients from the microbasins, and have a pronounce impact on the quality of streamwater. Sulfate export exceeded atmospheric rainfall inputs (measured as wet deposition) in all three microbasins, suggesting an additional dry depositions of SO ₄ ^2? and geologic weathering.     

Assessment of Critical Loads in Tropical Sal (Shorea robusta Gaertn. F.) Forests of Doon Valley Himalayas, India

The present study was conducted in tropical Sal forest ecosystem of the Doon valley in the Indian Himalayas to assess the critical load of sulfur and nitrogen and their exceedances. The observed pattern of throughfall ionic composition in the study are Ca²⁺>K⁺>Mg²⁺>Cl^?>?HCO3^?>?Na⁺>NO ₃ ^? >?SO ₃ ^2? ???NH ₄ ⁺ >F^?. The sum of cation studied is 412.29 ??eq l^?1 and that of anions is 196.98 ??eq l^?1, showing cation excess of 215.31 ??eq l^?1. The cations, namely Ca²⁺, Mg²⁺, K⁺, Na⁺, and NH ₄ ⁺ , made a contribution of about 67% of the total ion strength, where as anion comprising of SO ₄ ^2? , Cl^?, NO ₃ ^? , and HCO ₃ ^? contributed 33%. The chief acidic components were Cl^?C (12%) and HCO ₃ ^? (8%), while the presence of SO ₄ ^2? (5%) and NO ₃ ^? (6%), respectively. Percentage contribution of bole to total aboveground biomass was ??72.38% in comparison to 2.24?C2.93% of leaf biomass, 10.34?C10.96% of branch biomass and 13.21?C17.07% of bark biomass. There was high and significant variation (P?<?0.001) in the total aboveground biomass produced at different sites. The aboveground net primary productivity (ANPP) in these sites ranged between 2.09 and 9.22 t ha^?1 year^?1. The base cations and nitrogen immobilization was found to be maximum in bole. The net annual uptake of the base cations varied from 306.85 to 1,311.46 eq ha^?1 year^?1 and of nitrogen from 68.27 to 263.51 eq ha^?1 year^?1. The critical appraisal of soil showed that cation exchange capacity lied between 18.37 and 10.30 Cmol (p+) kg^?1. The base saturation percentage of soil was as high as 82.43% in Senkot, whereas in Kalusidh it was just 44.28%. The local temperature corrected base cation weathering rates based on soil mineralogy, parent material class, and texture class varied from 484.15 to 627.25 eq ha^?1 year^?1, showing a weak potentiality of the system to buffer any incoming acidity and thus providing restricted acid neutralizing capacity to keep the ecosystem stable under increased future deposition scenarios in near future. The appreciable BS of the soil indicates the presence of intense nutrient phytorecycling forces within this climate and atmospheric deposition in replenishing base cations in the soil, which includes intrinsic soil-forming processes, i.e., weathering. The highest value of critical load for acidity was 2,896.50 eq ha^?1 year^?1 and the lowest was 2,792.45 eq ha^?1 year^?1. The calculated value of the minimum critical loads for nitrogen varied from 69.77 to 265.01 eq ha^?1 year^?1, whereas the maximum nitrogen critical load ranged between 2,992.63 and 4,394.45 eq ha^?1 year^?1. The minimum and the maximum critical loads of sulfur ranged between 2,130.49 and 3,261.64 eq ha^?1 year^?1 and 2,250.58 and 3,381.73 eq ha^?1 year^?1, respectively. The values of exceedance of sulfur and nitrogen were negative, implying that in the current scenario Sal forests of the Doon valley are well protected from acidification.     

Long-term sulfate dynamics at lange bramke (Harz) used for testing two acidification models

At Lange Bramke (Harz) soil solution and runoff concentrations of major elements were observed over 16 yr. During this period acid deposition was high but showed a marked decrease of H⁺ and SO ₄ ^2? both in concentrations and fluxes over the last five years. Among others, this record reveals the following patterns: seasonality in the signals for SO ₄ ^2? and NO ₃ ^? in runoff which are synchronous; an accumulation of SO ₄ ^2? in the soil, initially up to 50% of the deposition fluxes; apparently no correlation between runoff and SO ₄ ^2? concentration, and no long-term trend in runoff concentration of SO ₄ ^2? . In this paper we use these patterns in the data set from Lange Bramke to test two established acidification models. The test criterion is that the algorithms employed by the SO ₄ ^2? modules of these models must be able to reproduce these features. To that end, both models need not to be run as it can be shown that even with completely unrestricted parameter values the two algorithms are unable to match the observed SO ₄ ^2? dynamics. The MAGIC model (Cosbyet al., 1985) is unable to reproduce, given the existence of net SO ₄ ^2? accumulation, the constant SO ₄ ^2? concentration in runoff during the last 16 years. The second model, BEM (Prenzel, 1986), is succesful in reconstructing the constant SC>4~ levels in runoff. However, on a monthly time scale BEM predicts a shift between the periodic maximum concentrations of SO ₄ ^2? and NO ₃ ^? which is not observed in the data.     

