Report Number: 9
Year: 1979

Role of the Blue-Green Alga Nostoc muscorum as a Possible Nitrate Source to the Groundwaters of Guam

An investigation of the nitrogen-fixing, blue-green alga Nostoc muscorum Ag. as a possible contributor of nitrate to the groundwater of Guam was carried out from October 1977 to January 1979. Total potential nitrate contribution was determined by combining data obtained for ammonia excretion (a maximum of 1.39 μg/NH4/g Nostoc/hr), percent nitrogen (3.38%), and growth rates (40% increase per week) with algal biomass estimates for Guam (2.6 x 106 kg) to obtain a value of 1.3 μg NO3-N/mL rainwater. Soil percolate studies were similarly extrapolated to produce a corresponding value of 6.5 x 10-4 ug NO3-N/mL rainwater. Both values are well below those obtained from the groundwater, i.e., 2μg NO3-N/mL. It is concluded that Nostoc muscorum does not contribute significantly to the high nitrate content of Guam’s groundwater.

Deborah A. Grosenbaugh