Field observations show that microcystin concentration increases when phosphorus (without nitrogen) is reduced
Cyanobacterial harmful algae blooms (e.g. those of Microcystis) and their toxins (e.g. microcystins - MCs) threaten the safe use of lakes for drinking and recreation and this hazard is expected to increase in a warming climate. This is an urgent environmental problem, but there is no scientific consensus about the best management approach. Reducing inputs of the growth-limiting nutrient phosphorous (P) can be successful in decreasing cyanobacterial biomass but the effect on toxin concentration is unclear. The underlying mechanisms, and evidence from laboratory experiments and models suggests toxin concentrations may actually increase. What has been missing is field data to support or refute this hypothesis. Here, we present two analyses of the National Lakes Assessment (NLA) dataset. The first focuses on changes in MC concentration within individual lakes across time. In the second analysis, we applied Generalized Additive Models (GAMs) across all lakes and time points. Both analyses show that when P only is reduced, Chlorophyll a decreases but MC concentration does not decrease proportionally. In fact, MC concentration increases for moderate P reductions and only decreases for more extreme P reductions. A dual reduction of nitrogen and P, however, results in a decrease of biomass and toxins. This supports a management approach of dual nutrient reduction.
Presentation Preference: Oral
Primary Presenter: Charlotte Schampera, TU Berlin (schampera@tu-berlin.de)
Authors:
Charlotte Schampera, TU Berlin (schampera@tu-berlin.de)
Julian Merder, Carnegie Institution for Science (jmerder@carnegiescience.edu)
Thomas Niemeyer, TU Berlin (t.niemeyer@campus.tu-berlin.de)
Julia Pries, TU Berlin (julia-pries1@web.de)
Ferdi Hellweger, TU Berlin (ferdi.hellweger@tu-berlin.de)
Field observations show that microcystin concentration increases when phosphorus (without nitrogen) is reduced
Category
Scientific Sessions > SS39 - Taking the pulse of phosphorus sustainability: challenges and solutions across the freshwater to marine continuum
Description
Time: 05:15 PM
Date: 31/3/2025
Room: W205CD