Ordnance Datum Research Articles

Seasonal mobility of transverse finger bars within a mixed sand-gravel bay measured using X-band Radar

Transverse finger bars have largely been associated with sandy coasts. Here we show that these features persist within a wider mixed sediment environment, adjacent to a shingle cuspate foreland, which has not been previously reported. Details of the bars' characteristics were gleaned from analysis of bathymetry data, whilst weekly migration rates were inferred from remote sensing of the sea surface roughness as a proxy of undulating bedforms, using X-band radar reflectance data. The bars were on average ~380 m long, had wavelengths of ~160 m, amplitudes of approximately 0.2 to 0.6 m and were orientated 30° to shore normal. They were found in water depths between −3.3 and −5.8 m Ordnance Datum. The bars migrated by approximately 150 m over the first ‘winter’ observation period (15/11/2020–02/04/2021) and 70 m in the following winter period (Sept 2021–Feb 2022) but showed virtually no signs of movement during the intervening summer months. Analysis of hydrodynamic conditions suggested the bar mobility was related to the dominant longshore currents resulting from high angle, south westerly waves. Low amplitude rhythmic bedforms were also found in the upper beach, migrating at a similar rate to the nearshore bars, which are thought to be driven by high-angle wave instability.

10Be exposure age dating of Late Quaternary relative sea level changes and deglaciation of W Jura and NE Islay, Scottish Inner Hebrides

ABSTRACTNew 10Be exposure age dating and geomorphological mapping of emerged shoreline features in W Jura and NE Islay throw new light on the regional pattern of ice sheet deglaciation and late-glacial relative sea level change. We conclude that the oldest and highest emerged shorelines in this area were produced ~15.7–16.3 ka, shortly after ice sheet deglaciation ~16.5 ka. It is envisaged that the first incursion of marine waters into coastal areas took place close to a former ice sheet margin that oscillated in position across this part of the Scottish Inner Hebrides. The first evidence of late-glacial marine sedimentation following deglaciation consists of emerged marine terrace fragments and unvegetated gravel beach ridges, the former represented by a prominent glacio-isostatically tilted shoreline that declines in altitude NE to SW, from ~40 m above ordnance datum (OD) in NW Jura to ~19 m OD in central Islay. In W Jura, north of Loch Tarbert, spectacular staircases of up to 55 unvegetated gravel beach ridges were formed shortly after regional deglaciation, possibly within 1 ka. A preliminary estimate of the average rate of relative sea level lowering across W Jura between deglaciation and the Younger Dryas is in the order of ~7 mmyr−1. Geomorphological evidence from Shian Bay, W Jura, indicates a truncation of the late-glacial beach ridge staircases by a large 480-m-long beach ridge (the Colonsay Ridge) at ~14.9 ka, when former relative sea level was at ~18 m OD. This ridge may represent the product of either a stillstand in the progressive lowering of relative sea level during the late-glacial or a reversal. This raises the intriguing possibility of an association between ridge formation and the timing of the well-established global meltwater pulse 1A between ~14.65 and ~14.8 ka.

Elton Reservoir slip

Elton Reservoir was built between 1804 and 1808 to supply water to the Manchester, Bolton and Bury Canal. The canal is no longer open for boat traffic, but the reservoir does provide a sweetening flow. The reservoir is retained by a 600 m long embankment dam with a maximum height of 8.8 m, has a capacity of 923 000 m3 and a surface area of 22 hectares. Top water level in the reservoir is 87.70 mAOD (above ordnance datum). The Canal & River Trust (the Trust) is the reservoir owner. The reservoir has experienced a number of embankment slips in the past with the most recent being in 2012. The water level was subsequently reduced until repair works could be undertaken. A length of unlined spillway channel along the toe of the embankment suffering from erosion was repaired at the same time. The opportunity was taken to complete other remedial works including making the operation of the scour valve within the confined space of the outlet tunnel less onerous. This paper outlines the investigation works undertaken and the various options considered with respect to repairing the slip and providing embankment stabilisation, which led to the preferred solution of counterfort drains.