Influence of Catchment Characteristics and Flood Type on Relationship Between Streamwater Chemistry and Streamflow: Case Study from Carpathian Foothills in Poland

The study aimed to determine the influence of catchment characteristics and flood type on the relationship between streamflow and a number of chemical characteristics of streamwater. These were specific electrical conductivity (SC), pH, the concentrations of main ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO ₃ ^? , SO ₄ ^2? , and Cl^?), and nutrients (NH ₄ ⁺ , NO ₂ ^? , NO ₃ ^? , and PO ₄ ^3? ). These relationships were studied in three small catchments with different geological structure and land use. Several flood types were distinguished based on the factors that initiate flooding and specific conditions during events. Geological factors led to a lower SC and main ion concentrations at a given specific runoff in catchments built of resistant sandstone versus those built of less resistant sediments. A lower concentration of nutrients was detected in the semi-natural woodland catchment versus agricultural and mixed-use catchments, which are strongly impacted by human activity. The strongest correlation between streamflow and the chemical characteristics of water was found in the woodland catchment. Different types of floods were characterized by different ion concentrations. In the woodland catchment, higher SC and higher concentrations of most main ions were noted during storm-induced floods than during floods induced by prolonged rainfall. The opposite was true for the agricultural and mixed-use catchments. During snowmelt floods, SC, NO ₃ ^? , and most main ion concentrations were higher when the soil was unfrozen in the agricultural and mixed-use catchments versus when the soil was frozen. In the case of the remaining nutrients, lower concentrations of NH ₄ ⁺ were detected during rain-induced floods than during snowmelt floods. The opposite was true of PO ₄ ^3? .     

Adsorption features of Cu(II), Pb(II), and Zn(II) by an ordinary chernozem from nitrate,chloride, acetate,and sulfate solutions

The effect of Cl^?,SO ₄ ^2? , CH₃COO^?, and NO ₃ ^? anions on the adsorption of copper, lead, and zinc by an ordinary chernozem has been studied. The effect of the anions on the adsorption of Cu²⁺, Pb²⁺, Zn²⁺ ions is significant but uncertain. It has been shown that the attendant anions affect the shape of the adsorption isotherms, which are described by the Langmuir, Freundlich, or Henri equations. The constants of the adsorption from a nitrate solution calculated from the Langmuir equation (K _L) decrease in the following order: Cu²⁺ > Pb²⁺ >> Zn²⁺. The values of the maximum adsorption (C _max) decrease in the following order: Cu²⁺ ≥ Zn²⁺ > Pb²⁺ for acetate solutions and in the series Pb²⁺ > Zn²⁺ ≥ Cu²⁺ for nitrate solutions. The values of the Henry constants (K _H) calculated for the adsorption of the same cations from chloride solutions decrease in the same order as the values of K _L. The CH₃COO^? anion has the highest effect on the constant values. The NO ₃ ^? and Cl^? anions “switch their places” depending on the attendant cation, but their effect is always lower than that of the acetate anion. The values of C _max for copper and zinc are most affected by the CH₃COO^? anion, and the adsorption of zinc is most affected by the Cl^? and NO ₃ ^? anions. The assessment of the mobility of the adsorbed cations from the extraction with ammonium acetate (pH 4.8) has shown that the content of the desorbed metals is always lower than the content of the adsorbed cations and varies from 0.025 to 83%. According to their mobility, the adsorbed metals form the following order: Zn²⁺ > Pb²⁺ > Cu²⁺. The effect of the attendant anions on the extractability of the adsorbed cations decreases in the following order: chlorides > sulfates > acetates > nitrates.     

