Comparison of Activated Sludge Technologies by Particle Size Analysis

This paper analyses the influence of activated sludge technologies on the Particle Size Distribution (PSD) of urban wastewater treatment plants operating under real conditions. The activated sludge treatment systems selected for the analysis are the most widely used in wastewater treatment installations: (a) double step activated sludge, (b) medium load activated sludge, (c) prolonged aeration, and (d) membrane bioreactors The main quality parameters (suspended solids, turbidity, and COD) and PSD in the influent and effluent of each different activated sludge treatment were analyzed during 1?year. The PSD was fitted using the power law ( $ n\left( {{d_{\text{P}}}} \right) = \frac{{\partial {\text{N}}\left( {{d_{\text{p}}}} \right)}}{{\partial {d_{\text{p}}}}} = A \cdot d_{\text{p}}^{{ - b \cdot {\text{Log}}\left( {{d_{\text{p}}}} \right)}} $ ) obtaining coefficients A and b to define the particle distribution. Mathematical correlations between this coefficients and the rest of parameters studied were found $ \left( {\matrix{ {{\text{SS}} = {0}{.0126} \cdot {A^{{{0}{.781}}}},} &{{\text{Turbidity}} = 15.5814 + 1.164 \cdot {{10}^3} \cdot A{,}} &{{\text{COD}} = \frac{{1}}{{{0}{.0133} + \cdot \frac{{{49}{.85}}}{\text{A}}}}} \\ }<!end array> } \right) $ . The relation with the average particle size by mass was also found, ( $ {d_{\text{pma}}} = - 11.6502 + \frac{{50.4265}}{b} $ ). Moreover, a relation between PSD and the particle elimination efficiency of the secondary treatment was study, ( $ \eta = 0.1434 - \frac{{0.5602}}{{{A_{\text{rel}}}}} + \frac{{0.7490}}{{{b_{\text{rel}}}}} $ ). Finally, the particulate matter nature was assessed by SEM-EDX. It can be concluded that membrane bioreactor is the technology that produces the best water quality effluent due to physic process of particle separation by ultrafiltration membrane technology.     

An improved nitrogen difference method for estimating biological nitrogen fixation in legume-based intercropping systems

The nitrogen difference method (NDM) for quantifying N₂ fixation, based on the same amount of soil N exploited by N₂-fixing and non-N₂-fixing plant, may not be suitable to plants with different root traits. We tested the reliability of NDM in legume-based intercropping systems by two field experiments in Northwest China. In experiment 1, faba bean (Vicia faba), pea (Pisum sativum), and soybean (Glycine max) grew solely or intercropped with maize (Zea mays) with two N application rates (0, 225 kg ha^?1). The biomass of faba bean, pea, and maize was significantly increased, whereas that of soybean was decreased when intercropped than solely grown. Aggressivity analyses demonstrate greater N competition ability of faba bean and pea, but not soybean, than maize. An improved NDM (INDM) could mitigate these effects: $ {N_{{\text{fix - int}}}} = \left[ {{N_{{\text{leg - int}}}} + \frac{{1 - x}}{x}{N_{{\text{ref - int}}}} - \frac{{{N_{{\text{ref - sole}}}}}}{x}} \right] + \left[ {{\text{soil}}{N_{{\text{leg - int}}}} + \frac{{1 - x}}{x}{\text{soil}}{N_{{\text{ref - int}}}} - \frac{{{\text{soil}}{N_{{\text{ref - sole}}}}}}{x}} \right] $ , where x and 1???x are planting area of legume and non-legume in the intercropping system. Compared to traditional NDM (TNDM, $ {N_{{\text{fix - int}}}} = \left[ {{N_{{\text{leg - int}}}} - {N_{{\text{ref - sole}}}}} \right] + \left[ {{\text{soil}}{N_{{\text{leg - int}}}} - {\text{soil}}{N_{{\text{ref - sole}}}}} \right] $ ), %N _dfa (N derived from air) by INDM was decreased by 54.3% and 39.8% for faba bean, 44.7% and 5.0% for pea, but increased by 113.5% and 191.0% for soybean at the two N application rates, indicating different %N _dfa quantifications between the two methods. In experiment 2, %N _dfa of sole or intercropped faba bean was quantified by TNDM, INDM, and ¹⁵N natural abundance method (NA). The %N _dfa only by INDM correlated significantly with that from NA. Both interspecific root interactions and N loss affect %N _dfa estimation. Our results suggested that INDM could be more suitable than TNDM for quantifying %N _dfa of a N₂-fixing plant in intercropping systems.     

