Chemical dynamics of N-containing ionic species in a boreal forest snowcover during the spring melt period

A study of the changes in the ionic loads of NO, NH, SO and H⁺ in a boreal forest snowpack at Lake Laflamme, Québec was carried out using hydrological and chemical data from field lysimeters. The results showed that depletion of the N-containing species occurs periodically in the snowpack during meltwater discharge. Rain-on-snow events led to in-pack losses of NO and NH at a rate of 130 μeq m^?2 day^?1 and 101·3 μeq m^?2day^?1 respectively. On dry days, however, dry deposition and deposition of organic debris from the canopy resulted in increases of 183·3 μeq m^?2day^?1 for NO and 4·5 μeq m^?2day^?1 for NH in the pack. In contrast, SO₄^2? showed continual in-pack increases due to deposition of 5·0 μeq m^?2day^?1 for wet days and 92·6 μeq m^?2day^?1 for dry days. The depletion of NO and NH is due to microbiological uptake of these nutrients during periods when the free water content of the pack is high. Controlled melts in a laboratory snowmelt simulator containing snow and organic matter from the forest canopy at Lake Laflamme showed losses of NO and NH similar to those observed in the field. As the microbiological uptake proceeds at a rate comparable to that of ionic load increases in the pack by dry deposition, models of the chemical dynamics of snowmelt should take the former into account in any system where organic content of the snowpack is appreciable.     

Solutes in overland flow following fire in eucalyptus and pine forests,northern Portugal

Small bounded plots were used to investigate dissolved nutrient losses in overland flow in eucalyptus and pine forests in northern Portugal following understorey fires. Losses of NON, POCa²⁺, Mg²⁺ and K⁺ were measured over 19 months during the first 2–3 years after fire. Solute losses in overland flow increased after fire in eucalyptus and pine terrain due to the mineralization of litter and vegetation and increased overland flow. The data suggest that (i) elevated losses persist for at least 2 and 3 years at the pine and eucalyptus sites respectively and (ii) soluble losses of POK⁺ in a post‐fire cycle may exceed those adsorbed to eroded material. Losses of POalthough relatively small, are potentially the most detrimental to soil fertility and forest productivity because of the limited opportunity for P replenishment and correspondingly high P losses adsorbed to eroded sediment. Copyright © 2000 John Wiley & Sons, Ltd.     

Accuracy of kinematic wave and diffusion wave approximations for time-independent flows

Errors in the kinematic wave and diffusion wave approximations for time-independent (or steady-state) cases of channel flow were derived for three types of boundary conditions: zero flow at the upstream end, and critical flow depth and zero depth gradient at the downstream end. The diffusion wave approximation was found to be in excellent agreement with the dynamic wave approximation, with errors in the range 1–2% for values of KF (? 7.5), where K is the kinematic wave number and F₀ is the Froude number. Even for small values of KF (e.g. KF²₀ = 0.75), the errors were typically less than 15%. The accuracy of the diffusion wave approximation was greatly influenced by the downstream boundary condition. The error of the kinematic wave approximation was found to be less than 13% in the region 0.1 ? x ? 0.95 for KF = 7.5 and was greater than 30% for smaller values of KF (? 0.75). This error increased with strong downstream boundary control.     

Temporal trends of bulk precipitation and stream water chemistry (1977–1997) in a small forested area,Krusné hory,northern Bohemia,Czech Republic

