AVAILABILITY OF POTASSIUM TO RYEGRASS FROM SCOTTISH SOILS II. UPTAKE OF INITIALLY NON-EXCHANGEABLE POTASSIUM

The stable desorption parts of soil Quantity/Intensity isotherms were used to determine the contributions of initially exchangeable and non-exchangeable potassium to plant uptake from ten soils. The activity ratio, AR^K= a_K/√^aC_a, Mg at which K was first taken up from non-exchangeable sources varied from 3 × 10^?3 to 8 × 10^?3 M^1/2 depending on the soil. Uptake rates of two categories of initially non-exchangeable K were linearly related to √times;. The first category appeared to be close to equilibrium with the initially exchangeable K, and gave effective diffusion coefficients of 10^?7 cm² s^?1 for four soils. The second category gave diffusion coefficients from 10^?20 to 10^?22 cm² s^?1, probably came from internal surfaces of micaceous clays, and began to be released at activity ratios below 3 × 10^?4 to 6 × 10^?4 M^1/2 depending on soil type. The soils fell into three groups, broadly consistent with soil series, on their ability to release the second category of potassium.     

Diffusion coefficients of nitrate, chloride, sulphate and water in cracked and uncracked Chalk

The rates of diffusion of chloride, sulphate and water, labelled respectively with ³⁶Cl, ³⁵S and ³H, and unlabelled nitrate, were measured in small cylindrical Chalk monoliths. Using a simple mathematical model, diffusion coefficients were calculated to provide a basis for comparing the movement of these substances through Chalk rock in the absence of hydrostatic pressure gradients. The diffusion coefficients of chloride and nitrate were similar, with a range of values (0.52–3.23 × 10^?6 cm² s^?1) and (0.53–3.20 × 10^?6 cm² s^?1) respectively. These were slightly less than for tritiated water (0.60–3.51 × 10^?6 cm² s^?1), while the coefficient for sulphate was about half that of the others (0.28–1.47 × 10^?6 cm² s^?1). The coefficients indicate the absence of any interaction with the Chalk surfaces.     

Fuller's earth and fired clay as adsorbents for dyestuffs

The ability of Fuller's earth to adsorb a basic dye (Astrazone Blue — Basic Blue 69) and an acidic dye (Telon Blue - Acid Blue 25) has been studied. The equilibrium saturation adsorption capacities were 1200 mg dye g^?1 Fuller's earth and 220 mg dye g^?1 Fuller's earth for Astrazone Blue and Telon Blue, respectively. The kinetics of the adsorption processes were studied in an agitated batch adsorber. The time to reach 90% equilibrium value was achieved in less than 1 h. The variables investigated were agitation, adsorbent mass, initial dye concentration and temperature. A limited number of studies were undertaken using a fired clay but significantly lower saturation capacities were obtained, namely, 7 mg dye g^?1 fired clay and 40 mg dye g^?1 fired clay for Telon Blue and Astrazone Blue, respectively.     

Reduction of Cr(VI) by soil humic acids

The rate of hexavalent chromium reduction by a soil humic acid (SHA) was investigated in aqueous solutions where concentrations of Cr(VI), H⁺, and SHA were independently varied. Rate experiments were done with a large excess of SHA over Cr(VI). Rates of reduction depend strongly on [H⁺], increasing with decreasing pH. Typical Cr(VI)-SHA reactions display a nonlinear reduction of Cr(VI) with time that cannot be modelled with simple first- or second-order rate equations. An empirical rate equation is developed for Cr(VI)-soil humic acid reactions over a range of experimental conditions. The model is in part based on a reactive continuum concept developed for soil fulvic acids. The rate equation describing Cr(VI) reduction by SHA is: R= -(k₀+k[H⁺]^1/2)[HCrO₄^?]^1/2X_e^?1, where k₀ is (8·3 ± 1·2) × 10^?12, s^?1k is (2·04 ± 0·05) × 10^?9 l^1/2 mol^?1/2 s^?1, and X_e is the equivalent fraction of SHA oxidized. The rate equation adequately models Cr(VI) reduction in an experiment with [Cr(VI)]₀ four times greater than the maximum concentration used in its derivation. Cr(VI) reduction at pH 3 by two other SHAs can also be modelled using the rate equation. The difference between the rate coefficients for the humic acid and the fulvic acid from the same soil was greater than the difference in the rate coefficients for humic acids from different soils.     