INFLUENCE OF ERRORS IN DETERMINATION OF TRACING SLOPE ON THE ACCURACY OF GEODETIC BASE FOR ROUTE

The purpose of this article is to study and develop a methodological approach tosolving the problem of accuracy of the geodetic base of the route. For this purpose, the followingtasks are set: mathematical substantiation the dependence of the line length on the ratio of the traceslope and the guide slope; description of the function of optimal use of the guiding slope at highspeed; determination of the impact of errors in the course of the geodetic justification on the routelength. Starting from the determined point and further to the right, artificial development of the lineis required. Because when a trace is planed using level curves, this point can be reached sooner orlater, and in some cases, this point can not be reached not at all, the line length designed accordingto the plan will be slightly different than in the case of tracing with usage the exact data. Thus, theobtained results indicate the following. If the error positions during a high-speed segment are suchthat the ordnance datum of the passage is less than the truth, the route length will be less than thetrue and vice versa. This trivial result indicates that the location of geodetic support points ondifferent sides of the pass is not recommended. It is established that due to the accumulation of errorsin the transmission of coordinates in the working substantiation networks, the conditions of the linedesign and the amount of operating costs change. It is mathematically substantiated that the linelength depends on the depth of the excavation on the pass and the height of the embankment at thepoint, and also on the difference of ordnance datum at these points. The difference between the traceslope and the guiding slope has an inversely proportional effect. In addition, the function of optimaluse of the guide slope at a high-speed segment has the form of a broken line according to its fracturesthe need for artificial development of the route can be established. The influence of errors in the course of the working justification is manifested in the discrepancy between the true and projectedroute length. If this error is not taken into account, it will lead to significant overspending duringbuilding a longer line than necessary. Further development of the problem of increasing the accuracyof tracing and reducing the impact of errors is planned in the direction of creating methods of digitalmodelling and automated programs.

Foraging habitat selection by breeding Herring Gulls (Larus argentatus) from a declining coastal colony in the United Kingdom

Individual foraging specialisms among generalist species can have important consequences for demographic rates. We investigated the habitat preferences of breeding Herring Gulls (Larus argentatus) at South Walney, a declining coastal colony in the UK, comparing results to a previous assessment made three decades before, when the breeding population was higher, which indicated substantial use of terrestrial, intertidal and anthropogenic resources. We used a two-stage Resource Selection Function (RSF) analysis to assess the habitat selection of 21 Herring Gulls fitted with GPS tags over three breeding seasons (2014–16). By generating pseudo-absences within the minimum convex polygon surrounding individual level GPS fixes, we first used logistic regression models to relate presence/absence for each individual to habitat. Selection for mussel bed areas was also modelled specifically as a function of phase of tide, time of day, period within the breeding season, year as well as individual covariates of mass, sex and hatching success. Second, individual RSF coefficients were extracted from the logistic regression models and used as response variables in linear models.Herring Gulls significantly selected for mussel beds and other coastal habitats (75% of all fixes away from the colony occurring in these habitats). Selection for mussel bed sites was significantly greater during the first half of the breeding season, March–May, compared with June–August, while there was also significant positive selection for this habitat between −3 and −2 m tide height (ordnance datum).There has been an apparent reduction in the range of food resources utilised by Herring Gulls at South Walney in recent years with a greater propensity for intertidal specialists within the tracked sample and, in particular, little use was made of urban and landfill areas. Therefore, better understanding of the intertidal resources available and considered management will be beneficial to balance the needs of conservation and commercial and social interests of the nearby shellfisheries.

From dust till drowned: the Holocene landscape development at Norderney, East Frisian Islands

AbstractWithin the multidisciplinary WASA project, 160 cores up to 5 m long have been obtained from the back-barrier area and off the coast of the East Frisian island of Norderney. Thirty-seven contained basal peats on top of Pleistocene sands of the formerGeestand 10 of them also had intercalated peats. Based on 100 acclerator mass spectrometry (AMS)14C dates and analyses of botanical as well as zoological remains from the peats, lagoonal sediments and the underlying sands, a variety of distinct habitats have been reconstructed. On the relatively steep slopes north of the present island, a swampy vegetation fringe several kilometres wide with carrs of alder (Alnus glutinosa) moved in front of the rising sea upwards of theGeestas it existed then until roughly 6 ka, when the sea level reached the current back-barrier region of Norderney at around −6 m NHN (German ordnance datum). From then on for nearly 4000 years a changing landscape with a mosaic of freshwater lakes and fens existed within this area. It was characterised by various stands ofCladium mariscus(fen sedge), alternating with brackish reed beds withPhragmites australis(common reed) and salt meadows withAster tripolium(sea aster),Triglochin maritima(sea arrowgrass),Juncus gerardii(saltmarsh rush) as well as mudflats withSalicornia europaea(common glasswort). As far as shown by our cores, this highly diverse, and for humans potentially attractive landscape was at least some 4 km wide and followed the coast for about 10 km. Before the rising sea caused diversification of habitats, wet heath as well as dry and dusty sand areas existed. In the course of time, parts of the wet heath turned into raisedSphagnumbogs under an oceanic precipitation regime before this diverse landscape was drowned by the rising sea and finally covered by marine sediments, while the earlier sediments and peats were partly eroded and redeposited.