The Krusné hory (Erzgebirge or Ore Mountains) has been heavily affected by high atmospheric pollutant deposition caused by fossil fuel combustion in an adjacent Tertiary coal basin. Long‐term routine sampling of bulk precipitation (1977–1996) and stream water (1977–1998) in a forested area on the south‐eastern slope of the mountains were used to evaluate trends and patterns in solute concentration and flux with respect to controlling processes. From 1977 to 1996, the annual volume‐weighted Ca²⁺ and SOconcentrations decreased in bulk precipitation. However, after 1989, when a pronounced and continuous decrease occurred in coal production, annual volume‐weighted concentrations decreased for most solutes, except H⁺. The concentration decreases were marked, with 1996 levels at or below 50% of those in 1989. The lack of a trend in H⁺ is attributed to similar decreases in both acid anions and neutralizing base cations. Stream water concentrations of most solutes, i.e. H⁺, Ca²⁺, Mg²⁺, SONOwere highest at the onset of sampling in 1977, decreased markedly from 1977 to 1983 and decreased more gradually from 1983 to 1998. The spruce forest die‐back and removal reduced dry deposition of these solutes by reducing the filtering action, which was provided by the forest canopy. A notable decrease in stream water Ca²⁺ concentrations occurred after 1995 and may be due to the depletion of Ca²⁺, which was provided by catchment liming in 1986, 1988 and 1989. Solute flux trends in bulk atmospheric deposition and stream water generally were not significant and the lack of trend is attributed to the large interannual variability in precipitation quantity and runoff, respectively. All solutes except Na⁺ varied seasonally. The average seasonal concentrations varied between the solutes, but for most solutes were highest in winter and spring and lowest in summer, correlating with the seasonal trend in runoff. For Ca²⁺, Mg²⁺ and SOthe concentration minimum occurs in September and the maximum occurs in February or March, correlating with the seasonal baseflow. These solutes are primarily controlled by the contribution of soil water and groundwater to stream flow. During snowmelt, the meltwater generally causes concentrations to decrease as soil water and groundwater are diluted. For NO₃ , average minimum concentrations occur in August at the end of the growing season concurrent with the lowest stream flow, and the maximum occurs in February and March with high stream flow during snowmelt. Seasonal stream water NOconcentration variations are large compared with the long‐term decrease. Copyright © 1999 John Wiley & Sons, Ltd.     

Solute concentrations of overland flow water in a cultivated field: spatial variations,intra‐ and inter‐storm trends

Major solute concentrations in overland flow water (OFW) were measured in an agricultural field of Brittany (western France). Two storm events were monitored in detail to examine the short time‐scale processes. During one year, samples were taken at different positions on the slope after each storm event to describe the spatial and seasonal variations of OFW chemistry. Although the total dissolved load in OFW is not much higher than in rain water, distinctive features are observed. K⁺, Ca²⁺, NH₄ , Cl⁻ and SOare the major solutes. The main origin of the elements (sea salts, exchangeable soil complex or fertilizers) determined most of the variations observed. Spatial variations along the slope are mainly seen for exchangeable cations, while seasonal variations are predominant for sea salts. Rainfall intensity and suspended sediment load induce strong differences between the two storm events studied in detail. However, the within‐storm variations and the seasonal monitoring show that this relationship is complex. Within‐storm variations suggest that, in addition to desorption processes, mixing with pre‐event water may occur. The lack of a relationship between sediment load and dissolved load is attributed to the high rate of the exchange processes, which has been checked by a simple experiment in vitro. It is concluded that the conditions of the transit of water on the field (velocity, length, status of the surface, crusted or not) may well play a major role in the chemical changes between rain water and OFW. The results suggest that vegetated buffer strips designed to reduce the sediment load only, and not the amount of overland flow, will have little effect on the transfer of dissolved pollutants to the watercourses. Copyright © 1999 John Wiley & Sons, Ltd.     

Geochemistry of meteoric diagenesis in carbonate islands of the northern Bahamas: 1. Evidence from field studies

Processes driving carbonate diagenesis in islands of the northern Bahamas are investigated using major ion, dissolved oxygen and dissolved organic carbon analyses of water samples from surface and ground waters, and measurements of soil gas P. Meteoric waters equilibrate with aragonite, but reactions are water controlled rather than mineral‐controlled and drive dissolution rather than concurrent precipitation of calcite. Surface runoff waters equilibrate with atmospheric P and rapidly recharge the vadose zone, limiting subaerial bedrock dissolution to only 6·6–15 mg l^?1 Ca. P of soil gas measured in the summer wet season ((7·4 ± 3·7) × 10^?3 atm) is elevated compared with that of the atmosphere, despite the thin skeletal organic nature of the soil and the discontinuous soil cover. Soil waters retained in surface pockets are equilibrated with respect to aragonite and have dissolved 51 ± 19 mg l^?1 Ca. This is substantially less than the 93 ± 18 mg l^?1 Ca in samples from pumping boreholes that sample meteoric waters from the freshwater lens. The high P of the freshwater lens ((16 ± 8·3) × 10^?3 atm for pumping boreholes) suggests that significant additional CO₂ may be derived by oxidation of soil‐ and surface‐derived organic carbon within the lens. The suboxic nature of the majority of the freshwater lens and the observed depletion in sulphate support this suggestion, and indicate that both aerobic and anaerobic oxidation may take place. Shallow lens samples from observation boreholes are calcite supersaturated and have a lower P than deeper lens waters, indicating that CO₂ degasses from the water table, driving precipitation of calcite cements. We suggest that the geochemical evolution of waters in the vadose zone and upper part of the freshwater lens may be determined by the presence of a body of ground air with P controlled by production in the freshwater lens and soil and by degassing to the atmosphere. Copyright © 2007 John Wiley & Sons, Ltd.     

