Longitudinal Patterns of Ecosystem Processes and Community Structure in a Subarctic River Continuum

Abstract

Ecosystem processes and community structure in running waters of the boreal forests of Quebec, Canada, are strongly influenced by climate and channel geomorphology. Here we present an overview of a project examining longitudinal trends as small streams gradually coalesce into large rivers, summarizing our results in a series of budgets and predictive equations describing changes in organic carbon dynamics and community structure. There were significant trends with stream order for 70% of the 73 components, processes, and ratios examined. Of 46 independent components examined, 63% showed a significant trend with stream order. As stream size increased from 1st to 9th order there was a decrease in total carbon inputs (i.e., precipitation, throughfall, primary production, and allochthonous materials) followed by a gradual increase due to greater primary production in streams >6th order. The standing stock of carbon decreased exponentially downstream, and total carbon outputs (i.e., respiration, leaching, methane evasion, and insect emergence) increased slightly downstream. Nevertheless, some ecosystem-level processes, as well as community structure, showed equivocal trends, which were apparently due to the hierarchical scale of examination and the relative degree of physicochemical vs. biological control of the processes and communities. The data, when placed in a watershed perspective, showed that total carbon inputs were evenly distributed by steam order throughout the 19 871-km 2 Moisie River drainage network. Most carbon was stored in the small 1st to 3rd order streams, whereas the majority of organic carbon was metabolized in the 7th to 9th order rivers. Fluvial transport of organic carbon to the Gulf of St. Lawrence was nearly three times that of the measured total annual input, suggesting that inputs of dissolved organic carbon in groundwater were more important than previously expected.Ecosystem-level measurements of carbon retention and utilization also showed significant trends with stream order. The spiraling length for carbon increased exponentially from 8-15 km in small streams to 426 km in the 9th order river. There was a concomitant decrease in reach retention with stream order, while the rate coefficient of respiration and rate of downstream movement increased with order. The stream metabolism index, a measure of ecosystem efficiency, increased from 1st to 7th order, thereafter decreasing as streams became larger. These trends with stream order were related to physical gradients in channel dimensions, hydrology, riparian influences, and sunlight. We conclude that these subarctic lotic ecosystems have numerous strong relationships with stream order and that the dynamics can be described by a relatively small set of predictive equations.

Distribution patterns of fish communities with respect to environmental gradients in Korean streams

“…Kuehne (1962) studied the relationship between fish distribution and stream order; this correlation that has been frequently used when analyzing the longitudinal distribution of fish. Normally, the relationship between fish distribution and stream order is well matched with longitudinal fish distribution (Naiman et al, 1987;Beecher et al, 1988;Paller, 1994;Jang et al, 2008), although exceptions have been reported (Hughes and Gammon, 1987;Omernik, 1981, 1983). Although altitude alone can effectively predict fish distribution, a combination of altitude and stream order is more effective in this respect.…”

Spatial and temporal organization of aquatic insects assemblages in the longitudinal gradient of a tropical river

“…Many other studies have tried to explain the macroinvertebrate patterns along the longitudinal section of rivers Winterbourn et al, 1981;Culp & Davies, 1982;Cushing et al, 1983;Statzner & Higler, 1985;Naiman et al, 1987;Brussock & Brown, 1991;Palmer et al, 1994). To explain the observed faunal gradient along the rivers in these studies, two different views have emerged.…”

Mechanisms of carbon storage in mountainous headwater rivers

“…Headwaters contribute significantly to CO 2 outgassing via microbial activity 3 , which partly reflects the geomorphic complexity of low-order streams created by spatial variations of hydraulics and substrate 4 . In temperate environments and higher latitudes, headwater rivers can also store disproportionate amounts of carbon in coarse dead wood relative to downstream portions of river networks 5 . The rate at which organic matter is delivered to headwater rivers, and the conditions that facilitate either storage or downstream export of this organic matter, thus exert important influences on watershed-scale carbon fluxes.…”