Activity 1: Metal Rack Design & Deployment

The overall design of the sampling rack and materials is simple and can be deployed in various aquatic or marine environments with proper planning. The following design is modified from Frederick and colleagues (2000, 2018) and the VIRTUE project.

Procedures

1. Drill one hole horizontally 5.0 cm from the top of a solid, round aluminum rod (1.27 cm in diameter and 61 cm in length). This hole will be used for threading metal wire that will be used to hang the rack from a pier or dock.
2. A second hold is drilled 5.0 cm from the bottom of the rod for the metal cotter pin to hold all the discs and spacers in place. The diameter of the holes need to accommodate the size of the metal wire (0.32 cm width) at the top and the chosen cotter pin size at the bottom of the rod.
3. Attach 1 stainless steel cotter pin to the bottom of the aluminum rod.
4. Cut pieces of aluminum pipe or conduit (hollow, 1.3 cm) to 10.2 cm in length. These rack spacers are used to separate the sets of discs on the rod.
5. Drill a 1.27 cm hole through center of each 10 cm round aluminum disc (slightly larger than the diameter of the aluminum rod). The discs should be 0.3 cm in thickness. We use 10 discs (5 sets of 2) on each rack.
6. Measure a 90° angle on each disc and notch the outer edges of the disc at this angle—this will allow you to stay consistent when sampling 25% of each disc later on.
7. Slide 1-2 disc(s) onto the rod above the cotter pin. Slide on a piece pipe over the rod, then 1-2 disc(s), another pipe, etc. up to the top of the rod. We use 10 discs (5 sets of 2) on each rack.
8. Use a 0.32 cm width metal wire to hang the rack from the aluminum rod and secure to a pier, dock, cleat or other secure fixture. There are many methods for securing the wire. One that works well uses 4 metal ferrules (2 on the wire near the rod end and 2 on the wire near the secured end near the pier or cleat) to hold the wire in place and prevent it from slipping loose. Metal ferrules are used for looping the metal wire and making a self-arresting loop.
9. Lower the rack slowly into the water; ensure that the depth of the rack is below the low-tide mark (if applicable) and that the top of the rack is 1 m below the surface. If you prefer, a long wire can be used with a float attached so the rack will move with the tide. Racks will be oriented vertically in the water. After an initial period of a few days to one week, a biofilm will develop on the discs.

Formative assessment prompt.

(It is suggested that this prompt be performed over a series of days as students learn about the project.) Students will work in small groups (three or four) to develop strategies that will propose to improve or alter methods for deploying racks and will account for local conditions (water flow, light penetration, overall water quality, etc.). Students should write a plan for deployment that includes the length of time on the water and how often the discs will be checked.