Interbiome comparison of stream ecosystem dynamics

Studies were conducted in four distinct geographic areas (biomes/sites) in northernUnited States to examine changes in key ecosystem parameters: benthic organic matter (BOM),transported organic matter (TOM), community production and respiration, leaf pack decomposition,and functional feeding-group composition along gradients of increasing stream size. Four stationsranging from headwaters (1st or 2nd order) to midsized rivers (5th to 7th order) were examined ateach site using comparable methods. The results for each parameter are presented and discussed inlight of the River Continuum Concept of Vannote et al. (1980). The postulated gradual change in astream ecosystem's structure and function is supported by this study. However, regional and localdeviations occur as a result of variations in the influence of: (1) watershed climate and geology, (2)riparian conditions, (3) tributaries, and (4) location-specific lithology and geomorphology. In partic-ular, the continuum framework must be visualized as a sliding scale which is shifted upstream ordownstream depending on macroenvironmental forces (I and 2) or reset following the application ofmore localized "micro"-environmental influences (3 and 4). Analysis of interactions between BOMand TOM permitted evaluation of stream retentiveness for organic matter. Headwaters generally weremost retentive and downstream reaches the least. Estimates of organic matter turnover times rangedbetween 0.2 and 14 yr, and commonly were 1-4 yr. Both turnover times and distances were deter-mined primarily by the interaction between current velocity and stream retention. Biological processesplayed a secondary role. However, the streams varied considerably in their spiraling of organic matterdue to differences in the interplay between retentiveness and biological activity. Differences in therelative importance of retention mechanisms along the continuum suggest that headwater streamecosystems may be functionally more stable, at least to physical disturbances, than are their inter-mediate river counterparts.
Key words: benthic organic matter; carbon cycling; community metabolism; Idaho; invertebratefunctional groups; Michigan; Oregon; Pennsylvania; River Continuum Concept; seston; spiraling;stream ecosystems; transported organic matter.