Predicting when a drinking water source will be affected by taste and odour (T&O) metabolites, produced by cyanobacteria, is challenging yet critical for supply management. A low ratio total nitrogen to total phosphorus (TN:TP) can select for cyanobacteria growth, and high ammonium to nitrate ratios (NH₄⁺:NO₃^-) can trigger T&O formation. Water from a drinking water reservoir in the UK, with a realistic phytoplankton community, was incubated for 23 days at 20°C with 12-hour day-night cycles. Oxygen was measured continuously as a proxy for primary productivity. Six nutrient treatments were added, three NH₄⁺:NO₃^- ratios (high = 1:1, medium = 1:10 and low = 1:100) combined with two TN:TP ratios (high = 100:1 and low = 10:1), representing observed conditions whilst targeting the extremes. Productivity at high NH₄⁺:NO₃^- and low TN:TP increased after 7 days, peaked at 2 weeks, and then declined. Both treatments with low NH₄⁺:NO₃^- took 2 to 3 weeks to become productive, but productivity was maintained for longer and reached higher levels. Elevated T&O concentrations occurred in four treatments; low NH₄⁺:NO₃^- with high or low TN:TP ratios as well as medium or high NH₄⁺:NO₃^- with low TN:TP. To predict T&O events, nutrient ratios, concentrations, and a proxy for in situ primary productivity must be measured. The difference in lag-time between NH₄⁺ and NO₃^- addition and subsequent primary productivity, indicate that direct relationships might disguise the real process. Therefore, laboratory and in situ studies should be undertaken to understand the site-specific drivers of T&O events.

Primary Presenter: Inge Elfferich, Cardiff University (elfferichi@cardiff.ac.uk)

Authors:

Inge Elfferich, Cardiff University  (elfferichi@cardiff.ac.uk)

Elizabeth Bagshaw, University of Bristol, School of Geographical Sciences  (eb1689@bristol.ac.uk)

Rupert Perkins, Cardiff University  (perkinsr@cardiff.ac.uk)

Gemma Godwin, Dwr Cymru Welsh Water  (gemma.godwin@dwrcymru.com)