Determining Phosphorus-sediment Interactions in a Groundwater-fed River through In Situ Measurement
Abstract
In stream processing is potentially important in the regulation and availability of nutrients to riverine flora and also in attenuating point and non-point source inputs to rivers, such as wastewater outflows and agricultural runoff. Phosphorus is an important macronutrient and often cited as a limiting factor to plant and algal growth in freshwater systems. The particle-reactive nature of the orthophosphate anion means that river sediments can play an important role in phosphorus attenuation and availability in rivers. However, it is also known that plant root exudates can also affect the mobilisation of sediment adsorbed phosphorus. Results are presented from high resolution (centimetre) measurements of vertical riverbed pore water profiles at a field site in the River Leith, Cumbria, UK. The River Leith is a sub-catchment of the River Eden and is characterised by significant groundwater-surface water interactions at the monitoring site. In situ measurements of soluble reactive phosphorus (SRP) in riverbed pore waters were made using passive sampling diffusive gradient and diffusive equilibration in thin film (DGT and DET) probes. These probes allow in situ measurements of riverbed pore waters to be made to a depth of 30 cm below the riverbed at centimetre resolution. The resulting profiles provide information on the variability in phosphorus pore waters for vegetated and non-vegetated regions of the riverbed. The impact of vegetated root zones in riverbed sediments is poorly characterised for hyporheic exchanges. 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 provides additional information on the redox status of riverbed sediments. Initial results show spatial and temporal variability of phosphorus in different sedimentary environments and also between vegetated and non-vegetated areas of the riverbed. Corresponding variations in manganese concentrations indicate changes in redox chemistry at these sites. This work demonstrates the different potentials of riverbed sediments to release phosphorus, which has consequences for mobilisation of phosphorus in hyporheic exchanges.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.H53F1488M
- Keywords:
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- 0452 BIOGEOSCIENCES / Instruments and techniques;
- 0496 BIOGEOSCIENCES / Water quality;
- 1830 HYDROLOGY / Groundwater/surface water interaction;
- 0409 BIOGEOSCIENCES / Bioavailability: chemical speciation and complexation