Physiological ecology and structure of benthic communities in a woodland stream

Graduation date: 1966This thesis reports a portion of a general ecological study of\ud a stream under conditions of controlled flow and low levels of organic\ud enrichment. It is concerned with the effects of experimental variations\ud of light intensity and concentration of soluble organic enrichment\ud imposed on seasonal variations of temperature and total light\ud energy received upon the periphyton and benthic plants. Suitable enrichment\ud was predicated on establishment and maintenance of an abundant\ud growth of Sphaerotilus and involved the isolation and study of\ud this organism in pure cultures, in laboratory streams as well as in\ud the experimental stream.\ud Abundant growth of Sphaerotilus was obtained in cultures at\ud temperatures of 5, 10, 15, 20, 25, and 30°C while in the laboratory\ud streams and the experimental stream, the organism produced abundant\ud growths at a range of temperatures from 2 to 12°C. A variety\ud of carbon and nitrogen sources was investigated for maintenance of\ud growth of Sphaerotilus. Abundant growth was produced when the enrichment\ud included a specific nitrogen source combined with a specific\ud carbon source. A carbon-nitrogen ratio of 8 to 1 proved satisfactory\ud for maintaining Sphaerotilus in the stream.\ud An investigation of the cropping effect of stream snails indicated\ud that the presence of large numbers of snails decreased the standing\ud crop of Sphaerotilus both in the laboratory streams and the experimental\ud stream.\ud A method was devised for determining the daily mean percentages\ud of full sunlight reaching the four experimental sections of Berry\ud Creek. Approximately 4 percent reached the shaded sections and 50\ud percent reached the light sections during the summer months. The\ud range of mean saturating light intensities on the four experimental\ud sections was from 250 to 950 footcandles.\ud Methods designed to sample the plant communities in the experimental\ud sections of the stream included: artificial substrates\ud (microscope slides) used to observe the density and diversity of\ud micro-algae; a system of grids used to record distribution of the\ud plant biomass; and the removal of a portion of the stream substrate\ud for the detailed examination of the benthic community. Both microscopic\ud and macroscopic observations indicated that twice as many\ud species and greater numbers of autotrophic organisms were present\ud in the unenriched than in the enriched sections. Sub-samples of the harvested and homogenized materials\ud scoured from the stream substrate, were used to determine biomass,\ud organic matter, caloric content and pigment content. The biomasses\ud from the enriched sections were greater than those from the unenriched\ud sections, but contained large amounts of silt and were lower\ud in organic matter and caloric content. The mean percentages of organic\ud matter for the sections were: shaded, unenriched-33; light, unenriched-42; shaded, enriched-19 and light, enriched-19.\ud The range of chlorophyll a from the four experimental sections\ud was 0.03 to 0.28 g/m². The concentration of chlorophyll, when representing\ud spatial and seasonal variations, is an acceptable measure\ud of the productive ability of communities in shallow, rapidly flowing\ud streams.\ud A photosynthesis-respiration chamber was used to determine\ud primary production and community respiration for each of the experimental\ud sections. The range of rates of gross primary production\ud expressed as mean O₂,g /m²/day for the unenriched sections was\ud 0.62-2.47 and 0.53-0.59 for the enriched sections. Annual rates of\ud gross primary production in glucose equivalents ranged from 0.07\ud kg/m² for the enriched sections to 0.30 for the unenriched.\ud The stream communities were characterized as heterotrophic\ud communities with production-respiration ratios ranging from 0.47-0.65 for the unenriched and 0.16-0.20 for the enriched sections.\ud The efficiency of the fixation of light energy as organic matter was\ud 1.90-2.23 for the unenriched and 0.37-2.70 for the enriched sections.\ud The photosynthetic efficiencies of the communities on the experimental\ud sections of Berry Creek were much lower than those reported\ud for most laboratory communities, but were comparable to\ud other natural aquatic communities