Urban Metal Flows – A Case Study of Stockholm. Review and Conclusions

Metals have rapidly accumulated in the anthroposphere, especiallyin urban areas, indicating possible environmental and resource problems. Here, Stockholm City was chosen for a case study of urban metal flows, i.e. metal inflow to, metals in the stock of,and metal outflow from the anthroposphere to the biosphere. Themetal stock of Stockholm is large and still growing. The large amounts of metals in the solid waste fraction totally dominatethe outflow from the city. For major parts of the stock, the emissions from goods in use are negligible. There are, however,goods applications corresponding to significant emissions: e.g. the traffic sector (Cu, Zn, Cr, Ni, Pb), the tapwater system (Cu), roofs/fronts or other metal surfaces (Cu, Zn). Today's known metal flows from the anthroposphere of Stockholm to the biosphere and sewage sludge are quantitatively dominated by Zn(34 ton y^-1) and Cu (14 ton y^-1). Historical and present emissions have resulted in high metal concentrations insediments (especially Cd, Hg and Pb, but also Cu and Zn), groundwater (Cu, Hg) and in soils (Hg, Cu, Pb). At present theannual median concentrations are below the Swedish limits for metals in sewage sludge, even if the safety margins aresmall for Cd, Hg and to some extent Cu. The flows of Cu and Zn to Stockholm soils are high with a significant accumulationindicating an environmental impact in a longer time perspective.High levels of metals in surface sediments in the waterenvironments reflects an ongoing input where these metals aretransported from known (Cu, Zn) and or partly unknown (Cd, Hg, Pb) sources. In future urban areas, monitoring of metal flows must be performed both in the anthroposphere and the biospherein order to have a pro active approach to urban environmentalproblems and to get prompt answers to measures taken.     

A Comparison Between Corrosion Rates and Runoff Rates from New and Aged Copper and Zinc as Roofing Material

Recently there has been anincreased environmental concern in severalcountries in Europe, in particular in Sweden andin the Netherlands regarding the amount of copperand zinc that is released from building materialsinto society. Due to lack of runoff data, thelegislators have so far used corrosion ratesmeasured during the last 20 years to calculatequantities of metal released from buildingsassuming that the quantity of metal corrosionequals the quantity of metal runoff. Withdecreasing levels of environmental pollutantsduring the last decade in Europe, it is importantto determine more recent and hence morerepresentative corrosion and runoff rates to beused in the calculations. For this reason a field exposure program was implemented during 48 weeks in an urbanatmosphere in Sweden determining corrosion andrunoff rates for copper and zinc of differentage. New copper exposed for 48 weeks in the urbanatmosphere shows a corrosion rate of 6.7gm^-2y^-1 and an almost constant runoff rate of1.3 gm^-2y^-1 during the period. Therunoff rate is significantly lower than thecorrosion rate and represents only a fraction(20%) of the total amount of corroded metalduring this period. Zinc shows a graduallydecreasing corrosion rate with time being 5.0gm^-2y^-1 after 48 weeks of exposure. Therunoff rate is relatively stable with an averagerate of 3.1 gm^-2y^-1 during the sameperiod. This value represents 60% of the totalamount of corroded zinc. The effect of panel age has been investigatedin parallel field and laboratory studies. Theresults show that naturally aged copper exhibitssomewhat higher average runoff rates (2 gm^-2y^-1) than new copper, probably due to acombined effect of storage and weatherconditions. No significant difference in runoffrate can be found between new and naturally agedzinc. The field and laboratory investigationsshow that precipitation rate and amount influence the magnitude of the runoff rate forboth copper and zinc.     

