Restoration of eutrophic lakes in Iowa, USA

Lakes provide significant ecosystem services that are compromised by human degradation. Watershed and in-lake restoration are used to improve the physical, chemical, and biological condition of lakes, but their success is rarely evaluated. Our objectives were to compare water quality and biological conditions following in-lake, watershed, or a combination of both restoration activities in 20 lakes throughout Iowa, USA compared to reference systems. Lake-specific responses to restoration were variable, making it challenging to detect systematic effects in water quality parameters. Secchi depth generally improved following restoration, particularly in natural in-lake restorations and following sediment removal, fishery renovation, and with the number of restoration practices implemented, but improvements were not sustained. Restoration also tended to reduce nutrient and plankton concentrations and relative abundance of some benthic fishes. Due to the prolonged degradation of eutrophic lakes, it may be unrealistic to expect immediate and long-lasting water quality improvements. In-lake restoration in natural lakes may be the most likely to have detectable effects, but our results also highlight the need for improved restoration documentation and additional research to identify factors associated with restoration success. Our results are useful for guiding lake restoration practices and educating lake users and stakeholders on expected restoration outcomes.