Geochemical reactivity of subsurface sediments as potential buffer to anthropogenic inputs: a strategy for regional characterization in the Netherlands

Abstract

Purpose Sedimentary aquifers are prone to anthropogenic disturbance. Measures aimed at mitigation or adaptation require sound information on the reactivity of soil/sediments towards the infiltrating water, as this determines the chemical quality of the groundwater and receiving surface waters. Here, we address the issues of relevant sediment properties, adequate analytical methods, borehole location selection, detail of stratification, and required sample size, to develop a protocol for efficient characterization of subsurface reactivity on a regional scale. Materials and methods The sequence of geological formations in the Dutch part of the North Sea Basin is documented in the form of systematic descriptions of some 450,000 borings. The basic data are stored in a database that also includes a limited amount of geochemical data collected for specific research projects. Based on the borehole descriptions, a Digital Geological Model of the Netherlands (DGM) has recently been completed. We combined the results of a statistical analysis of the existing geochemical data with theoretical and practical considerations, to assess the degree of variability of subsurface reactivity, the relevance of different DGM-based stratifications, and the efficiency and possible redundancy of analytical parameters. Results and discussion We present two protocols for the quantitative characterization of the reactive properties of the soil and subsurface sediments of the Netherlands, down to a depth of about 30 m below surface level. As numerous strategies are already available for soil surveying, the facies-based protocol for boring and sampling is aimed at subsoil sediments. Stratification is a combination of regional, lithological, and lithostratigraphical classifications. Selection of borehole locations and sampling depths is first based on the a priori information. Given the results of the first round, additional boring, sampling and analysis are performed when necessary. The analytical protocol also applies to soil surveys. It deploys limited means to obtain the most relevant information on subsurface reactivity in view of the priority environmental issues identified. Conclusions With the progress of technologies for aquifer architecture characterization and routine chemical analysis, assessment of subsurface reactivity on a regional scale has now become feasible. Lithological stratification is essential, but regional and lithostratigraphical variability cannot be ignored. With adequate stratification, a sample size of 45 per stratum was found sufficient in most instances. The key analytes chosen appear to be statistically independent; hence, a further reduction in analytical techniques would result in serious loss of information.

Groundwater salinity variation in Upazila Assasuni (southwestern Bangladesh), as steered by surface clay layer thickness, relative elevation and present-day land use

“…The large difference in lithology indicates that the location of the channel was stable throughout the progradation. Possibly, mangrove vegetation in the floodplains prevented the channels from meandering due its ability to capture sediments up to the mean high water level (Furukawa and Wolanski, 1996;Auerbach et al, 2015) and to protect land against erosion (Van Santen et al, 2007;Kirwan and Megonigal, 2013). This difference in lithology steered the influence of surface water on groundwater during the rest of the Holocene.…”

The mineralogy of suspended matter, fresh and Cenozoic sediments in the fluvio-deltaic Rhine–Meuse–Scheldt–Ems area, the Netherlands: An overview and review

“…Pyrite content and pyrite-bound Fe are often calculated from the total S content for clastic sediments, where total S content is assumed to represent pyrite (Van Gaans et al, 2011;Griffioen et al, 2012):…”

“…The mixture of minerals together with organic matter influences the pore water composition, the soil's pedological evolution and fertility, the fate of pollutants in the subsurface, the porosity and permeability as geohydrological properties and the geomechanical strength of the subsurface. More specifically, mineralogical composition plays an important role in sediment reactivity (Van Gaans et al, 2011), greatly influencing surface complexation and ion exchange of cations and anions, sorption of organic substances, denitrification and other redox reactions, as well as the weathering processes. Insight into this reactivity is needed for environmental management issues such as drainage-induced oxidation, aquifer storage and recovery, natural attenuation of pollutants, leaching of nutrients from farmland, reactive transport and secondary mobilisation of trace metals, and transfer of pollutants or nutrients from aquatic sediments to the water column or vice versa.…”

Impacts of Shallow Geothermal Energy on Groundwater Quality

“…It would be good to derive a more generic relationship between the geochemical reactivity of the Dutch geological formations (Gaans et al 2011;Griffioen et al 2012) and the response of these to temperature increases. A crucial next step is to validate the results of this study in field SGE systems (operating at 25°C or higher) in the Sterksel formation and to investigate the potential arsenic mobilization in other geological formations.…”