Successional changes associated with benthic assemblages in experimental streams Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3x816q319

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  • Experimental streams constructed by the Weyerhaeuser Company, Tacoma, Washington, at Kalama Springs, Washington, were used to observe successional changes in the benthos. Community changes were observed relative to experimental manipulations of light intensity and nitrate concentration in two experiments. The development of benthic assemblages was followed for 150 days after a simulated freshet that removed most of the plant and animal biomass from the streams. The development of the benthic assemblages was quantified with measures of composite properties (organic matter and pigment concentrations); primary production and community respiration; the taxonomic structure, biomass, and export of plants; and the taxonomic structure, biomass, and export of animals. A photosynthesis-respiration chamber was used to measure the rate of benthic primary production at light saturation and to establish the relationship between primary production and light intensity. Multivariate analyses (discriminant and principal components analyses) were used to analyze temporal changes in algal taxonomic structure within a riffle and differences among riffles exposed to different experimental conditions. Successional changes in benthic assemblages that occurred in all riffles were described by a series of three stages taxonomically distinguished by Diatoma hiemale v. mesodon (stage I), chironomids (stage II), and Zygnema (stage III). These stages were characterized by a rapid increase of algae (stage I), an increase of faunal biomass and export (stage II), and a subsequent increase of algae with a decrease in faunal export (stage III). The rate of primary production was higher in riffles exposed to high solar radiation than riffles receiving low radiation, and higher in the nitrate-enriched riffles than in the unenriched riffles if solar radiation was high. High algal biomasses (stage I and III) and high faunal export (stage II) were observed in riffles subjected to relatively high solar radiation. The behavior of the benthic assemblages with time was interpreted as the reorganization and stabilization of two levels of organization - the benthos and stream system - within the structural hierarchy of the lotic ecosystem. The developmental stages were the reorganization of the producer (algal) subsystem that resulted in an increase in primary production (stage I), stabilization of the producer and consumer (faunal)subsystems of the benthos system (stage II), reorganization of the benthos system that resulted in an increase in primary production and a decrease in community respiration (stage III), and stabilization of the stream system (hypothesized stage IV). Conceptually, benthic assemblages of natural streams are perceived to exist in a tension between environmental stress and the evolution of hierarchical organization that represents the decomposition and composition of structure in the lotic ecosystem, respectively.
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