Diffusion of cattle manure solution through a wet porous stratum with reaction

A process governing the transport rate of cattle manure as measured by their COD (chemical oxygen demand) through a wet porous stratum is investigated under simulated conditions. A mathematical model of the system is presented. The model simulates diffusion and biological reaction processes taking place simultaneously in the system. Experimental observations have been made to determine the diffusion coefficient and the biological reaction rate constant of the cattle manure solution. Values of approximately 6.76 × 10^?6 cm² s^?1 for the diffusion coefficient and 3.05 × 10^?2 day^?1 for the reaction rate constant at the temperature of 25 ± 2°C were obtained. For the system with known diffusion coefficient and reaction rate constant, the analytical expressions obtained here can be used to approximately evaluate or predict the rates that animal wastes, under conditions similar to those in this study, will contaminate surface water, soil or ground water.     

Tillage effects and specific energy requirements of rotary tillage

Rotary tillage experiments were carried out under laboratory conditions in 3 types of Dutch soil. The moisture contents were set at 6 levels. Two tools were used; a knife blade and a tine. The energy required to work the soil was assessed with a pendulum.The specific energy requirement was expressed in units per volume of loosened soil, EV (kJ m^?3) and also in units per surface area of loosened soil, EA (kJ m^?2). In silty clay loam EV ranged between 153 and 160 kJ m^?3 for the knife blade, and increased from 170 to 280 kJ m^?3 for the tine, when the moisture content increased from 17 to 22%. EA increased from 2.5 to 9 kJ m^?2 × 10^?1 for the knife blade and from 3.8 to 10.5 kJ m^?2 × 10^?1 for the tine, when the moisture content increased from 17 to 22%.In sandy loam EV decreased from 110 to 75 kJ m^?3 for the knife blade and from 165 to 130 kJ m^?3 for the tine, when the moisture content increased from 9.5 to 17% EA increased from 1 to 2.5 kJ m^?2 × 10^?1 for the knife blade and increased from 2.7 to 2 kJ m^?2 × 10^?1 for the tine, when the moisture content increased from 9.5 to 17%.In silty loam EV decreased from 117 to 95 kJ m^?3 for the knife blade and from 170 to 137 kJ m^?3 for the tine, when the moisture content increased from 17 to 22%. EA increased from 3.7 to 5 kJ mm^?2 × 10^?1 for the knife blade, and from 3 to 5.5 kJ m^?2 × 10^?1 for the tine, when the moisture content increased from 17 to 22%.The energy requirement was related to penetration resistance, shearing resistance and modulus of elasticity. In silty clay loam the penetration resistance decreased from 3.9 to 2.6 MPa × 10^?1, the shear resistance hardly changed and ranged between 0.8 and 0.9 MPa × 10^?1, and the modulus of elasticity decreased from 46 to 23 MPa × 10^?1, when the moisture content increased from 17 to 22%.In sandy loam the penetration resistance decreased from 5.5 to 1.9 MPa × 10^?1, the shear resistance decreased from 0.6 to 0.4 MPa × 10^?1 and the modulus of elasticity decreased from 84 to 15 MPa × 10^?1, when the moisture content increased from 9.5 to 17%. In silty loam, the penetration resistance decreased from 3.6 to 1.7 MPa × 10^?1, the shear resistance decreased from 0.6 to 0.4 MPa × 10^?1 and the modulus of elasticity decreased from 58 to 11 MPa × 10^?1 when the moisture content increased from 17.5 to 22%.     