Ion mass budgets for small forested catchments in Finland

Ion mass and H⁺ budgets were calculated for three pristine forested catchments using bulk deposition, throughfall and runoff data. The catchments have different soil and forest type characteristics. A forest canopy filtering factor for each catchment was estimated for base cations, H⁺, Cl^? and SO ₄ ^2? by taking into account the specific filtering abilities of different stands based on the throughfall quality and the distribution of forest types. Output fluxes from the catchments were calculated from the quality and quantity of the runoff water. Deposition, weathering, ion exchange, retention and biological accumulation processes were taken into account to calculate catchment H⁺ budgets, and the ratio between external (anthropogenic) and internal H⁺ sources. In general, output exceeded input for Na⁺, K⁺, Ca²⁺, Mg²⁺, HCO ₃ ^? (if present) and A^? (organic anions), whereas retention was observed in the case of H⁺, NH ₄ ⁺ , NO ₃ ^? and SO ₄ ^2? . The range in the annual input of H⁺ was 22.8–26.3 meq m^?2 yr^?1, and in the annual output, 0.3–3.9 meq m^?2 yr^?1. Compared with some forested sites located in high acid deposition areas in southern Scandinavia, Scotland and Canada, the catchments receive rather moderate loads of acidic deposition. The consumption of H⁺ was dominated by base cation exchange plus weathering reactions (41–79 %), and by the retention of SO ₄ ^2? (17–49 %). The maximum net retention of SO ₄ ^2? was 87% in the HietajÄrvi 2 catchment, having the highest proportion of peatlands. Nitrogen transformations played a rather minor role in the H⁺ budgets. The ratio between external and internal H⁺ sources (excluding net base cation uptake by forests) varied between 0.74 and 2.62, depending on catchment characteristics and acidic deposition loads. The impact of the acidic deposition was most evident for the southern Valkeakotinen catchment, where the anthropogenic acidification has been documented also by palaeolimnological methods.     

Analysis of Decadal Time Series in Wet N Concentrations at Five Rural Sites in NE Spain

Nitrogen emissions have grown in Spain during the last 15 years. As precipitation scavenges gases and aerosols from the atmosphere, an effect on rainwater concentrations can be expected. However, time-series studies on wet N concentrations in the Iberian Peninsula are very scarce. This paper aims to fill this gap by analysing weekly rainfall N concentrations at a set of rural sites in Catalonia (NE Spain) from 1995/1996 to 2007 and a forest site monitored from 1983 to 2007. The sites encompass a range of rural environments and climate conditions, from the inland pre-Pyrenees (Sort) to the Mediterranean coast (Begur) and from north (Sort and Begur) to central (Palautordera and La Castanya) and south Catalonia (La Senia). We found a 1-year cycle for concentrations of NH ₄ ⁺ and NO ₃ ^? whereby higher values were reached at the end of spring–early summer, except at the easternmost coastal site of Begur. Weekly NH ₄ ⁺ concentrations decreased with time at all sites (except at La Senia) whilst NO ₃ ^? concentrations increased at all sites during the same period. Rainfall SO ₄ ^2? concentrations decreased with time at all sites. The opposite trends in NO ₃ ^? and SO ₄ ^2? concentrations determined a shift in the relative acid contribution of those anions during the 12–13-year period. To interpret the increasing trend, mean annual NO ₃ ^? concentrations were regressed against NO₂ Spanish emissions and to some indicators of local anthropogenic activity. The increase at Sort and Palautordera showed good correlation with local anthropogenic indicators. Wet inorganic N deposition ranged between 4.2 and 6.7 kg ha^?1 year^?1. When including estimates of dry deposition, total annual deposition rose up to 10–20 kg ha^?1 year^?1, values that have been found to initiate adverse effects on Mediterranean-type forest ecosystems.     

Interaction between nitrogen fertilization,rainfall and groundwater pollution in sandy soil

A 2 yr field study on the influence of N fertilization and rainfall on groundwater pollution was carried out in the sandy area of Belgium. The NO _inf3 ^sup? -N and Cl^? content of the groundwater at 0.5, 1.0, 1.5, and 2.0 m depths was monitored every two weeks on a field, grown with barley in 1980 and with maize in 1981. Turnips for cattle feed were grown in between the two crops. The total annual rainfall during the period under study was about 800 mm. The NO _inf3 ^sup? -N content at all depths was at all times above 11.3 mg NO _inf3 ^sup? -N dm^?3, the WHO safe limit. Fluctuation of the NO _inf3 ^sup? -N content occurred mainly at 0.5 and 1.0 m. The concentration at 1.5 and 2.0 m depths was higher most of the time than at 0.5 and 1.0 m. Leaching of NO _inf3 ^sup? -N into deeper layers occurred when there was heavy rainfall. There was no important loss of NO _inf3 ^sup? -N through denitrification at 1.5 and 2.0 m depths.     

