Newman Lake restoration: A case study Part III. Hypolimnetic oxygenation

Abstract

Since the mid-20th century, oxygen status at the sediment–water interface (SWI) has been implicated in regulating lake internal phosphorus loading. In deeper lakes, summer hypolimnetic oxygen depletion may thus play a critical role in phosphorus cycling and lake trophic status. Hypolimnetic aeration (HA) has been utilized for more than 4 decades to prevent development of anoxia, decrease internal phosphorus load, and enhance fisheries. Most recently, interest has shifted to hypolimnetic oxygenation (HO) for potential performance and economic advantages. In Newman Lake, hypolimnetic oxygenation was initiated in 1992 when the first lake application of downflow contact bubble oxygenation (Speece Cone technology) was installed. Oxygenation at Newman has reduced growing season Nürnberg Anoxic Factors (AF) from a range of about 30–60 d to <10 d. We propose that differences in predicted versus observed AF based on phosphorus may be utilized to assess lake restoration performance. Newman Lake has demonstrated the importance of operating the system at full capacity, as lower oxygen delivery rates do not produce proportional hypolimnetic oxygen concentrations, as well as other insights into HO system sizing and design.