Characteristic Variation of Concentration and Chemical Form in Sulfur, Nitrate, Ammonium, and Chloride Species Observed at Urban and Rural Sites of Japan

A field survey on the concentration of chemical species in particulate matter and gaseous compounds at two monitoring sites with different site classifications (urban and rural) was conducted over three years. Total (particulate matter + gaseous compounds) concentrations at the rural site were significantly lower than those at the urban site for all species (sulfur $\left( {{\text{SO}}^{{{\text{2 - }}}}_{{\text{4}}} {\left( {\text{p}} \right)}} \right.$ and SO₂(g)), nitrate ${\text{(NO}}_{{{\text{3}}^{{\text{ - }}} }} {\left( {\text{p}} \right)}$ and HNO₃(g)), ammonium ${\text{(NH}}_{{{\text{4}}^{{\text{ + }}} }} {\text{(p)}})$ and ammonia (NH₃(g)), and chloride (Cl^? (p) and HCl (g))), which is thought to reflect classification of the site. The difference in the sulfur concentration at the urban and rural sites was characterized by the difference in SO₂ (g) concentration. Further, a clear seasonality was observed for the nitrate species. The HNO₃ (g) concentration was high in the summer compared with other seasons at both the urban and rural sites. The ${\text{NH}}_4^ + \left( {\text{p}} \right)$ concentration levels were approximately the same as those of NH₃ (g) at both sites. The molar ratios of the particulate matter concentration to the total concentration showed different characteristics; the nitrate, ammonium and ammonia, and chloride species showed a clear seasonal variation: low in summer and high in winter and the values were similar regardless of the site. On the other hand, the sulfur species showed constant values at both the urban and rural sites, however the concentrations were significantly different for the two sites. Ammonium accounted for the largest proportion of cations in the particulate matter, regardless of the site classification. In contrast, ${\text{SO}}_4^{2 - } \left( {\text{p}} \right)$ accounted for the largest proportion of anions at the rural site, whereas ${\text{NO}}_3^ - \left( {\text{p}} \right)$ was comparable to ${\text{SO}}_4^{2 - } \left( {\text{p}} \right)$ at the urban site. Ammonia accounted for the largest proportion of all chemical species at both sites. Seasonal analysis of the proportional distribution in particulate matter and gaseous compounds provides information on atmospheric conditions.     

Degradation Kinetics of an Aged Hydrocarbon-Contaminated Soil

PM2.5 and PM10 samples were collected in the urban atmosphere of Elche (southeastern Spain) between December 2004 and November 2005. The samples were analyzed for mass and water-soluble inorganic ions (Na⁺, ${\text{NH}}^{{\text{ + }}}_{{\text{4}}}$ , K⁺, Ca²⁺, Mg²⁺, Cl^?, ${\text{NO}}^{{\text{ - }}}_{{\text{3}}}$ and ${\text{SO}}^{{{\text{2 - }}}}_{{\text{4}}}$ ) with the aim of investigating the influence of the climatic and geographic features of a coastal semiarid area on the contribution of these species to PM levels. Secondary inorganic ions ( ${\text{SO}}^{{{\text{2 - }}}}_{{\text{4}}}$ , ${\text{NO}}^{{\text{ - }}}_{{\text{3}}}$ , ${\text{NH}}^{{\text{ + }}}_{{\text{4}}}$ ) were the major components in the fine fraction (PM2.5), accounting for 40% of the total mass. The relationship between non-marine ${\text{SO}}^{{{\text{2 - }}}}_{{\text{4}}}$ and ${\text{NH}}^{{\text{ + }}}_{{\text{4}}}$ indicated that fine sulfate particles were completely neutralized by ammonium. In the coarse fraction (PM10–2.5), nitrate (as NaNO₃ and Ca(NO₃)₂), together with crustal (CaCO₃) and marine species (NaCl) accounted for almost 50% of the total mass. Fine sulfate and coarse nitrate showed summer maximums. In contrast, the concentrations of fine ${\text{NO}}^{{\text{ - }}}_{{\text{3}}}$ were lowest in the warm period. Ammonium presented both winter and summer maximums. The levels of marine ions, except for coarse Cl^?, were highest in summer when the dominant wind flow is from the sea. No significant seasonal variations were observed for coarse Ca²⁺ and ${\text{SO}}^{{{\text{2 - }}}}_{{\text{4}}}$ . The concentrations of all inorganic ions increased during Saharan dust events, in particular, fine ${\text{NH}}^{{\text{ + }}}_{{\text{4}}}$ and ${\text{SO}}^{{{\text{2 - }}}}_{{\text{4}}}$ and coarse $NO_3^ - $ . Coarse calcium was proved not to be a good tracer for this type of episode in our region since the average levels of this cation are elevated and the relative increase in its concentrations during African events was not as high as expected.     

