The Role of Autochothnous Production in the Formation of Dissolved and Particulate Organics in Laboratory Streams

Abstract

The role of autochthonous production in the formation of dissolved and fine particulate organic carbon (DOC and FPOC) was studied in simplified communities in six laboratory streams. Production of DOC and FPOC by laboratory stream communities exposed to low (170 ft-c), intermediate (260 ft-c), and high (450 ft-c) light intensities was determined periodically under conditions where allochthonous inputs could be carefully monitored. Possible relationships between DOC and FPOC production and community structure, primary production, and community respiration were examined. The production of DOC by laboratory stream communities was approximately 4 to 53 percent of the total carbon fixed in photosynthesis. As light intensity, gross primary production, and periphyton standing crop decreased, the percentage of DOC produced increased. FPOC concentrations were approximately 1/3 to 1/9th DOC concentrations. The production of DOC and FPOC by the laboratory periphyton communities exposes the communities to concentrations similar to those found in natural streams .and suggests that the contribution of DOC and FPOC by periphyton communities to lotic ecosystems could be significant. Light intensity is the major factor controlling production of DOC and FPOC in the laboratory streams. Periphyton productivity and standing crop play a secondary role in the regulation of DOC and FPOC production.