Removal of Bromate from Water Using De‐Acidite FF‐IP Resin and Determination by Ultra‐Performance Liquid Chromatography‐Tandem Mass Spectrometry

Contamination of water due to bromate is a severe health hazard. The aim of the present study was to remove bromate from water using a crosslinked polystyrene based strongly basic anion exchange resin De‐Acidite FF‐IP. Batch experiments were performed to study the influence of various experimental parameters such as effect of pH, contact time, temperature, and effect of competing anions on bromate removal by De‐Acidite FF‐IP resin. At optimum parameters, the removal rate of bromate was very fast and 90% removal took place in 5 min and equilibrium was established within 10 min. The presence of competitive anions reduced the bromate adsorption in the order of Cl^? > F^? > CO > SO > NO > PO. The practical utility of this resin has been demonstrated by removing bromate in some of the commercial bottled water from Saudi Arabia. The level of bromate was determined using a very sensitive, precise and rapid method based on ultra‐performance liquid chromatography‐tendem mass spectrometry (UPLC‐MS/MS).     

Hydrochemical variations during flood pulses in the south‐west China peak cluster karst: impacts of CaCO3–H2O–CO2 interactions

High‐resolution measurements of rainfall, water level, pH, conductivity, temperature and carbonate chemistry parameters of groundwater at two adjacent locations within the peak cluster karst of the Guilin Karst Experimental Site in Guangxi Province, China, were made with different types of multiparameter sonde. The data were stored using data loggers recording with 2 min or 15 min resolution. Waters from a large, perennial spring represent the exit for the aquifer's conduit flow, and a nearby well measures water in the conduit‐adjacent, fractured media. During flood pulses, the pH of the conduit flow water rises as the conductivity falls. In contrast, and at the same time, the pH of groundwater in the fractures drops, as conductivity rises. As Ca²⁺ and HCO₃^? were the dominant (>90%) ions, we developed linear relationships (both r² > 0·91) between conductivity and those ions, respectively, and in turn calculated variations in the calcite saturation index (SI_C) and CO₂ partial pressure (P) of water during flood pulses. Results indicate that the P of fracture water during flood periods is higher than that at lower flows, and its SI_C is lower. Simultaneously, P of conduit water during the flood period is lower than that at lower flows, and its SI_C also is lower. From these results we conclude that at least two key processes are controlling hydrochemical variations during flood periods: (i) dilution by precipitation and (ii) water–rock–gas interactions. To explain hydrochemical variations in the fracture water, the water–rock–gas interactions may be more important. For example, during flood periods, soil gas with high CO₂ concentrations dissolves in water and enters the fracture system, the water, which in turn has become more highly undersaturated, dissolves more limestone, and the conductivity increases. Dilution of rainfall is more important in controlling hydrochemical variations of conduit water, because rainfall with higher pH (in this area apparently owing to interaction with limestone dust in the lower atmosphere) and low conductivity travels through the conduit system rapidly. These results illustrate that to understand the hydrochemical variations in karst systems, considering only water–rock interactions is not sufficient, and the variable effects of CO₂ on the system should be evaluated. Consideration of water–rock–gas interactions is thus a must in understanding variations in karst hydrochemistry. Copyright © 2004 John Wiley & Sons, Ltd.     