Absolute vertical motion of the Amsterdam Ordnance Datum (NAP)

Abstract. The backbone of the Amsterdam Ordnance Datum (NAP) is a network of about 400 primary subsurface markers. Relative movements between the primary subsurface markers are measured with spirit levelling once in 10–20 years. However, little is known about absolute vertical movements of the primary network. This information is indispensable for the interpretation of water level measurements at the tide gauges along the Dutch coast. It may be provided by gravity measurements. Here we present a time-series analysis of more than twenty years of gravity measurements at the stations Westerbork, Epen, Zundert, and Radio Kootwijk. It reveals that only station Epen shows a statistically significant movement of -0.252±0.066 µGal yr−1, which corresponds to an uplift of 1.3±0.5 mm yr−1. For the other stations, the trends are statistically not different from zero at a significance level of 0.05. Corrections for water table variations are found to be indispensable; peak-to-peak amplitudes range from 4 µGal (Westerbork) to 28 µGal (Radio Kootwijk). Depsite some fundamental objections, corrections for instrumental offsets reduce the data scatter. First experiments with 7 years of soil moisture data acquired at station Radio Kootwijk reveal that the gravity signal of soil moisture variations has a standard deviation of 2.2 µGal, which is comparable to the noise standard deviation of measured gravity.

Maximum Holocene groundwater levels and associated extension of peat in the border zone of ‘Het Gooi’ (the Netherlands): a reconstruction based on the study of soil transects

Abstract The area ‘Het Gooi’ in the Netherlands is part of a Pleistocene ice-pushed ridge system that partially drowned during the Holocene upon sea level and associated groundwater rise. As a result, the ridge system was gradually encroached by peat. From the late Middle Ages onward, man reclaimed the peatlands surrounding Het Gooi, heavily reducing their extension and lowering the regional groundwater level by increasingly intensive drainage. Based on historical and archaeological arguments, several authors assume that the Holocene peat cover in the border zones of ‘Het Gooi’ formed the extension of large raised peat bogs that formed further to the west and east, respectively. They presume that in the late Middle Ages these extensions reached ‘upslope’ to a maximum altitude of 3 m + NAP (Dutch Ordnance Datum – approximating mean sea level). However, the original extension is difficult to reconstruct, as this peat has disappeared as a result of its exploitation and oxidation, if having been present at all. In this study, the maximum extension of the Holocene peat cover on the ice-pushed ridge system was reconstructed based on soil characteristics. Used soil characteristics concerned the presence of iron coatings around sand grains and the upper boundary of gleyic features, because these are indicators for the mean highest groundwater level (MHG). For peat to form, this MHG needs to be at or just above the ground surface for most of the year. Based on study of a number of soil transects, we reconstructed to what maximum altitude peat encroachment may have occurred. This ‘maximum extension’ can alternatively be described as the maximum altitude of the bottom of the peat onlapping the ridge system. In the western border zone, this peat cover was found to have reached to c. NAP or just above, near Hilversum. No indications were found for the occurrence of raised bogs. We conclude that the phreatic groundwater level in this zone was controlled by the sea level and associated lake levels (Naardermeer and Horstermeer), a dominant role being played by the shallow presence of Pleistocene formations with a high hydraulic conductivity. In the eastern border zone, altitudes were more variable and in places reached 2 m + NAP. Peat at this higher elevation probably formed under the influence of a higher phreatic groundwater level, induced by the presence of a clayey Eemian fill with low hydraulic conductivity in the adjacent glacial basin (the Eem valley). This study demonstrates the value of detailed soil transect studies for palaeogeographical reconstructions of the former Holocene peat cover in Pleistocene landscapes of NW Europe. It also provides independent data for validation of geohydrological models for such landscapes.

