Sewage effluent clean-up reduces phosphorus but not phytoplankton in lowland chalk stream (River Kennet, UK) impacted by water mixing from adjacent canal

Neal, Colin; Martin, Ellie; Neal, Margaret; Hallett, John; Wickham, Heather D.; Harman, Sarah A.; Armstrong, Linda K.; Bowes, Mike J.; Wade, Andrew J.; Keay, David. 2010 Sewage effluent clean-up reduces phosphorus but not phytoplankton in lowland chalk stream (River Kennet, UK) impacted by water mixing from adjacent canal. Science of the Total Environment, 408. 5306-5316.

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Information is provided on phosphorus in the River Kennet and the adjacent Kennet and Avon Canal in southern England to assess their interactions and the changes following phosphorus reductions in sewage treatment work (STW) effluent inputs. A step reduction in soluble reactive phosphorus (SRP) concentration within the effluent (5 to 13 fold) was observed from several STWs discharging to the river in the mid-2000s. This translated to over halving of SRP concentrations within the lower Kennet. Lower Kennet SRP concentrations changed from being highest under baseflow to highest under stormflow conditions. This represented a major shift from direct effluent inputs to a within- catchment source dominated system characteristic of the upper part to the catchment. Average SRP concentrations in the lower Kennet reduced over time towards the target for good water quality. Critically, there was no corresponding reduction in chlorophyll-a concentration, the waters remaining eutrophic when set against standards for lakes. Following the up gradient input of the main water and SRP source (Wilton Water), SRP concentrations in the canal reduced down gradient to below detection limits at times near its junction with the Kennet downstream. However, chlorophyll concentrations in the canal were an order of magnitude higher than in the river. This probably resulted from long water residence times and higher temperatures promoting progressive algal and suspended sediment generation that consumed SRP. The canal acted as a point source for sediment, algae and total phosphorus to the river especially during the summer months when boat traffic disturbed the canal’s bottom sediments and the locks were being regularly opened. The short-term dynamics of this transfer was complex. For the canal and the supply source at Wilton Water, conditions remained hypertrophic when set against standards for lakes even when SRP concentrations were extremely low.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: CEH Topics & Objectives 2009 - 2012 > Water > WA Topic 1 - Variability and Change in Water Systems > WA - 1.1 - Continued long term monitoring and integrated observation of freshwater systems
UKCEH and CEH Sections/Science Areas: Acreman
ISSN: 0048-9697
Additional Keywords: Kennet, canal, river, phosphorus, sediment, chlorophyll, effluent, eutrophication
NORA Subject Terms: Chemistry
Date made live: 23 Sep 2010 10:59 +0 (UTC)

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