Shallow freshwater ecosystems are experiencing increasingly frequent blooms of macroalgal blanket weed, which can cause surface proliferations that can negatively impact aquatic ecosystem functions and aesthetics. Although elevated nutrient concentrations in freshwaters are a pre-requisite for excessive algal growth, much less is understood about other abiotic factors controlling bloom growth rate and extents. To address this knowledge gap, we carried out a series of 990L indoor mesocosm (Limnotron) experiments to investigate the effects of light intensity, photoperiod and water temperature on the growth and surface bloom formation of blanket weed. These experiments combined underwater and surface photography to quantify change in algal area over time. The results demonstrated the existence of a minimum threshold of photoperiod and light intensity for bloom formation and substantial algal growth. Surface blooms did not occur when the photoperiod was too short, suggesting day length is a limiting factor. We also found that temperatures between 16-22 degrees Celsius were the thermal optimum for algae to form surface blooms, whilst the highest growth rate of algae on the sediment occurred at 14 degrees Celsius. With the increasing impact of climate change on freshwater ecosystems, these data will help predict the occurrence of surface blooms and assess which waterbodies could be under threat of blanket weed blooms in the future.

Primary Presenter: Hannah Kemp, University of Nottingham (hannah.kemp@nottingham.ac.uk)

Authors:

Hannah Kemp, University of Nottingham, UK  (hannah.kemp@nottingham.ac.uk)

Stephen Dugdale, University of Nottingham, UK  (stephen.dugdale@nottingham.ac.uk)

Alexandra Zieritz, University of Nottingham, UK  (alexandra.zieritz@nottingham.ac.uk)

Nico Helmsing, Netherlands Institute of Ecology (NIOO-KNAW), The Netherlands  (n.helmsing@nioo.knaw.nl)

Suzanne Wiezer, Netherlands Institute of Ecology (NIOO-KNAW), The Netherlands  (s.wiezer@nioo.knaw.nl)

Lisette de Senerpont Domis, Netherlands Institute of Ecology (NIOO-KNAW), The Netherlands  (l.desenerpontdomis@nioo.knaw.nl)

Stephen Maberly, UK Centre for Ecology & Hydrology, Lancaster Environment Centre, UK   (scm@ceh.ac.uk)

Martyn Kelly, Bowburn Consultancy, UK  (mgkelly@bowburn-consultancy.co.uk)

Suzanne McGowan, Netherlands Institute of Ecology (NIOO-KNAW), The Netherlands  (s.mcgowan@nioo.knaw.nl)