Extraction of soil solution by drainage centrifugation—effects of centrifugal force and time of centrifugation on soil moisture recovery and solute concentration in soil moisture of loess subsoils

The solute concentration in the subsoil beneath the root zone is an important parameter for leaching assessment. Drainage centrifugation is considered a simple and straightforward method of determining soil solution chemistry. Although several studies have been carried out to determine whether this method is robust, hardly any results are available for loess subsoils. To study the effect of centrifugation conditions on soil moisture recovery and solute concentration, we sampled the subsoil (1.5–3.0 m depth) at commercial farms in the loess region of the Netherlands. The effect of time (20, 35, 60, 120 and 240 min) on recovery was studied at two levels of the relative centrifugal force (733 and 6597g). The effect of force on recovery was studied by centrifugation for 35 min at 117, 264, 733, 2932, 6597 and 14,191g. All soil moisture samples were chemically analysed. This study shows that drainage centrifugation offers a robust, reproducible and standardised way for determining solute concentrations in mobile soil moisture in silt loam subsoils. The centrifugal force, rather than centrifugation time, has a major effect on recovery. The maximum recovery for silt loams at field capacity is about 40%. Concentrations of most solutes are fairly constant with an increasing recovery, as most solutes, including nitrate, did not show a change in concentration with an increasing recovery.     

Responses of wintering geese to the designation of goose foraging areas in The Netherlands

The Netherlands is important for wintering migratory herbivorous geese, numbers of which have rapidly increased, leading to conflict with agriculture. In 2005/2006, a new goose management policy aimed to limit compensation payments to farmers by concentrating foraging geese in 80 000 ha of designated ‘go’ areas—where farmers received payment to accommodate them—and scaring geese from ‘no go’ areas elsewhere. Monthly national counts of four abundant goose species during 10 years prior to the new policy and in 8 years following implementation found that 57% of all goose days were spent within ‘go’ areas under the new management, the same as prior to implementation. Such lack of response suggests no predicted learning effects, perhaps because of (i) increases in abundance outside of ‘go’ areas, (ii) irregularly shaped boundaries and enclaves of ‘no go’ farmland within ‘go’ areas and/or (iii) insufficient differences in disturbance levels within and outside designated areas.     

The Fate and Behavior of Mercury in Coal-Fired Power Plants

Abstract

For the past 22 years in the Netherlands, the behavior of Hg in coal-fired power plants has been studied extensively. Coal from all over the world is fired in Dutch power stations. First, the Hg concentrations in these coals were measured. Second, the fate of the Hg during combustion was established by performing mass balance studies. On average, 43 ± 30% of the Hg was present in the flue gases downstream of the electrostatic precipitator (ESP; dust collector). In individual cases, this figure can vary between 1 and 100%. Important parameters are the Cl content of the fuel and the flue gas temperature in the ESP. On average, 54 ± 24% of the gaseous Hg was removed in the wet flue-gas desulfurization (FGD) systems, which are present at all Dutch coal-power stations. In individual cases, this removal can vary between 8% (outlier) and 72%.

On average, the fate of Hg entering the power station in the coal was as follows: <1% in the bottom ash, 49% in the pulverized fuel ash (ash collected in the ESP), 16.6% in the FGD gypsum, 9% in the sludge of the wastewater treatment plant, 0.04% in the effluent of the wastewater treatment plant, 0.07% in fly dust (leaving the stack), and 25% as gaseous Hg in the flue gases and emitted into the air. The distribution of Hg over the streams leaving the FGD depends strongly on the installation. On average, 75% of the Hg was removed, and the final concentration of Hg in the emitted flue gases of the Dutch power stations was only ~3 μg/m_STP ³ at 6% O₂. During co-combustion with biomass, the removal of Hg was similar to that during 100% coal firing.

Speciation of Hg is a very important factor. An oxidized form (HgCl₂) favors a high degree of removal. The conversion from Hg⁰ to HgCl₂ is positively correlated with the Cl content of the fuel. A catalytic DENOX (SCR) favors the formation of oxidized Hg, and, in combination with a wet FGD, the total removal can be as high as 90%.     

The Influence of Floodplain Vegetation Succession on Hydraulic Roughness: Is Ecosystem Rehabilitation in Dutch Embanked Floodplains Compatible with Flood Safety Standards?