Total Lead and Stable Lead Isotopes in Stockholm Sediments

Lead (Pb) in the environment is derived from both naturaland anthropogenic sources. The aim of this study is to estimate the isotopic signature of anthropogenic Pb in sediments from a highly contaminated area (Stockholm), to discuss the influence of different sources on this signature, and to suggest natural Pb background concentrations. Also distribution patterns and differences between different water areas in Stockholm have been studied, both by total Pb and stable Pb isotopes. In 1993, sediment samples were collected at 24 stations in the Stockholm area and analysed for total Pb, zirconium (Zr), scandium (Sc) and stable Pb isotopes (^{204, 206-208}Pb). Total Pb data show that the Stockholm sediments are severely contaminated by Pb. The contamination seems to be rather local since the small lakes surrounding the central parts of Stockholm are much less effected than the central parts. Stockholm is clearly influenced by anthropogenic and natural sources, but in some of the small lakes also by Pb in zircons from the geological basement. The anthropogenic Pb in Stockholm has typical ²⁰⁷Pb/²⁰⁶Pb ratios of 0.85–0.89 and ²⁰⁸Pb/²⁰⁴Pb ratios of 36–38, which are distinct from natural sources. Pb/Sc ratios suggest that the natural background Pb concentration is 10–20 mg kg^-1 d.w.     

Concentrations and Pools of Heavy Metals in Urban Soils in Stockholm,Sweden

The concentrations of heavy metals (Cd, Cr, Cu, Hg, Ni, Pb andZn) and arsenic (As) were surveyed and the metal pools estimatedin soils in Stockholm Municipality. The sampling sites were distributed all over the entire municipality with a higher sampling density in the city centre. Soils were sampled to a maximum depth of 25 to 60 cm. Soil texture, total-C content, electrical conductivity and pH were analysed. Heavy metal concentrations were determined after wet digestion with boiling7 M HNO₃.The results showed a wide range in heavy metal concentrations, as well as in other soil properties. The city centre soils constituted a rather homogeneous group whereas outside this areano geographical zones could be distinguished. These soils were grouped based on present land use, i.e. undisturbed soils, public parks, wasteland (mainly former industrial areas), and roadside soils. The city centre and wasteland soils generally hadenhanced heavy metal concentrations to at least 30 cm depth compared to park soils outside the city centre and rural (arable)soils in the region, which were used to estimate background levels. For example, the mean Hg concentration was 0.9 (max 3.3)mg kg^-1 soil at 0–5 cm and 1.0 (max 2.9) at 30 cm depth in the city centre soils, while the background level was 0,04 mg kg^-1. Corresponding values for Pb were 104 (max 444) and135 (max 339) mg kg^-1, at 0–5 and 30 cm, respectively, while the background level was 17 mg kg^-1.The average soil pools (0–30 cm depth) of Cu, Pb and Zn were 21,38 and 58 g m^-2 respectively, which for Pb was 3–4 timeshigher and for Cu and Zn 1.5–2 times higher than the backgroundlevel. The total amount of accumulated metals (down to 30 cm)in the city centre soils (4.5^*10 ⁶ m² public gardens and green areas) was estimated at 80, 1.1, 120 and 40 t for Cu, Hg, Pb and Zn, respectively. The study showed (1) thatfrom a metal contamination point of view, more homogeneous soilgroups were obtained based on present land use than on geographicdistance to the city centre, (2) the importance of establishing a background level in order to quantify the degree of contamination, and (3) soil samples has to be taken below the surface layer (and deeper than 30 cm) in order to quantify theaccumulated metal pools in urban soils.     

In Situ flushing of contaminated soils from a refinery: Organic compounds and metal removals

