Analysis of Chemical Modifications of Ecosystems by Means of Microalgae

In marine ecosystems, microalgae are important components as they transform large quantities of inorganic compounds into biomass thereby impacting environmental chemistry. Of particular relevance is phytoplankton’s sequestration of atmospheric CO₂, a greenhouse gas, and nitrate, one cause of harmful algal blooms. On the other hand, microalgae sensitively respond to changes in their chemical environment, which initiates adaptations of their chemical composition and physical parameters. Analytical methodologies were developed in this study that utilize microalgae’s adaptation as a novel approach for in-situ environmental monitoring.To analyze the chemical composition and physical parameters of live microalgae cells (Nannochloropsis oculata), ATR FT-IR spectroscopy has been employed. From time-series IR spectra, the formation of biosediment can be monitored and it has been shown that nutrient availability has an observable impact. Since biosediment formation is governed by several biological parameters, this enables studies of the chemical environment’s impact on physical parameters of the cells.Moreover, the spectroscopic signatures of microalgae grown under 25 different CO₂ and NO_3^- mixtures (200 – 600 ppm CO₂, and 0.35 – 0.75 mM NO_3^-) have been used with a novel nonlinear modeling methodology coined ‘Predictor Surfaces’ that relates the nonlinear responses of the cells to their chemical environment. This approach was used to measure CO2 concentrations in the atmosphere above the algae cultures as well as dissolved nitrate concentrations within the growth medium simultaneously. The achieved precision of concentration predictions were a few percent of the measurement range. The effects of these pollutants on the formation of biomass were also determined and it was found that the cells’ growth rate was strongly, and nonlinearly, dependent on the availably of nitrate. In addition, it was found that algae cultures become more active when exposed to a decrease in atmospheric carbon dioxide levels. This methodology will open new approaches to study the link between concentration levels of anthropogenic pollutants within an ecosystem and their biological impacts.