Flow variability plays an important role in structuring lotic communities, yet comparatively little is known about processes governing assemblage dynamics in stream ecosystems with stable environmental conditions, such as spring-fed rivers. Volcanic spring-fed rivers (hereafter spring-fed rivers) occur in geologically active landscapes of the western USA and around the globe. We sampled invertebrate assemblages and quantified primary productivity and habitat characteristics of spring-fed and runoff rivers in northern California over 4 seasons. We predicted that abiotic factors would be more stable and nutrient availability greater and that invertebrate density would be greater and diversity lower in spring-fed than in runoff rivers. Runoff rivers exhibited high variability in discharge and temperature, whereas spring-fed rivers were relatively stable with high naturally occurring nutrient levels. On average, NO3- and PO43- concentrations were 40x greater in spring-fed than in runoff rivers. Spring-fed rivers supported nearly 7 to 16x greater densities of invertebrates than runoff systems, depending on season. However, invertebrate species richness was greater in runoff rivers in all seasons. Spring-fed river invertebrate assemblages were strongly correlated with elevated nutrient concentrations and basal C sources, whereas runoff assemblages were associated with discharge variability and median substrate size. We suggest that strong differences in abiotic variability between spring-fed and runoff rivers play an important role in determining invertebrate assemblage structure. Because spring-fed rivers exhibit more stable temperatures throughout the year and lower temperatures during the summer than runoff rivers, they may provide essential refugia for coldwater taxa in a warming climate.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/621412 |
| Date | 09 1900 |
| Creators | Lusardi, Robert A., Bogan, Michael T., Moyle, Peter B., Dahlgren, Randy A. |
| Contributors | Univ Arizona, Sch Nat Resources & Environm |
| Publisher | UNIV CHICAGO PRESS |
| Source Sets | University of Arizona |
| Language | English |
| Detected Language | English |
| Type | Article |
| Rights | © 2016 by The Society for Freshwater Science. |
| Relation | http://www.journals.uchicago.edu/doi/10.1086/687114 |
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