Identifying multiple stressor controls on phytoplankton dynamics in the River Thames (UK) using high-frequency water quality data

Abstract

Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. AbstractRiver 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, southernEngland 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 o C) and flow (less than 30 m 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.

Weekly water quality monitoring data for the River Thames (UK) and its major tributaries (2009–2013): The Thames Initiative research platform

“…Peaks in chlorophyll concentrations occurred between April and June of each year, but the magnitude and duration of chlorophyll peaks varied greatly between years. The timing and magnitude of blooms has been shown to be related to SRP and dissolved silicon concentrations, sunlight duration, river flow and water temperature, and is fully described in Bowes et al (2016). The largest and sustained chlorophyll peaks are observed in the middle and lower Thames sites, and the 5 longer tributaries (River Cherwell, River Thame), especially those connected to canal systems, indicating the importance of residence time (Bowes et al, 2012a).…”

“…Since its commencement in March 2009, the Thames Initiative data has been used to quantify nutrient dynamics Skeffington et al, 2015;Wade et al, 2012), nutrient sources , phytoplankton dynamics (Bowes et al, 2012a;Bowes et al, 2016;Read et al, 2014) and bacterioplankton biodiversity . The resulting data sets 10 have been extensively used as a modelling resource (Bussi et al, 2017;Bussi et al, 2016;Hutchins et al, 2016;Whitehead et al, 2015).…”

Carbon, Nitrogen, and Phosphorus Stoichiometry and Eutrophication in River Thames Tributaries, UK

“…Many samples with high TP concentrations and TDP R above 13% did not yield Chl‐a concentrations above 30 μg L −1 . Factors other than nutrient concentrations (e.g., light, water temperature, flow/residence time) most likely limited phytoplankton accumulation during these periods (Bowes et al, 2016). All physicochemical thresholds must be met in nonlimiting ranges for phytoplankton blooms to exceed 30 μg Chl‐a L −1 .…”

Drivers of interannual and intra‐annual variability of dissolved organic carbon concentration in the River Thames between 1884 and 2013

“…The River Thames Basin is a temperate lowland catchment located in South East England. It drains a 9,948‐km 2 mineral soil–dominated catchment, from its source in the Cotswold Hills to its tidal limit at Teddington Lock upstream of London (Bowes et al, ; Marsh & Hannaford, ). It has a large urban population that has grown fourfold since the 1880s (rising from less than 1 to 3.7 million in 2007).…”