Abstract
Land managers increasingly use wetland restoration to improve water quality, particularly in cultivated landscapes. In agricultural wetland restoration, managers regularly excavate accumulated sediments eroded from the surrounding landscape to increase water storage capacity, decrease invasive species cover, or improve water quality. However, it is unclear whether the effects of sediment excavation are influenced by wetland hydroperiod. Additionally, we lack data on how long excavation effects persist in restored wetlands. We examined dissolved nutrient concentrations (i.e., NH41, NO3–, total dissolved N, soluble reactive P, total dissolved P, and dissolved organic C) as proxies for water quality in 54 restored agricultural wetlands ranging from 1 to 10 y post-restoration in the Prairie Pothole Region of west central Minnesota, USA. In 26 of these wetlands, restoration practitioners restored natural (i.e., either seasonal or semipermanent inundation) hydrological regimes by removing subsurface tile drainage and plugging surface drainage ditches (business-as-usual treatment). In 28 wetlands, practitioners re-moved accumulated sediment and redeposited it on the surrounding landscape (excavated treatment) prior to restoring hydrology. We found that wetlands in the excavated treatment group initially experienced reduced dissolved P concentrations, but over time P levels increased, particularly in wetlands with shorter hydroperiods. Excavated wetlands had lower NH41 and dissolved organic C concentrations compared with business-as-usual wetlands, but the trend was driven by differences between restoration treatments in semipermanent wetlands. N and P dynamics were almost universally related to hydroperiod, both immediately following restoration and over the ensuing years. We postulate that the effects of hydroperiod are likely related to differences in redox conditions via direct mechanisms (water level fluctuations related to hydroperiod) and indirect mechanisms (development of dense emergent macrophyte communities in seasonal wetlands). In basins with seasonal hydroperiod, inorganic N concentrations decreased over time and inorganic P concentrations increased, suggesting net P mobilization con-current with growing N limitation. Our results illustrate that hydroperiod regulates the expression of legacy P following wetland restoration, with little long-term effect of sediment removal on water quality outcomes.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 70-87 |
| Number of pages | 18 |
| Journal | Freshwater Science |
| Volume | 42 |
| Issue number | 1 |
| DOIs | |
| State | Published - Mar 2023 |
Bibliographical note
Funding Information:Primary funding was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources. Additional funding was provided by the United States Environmental Protection Agency (USEPA) under the Science to Achieve Results Graduate Fellowship Program. The USEPA has not officially endorsed this publication, and the views expressed herein may not reflect the views of the USEPA. This project was made possible by logistical support and collaboration with the United States Fish and Wildlife Service, the Minnesota Private Lands Office, and the private landowners who restored previously drained wetlands and granted us access to their properties. The SFS Endowed Publication Fund paid some of the publication costs of this paper. Thank you.
Funding Information:
Author contributions: SGW conceived, designed, and imple-mented the study; analyzed and interpreted the data; and wrote the manuscript. JCF contributed to data interpretation and analysis and contributed to writing the manuscript. Primary funding was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources. Addi-tional funding was provided by the United States Environmental Protection Agency (USEPA) under the Science to Achieve Results Graduate Fellowship Program. The USEPA has not officially endorsed this publication, and the views expressed herein may not reflect the views of the USEPA. This project was made possible by logistical support and collaboration with the United States Fish and Wildlife Service, the Minnesota Private Lands Office, and the private landowners who restored previously drained wetlands and granted us access to their properties. The SFS Endowed Publication Fund paid some of the publication costs of this paper. Thank you.
Publisher Copyright:
© 2023 The Society for Freshwater Science. All rights reserved.
Keywords
- carbon
- depressional wetland
- nitrogen
- phosphorus
- Prairie Pothole Region
- restoration
- sediment