Photocatalytic Degradation of 17α‐Ethinylestradiol and Inactivation of Escherichia coli Using Ag‐Modified TiO2 Nanotube Arrays

Ag‐modified TiO₂ nanotube arrays (Ag/TiO₂ NAs) were prepared and employed as a photocatalyst for degradation of 17α‐ethinylestradiol (EE2) and inactivation of Escherichia coli. The as‐synthesized Ag/TiO₂ NAs were characterized by field‐emission scanning electron microscope (FESEM), X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS). It was found that metallic Ag nanoparticles were firmly deposited on the TiO₂ NAs with the pore diameter of 100 nm and the length of 550 nm. Photocatalytic degradation of EE2 and inactivation of E. coli were enhanced effectively in an analogical trend using Ag/TiO₂ NAs. In particular, Ag/TiO₂ NAs exhibited the antimicrobial activity even in the absence of light. The Ag acted as a disinfection agent as well as the dopant of the modified TiO₂ NAs photocatalysis by forming a Schottky barrier on the surface of TiO₂ NAs. Inorganic ions suppressed the rates of photocatalytic degradation of EE2, with HCO having a more pronounced effect than NO or SO. Humic acid (HA) was found to increase the rate of EE2 degradation.     

Monitoring of Impact of Ferti‐irrigation by Post‐methanated Distillery Effluent on Groundwater Quality

The impact assessment of molasses‐based distillery‐effluent irrigation on groundwater quality around village Gajraula in the district of Jyotiba Phule Nagar, Uttar Pradesh, India was studied by sampling groundwater on monthly intervals consecutively for summer, winter and monsoon seasons during 2006–2007 and water quality parameters, viz. pH, electrical conductivity (EC), chloride (Cl^?), sulphate (SO), nitrate (NO), chemical oxygen demand (COD), total solids (TS), total dissolved solids (TDS), sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), zinc (Zn²⁺), iron (Fe³⁺), and total coliforms (TC) were monitored. Results depicted that the values of all parameters decreased with increasing depth of water table. Sulphate, nitrate and potassium contents were maximal in agricultural site during monsoon while EC, Cl^?, TS, TDS, Na⁺, Ca²⁺, Mg²⁺, Zn, and Fe were maximal in industrial sites during summer. Groundwater samples of residential site harboured maximum coliforms especially during monsoon, highlighting threat to groundwater. Significant positive correlation matrix between coliforms with nitrate, sulphate and potassium ions explained their survival on these nutrients. To overcome this, important measures emphasizing improvement in effluent treatment technology matching site‐specific characteristics are recommended for eco‐friendly ferti‐irrigation.     

Adsorption of Complex Pollutants from Aqueous Solutions by Nanocomposite Materials

In view of water pollutants becoming more complex, both anionic and cationic pollutants need to be removed. The multi‐pollutants simultaneous removal is paid more and more attention. Hence, development composite materials for treatment complex wastewater are the aim of this study. In this research, iron–nickel nanoparticles deposited onto aluminum oxide (α‐Al₂O₃) and carbon nanotubes (CNTs) to form nanocomposite materials Fe–Ni/Al₂O₃ and Fe–Ni/CNTs, respectively, were used as adsorbents. The adsorption capacities of Fe–Ni/Al₂O₃ and Fe–Ni/CNTs for AO7, HSeO, and Pb²⁺ were observed to be 5.46, 8.28, 27.02, and 25.6 mg/g, 15.29 and 17.12 mg/g, separately. The composite materials with negative charges were superior in adsorption of anionic pollutants. Using orthogonal experimental design and analysis of variance to co‐treat dye AO7, HSeO and Pb²⁺ in aqueous solutions, seven testing factors were included: (1) adsorbent types, (2) amount of iron, (3) solution pHs, (4) AO7 concentrations, (5) Pb²⁺ concentrations, (6) HSeO concentrations and (7) reaction time. The experimental results showed that the removal of complex pollutants AO7, HSeO, and Pb²⁺ on Fe–Ni/CNTs could reach up to 90% in the optimal treatment conditions. When using Fe–Ni/CNTs as the adsorbent, the sorption isothermals were well fitted in the Freundlich isotherm, and R² could reach up to 0.98.     

