A high‐resolution pollen and geochemical analysis of late Holocene human impact and vegetation history in southern Cumbria,England

The historic era, which in Cumbria begins with the Roman invasion of AD 71, is a frequently neglected period in palaeoecological research, but its study can bring benefits in improving knowledge of landscape history and in understanding the significance and limitations of palaeoecological records. Pollen and geochemical data are presented for late Holocene records from Deer Dyke and Hulleter Mosses in southern Cumbria. The records show initially low levels of anthropogenic impact, followed by a phase of forest clearance and mixed agriculture from the 7th to 11th centuries AD. The timing of these clearances suggests that they were initially Anglo‐Saxon in origin, rather than Norse. Further clearances in the 16th century AD are interpreted as a response to monastic dissolution and late Tudor population pressures; the landscapes reached their contemporary form following extensive clearances in the 17th century AD. Silicon and titanium concentrations at Deer Dyke Moss were used to reconstruct past levels of atmospheric dust loading, which is broadly related to soil erosion. Geochemical influx was found to peak during periods of landscape transition rather than from established land use. This relationship with pollen data is thought to reflect the predominantly low levels of anthropogenic impact in the region, which changes as substantial woodland clearances during the 16th century AD and continuous land use pressure since then have greatly increased the supply of airborne dust. Copyright © 2008 John Wiley & Sons, Ltd.     

The Humphrey Head Borehole: Evidence for Carboniferous vulcanicity and Permian dolomitization in the southern Lake District

In south Cumbria, Permo-Triassic breccias and conglomerates (‘brockram’) are exposed only at Rougholme Point on the Cartmel peninsula. In 1973 the Institute of Geological Sciences Humphrey Head borehole penetrated 257 m of brockram before entering probable Upper Carboniferous sediments. The brockram consists of pebbles of carbonate, chert and basalt in a matrix of haematite-stained quartz sand. Carbonate and chert fragments were derived from the upper part of the Carboniferous Limestone sequence exposed today nearby. Basalt clasts were derived from lavas, which appear to have cooled in a subaqueous environment, at least in part. They were locally derived and are the only certain evidence for Carboniferous volcanic activity in south Cumbria. As volcanic fragments increase in abundance towards the base of the borehole they must have been derived from the top of the succession being eroded and are probably of Brigantian age. Carbonate fragments were dolomitized soon after incorporation in the brockram, probably by saline fluids derived from the evaporative Zechstein Sea. The dolomitization was incomplete, leaving remnant limestone cores to clasts which were subsequently dissolved. The resultant vugs were infilled by dolomite, calcite and gypsum cements, which have been partially weathered from outcropping brockram, leaving hollow pebbles.     

Late Holocene vegetational history,human impact and pollen representativity variations in northern Cumbria,England

The comparison of pollen diagrams and their inferred vegetational histories are an important component of palaeoecological research. Radiocarbon-dated pollen profiles from three cores taken from two adjacent mires located in northern Cumbria, Bolton Fell Moss and Walton Moss, have been used to reconstruct the Late Holocene vegetation history between the Bronze Age and the present day. The profiles have been interpreted in the light of available archaeological and historical records and, although the pollen records are broadly similar, there are some notable differences between them, particularly during Iron Age and medieval times. Dissimilarities between the diagrams are explored numerically, and the statistical and palynological results are discussed in relation to pollen representativity. The results suggest that it may be advantageous to construct more than one pollen diagram from a mire, or even adjacent mires, as extra-local pollen may be a more important part of the pollen rain than previously envisaged. © 1998 John Wiley & Sons, Ltd.     

The Relationships between Effective Porosity,Uniaxial Compressive Strength and Sonic Velocity of Intact Borrowdale Volcanic Group Core Samples from Sellafield

The effective porosity, saturated sonic velocity and saturated uniaxial compressive strength were determined on a large number of Borrowdale Volcanic Group volcaniclastic core samples from three boreholes at Sellafield, Cumbria. The work formed part of the UK Nirex Limited site investigation into whether the Sellafield area could be suitable as a repository for intermediate and low level radioactive waste. Most of the intact samples were of low to very low effective porosity, had a high sonic velocity and were very strong to extremely strong. However, a proportion of values deviated significantly from this. Bivariate analysis showed a negative relationship exists between sonic velocity and effective porosity. The cross plots of these two parameters with uniaxial compressive strength showed a wide range of strength values for samples of low effective porosity and high sonic velocity. Six failure types were identified during the uniaxial compressive strength tests. The strongest samples tended to fail through the matrix and the weakest rock samples tended to fail through haematized material or along haematized veins. Effective porosity and sonic velocity measurements could not distinguish between those samples that failed through the matrix and those that failed along discrete narrow veins. The presence of narrow haematized veins has a major effect on the intact rock strength.     

