Newman Lake restoration: A case study. Part I. Chemical and biological responses to phosphorus control

Abstract

In the late 1960s and early 1970s, summer and fall blooms of cyanobacteria began to occur in Newman Lake, Washington (zavg: 5.6 m, zmax: 9.0 m); through the next decade, these blooms intensified and became an annual occurrence. Community efforts in the mid-1980s sparked a Restoration Feasibility assessment of the lake and watershed that indicated total annual gross phosphorus loading of at least 3000 kg, with a major portion (∼83%) attributable to internal recycling associated with summer hypolimnetic oxygen depletion. Implementation activities began September 1989, with watershed controls and a whole-lake alum treatment, followed in 1992 by installation of a Speece cone for hypolimnetic oxygenation and in 1997 by addition of a dual-port, microfloc alum injection system. Average summer volume-weighted total phosphorus has declined from prerestoration levels exceeding 50 μg-P/L to an average of 21 μg-P/L over the past 7 years (15–28 μg-P/L). Most notably, peak annual biovolumes of cyanobacteria and their representation within the phytoplankton community have decreased substantially, with increased prevalence of diatoms, green and golden-brown algae. A clearwater phase following spring blooms of diatom and/or golden-brown algae has occurred during those last 7 years, although this phenomenon was observed in the prior three decades. Overall, the restoration has been a success, and lake response to nutrient reduction at Newman Lake is consistent with worldwide observations that emphasize the need for long-term perspectives and commitment in lake restoration and management. Continuation of internal load controls and increased emphasis on external nutrient abatement will be necessary to continue the positive water quality trends despite future development increases and land use changes.