Catalytic Reduction of Hexaminecobalt(III) by Pitch‐based Spherical Activated Carbon (PBSAC)

The wet ammonia (NH₃) desulfurization process can be retrofitted to remove nitric oxide (NO) and sulfur dioxide (SO₂) simultaneously by adding soluble cobalt(II) salt into the aqueous ammonia solution. Activated carbon is used as a catalyst to regenerate hexaminecobalt(II), Co(NH₃), so that NO removal efficiency can be maintained at a high level for a long time. In this study, the catalytic performance of pitch‐based spherical activated carbon (PBSAC) in the simultaneous removal of NO and SO₂ with this wet ammonia scrubbing process has been studied systematically. Experiments have been performed in a batch stirred cell to test the catalytic characteristics of PBSAC in the catalytic reduction of hexaminecobalt(III), Co(NH₃). The experimental results show that PBSAC is a much better catalyst in the catalytic reduction of Co(NH₃) than palm shell activated carbon (PSAC). The Co(NH₃) reduction reaction rate increases with PBSAC when the PBSAC dose is below 7.5 g/L. The Co(NH₃) reduction rate increases with its initial concentration. Best Co(NH₃) conversion is gained at a pH range of 2.0–6.0. A high temperature is favorable to such reaction. The intrinsic activation energy of 51.00 kJ/mol for the Co(NH₃) reduction catalyzed by PBSAC has been obtained. The experiments manifest that the simultaneous elimination of NO and SO₂ by the hexaminecobalt solution coupled with catalytic regeneration of hexaminecobalt(II) can maintain a NO removal efficiency of 90% for a long time.     

Hydrochemistry of meltwaters draining a polythermal‐based,high‐Arctic glacier,south Svalbard: II. Winter and early Spring

The hydrochemistry of naled and upwelling water sampled from the forefields of Finsterwalderbreen, Svalbard, during spring are used for the first time to infer the hydrology of overwinter meltwaters at a polythermal‐based glacier. Hydrochemical variations in naled are explained in terms of different water sources and their chemical alteration during freezing. Two water sources to naled are identified: surficially routed snowmelt and subglacial water. Naled that results from the freezing of the former is enriched in atmospherically derived ions such as Na⁺ and Cl⁻, and is believed to be formed during winter warm periods. Naled of subglacial origin contains relatively high proportions of crustally derived solute. It reflects the freezing of subglacial meltwaters that continue to issue from a subterranean upwellling during winter. An increasing dominance of SO²⁻₄ Mg²⁺, Na⁺ and Cl⁻ in subglacial naled with increasing distance from the upwelling reflects the progressive freezing of this water body and the associated removal of Ca²⁺ and HCO by calcite precipitation. These spatial trends are accentuated by the leaching of soluble ions from the naled close to its source by subsequent upwelling waters. The chemistry of spring upwelling waters, also of subglacial origin, strongly reflects this process. Meltwater produced by geothermal heating of glacier basal ice is believed to be the principal source of water to the subglacial drainage system during winter. Solute acquisition by this meltwater is limited by a scarcity of proton suppliers. Evolution of this dilute meltwater carries an imprint of ion exchange processes. Some stored subglacial water from the end of the previous ablation season may supplement the basal meltwater component in early winter. Copyright © 2000 John Wiley & Sons, Ltd.     

Zur Bestimmung des gesamten anorganischen Kohlenstoffes in natürlichen Gewässern durch Titration mit Salzsäure

The knowledge of total inorganic carbon concentration (c) is important for characterizing natural waters. It is usually measured by the titration alkalinity (“m-value”) and pH which depend on temperature and ionic strength. This paper demonstrates that Ca (and Mg) can influence the calculation of from titration alkalinity, too. Errors result from neglecting this influence. In such cases the share of ion pair CaCO amounts to more than 50 % of . General relationships among the influencing factors are given by tables calculated with the help of a BASIC computer programme for calculation from titration alkalinity, pH and Ca concentration.     

Using Chlorine Dioxide to Remove the Fouling of Ultrafiltration Membrane and Control Disinfection By‐Products

Ultrafiltration (UF) can remove natural organic matter (NOM) effectively. Moreover, chlorine dioxide (ClO₂) has been an alternative disinfectant as it forms fewer disinfection by‐products with NOM than chlorination does. Therefore, combining ClO₂ with UF may improve conventional purification processes. In this study, feed water containing humic acid with 4.07 mg/L total organic carbon (TOC) was dosed directly with various amounts of ClO₂ (0, 2, 5, 10, and 15 mg/L) before being filtered through a 5‐kDa UF membrane. With a low dose (2 mg/L ClO₂), UF removed humic acid effectively, as TOC was not detected in the permeate, and the permeate flux increased to about 80% of the initial permeate flux by cross flow. Moreover, the concentrations of ClO, ClO, and trihalomethanes in the permeate were below the United States Environmental Protection Agency guidelines.     