Use of point scale models to improve conceptual understanding in complex aquifers: An example from a sandstone aquifer in the Eden valley,Cumbria, UK

Understanding catchment functioning is increasingly important to enable water resources to be quantified and used sustainably, flood risk to be minimized, as well as to protect the system from degradation by pollution. Developing conceptual understanding of groundwater systems and their encapsulation in models is an important part of this understanding, but they are resource intensive to create and calibrate. The relative lack of data or the particular complexity of a groundwater system can prevent the development of a satisfactory conceptual understanding of the hydrological behaviour, which can be used to construct an adequate distributed model. A time series of daily groundwater levels from the Permo-Triassic sandstones situated in the River Eden Valley, Cumbria, UK have been analysed. These hydrographs show a range of behaviours and therefore have previously been studied using statistical and time series analysis techniques. This paper describes the application of AquiMOD, impulse response function (IRF) and combined AquiMOD-IRF methods to characterize the daily groundwater hydrographs. The best approach for each characteristic type of response has been determined and related to the geological and hydrogeological framework found at each borehole location. It is clear that AquiMOD, IRF and a combination of AquiMOD with IRF can be deployed to reproduce hydrograph responses in a range of hydrogeological settings. Importantly the choice of different techniques demonstrates the influence of differing processes and hydrogeological settings. Further they can distinguish the influences of differing hydrogeological environments and the impacts these have on the groundwater flow processes. They can be used, as shown in this paper, in a staged approach to help develop reliable and comprehensive conceptual models of groundwater flow. This can then be used as a solid basis for the development of distributed models, particularly as the latter are resource expensive to build and to calibrate effectively. This approach of using simple models and techniques first identifies specific aspects of catchment functioning, for example influence of the river, that can be later tested in a distributed model.     

A rapid rise in relative sea level ~9–7 cal ka bp along the SW Cumbria coast,NW England

Along the macro-tidal (10.7 m tide range) SW Cumbria coast in situ rooted tree stumps are infrequently exposed below present-day low Spring Tide elevations (≤−4.5 m OD). To date these remnants, we conducted a salvage operation at two sites on in situ rooted tree stumps exposed below the lowest tide levels; these sites are no longer exposed. We obtained four radiocarbon dates on these tree remnants and reference an earlier site recovered in 1972. One wood sample was identified as Quercus robur or Q. petraea, while samples from Haverigg and Kirby-in-Furness are tree Salix spp. The median group age for the rising relative sea level (RSL) that killed the trees was 8602 ± 243 bp cal a bp with an estimated Mean Tide Level (MTL) of ~≤−9 m. Evidence indicates that RSL rose ~10 m along this section of coast at a rate of between of between 18.5 and 8.7 mm a^–1 until ~6800 cal a bp , or earlier, before the rate of global sea level rise fell below that of the local glacial isostatic recovery. The transgression is coeval with rapid collapse and deglaciation of the Laurentide Ice Sheet in Hudson's Bay and slightly lags the global Meltwater Pulse-1C.     

An investigation into technetium binding in sediments

Coastal environments with reducing waters and/or sediments represent potential sinks for ⁹⁹Tc discharged to sea. Here, we have examined estuarine sediments from four geochemically distinct locations that have been exposed to ⁹⁹Tc discharged from Sellafield. Both the relative uptake and the operationally defined sediment “component” that holds the Tc were investigated in order to establish whether particular biogeochemical processes are predominately responsible for reducing and binding Tc in sediments. Despite the artefacts that can pose problems for sequential extractions, this scheme [Int. J. Environ. Anal. Chem. 51 (1993) 187] appears to be robust with regard to Tc. The results show that relative uptake of Tc varied greatly between the sites, with the highest occurring at an almost permanently anoxic fjord (Mariager Fjord, Denmark), followed by a brackish, seasonally eutrophic fjord (Roskilde Fjord, Denmark), then a sub-oxic salt marsh (which receives particle bound radionuclides from a more reducing mud patch; Esk Estuary, UK) and finally sulfidic and iron-reducing muddy sandy sediments (Needle's Eye, Solway Firth, Scotland). High relative uptake at the fjords was explained by the greater mixing of Tc-labelled oxic seawater into the part of the system where reduction of TcO₄⁻ was possible. Uptake at Mariager Fjord was higher than at Roskilde Fjord, reflecting the highly reducing geochemical conditions in the water body. Low uptake at Needle's Eye may be related to the speciation of technetium at this site as the sequential extraction data suggest that Tc is associated with the carbonate phase here. Tc carbonates are largely soluble, and this is the first observation of Tc association with carbonate fractions in the natural environment. The other three sites showed that organic matter, in conjunction with reducing conditions, was very important for binding and retaining Tc in sediments. The specific role of sulfides in controlling Tc retention in sediments was unclear because sulfides and organic matter are leached simultaneously in the sequential extraction scheme we applied, but there was evidence that Tc was not associated with acid-volatile iron monosulfides.