Factors controlling phytoplankton dynamics in lotic systems remain poorly understood relative to those in standing waters, especially in smaller and mid-size streams. Here, we evaluate relationships between stream flow, suspended algal biomass, and particulate organic carbon over multiple years for a mid-size river network draining an intensively managed agricultural landscape in the Midwestern USA. As expected, we found that mid-size reaches (4th–6th order) yielded higher chlorophyll concentrations than smaller reaches (1st–3rd order); however, all reach types exhibited chlorophyll concentrations that could be considered eutrophic. Suspended algae accounted for approximately 20% of total suspended carbon in the river network, on average. Over time, the highest levels of suspended algal biomass across all sites were associated with intermediate–high flow conditions (above median discharge but below ~25% exceedance probabilities). Lakes and wetlands were also sources of suspended algal biomass to the stream network, although substantial phytoplankton production appeared to occur in-channel apart from lentic inputs. Our findings highlight the importance of flow as a regulator of suspended algal biomass, and suggest that moderate flow events act to mobilize algae from benthic habitats or other refugia.
Bibliographical noteFunding Information:
This research was supported by the National Science Foundation under Grant No. 1209402 Water, Sustainability and Climate (WSC)âCategory 2, Collaborative: Climate and human dynamics as amplifiers of natural change: a framework for vulnerability assessment and mitigation planning. We thank many people who contributed to the collection and processing of samples in the field and the lab, and without whom this work would not have been possible: Sandra Brovold, Shelly Rorer, Katie Kemmit, Erika Senyk, Andrea Keeler, Wendy Hughes, Nick Omodt, Rachel Van Allen, Cathleen Nyugen, Sally Donovan, Alex Bahr, Anika Bratt, Anna Baker, Winnie Winikoff, Evelyn Boardman, and Ben Janke. We also thank two anonymous reviewers for their careful and very helpful comments on an earlier draft of this manuscript.
© 2016, Springer International Publishing Switzerland.
- River continuum concept
- River wave concept
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Characterization of streams and rivers in the Minnesota River Basin Critical Observatory: water chemistry and biological field collections, 2013-2016