Stream chemistry impacts of conifer harvesting in welsh catchments

Hydrochemical data have been collected for between 6 and 9 years from forest harvesting experiments in small catchments (>10 ha) at Plynlimon and Beddgelert, Wales, UK. Felling resulted in rapid increases in NO ₃ ^? and K⁺ concentrations at both sites. A maximum of 3.2 mg N L^?1 was observed at Plynlimon about one year after the start of felling. Concentrations declined to control stream values (0.5 mg N L^?1) after 5 years. At Beddgelert, NO ₃ ^? concentrations in the manipulated catchments remained above those in the unfelled control catchment for three years, before declining below control values. The NO ₃ ^? pulse was related to increased rates of mineralization and nitrification in the soil after felling. The initial increase in K⁺ concentration after felling at Plynlimon was followed by a slow decline, but concentrations were still above those in the control stream after 5 years. From 4 to 8 years after felling at Beddgelert, K⁺ concentrations fell below and then generally remained lower than control values. The NO ₃ ^? pulse after felling at Plynlimon sustained inorganic anion concentrations above those in the control stream for the first 18 months after felling. As the NO ₃ ^? pulse declined, inorganic anion concentrations decreased to below those in the control stream about 4 years after felling. At Beddgelert, the smaller increase in NO ₃ ^? concentrations had less of an effect on inorganic anion concentrations which decreased after felling relative to values in the control stream. The increase in NO ₃ ^? was associated with temporary streamwater acidification in the felled catchments due to the increased rates of nitrification and nitrate leaching. At Plynlimon, streamwater filterable Al concentrations declined after felling, but controls on Al behaviour are complex and not explained by simple equilibrium relationships with Al(OH)₃ or by variations in inorganic anion concentrations. At Beddgelert, felling had no effect on stream water filterable Al concentrations. Felling at Plynlimon led to a large reduction in streamwater Cl^?, Na⁺ and SO ₄ ^2? concentrations. At Beddgelert reductions in SO ₄ ^2? and ‘sea salt’ ion concentrations were less clear, reflecting the smaller proportions of the catchments which were harvested. Felling had no deleterious effects on water quality, apart from a temporary slight further decline in stream pH at Beddgelert. Increases in NO ₃ ^? concentrations were short-lived and concentrations were well below drinking water standards. Filterable Al concentrations were already higher than statutory standards, but were not increased or decreased through felling.     

Mercury antagonists: Effects of sodium chloride and sulfur group (VIa) compounds on excystment of the brine shrimp artemia

Brine shrimp excystment, although highly resistant, is severely inhibited by mmolar mercuric chloride. The presence of 100 mmolar NaCl largely prevents the toxic response. The chloride effect can be explained if the toxic Hg species, neutral HgCl₂, is converted into HgCl _inf3 ^sup2? and HgCl _inf4 ^sup2? since charged species not likely to penetrate cyst walls. Other Hg antagonists include SO _in3 ^su2? , SeO _inf3 ^sup2? , TeO _inf3 ^sup2? and TeO _inf4 ^sup2? , but not SO _inf4 ^sup2? and SeO _inf4 ^sup2? . The activity of both Te species can be explained by ready reduction of Te(VI) to Te(IV). Significant anti-mercurial effects were seen in mmolar thiols, ethionine and organoselenium compounds. Thiamine and methionine were both active Hg antagonists at 10 to 30 mmolar levels. The activities of S, Se and Cl^? compounds show that both geochemical and physiological modes of defense against and adaptation to high Hg levels exist.     

Difference in the Use of a Quartz Filter and a PTFE Filter as First-Stage Filter in the Four-Stage Filter-Pack Method

We evaluated the differences in the use of a quartz filter and a polytetrafluoroethylene (PTFE) filter as a first (F0)-stage filter in a four-stage filter-pack method. A four-stage filter-pack method can completely collect sulfur species (SO₂ and SO ₄ ^2? ), nitrate species (HNO₃ and NO ₃ ^? ), and ammonium species (NH₃ and NH ₄ ⁺ ) with little or no leakage irrespectively of the first-stage filter used. On the other hand, a seasonal variation was observed in the efficiency of collection between the quartz filter and the PTFE filter depending on the material to be collected. There was no seasonal variation in the efficiency of collection in sulfur species; in contrast, a clear seasonal variation was observed for the nitrate and ammonium species. As for NO ₃ ^? , the PTFE filter was more vulnerable than the quartz filter at air temperatures below 21°C, while the quartz filter was more vulnerable than the PTFE filter at air temperatures exceeding 21°C. A similar vulnerability for air temperature was observed for NH ₄ ⁺ , although the threshold air temperature was 23°C for NH ₄ ⁺ . Consequently, the evaporation loss of NO ₃ ^? would be mainly attributable to the volatilization of NH₄NO₃, although it is also partially due to the volatilization of NH₄Cl.     

