Steven D. Comfort
Date of this Version
A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science
Major: Natural Resource Sciences
Under the supervision of Professor Steven D. Comfort
Lincoln, Nebraska, November 2023
Reservoirs and ponds contribute significantly to the quality of life in Nebraska by providing numerous opportunities for outdoor recreation and adding aesthetics to the landscape. Storm water retention ponds, typically found in urban areas, are a subset of ponds that provide an important service by facilitating nutrient and sediment retention and aiding in flood control. Urban storm water retention ponds are especially vulnerable to water quality degradation and eutrophication due to a higher percentage of impervious areas (i.e., streets, sidewalks, parking lots) within the watershed and the increased runoff that results.
Changes in watershed practices that reduce external nutrient loading (specifically, nitrogen and phosphorus) are required for the long-term recovery of eutrophic reservoirs. However, signs of recovery are often not observed in the initial years following external load reduction due to internal nutrients accumulated in the water column and sediment (Jeppesen et al., 1991). Internal loads of phosphorus have been shown to delay reservoir recovery for decades (Carleton and Lee, 2023; Søndergaard et al., 1999; Welch and Cooke, 2005). This delay erodes public support for changes to watershed management practices. Thus, it is necessary to have techniques that both reduce external nutrient loading and others that mitigate the effects of internal nutrients, so that real-time improvements in water quality can be realized.
This research project demonstrated a combined biological and chemical approach to removing internal nutrients from a eutrophic pond in Nebraska (McKercher et al., 2022. McCright et al., 2023). In this approach, we installed floating treatment wetlands (FTWs) and an airlift pump that contained a slow-release lanthanum-wax composite. The airlift pump aerated the water and released lanthanum to sequester phosphorus while the wetland plants provided a biological sink for nitrate removal via denitrification and plant uptake of nitrogen and phosphorus. Success of the project was measured by obtaining detailed baseline water quality measurements before treatment and temporal changes to water quality parameters during treatment.
To determine sustainability of the biological-chemical approach, this research continued with the research initiated and reported by McKercher et al., (2022) and then focused on quantifying nitrate removal from FTWs under differing dissolved oxygen concentrations.
Advisor: Steven D. Comfort