Elymus athericus encroachment in Wadden Sea salt marshes is driven by surface elevation change

AbstractQuestionsWhat are the main drivers of vegetation succession and the encroachment of Elymus athericus (Link) Kerguélen in ungrazed Wadden Sea salt marshes? Is (a) elevation, a proxy for tidal inundation and thus abiotic conditions, limiting the expanse of Elymus. Does sedimentation increase the spread of Elymus by (b) leading to surface elevation change or does it (c) add nitrogen and thereby allows Elymus to grow in lower elevation?LocationSalt marsh at Sönke‐Nissen‐Koog, Wadden Sea National Park Schleswig‐Holstein, Germany.MethodsThe experiment was established in 2007 in the high marsh and consisted of four blocks of 12 m × 8 m. The blocks differed in surface elevation change during the experiment. Each block was subdivided into 24 plots of 1 m × 1 m. The original elevation of all plots in relation to the German ordnance datum (NHN) was assessed at the start of the experiment. Plots within the blocks were randomly assigned to one of the three N fertilization treatments. Within each plot we planted five randomly chosen individuals of Elymus. After four years of treatment, the vegetation composition and cover were recorded in all plots and aboveground biomass was collected.ResultsOriginal elevation was found to be a main driver of succession favouring Elymus and other late‐successional plants. There was no effect of N fertilization, but a positive effect of surface elevation change on Elymus cover was detected.ConclusionsWe can conclude that the positive effect of surface elevation change on Elymus is based on the resulting higher elevation and more favourable abiotic conditions caused by sedimentation, but not by the addition of nitrogen with the freshly deposited sediment. This case, therefore, is an example for an ecosystem in which encroachment is driven by a natural factor, rather than anthropogenic eutrophication.

Height system connection between island and mainland using a hydrodynamic model: a case study connecting the Dutch Wadden islands to the Amsterdam ordnance datum (NAP)

We present an efficient and flexible alternative method to connect islands and offshore tide gauges with the height system on land. The method uses a regional, high-resolution hydrodynamic model that provides total water levels. From the model, we obtain the differences in mean water level (MWL) between tide gauges at the mainland and at the islands or offshore platforms. Adding them to the MWL relative to the national height system at the mainland’s tide gauges realizes a connection of the island and offshore platforms with the height system on the mainland. Numerical results are presented for the connection of the Dutch Wadden islands with the national height system (Normaal Amsterdams Peil, NAP). Several choices of the period over which the MWLs are computed are tested and validated. The best results were obtained when we computed the MWL only over the summer months of our 19-year simulation period. Based on this strategy, the percentage of connections for which the absolute differences between the observation- and model-derived MWL differences are le 1 cm is about 34% (46 out of 135 possible leveling connections). In this case, for each Wadden island we can find several connections that allow the transfer of NAP with (sub-)centimeter accuracy.

Lateglacial and Holocene relative sea‐level changes and first evidence for the Storegga tsunami in Sutherland, Scotland

ABSTRACTWe reconstruct one of the longest relative sea‐level (RSL) records in north‐west Europe from the north coast of mainland Scotland, using data collected from three sites in Loch Eriboll (Sutherland) that we combine with other studies from the region. Following deglaciation, RSL fell from a Lateglacial highstand of +6−8 m OD (Ordnance Datum = ca. mean sea level) at ca. 15 k cal a BP to below present, then rose to an early Holocene highstand and remained at ca. +1 m OD between ca. 7 and 3 k cal a BP, before falling to present. We find no evidence for significant differential Holocene glacio‐isostatic adjustment between sites on the north‐west (Lochinver, Loch Laxford), north (Loch Eriboll) and north‐east (Wick) coast of mainland Scotland. This suggests that the region was rapidly deglaciated and there was little difference in ice loads across the region. From one site at the head of Loch Eriboll we report the most westerly sedimentary evidence for the early Holocene Storegga tsunami on the Scottish mainland. The presence of the Storegga tsunami in Loch Eriboll is predicted by a tsunami wave model, which suggests that the tsunami impacted the entire north coast of Scotland and probably also the Atlantic coastline of north‐west Scotland.

