Anthropogenic contribution to the geological and geomorphological record: a case study from Great Yarmouth, Norfolk, UK

Reconstruction of artificial or anthropogenic topographies, sediment thicknesses and volumes provides a mechanism for quantifying anthropogenic changes to sedimentary systems in the context of the proposed Anthropocene epoch. We present a methodology for determining the volumetric contribution of anthropogenic deposits to the geological and geomorphological record and apply it to the Great Yarmouth area of Norfolk, UK. 115 boreholes, drilled to a maximum depth of 6 m below ground level, were used to determine the thickness and distribution of seven geo-archaeological units comprising natural and anthropogenic deposits in the central Great Yarmouth area. This was supplemented by additional depth information derived from 467 existing ground investigation boreholes and published 1:50 000 scale geological maps. The top and base of each geo-archaeological unit were modelled from elevations recorded in the borehole data. Grids were produced using a natural neighbour analysis with a 25 m cell size using MapInfo 8.0 Vertical Mapper 3.1 to produce palaeotopographical surfaces. Maximum, minimum and average elevations for each geo-archaeological unit generally increase with decreasing age with the exception of the Early-Medieval palaeotopographical surface which locally occurs at higher elevations than that of the younger Late-Medieval unit. The total sediment volume for the combined Modern, Post-Medieval, Late-Medieval and Early-Medieval geo-archaeological units is 10.91x105m3. The total sediment volume for the Aeolian, River Terrace and Marine geo-archaeological units combined is 65.58 x105m3. Anthropogenic sedimentation rates were calculated to increase from ~ 590 m3/yr during the Early-Medieval period, ~ 1500 m3/yr during the Post-Medieval period and ~ 2300 m3/yr during the Modern period. It is estimated that the combined anthropogenic geo-archaeological units contribute approximately 15% of the total volume of sediments that would have been traditionally considered natural Holocene deposits in the Great Yarmouth area. The results indicate that an approach combining geological and archaeological deposits modelling can be used to quantify anthropogenic landscape impact and its associated sediment flux

The Influence Of Particle Size And Frictional/Cohesional Shear Strength Components On UK Salt Marsh Substrate Stability

Salt marshes and tidal flats contribute valuable ecosystem services, by providing habitats, storing pollutants and reducing flood and erosion risk in the coastal hinterland. However, salt marsh areal extent is decreasing both globally and regionally (e.g. in Northwest Europe). While we know that salt marshes are retreating, this could be occurring due to biological, geochemical and geotechnical properties of the marsh and tidal flat, and/or due to changes in hydrodynamic forcing. Until now, very few studies have assessed how substrate geotechnical properties influence both the erosion processes and the erodibility of the marsh edge and tidal flat surface. Here, we compare frictional and cohesional strength components at two hydrodynamically-similar but sedimentologically-different salt marshes and tidal flats in the UK. As such, we assess how sediment composition and behavior may influence marsh resistance to hydrodynamic forcing.This work was funded by a NERC PhD studentship (LCAG/329; 2016-2020), and a Collaborative Award in Science and Engineering with the British Geological Survey (LCAG/352)

Effects of caustic cleaning on pore size of nanofiltration membranes and their rejection of trace organic chemicals

The aim of this study was to assess the impact of caustic cleaning on the rejection of three different trace organic chemical (TrOC) groups (i.e. neutral hydrophilic, neutral hydrophobic and negatively charged) by two nanofiltration (NF) membranes ‒ namely NF270 and NF90. Chemical cleaning was simulated by exposing virgin membrane samples to commercial caustic cleaning formulations as well as sodium hydroxide solutions containing analytical grade additives such as sodium dodecyl sulfate or ethylenediaminetetraacetic acid. The membrane average pore size before and after exposure to a commercially available caustic cleaning formulation was determined based on the pore transport model. The results show that caustic chemical cleaning could cause an increase in the membrane pore size, leading to an increase in permeability and decrease in rejection of conductivity. The impact of caustic cleaning on the pore size and solute rejection was a function of the membrane active skin layer and the chemistry of the cleaning formulation. Caustic cleaning led to a small increase in pore size of the NF270 membrane and resulted in a notable increase in the permeability and salt passage. By contrast, the impact on the NF90 membrane was negligible. The influence of caustic cleaning on TrOC rejection was dependent on physical characteristics of each TrOC including their molecular size, charge, and hydrophobicity. The rejection of neutral and hydrophobic TrOC by the NF270 membrane decreased significantly after exposure to caustic cleaning formulation. However, because the rejection of negatively charged TrOC is governed mostly by electrostatic interaction, their rejection was not significantly affected by caustic cleaning