Water, acid oligotrophic

Hydrilla tolerates a wide range of ecological conditions. It occurs in water that is clear to very turbid, oligotrophic to highly eutrophic and at depths of more than 15 meters. It can tolerate alkaline to acidic conditions and moderate salinity. Its low light requirement enables it to successfully compete with other submersed aquatic plants ( ). 

A recent improvement builds on the fluorometric analysis of ammonium concentration (Holmes et al., 1999) with OPA (ortho-phthalaldehyde). Johnston et al. (2003) extracted the OPA-NH4+ derivative (1 -sulfonato-iso-indole) by soHd phase extraction and found that derivatized amino acids were not retained along with the indole on the column so that the method was specific. Since they developed the method for natural abundance work, the requisite high precision obhged analysis by CF-IRMS and its attendant high mass requirement (7.14 pmol N for a standard deviation of 0.5%o) that is difficult to achieve in oligotrophic waters. Since tracer experiments do not require such high precision, a lower mass could likely be used with the inherently lower precision GC—MS. 

EPSs can sequester nutrient materials from the surrounding environment as part of a general microbial strategy for survival under oligotrophic conditions like many of the extreme environments. EPS matrix binds and accumulates biodegradable compounds and cations from the bulk water phase. An increased production of EPS has been reported when there is lack of nutrients in the environment. The anionic nature of the exterior polysaccharides due to the presence of sulfates and uronic acids residues can help interaction with cations such as metals and capture essential minerals and nutrients. Sand and Gehrke found that there was a correlation between the presence of Fe ions within the EPS layer and the extent of metabolism in acidophilic bacteria. 

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