Coke Wastewater Treatment by a Three-Step Activated Sludge System

The treatment of industrial coke wastewater was studied in a laboratory-scale activated sludge system. The concentrations of the main pollutants in the wastewater ranged between 800 and 1870 mg COD/l, 100–221 mg phenols/l, 198–427 mg SCN/l, 133–348 mg ${\text{NH}}_4^ + - {{\text{N}} \mathord{\left/ {\vphantom {{\text{N}} {\text{l}}}} \right. \kern-0em} {\text{l}}}$ and 11–41 mg CN^?/l. To avoid inhibition phenomena resulting from the high concentrations of thiocyanate, ammonium nitrogen and cyanide a three-step process was implemented. The first step was anoxic for the removal of nitrates, followed by an oxic step during which biodegradation of phenols and thiocyanates took place, and by a second oxic step to oxidize ammonium nitrogen to nitrate. The dilution effect due to the recirculation of the final effluent to the head of the process and also, the separation of the nitrification step from the biodegradation of thiocyanate led to much higher efficiencies than when the process was carried out simultaneously. Very high removals were obtained (99% phenols, 97% SCN^?, 63% COD, 98% ${\text{NH}}_4^ + - {\text{N}}$ , 90% total-N and 99% cyanide) employing hydraulic residence times of 15.4 h for denitrification, 98 h for phenol and thiocyanate biodegradation and 86 h for nitrification.     

Influence of DCD and DMPP on soil N dynamics after incorporation of vegetable crop residues

We have investigated the effect of two nitrification inhibitors, 3,4-dimethylpyrazole phosphate (DMPP) and dicyandiamide (DCD), on the accumulation of and after incorporation of cauliflower residues in incubation experiments. Cauliflower leaves were incubated with soil and DCD or DMPP at two application rates [8.93 and 17.9 mg active component (ac) kg⁻¹ for DCD; 0.89 and 1.79 mg ac kg⁻¹ for DMPP]. Both doses of DCD and DMPP increased on average by 18.9 and 26.0 mg N kg⁻¹ for DCD1 (during 30 days) and DCD2 (during 45 days), respectively, and on average by 14.4 mg N kg⁻¹ for DMPP1 and DMPP2 during a period of at least 95 days. In DCD-treated soils, data followed an S-shaped curve, indicating that nitrification restarted during the experiment: inhibition was on average 24% during 35 days for DCD1 and on average 45% during 49 days for DCD2. Thereafter, amount in DCD-treated soils exceeded that of the cauliflower-only treatment by 31% for DCD1 and 78% for DCD2, probably due to a nitrogen release from DCD itself and a priming effect induced by DCD. In DMPP-treated soils, data followed a linear pattern since nitrification was inhibited during the complete incubation (95 days): inhibition was on average 56 and 64% for DMPP1 and DMPP2, respectively. DMPP did not affect the N mineralization of the crop residues. Under favourable conditions, DCD is able to inhibit the nitrification from crop residues for 50 days and DMPP for at least 95 days. Hence, especially DMPP shows a potential to reduce leaching after incorporation of crop residues.     

