What is Diver Assisted Suction Harvesting (DASH)?
For the first time in the Adirondack Park’s history, the Adirondack Park Agency (APA) has approved the use of diver assisted suction harvesting (DASH) as a control method for Eurasian Watermilfoil (EWM). A jurisdictional determination of approval was provided to Aqualogic Inc. (Aqualogic); a company based out of Gilford, New Hampshire that focuses on integrated management techniques for aquatic invasive plants. During DASH divers swim along the lake bottom to hand harvest target plant species. A key difference between DASH and more traditional hand harvesting methods is that divers don’t have to come to the surface as often to dispose of harvested plants. Instead, divers carefully feed the aquatic vegetation into the intake of a submerged suction hose that transports water and the plant material to the surface and into a boat’s bagging station. This means divers spend less time at the water’s surface and more time at the bottom, harvesting plants.
What is Eurasian watermilfoil (EWM)?
Of all the aquatic invasive plant species in the Adirondacks, Eurasian watermilfoil (Myriophyllum spicatum) is one of the most well-known and widespread. This submerged aquatic invasive plant is well adapted to the region’s climate and often thrives in lakes and ponds when introduced. Approximately 60 Adirondack lakes and ponds currently have infestations of EWM. Due to factors such as a lack of natural predators and the plant’s ability to monopolize resources, EWM can quickly proliferate in a waterbody. Dense mats of EWM eventually form that outcompete native aquatic plant species, impede recreational boating and swimming, and reduce shoreline property values.
A Day on Minerva Lake with Aqualogic
In early May I was fortunate to join the Adirondack Park Agency’s Freshwater Analyst, Leigh Walrath, on a trip to Minerva Lake where the lake association and town have been combating an aggressive infestation of EWM. The town had recently decided to pursue DASH with Aqualogic after failed attempts to maintain the infestation, over previous years, with traditional hand harvesting techniques. My goal for the day was to shadow the Aqualogic team as they worked and gain a better understanding of the DASH method and its effectiveness. We first arrived at Minerva Beach and started the half mile paddle north towards the EWM harvesting area. As we glided into a hidden bay, the Aqualogic team temporarily halted operations to welcome us aboard their barge.
After brief introductions, John Jude, President of Aqualogic Inc., and his son Dominic started the DASH unit while another diver waited in the water. Cold, clear water quickly began to rush out of a long suction hose and over a sorting tray within the boat. Looking over the port side of the harvester, I could see the large, black suction hose move through the water as the diver slowly made his way along the bottom of the lake. It wasn’t long before a large EWM plant shot out of the hose and fell into the sorting tray. Dominic quickly grabbed the sample to demonstrate how the entire plant had been harvested including roots, stem, and leaves. He then placed the plant in a porous bag, suspended at the end of the sorting tray, for disposal. The DASH system is meant to completely remove aquatic vegetation while not suctioning or dredging lake bottom sediments. Aqualogic’s DASH unit also has a triple filtration system that filters harvest water extensively before it is allowed to reenter the lake.
After a few minutes of harvesting additional EWM plants, Leigh and I were shown how the crew combats EWM fragments that may be floating on the water’s surface. Dominic noticed a few fragments so he ventured to the back of the harvester and grabbed what looked like a modified version of a pool skimmer. He quickly extended it from the side of the boat and scooped up a floating EWM fragment. “On the suction barge we have 2 tenders that keep a constant look out for any floating fragments during operation” Dominic stated. “At the end of a dive the diver floats on the surface and removes any fragment that he and/or the tenders can see. On site we also have a floating fragment barrier to be used as needed.” One of the most common concerns associated with EWM is its ability to spread through fragmentation. Even just a small section of plant material has the potential to sprout roots and start a new infestation. Dominic also commented on the level of strategic planning that took place prior to the beginning of DASH on Minerva Lake this year; “taking into account the current in the lake and the differences in densities of EWM we concluded that it would be most effective to start in the Northeastern Cove and move to the Northwestern Cove this season.”
As of August 4th the team has removed an estimated 52,800 lbs. (2640 bags) of EWM in 43 days of diving with a record 2,200 lbs. (110 bags) being harvested in a single day. According to Dominic the team is currently 2/3 of the way into the contract and is projected to pull 75,000 lbs. of EWM by the end of the season. Upon interview, Steve Mcnally, Town of Minerva Supervisor, said “we have been very pleased with the DASH approach this year. So far we are harvesting more than twice as much as we did with conventional hand harvesting. Although that in itself sounds good the amount of weeds available to harvest has increased this year because of the dry, sunny days; resulting in low water. We plan on using the DASH system going forward next year and beyond as long as we continue to see gains.”
With so much EWM being harvested from Minerva Lake this season I began to wonder what happened to all that harvested plant material. I was pleased to hear from Dominic that the vegetation is composted and given to a local garden club for use as fertilizer. Aqualogic still has a significant amount of harvesting ahead of them, but preliminary results may indicate that Minerva Lake is back on track in its DASH for sustained EWM control.