Hydrology Research In Press, Uncorrected Proof © IWA Publishing 2012  |  doi:10.2166/nh.2012.029

Reconciling observed and modelled phytoplankton dynamics in a major lowland UK river, the Thames

Attila N. Lázár, A. J. Wade, P. G. Whitehead, C. Neal and M. Loewenthal

School of Human and Environmental Sciences, University of Reading, Reading, RG6 6AB, UK E-mail: a.n.lazar@reading.ac.uk
School of Geography and the Environment, University of Oxford, Oxford, OX1 3QY, UK
Centre for Ecology and Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, OX10 8BB, UK
Environment Agency, Reading, RG2 0SF, UK

First received 00 Month 0000; accepted in revised form 00 Month 0000. Available online 27 April 2012

This study aims to elucidate the key mechanisms controlling phytoplankton growth and decay within the Thames basin through the application of a modified version of an established river-algal model and comparison with observed stream water chlorophyll-a concentrations. The River Thames showed a distinct simulated phytoplankton seasonality and behaviour having high spring, moderate summer and low autumn chlorophyll-a concentrations. Three main sections were identified along the River Thames with different phytoplankton abundance and seasonality: (i) low chlorophyll-a concentrations from source to Newbridge; (ii) steep concentration increase between Newbridge and Sutton; and (iii) high concentrations with a moderate increase in concentration from Sutton to the end of the study area (Maidenhead). However, local hydrologic (e.g. locks) and other conditions (e.g. radiation, water depth, grazer dynamics, etc.) affected the simulated growth and losses. The model achieved good simulation results during both calibration and testing through a range of hydrological and nutrient conditions. Simulated phytoplankton growth was controlled predominantly by residence time, but during medium–low flow periods available light, water temperature and herbivorous grazing defined algal community development. These results challenge the perceived importance of in-stream nutrient concentrations as the perceived primary control on phytoplankton growth and death.

Keywords: algae; dynamic model; environmental controls; phytoplankton; River Thames; seasonality

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