Gross nitrogen mineralisation and fungi-to-bacteria ratios are negatively correlated in boreal forests

In terrestrial ecosystems, gross nitrogen mineralisation is positively correlated to microbial biomass but negatively to soil organic matter C-to-N ratios; the influence of the microbial community structure is less well known. Here, we relate rates of gross N mineralisation to fungi-to-bacteria ratios in three natural forest types of contrasting N availability and in a long-term N-loading experiment in a boreal forest. We report, for the first time, a strong negative correlation between gross N mineralisation and the fungi-to-bacteria ratio ( = 0.91, P = 0.0005, N = 7). There was also a negative correlation between gross N mineralisation and the C-to-N ratio ( = 0.89, P = 0.001, N = 7), but a weaker positive correlation between gross N mineralisation and soil pH ( = 0.64, P = 0.019, N = 7). Our analysis suggests that soil fungi-to-bacteria and C-to-N ratios are interrelated and that they exert strong influences on soil N cycling in boreal forests.     

Precipitation Chemistry as an Indicator of Urban Air Quality in Mersin, North-Eastern Mediterranean Region

The chemical composition of precipitation in the city of Mersin on the Mediterranean coast of Turkey has been studied. Spatial and temporal variability of rainwater constituents have been determined from samples collected at two central and two suburban stations for the December 2003–May 2005 period. A total of 246 samples covering all precipitation events were analyzed to determine pH, conductivity, as well as major anion (Cl^?, ${\text{NO}}_3^ - $ , ${\text{SO}}_4^{2 - } $ ); major cation (H⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, ${\text{NH}}_4^ + $ ) and formaldehyde (HCHO) concentrations. The pH varied within a range of 4.8–8.5, with only 8 out of 246 samples being acidic (pH?<?5.6), and the remaining highly alkaline samples being neutralized by either ${\text{NH}}_4^ + $ in rainwater, or by CaCO₃ resulting from wet deposition of atmospheric dust. The volume weighted mean ΣAnion/ΣCation ratio was 0.49. The equivalent concentration of major ionic species followed the order: ${\text{Ca}}^{2 + } > {\text{HCO}}_3^ - > {\text{SO}}_4^{2 - } > {\text{Cl}}^ - > {\text{NH}}_4^ + > {\text{Na}}^ + > {\text{Mg}}^{2 + } > {\text{NO}}_3^ - > {\text{K}}^ + > {\text{H}}^ + $ . Formaldehyde concentrations varied in the range of 0.01–17.9 μM, and was found to be dependent on precipitation volume. Relatively higher ${\text{NH}}_4^ + $ , ${\text{SO}}_4^{2 - } $ , ${\text{NO}}_3^ - $ and HCHO concentrations, mainly of anthropogenic origin, measured near the city center suggest increased pollution from local anthropogenic sources, e.g., residential heating, industrial and/or traffic emissions. In general, the results of this study suggest local precipitation chemistry is more strongly influenced by natural (mineral dust and marine) sources compared to anthropogenic ones.     

Chemical Characterization of Rain and Fog Water in the Cervenohorske Sedlo (Hruby Jesenik Mountains, Czech Republic)

Field study at the Cervenohorske sedlo (1,013 m a.s.l.) (Hruby Jesenik Mountains, the Czech Republic, Central Europe) during 1999–2002 has been conducted in order to analyse the chemistry of rain/snow water using bulk and throughfall collector and fog/cloud water using modified passive Grunow collector. Fog water input to coniferous forest (Picea abies) was quantified using canopy balance method. For all samples pH, and the concentrations of $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ , Ca²⁺, K⁺, Mg²⁺, Na⁺, Cl^?, $ {\text{NO}}^{{\text{ - }}}_{{\text{3}}} $ , and $ {\text{SO}}^{{{\text{2 - }}}}_{{\text{4}}} $ were measured. The volume-weighted mean pH value varied from 4.92 to 5.43 in open bulk precipitation, from 4.30 to 4.71 in throughfall and from 4.66 to 5.23 in fog water. The fog droplets generally contain higher ion concentrations than rainwater. The related enrichment factors lie between 1.1 and 10.7 for the relevant species. The fog samples exhibit higher concentrations of $ {\text{NO}}^{{\text{ - }}}_{{\text{3}}} $ and $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ as compared to the bulk samples during 2000–2002. $ {\text{NO}}^{{\text{ - }}}_{{\text{3}}} $ are 5.7–10.7 times more concentrated in fog water and $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ are 3.4–7.2 times more concentrated in fog water. These differences may result from the height and characteristics of formation of the droplets. Based on canopy balance method, the annual fog water inputs were estimated to be 22 and 19% of rain and snow annual amounts in 1999 and 2000, respectively. For $ {\text{NO}}^{{\text{ - }}}_{{\text{3}}} $ , $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ , and $ {\text{SO}}^{{{\text{2 - }}}}_{{\text{4}}} $ , the contribution of fog deposition in total (bulk + fog) deposition is estimated as 54, 47, and 42%, respectively.     