This article demonstrates the applicability of in situ flushing for the remediation of soil contaminated with petroleum hydrocarbons at a Mexican refinery. The initial average total petroleum hydrocarbon (TPH) concentration for the demonstration field test was 55,156 g/kg. After six weeks of in situ flushing with alternate periods of water and water/surfactant, an average concentration of 1,407 mg/kg was reached, achieving a total removal efficiency of 98 percent. At the end of the process, no hydrocarbons such as diesel; gasoline; benzene, toluene, ethyl benzene, and xylene (BTEX); or petroleum aromatic hydrocarbons (PAHs) were found. Iron washing achieved a removal efficiency of 70 percent, and for vanadium, the removal efficiency was 94.4 percent. The volume of soil treated was 41.6 m³ (38 m²), equivalent to 69.5 tons of soil. A rough calculation of the process costs estimated a total cost of $104.20/m³ ($114.00/m²). Our research indicates that there are a few studies demonstrating in situ flushing experiences under field conditions where both organic (TPH, diesel, gasoline, PAHs, BTEX) and metal (iron and vanadium) removals are reported. © 2004 Wiley Periodicals, Inc.     

Selection of adsorbents for treatment of leachate: batch studies of simultaneous adsorption of heavy metals

The simultaneous adsorption of copper (Cu), cadmium (Cd), nickel (Ni), and lead (Pb) ions from spiked deionized water and spiked leachate onto natural materials (peat A and B), by-product or waste materials (carbon-containing ash, paper pellets, pine bark, and semi-coke), and synthetic materials (based on urea-formaldehyde resins, called blue and red adsorbents) or mixtures thereof was investigated. The adsorbents that gave the highest metal removal efficiencies were peat A, a mixture of peat B and carbon-containing ash, and a mixture of peat A and blue. At an initial concentration of 5 mg/l for each metal, the removal of each species of metal ion from spiked water and spiked leachate solutions was very good (>90%) and good (>75%), respectively. When the initial concentration of each metal in the solutions was twenty times higher (100 mg/l), there was a noticeable decrease in the removal efficiency of Cu²⁺, Cd²⁺, and Ni²⁺, but not of Pb²⁺. Langmuir monolayer adsorption capacities, q_m, on peat A were found to be 0.57, 0.37, and 0.36 mmol/g for Pb²⁺, Cd²⁺, and Ni²⁺, respectively. The order of metal adsorption capacity on peat A was the same in the case of competitive multimetal adsorption conditions as it was for single-element adsorption, namely Pb²⁺ > Cd²⁺ ≥ Ni²⁺. The results show that peat alone (an inexpensive adsorbent) is a good adsorbent for heavy metal ions.     

Copper stabilization in beneficial use of waterworks sludge and copper-laden electroplating sludge for ceramic materials

A promising strategy for effectively incorporating metal-containing waste materials into a variety of ceramic products was devised in this study. Elemental analysis confirmed that copper was the predominant metal component in the collected electroplating sludge, and aluminum was the predominant constituent of waterworks sludge collected in Hong Kong. The use of waterworks sludge as an aluminum-rich precursor material to facilitate copper stabilization under thermal conditions provides a promising waste-to-resource strategy. When sintering the mixture of copper sludge and the 900 °C calcined waterworks sludge, the CuAl₂O₄ spinel phase was first detected at 650 °C and became the predominant product phase at temperatures higher than 850 °C. Quantification of the XRD pattern using the Rietveld refinement method revealed that the weight of the CuAl₂O₄ spinel phase reached over 50% at 850 °C. The strong signals of the CuAl₂O₄ phase continued until the temperature reached 1150 °C, and further sintering initiated the generation of the other copper-hosting phases (CuAlO₂, Cu₂O, and CuO). The copper stabilization effect was evaluated by the copper leachability of the CuAl₂O₄ and CuO via the prolonged leaching experiments at a pH value of 4.9. The leaching results showed that the CuAl₂O₄ phase was superior to the CuAlO₂ and CuO phases for immobilizing hazardous copper over longer leaching periods. The findings clearly indicate that spinel formation is the most crucial metal stabilization mechanism when sintering multiphase copper sludge with aluminum-rich waterworks sludge, and suggest a promising and reliable technique for reusing both types of sludge waste for ceramic materials.     

