Doing more than skimming the surface
In a continuing series on marine debris to mark World Oceans Day on Tuesday, Bermuda Marine Debris Taskforce members Hannah Horsfield and Julie Cross Steele look at methods of skimming trash off the surface of oceans, inland waters and harbours
As marine plastic accumulates in the ocean at an alarming rate, the need for efficient and sustainable remediation is urgent. It is estimated that there are 5.25 trillion pieces of plastic in our ocean with approximately 8.3 million tonnes entering the seas each year. A combination of sustainable technologies and adopting preventive behaviours is our best chance of ensuring that there will always be more fish than plastic in the ocean.
Organisations such as the Ocean Cleanup are deploying large-scale technologies to address the massive plastic gyres and to intercept plastic at the mouth of major rivers and waterways.
An example of a smaller scale interceptor can be seen in Baltimore. “Mr Trash Wheel” catches riverine trash before it has a chance to reach the ocean. A floating boom diverts the trash on the river towards the cute and cleverly covered barge. River currents and solar panels power a water wheel which drives the conveyor belt, depositing the trash into floating replaceable dumpsters. In the seven years of operation, trash wheels in Baltimore have collected more than one million polysterene containers and plastic bottles and more than 12 million cigarette butts.
Tech solutions for Bermuda must take into consideration the scale and the sources of the plastic debris. Bermuda has experimented with one type of marine pollution skimmer. Sea Bins, a floating trash-bin-sized skimmer with a pump and filter, were placed around Hamilton Harbour beginning in 2017. While successful at removing some of the floating trash around marinas such as at Hamilton Princess Marina, Royal Hamilton Amateur Dinghy Club and Royal Bermuda Yacht Club, daily upkeep proved fairly problematic.
The Marina Trash Skimmer is an alternative technology that has proven to be successful in many coastal cities in the United States. This device can filter 300 gallons of water per minute and looks like a submerged dumpster attached to a floating dock. The circulation pump of the Marina Trash Skimmer creates a surface current that collects trash, soaks up oil and traps floating debris. Waste is easily removed dockside by opening the lid and netting out the contents.
While plastic capture around marinas would help reduce our contribution to the marine debris problem, Bermuda has no single-point source where plastic enters the sea. Trash from our small island is often blown into the ocean. Once it enters the water, plastic becomes very challenging to remove as 70 per cent sinks to depths that cannot be skimmed, and is mistaken for food by ocean life at every level of the food chain.
Another natural collection point for floating debris is within the prop roots of the fragile mangroves, which serve as nurseries for juvenile fish. In the Sargasso Sea, plastics mingle with the sargassum, another important nursery and feeding area for ocean inhabitants.
The best measure to prevent more ocean-destined debris is actually a simple no-tech hack: a secure, regularly emptied trash bin with a lid. Reducing fly-away plastic and proper disposal is the best way that Bermuda can help stem the plastic tide.
• Hannah Horsfield and Julie Cross Steele are the education officer and the education director respectively at the Bermuda Underwater Exploration Institute. They are members of the Bermuda Marine Debris Taskforce which is a group of local environmental and research organisations, which aims to promote awareness of the impact of marine debris landing on Bermuda’s beaches and affecting marine life and to propose solutions to the growing problem