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Phosphorus interactions in a groundwater fed river from in-situ sampling; the River Leith, Cumbria, UK

Dr Neil Mullinger, Lancaster Environment Centre, Lancaster University

Wednesday 19 October 2011, 1200-1300
LEC Training Room 2

Centre for Sustainable Water Management Seminar

This seminar will cover two threads of research carried out at a site on the River Leith, a sub-catchment of the River Eden in Cumbria, over a range of scales.

The first part of the talk will present some time series data collected from an on-site laboratory making measurements of total phosphorus (TP) and reactive phosphorus (RP) at high temporal resolution (hourly). The instrumental set up is designed to provide high resolution baseline data to inform other activities and projects at the site. Some of the temporal relationships that phosphorus was found to have with discharge will be discussed here. Clusters of high phosphorus-low discharge and low phosphorus-high discharge are observed. These clusters were more distinct in the TP data. The impacts of hydrological events on catchment phosphorus loads were also examined. Flows > 0.5 m³ s⁻¹ accounted for 29% of observations but accounted for 75% of the catchment TP load and 78% of the catchment SRP load.

Secondly, measurements of vertical riverbed pore water profiles made using passive sampling diffusive gradient & diffusive equilibration in thin film probes (DGT & DET respectively) will be examined. These probes allow in situ measurements of riverbed pore water profiles to be made in the river bed to a depth of 28cm at centimetre resolution. The resulting profiles provide information on the variability in phosphorus pore waters for sites with different sediment characteristics and also indicate the impacts of biological factors on these profiles. Comparison of the vertical profiles obtained by DGT and DET probes identifies the potential of sediments to act sources or sinks of in-stream phosphorus. Simultaneous analysis for redox sensitive elements (in this case manganese) may provide additional information on the redox status of river bed sediments. Spatial variability of phosphorus in different sediments was characterised and correlated with sediment particle size and the presence or absence of vegetation. Temporal variability in pore water concentrations were also observed between summer and winter sampling periods.