Spatial and temporal changes in chlorophyll-a concentrations in the River Thames basin, UK: are phosphorus concentrations beginning to limit phytoplankton biomass?

Bowes, M.J.; Gozzard, E.; Johnson, A.C.; Scarlett, P.M.; Roberts, C.; Read, D.S.; Armstrong, L.K.; Harman, S.A.; Wickham, H.D.. 2012 Spatial and temporal changes in chlorophyll-a concentrations in the River Thames basin, UK: are phosphorus concentrations beginning to limit phytoplankton biomass? Science of the Total Environment, 426. 45-55. 10.1016/j.scitotenv.2012.02.056

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Abstract/Summary

Chlorophyll-a and nutrient concentrations were monitored at weekly intervals across 21 river sites throughout the River Thames basin, southern England, between 2009 and 2011. Despite a 90% decrease in soluble reactive phosphorus (SRP) concentration of the lower River Thames since the 19905, very large phytoplankton blooms still occur. Chlorophyll concentrations were highest in the mid and lower River Thames and the larger tributaries. Lowest chlorophyll concentrations were observed in the smaller tributaries, despite some having very high phosphorus concentrations of over 300 mu g l(-1). There was a strong positive correlation between river length and mean chlorophyll concentration (R-2=0.82), and rivers connected to canals had ca. six times greater chlorophyll concentration than 'natural' rivers with similar phosphorus concentrations, indicating the importance that residence time has on determining phytoplankton biomass. Phosphorus concentration did have some influence, with phosphorus-enriched rivers having much larger phytoplankton blooms than nutrient-poor rivers of a similar length. Water quality improvements may now be capping chlorophyll peaks in the Rivers Thames and Kennet, due to SRP depletion during the spring/early summer phytoplankton bloom period. Dissolved reactive silicon was also depleted to potentially-limiting concentrations for diatom growth in the River Thames during these phytoplankton blooms, but nitrate remained in excess for all rivers throughout the study period. Other potential mitigation measures, such as increasing riparian shading and reducing residence times by removing impoundments may be needed, alongside phosphorus mitigation, to reduce the magnitude of phytoplankton blooms in the future.

Item Type:	Article
Identification Number/DOI:	10.1016/j.scitotenv.2012.02.056
Programmes:	CEH Topics & Objectives 2009 onwards > Water > WA Topic 1 - Variability and Change in Water Systems > WA - 1.1 - Continued long term monitoring and integrated observation of freshwater systems CEH Topics & Objectives 2009 onwards > Water > WA Topic 2 - Ecohydrological Processes > WA - 2.3 - Assess the responses of river, lake and wetland ecosystems to ecohydrological drivers
CEH Sections:	Acreman Hails
ISSN:	0048-9697
Additional Keywords:	nutrient, algae, phytoplankton, water quality, River Thames, eutrophication
NORA Subject Terms:	Earth Sciences Management Chemistry
Date made live:	03 Sep 2012 15:08
URI:	http://nora.nerc.ac.uk/id/eprint/19374

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