Effect of aeration modes on the characteristics of composting emissions and the NH3 removal efficiency by using biotrickling filter

A pilot biotrickling filter (BTF) packed with ZX02 fibrous balls as packing material was tested for the treatment of ammonia (NH₃) released from a composting plant of dairy manure. In order to investigate the effects of three compost aeration modes (mode Co-I, Co-II and In-II) on the NH₃ removal efficiency, a field experiment was continuously carried out for more than eight months. The results demonstrated that under the intermittent aeration mode (In-II), the NH₃ removal efficiency reached 99.2 ± 0.1% when the inlet NH₃ concentration was 7.5-32.3 mg m⁻³ (9.8-42.5 ppmv). The maximum and critical elimination capacity of the biotrickling filter was 22.6 and 4.9 g NH₃ m⁻³ h⁻¹, respectively. The effluent concentration of NH₃ was lower than 1.0 mg m⁻³, which meets the first class discharge standards of GB14554-93. When the concentration of free ammonia in the trickling liquid was varied from 0.1 to 0.4 mg L⁻¹, the nitrification yield was between 47.9% and 103.8%. In addition, the optimum liquid tricking velocity (LTV) of the biotrickling filter was 0.5 m³ m⁻² h⁻¹ for low inlet concentrations and 2.2 m³ m⁻² h⁻¹ for high inlet concentrations. Therefore, the use of the biotrickling filter for the compost under the third aeration mode (In-II) yielded an effective optimum NH₃ removal and reduced the nitrogen loss in the compost.     

Heavy Metals in Stockholm Groundwater – Concentrations and Fluxes

Sampling of groundwater in theQuaternary deposits was carried out at 70 sitesin Stockholm for, among other things, metalanalyses. The objectives were to get a notion of the metal content and to get a basis for anestimation of the order of magnitude of thegroundwater transported metal contribution to themain surface water bodies in comparison to otherroutes. Thus, in three watershed areaswithin the Stockholm Town, groundwater flow andmetal concentration propagation were simulatedand metal fluxes were calculated. Theconcentrations of heavy metals were in generalfound to be very high in comparison withgroundwater in forested areas. This was mostpronounced for mercury (Hg) and copper (Cu). Themost remarkable result was a Hg concentration of4.57 g L^-1 in the vicinity of a closed downhospital. The annual contribution of heavy metals(kg) by groundwater to the main surface waterbodies was estimated to: As (2.2), Cd (0.20), Co(4.9), Cr (3.1), Cu (34), Hg (0.06), Ni (28), Pb(2.2) Zn (118). These fluxes are much smallerthan those in forest ecosystems, due to lowergroundwater recharge in urban areas, where agreat part of the runoff is diverted bylandsealing, drainage, tunnels etc. The modelingresults emphasize the importance of the sorptionprocesses indicating that the modeled areas arein a non-steady state condition. It also showsthat the sources generating elevatedconcentrations of the high adsorptive metals Pband Hg are likely to be nearby.     

Field scale N2O flux measurements from grassland using eddy covariance

In order to assess nitrous oxide (N₂O) emissions from typical intensively managed grassland in northern Britain fluxes were measured by eddy covariance using tuneable diode laser absorption spectroscopy from June 2002 to June 2003 for a total period of 4000 h. With micrometeorological techniques it is possible to obtain a very detailed picture of the fluxes of N₂O at field scale (10³–10⁴ m²), which are valuable for extrapolation to regional scales. In this paper three of the four fertilizer applications were investigated in detail. N₂O emissions did not always show a clear response. Hourly fluxes were very large immediately after the June 2002 nitrogen fertilizer application, peaking at 2.5 mg N₂O–N m^?2 s^?1. Daily fluxes were averaging about 300 ng N₂O m^?2 s^?1 over the 4 days following fertilizer application. The response of N₂O emissions was less evident after the August fertilization, although 2 days after fertilizer application an hourly maximum flux of 554 ng N₂O–N m^?2 s^?1 was registered. For the rest of August the flux was undetectable. The differences between fertilization events can be explained by different environmental conditions, such as soil temperature and rainfall. A fertiliser-induced N₂O emission was not observed after fertilizer application in March 2003, due to lack of rainfall. The total N₂O flux from June 2002 to June 2003 was 5.5 kg N₂O–N ha^?1y^?1, which is 2.8% of the total annual N fertilizer input.     

