J. Griffioen

Global trends and uncertainties in terrestrial denitrification and N2O emissions

Soil nitrogen (N) budgets are used in a global, distributed flow-path model with 0.5° × 0.5° resolution, representing denitrification and N2O emissions from soils, groundwater and riparian zones for the period 1900–2000 and scenarios for the period 2000–2050 based on the Millennium Ecosystem Assessment. Total agricultural and natural N inputs from N fertilizers, animal manure, biological N2 fixation and atmospheric N deposition increased from 155 to 345 Tg N yr−1 (Tg = teragram; 1 Tg = 1012 g) between 1900 and 2000. Depending on the scenario, inputs are estimated to further increase to 408–510 Tg N yr−1 by 2050. In the period 1900–2000, the soil N budget surplus (inputs minus withdrawal by plants) increased from 118 to 202 Tg yr−1, and this may remain stable or further increase to 275 Tg yr−1 by 2050, depending on the scenario. N2 production from denitrification increased from 52 to 96 Tg yr−1 between 1900 and 2000, and N2O–N emissions from 10 to 12 Tg N yr−1. The scenarios foresee a further increase to 142 Tg N2–N and 16 Tg N2O–N yr−1 by 2050. Our results indicate that riparian buffer zones are an important source of N2O contributing an estimated 0.9 Tg N2O–N yr−1 in 2000. Soils are key sites for denitrification and are much more important than groundwater and riparian zones in controlling the N flow to rivers and the oceans.

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.

Geochemical calculations and observations on salt water intrusions. II. Validation of a geochemical model with laboratory experiments

Column experiments with aquifer sediments have been performed. A description is given of procedures and equipment which can maintain the anaerobic status of the sediments from sampling in the field to subsequent experimentation in the laboratory. From two sediments native pore solutions were displaced with SrCl2 solutions; another was percolated alternately with groundwater and once diluted seawater. The chromatographic pattern which develops when exchangeable cations are eluted, was modelled with the earlier presented geochemical (multicomponent) transport model. Proper description of the SrCl2-elution required reformulation of the cation exchange reaction for one sediment; the other sediment showed proton buffering and calcite dissolution with slow kinetics. These elutions could be modelled with constant exchange coefficients, but during fresh/saltwater displacements the selectivity for Ca/Mg exchange was variable.

Potassium adsorption ratios as an indicator for the fate of agricultural potassium in groundwater

Fertilization of agricultural land in groundwater infiltration areas often causes deterioration of groundwater quality. In addition to nitrogen and phosphorous, potassium deserves attention. The fate of potassium in the subsurface is controlled mainly by cation-exchange. Use of the Potassium Adsorption Ratio (PAR), analogous to the Sodium Adsorption Ratio (SAR) allows one to distinguish between leaching of agricultural potassium to groundwater and desorption of potassium due to increased hardness associated with increased manure spreading on a calcareous soil. Two regional field studies in The Netherlands indicate that groundwater below infiltration areas with agricultural land use, has increased PAR values compared to pristine groundwater in seepage areas and groundwater below infiltration areas with forest. Downward transport of agricultural potassium is retarded compared to conservative chloride due to cation-exchange. In one field study silicate weathering is found to be a potential source for K in pristine groundwater when the residence time is long and easily weatherable silicates, such as glauconite, are present.

Bio)geochemical reactions in aquifer material from a thermal energy storage site

Abstract The mobilization of organic compounds and the release of CO2 was studied in aquifer material from a site chosen for thermal energy storage (ETS). These processes have been measured aerobically and anaerobically within a temperature range of 4–95°C in sediment samples consisting of either quartz-rich coarse sand or peaty clay. At temperatures above 45°C organic carbon compounds, including fulvic acids, were mobilized from both sediments resulting in an increased chemical oxygen demand of the water phase. Complexation of calcium and magnesium by fulvic acids resulted in the supersaturation of the water phase with regard to calcite and dolomite and thus prevented the precipitation of these carbonates. The highest rates of CO2 release were observed during the first 4 days. Aerobically, the maximum velocity for CO2 formation varied between 35 and 800 (sand) or 15 and 150 (peaty clay) μmol CO2 per gram volatile solids per day. Anaerobically, similar rates were observed, namely 25–500 (sand) and 10–110 (peaty clay) μmol CO2 per gram volatile solids. At temperatures above 55°C, CO2 was produced purely chemically.

Uptake of phosphate by iron hydroxides during seepage in relation to development of groundwater composition in coastal areas

Seepage of o-PO 4 -rich groundwater may give rise to surface water eutrophication. Hydrogeochemical modeling based on groundwater quality data from the coastal lowland of The Netherlands was performed to relate in a general way the fixation of PO 4 at the oxic/anodic interface in the surface water sediment to the development of the composition of anoxic groundwater that seeps through these sediments. Solid-solution aqueous-solution modeling with the end members ferrihydrite and strengite shows that pH and the aqueous Fe(II):PO 4 ratio determine the uptake of PO 4 in iron hydroxides following the oxidation of Fe(II) during seepage

Nature and extent of carbonate precipitation during aquifer thermal energy storage

