Diatom community responses to environmental variables in tropical island streams

TitleDiatom community responses to environmental variables in tropical island streams
Publication TypeThesis
Year of Publication2008
AuthorsBryan, B
Number of Pages295
UniversityUniversity of Puerto Rico
CityRio Piedras
Accession NumberLUQ.1098

Diatoms have been recognized as potentially useful biological indicators of stream water quality because of their position at the foundation of the food web and their widely variable responses to physicochemical parameters such as salinity and nutrients among species. The hypotheses for this study were (1) diatoms could be used to reflect changes in water chemistry among sites with different land uses in one river; (2) these patterns would be consistent among several rivers with varying geology and climate; (3) the influence of major ions versus inorganic nutrients could be separated with enrichment of artificial streams. A survey of diatom communities along the Rio Mameyes determined that a temperate zone pollution tolerance index (PTI) detected community shifts that were correlated with changes in chemistry and apparently with surrounding land use. Confirmation of this pattern was sought in five rivers around the island with unique geoclimatic combinations. There was a relationship between shifts in the PTI and changes in chemistry, although this was not linked to land use. The artificial stream experiment involved additions of salt, ammonium, nitrate, and phosphate to channels containing cultivated diatoms. None of the species encountered were negatively impacted by any of the treatments. The number of species with higher sensitivities actually increased in very high concentrations of phosphate. It was concluded from the surveys of the island rivers and the artificial stream experiment that (1) the response of diatom communities to changes in chemistry can be characterized with the PTI; (2) differences in chemistry and diatom communities were stronger among watersheds than land uses (3) the diatoms encountered were indifferent to salt, and thus nutrients are stronger than major ions in driving community shifts. The negative impact that excessive nutrients have on diatom communities in the field was not seen in the artificial streams and therefore must be due to a combination of factors associated with increased nitrogen and phosphorus. The paucity of knowledge of Puerto Rican diatom species and their ecologies has been greatly expanded. Ecological limits and possible high endemism should be verified with more surveys around the island and the Caribbean.