title: Identifying multiple stressor controls on phytoplankton dynamics in the River Thames (UK) using high-frequency water quality data.
abstract: River phytoplankton blooms can pose a serious risk to water quality and the structure and function of aquatic ecosystems. Developing a greater understanding of the physical and chemical controls on the timing, magnitude and duration of blooms is essential for the effective management of phytoplankton development. Five years of weekly water quality monitoring data along the River Thames, southern England were combined with hourly chlorophyll concentration (a proxy for phytoplankton biomass), flow, temperature and daily sunlight data from the mid-Thames. Weekly chlorophyll data was of insufficient temporal resolution to identify the causes of short term variations in phytoplankton biomass. However, hourly chlorophyll data enabled identification of thresholds in water temperature (between 9 and 19°C) and flow (<30m(3)s(-1)) that explained the development of phytoplankton populations. Analysis showed that periods of high phytoplankton biomass and growth rate only occurred when these flow and temperature conditions were within these thresholds, and coincided with periods of long sunshine duration, indicating multiple stressor controls. Nutrient concentrations appeared to have no impact on the timing or magnitude of phytoplankton bloom development, but severe depletion of dissolved phosphorus and silicon during periods of high phytoplankton biomass may have contributed to some bloom collapses through nutrient limitation. This study indicates that for nutrient enriched rivers such as the Thames, manipulating residence time (through removing impoundments) and light/temperature (by increasing riparian tree shading) may offer more realistic solutions than reducing phosphorus concentrations for controlling excessive phytoplankton biomass.
authors.affiliation: Centre for Ecology & Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB, UK. Electronic address: mibo@ceh.ac.uk.
authors.forename: M J
authors.initials: MJ
authors.lastname: Bowes
authors.affiliation: Environment Agency, National Water Quality Instrumentation Service, Caversham Lakes, , Henley Road, Reading, Berkshire RG4 9RA, UK.
authors.forename: M
authors.initials: M
authors.lastname: Loewenthal
authors.affiliation: Centre for Ecology & Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB, UK.
authors.forename: D S
authors.initials: DS
authors.lastname: Read
authors.affiliation: Centre for Ecology & Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB, UK.
authors.forename: M G
authors.initials: MG
authors.lastname: Hutchins
authors.affiliation: Centre for Ecology & Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB, UK; Loughborough University, Geography Department, Loughborough, Leicestershire LE11 3TU, UK.
authors.forename: C
authors.initials: C
authors.lastname: Prudhomme
authors.affiliation: Centre for Ecology & Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB, UK.
authors.forename: L K
authors.initials: LK
authors.lastname: Armstrong
authors.affiliation: Centre for Ecology & Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB, UK.
authors.forename: S A
authors.initials: SA
authors.lastname: Harman
authors.affiliation: Centre for Ecology & Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB, UK.
authors.forename: H D
authors.initials: HD
authors.lastname: Wickham
authors.affiliation: Centre for Ecology & Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB, UK.
authors.forename: E
authors.initials: E
authors.lastname: Gozzard
authors.affiliation: Centre for Ecology & Hydrology, Bush Estate, Penicuik, Midlothian EH26 0QB, UK.
authors.forename: L
authors.initials: L
authors.lastname: Carvalho
mesh_terms: D002734:Chlorophyll / Q000032:analysis; D004739:England; D004784:Environmental Monitoring; D005068:Eutrophication; D010839:Phytoplankton / Q000254:growth & development*; D045483:Rivers / Q000737:chemistry*; D012621:Seasons; D013312:Stress, Physiological; D013696:Temperature; D014872:Water Movements; D060753:Water Quality
chemical_list: D002734:Chlorophyll
keywords: Algal bloom; Automated monitoring; Chlorophyll; Eutrophication; Nutrients; Water quality