Abstract Heating of calcite-saturated groundwater induces no precipitation to thermodynamic equilibrium with respect to end-member Ca-carbonates. Column experiments, using native groundwater and aquifer sediment, were performed to study the controlling factors in the kinetics of carbonate precipitation for a natural system by injection of groundwater in a sediment core at 90°C. The temperature increase induced a fast precipitation of a Ca Fe-carbonate, containing Mn and phosphate, and a Ca Mg Fe-carbonate, containing Mn, within at most 10 h. Both precipitates varied in composition and were partly amorphic, partly crystalline. Prolonged precipitation, after almost all Fe[II] had been removed, was extremely slow despite a twelve-fold supersaturation with respect to end-member calcite. The resulting supersaturation cannot be explained by either calcite precipitation kinetics, Mg-inhibition, Mg-calcite solubility control, or Ca-organic acid complexing, because these factors may explain a two-fold supersaturation at most. The maintenance of supersaturation is attributed to inhibition of precipitation by phosphate and/or organic acids. The influence of secondary reactions, as cation-exchange and silicate weathering, is of minor importance on the carbonate chemistry. Cation-exchange was observed in the initial stages of heated water injection. Potassium, NH 4 and Fe become desorbed upon temperature increase. Related Ca-adsorption is insufficient to avoid Ca-carbonate precipitation. Weathering of silicates occurs continuously and leads to the release of Na, Ca and Mg.

3D geology in a 2D country : Perspectives for geological surveying in the Netherlands

Over the last ten to twenty years, geological surveys all over the world have been entangled in a process of digitisation. Their paper archives, built over many decades, have largely been replaced by electronic databases. The systematic production of geological map sheets is being replaced by 3D subsurface modelling, the results of which are distributed electronically. In the Netherlands, this transition is both being accelerated and concluded by a new law that will govern management and utilisation of subsurface information. Under this law, the Geological Survey of the Netherlands has been commissioned to build a key register for the subsurface: a single national database for subsurface data and information, which Dutch government bodies are obliged to use when making policies or decisions that pertain to, or can be affected by the subsurface. This requires the Survey to rethink and redesign a substantial part of its operation: from data acquisition and interpretation to delivery. It has also helped shape our view on geological surveying in the future. The key register, which is expected to start becoming operational in 2015, will contain vast quantities of subsurface data, as well as their interpretation into 3D models. The obligatory consultation of the register will raise user expectations of the reliability of all information it contains, and requires a strong focus on confidence issues. Building the necessary systems and meeting quality requirements is our biggest challenge in the upcoming years. The next step change will be towards building 4D models, which represent not only geological conditions in space, but also processes in time such as subsidence, anthropogenic effects, and those associated with global change.

Geogenic and agricultural controls on the geochemical composition of European agricultural soils

PurposeConcern about the environmental impact of agriculture caused by intensification is growing as large amounts of nutrients and contaminants are introduced into the environment. The aim of this paper is to identify the geogenic and agricultural controls on the elemental composition of European, grazing and agricultural soils.Materials and methodsRobust factor analysis was applied to data series for Al, B, Ca, Cd, Co, Cu, Fe, K, Mg, Mn, Na, Ni, P, S, Se, Sr, U, Zn (ICP-MS) and SiO2, K2O, Na2O, Fe2O3, Al2O3 (XRF) based on the European GEMAS dataset. In addition, the following general soil properties were included: clay content, pH, chemical index of alteration (CIA), loss on ignition (LOI), cation exchange capacity (CEC), total organic carbon (TOC) and total carbon and total sulfur. Furthermore, this dataset was coupled to a dataset containing information of historic P2O5 fertilization across Europe. Also, a mass balance was carried out for Cd, Cu and Zn to determine if concentrations of these elements found in the soils have their origin in historic P2O5 fertilization.Results and discussionSeven geogenic factors and one agricultural factor were found of which four prominent ones (all geogenic): chemical weathering, reactive iron-aluminum oxide minerals, clay minerals and carbonate minerals. Results for grazing and agricultural soils were near identical, which further proofs the prominence of geogenic controls on the elemental composition. When the cumulative amount of P2O5 fertilization was considered, no extra agriculture-related factors became visible. The mass balance confirms these observations.ConclusionsOverall, the geological controls are more important for the soil chemistry in agricultural and grazing land soils than the anthropogenic controls.

Geochemistry and flooding as determining factors of plant species composition in Dutch winter-flooded riverine grasslands

Dutch water policy aims for more frequent, controlled flooding of river valley floodplains to avoid unwanted flooding elsewhere; in anticipation of increased flooding risks resulting from climate changes. Controlled flooding usually takes place in winter in parts of the valleys which had not been subject to flooding in the last decades. It may thus affect existing nature with its conservation values. The goal of this study was to clarify the geochemical and hydrological factors determining plant species composition of winter-flooded river valley grasslands. A correlative study was carried out in 43 sites in 13 Dutch river valley floodplains, with measurements of flooding regime, vegetation composition, soil nutrients and soil pH status. With the use of canonical correspondence analysis (CCA) the plant species composition was investigated in relation to the geochemical variables and the winter winter-flooding regime. We found that the distributions of target species and non-target species were clearly correlated with geochemical characteristics and flooding regime. Clustering of sites within the CCA plots has led us to distinguish between four types of winter flooding in our areas: floodplains with (a) accumulating rain water, (b) low groundwater levels flooded with river water, (c) discharging groundwater and (d) high groundwater levels flooded with river water. Our major conclusions are (1) the winter groundwater level of winter-flooded grasslands was important for evaluating the effects of winter flooding on the geochemistry and plant species composition, and (2) winter winter-flooding effects were largely determined by the nature of the flooding. A high frequency of flooding particularly favoured a small set of common plant species. In areas with groundwater seepage, winter flooding may provide geochemical conditions suitable for diverse vegetation types with rare species. Rainwater flooded sites appeared less suitable for most target species.