SYMPOSIA PAPER Published: 01 January 1969

Uptake and Assimilation of Nitrogen in Microecological Systems


A study of biological effects on water quality utilized recirculating laboratory streams. The sole nitrogen source in one stream was Ca(NO3)2 and in the other was yeast extract. Soluble organic nitrogen from the yeast extract decreased rapidly accompanied by large increases in bacteria and in ammonia. Nitrite and nitrate increased slightly. Bacteria and combined nitrogen decreased rapidly after the initial rise. In the stream with the inorganic nitrogen medium, about half of the nitrate disappeared in two weeks, and nitrate was undetectable after the third week. Bacterial counts were relatively low and constant. Periphyton increased in both streams as nutrients decreased, reaching quasi steady states after about four weeks. The rate of biomass increase was greater in the inorganic medium. Chlorophyll increased rapidly in both streams, reached a maximum the third week, then decreased.

Nitrogen assimilation followed characteristic patterns. Nitrate was directly assimilated by algae. A slight denitrification occurred at high-nitrate concentrations. Organic nitrogen was converted to ammonia by proteolytic bacteria, during which process some nitrogen might have escaped as gaseous ammonia. Ammonia from organic compounds was partly assimilated by algae and partly nitrified by bacteria. Nitrate of bacterial origin was assimilated by algae. Nitrification apparently was not of major importance in converting organic nitrogen to algal biomass.

Laboratory streams simulate natural streams in diurnal cycles of pH and dissolved oxygen, in periphyton growth rate and biomass, and in assimilation of nutrients. Use of model systems to study natural processes under controlled conditions appears justified.

Author Information

Ehrlich, GG
U.S. Geological Survey, Menlo Park, Calif.
Slack, KV
U.S. Geological Survey, Menlo Park, Calif.
Price: $25.00
Contact Sales
Reprints and Permissions
Reprints and copyright permissions can be requested through the
Copyright Clearance Center
Developed by Committee: D19
Pages: 11–23
DOI: 10.1520/STP32025S
ISBN-EB: 978-0-8031-4579-5
ISBN-13: 978-0-8031-0066-4