Geochemistry of meteoric diagenesis in carbonate islands of the northern Bahamas: 2. Geochemical modelling and budgeting of diagenesis

Geochemical characterization and numerical modelling of surface water and ground water, combined with hydrological observations, provide quantitative estimates of meteoric diagenesis in Pleistocene carbonates of the northern Bahamas. Meteoric waters equilibrate with aragonite, but water‐ rather than mineral‐controlled reactions dominate. Dissolutional lowering of the undifferentiated bedrock surface is an order of magnitude slower than that within soil‐filled topographic hollows, generating small‐scale relief at a rate of 65–140 mm ka^?1 and a distinctive pocketed topography. Oxidation of organic matter within the subsoil and vadose zones generates an average P of 4·0 × 10^?3 atm, which drives dissolution during vadose percolation and/or at the water table. However, these dissolution processes together account for <60% of the average rock‐derived calcium in groundwaters pumped from the freshwater lens. The additional calcium may derive from oxidation of organic carbon within the lens, accounting for the high P of the lens waters. Mixing between meteoric waters of differing chemistry is diagenetically insignificant, but evapotranspiration from the shallow water table is an important drive for subsurface cementation. Porosity generation in the shallow vadose zone averages 1·6–3·2% ka^?1. Phreatic meteoric diagenesis is focused near the water table, where dissolution generates porosity at 1·4–2·8% ka^?1. Maximum dissolution rates, however, are similar to those of evaporation‐driven precipitation, which occludes porosity of 4·0 ± 0·6% ka^?1. This drives porosity inversion, from primary interparticle to secondary mouldic, vug and channel porosity. In the deeper freshwater lens, oxidation of residual organic carbon and reoxidation of reduced sulphur species from deeper anaerobic oxidation of organic carbon may generate porosity up to 0·06% ka^?1. Meteoric diagenesis relies critically on hydrological routing and vadose thickness (controlled by sea level), as well as the geochemical processes active. A thin vadose zone permits direct evaporation from the water table and drives precipitation of meteoric phreatic cements even where mineral stabilization is complete. Copyright © 2007 John Wiley & Sons, Ltd.     

Atmospheric and Surface Water Pollution Interpretation in the Gdańsk Beltway Impact Range by the Use of Multivariate Analysis

The present study deals with the application of the hierarchical cluster analysis and non‐parametric tests in order to interpret the Gdańsk Beltway impact range. The data set represents concentration values for major inorganic ions (Na⁺, NH, K⁺, Mg²⁺, Ca²⁺, F⁻, Cl⁻, NO, and SO) as well as electrolytic conductivity and pH measured in various water samples [precipitation, throughfall water, road runoff, and surface water (drainage ditches, surface water reservoirs, and spring water)] collected in the vicinity of the beltway. Several similarity groups were discovered both in the objects and in the variables modes according to the water sample. In the majority of cases clear anthropogenic (fertilizers usage and transport, road salting in winter) and semi‐natural (sea salt aerosols, erosion of construction materials) impacts were discovered. Spatial variation was discovered for road runoff samples and samples collected from surface water reservoirs and springs. Surprisingly no clear seasonal variability was discovered for precipitation chemistry, while some evidences for existing of summer and winter specific chemical profile was discovered for road runoff samples. In general, limited range of the Gdańsk Beltway impact was proven.     

Regulating Environmental Factors of Nutrients Release from Wheat Straw Biochar for Sustainable Agriculture

