Determination of Reaeration Coefficients: Whole-Lake Approach

Onondaga Lake, N.Y., experiences a marked annual dissolved oxygen depletion over the entire water column at fall turnover. Depletion occurs as a result of the entrainment of reduced substances that have accumulated in the lake's hypolimnion over the summer. Recovery (return to near-saturated conditions) occurs over a period of 3–4 weeks. Observations of dissolved oxygen (DO) levels during the recovery period of two years are used to calculate the reaeration coefficient ( K a,20= 0.22 d −1 in 1989, and 0.13 d −1 in 1990) and the liquid film transfer coefficient for oxygen ( K L,20= 2.64 m⋅d −1 in 1989, and 1.50 m⋅d −1 in 1990). Local wind measurements are used to develop an empirical relationship between wind speed ( U10, m⋅s −1) and K L,20: K L,20=α⋅U10β, with α= 0.2; β= 1.0 for U10≤ 3.5 m⋅s −1 and α= 0.057; and β= 2.0 for U10> 3.5 m⋅s −1. Model output and field observations are compared with estimates generated using other published relationships.