In both fresh and marine environments, benthic organisms are quick to colonize on instrumentation and deployment hardware used to collect environmental data.

Saltwater environments are particularly difficult to manage due to the variety of calcium carbonate-building species that will encrust almost any surface. Without proper preventive measures, these organisms will encrust the instrument and skew the data outputs or even damage the instrument itself. The photo below (r shows an In-Situ Aqua TROLL 600 fixed to an underwater piling in the Caribbean Sea. You can see from the minimal growth on the sonde that it hasn’t been there long. But in time barnacles and other sessile organisms will cover the instrument, unless antifouling technology and methods are used to protect it.

The Aqua TROLL Multiparameter Sonde has several native antifouling capabilities built into every instrument. They include:

Interlocking, Flat-Faced Sensors

The pie-shaped Aqua TROLL sensors are seated firmly against each other when installed on the sonde. A tight fit prevents organisms from growing and sediment from settling in between them.

The only areas within the sonde that are open for water flow, and therefore vulnerable to sediment and biofouling, are the sensor faces. But because they’re flat, without grooves or crevices, they’re easier to keep clean.

Restrictor

The Aqua TROLL Restrictor slips over the sensors and screws on with tight precision, minimizing space between the inside of the restrictor and the sensors so organisms can’t establish and sediment can’t settle. In the photograph below right you can see that while the sonde body is covered in biological fouling, the sensors are clean. The restrictor helps protect them, extending their usable life and making maintenance easier. To enhance the Aqua TROLL’s intrinsic antifouling features, In-Situ provides these optional tools to further inhibit bio-growth.

Antifouling Wiper

This dual-sided wiper is designed to wipe both the sensor faces and the inside of the restrictor end cap. This prevents growth from occurring on the only two surfaces available inside the restrictor. As it automatically rotates and wipes, it removes sediment and biofilms, which are precursors to encrusting organisms. Flat sensor faces enable the wiper to easily clean the entire sensing area.

Antifouling Restrictor

The Antifouling Restrictor is made of a copper alloy for additional biofouling prevention. Copper is a powerful biocide used in many different marine applications to inhibit biological growth. For the Aqua TROLL, the Antifouling Restrictor provides two-fold protection. First, it prevents organisms from growing directly on its surface, making it easy to clean and maintain. Second, and perhaps more importantly, the restrictor slowly “dissolves,” releasing copper compounds into the surrounding water, including within the restrictor where the sensors and wiper are located. This copper “cloud” is toxic to organisms as they respirate, taking in water and the copper compounds.

Solid copper alloys change color and appearance in water as they age, which in the case of the restrictor, could affect optical sensor measurements if not accounted for. Manufacture of the Aqua TROLL Antifouling Restrictor includes an accelerated aging process performed in the factory to elicit changes that would naturally occur during field deployment.

While the restrictor’s appearance will continue to change over time, this process ensures that these changes won’t compromise measurements. Additionally, calibrations with the Antifouling Restrictor are performed with an included calibration sleeve, to ensure accuracy by matching deployment conditions while minimizing the amount of calibration solution required.

Aqua TROLL Shield (Aqua TROLL 100 and 200)

This system includes a copper pressure sensor nose cone and a conductivity sensor sleeve to prevent biofouling on the Aqua TROLL 100 and 200 instruments. It provides the same biocidal protection as the Antifouling Restrictor, preventing organisms from settling inside the conductivity cell or pressure transducer and compromising data quality. In addition to In-Situ’s antifouling solutions, other off-the-shelf tools can be used to prevent fouling on your sonde and sensors.

Plastic Wrap

Wrapping plastic around the body of the sonde can help prevent fouling on the sonde itself. The plastic acts as a sacrificial surface on which barnacles and other organisms can grow and can be discarded at each maintenance visit. You can use anything from kitchen cling wrap to shrink wrap to trash bags, secured with duct tape or copper tape. When wrapping your sonde, make sure to leave the depth sensor port open to the water. Covering it could cause erroneous measurements.

Pro Tip: For easy removal, wrap a piece of sharp wire inside the plastic with the ends protruding. When it’s time to unwrap the sonde, simply pull on the wire (using heavy-duty gloves) so it cuts through the plastic.

Duct Tape

Duct tape is a good option for underwater deployments because it typically adheres for a long time in water. Use it to secure the plastic covering on the sonde. (Using duct tape directly on the sonde won’t damage the instrument, but the tape will be harder to remove.) Use brightly colored duct tape if possible; in the case of a lost sonde, neon colors like green or orange are much easier to spot underwater than neutral colors like black, brown or gray.

Off-the-Shelf Copper Components

As mentioned, copper is a highly effective biocide in aquatic environments. Placing copper around the body of the sonde helps prevent fouling there as well. Use copper tape with, or instead of, duct tape to secure a plastic covering around the sonde body.

Copper braid can be used to cover the entire instrument without inhibiting water flow into the depth port. Braiding can also be secured in place with brightly colored duct tape.
Copper mesh, which can be purchased in large rolls and cut to size, is another option. Simply wrap the sonde in the mesh and secure it with zip ties on either end. Copper mesh doubles as an antifouling measure and an effective deterrent for larger creatures like small crabs and fish that might try to take up residence inside the restrictor.

Stilling Well/Pipe

A perforated stilling well is often an essential part of every sonde deployment station. The perforations allow water to flow through the well and over the sensors while protecting the sonde from large objects that could damage it. A stilling well can also help prevent fouling if it’s coated with an antifouling paint or coating.

Antifouling Coatings

You’ll find a variety of antifouling coatings on the market. It’s advisable to apply these coatings on the stilling well used for deployment rather than on the sonde body itself. Copper-based antifouling paint with biocidal properties is one option. Others include coatings such as ClearSignal, Maringlide or Propspeed, which keep surfaces clean by making them too slippery for organisms to attach to. You can see in the photo below a PVC sonde well painted with a copper-based antifouling paint.

Pro Tip: In addition to painting the outside, pour paint inside the stilling well to enhance the copper “cloud” and prevent growth on the instrumentation inside.

Whether in fresh water or marine environments, unchecked biofouling can damage instruments and affect data quality. Aqua TROLL water quality sondes are designed to inhibit bio growth, reduce maintenance requirements and deliver decision-quality data over the long term. With the addition of technology such as the Anitfouling Wiper and Antifouling Restrictor, as well as off-the-shelf solutions, you can reduce trips to the field and trust that your In-Situ equipment will perform in high-fouling environments.