A Century of Sea Level Measurements at Newlyn, Southwest England

ABSTRACTThe Newlyn Tidal Observatory is the most important sea level station in the United Kingdom. It commenced operations in 1915 as part of the Second Geodetic Levelling of England and Wales, and the mean sea level determined from the tide gauge during the first six years (May 1915–April 1921) defined Ordnance Datum Newlyn (ODN) which became the national height datum for the whole of Great Britain. The 100 years of sea level data now available have contributed significantly to many studies in oceanography, geology, and climate change. This paper marks the centenary of this important station by reviewing the sea level (and, more recently, detailed land level) measurements and Newlyn's contributions to UK cartography, geodesy and sea-level science in general. Recommendations are made on how sea and land level measurements at Newlyn might be enhanced.

Construction of an evolutionary deglaciation model for the Irish midlands based on the integration of morphostratigraphic and geophysical data analyses

AbstractAlternative, established models for the deglaciation of the midlands of Ireland are tested against an interpretation of a suite of deglacial sediments covering an area of 600 km2 in the east central midland area. Interpretation of the sediments is based on geomorphological mapping, lithostratigraphic characterization of exposures and geotechnical data supported by electrical resistivity tomography (ERT) and ground penetrating radar (GPR). GPR depicted small‐scale sedimentological and deformational structures within low‐conductivity soft sediments, such as cross‐bedding, planar bedding, channel‐like features and faulting planes, and revealed the internal architecture of eskers, glaciodeltas, subaqueous fans and raised bogs. ERT data permitted the detection of depth to bedrock and the lithological characterization of unconsolidated sediments. The ten sites presented were surveyed by traditional mapping methods and/or geophysical techniques. This allowed the construction of a local model of the deglaciation of the area which recognized five main stages. An ice sheet covering most of Ireland withdrew as a single body as far as the midlands. At this stage, two main directions of ice retreat are identified from the spatial distribution of meltwater/overflow channels, esker and morainic ridges, and ice‐marginal glaciolacustrine deposits. A pattern of deglacial sedimentation into an expanding ice‐marginal glacial lake is depicted. The glacial lake was dammed to the west by two ice dome fronts, one decaying to the north‐west and another to the south‐west, and by the Shannon Basin watershed to the east. Glacial lake outlets identified along the watershed and the altitude of the topset/foreset interface zone depicted in glaciodeltaic deposits allowed the identification of three lake water levels. The highest level is at 87–89 m Ordnance Datum (OD), the second lake level at 84 m OD and the third at 78 m OD. Copyright © 2012 John Wiley & Sons, Ltd.

Corrigendum: Pleistocene Rhine–Thames landscapes: geological background for hominin occupation of the southern North Sea region

In the paper ‘Pleistocene Rhine–Thames landscapes: geological background for hominin occupation of the southern North Sea region’ of Hijma et al. (2012), there were four errors. (i) In the Chronology key at the bottom of Fig. 6, ‘Unit S5: late MIS 2’ should have been changed to ‘Unit S5: late MIS 6’ to read ‘Unit S5: late MIS 6, Meuse-dominated fluvial deposits’. (ii) In Fig. 4, ‘Bélvèdere’ should be ‘Belvédère’. (iii) In Figs 6 and 7, the numerical errors of the calibrated ages are the 1σ error, and not the 2σ error (i.e. in Fig. 6 below panel II “2sigma cal BP” should be “1sigma cal BP“ and in Fig. 7 below panel V “2sigma cal BP” should be “1sigma cal BP”). (iv) In Figure 7, section V, three small areas had no colour (right part of the section, around -25 m) and should have been dark green behind a white label (EH, indicating Early(-middle) Holocene, fine clastic onshore deposits). The corrected Fig. 7 is reproduced below. We apologise for any inconvenience caused. Geological cross-sections IV-VII for Subarea B. Transect locations are given in Fig. 2. ‘P’, occurrence of pumice. All depths are in metres relative to present MSL (Netherlands ordnance datum NAP). For legend, see Fig. 6.

Drainage ditch-aquifer interaction with special reference to surface water salinity in the Thurne catchment, Norfolk, UK

Open drainage ditches located in low permeability material can interact with an underlying aquifer, especially if the drains almost or totally penetrate through to the aquifer. This interaction can be represented by drain coefficients incorporated in regional groundwater models. The drain coefficients depend on both the vertical distance from the base of the drain to the aquifer and the hydraulic conductivities of the low permeability deposits and the underlying aquifer. In a case study of drained marshes in the Thurne catchment in Norfolk, UK, drains with a water level below ordnance datum (OD) draw in saline water from the coast and freshwater from recharge areas. Pathlines, derived from a regional groundwater model analysis, explain the salinities measured in drains. In addition a series of vertical section numerical model solutions are used to develop general guidance on the selection of drain coefficients.

