EAPSI: Carbon Limitation, Algal Ecology, and Greenhouse Gases: Can Algal Blooms Fight Climate Change?

Vandam Bryce R, Morehead City NC

Investigators

Abstract

The increasing frequency and magnitude of harmful algal blooms (HABs) is a global problem, exacerbated by rising temperatures and cultural eutrophication, and is most severe in regions experiencing rapid urbanization and agricultural development. The Taihu basin, China, is a poster child of this type of region and frequently experiences severe HABs, often dominated by the neurotoxin producing cyanobacteria of the genera Microcystis. While the overall duration and size of a bloom is limited by the supply of nitrogen and phosphorus, there is growing evidence that carbon (C) availability may also limit growth in some cases. The proposed research is a collaborative project with Prof. Guangwei Zhu (Nanjing Institute of Geography and Limnology) investigating the potential for C limitation, the role it may play in phytoplankton ecology, and possible implications for global C cycling. A diverse suite of tools, including stable isotopes, diagnostic photopigments, and other biogeochemical indicators will be used to better constrain the aforementioned processes. The proposed research will advance our understanding of the Taihu system, one that is a model for other heavily impacted ecosystems worldwide. HABs, like those common to Taihu, are complex events with diverse biogeochemical drivers and the potential for numerous environmental feedbacks, many of which are poorly understood. Results from this study will help determine the degree to which one of these drivers, C limitation, may affect the bloom size and dominance of potentially toxic HAB species in this environmentally and economically vital lake. Inorganic C fixation during dense phytoplankton blooms can reach extremely high rates, removing dissolved CO2 faster than can be supplied by air-sea exchange and respiration. Species capable of assimilating inorganic C as bicarbonate (H2CO3) such as the toxin-producing Microcystis will therefore be at a competitive advantage when CO2 becomes limiting. In the proposed research, ?Ý13C of phytoplankton will be used as an indicator of C sources and acquisition strategies, while an analysis of photopigments by HPLC will be used to investigate the effects of C availability on phytoplankton ecology during the progression of a bloom in the hypereutrophic lake Taihu, China. This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Chinese Ministry of Science and Technology.