Nutrient limitation of the nuisance, stalk-forming diatom, <i>Didymosphenia geminata</i>, in Rocky Mountain streams

Abstract

The range of some algae has been increasing in recent years due to either internal (genetic) or external (environmental) factors that have been expanding both the nutrient and pH range at which they can survive. Didymoshenia geminata (didymo) is a species of diatom with a silica casing that can form nuisance blooms on stream beds excluding native species of algae. Understanding the water chemistry that allows for the explosive growth of this diatom is necessary in reducing the spread of the carbon rich, extra cellular stalks it produces. We believe that the addition of sulfate and phosphorus will increase both the diatom cell and stalk production. Nutrient diffusing substrates using nutrient enriched agar were placed in flower pots with 12 treatments (including a control) containing various combinations of phosphorus, sulfate, silicate, and nitrogen. One hundred and eight pots in nine blocks were then placed in the East River in Western Colorado for twenty days at which point measures of chlorophyll a, ash free dry mass (organic matter), and visual counts of both cell and stalk were taken from each sample. Our results showed that the addition of phosphorus containing treatments increased the number of didymo cells while the addition of sulfate containing treatments increased the stalk production significantly more than any other nutrient combination. Nitrogen and silicate were shown to have no significant growth effects by themselves. Since the East River is known to be phosphorus limited, we conclude the D. geminata in this water system has few cells but more stalk and so can be considered a nuisance bloom condition that can adversely affect benthic habitat.

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