Wet and dry deposition of sulphates and nitrates in Eastern Canada: 1979–1982

Daily air and precipitation chemistry observations at six rural locations in eastern Canada were analyzed to obtain wet and dry deposition. Dry deposition was calculated from air concentrations using deposition velocities originating from a recent literature review and synthesis exercise involving land use types. Total annual deposition ranges for \({\text{SO}}_{\text{4}}^{\text{ = }} \) from 10 to 86 mmol m^?2 and for \({\text{NO}}_{\text{3}}^{\text{ - }} \) excluding N0₂ contributions to dry deposition from 13 to 62 mmol m^?2. Dry deposition accounts for an estimated 22 and 21% of the total \({\text{SO}}_{\text{4}}^{\text{ = }} \) and \({\text{NO}}_{\text{3}}^{\text{ - }} \) deposition, respectively. For \({\text{NO}}_{\text{3}}^{\text{ - }} \) , this fraction increases to 30% if N0₂ concentration to dry deposition is included. There is a marked seasonal variation in total \({\text{SO}}_{\text{4}}^{\text{ = }} \) deposition but not in that of \({\text{NO}}_{\text{3}}^{\text{ - }} \) . Both wet and dry deposition are episodic. 20% of daily events deliver between 47 and 70% of the deposition.     

Degradative Oxidation of 2,4,6 Trichlorophenol Using Advanced Oxidation Processes – A Comparative Study

In the present study, a comparative assessment of 2,4,6-T (2,4,6-Trichlorophenol) degradation by different AOPs (Advanced Oxidation Processes – UV, UV/ H₂O₂, Fenton, UV/Fenton and UV/TiO₂) in the laboratory scale is performed. The effects of different reactant concentrations and pH are assessed. 2,4,6-T removal, Total Organic Carbon mineralization (TOC) and dechlorination are monitored. Of all the AOPs, UV/Fenton process is more effective in degrading 2,4,6-T. The optimum conditions obtained for the best degradation with UV/Fenton are: pH?=?3, Fe⁺² concentration of about 5 ppm, and peroxide concentration of 100 ppm for an initial 100 ppm of 2,4,6 T concentration at room temperature. In these conditions, a pseudo first-order rate constant is evaluated. The degradation rate of 2,4,6 T followed the order: $$ {{{\text{UV}}} \mathord{\left/ {\vphantom {{{\text{UV}}} {{\text{Feton}}}}} \right. \kern-\nulldelimiterspace} {{\text{Feton}}}} > {{{\text{UV}}} \mathord{\left/ {\vphantom {{{\text{UV}}} {{\text{TiO}}_{\text{2}} > {{{\text{UV}}} \mathord{\left/ {\vphantom {{{\text{UV}}} {{\text{H}}_{\text{2}} {\text{O}}_{\text{2}} > {\text{Feton}}}}} \right. \kern-\nulldelimiterspace} {{\text{H}}_{\text{2}} {\text{O}}_{\text{2}} > {\text{Feton}}}}}}} \right. \kern-\nulldelimiterspace} {{\text{TiO}}_{\text{2}} > {{{\text{UV}}} \mathord{\left/ {\vphantom {{{\text{UV}}} {{\text{H}}_{\text{2}} {\text{O}}_{\text{2}} > {\text{Feton}}}}} \right. \kern-\nulldelimiterspace} {{\text{H}}_{\text{2}} {\text{O}}_{\text{2}} > {\text{Feton}}}}}} > {\text{UV}} $$      

Agricultural Impacts on Lake and Stream Water Quality in Grand Lake St. Marys, Western Ohio