One mechanism by which biochar application enhances soil nutrient availability is through direct nutrients release from biochar. However, factors controlling the release processes are poorly understood. In this study, the effects of pH, biochar to water ratio, temperature, ionic strength, and equilibration time on the release of PO, NO, NH, K⁺, Na⁺, Ca²⁺, and Mg²⁺ from biochar were evaluated in simulated experiments. The release of PO, K⁺, Ca²⁺, and Mg²⁺ was significantly affected by extraction pH, suggesting that their release from biochar was pH dependent or an H⁺‐consuming process. Correlation analysis indicated that PO and Ca²⁺, PO and Mg²⁺, and Ca²⁺ and Mg²⁺ were co‐solubilized with increasing soil acidity. To a lesser extent, the recovery of the nutrients was also affected by the ratio of biochar to water: more nutrients were soluble with more water supply. In contrast, the release of Na was not affected by pH while the concentration increased with decreasing biochar to water ratio. Meanwhile, other factors (temperature, ionic strength, and equilibration time) had less effect on nutrient release from biochar. Under the influence of pH, the patterns of NO and PO release from biochar were different: extractable NO concentration was not affected by the pH but more PO was released in strongly acidic conditions. Our data suggested that P was mainly retained in inorganic forms while N was in organic forms in biochar. We conclude that environmental factors have marked influences on nutrients release from biochar.     

Diel patterns in coastal‐stream nitrate concentrations linked to evapotranspiration in the riparian zone of a low‐relief,agricultural catchment

Evapotranspiration (ET) can cause diel fluctuations in the elevation of the water table and the stage in adjacent streams. The diel fluctuations of water levels change head gradients throughout the day, causing specific discharge through near‐stream sediment to fluctuate at the same time scale. In a previous study, we showed that specific discharge controls the residence time of groundwater in streambed sediment that, in turn, exerted the primary control on removal from groundwater passing through the streambed. In this study, we examine the magnitude of diel specific discharge patterns through the streambed driven by ET in the riparian zone with a transient numerical saturated–unsaturated groundwater flow model. On the basis of a first‐order kinetic model for removal, we predicted diel fluctuations in stream concentrations. Model results indicated that ET drove a diel pattern in specific discharge through the streambed and riparian zone (the removal zones). Because specific discharge is inversely proportional to groundwater travel time through the removal zones and travel time determines the extent of removal, diel changes in ET can result in a diel pattern in concentration in the stream. The model predictions generally matched observations made during summertime base‐flow conditions in a small coastal plain stream in Virginia. A more complicated pattern was observed following a seasonal drawdown period, where source components to the stream changed during the receding limb of the hydrograph and resulted in diel fluctuations being superimposed over a multi‐day trend in concentrations. Copyright © 2013 John Wiley & Sons, Ltd.     

Sediments,porewaters and diagenesis in an urban water body,Salford, UK: impacts of remediation

Contaminated sediments deposited within urban water bodies commonly exert a significant negative effect on overlying water quality. However, our understanding of the processes operating within such anthropogenic sediments is currently poor. This paper describes the nature of the sediment and early diagenetic reactions in a highly polluted major urban water body (the Salford Quays of the Manchester Ship Canal) that has undergone remediation focused on the water column. The style of sedimentation within Salford Quays has been significantly changed as a result of remediation of the water column. Pre‐remediation sediments are composed of a range of natural detrital grains, predominantly quartz and clay, and anthropogenic detrital material dominated by industrial furnace‐derived metal‐rich slag grains. Post‐remediation sediments are composed of predominantly autochthonous material, including siliceous algal remains and clays. At the top of the pre‐remediation sediments and immediately beneath the post‐remediation sediments is a layer significantly enriched in furnace‐derived slag grains, input into the basin as a result of site clearance prior to water‐column remediation. These grains contain a high level of metals, resulting in a significantly enhanced metal concentration in the sediments at this depth. Porewater analysis reveals the importance of both bacterial organic matter oxidation reactions and the dissolution of industrial grains upon the mobility of nutrient and chemical species within Salford Quays. Minor release of iron and manganese at shallow depths is likely to be taking place as a result of bacterial Fe(III) and Mn(IV) reduction. Petrographic analysis reveals that the abundant authigenic mineral within the sediment is manganese‐rich vivianite, and thus Fe(II) and Mn(II) released by bacterial reactions may be being taken up through the precipitation of this mineral. Significant porewater peaks in iron, manganese and silicon deeper in the sediment column are most probably the result of dissolution of furnace‐derived grains in the sediments. These species have subsequently diffused into porewater above and below the metal‐enriched layer. This study illustrates that the remediation of water quality in anthropogenic water bodies can significantly impact upon the physical and chemical nature of sedimentation. Additionally, it also highlights how diagenetic processes in sediments derived from anthropogenic grains can be markedly different from those in sediments derived from natural detrital material. Copyright © 2003 John Wiley & Sons, Ltd.