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

Benthic community metabolism was studied on four stream systems located in different biomes in the United States: the eastern deciduous forest (Pennsylvania, PA, and Michigan, MI), the high desert (Idaho, ID), and the coniferous forest (Oregon, OR). Studies were designed to test the hypothesis advanced within the River Continuum Concept that a transition in community metabolism will occur from a predominance of heterotrophy in headwaters to a predominance of autotrophy in mid-sized reaches, with a return to heterotrophy further downstream. Both gross primary productivity (GPP) and community respiration (CR₂₄) increased with downstream direction on all systems. Net daily metabolism (NDM, or GPP – CR₂₄) shifted from heterotrophy (–NDM, GPP < CR₂₄) to autotrophy (+NDM, GPP > CR₂₄) with downstream direction at all sites, supporting the hypothesis. Annual metabolism in the most upstream reach of all sites was dominated by respiration; however, the farthest downstream reach was not necessarily the most autotrophic. Site-specific factors affected manifestation of the trend. Photosynthesis predominated annual metabolism in reaches (designated 1–4 in order of increasing size) 2–4 in ID, 3 and 4 in OR, and 4 in MI. In PA annual photosynthesis was slightly greater than respiration only at Station 3. Photosynthesis was predominant most consistently in ID and respiration most often in PA. About half the reaches that were heterotrophic annually were autotrophic at one or more seasons. Annual means of benthic GPP, CR₂₄ and NDM ranged from 0.16 to 3.37, 0.36 to 2.88 and –0.73 to 0.50 g O₂ · m² · d¹, respectively. Metabolic rates were usually high in PA and MI (and sometimes ID) and almost always lowest in OR. Parameters accounting for most 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.