Influence of humic substances on photolysis of divalent mercury in aqueous solution

Mercury (II) solutions were irradiated by a simulated sunlight in the presence of humic acid (HA) or fulvic acid (FA). Results show that, under the experimental conditions and the FA and HA chosen, less than 20% of the Hg in solution was photolysed with a rate of (1.63±0.29)×10^?2 s^?1 (n=23) and the rest of (2.38±0.40)×10^?4 s^?1 (n=23) depending on the substitutes of humic substances to which Hg were bond. The sunlight photolysis lifetimes were estimated to be 4 and 250 sunlight hours respectively under summer conditions at Stockholm latitude.     

Use of wollastonite for the treatment of Cu(II) rich effluents

The adsorption technique using wollastonite has been applied for the removal of Cu(II) from aqueous solutions. The low concentration, high temperature and alkaline pH favor the removal of Cu(II). The Langmuir isotherm was used to represent the equilibrium data at different temperatures. The apparent heat of adsorption has been found to be 5.926 Cal mol^?1. The uptake of Cu(II) is diffusion controlled and the mass transfer coefficient is 3.6 × 10^?5 cm s^?1. The maximum removal of Cu(II) in alkaline medium has been explained on the basis of the uptake of hydrolyzed adsorbate species by the active surface sites of adsorbent.     

Effects of Single and Mixed Ion Solutions on Hydraulic and Physical Properties of a Clay Soil

In this work, the influence of solute concentration of two types of electrolyte solutions single-ion (Na) and mixed-ion (Na–Ca) systems on hydraulic and some physical properties of a clay soil was investigated. Saturated hydraulic conductivity (HC) declined noticeably using lower solute concentration in single ion system. The highest reduction in HC was observed at 250 mole_c m^?3 solute concentration. Application of high solute concentration of single-ion system reduced meanweight diameter (MWD) to less than half of the control treatment (0.16 mm compared with 0.33 mm). Resistance to penetrometer increased with decreasing solute concentration. In mixed-ion system the MWD was increased whereas the resistance to penetrometer was decreased. HC values ranged from 6.5?×?10^?4 to 9.0?×?10^?4 mm s^?1 in mixed ion system compared with 7.2?×?10^?4 to 13.0?×?10^?4 mm s^?1 in single-ion system. The improvement of some physical properties in mixed-ion solution treatment is attributed to the presence of calcium ion that usually acts as amendment to sodium-affected soil. Soil HC showed lower values at low solute concentrations.     

Effect of reduced air pressure on soil thermal conductivity over a wide range of water content and temperature

To clarify the role of air molecules in coupled heat and mass transfer in soil, we measured the thermal conductivity of three kinds of soil (Ando soil, Red Yellow soil, and Toyoura sand) under reduced air pressure over a wide range of water content and temperature (10–75°C). The thermal conductivity increased sharply under reduced air pressure above a critical water content of the soil, becoming several times larger than that under normal pressure (101 kPa). The maximum thermal conductivity for each soil was obtained below 75°C and was similar to the thermal conductivity of some metals such as Mn, Hg and stainless steel. When the soil was drier than its critical water content, the thermal conductivity did not increase under reduced air pressure. The hydraulic diffusivity at the critical water content for each soil was of the order of 10^?8 m² s^?1. This suggests that the latent heat transfer is enhanced by the circulation of the condensed water. However, very little is known about the effect of circulating water on the latent heat transfer under reduced air pressure. To make this clear, the thermal conductivity would need to be measured in the steady state under reduced air pressure.     

