Dust and Soil Enrichment Effects on Phytoplankton Growth and Community Composition in Subtropical Coastal Water

Nitrogen is generally thought to control coastal phytoplankton growth, and increasing nitrogen loading into coastal waters is commonly thought to be what leads to coastal eutrophication. Since dust and soils have been shown to be significant nutrient sources to coastal waters via runoff or atmospheric deposition, it is important to characterize the biological response to these inputs in diverse systems. This study focused on the impact of nutrients derived from dust and soils on phytoplankton growth and community composition in eutrophic (Baffin Bay, TX) and oligotrophic (Looe Key Reef, Florida Keys) systems of the Gulf of Mexico using experimental microcosms and field sampling. Results from field sampling in the Florida Keys showed that atmospheric dust deposition events rapidly stimulated growth of picoeukaryotes and picocyanobacteria during summer. Results from experimental microcosms conducted in Baffin Bay showed that the added inorganic and organic nutrients from the soil stimulated phytoplankton growth at times, but during times when significant phytoplankton growth was not observed, the effects may have been masked by other factors, such as competition by heterotrophic bacteria. These findings demonstrate that dust and soils can be an important nutrient source to coastal waters, but the phytoplankton response is dependent on the environmental setting. This is important to consider before attempts are made to generalize ecosystem responses to future changes in dust or soil deposition resulting from climate change.