Martin Thorp

Validation of host-specific Bacteriodales 16S rRNA genes as markers to determine the origin of faecal pollution in Atlantic Rim countries of the European Union

The recent implementation of the Revised Bathing Water Directive in the European Union has highlighted the need for development of effective methods to differentiate between sources of faecal contamination. It had previously been shown that amplification of 16S rRNA genes of host-specific Bacteriodales species using the HF183F and CF128F primers could be used as markers for human and bovine faecal contamination in the United States. This paper determined the sensitivity and specificity of these markers in four Atlantic Rim countries (France, Ireland, Portugal and the United Kingdom) to evaluate their usefulness in determining the origin of faecal contamination. It was shown that the HF183F marker displayed high sensitivity (80-100%) and specificity (91-100%), and is reliable as an indication of human faecal contamination. The CF128F marker displayed 100% sensitivity in all four countries. However, strong regional variations in specificity (41-96%) were observed, highlighting the need for local validation before this marker is employed in source tracking of faecal contamination.

Geomorphic response to rapid climatic and hydrologic change during the late pleistocene and early holocene in the humid and sub-humid tropics

Abstract The data base concerning late Quaternary environmental change in the humid tropics is dependent on records from scattered sites; the intensity and duration of wet-dry oscillations remain speculative, and the responses of hillslopes and river systems are based on over-simplified models. However, available evidence indicates that prolonged aridity affected all but a few favoured core areas of equatorial climate after 20,000 BP, lasting 5–7 ka. Dry conditions at the LGM were marked by semi-arid landforms and reduced steam activity. Large palaeofloods occurred after 13,000 BE but dry conditions returned after 11,000 BP, before the early Holocene pluvial led to abundant sedimentation lasting nearly 2 ka after 9500 BP, in Africa, Amazonia and Australasia. Erosion (channel cutting) and flood deposition occurred at the Pleistocene-Holocene transition, followed by multiple shifts from lateral to vertical accretion (fill-cut episodes) during the early Holocene, while thick overbank deposits formed during the later Holocene. Re-establishment of the lowland rainforests was delayed until after 9000 BP in Africa, Australia and Brazil and several wet-dry oscillations followed in the mid Holocene period. Hillslope activity at the LGM was marked by local sediment transfers and fan formation; at the termination sediment fluxes increased rapidly, but mass movement probably peaked after 10,000 BP Sediment delivery to stream channels was not immediate and large sediment stores remain on the landscape today, many in areas of potential sensitivity of erosion.

The age of the Pleistocene raised beach near Fethard, County Wexford, using infra red stimulated luminescence (IRSL)

Stratified sediments, interpreted to be part of the Courtmacsherry Formation Pleistocene raised beach that overlies a marine rock platform near Fethard. south Wexford, were sampled and dated using the technique of Infra Red Stimulated Luminescence (IRSL). The technique yielded ages for the formation of most of the raised beach of between c. 162 ka BP and c. 129 ka BP. These arc the first age determinations for the Courtmacsherry Formation itself and. as such, represent an important advance in the development of a chronostratigraphy of the Pleistocene in Ireland. These dates are consistent with results obtained by others using UTD dating of sediments overlying the Courtmacsherry Formation in County Kerry and, therefore, suggest that IRSL holds great promise for the dating of hitherto updateable sediments.

The timing of alluvial sedimentation and floodplain formation in the lowland humid tropics of Ghana, Sierra Leone and western Kalimantan (Indonesian Borneo)

Abstract Temporal patterns in floodplain genesis and alluvial sedimentation in lowlands tropical rain forest zones of Ghana, Sierra Leone and western Kalimantan (Indonesian Borneo) based upon 14 C age determinations are described. Alluvial low terraces or buried sediments in West Africa yielded ages of 36-21 ka. In west Kalimantan a widespread episode of alluviation has yielded dates of 54-51 ka. The 20-13 ka interval was characterised by channel incision with valley floor erosion and neither region records sedimentation. Holocene alluvial sedimentation and floodplain construction in West Africa occurred during two temporal intervals: 10-7 ka and 4 ka to present and in western Kalimantan in response to early Holocene sea level rise followed by late Holocene regression and coastal outgrowth. The clustering of 14 C dates closely corresponds to regional lake level fluctuations and vegetational changes and to global indications of climatic change. We propose that periods of more frequent episodes of accelerated floodplain erosion and reconstitution, channel morpho-sedimentary activity and alluvial accumulation (1) are responses to interstadial and interglacial periods of higher precipitation following intervening periods of cooler and drier conditions; and (2) may be synchronous during the last 60 ka throughout the African and Asian inner humid lowland tropics.

