Longitudinal Structure of an Agricultural Prairie River System and its Relationship to Current Stream Ecosystem Theory

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Abstract
The largescale structure of an agriculturally developed prarie river system in central Illinois was examined and compared with predictions from current stream ecosystem theory. High rates of primary productivity (> 15 g carbon .cntdot. m-2 .cntdot. d-1) were characteristic of the watershed, although longitudinal pattern in riparian vegetation, stream temperature, and primary productivity were inverted relative to typical streams in forested uplands. Empirical models of gross primary production and community respiration were developed. Light availability, mediated by both channel shading and turbidity, appeared to be the principal factor limiting primary productivity. Both nitrate and orthophosphorus were found in high concentrations throughout the watershed. Largescale patterns in nutrient availability suggest that landuse patterns, and particularly urbanization, strongly affected spatial and temporal distributions of both nutrients. Differences between prarie river systems and "prototype" structures envisioned by the River Continuum Concept (RCC) derive from the descriptive nature of the RCC, and its inability to incorporate nonstandard distributions of key driving variables. The use of empirical modelling in stream ecosystem studies is discussed.