Agricultural activities release variable products into air, soil and water ecosystems. The study was conducted to evaluate the impact of agriculture and concentrated livestock operations on stream and lake water quality in Grand Lake St. Marys watershed of north-western Ohio. Temporal water samples from the lake and the 6 feeding streams were collected bimonthly from January 2005 to May 2007, processed and measured for temperature, turbidity, pH, electrical conductivity (E _C), ammonium $\left( {{\text{NH}}_{\text{4}}^{\text{ + }} } \right)$ , nitrate $\left( {{\text{NO}}_{\text{3}}^ - } \right)$ , dissolved phosphorus (P), ultra-violet (UV) light absorption, and dissolved oxygen (DO), employing standard methods of analysis. The measured data were normalized and integrated into a simple index (WQ_Index) to evaluate overall water quality. Results showed that over 90% of the area in the watershed was under cropland with associated livestock operations. With a land area equal to 195 km² represented by the six major tributaries, the average animal density was over 240 units km^?2. As a result, land disposal of manure from confined feedings operations and direct deposit by grazing animals contributed to non-point sources of water pollution. While $\left( {{\text{NH}}_{\text{4}}^{\text{ + }} } \right)$ and P concentration, turbidity, and UV absorption peaked during the summer, the $\left( {{\text{NO}}_{\text{3}}^ - } \right)$ and DO concentration in both stream and lake water was lowest in the summer. Water sampled from the Coldwater, Beaver and Prairie creeks had higher turbidity, $\left( {{\text{NH}}_{\text{4}}^{\text{ + }} } \right)$ , and P than other creeks. However, DO concentration and UV absorption of water did not change significantly by the influence of streams. The WQ_Index peaked in both streams and lake water with greater water quality degradation in Beaver and Coldwater creek than other creeks. A significant relationship of WQ_Index with UV absorption and P accounted 84 to 90% of the variations in stream and lake water quality degradation. However, a strong linear relationship (r ²?=?0.81; p<0.01) between UV absorption and P concentration suggested a major contribution of P to the degradation of stream and lake water quality through algal blooming and associated eutrophication.     

Nitrification potential of marsh soils from two natural saline–alkaline wetlands

Few studies have been carried out on nitrification potential of marsh soils in natural saline wetlands with high alkalinity. The nitrification potentials of a closed wetland and an open wetland were monitored by an aerobic incubation at 25°C for 28 days. The relative nitrification index ( RNI,\frac\textNO₃^- \text - NNO₃^- - N + NH₄⁺ - N ) \left( {{\hbox{RNI,}}\frac{{{\text{NO}}_3^{-} {\text{ - N}}}}{{{\hbox{NO}}_3^{-} {\hbox{ - N}} + {\hbox{NH}}_4^{+} {\hbox{ - N}}}}} \right) rapidly increased with time in both wetlands and decreased with depth in soil profiles in both wetlands within the first 21 days. Nitrification proceeded much faster in the closed wetland than in the open wetland. The higher rate of nitrogen removal in closed wetlands than open wetland was probably due to the fast nitrification followed by denitrification or leaching loss.     

Seasonal and Annual Fluxes of Inorganic Constituents in a Small Catchment of a Japanese Cedar Forest near the Sea of Japan

Fluxes of major ions in rainfall (RF), throughfall plus stemflow (TF + SF), and stream water (SW) were measured for five water years in a small catchment of a Japanese cedar forest near the Sea of Japan. The fluxes of most ions in RF and in TF + SF, including the non-sea-salt constituents, increased from late autumn to midwinter owing to the seasonal westerly wind. The concentrations of most ions in SW showed no obvious seasonal trend during the study period, whereas ${\text{NO}}_3 ^ - $ concentrations were lowest in summer, with a small seasonality. The Ca²⁺ and Mg²⁺ outputs in SW were approximately 3.7 and 1.8 times the TF + SF inputs of these cations, respectively. The large net outputs of base cations in the catchment may indicate a decrease in the soil's acid-neutralizing capacity. Annual dissolved inorganic nitrogen inputs in RF and in TF + SF were 17.7 and 17.9 kg N ha^?1 year^?1, respectively, which exceeded previously published thresholds in Europe and the U.S. (i.e., the values at which these inputs increased ${\text{NO}}_3 ^ - $ levels in SW) and equaled the highest level of nitrogen deposition previously reported in Japan. The ${\text{NO}}_{\text{3}} ^{\text{ - }} $ concentrations in SW were relatively high even in summer. During high-precipitation events, ${\text{NO}}_{\text{3}} ^{\text{ - }} $ concentrations in SW increased with increasing water discharge, and the pH decreased simultaneously during several events. Nitrogen deposition may contribute to the high ${\text{NO}}_{\text{3}} ^{\text{ - }} $ concentrations in SW and the temporary acidification that occurred during the rain events.     

