Abstract
For many floodplain rivers, reinstating wetland connectivity is necessary for ecosystems to recover from decades of regulation. Environmental return flows (the managed delivery of wetland water to an adjacent river) can be used strategically to facilitate natural ecosystem connectivity, enabling the transfer of nutrients, energy, and biota from wetland habitats to the river. Using an informal adaptive management framework, we delivered return flows from a forested wetland complex into a large lowland river in south-eastern Australia. We hypothesized that return flows would (a) increase river nutrient concentrations; (b) reduce wetland nutrient concentrations; (c) increase rates of ecosystem metabolism through the addition of potentially limiting nutrients, causing related increases in the concentration of water column chlorophyll-a; and (d) increase the density and species richness of microinvertebrates in riverine benthic habitats. Our monitoring results demonstrated a small increase in the concentrations of several key nutrients but no evidence for significant ecological responses was found. Although return flows can be delivered from forested floodplain areas without risking hypoxic blackwater events, returning nutrient and carbon-rich water to increase riverine productivity is limited by the achievable scale of return flows. Nevertheless, using return flows to flush carbon from floodplains may be a useful management tool to reduce carbon loads, preparing floodplains for subsequent releases (e.g., mitigating the risk of hypoxic blackwater events). In this example, adaptive management benefited from a semi-formal collaboration between science and management that allowed for prompt decision-making.
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Acknowledgements
We are grateful to many people who assisted with the planning and implementation of this work including various industry partners listed in this manuscript. Bradley Clarke-Wood, Jo Ocock, Carmen Amos, Erin Lennon, and Rohan Rehwinkel assisted with fieldwork. Claire Sives, Phil Morris, and Martin Forrest assisted with microinvertebrate processing. Site figure provided by the Spatial Analysis Network (SPAN) at Charles Sturt University. This research was funded by the Commonwealth Environmental Water Office under the Long-Term Intervention Monitoring program. The views and conclusions expressed in this paper are those of the authors and do not necessarily represent the official policies, either expressed or implied, by the respective organizations.
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Wolfenden, B.J., Wassens, S.M., Jenkins, K.M. et al. Adaptive Management of Return Flows: Lessons from a Case Study in Environmental Water Delivery to a Floodplain River. Environmental Management 61, 481–496 (2018). https://doi.org/10.1007/s00267-017-0861-0
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DOI: https://doi.org/10.1007/s00267-017-0861-0