Benthic community metabolism in four temperate stream systems: an inter-biome comparison and evaluation of the river continuum concept

To test the hypothesis included in the river continuum concept that a transition in community metabolism would occur from a predominance of heterotrophy in headwaters to a predominance of autotrophy in middle reaches, with a return to heterotrophy further downstream, a study was carried out on benthic community metabolism in 4 streams in different types of biome in the U.S.A., including eastern deciduous forest, high desert, and western coniferous forest. Both gross primary productivity and community respiration increased in the downstream direction in all the streams studied, and net daily metabolism shifted from heterotrophy to autotrophy in a downstream direction, supporting the hypothesis. However, site-specific factors affected this trend. The most important factors causing variance in multiple linear regression analyses of the combined metabolism data from all sites were indicators of stream size, photosynthetically-active radiation, temperature, and chlorophyll-a concentration.