Methodological approach to assess the effect of soil ageing on selenium behaviour: first results concerning mobility and solid fractionation of selenium

The aim of the study presented here is to determine the impact of short- and medium-term transformations (0–3 years) of the soil organic matter (SOM) on the major processes and parameters that enable or inhibit selenite, Se(+IV), transfers between the soil components (solid, liquid or gaseous). Three types of soil of similar mineralogical origin but containing diverse quantities and qualities of SOM were first contaminated with Se(+IV) and incubated at 28°C. Soils were sampled throughout the incubation period to characterise the mobility of Se (batch and soil column experiments) and also its fractionation within the soil compartments (selective extractions and size-density fractionation). The following are the main results obtained within the first month of incubation. (a) Selenium was partly volatilized during soil incubation (<0.1%), (b) Se extracted with CaCl₂ (5×10⁻⁴ M) was equally small for the three soil samples (∼1–5%), suggesting that Se was strongly sorbed on the solid phase and (c) at least 10% of Se was associated to the particulate organic matter ${\left( {{\text{POM}}_{{ > {\text{50}}\mu {\text{m}}}} } \right)},${\left( {{\text{POM}}_{{ > {\text{50}}\mu {\text{m}}}} } \right)},whereas 60% of Se was extracted with soil humic substances. These results suggested that both SOM quantity and quality played a significant role in selenium retention. Furthermore, comparison between experimental and predicted variations of CO₂ fluxes (due to C mineralisation) and soil biomasses are presented. By this way, we estimated the capacity of the RothC model as an experimental gauging tool in the prediction of C turnover on a laboratory scale.     

Distribution of fertiliser N among fixed ammonium fractions as affected by moisture and fertiliser source and rate

The relevance of fixed in certain soils and its categorisation has made it necessary to re-examine N behaviour. A replicate factorial experiment was designed to investigate the influence of soil type, soil moisture and fertiliser source and rate on fixation dynamics with particular attention to the distribution between weakly and strongly fixed pools. Fixation of was <20% of added N for all soils except River Estate. The percentage of added N present as fixed was greater for the low application rate. Soil moisture did not significantly influence weakly fixed . However, the dry soil treatment showed greater fertiliser ¹⁵N present as strongly fixed . Fertiliser ¹⁵N present as weakly and strongly fixed decreased and increased, respectively, at the second sampling, indicating movement between the pools. The importance of the weakly fixed fraction as a transitory pool between strongly fixed and available was observed.     

The spatial and temporal variation of the sulphate to nitrate ratio in precipitation in eastern North America

Four years of precipitation chemistry data for eastern North America were used to investigate seasonal and geographical variations in \({\text{SO}}_{\text{4}}^{\text{ = }} {\text{/NO}}_{\text{3}}^{\text{ - }} \) ratio. Several distinct regimes occur. One, in the region of heaviest acidic deposition extending from the states south of the Great Lakes across New England and southeastern Canada, has a very strong seasonal variation in the \({\text{SO}}_{\text{4}}^{\text{ = }} {\text{/NO}}_{\text{3}}^{\text{ - }} \) molar ratio in deposition. The ratio ranges from about 1.5 in summer to about 0.5 in winter. Another, in the smaller area of Texas and surrounding states, shows the reverse seasonal pattern. Yet another, in the high plains states, has a double maximum in the ratio in Spring and Fall. The remainder of the region has an irregular seasonal pattern. Insight into the cause of \({\text{SO}}_{\text{4}}^{\text{ = }} {\text{/NO}}_{\text{3}}^{\text{ - }} \) variations was obtained using a simple chemical transport box model. It showed that the chemical transformation of S0₂ and NO_x in the atmosphere is a major factor. A comparison of model predictions and observations indicate that in the vicinity of mid-western American sources the molar ratio of amount of S0₂ oxidized in-cloud to that of N0₂ is O.5 in winter and 1.5 in summer.     

