On the validity of modeling concepts for (the simulation of) groundwater flow in lowland peat areas – case study at the Zegveld experimental field

The groundwater flow models currently used in the western part of The Netherlands and in other similar peaty areas are thought to be a too simplified representation of the hydrological reality. One of the reasons is that due to the schematization of the subsoil, its heterogeneity cannot be represented adequately. Moreover, the applicability of Darcy's law in these types of soils has been questioned, but this law forms the basis of most groundwater flow models. With the purpose of assessing the typical heterogeneity of the subsoil and to verify the applicability of Darcy's law fieldwork was completed at a research site in the western part of The Netherlands. The assessments were carried for the so called Complex Confining Layer (CCL), which is the Holocene peaty to clayey layer overlying Pleistocene sandy deposits. Borehole drilling through the CCL with a hand auger was completed and revealed the typical heterogeneous character of this layer showing a dominance of muddy, humified peat which is alternated with fresher peat and clay. Slug tests were carried out to study the applicability of Darcy's law given that previous studies suggested the non validity for humified peat soils given by a variable hydraulic conductivity K with the hydraulic gradient. For higher humification degrees, the experiments indeed suggested a variable K, but this seems to be the result of the inappropriate use of steady-state formulae for transient experiments in peaty environments. The muddy peat sampled has a rather plastic nature, and the high compressibility of this material leads to transient behavior. However, using transient formulae, the slug tests conducted for different initial hydraulic heads showed that there was hardly any evidence of a variation of the hydraulic conductivity with the hydraulic gradient. Therefore, Darcy's law can be used for peat soils. The heterogeneity of the subsoil and the apparent applicability of Darcy's law were taking into account for the detailed heterogeneous model that was prepared for the research site. A MODFLOW model consisting of 13 layers in which 4 layers represent the heterogeneous CCL was set up for an average year assuming steady state conditions and for the winter of 2009 to 2010 adopting transient conditions. The transient model was then extended for a whole hydrological year and for an eight year period with the objective of visualizing the flowpaths through the CCL. The results from these models were compared with a 10 layer model whereby the CCL is represented by a single layer assuming homogeneity. From the comparison of the two model types the conclusion could be drawn that a single layer schematization of the CCL produces flowpath patterns which are not the same but still quite similar to a 4 layer representation of the CCL. However, the single layer schematization results in a considerable underestimation of the flow velocity, and subsequently a longer travel time, through the CCL. Therefore, a single layer model of the CCL seems quite appropriate to represent the flow behavior of the shallow groundwater system, but would be inappropriate for transport modeling through the CCL.

Physical properties of the mor layer in a Scots pine stand I. Hydraulic conductivity

Hydraulic conductivity in the mor layer of a Scots pine (Pinus sylvestris L.) stand was measured in undisturbed samples using the constant-head permeameter and instantaneous-profile method. Saturated hydraulic conductivity (Ks) averaged 2.9 × 102 m d−1. With a decrease in matric potential (ψ) from −4 kPa to −70 kPa the unsaturated hydraulic conductivity (K(ψ)) decreased from 3.1 × 10−3 to 1.1 × 10−8 m d−1. Ks and K(ψ) were similar to those reported in the literature for low-humified peat. The variation in hydraulic conductivity within a stand of Scots pine at a given matric potential was large, ranging from one to two orders of magnitude. Key words: F horizon, humus, hydraulic properties of soil

Ecological tolerance and niche structure of Sphagnum along a pollution gradient near Sudbury, Ontario, Canada

Accumulations of Cu and Ni were measured in four Sphagnum species occupying overlapping niches at varying distances from the smelter at Falconbridge, Ont. A distinct relationship existed between the metal content of Sphagnum russowii and the reciprocal of the distance from the pollution source. Accumulations of Cu and Ni in the partially humidified peat subtending the living Sphagnum were significantly higher than the concentrations retained in the moss plants, particularly on sites having high metal loadings. Concentrations of Cu and Ni were not significantly different between species occupying overlapping height and pH zonations. There existed a significant relationship between metal accumulations in the capitula of Sphagnum russowii, Sphagnum magellanicum, and Sphagnum riparium and the partially humified peat below the living moss.

Metal accumulation by bryophytes in some zinc-rich blanket bogs, Selwyn Mountains, Yukon Territory

Collections of Pohlia wahlenbergii, Leptobryum pyriforme, Philonotis fontana, and Drepanocladus aduncus were made at the XY Zn–Pb sulphide deposit, Howard's Pass, Y.T., Canada. Brilliant lime green growths of mosses flourish in hillside blanket bogs fed by Zn-, Pb-, and Cd-rich spring waters derived from faults which crosscut sulphide mineralizations. All species showed elevated levels of accumulation of these metals, but the concentration of Zn in the upper thalli was higher than Pb or Cd. However, the relative enrichments favour accumulation of Pb rather than Cd and Zn. The bryophyte D. aduncus is unusual in that it gathers cadmium in preference to Pb and Zn, according to calculated relative enrichment factors. The bog materials which provide the substrate for moss blankets are unusual in composition; more than 60% of the material comprises secondary Zn minerals, viz., zincic calcite ((Zn,Ca)CO3), smithsonite (ZnCO3), and wurtzite (ZnS), and the remainder is humified peat derived from buried moss strata. The end product of burial and replacement of decaying moss layers is the hydrated zinc silicate, hemimorphite (Zn4Si2O7(OH)2∙H2O), which results from the cell by cell replacement of moss fibre with complete preservation of the rhizoid structure.

A Site at Stump Cross, near Grassington, Yorkshire, and the Age of the Pennine Microlithic Industry

The site described in this paper lies on the Yorkshire Pennines, slightly over 1,200 feet O.D., half a mile north-west of Stump Cross Cavern and five miles east of Grassington (Nat. Grid 082640). The solid rock there is an eastward extension of the Great Scar Limestone, pitted by numerous swallow holes and clothed by a thin and intermittent mantle of clayey glacial drift. Only a hundred yards to the north and half a mile to the south-east of the site the Millstone Grit replaces the limestone at the surface. In the vicinity of the site the vegetation is dominated by Calluna vulgaris and Eriophorum vaginatum growing over a podsol or a shallow, highly humified, peat.

GROWTH AND SURVIVAL OF BACTERIA IN PEAT: II. PEAT PELLETS

Pellets prepared from spongy, unhumified peat, were found to be well suited to the growth of the test organisms and were superior to pellets made from compressed, well humified peat. Sterilization had the effect of lowering somewhat the absorptive capacity of the spongy pellets and increased the buffering capacity. Neutralization was essential for sterilized pellets in maintaining viable organisms, though it was much less important with unsterilized peat. In contrast to powdered, humified peat, pellets of spongy peat showed to best advantage when allowed to become air-dry immediately following inoculation. In pellets subjected to immediate desiccation, the test organisms attained a much greater development, and were maintained in greater numbers than in peat kept moist or when desiccation was delayed.