Holocene relative sea levels and related prehistoric activity in the Forth lowland, Scotland, United Kingdom

Changes in relative sea level (RSL) and their effect on the distribution of human activity in the Forth lowland, Scotland, UK between ca 11,700 and ca 2000 calibrated years before present (BP) are examined. Block uplift of shorelines occurred over a longer period than previously thought, continuing to at least around 4700 BP. New graphs of RSL change, based upon an analysis of previous work and evidence from new sites using standard morphological and stratigraphical analyses, support a fall in RSL in the early Holocene during which buried estuarine surfaces were formed, followed by a marked reversal on a centennial, perhaps even decadal, scale sometime around 9900–9500 BP from a falling sequence to a rising one. There may have been a short-lived fluctuation in the rising RSL ca 8300 BP, and the Holocene Storegga Slide tsunami of ca 8100 BP was widespread in the lowland. The rising RSL culminated at the Main Postglacial Shoreline, reached ca 7800 BP, when Mean High Water Spring Tides (MHWS) lay within the range 14.6–16.5 m British Ordnance Datum (OD) in the western lowland. This is the highest published Holocene RSL in Britain and Ireland. The subsequent fall in RSL stabilised at a second shoreline, the Blairdrummond Shoreline, from which regression was occurring at ca 4700 BP. RSL later fell to a lower shoreline at ca 3900 BP before reaching present levels within the last three millennia. Comparison between the empirical evidence for RSL change in this area and glacial isostatic adjustment models indicates both similarities and differences. Records of archaeological sites and artefacts in the lowland and surrounding areas are discussed. Maps showing the evolution of the estuary are compared with the distribution of Mesolithic, Neolithic, Bronze Age and Iron Age activity. Evidence for Mesolithic people indicates the opportunistic use of available resources as RSL rose and the estuary expanded to its maximum extent. Neolithic people were also attracted to the estuary, building at least one platform from which to exploit resources and accumulating middens along the shoreline for over 2000 years. Bronze Age people were present across the emerging saltmarshes and mudflats before raised peat mosses, already extensive at the head of the lowland, developed more widely. In the Iron Age, the area could be accessed both between the peat mosses of the western lowland and across newly emergent land in the east as RSL continued to fall.

Factors affecting nitrate distribution in shallow groundwater under a beef farm in South Eastern Ireland

Groundwater contamination was characterised using a methodology which combines shallow groundwater geochemistry data from 17 piezometers over a 2 yr period in a statistical framework and hydrogeological techniques. Nitrate–N (NO 3-N) contaminant mass flux was calculated across three control planes (rows of piezometers) in six isolated plots. Results showed natural attenuation occurs on site although the method does not directly differentiate between dilution and denitrification. It was further investigated whether NO 3-N concentration in shallow groundwater (<5 m below ground level) generated from an agricultural point source on a 4.2 ha site on a beef farm in SE Ireland could be predicted from saturated hydraulic conductivity ( K sat ) measurements, ground elevation (m Above Ordnance Datum), elevation of groundwater sampling (screen opening interval) (m AOD) and distance from a dirty water point pollution source. Tobit regression, using a background concentration threshold of 2.6 mg NO 3-N L −1 showed, when assessed individually in a step wise procedure, K sat was significantly related to groundwater NO 3-N concentration. Distance of the point dirty water pollution source becomes significant when included with K sat in the model. The model relationships show areas with higher K sat values have less time for denitrification to occur, whereas lower K sat values allow denitrification to occur. Areas with higher permeability transport greater NO 3-N fluxes to ground and surface waters. When the distribution of Cl − was examined by the model, K sat and ground elevation had the most explanatory power but K sat was not significant pointing to dilution having an effect. Areas with low NO 3 concentration and unaffected Cl − concentration points to denitrification, low NO 3 concentration and low Cl − chloride concentration points to dilution and combining these findings allows areas of denitrification and dilution to be inferred. The effect of denitrification is further supported as mean groundwater NO 3-N was significantly ( P < 0.05) related to groundwater N 2/Ar ratio, redox potential (Eh), dissolved O 2 and N 2 and was close to being significant with N 2O ( P = 0.08). Calculating contaminant mass flux across more than one control plane is a useful tool to monitor natural attenuation. This tool allows the identification of hot spot areas where intervention other than natural attenuation may be needed to protect receptors.