Airborne contaminants at waste treatment plants

Airborne contaminants in Finnish waste treatment plants were studied at two plants using mainly manual sorting and one incineration plant. Air samples were analysed for mesophilic and thermotolerant bacteria, mesophilic fungi, endotoxin, dust and heavy metals (lead, cadmium). The concentrations of mesophilic bacteria in the working air of the waste treatment plants were under 2 × 10⁴ colony forming units (cfu) m⁻³ and the concentrations of mesophilic fungi were under 7 × 10⁴ cfu m⁻³. There was no seasonal variation in the concentrations of bacteria, but the concentrations of fungi were highest in autumn at the waste incineration plant. The concentrations of microbes recorded with two sampling methods, the Andersen and Nuclepore filter methods, differed but were usually of the same order of magnitude. The identified bacteria did not include any potent pathogens. In manual sorting the level of organic dust reached 38 mg m⁻³, whereas the 8-h hygiene limit value for organic dust is 5mg m⁻³ and the 15-min hygiene limit value is 10 mg m⁻³. The endotoxin levels were all below 30 ng m⁻³ and the concentrations of heavy metals were low.     

Field scale N2O flux measurements from grassland using eddy covariance

In order to assess nitrous oxide (N₂O) emissions from typical intensively managed grassland in northern Britain fluxes were measured by eddy covariance using tuneable diode laser absorption spectroscopy from June 2002 to June 2003 for a total period of 4000 h. With micrometeorological techniques it is possible to obtain a very detailed picture of the fluxes of N₂O at field scale (10³–10⁴ m²), which are valuable for extrapolation to regional scales. In this paper three of the four fertilizer applications were investigated in detail. N₂O emissions did not always show a clear response. Hourly fluxes were very large immediately after the June 2002 nitrogen fertilizer application, peaking at 2.5 mg N₂O–N m^–2 s^–1. Daily fluxes were averaging about 300 ng N₂O m^–2 s^–1 over the 4 days following fertilizer application. The response of N₂O emissions was less evident after the August fertilization, although 2 days after fertilizer application an hourly maximum flux of 554 ng N₂O–N m^–2 s^–1 was registered. For the rest of August the flux was undetectable. The differences between fertilization events can be explained by different environmental conditions, such as soil temperature and rainfall. A fertiliser-induced N₂O emission was not observed after fertilizer application in March 2003, due to lack of rainfall. The total N₂O flux from June 2002 to June 2003 was 5.5 kg N₂O–N ha^–1y^–1, which is 2.8% of the total annual N fertilizer input.     

Fluxes and Loading of Heavy Metals, Benzo[a]pyrene and Oil Products in Vilnius City

The concentrations of heavy metals Pb, Cd, Cu, Zn and Hg, benzo[a]pyrene and oil products (C₁₅–C₂₈) in bulk (wet and dry) atmospheric deposition in Vilnius city in 2005–2006 were analysed. The highest flux to the ground surface of the city residential area, reaching 1,680 mg m^?2 year^?1, was determined for oil products, which in atmospheric bulk deposition was estimated to be mainly in the form of solid sediments. Among heavy metals, the highest flux was determined for Zn (113.5 mg m^?2 year^?1), while the lowest flux was determined for Hg (0.06 mg m^?2 year^?1). The flux of investigated pollutants ranges from a few times, or for some pollutants, up to one order of magnitude higher at the urban sampling site in comparison to residential or background sites. Some hundred tons of oil products, approximately 52 tons of zinc and a considerably lower amount of mercury, benzo[a]pyrene and cadmium deposit yearly to the ground and water surface of Vilnius city. Metallic constructions related to transport and buildings, automobile exhausts, spills of fuel and lubricants are suggested to be the factors which result in the accumulation of high amounts of heavy metals, oil products and other pollutants on the ground surface of the city.     

