Innovation versus Invasive: Two motors drive the suction harvester hose (submerged) that vacuums the entire plant - including roots - hand-removed by a diver. Captured plants are then forced down the steel paddock and into mesh bags.
Suction Harvester Shows Promise and Limitations
By Paul Gregory, Invasive Aquatic Species Staff, Maine Department of Environmental Protection
Mid-August use of a suction harvester on three Maine lakes infested with variable-leaf milfoil confirmed that this technology has its advantages and drawbacks…just like any technique for the removal of invasive aquatic plants.
Suction harvesting is a mechanized acceleration of hand removal; a diver hand-pulls the aquatic plant—roots and all—and then tosses it to a motorized suction hose. Through the vacuum hose, the vegetation is forced to the surface and down a steel paddock and into a 50-pound mesh bag.
Using the suction harvester.
The advantage of suction harvesting over classic hand-removal is the amount of plant material gathered. Rather than collect plants, pack mesh bags underwater and then pass them along to a surface worker by hand, the suction harvesting diver’s job is more straightforward—simply gathering and feeding plants into the vacuum hose. A second crewmate bags the vegetation from a surface station.
Indeed, suction harvesting exceeds what one or a small team of divers can remove in the same span of time. Thick patches of variable-leaf milfoil were best suited for the harvester, enabling the two-man crew to collect a dozen to 16 bags per hour.
In that same time, however, the mechanized method instantly disturbed the lake bottom, making waters in the control site turbid, limiting visibility. It also caused a significant amount of fragmentation. A third person was necessary to catch escaping fragments. Fragmentation and disturbance of the lake bottom can invite new infestations.
Attaching a fresh bag to the harvester.Up to four-hour equipment set-up/take-down times need to be considered when comparing the efficacy of suction harvesting and classic hand-removal efforts.
The pilot was undertaken on Little Sebago Lake in Gray, Lake Arrowhead in Waterboro and Messalonskee Lake, Belgrade. Sponsored by Maine DEP’s Invasive Species Program, the goals of siccing the suction harvester on the milfoil were to assess its effectiveness, to demonstrate the technology first-hand to DEP-ers and residents, and to provide some relief to areas thick with the nuisance plant. ChemFree Aquatics of Rochester, NY, was the contractor.
50 pound mesh bags of harvested milfoil.
Part of that day's harvest.