Calibrating soil respiration measures with a dynamic flux apparatus using artificial soil media of varying porosity

Measurement of soil respiration to quantify ecosystem carbon cycling requires absolute, not relative, estimates of soil CO₂ efflux. We describe a novel, automated efflux apparatus that can be used to test the accuracy of chamber‐based soil respiration measurements by generating known CO₂ fluxes. Artificial soil is supported above an air‐filled footspace wherein the CO₂ concentration is manipulated by mass flow controllers. The footspace is not pressurized so that the diffusion gradient between it and the air at the soil surface drives CO₂ efflux. Chamber designs or measurement techniques can be affected by soil air volume, hence properties of the soil medium are critical. We characterized and utilized three artificial soils with diffusion coefficients ranging from 2.7 × 10^?7 to 11.9 × 10^?7 m² s^?1 and porosities of 0.26 to 0.46. Soil CO₂ efflux rates were measured using a commercial dynamic closed‐chamber system (Li‐Cor 6400 photosynthesis system equipped with a 6400‐09 soil CO₂ flux chamber). On the least porous soil, small underestimates (< 5%) of CO₂ effluxes were observed, which increased as soil diffusivity and soil porosity increased, leading to underestimates as high as 25%. Differential measurement bias across media types illustrates the need for testing systems on several types of soil media.     

Turbulent mixing accelerates PAH desorption due to fragmentation of sediment particle aggregates

Purpose

Stripping contaminants from sediments with granular activated carbon (GAC) is a promising remediation technique in which the effectiveness depends on the rate of contaminant extraction from the sediment by the GAC. The purpose of the present study was to investigate the effect of mixing intensity on the short-term extraction rate of polycyclic aromatic hydrocarbons (PAHs) from contaminated sediment.

Materials and methods

PAH desorption from sediment at a wide range of rotational speeds (min^?1; rotations per minute (rpm)) was monitored by uptake in Tenax polymeric resins using a completely mixed batch reactor. Desorption data were interpreted using a radial diffusion model. Desorption parameters obtained with the radial diffusion model were correlated with particle size measurements and interpreted mechanistically.

Results and discussion

Fast desorption rate constants, D _e /r ², with D _e the effective diffusion coefficient and r the particle radius, ranged from 3.7 × 10^?3 to 1.1 × 10^?1 day^?1 (PHE) and 6 × 10^?6 to 1.9 × 10^?4 day^?1 (CHR), respectively, and increased with the intensity of mixing. The D _e /r ² values would correspond to D _e ranges of 1.8 × 10^?14–1.2 × 10^?16 m² × day^?1 and 1.8 × 10^?12–3.7 × 10^?15 m² × day^?1, assuming fast desorption from the measured smallest particle size (9 μm) classes at 200 and 600 rpm, respectively.

Conclusions

Desorption of PAHs was significantly accelerated by a reduction of particle aggregate size caused by shear forces that were induced by mixing. The effective intra-particle diffusion coefficients, D _e , were larger at higher mixing rates.

     

Soil Ammonium Diffusion Constraints Contribute to Large Differences in Nitrogen Supply to Rice in the Southern United States

This study was to determine if diffusion of soil ammonium may explain why many sandy soils have greater nitrogen (N)–supplying capacity to rice than clay soils. A laboratory procedure using transient-state methods measured the linear movement of soil ammonium (NH₄) in tubes packed with five field soils under aerobic conditions. Ammonium diffusion was measured by sectioning tubes after 48 h of equilibration and then measuring NH₄ by steam distillation. Effective diffusion coefficients, D_e, and NH₄ diffusion distance, d, per day ranged from D_e = 4.6 × 10^?5 cm² d^?1 and 1.5 cm d^?1 for Katy sandy loam to D_e = 2.9 × 10^?7 cm² d^?1 and 0.11 cm d^?1 for League clay. Ammonium diffusion distance d was strongly related to soil clay content and hence was predicted by d = Y × {[100/(% clay)] ? 1}, where Y is set to 0.1. Predicted d and measured d were highly related (R² = 0.99).     