A novel methodology to estimate the evolution of construction waste in construction sites

This paper focuses on the accumulation of construction waste generated throughout the erection of new residential buildings. A special methodology was developed in order to provide a model that will predict the flow of construction waste. The amount of waste and its constituents, produced on 10 relatively large construction sites (7000-32,000 m² of built area) was monitored periodically for a limited time. A model that predicts the accumulation of construction waste was developed based on these field observations. According to the model, waste accumulates in an exponential manner, i.e. smaller amounts are generated during the early stages of construction and increasing amounts are generated towards the end of the project. The total amount of waste from these sites was estimated at 0.2 m³ per 1 m² floor area. A good correlation was found between the model predictions and actual data from the field survey.     

Chitosan Functionalization with Amino Acids Yields to Higher Copper Ions Adsorption Capacity

Chitosan (Chi) beads were conjugated with three different amino acids [namely, glutamic acid (GLU), methionine (MET), and taurine (TAU)] aiming to increase the divalent copper ions uptake in aqueous media. Scanning Electron Microscopy evidenced the development of a large porous structure after amino acid functionalization, associated with the increase in a number of amino groups in the polymer backbone. X-Ray Photoelectron Spectroscopy and Fourier-Transform Infrared Spectra analyses were also employed to assess the conjugation of these three different amino acids in chitosan backbone. Adsorption experiments were conducted in a batch process, at 298 K, and kinetic data indicated a slightly better fitting for the pseudo-first-order model when compared to pseudo-second order. Intraparticle diffusion model suggested a three-step mechanism for Cu(II) adsorption kinetics, limited by the third step, the intraparticle diffusion. The isotherm data fitting to the traditional Langmuir and Freundlich models indicated a better fit for the former case. The amino acid conjugation resulted in the increase of the maximum adsorption capacity for Cu(II) from 1.30 mmol g^?1 prior to amino acid conjugation to values as high as 2.31 mmol g^?1, 2.40 mmol g^?1 and 2.68 mmol g^?1 for Chi–TAU, Chi–GLU, and Chi–MET, respectively. These results are attributed to the introduction of additional amino groups and new carboxylate and amino acid residues into the chitosan backbone, which might also be explored for amino acid demanding applications.     

Removal of Iron and Copper Ions from the Liquid Phase by Modified Polymeric Membranes

Preparation of polymeric membranes based on cellulose acetate and modified by adding different amounts of a pore generating agent, which was polyvinylpyrrolidone (PVP), is presented and potential application of the membranes obtained for the removal of iron and copper ions from liquid phase is examined. Addition of various amounts of PVP has an impact on the physical (porosity, equilibrium water content and permeability) and chemical (content of the surface oxygen group, pH) properties of the membranes obtained. Filtration of iron and cupper solution leads to significant changes in the total content of surface oxygen groups, however the acidic oxygen groups remain dominant. With the content of PVP increasing within a certain range, the membrane permeability is improved. The membranes obtained show higher efficiency in removal of Fe³⁺ than Cu²⁺ ions, but with increasing content of PVP the efficiency in iron ions removal decreases and the total filtration resistance decreases after filtration of iron ions solutions.     

Pilot scale evaluation of the BABIU process – Upgrading of landfill gas or biogas with the use of MSWI bottom ash

Biogas or landfill gas can be converted to a high-grade gas rich in methane with the use of municipal solid waste incineration bottom ash as a reactant for fixation of CO₂ and H₂S. In order to verify results previously obtained at a laboratory scale with 65–90 kg of bottom ash (BA), several test runs were performed at a pilot scale, using 500–1000 kg of bottom ash and up to 9.2 N m³/h real landfill gas from a landfill in the Tuscany region (Italy). The input flow rate was altered. The best process performance was observed at a input flow rate of 3.7 N m³/(h t_BA). At this flow rate, the removal efficiencies for H₂S were approximately 99.5–99%.     