Here, we show for one of the Dutch Rhine River branches that large-scale riverine ecosystem rehabilitation and related vegetation succession may lead to up to 0.6 m higher river flood levels, because of increased hydraulic roughness. We hydraulically modeled future succession stages of embanked floodplain vegetation, following from present ecosystem rehabilitation plans for the 124-km-long river IJssel, and found flood levels exceeding the safety levels (related to dike heights). Our models take into account river engineering measures that are presently carried out, aimed at enhancing the river discharge capacity in order to meet required safety standards. Our study shows that there is a pressing need for integrated hydraulic-ecological evaluation of river engineering measures and ecosystem rehabilitation plans in the Rhine embanked floodplains. An important conclusion also is that hydraulic evaluation of planned vegetation goals only is inadequate, because flow resistance of preceding succession stages may be higher.     

Regulating Functional Foods in the European Union: Informed Choice versus Consumer Protection?

Due to the rise of functional foods,the distinction between foods and medicines hasbecome increasingly blurred. A new EUregulation covering health claims and otherclaims on food and drink products is on thedocks. A basic motive of legal regulation oflabeling and advertising is to inform andprotect the consumer. Promotion of informedchoice and consumer protection may, however, beconflicting objectives. A further problemsprings from the fact that choice, likeconsent, is a propositional attitude andtherefore opaque. Thus it is extremelydifficult for regulators to fasten onparticular formulations of claims. Despite theprofessed respect for the autonomy of theconsumer, paternalism is never far away andeasily enters in various guises.     

Reactive transport modelling of biogeochemical processes and carbon isotope geochemistry inside a landfill leachate plume

The biogeochemical processes governing leachate attenuation inside a landfill leachate plume (Banisveld, the Netherlands) were revealed and quantified using the 1D reactive transport model PHREEQC-2. Biodegradation of dissolved organic carbon (DOC) was simulated assuming first-order oxidation of two DOC fractions with different reactivity, and was coupled to reductive dissolution of iron oxide. The following secondary geochemical processes were required in the model to match observations: kinetic precipitation of calcite and siderite, cation exchange, proton buffering and degassing. Rate constants for DOC oxidation and carbonate mineral precipitation were determined, and other model parameters were optimized using the nonlinear optimization program PEST by means of matching hydrochemical observations closely (pH, DIC, DOC, Na, K, Ca, Mg, NH4, Fe(II), SO4, Cl, CH4, saturation index of calcite and siderite). The modelling demonstrated the relevance and impact of various secondary geochemical processes on leachate plume evolution. Concomitant precipitation of siderite masked the act of iron reduction. Cation exchange resulted in release of Fe(II) from the pristine anaerobic aquifer to the leachate. Degassing, triggered by elevated CO2 pressures caused by carbonate precipitation and proton buffering at the front of the plume, explained the observed downstream decrease in methane concentration. Simulation of the carbon isotope geochemistry independently supported the proposed reaction network.     

Biogeochemistry and isotope geochemistry of a landfill leachate plume

The biogeochemical processes were identified which improved the leachate composition in the flow direction of a landfill leachate plume (Banisveld, The Netherlands). Groundwater observation wells were placed at specific locations after delineating the leachate plume using geophysical tests to map subsurface conductivity. Redox processes were determined using the distribution of solid and soluble redox species, hydrogen concentrations, concentration of dissolved gases (N(2), Ar, and CH(4)), and stable isotopes (delta15N-NO(3), delta34S-SO(4), delta13C-CH(4), delta2H-CH(4), and delta13C of dissolved organic and inorganic carbon (DOC and DIC, respectively)). The combined application of these techniques improved the redox interpretation considerably. Dissolved organic carbon (DOC) decreased downstream in association with increasing delta13C-DOC values confirming the occurrence of degradation. Degradation of DOC was coupled to iron reduction inside the plume, while denitrification could be an important redox process at the top fringe of the plume. Stable carbon and hydrogen isotope signatures of methane indicated that methane was formed inside the landfill and not in the plume. Total gas pressure exceeded hydrostatic pressure in the plume, and methane seems subject to degassing. Quantitative proof for DOC degradation under iron-reducing conditions could only be obtained if the geochemical processes cation exchange and precipitation of carbonate minerals (siderite and calcite) were considered and incorporated in an inverse geochemical model of the plume. Simulation of delta13C-DIC confirmed that precipitation of carbonate minerals happened.