RESPONSE OF LISIANTHUS TO IRRIGATION WITH SALINE WATER: ION RELATIONS

Eustoma grandiflorum (Raf.) Shinn. (lisianthus) is a moderately salt tolerant species that can be produced commercially under irrigation with saline wastewaters prevalent in two salt-affected areas of California. The objective of the present studies was to determine the effect of irrigation with saline waters of two different compositions on the ion accumulation and ion relations of lisianthus ‘Pure White’ and ‘Echo Blue’. The ionic composition of irrigation waters simulated the compositions typical of i) seawater dilutions (SWD) and ii) concentrations of Colorado River water (CCRW). Electrical conductivities (EC) of SWD and CCRW were between 2 and 12 dS · m^?1. Plants irrigated with CCRW were higher in Ca²⁺ compared to plants irrigated with SWD water. Calcium was also higher in ‘Pure White’ than in ‘Echo Blue’. Increasing EC of irrigation water caused a significant decrease in shoot and leaf Ca²⁺ concentration in ‘Echo Blue’, but had no effect on Ca²⁺ content of ‘Pure White’ shoots and leaves. Magnesium concentration in ‘Echo Blue’ was higher than in ‘Pure White’. Electrical conductivity did not significantly affect Mg²⁺ concentration of either cultivar, despite the increasingly higher external concentration. Potassium concentration of young and mature leaves of ‘Echo Blue’ increased as EC increased from 2 to 8 dS · m^?1, then decreased significantly once EC exceeded 8 dS · m^?1. Potassium concentration of ‘Pure White’ leaves decreased over the range of salinity treatments tested, suggesting that the reduced potassium ion (K⁺) activity at EC levels of 8 dS · m^?1, or less, that resulted in lower leaf?K⁺ in ‘Pure White’ did not cause a decrease in K⁺ uptake in ‘Echo Blue’. Increases in external Na⁺ caused a significant increase in Na⁺ in ‘Pure White’ leaves and these plants exhibited the best growth even when levels of Na⁺ were high enough to be considered detrimental for growth.     

Mobility and Availability of Copper in Agricultural Soils Irrigated from Water Treated with Copper Sulfate Algaecide

A mesocosm system was designed to study evaporation kinetics and transport of TCE in flowing surface water. The airtight unit, with a total internal volume of 52.01?×?10^?2 m³, was fabricated with glass and Teflon material, and was provided with 8.53 m long channel to simulate water flow in an open channel. The peristaltic pumps, connected to the inlet and the outlet of the mesocosm, provided a constant water flow through the channels. The experimental studies were conducted at two different velocities, 9.42?×?10^?3 and 4.71?×?10^–3 m/s, respectively. For both the velocities, a tracer (NaBr) test confirmed uniform water flow in the channels. The total length and the length between the sampling ports were found sufficient to record gradual decrease in TCE concentrations along the direction of the flow in the channels. The volatilization coefficient for TCE was found to be 0.49 and 1.07 h^?1 for the experiments conducted at lower and higher water velocities, respectively. The TCE evaporation half life (t 1/2) and the corresponding evaporation half distance (d 1/2) were 1.41 h and 23.98 m for lower velocity, and 0.65 h and 21.96 m for higher velocity, respectively.     

A field trial to evaluate the pollution potential to ground and surface waters from woodchip corrals for overwintering livestock outdoors

