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The dominance of 'old' pre-event water in headwater storm runoff has been recorded in numerous upland catchment studies; however, the mechanisms by which this pre-event water enters the stream channel are poorly understood. Understanding these processes is fundamental to determining the controls on surface water quality and associated impacts on stream ecology. Previous studies in the upland forested catchment of the Afon Hafren (River Severn) at Plynlimon, mid-Wales, identified an active bedrock groundwater system that was discharging into the stream channel during storm response. Detailed analysis showed that these discharges were small and could not account for the majority of pre-event storm water response identified at this site; pre-event storm runoff had to be sourced predominantly from further upstream. An intensive stream survey was used to determine the spatial nature of groundwater-surface water (GW-SW) interactions in the Hafren Catchment. Detailed physico-chemical in-stream profiling identified a marked change in water quality indicating a significant discrete point of bedrock groundwater discharge upstream of the Hafren Transect study site. The in-stream profiling showed the importance of high spatial resolution sampling as a key to understanding processes of GW-SW interaction and how quick and cost-effective measurements of specific electrical conductance of stream waters could be used to highlight in-stream heterogeneity. This approach is recommended for use in headwater catchments for initial characterisation of the stream channel in order to better locate instrumentation and to determine more effective targeted sampling protocols in upland catchment research. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper reports the findings of a 12 month field monitoring programme at Wytham (Oxfordshire, UK), which examined the leaching of the phenylurea herbicide, isoproturon, from an agricultural clay hillslope to the adjacent ephemeral stream. Isoproturon was shown to reach the drains (at 50 cm depth) through a combination of vertical and lateral macropore flow through wormholes and inter-pedal cracks. Seasonal changes in hydrological response were also observed at the site, withlateral flow through inter-pedal cracks providing an important routeby which herbicide was transported during autumn and early spring when the clay soils were wetting up. Concentrations of isoproturon in drainflow frequently exceeded the Environment Agency's (EA) non-statutory Environmental Quality Standard (EQS) of 20 mu g/l for isoproturonin surface waters. Even under low intensity rainfall (less than 1 mm/hr) the saturated region at the base of the hillslope was shown to conduct macropore flow containing significantly high concentrations ofherbicide to the drain. The results of this study suggest that thoseregions close to surface waters which are areas of converging hydrological flow may be key contributors to the problem of isoproturon contamination of surface waters. [ABSTRACT FROM AUTHOR]

The importance of upland groundwater systems in providing a medium for nitrogen transformations and processes along flow paths is investigated within the Afon Gwy moorland catchment, Plynlimon, mid-Wales. Dissolved organic nitrogen (DON) was found to be the most abundant form of dissolved nitrogen (N) in most soils and groundwaters, accounting for between 47 and 72% of total dissolved nitrogen in shallow groundwater samples and up to 80% in deeper groundwaters. Groundwater DON may also be an important source of bio-available N in surface waters and marine systems fed by upland catchments. A conceptual model of N processes is proposed based on a detailed study along a transect of nested boreholes and soil suction samplers within the interfluve zone. Shallow groundwater N speciation reflects the soilwater N speciation implying a rapid transport mechanism and good connectivity between the soil and groundwater systems. Median nitrate concentrations were an order of magnitude lower within the soil zone (<5-31 microg/L) than in the shallow groundwaters (86-746 microg/L). Given the rapid hydrostatic response of the groundwater level within the soil zone, the shallow groundwater system is both a source and sink for dissolved N. Results from dissolved N(2)O, N(2)/Ar ratios and dissolved N chemistry suggests that microbial N transformations (denitrification and nitrification) may play an important role in controlling the spatial variation in soil and groundwater N speciation. Reducing conditions within the groundwater and saturated soils of the wet-flush zones on the lower hillslopes, a result of relatively impermeable drift deposits, are also important in controlling N speciation and transformation processes.

Through north west Europe, concern has been growing in recent years about the predatory nature of Artioposthia triangulata on indigenous earthworm species. In this study, the consequence of earthworm depletion by A. triangulata on soil structure and related hydrological processes is examined. Field measurements compare differences in saturated hydraulic conductivity between sites overrun by A. triangulata and neighbouring unaffected sites. Laboratory experiments were conducted on soil cores containing worms only, worms and A. triangulata, and a control with no worms or A. Triangulata. Differences in the water release characteristic and bulk density between treatments was studied. It is concluded that in the short term, infestation by flatworms and consequent depletion of earthworms will increase infiltration. However, as macropores degenerate or are removed over time, an increased risk of surface run off may result in increased pollution and flood hazards, whilst reduced drainage and subsequent waterlogging may reduce agricultural productivity in certain soils. More research into understanding the processes is required.