A comparative study of two composts as filter media for the removal of gaseous reduced sulfur compounds (RSCs) by biofiltration: Application at industrial scale

This work presents the use of two composts as filter media for the treatment by biofiltration of odors emitted during the aerobic composting of a mixture containing sewage sludge and yard waste. The chemical analysis of the waste gas showed that the malodorous compounds at trace level were the reduced sulfur compounds (RSCs) which were dimethyl sulfide (Me₂S), methanethiol (MeSH) and hydrogen sulfide (H₂S). Laboratory tests for biofiltration treatment of RSCs were performed in order to compare the properties of two filter media, consisted of a mature compost with yard waste (YW) and a mixture of mature compost with sewage sludge and yard waste (SS/YW). The maximum elimination capacity (EC) values obtained with the YW mature compost as packing material were 12.5 mg m^?3 h^?1 for H₂S, 7.9 mg m^?3 h^?1 for MeSH and 34 mg m^?3 h^?1 for Me₂S, and the removal efficiency decreased in the order of: H₂S > MeSH > Me₂S. Moreover, the YW compost filter medium had a better behavior than the filter medium based on SS/YW in terms of acclimation of the microbial communities and moisture content. According to these results, a YW mature compost as packing material for an industrial biofilter were designed and this industrial biofilter was found effective under specified conditions (without inoculation and addition of water). The results showed that the maximum EC value of RSCs was 935 mg m^?3 h^?1 (100% removal efficiency, RE) for an inlet loads (IL) between 0 and 1000 mg m^?3 h^?1. Thus, YW compost medium was proven efficient for biofiltration of RSCs both at laboratory and industrial scale.     

The Application of Stable Isotopes for Assessing the Hydrological, Sulfur, and Iron Balances of Acidic Mining Lake ML 111 (Lusatia, Germany) as a Basis for Biotechnological Remediation

Stable isotope (¹⁸O–H₂O, ²H–H₂O ³⁴S–SO₄ ^2-) andhydrochemical data (SO₄ ^2-, Fe-concentrations) have beenused to estimate the annual groundwater inflow and outflow of mining lake ML 111 and to calculate the total amount of dissolvedsulfate and iron that is carried into the lake by groundwater. The hydrological balance suggests an annual groundwater inflow of 23 700 m³ and an annual groundwater outflow of 15 700 m³. The calculation of the sulfur and iron balances yielded an annual sulfate input of 37 800 kg and an annual iron input of 7000 kg with the groundwater inflow. Furthermore it was shown that significant fluxes of these elements go into the lake sediments which results in continuous release of acidity in the lake water.     

The release of nitrous oxide from the intertidal zones of two European estuaries in response to increased ammonium and nitrate loading

Nitrous oxide (N₂O) release and denitrification rates were investigated from the intertidal saltmarsh and mudflats of two European river estuaries, the Couesnon in Normandy, France and the Torridge in Devon, UK. Sediment cores and water were collected from each study site and incubated for 72 h in tidal simulation chambers. Gas samples were collected at 6 and 12 h intervals from the chambers during incubation. From these N₂O emission rates were calculated. The greatest rates for both N₂O production and denitrification were measured from saltmarsh cores. These were 1032 μmol N₂O m^?2 day^?1 and 2518 μmol N₂ m^?2 day^?1, respectively, from the Couesnon and 109 μmol N₂O m^?2 day^?1 and 303 μmol N₂ m^?2 day^?1 from the Torridge. A strong positive correlation was apparent with N₂O emission rates and ammonium concentration in the sediment, nitrate concentration in floodwater and sediment aerobicity.