Outwintering beef cattle on woodchip corrals offers stock management, economic and welfare benefits when compared with overwintering in open fields or indoors. A trial was set up on a loamy sand over sand soil to evaluate the pollution risks from corrals and the effect of design features (size and depth of woodchips, stocking density, and feeding on or off the corral). Plastic‐lined drainage trenches at 9–10 m spacing under the woodchips allowed sampling of the leachate. Sampling of the soil to 3.6 m below the corral allowed evaluation of pollutant mitigation during vadose zone transport. Mean corral leachate pollutant concentrations were 443–1056 mg NH₄‐N L^?1, 372–1078 mg dissolved organic carbon (DOC) L^?1, 3–13 mg NO₃‐N L^?1, 8 × 10⁴–1.0 × 10⁶Escherichia coli 100 mL^?1 and 2.8 × 10²–1.4 × 10³ faecal enterococci 100 mL^?1. Little influence of design features could be observed. DOC, NH₄ and (in most cases) E. coli and faecal enterococci concentrations decreased 10²–10³ fold when compared with corral leachate during transport to 3.6 m but there were some cores where faecal enterococci concentrations remained high throughout the profile. Travel times of pollutants (39–113 days) were estimated assuming vertical percolation, piston displacement at field moisture content and no adsorption. This allowed decay/die‐off kinetics in the soil to be estimated (0.009–0.044 day^?1 for DOC, 0.014–0.045 day^?1 for E. coli and 0–0.022 day^?1 for faecal enterococci). The mean [NO₃‐N] in pore water from the soil cores (n = 3 per corral) ranged from 114 ± 52 to 404 ± 54 mg NO₃‐N L^?1, when compared with 59 ± 15 mg NO₃‐N L^?1 from a field overwintering area and 47 ± 40 mg NO₃‐N L^?1 under a permanent feeding area. However, modelling suggested that denitrification losses in the soil profile increased with stocking density so nitrate leaching losses per animal may be smaller under corrals than for other overwintering methods. Nitrous oxide, carbon dioxide and methane fluxes (measured on one occasion from one corral) were 5–110 g N ha^?1 day^?1, 3–23 kg C ha^?1 day^?1, and 5–340 g C ha^?1 day^?1 respectively. Ammonia content of air extracted from above the woodchips was 0.7–3.5 mg NH₄‐N m^?3.     

Simplified Fixed Bed Design Models for the Adsorption of Acid Dyes on Novel Pine Cone Derived Activated Carbon

A novel activated carbon has been prepared by the activation of ground pine cones using phosphoric acid activation, and the nitrogen Brunauer?CEmmett?CTeller surface area was 869 m² g^?1. Equilibrium isotherms were performed to assess the capacity of the activated carbon using two acidic dyes, namely Acid Blue 113 and Acid Black 1. The monolayer equilibrium isotherm capacities of Acid Blue 113 and Acid Black 1 were 286 and 458 mg dye/g C, respectively. These capacities are significantly higher than commercial carbons and other literature carbons. For the first time, these carbons were tested in fixed bed experimental systems and data analysed using the bed depth service time model (BDST) and the carbon usage rate (CUR) model. In the fixed bed studies, the key parameters for a 20-cm bed depth for the BDST model at 50% breakthrough capacity are (a) for Acid Black, the BDST capacity is 149 mg dye/g carbon and operating time is 1,530 min and (b) for Acid Blue, the breakthrough capacity is 9 mg of dye/g of carbon and operating time is 195 min. The fixed bed study indicates that the BDST design models can be applied satisfactorily, and the pine cone carbon has significant potential but a more mesoporous pine cone carbon is preferable for the larger Acid Black dye. The CUR design method was not successful.     

Field study on colloid transport using fluorescent microspheres

Understanding colloid movement through the vadose zone is important, because colloids may facilitate transport of some less mobile contaminants. Experimental evidence of colloid transport in the vadose zone, especially at the field scale, is rare. We developed and tested a method to detect and quantify local concentrations of fluorescent microspheres (MS) with a diameter of 1 μm in unsaturated soil based on fluorescent microscopy. The detection limit was 400 × 10⁶ MS kg^?1 field‐moist soil for an automated counting method, and 20 × 10³ MS kg^?1 for manual counting. To test the method in the field, we applied a 40‐mm pulse with an input concentration of 14.6 × 10⁹ MS litre^?1 on two plots during 6 hours, together with bromide (Br^?) and the food dye Brilliant Blue (BB). The concentrations of MS were determined on horizontal cross‐sections by a randomly distributed sampling scheme, either directly after application or 90 days after application and a rainfall of 100 mm. Mass recoveries for the MS of 85 and 65% were acceptable in view of the field conditions. Even after infiltration of particle‐free water, the largest MS concentrations were measured at the soil’s surface, which pointed at physical retention mechanisms. An additional selective sampling of hydrologically active preferential flow pathways, guided by the dye infiltration patterns, revealed that the MS were transported to similar depths as BB, that is 0.80 m directly after irrigation and 1.7 m after 90 days. This implies that also a small fraction of the particulate tracers was rapidly transported to larger depths, regardless of their physico‐chemical properties.     

