Browsing by Author "Howden, Nicholas J. K."

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    An assessment of the risk to surface water ecosystems of groundwater P in the UK and Ireland
    (Elsevier , 2010-03-15T00:00:00Z) Holman, Ian P.; Howden, Nicholas J. K.; Bellamy, Patricia H.; Willby, N.; Whelan, Michael J.; Rivas Casado, Monica
    A good quantitative understanding of phosphorus (P) delivery is essential in the design of management strategies to prevent eutrophication of terrestrial freshwaters. Most research to date has focussed on surface and near-surface hydrological pathways, under the common assumption that little P leaches to groundwater. Here we present an analysis of national patterns of groundwater phosphate concentrations in England and Wales, Scotland, and the Republic of Ireland, which shows that many groundwater bodies have median P concentrations above ecologically significant thresholds for freshwaters. The potential risk to receptor ecosystems of high observed groundwater P concentrations will depend on (1) whether the observed groundwater P concentrations are above the natural background; (2) the influence of local hydrogeological settings (pathways) on the likelihood of significant P transfers to the receptor; (3) the sensitivity of the receptor to P; and, (4) the relative magnitude of P transfers from groundwater compared to other P sources. Our research suggests that, although there is often a high degree of uncertainty in many of these factors, groundwater has the potential to trigger and/or maintain eutrophication under certain scenarios: the assumption of groundwater contribution to river flows as a ubiquitous source of dilution for P-rich surface runoff must therefore be questioned. Given the regulatory importance of P concentrations in triggering ecological quality thresholds, there is an urgent need for detailed monitoring and research to characterise the extent and magnitude of different groundwater P sources, the likelihood for P transformation and/or storage along aquifer- hyporheic zone flow paths and to identify the subsequent risk to receptor ecosystems. (C) 2009 Elsevier B.V. All rights reserved.
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    An evaluation of the restoration programme for a cut over section of Wedholme Flow raised mire
    (Cranfield University, 2008-09) Lewis, Graham; Howden, Nicholas J. K.
    Wedholme Flow, Cumbria is the site of the largest lowland raised mire remaining in the UK. It forms part of a group of ombrotrophic mires known as the Solway mosses, situated in the north west of England. As with all remaining raised mires in the UK, Wedholme Flow has suffered some historical degradation largely caused by cutting of peat at the site’s periphery for fuel. More recently large sections of the mire surface have been commercially mined mainly for horticultural use. These include sections which have been cut over by hand leaving baulks or upstanding strips of unmolested peat between cuttings but also sections of the mire surface that have been strip mined or milled using machinery. Because of the complete loss of Sphagnum the sections of the mire surface that have been milled represent a particular challenge in terms of restoration. The reinstatement of the Sphagnum layer or acrotelm typical of raised mire sites is an important restoration objective. In order for Sphagnum to re-colonise a cut over mire site the water table must remain in close proximity to the surface of the peat throughout the year. The absence of an acrotelm however contributes to seasonal water table fluctuation by decreasing surface storage and allowing increased evaporation from the surface .On cutover mire sites primary restoration efforts centre on raising the water table sufficiently to facilitate Sphagnum re-colonisation and growth with a view to restoring a functioning acrotelm. This study provides a critical appraisal of a restoration programme that aims to raise water levels on a cutover section of Wedholme Flow in Cumbria. The restoration programme was undertaken by Natural England who own and manage the site. Since acquiring the cut-over section of the site bunds and peat plugs have been installed to reduce drainage and raise the water table. Boreholes have been installed on site to monitor changes in water level during and after the restoration. The progress of the restoration programme is evaluated through examination of the water balance, available groundwater data and a review of contemporary literature. Recommendations for further restoration and monitoring are made.
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    Exploring the role of hydrological pathways in modulating multi-annual climate teleconnection periodicities from UK rainfall to streamflow
    (European Geosciences Union, 2021-04-23) Rust, William; Cuthbert, Mark; Bloomfield, John; Corstanje, Ron; Howden, Nicholas J. K.; Holman, Ian P.
    An understanding of multi-annual behaviour in streamflow allows for better estimation of the risks associated with hydrological extremes. This can enable improved preparedness for streamflow-dependant services, such as freshwater ecology, drinking water supply and agriculture. Recently, efforts have focused on detecting relationships between long-term hydrological behaviour and oscillatory climate systems (such as the North Atlantic Oscillation – NAO). For instance, the approximate 7 year periodicity of the NAO has been detected in groundwater-level records in the North Atlantic region, providing potential improvements to the preparedness for future water resource extremes due to their repetitive, periodic nature. However, the extent to which these 7-year, NAO-like signals are propagated to streamflow, and the catchment processes that modulate this propagation, are currently unknown. Here, we show statistically significant evidence that these 7-year periodicities are present in streamflow (and associated catchment rainfall), by applying multi-resolution analysis to a large data set of streamflow and associated catchment rainfall across the UK. Our results provide new evidence for spatial patterns of NAO periodicities in UK rainfall, with areas of greatest NAO signal found in southwest England, south Wales, Northern Ireland and central Scotland, and show that NAO-like periodicities account for a greater proportion of streamflow variability in these areas. Furthermore, we find that catchments with greater subsurface pathway contribution, as characterised by the baseflow index (BFI), generally show increased NAO-like signal strength and that subsurface response times (as characterised by groundwater response time – GRT), of between 4 and 8 years, show a greater signal presence. Our results provide a foundation of understanding for the screening and use of streamflow teleconnections for improving the practice and policy of long-term streamflow resource management