Freshwater Benthic Algal Response to Elevated Carbon Dioxide | mfield

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Freshwater Benthic Algal Response to Elevated Carbon Dioxide

Project Abstract:

The effects of elevated atmospheric carbon dioxide on freshwater algae are relatively understudied, though terrestrial plants grown under elevated atmospheric carbon dioxide concentrations have been shown to produce increased biomass, structural compounds and chemical defenses. If similar effects occur for freshwater algae, impacts would propagate through other trophic levels of aquatic ecosystems. In this study, flow-through systems will be used to simulate a temperate stream. Benthic algae will be grown under ambient (380 ppm CO2) and elevated (1,000 ppm CO2, a worst-case scenario under a fossil fuel-intensive future world) CO2 conditions. Changes in biomass, community dynamics, pigment production, and chemical defenses will be quantified. The study will improve understanding of elevated CO2 effects on a freshwater ecosystem and contribute towards understanding of the role of freshwater algae in carbon capture and storage and in the future global carbon cycle.

Methods:

<p> <style type="text/css"> </style> </p><p style="margin-bottom: 0in;">The study will occur at the Stream Research Facility at UMBS and will build on the preliminary data acquired during 2009 and 2010. Stream water from the East Branch of the Maple River will be pumped through artificial stream channels. Half of the channels will be provided with a constant carbon dioxide concentration of approximately 1,000 ppm, and the other half will serve as the control. Sterile ceramic tiles will be placed in each channel to provide colonization substrate for benthic species; tiles will be processed weekly for 6 weeks. Measurements will include temperature, light and pH (daily), dissolved inorganic carbon (biweekly), and dissolved inorganic nitrogen and dissolved inorganic phosphorus (weekly).</p><p style="margin-bottom: 0in;">Samples will be processed as summarized below.</p><p style="margin-left: 0.25in; margin-bottom: 0in;"><i>Hypothesis 1: Elevated CO</i><sub><i>2</i></sub><i> will affect benthic algal abundance and community composition.</i></p><p style="margin-left: 0.5in; margin-bottom: 0in;">Algal biomass will be determined through dry mass and ash-free dry mass measurements, and permanent diatom slides will be made for use in determining shifts in diatom species dominance. Samples from each stream channel will be preserved in formalin for use in determining changes in algal species or group dominance through microscopy.</p><p style="text-indent: 0.25in; margin-bottom: 0in;"><i>Hypothesis 2: Algal cell composition will change under elevated CO</i><sub><i>2</i></sub><i> conditions.</i></p><p style="margin-left: 0.5in; margin-bottom: 0in;">To determine elemental composition, nitrogen and phosphorus content will be measured and C:N:P will be calculated to compare ratios between treatments. A combination of high-performance liquid chromatography (HPLC) and absorbance spectroscopy will be used to separate and identify pigments that are diagnostic of specific algal groups and taxa.</p><p style="margin-left: 0.25in; margin-bottom: 0in;"><i>Hypothesis 3: Carbon fixation activity of freshwater algae will be enhanced under elevated CO</i><sub><i>2</i></sub><i>.</i></p><p align="JUSTIFY" style="margin-left: 0.5in; margin-bottom: 0in;"><sup>14</sup>C assays and dot blot hybridization will be used to determine RubisCO diversity and abundance under ambient and elevated CO<sub>2 </sub>conditions, to corroborate microscopy and as a measure of carbon fixation potential.</p>

Funding agency:

NSF-IGERT