Water quality data
The water quality datasets accessed in MaRIUS include:
- Complete 2 year water-quality data set of River Thames at Swinford
- Complete 2 year water quality data set of Farmoor reservoir
- Accompanying phytoplankton characterisation by flow cytometry
Water quality data for River Thames at Swinford – Phosphorus concentration.
Water quality data for River Thames at Swinford – Chlorophyll concentration.
Task B4 generated the weekly water quality and biological data from two sites on the River Thames and Farmoor reservoir. These were the key data required to investigate how changes in nutrients and flow would affect phytoplankton ecology and the likelihood of algal blooms. Samples were manually recorded at weekly intervals and analysed at the CEH Wallingford laboratories using standard protocols. Phytoplankton was characterised by Flow Cytometry.
Water quality modelling
- Droughts cause reduction in low flows and therefore increase phosphorus concentration in the river due to decreased availability of water to dilute wastewater effluents.
- Climate change is expected to increase drought severity and phosphorus concentration in rivers, but the response of phytoplankton varies depending on the functional group.
River water quality is fundamental for ecosystems and water supply. Yet, the impacts of droughts on river water quality are poorly understood, due to lack of extensive data and the non-linear interactions between different natural and human-induced processes. The objective of this work package is to understand how droughts affect nutrients, sediment and phytoplankton in river systems, taking into account the further complexity added by climate change and anthropogenic pressures.
In this task, the River Thames is used as a case-study, due to its importance as a freshwater supplier and effluent recipient and to its high conservation value. Hydrological and water quality models are developed to understand the system behaviours. These models are then used to explore the impact of climate variability and land-use change on river water quality. Different methodological approaches are used, such as coupling the water quality models with climate models, or exploring the sensitivity of the water quality models to the climatic input (scenario-neutral methodology).
Conceptual scheme of the scenario-neutral methodology applied to a sediment model.
Droughts cause an increase phosphorus concentration in the river due to decreased availability of water to dilute wastewater effluents.
Under current land-use and phosphorus removal mitigation strategies, average phosphorus concentrations range from 0.11 to 0.16 mg L-1, being inversely proportional to precipitation due to the dominance of sewage effluent inputs at this site (Bowes et al., 2015). When an increase in agricultural land use is applied, the average phosphorus concentration increases up to between 0.15 and 0.18 mg L-1. In this case, phosphorus concentration is still inversely proportional to rainfall, although for increases in precipitation greater than 20% this trend inverts and precipitation is directly proportional to phosphorus concentration. This suggests a shift from a point source-dominated to a diffuse source-dominated regime, due to the joint effect of increased rainfall and expansion of agricultural land. The average phosphorus concentration drops to 0.07-0.09 mg L-1 if a combined phosphorus removal strategy is implemented.
Effect of combined climate alteration (precipitation and temperature), land-use change and phosphorus removal mitigation strategies on the average phosphorus content of the River Thames (UK) at Runnymede. Circles: current conditions of land-use and current phosphorus removal mitigation strategies; squares: expansion of agricultural land) and current phosphorus removal mitigation strategies; diamonds: expansion of agricultural land and optimal phosphorus removal mitigation strategies (combined reduction of fertiliser and phosphorus removal from wastewater). The horizontal solid line represents the current average phosphorus concentration. The red rectangle defines the space of precipitation changes forecast by the UKCP09
Climate change impacts
Climate change is expected to increase drought severity and phosphorus concentration in rivers, but the response of phytoplankton varies depending on the functional group.
Precipitation, and hence flow, is the key control for Microcystis-like cyanobacteria and diatoms and large chlorophytes: i.e. phytoplankton concentration is much more sensitive to changes in precipitation than to changes in temperature. Temperature is the main control for cyanobacteria – although cyanobacteria are also sensitive, to a lesser extent, to changes in precipitation. Picoalgae appear to be driven by both precipitation and temperature. Similarly, Chlorophytes are driven by both climatic stressors, although for low values of temperature change, precipitation seems to prevail as the key control.
The sensitivity of phytoplankton to climate change is smaller for diatoms, chlorophytes and Microcystis-like cyanobacteria and higher for picoalgae and cyanobacteria. For example, while cyanobacteria can double their average concentration in reach 1 for an increase in temperature of +3°C, chlorophytes only show an increase between 5 and 10%.
Chlorophytes, diatoms and Microcystis-like cyanobacteria decrease their concentration along with precipitation, while cyanobacteria and picoalgae increase it.
Change in the average phytoplankton abundance in the River Thames (UK) in reach 1 due to climate alteration (precipitation and temperature), under current conditions of land-use and current phosphorus removal mitigation strategies. In each plot, the x-axis represents the alteration in temperature (°C), the y-axis the alteration in precipitation (%), while the resulting change in average phytoplankton cell abundance is represented with colours. Each plot is associated with a different phytoplankton group (diatoms, chlorophytes, picoalgale, cyanobacteria and Microcystis-like cyanobacteria). The black dots represent the changes in precipitation and temperature of 10,000 UKCP09 change factors.
- G. Whitehead, G. Bussi, M.J. Bowes, D.S. Read, M.G. Hutchins, J.A. Elliott, S.J. Dadson. 2015. Dynamic modelling of multiple phytoplankton groups in rivers with an application to the Thames River system in the UK. Environmental Modelling & Software. 74, 75-91. doi:10.1016/j.envsoft.2015.09.010.
- G. Bussi, P.G. Whitehead, M.J. Bowes, D.S. Read, C. Prudhomme, S.J. Dadson. 2016. Impacts of climate change, land-use change and phosphorus reduction on phytoplankton in the River Thames (UK). Science of the Total Environment. doi:10.1016/j.scitotenv.2016.02.109.
- G. Bussi, S.J. Dadson, M.J. Bowes, P.G. Whitehead. 2016. Using sediment rating curves to identify the effect of seasonal and inter-annual disturbances on the sediment transport of the River Thames (UK). Journal of Hydrological Engineering.
- G. Bussi, S.J. Dadson, C. Prudhomme, P.G. Whitehead. 2016. Climate and land-use change impacts on sediment transport in the River Thames (UK). Journal of Hydrology.
- G. Bussi, S. Dadson. 2015. Analysis of the fine sediment dynamics in the River Thames catchment (UK) using a sediment rating curve approach. Geophysical Research Abstracts. EGU General Assembly 2015. Vienna, Austria. April 2015. ISSN 1029-7006. Open presentation
- G. Bussi, P. Whitehead, M. Bowes, D. Read, S. Dadson. 2015. Dynamic modelling of five different phytoplankton groups in the River Thames (UK). Geophysical Research Abstracts. EGU General Assembly 2015. Vienna, Austria. April 2015. ISSN 1029-7006. Open poster
- G. Bussi, P. Whitehead, S. Dadson. 2016. Modelling climate change, land-use change and phosphorus reduction impacts on phytoplankton in the River Thames (UK). Geophysical Research Abstracts. EGU General Assembly 2016. Vienna, Austria. April 2016. ISSN 1029-7006. Open presentation
- G. Bussi, S. Dadson, P. Whitehead. 2016. Modelling the impacts of climate and land-use change on the sediment transport of the River Thames (UK). Geophysical Research Abstracts. EGU General Assembly 2016. Vienna, Austria. April 2016. ISSN 1029-7006. Open poster