Glacier Dynamics around Slieve Bloom, Central Ireland

Analyses of both till and glacioaqueous sedimentary fabrics and their lithological characteristics have been carried out on sediments sampled at eight sites located around the northern margin and piedmont of Slieve Bloom. Results indicate that Slieve Bloom was overtopped by ice (lowing locally from between the south-south-west and west. The pattern of ice (low indicated by the sedimentary fabrics, the presence in the glacigenic sediments of a distinctive variety of Galway granite and the spatial variability of limestone in these sediments indicate that this local flow direction resulted from the deflection to the north-north-east of ice (lowing from the west. As the most widely accepted ice flow model for this region during the last glaciation requires ice (low to have been from between north-north-west and north-north-east, the results presented in this paper have important implications for the modelling of regional ice (low in the Irish midlands during the last glaciation.

Dating recent alluvial sediments in the Wicklow Mountains

Modern floodplain sediments in the Wicklow Mountains display a stratigraphy and sedimentology that contrasts them with earlier Holocene alluvium. During previous research 14 C dates of lightly constrained stratigraphies in one valley indicated a commencement date between 190+/-60 yr BP and 580+/-50 yr BP and mining generated enhanced lead metal values in another valley implied a commencement date there of AD 1780–1800. The paper presents the results of a 14 C dating programme the objects of which were to date (a) more definitively their commencement throughout the Wicklow Mountains and (b) their internal stratigraphies with a view to establishing a Hood chronology. AMS and radiometric 14 C dating techniques were applied to organic fractions and paniculate organic matter extracted from thin organic-rich layers within sampled sedimentary sequences. The dates spanned 780+/-60 BP to 3396+/-46 BP and provided neither a Coherent commencement period nor an accurate chronostratigraphy and the modern sediments appear to be dominated by old carbon derived from the catchment blanket peats. Although these results show that the immediate research aims cannot be achieved using 14 C dating they have led to a clearer understanding of the sourcing and dynamics of the modern style of sedimentation.

The response of geomorphic systems to climatic and hydrological change during the Late Glacial and early Holocene in the humid and sub-humid tropics

Abstract Dated alluvial stratigraphies indicative of late Quaternary environmental change in the humid tropics have increased, but the database remains inadequate and the intensity and duration of wet-dry oscillations and responses of hillslopes and river systems remain poorly understood. Dry conditions at the Last Glacial Maximum were marked by semi-arid landforms with reduced stream activity. Large palaeofloods, valley-floor erosion, channel cutting and flood deposition occurred at the Pleistocene-Holocene transition after 13 000 BP. Distinctive floodplains and stratigraphies characterized by multiple shifts from lateral to vertical accretion were built initially over a period of nearly 2 ka after 9 500 BP during the early Holocene pluvial in Africa, Kalimantan and Amazonia during and after re-establishment of the lowland rainforests. Several wet-dry climatic oscillations followed in the mid-Holocene period and are marked by alluvial cut and fill sequences and by slightly thinner but coarse textured floodplain overbank sediments.

The Fluvial Concentration of Heavy Minerals in the Slieve Bloom Mountains, Central Ireland

The detrital mineralogies of both alluvial sediments and their glacigenic and bedrock sedimentary sources undergoing fluvial entrainment in the mountains are outlined. Relationships between patterns of heavy mineral concentration in the alluvial sediments and the controlling factors of source material distribution and provenance, the hydrodynamics of heavy minerals, the spatial variability in process environments of concentration and the interaction of these factors are deduced and the spatial distributions of correlated heavy mineral assemblages and concentrations are explained. Thus, a better understanding is gained of the processes and process interactions responsible for alluvial heavy mineral concentration in paraglacial environments.

Rainfall-triggered slope failures in eastern Ireland

Abstract A rain storm (>1‐in‐200 yr) following high antecedent rainfall in August 1986 triggered four debris slide‐flows on the slopes of the Cloghoge Valley in eastern Ireland. Failures occurred at the bedrock interface underlying shallow (∼1 m) soils on slopes between 19° and 35°. Resistance to shear of the soil ranges from 26 to 32 kN/m2 and liquid limits range between 34 percent and 58 percent and these thresholds were exceeded. The debris slides were rapidly transformed into high velocity debris flows that felled trees, stripped bark and incised gullies. The average velocities were estimated to be between 3 and 7 m/s. Factors influencing failure location include local slope morphology, soil depth, preferential groundwater seepage, and natural and anthropogenic surface runoff routing. Conclusions are drawn as to the general mechanisms of small‐scale slope failures resulting from saturating rainfall on upland glaciated slopes.

A mid-Holocene alluvial deposit beneath blanket peat in the Upper Liffey Valley, county Wicklow, Ireland

A 750m section on a hillside in the upper Liffey Valley, county Wicklow has exposed a small valley buried beneath blanket peat. The section shows two alluvial sequences underlain by a stone line over regional till and weathered granite. 14C dates from wood in the sediments indicate that the older alluvium formed between 4950-4550 cal. BP and the younger between 3470-3000 cal. BP. Wood in the basal layer of the overlying peat yielded a date of 2310-2150 cal. BP. The younger alluvium shows the effects of soil paludification prior to the peat expansion and dated pollen analyses elsewhere in the upper catchment show that blanket peat began spreading over most areas above 350m after 40003600 BP. The buried valley contributed sediments to the mid-Holocene floodplains in the upper Liffey valley prior to the extension of blanket peat.