Assessment of the potential for dredged material dispersal from dumping sites in the Gulf of Gdańsk

Purpose

Environment-friendly management of sites used for disposal of locally generated sedimentary material involves designation of an optimal dumping site location which will render the dredged material re-usable for beneficial purposes. The objective of this research was to determine whether wind, waves, and currents can induce transport of sediment from offshore dumping sites located at intermediate depths in the southern Baltic.

Materials and methods

The problem was addressed by exploring potential sediment transport from two sites located in the Gulf of Gdańsk at depths of about 20 m. A total of 29 combinations of hydrodynamic variables, representing the most extreme possible situations in the area, including eight theoretical uniform wind fields over the entire Baltic Sea from the W, NW, N, NE, E, SE, S, and SW sectors, the wind speed of 30 m s^?1, as well as 21 historical extreme storms, retrieved from the HIPOCAS project database, were used.

Results and discussion

The bottom velocities resulting from waves and currents at the dumping sites considered were computed using wave models (WAM, SWAN) and the M3D hydrodynamic model (based on the POM model). To estimate the velocities critical for bedload transport, formulae developed by Soulsby (1997) and Sawamoto and Yamashita (Proc Coastal Sediments 87:415–423, 1987) were used. The volumetric bedload transport was computed based on Meyer-Peter and Müller (1948). The model simulations demonstrated that, for the storm conditions analyzed, the current velocity in the area of the two dumping sites would be so low that it would practically not affect the magnitude of the bottom sediment transport. Thus, the resultant volume of bedload transported would be equal to that generated by the wave action. For the heaviest historical storm, the maximum transport is about 3?×?10^?5 m² s^?1.

Conclusions

Under conditions of theoretical storms, the bottom orbital velocities would be higher and the resultant sediment transport would reach almost 7?×?10^?5 m² s^?1 for northerly winds. However, this value is still very low compared with the volume of sediment being dumped. The findings of this study may prove useful in designation of future dumping sites.

     

Dynamics of Atmospheric Aerosol Number Size Distributions in the Eastern Mediterranean During the ��SUB-AERO�� Project

Measurements of number size distributions of submicron aerosols have been performed at the Eastern part of Mediterranean as part of an extensive measurement campaign to study photo-oxidants and aerosols (SUB-AERO Project). The measurements were made at the Finokalia station on the island of Crete (Greece) and onboard the research vessel ??Aegaeon??. Two campaigns were performed during July 2000 and January 2001 using two scanning mobility particle sizers. The particle distributions measured in the range between 7.8 < d _p < 327 nm during the summer measurements and between 7.5 < d _p < 316 nm during the winter measurements, where d _p is the mobility particle diameter. The concentration of ultrafine particles (7.5 < d _p < 30 nm) was higher during the winter period and varied mainly between 5 × 10¹ and 2 × 10³?cm^?3 with concentration peak values for this mode exceeding 1 × 10⁴?cm^?3. During the summer campaign, an average number concentration of 1 × 10²?cm^?3 at Finokalia and about 5 × 10¹?cm^?3 aboard the ??Aegaeon?? vessel was measured. An average concentration of 1 × 10³?cm^?3 was measured for the particles in the size range between 30 and 100 nm, whereas in the size range 100?C300 nm, the measured concentration ranged between 1 × 10² and 5 × 10³?cm^?3. Diurnal patterns in number concentrations were observed in connection with the transport of air masses and local sources. During the winter period, three nucleation events were observed in connection with the appearance of a particle mode at 20 nm.