Tropical Diatoms of Costa Rica
Ecology

Ecology

Diatom community changes in geothermal and nongeothermal streams

The second aspect of this research examines periphyton community structure and the relationship with solute concentrations, primarily phosphorus. Questions regarding differences among high and low solute streams and seasonal differences among streams will be addressed with this data.

We have been examining patterns of diatom response in light-limited streams in response to solute differences. Because of geological activity, some streams at La Selva Biological Station receive point-source groundwater high in solutes (e.g., P, K, Ca, Si, and Mn). Sites chosen along a phosphorus gradient have been sampled seasonally. Whereas algal cell densities are similar in sites along this gradient, there are dramatic differences in community composition among high or low solute sites. Our preliminary results suggest that a suite of solutes, including phosphorus, most likely influences diatom assemblages in high-solute streams. The species assemblage is composed of many taxa which are associated with high conductivity systems. The low-solute streams have diatom assemblages characteristic of poorly buffered, oligotrophic conditions, and, more importantly, low pH (e.g., Stenopterobia spp., Eunotia spp., and Frustulia spp.). While these low-solute streams generally have a circumneutral pH, the diatom community is indicative of poor buffering capacity. Preliminary work by Britt Carlson (REU research) also demonstrates that light levels may not be important in predicting diatom assemblages in these low-light streams.