Simultaneous Removal of H2S, NH3, and Ethyl Mercaptan in Biotrickling Filters Packed with Poplar Wood and Polyurethane Foam: Impact of pH During Startup and Crossed Effects Evaluation

The present work discusses the startup and operation of different biotrickling filters during the simultaneous removal of NH₃, H₂S, and ethyl mercaptan (EM) for odor control, focusing on (a) the impact of pH control in the stability of the nitrification processes during reactor startup and (b) the crossed effects among selected pollutants and their by-products. Two biotrickling filters were packed with poplar wood chips (R1 and R2A), while a third reactor was packed with polyurethane foam (R2B). R2A and R2B presented a pH control system, whereas R1 did not. Loads of 2?C10?g N?CNH₃ m^?3?h^?1, 5?C16?g S?CH₂S m^?3?h^?1, and 1?C6?g EM m^?3?h^?1 were supplied to the bioreactors. The presence of a pH control loop in R2A and R2B proved to be crucial to avoid long startup periods and bioreactors malfunctioning due to biological activity inhibition. In addition, the impact of the presence of different concentrations of a series of N species (NH ₄ ⁺ , NO ₂ ^? , and NO ₃ ^? ) and S species (SO ₄ ^2? and S^2?) on the performance of the two biotrickling filters was studied by increasing their load to the reactors. Sulfide oxidation proved to be the most resilient process, since it was not affected in any of the experiments, while nitrification and EM removal were severely affected. In particular, the latter was affected by SO ₄ ^2? and NO ₂ ^? , while nitrification was significantly affected by NH ₄ ⁺ . The biotrickling filter packed with polyurethane foam was more sensitive to crossed effects than the biotrickling filter packed with poplar wood chips.     

Adverse Effects of Ammonia on Nitrification Process: the Case of Chinese Shallow Freshwater Lakes

Nitrification is a process in which ammonia is oxidized to nitrite (NO ₂ ^? ) that is further oxidized to nitrate (NO ₃ ^? ). The relations between these two steps and ambient ammonia concentrations were studied in surface water of Chinese shallow lakes with different trophic status. For the oxidations of both ammonia and NO ₂ ^? , more eutrophic lakes generally showed significantly higher potential and actual rates, which was linked with excessive ammonia concentrations. Additionally, both potential and actual rates for ammonia oxidation were higher than those for NO ₂ ^? oxidation in the more eutrophic lakes, while in the lakes with lower trophic status, both potential and actual rates for ammonia oxidation were almost equivalent to those for NO ₂ ^? oxidation. This can be explained by the excessive unionized ammonia (NH₃) concentration that inhibits nitrite-oxidizing bacteria in the more eutrophic lakes. The laboratory experiment with different ammonia concentrations, using the surface water in a eutrophic lake, showed that ammonia oxidation rates were proportional to the ammonia concentrations, but NO ₂ ^? oxidation rates did not increase in parallel. Furthermore, NO ₂ ^? oxidation was less associated with particles in natural water of the studied lakes. Without effective protection, it would be selectively inhibited by the excessive ammonia in hypereutrophic lakes, resulting in NO ₂ ^? accumulation. Shortly, the increased concentrations of ammonia cause a misbalance between the NO ₂ ^? -producing and the NO ₂ ^? -consuming processes, thereby exacerbating the lake eutrophication.     

Arsenic Uptake from Arsenic-Contaminated Water Using Hyperaccumulator Pteris vittata L.: Effect of Chloride, Bicarbonate, and Arsenic Species

High As groundwater normally contained high concentrations of Cl^? and HCO ₃ ^? . This study examined the effects of Cl^?, HCO ₃ ^? , and As species on As uptake by hyperaccumulator Pteris vittata. Plants were exposed hydroponically to 5.0?mg/L As(III) or As(V) in the presence of 0, 0.5, 1, 2, 5, 10, and 20?mM of Cl^? or HCO ₃ ^? for 10?days. Addition of high Cl^? concentrations (>10?mM) slightly inhibited P. vittata growth (biomass), while generally had no significant effect on plant As uptake. High solution pH resulted in reduced plant growth and As uptake, which attributed to the inhibitory effects in HCO ₃ ^? treatments with the high pH of the high HCO ₃ ^? concentration. It was speculated that addition of HCO ₃ ^? (<20?mM) would have no significant effect on plant growth and As uptake. The inhibitory effect of HCO ₃ ^? on As translocation was less apparent in the As(III) solutions than the As(V) solutions. For the high As groundwater with As(III) as the predominant species, high pH, instead of high concentrations HCO ₃ ^? and Cl^?, was expected to inhibit As uptake. The results suggested that optimum plant growth and maximum As hyperaccumulation could be achieved by adjusting solution pH in the growth media (around 7.2).