Relationship between water chemistry and the distribution of the endangered aquatic quillwort Isoetes sinensis Palmer in China

The progressive decline in populations of Isoetes sinensis Palmer in China has been attributed to deteriorating water quality; however, no data have been adduced to support this assumption. In this study we identified locations in China that presently have populations of I. sinensis and locations where the species has been extirpated. We measured various water chemistry parameters at these sites, as well as at similar sites within the distribution range of I. sinensis but from where the species has never been recorded. The results indicate that distribution and occurrence of I. sinensis are closely correlated with water chemistry. Water samples drawn from habitats from where I. sinensis has been extirpated had higher concentrations of heavy metal ions, particularly chromium VI (Cr6+). In addition, these samples consistently yielded higher readings for dissolved carbon dioxide, water hardness, and concentration of nitrates.