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

Abstract

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 (CR 24 ) increased with downstream direction on all systems. Net daily metabolism (NDM, or GPP -CR 2 4 ) shifted from heterotrophy (-NDM, GPP < CR 24 ) to autotrophy (+NDM, GPP > CR 2 4 ) 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, CR 24 and NDM ranged from 0.16 to 3.37, 0.36 to 2.88 and -0.73 to 0.50 g 02 m 2 d 1, respectively. Metabolic rates were usually high in PA and Ml (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.

Longitudinal patterns of metabolism in a southern Appalachian river

“…This result is similar to other studies of forested streams (Minshall et al 1983, Naiman 1983, Bott et al 1985; however, metabolism in grassland rivers has generally indicated little longitudinal trend in net metabolism because of high GPP in upstream river reaches where there is no gallery forest (Wiley et al 1990, Young andHuryn 1996). Meyer and Edwards (1990) suggested that NEP was a more useful indicator of organic matter transitions than P/R when considering C budgets in stream systems because NEP demonstrates the amount of C deficit or surplus.…”

“…Walker Camp Prong, in the Great Smoky Mountain National Park, Tennessee, had the lowest NPP of streams compared here (Mulholland et al 1986). Although NPP at our upstream sites was low, our downstream sites had NPP values that were higher than other eastern US streams (Hoskin 1959, Hornberger et al 1977, Sumner and Fisher 1979, Hill and Webster 1982, Bott et al 1985 but lower than streams from the midwest (Bott et al 1985, Wiley et al 1990). NPP at our most downstream site was very similar to the New River, Virginia, another mid-sized southern Appalachian river (Hill and Webster 1982).…”

“…Vannote et al (1980), in their river continuum concept (RCC), suggested that ecosystem metabolism shifts from heterotrophy to autotrophy along a continuum from headwaters to downstream. Many studies have demonstrated support for the RCC, particularly in regions where headwater streams are forested (Bott et al 1985, Naiman et al 1987, Minshall et al 1992. In these regions, mid-sized rivers (4th-to 6th-order) generally represent metabolic transition zones between forested heterotrophic streams [Volume 22 M. E. MCTAMMANY ET AL. and open-canopied autotrophic rivers (Vannote et al 1980, Bott et al 1985, Naiman et al 1987, Minshall et al 1992.…”

“…Many studies have demonstrated support for the RCC, particularly in regions where headwater streams are forested (Bott et al 1985, Naiman et al 1987, Minshall et al 1992. In these regions, mid-sized rivers (4th-to 6th-order) generally represent metabolic transition zones between forested heterotrophic streams [Volume 22 M. E. MCTAMMANY ET AL. and open-canopied autotrophic rivers (Vannote et al 1980, Bott et al 1985, Naiman et al 1987, Minshall et al 1992. By studying metabolism in 4th-to 6th-order stream reaches, we can determine the location of the heterotrophic to autotrophic transition and associated longitudinal changes in C supply and demand.…”

Eutrophication and trophic state in rivers and streams

“…Heterotrophic state was considerably less variable, ranging about 10-fold with the central one third of the distribution falling between 6.7 and 8.3 g O 2 m Ϫ2 d Ϫ1 (Table 5). Bott et al (1985) reviewed studies of ϳ70 streams with Fig. 2.…”