FACTORS ASSOCIATED WITH DOMINANCE OF THE FILAMENTOUS GREEN-ALGA CLADOPHORA-GLOMERATA

Cladophora glomerata is a filamentous green alga dominant in many large rivers of Montana, U.S.A. I studied several factors which may be associated with nuisance (> 100 mg m-2 chl a, Welch et al., Hydrobiologia 157, 161-168, 1988) C. glomerata biomass: temperature, pH, conductivity, NH4+, soluble reactive phosphorus (SRP), NO3-, flow and epiphyte load. Samples were collected at 6 sites, ranging from an irrigation ditch to large rivers. Low flow, high NH4+ and low epiphyte loads were all correlated (P < 0.05) with high biomass. The negative correlation between flow and biomass was related to low biomass observed during early summer and autumn runoff events, and a peak biomass which occurred during summer low flow. Positive correlations of C. glomerata with NH4+ were influenced by data from a site receiving secondary sewage effluent. Nevertheless, biomass greater than 100 mg m-2 chl a was observed in other sites with 90% lower nutrient levels. These data indicate that it may be difficult to significantly lower biomass of the common weedy alga C. glomerata in rivers similar to those sampled in this study.