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

• Published in: Ecology
• Main Authors: Naiman, Robert J., Melillo, Jerry M., Lock, Maurice A., Ford, Tim E., Reice, Seth R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1987
• Subjects: Canada; Subarctic
• Online Access: http://dx.doi.org/10.2307/1939199; http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.2307%2F1939199; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.2307%2F1939199; https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.2307/1939199

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 stream 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 ...