Oxygen-18 study of the atmospheric-aquatic linkage in adirondack watersheds

Twelve monthly measurements were made of the δ¹⁸O of the water and of the dissolved sulfates in inlet streams and in outlet streams of lakes in three watersheds in the Adirondack Park region of New York. The average \(\delta ^{18} {\text{O}}_{{\text{H}}_{\text{2}} {\text{O}}}\) of the surface waters (streams and lakes) of the three watersheds was in the typical range of seasonally varying \(\delta ^{18} {\text{O}}_{{\text{H}}_{\text{2}} {\text{O}}}\) of precipitation water, whereas the \(\delta ^{18} {\text{O}}_{{\text{SO}}_{\text{4}}^{{\text{2 - }}} }\) of the surface waters was significantly lower than the typical range of seasonally varying \(\delta ^{18} {\text{O}}_{{\text{SO}}_{\text{4}}^{{\text{2 - }}} }\) in precipitation water. Two possible causes for the apparent alteration of δ¹⁸O of the sulfates during percolation of the water through various strata in the ground link between the atmosphere and the watershed lakes are: (1) bacterial redox cycling, in which the sulfate is reduced, allowing isotopic equilibration between the HS0₃ ^? ion and associated water, and then catalytically reoxidized to sulfate; and (2) ion exchange, in which the soil strata, containing chemically fixed sulfates, behave as a “column” that is not in sulfate-ion equilibrium with sulfates in the atmospheric recharge water.     

Input–Output Budgets for Inorganic Nitrogen Under Acid Rain in a Subtropical Evergreen Mixed Forest in Central-South China

Inorganic nitrogen deposition and leaching in stream water were monitored from January, 2001 to December, 2004 in a subtropical evergreen mixed forest in central-south China. The seasonal concentration and flux of inorganic nitrogen in bulk precipitation and stream water, seasonal mean net retention of nitrogen and net flux of H⁺ transformed by nitrogen were estimated and quantified in Shaoshan forest. The research results show that the correlation coefficient of fluxes between bulk precipitation and stream water is significant, with a coefficient 0.916 at the 0.01 level. Mean fluxes of inorganic nitrogen input are 2.62 g m^?2 a^?1 and 0.516 g m^?2 a^?1 in form of bulk precipitation and dry deposition respectively, and output in stream water is around 0.22 g m^?2 a^?1, which indicates that most of nitrogen input is reserved in the forest. Net retention of nitrogen reaches 2.916 g m^?2 a^?1, just higher than other study plots over the world. Along with the translating of nitrogen ( ${\text{NH}}_4^ + - {\text{N}}$ and ${\text{NO}}_3^ - - {\text{N}}$ ), H⁺ is imported to the forest ecosystem at the same time. At our study plots, net flux of H⁺ transformed by nitrogen is about 73.57 mmol m^?2 a^?1. The positive value suggests that Shaoshan forest is still a finer buffering system to nitrogen deposition and it is far from nitrogen saturation in spite of the high nitrogen deposition.     

Calculating Dry Deposition and Canopy Exchange with the Canopy Budget Model: Review of Assumptions and Application to Two Deciduous Forests

The canopy budget model simulates the interaction of major ions within forest canopies based on throughfall and precipitation measurements. The model has been used for estimating dry deposition and canopy exchange fluxes in a wide range of forest ecosystems, but different approaches have been reported. We give an overview of model variations with respect to the time step, type of open-field precipitation data, and tracer ion, and discuss the strengths and weaknesses of different assumptions on ion exchange within forest canopies. To examine the effect of model assumptions on the calculated fluxes, nine approaches were applied to data from two deciduous forest plots located in regions with contrasting atmospheric deposition, i.e. a beech (Fagus sylvatica L.) plot in Belgium and a mixed sugar maple (Acer saccharum Marsh.) plot in Quebec. For both forest plots, a semi-annual time step in the model gave similar results as an annual time step. Na⁺ was found to be more suitable as a tracer ion in the filtering approach than Cl^? or ${\text{SO}}_4^{2 - } $ . Using bulk instead of wet-only precipitation underestimated the potentially acidifying deposition. To compute canopy uptake of ${\text{NH}}_4^ + $ and H⁺, ion exchange with K⁺, Ca²⁺, and Mg²⁺ as well as simultaneous cation and anion leaching should be considered. Different equations to allocate ${\text{NH}}_4^ + $ vs H⁺ uptake had most effect on the estimated fluxes of the cation that was less important at a plot. More research is needed on the relative uptake efficiency of H⁺, ${\text{NH}}_4^ + $ , and ${\text{NO}}_{_3 }^{\text{ - }} $ for varying tree species and environmental conditions.