Isotopic variability in the intertidal acorn barnacle Semibalanus balanoides : a potentially novel sea-level proxy indicator

Abstract We report variations in the δ 13 C and δ 18 O values of barnacle skeletal carbonate as well as the δ 13 C and δ 15 N value of tissue from specimens of the acorn barnacle S. balanoides , as a function of elevation within its living range on the Isle of May, Scotland. Individuals were sampled over a 3.50 m range at 0.25 m intervals (1.00–4.50 m above ordnance datum). Carbonate δ 18 O values (2.44±0.13‰ [1σ], n=45) and tissue δ 15 N values (8.17±0.42‰, n=15) do not vary systematically with elevation. The δ 13 C value of shell carbonate increases with elevation by c. 1‰ (total range: −0.77‰ to +0.63‰), but the variability between samples at the same elevation suggests that this relationship will be of limited use in constraining palaeo-elevation. By contrast, tissue δ 13 C values show systematic variation with elevation, increasing by c . 8‰ (total range: −19.36‰ to −8.77‰) with increasing elevation. These results suggest that there is potential to use the tissue δ 13 C values to determine the elevation of a Fixed Biological Indicator (FBI) such as S. balanoides within its living range. If this is also true of the organic matrix of the carbonate skeleton, and if this organic matrix is preserved in Holocene FBIs, then the potential exists to use carbon isotopes to more precisely constrain the palaeo-elevation of FBIs within their living range and hence palaeo sea-level. The small range of carbonate δ 18 O values suggests that oxygen isotopes in FBIs can be used to constrain water δ 18 O values if an independent estimate of temperature is available, or temperature if an independent estimate of salinity is available.

Eutrophication of Tamar Lakes (1975–2003): a case study of land‐use impacts, potential solutions and fundamental issues for the Water Framework Directive

AbstractTamar Lakes is comprised of two reservoirs, which are located in South West England and in the headwaters of River Tamar at approximately 135 m above ordnance datum. Upper Tamar Lake (UTL) is a direct feed source reservoir of potable water in North Cornwall. Immediately following completion in 1975, UTL was subject to intense blue‐green algal blooms that continue to the present. These blooms create operational problems for water treatment, especially in hot‐dry years. Lower Tamar Lake (LTL) was constructed as a water supply reservoir in 1819 and became obsolete following UTL coming on‐line. Detailed water quality investigations over a period of some 28 years have confirmed the source of nutrient enrichment that fuels the algal blooms to be agriculturally derived, corresponding with a substantial increase in livestock farming. Associated poor land management practices, such as extensive field drainage and inappropriate slurry disposal to land, are linked with substantial elevations in organic contaminants such as ammonia, biochemical oxygen demand (BOD) and suspended solids (SS) during rainfall events. Evidence demonstrates that both reservoirs act as primary treatment lagoons, substantially reducing the worst of these pollutants and providing significant environmental gain. The implications of the Common Agricultural Policy (CAP), the Water Framework Directive (WFD) and regulatory monitoring are discussed in relation to resource management.

Risk Assessment of some Revetments in Southwest Wales, United Kingdom

The new risk assessment model in which the second-order reliability method and the importance sampling Monte Carlo (ISMC) simulations were interrelated was implemented to Wiseman’s Bridge, Newport, and Broadhaven revetments in the Pembrokeshire Coast National Park, southwest Wales, United Kingdom. The tidal range of the site and the storm surge were randomly generated at the first stage of ISMC simulation from the probability distributions describing the phenomena. At the second stage, the damage probability was predicted by approximating the limit-state surface by a quadratic one having the identical curvature at the design point. Newport and Broadhaven revetments were safe, but the revetment at Wiseman’s Bridge needed strong maintenance. The risk assessment model reflected the effect of water level changes (circa 6 m above ordnance datum) on the reliability of rubble mound revetments by simulating the environmental conditions at the sites. As the uncertainties inherent in design parameters were extensiv...