“Gradual Entrainment Lake Inverter” (GELI): A novel device for experimental lake mixing

Abstract

A Gradual Entrainment Lake Inverter (GELI) designed to destroy thermal stratification was constructed and used to destratify a darkly stained humic lake. The GELI was developed to gain insight to the effects of altered lake‐mixing regimes, but has utility in other mixing applications. The GELI comprises an 8.25 m diameter rubber membrane with a tubular inflatable ring around its circumference that can be raised and lowered repeatedly through the water column using compressed air to control the buoyancy of the ring. Three mixing mechanisms for the GELIs were observed: (i) the increase of high‐frequency internal waves (ii), shear and circulation resulting from lateral exchange flows, and (iii) generation of turbulence via both surface spreading and a trailing wake. Field experiments of the GELI reset vertically stratified variables to a near‐homogeneous state. As the surface to bottom water column temperature differential changed from 19.2°C to 0.2°C, dissolved oxygen concentrations increased transiently from below detection to 2.8 mg L−1 in the hypolimnion and decreased from 7.0 to 3.2 mg L−1 in the epilimnion. Results demonstrate that the GELI is an efficient lake‐mixing device that can minimize gas exchange associated with traditional mixing methods, and the GELI is particularly useful when circumstances require nondisruption of this parameter. The GELI can also be useful in hydrodynamic studies as an internal wave generation device.